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Blue appendages and temperature acclimation increase survival during acute heat stress in the upside-down jellyfish, Cassiopea xamachana
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Abstract
Upside-down jellyfish ( Cassiopea sp. ) are highly tolerant to multiple abiotic stressors, including fluctuating temperatures associated with shallow marine habitats. This resilience may underlie the ability of Cassiopea sp. to inhabit a wide variety of tropical habitats across the globe. Additionally, Cassiopea sp. are marked by a conspicuous array of appendage coloration; individual medusae vary in the hue and number of oral appendages, which are often strikingly blue. The function of this coloration is not understood. We aimed to understand how extrinsic and intrinsic factors may shape thermal tolerance. Adult Cassiopea xamachana were collected from two sites that vary in daily temperature range within the Florida Keys and were subjected to acute lethal heat stress experiments. To quantify a whole-organism response to heat, we measured changes in bell pulsation, which likely plays a role in feeding, oxygen exchange, and symbiont uptake. Results show that C. xamachana from the two collection sites do not exhibit different responses to heat, suggesting that temperature fluctuations do not prime individuals for higher thermal tolerance. Additionally, C. xamachana with blue appendages survived significantly higher temperatures and exhibited less change in bell pulsation rates compared to non-blue individuals. Finally, color morphs were acclimated at either ambient (26 °C) or elevated (33 °C) temperatures. We found that acclimation at 33 °C, as well as appendage color in each treatment, led to higher survival under acute heat stress. Together, these findings highlight the importance of phenotypic plasticity and coloration in Cassiopea resilience during heat stress.
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Background
Global warming is causing large-scale disruption of cnidarian-Symbiodiniaceae symbioses fundamental to major marine ecosystems, such as coral reefs. However, the mechanisms by which heat stress perturbs these symbiotic partnerships remain poorly understood. In this context, the upside-down jellyfish Cassiopea has emerged as a powerful experimental model system.
Results
We combined a controlled heat stress experiment with isotope labeling and correlative SEM-NanoSIMS imaging to show that host starvation is a central component in the chain of events that ultimately leads to the collapse of the Cassiopea holobiont. Heat stress caused an increase in catabolic activity and a depletion of carbon reserves in the unfed host, concurrent with a reduction in the supply of photosynthates from its algal symbionts. This state of host starvation was accompanied by pronounced in hospite degradation of algal symbionts, which may be a distinct feature of the heat stress response of Cassiopea. Interestingly, this loss of symbionts by degradation was concealed by body shrinkage of the starving animals, resulting in what could be referred to as “invisible” bleaching.
Conclusions
Overall, our study highlights the importance of the nutritional status in the heat stress response of the Cassiopea holobiont. Compared with other symbiotic cnidarians, the large mesoglea of Cassiopea, with its structural sugar and protein content, may constitute an energy reservoir capable of delaying starvation. It seems plausible that this anatomical feature at least partly contributes to the relatively high stress tolerance of these animals in rapidly warming oceans.
7jQYTVpxtJyVhU5epTFb61Video Abstract
Rising ocean temperatures are threatening marine species and populations worldwide, and ectothermic taxa are particularly vulnerable. Echinoderms are an ecologically important phylum of marine ectotherms and shifts in their population dynamics can have profound impacts on the marine environment. The effects of warming on echinoderms are highly variable across controlled laboratory-based studies. Accordingly, synthesis of these studies will facilitate the better understanding of broad patterns in responses of echinoderms to ocean warming. Herein, a meta-analysis incorporating the results of 85 studies (710 individual responses) is presented, exploring the effects of warming on various performance predictors. The mean responses of echinoderms to all magnitudes of warming were compared across multiple biological responses, ontogenetic life stages, taxonomic classes, and regions, facilitated by multivariate linear mixed effects models. Further models were conducted, which only incorporated responses to warming greater than the projected end-of-century mean annual temperatures at the collection sites. This meta-analysis provides evidence that ocean warming will generally accelerate metabolic rate (+32%) and reduce survival (-35%) in echinoderms, and echinoderms from subtropical (-9%) and tropical (-8%) regions will be the most vulnerable. The relatively high vulnerability of echinoderm larvae to warming (-20%) indicates that this life stage may be a significant developmental bottleneck in the near-future, likely reducing successful recruitment into populations. Furthermore, asteroids appear to be the class of echinoderms that are most negatively affected by elevated temperature (-30%). When considering only responses to magnitudes of warming representative of end-of-century climate change projections, the negative impacts on asteroids, tropical species and juveniles were exacerbated (-51%, -34% and -40% respectively). The results of these analyses enable better predictions of how keystone and invasive echinoderm species may perform in a warmer ocean, and the possible consequences for populations, communities and ecosystems.
Global warming is causing large-scale disruption of cnidarian-Symbiodiniaceae symbioses fundamental to major marine ecosystems, such as coral reefs. However, the mechanisms by which heat stress perturbs these symbiotic partnerships remain poorly understood. In this context, the upside-down jellyfish Cassiopea has emerged as a powerful experimental model system. We combined a controlled heat stress experiment with isotope labeling and correlative SEM–NanoSIMS imaging to show that host starvation is a central component in the chain of events that ultimately leads to the collapse of the Cassiopea holobiont. Heat stress caused an increase in catabolic activity and a depletion of carbon reserves in the unfed host, concurrent with a reduction in the supply of photosynthates from its algal symbionts. This state of host starvation was accompanied by pronounced in hospite degradation of algal symbionts, which may be a distinct feature of the heat stress response of Cassiopea . Interestingly, this loss of symbionts by degradation was to a large extent concealed by body shrinkage of the starving animals, resulting in what could be referred to as ’invisible’ bleaching. Overall, our study highlights the importance of the nutritional status in the heat stress response of the Cassiopea holobiont. Compared with other symbiotic cnidarians, the large mesoglea of Cassiopea , with its structural sugar and protein content, may constitute an energy reservoir capable of delaying starvation. It seems plausible that this anatomical feature at least partly contributes to the relatively high stress tolerance of these animals in our warming oceans.
The phylogeny of the Upside-Down Jellyfish (Cassiopea spp.) has been revised multiple times in its history. This is especially true in the Florida Keys, where much of the Cassiopea stock for research and aquarium trade in the United States are collected. In August 2021, we collected 55 Cassiopea medusae at eight shallow water sites throughout the Florida Keys and sequenced COI, 16S, and 28S genes. Mitochondrial genes demonstrate that the shallow waters in Florida are inhabited by both Cassiopea xamachana and a non-native Cassiopea andromeda lineage, identified in multispecies assemblages at least thrice. While C. xamachana were present at all sites, the C. andromeda-mitotype individuals were present at only a minority of sites. While we cannot confirm hybridization or lack thereof between the C. xamanchana and C. andromeda lineages, these previously unknown multispecies assemblages are a likely root cause for the confusing and disputed COI-based species identities of Cassiopea in the Florida Keys. This also serves as a cautionary note to all Cassiopea researchers to barcode their individuals regardless of the location in which they were collected.
Temperature rules the lives of ectotherms. To perform basic biological functions, ectotherms must make behavioral adjustments to keep their body temperatures near a preferred temperature (Tpref). Many color polymorphic lizards are active thermoregulators and exhibit morph differences in traits related to thermoregulation, such as color, body size, and microhabitat use. The Aegean wall lizard, Podarcis erhardii, is a heliothermic lizard with orange, white, and yellow color morphs that differ in size, behavior, and microhabitat use. Here, we tested whether P. erhardii color morphs from the same population from Naxos island, Greece, differ in Tpref. We hypothesized that orange morphs would prefer lower temperatures than white and yellow morphs because orange morphs are often found on cooler substrates and in microhabitats with more vegetation cover. We obtained Tpref for 95 individuals using laboratory thermal gradient experiments of wild-caught lizards and found that orange morphs do, indeed, prefer cooler temperatures. Average orange morph Tpref was 2.85 °C lower than average white and yellow morph Tpref. Our results add support to the idea that P. erhardii color morphs have multivariate alternative phenotypes and present the possibility that thermally heterogeneous environments play a role in the maintenance of color polymorphism in this species.
Global warming is associated with an increase in sea surface temperature and its variability. The consequences of evolving in variable, fluctuating environments are explored by a large body of theory: when populations evolve in fluctuating environments the frequency of fluctuations determines the shapes of tolerance curves (indicative of habitats that organisms can inhabit) and trait reaction norms (the phenotypes that organisms display across these environments). Despite this well-established theoretical backbone, predicting how trait and tolerance curves will evolve in organisms at the foundation of marine ecosystems remains a challenge. Here, we used a globally distributed phytoplankton, Thalassiosira pseudonana , and show that fluctuations in temperature on scales of 3–4 generations rapidly selected for populations with enhanced trait plasticity and elevated thermal tolerance. Fluctuations spanning 30–40 generations selected for the formation of two stable, genetically and physiologically distinct populations, one evolving high trait plasticity and enhanced thermal tolerance, and the other, akin to samples evolved under constant warming, with lower trait plasticity and a smaller increase in thermal tolerance.
The jellyfish Cassiopea xamachana and C. frondosa co-occur within some habitats in the Florida Keys, but the frequency with which this occurs is low. It is hypothesized that the symbiosis with different dinoflagellates in the Symbiodiniaceae is the reason: the medusae of C. xamachana contain heat-resistant Symbiodinium microadriaticum (ITS-type A1), whereas C. frondosa has heat-sensitive Breviolum sp. (ITS-type B19). Cohabitation occurs at depths of about 3–4 m in Florida Bay, where the water is on average 0.36 °C cooler, or up to 1.1 °C cooler per day. C. frondosa tends not to be found in the warmer and shallower (
Many pigments, such as melanins, are widely distributed throughout the animal kingdom. Others have arisen as novelties in particular lineages, for example, the Green Fluorescent Protein (GFP) found in cnidarians. While GFPs, widely used as fluorescent tags in biomedical research, are the most famous cnidarian example, other novel proteins have also been identified within this phylum. A blue protein that contains a Kringle (KR) domain inserted within a Frizzled cysteine-rich domain (Fz-CRD) was previously described from the jellyfish Rhizostoma pulmo (named rpulFKz1), however little is known about this pigment’s evolution or distribution among cnidarians. We performed a systematic search for homologs of this protein in published genomes and transcriptomes of 93 cnidarians. Phylogenetic analyses revealed eight predicted proteins that possess both domains in the same arrangement and that fall within the same clade as rpulFKz1. The sequence of one of these proteins contains motifs that match sequenced peptides of Cassio Blue, the blue pigment from Cassiopea xamachana. Another one of these proteins belongs to Stomolophus meleagris, and chemical studies on blue pigments that may occur in this genus have shown similarities to rpulFKz1 and Cassio Blue. Therefore, we hypothesize that the eight rpulFKz1 homologs identified are also pigment precursors. All precursors identified were exclusive to jellyfish in the order Rhizostomeae, so we herein name this new pigment family “rhizostomins.” Not all rhizostomes analyzed are blue, however, so these rhizostomin proteins may also be responsible for other colors, or perform other biochemical and biophysical roles. Previous studies have hypothesized that cnidarian pigments are photoprotective, and this study serves as basis for future investigations not only on the function of rhizostomins, but also on potential biotechnological applications for these proteins.
Ocean warming is predicted to challenge the persistence of a variety of marine organisms, especially when combined with ocean acidification. Whilst temperature affects virtually all physiological processes, the extent to which thermal history mediates the adaptive capacity of marine organisms to climate change has been largely overlooked. Using populations of a marine gastropod (Turbo undulatus) with different thermal histories (cool vs. warm), we compared their physiological adjustments following exposure (8-week) to ocean acidification and warming. Compared to cool-acclimated counterparts, we found that warm-acclimated individuals had higher thermal threshold (i.e. increased CTmax by 2°C), which was unaffected by the exposure to ocean acidification and warming. Thermal history also strongly mediated physiological effects, where warm-acclimated individuals adjusted to warming by conserving energy, suggested by lower respiration and ingestion rates, energy budget (i.e. scope for growth) and O:N ratio. After exposure to warming, warm-acclimated individuals had higher metabolic rates and greater energy budget due to boosted ingestion rates, but such compensatory feeding disappeared when combined with ocean acidification. Overall, we suggest that thermal history can be a critical mediator of physiological performance under future climatic conditions. Given the relatively gradual rate of global warming, marine organisms may be better able to adaptively adjust their physiology to future climate than what short-term experiments currently convey.
The massive occurrence of jellyfish in several areas of the world is reported annually, but most of the data come from the northern hemisphere and often refer to a restricted group of species that are not in the genus Cassiopea. This study records a massive, clonal and non-native population of Cassiopea and discusses the possible scenarios that resulted in the invasion of the Brazilian coast by these organisms. The results indicate that this jellyfish might have invaded the Brazilian coast multiple times.
Extreme climatic events including marine heatwaves (MHWs) are becoming more frequent and severe in the Anthropocene. However, our understanding of how these events affect population dynamics of ecologically important species is limited, in part because extreme events are rare and difficult to predict. Here, we quantified the occurrence and severity of MHWs over 60 years in warm range edge kelp forests on both sides of the North Atlantic. The cumulative annual intensity of MHWs increased two- to four-fold during this period, coinciding with the disappearance of kelps. We experimentally demonstrated a relationship between strong and severe 2018 heatwaves and high kelp mortality in both regions. Patterns of kelp mortality were strongly linked to maximum temperature anomalies, which crossed lethal thresholds in both regions. Translocation and tagging experiments revealed similar kelp mortality rates on reefs dominated by healthy kelp forests and degraded sediment-laden algal ‘turfs’, indicating equal vulnerability to extreme events. These results suggest a mechanistic link between MHWs and broad-scale kelp loss, and highlight how warming can make ecosystem boundaries unstable, forcing shifts to undesirable ecosystem states under episodically extreme climatic conditions.
Coral bleaching is one of the main drivers of reef degradation. Most corals bleach and suffer mortality at just 1–2°C above their maximum monthly mean temperatures, but some species and genotypes resist or recover better than others. Here, we conducted a series of 18‐hr short‐term acute heat stress assays side‐by‐side with a 21‐day long‐term heat stress experiment to assess the ability of both approaches to resolve coral thermotolerance differences reflective of in situ reef temperature thresholds. Using a suite of physiological parameters (photosynthetic efficiency, coral whitening, chlorophyll a , host protein, algal symbiont counts, and algal type association), we assessed bleaching susceptibility of Stylophora pistillata colonies from the windward/exposed and leeward/protected sites of a nearshore coral reef in the central Red Sea, which had previously shown differential mortality during a natural bleaching event. Photosynthetic efficiency was most indicative of the expected higher thermal tolerance in corals from the protected reef site, denoted by an increased retention of dark‐adapted maximum quantum yields at higher temperatures. These differences were resolved using both experimental setups, as corroborated by a positive linear relationship, not observed for the other parameters. Notably, short‐term acute heat stress assays resolved per‐colony (genotype) differences that may have been masked by acclimation effects in the long‐term experiment. Using our newly developed portable experimental system termed the Coral Bleaching Automated Stress System (CBASS), we thus highlight the potential of mobile, standardized short‐term acute heat stress assays to resolve fine‐scale differences in coral thermotolerance. Accordingly, such a system may be suitable for large‐scale determination and complement existing approaches to identify resilient genotypes/reefs for downstream experimental examination and prioritization of reef sites for conservation/restoration. Development of such a framework is consistent with the recommendations of the National Academy of Sciences and the Reef Restoration and Adaptation Program committees for new intervention and restoration strategies.
Background
Anthozoa, Endocnidozoa, and Medusozoa are the 3 major clades of Cnidaria. Medusozoa is further divided into 4 clades, Hydrozoa, Staurozoa, Cubozoa, and Scyphozoa—the latter 3 lineages make up the clade Acraspeda. Acraspeda encompasses extraordinary diversity in terms of life history, numerous nuisance species, taxa with complex eyes rivaling other animals, and some of the most venomous organisms on the planet. Genomes have recently become available within Scyphozoa and Cubozoa, but there are currently no published genomes within Staurozoa and Cubozoa.
Findings
Here we present 3 new draft genomes of Calvadosia cruxmelitensis (Staurozoa), Alatina alata (Cubozoa), and Cassiopea xamachana (Scyphozoa) for which we provide a preliminary orthology analysis that includes an inventory of their respective venom-related genes. Additionally, we identify synteny between POU and Hox genes that had previously been reported in a hydrozoan, suggesting this linkage is highly conserved, possibly dating back to at least the last common ancestor of Medusozoa, yet likely independent of vertebrate POU-Hox linkages.
Conclusions
These draft genomes provide a valuable resource for studying the evolutionary history and biology of these extraordinary animals, and for identifying genomic features underlying venom, vision, and life history traits in Acraspeda.
Climate change refugia in the terrestrial biosphere are areas where species are protected from global environmental change and arise from natural heterogeneity in landscapes and climate. Within the marine realm, ocean acidification, or the global decline in seawater pH, remains a pervasive threat to organisms and ecosystems. Natural variability in seawater carbon dioxide (CO2) chemistry, however, presents an opportunity to identify ocean acidification refugia (OAR) for marine species. Here, we review the literature to examine the impacts of variable CO2 chemistry on biological responses to ocean acidification and develop a framework of definitions and criteria that connects current OAR research to management goals. Under the concept of managing vulnerability, the most likely mechanisms by which OAR can mitigate ocean acidification impacts are by reducing exposure to harmful conditions or enhancing adaptive capacity. While local management options such as OAR show some promise, they present unique challenges and reducing global anthropogenic CO2 emissions must remain a priority.
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Biological color may be adaptive or incidental, seasonal or permanent, species-or population-specific, or modified for breeding, defense or camouflage. Although color is a hugely informative aspect of biology, quantitative color comparisons are notoriously difficult. Color comparison is limited by categorization methods, with available tools requiring either subjective classifications, or expensive equipment, software, and expertise. We present an R package for processing images of organisms (or other objects) in order to quantify color profiles, gather color trait data, and compare color palettes on the basis of color similarity and amount. The package treats image pixels as 3D coordinates in a "color space," producing a multidimensional color histogram for each image. Pairwise distances between histograms are computed using earth mover's distance, a technique borrowed from computer vision, that compares histograms using transportation costs. Users choose a color space, parameters for generating color histograms, and a pairwise comparison method to produce a color distance matrix for a set of images. The package is intended as a more rigorous alternative to subjective, manual digital image analyses, not as a replacement for more advanced techniques that rely on detailed spectrophotometry methods unavailable to many users. Here, we outline the basic functions of colordistance, provide guidelines for the available color spaces and quantification methods, and compare this toolkit with other available methods. The tools presented for quantitative color analysis may be applied to a broad range of questions in biology and other disciplines.
Although the environment varies, adaptive trait plasticity is uncommon, which can be due to either costs or limitations. Currently there is little evidence for costs of plasticity; limitations are a more promising explanation, including information reliability. A possible cause for a decrease in information reliability is the channeling of environmental information through one trait that then affects the phenotype of a second trait, the information path. Using an individual‐based simulation model, I explored the ways in which configurations of trait interactions and patterns of environmental variation in space and time affect the evolution of phenotypic plasticity. I found that genotypes and phenotypes evolved to shorten and simplify the information path from the environment to fitness. A shortened path was characterized by a decrease in the amount of plasticity for traits that had a less direct connection between the environment of development and fitness. A simplified path was characterized by a decrease in the amount of plasticity for traits that had multiple paths between the environment and their phenotype. These results suggest that an eighth proposition be added to the theory of the evolution of phenotypic plasticity: Trait plasticity will evolve to minimize the information path between the environment and fitness.
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Coral photosynthetic endosymbionts (Symbiodinium) are phylogenetically very diverse, yet the extent of inter- and intraspecific functional variation within clades remains largely underexplored. Understanding this variability will be critical for future research on climate change mediated responses. A properly functioning thylakoid membrane is essential for optimal photosynthetic performance both in free living and in hospite conditions. Here, we analyse the thylakoid membrane melting points of 13 Symbiodinium strains from species in Clades B and A, grown at both control (26 degrees celcius) and high temperature (31 degrees celcius). We observed a broad range of responses to thermal stress regardless of taxonomic rank. Our results sup-port and augment a growing body of the literature demonstrating that functional differences among Symbiodinium spp. are as distinct at lower taxonomic levels (i.e. interspecific) as they are among major clades. These findings highlight the importance of assessing the variability of plastid traits across the Symbiodinium tree.
Background
The phylogeny of Cnidaria has been a source of debate for decades, during which nearly all-possible relationships among the major lineages have been proposed. The ecological success of Cnidaria is predicated on several fascinating organismal innovations including stinging cells, symbiosis, colonial body plans and elaborate life histories. However, understanding the origins and subsequent diversification of these traits remains difficult due to persistent uncertainty surrounding the evolutionary relationships within Cnidaria. While recent phylogenomic studies have advanced our knowledge of the cnidarian tree of life, no analysis to date has included genome-scale data for each major cnidarian lineage.
Results
Here we describe a well-supported hypothesis for cnidarian phylogeny based on phylogenomic analyses of new and existing genome-scale data that includes representatives of all cnidarian classes. Our results are robust to alternative modes of phylogenetic estimation and phylogenomic dataset construction. We show that two popular phylogenomic matrix construction pipelines yield profoundly different datasets, both in the identities and in the functional classes of the loci they include, but resolve the same topology. We then leverage our phylogenetic resolution of Cnidaria to understand the character histories of several critical organismal traits. Ancestral state reconstruction analyses based on our phylogeny establish several notable organismal transitions in the evolutionary history of Cnidaria and depict the ancestral cnidarian as a solitary, non-symbiotic polyp that lacked a medusa stage. In addition, Bayes factor tests strongly suggest that symbiosis has evolved multiple times independently across the cnidarian radiation.
Conclusions
Cnidaria have experienced more than 600 million years of independent evolution and in the process generated an array of organismal innovations. Our results add significant clarification on the cnidarian tree of life and the histories of some of these innovations. Further, we confirm the existence of Acraspeda (staurozoans plus scyphozoans and cubozoans), thus reviving an evolutionary hypothesis put forward more than a century ago.
Electronic supplementary material
The online version of this article (10.1186/s12862-018-1142-0) contains supplementary material, which is available to authorized users.
Coral bleaching is the detrimental expulsion of algal symbionts from their cnidarian hosts, and predominantly occurs when corals are exposed to thermal stress. The incidence and severity of bleaching is often spatially heterogeneous within reef-scales (<1 km), and is therefore not predictable using conventional remote sensing products. Here, we systematically assess the relationship between in situ measurements of 20 environmental variables, along with seven remotely sensed SST thermal stress metrics, and 81 observed bleaching events at coral reef locations spanning five major reef regions globally. We find that high-frequency temperature variability (i.e., daily temperature range) was the most influential factor in predicting bleaching prevalence and had a mitigating effect, such that a 1 °C increase in daily temperature range would reduce the odds of more severe bleaching by a factor of 33. Our findings suggest that reefs with greater high-frequency temperature variability may represent particularly important opportunities to conserve coral ecosystems against the major threat posed by warming ocean temperatures.
Local adaptation is ubiquitous, but the molecular mechanisms that give rise to this ecological phenomenon remain largely unknown. A year-long reciprocal transplant of mustard hill coral (Porites astreoides) between a highly environmentally variable inshore habitat and a more stable offshore habitat demonstrated that populations exhibit phenotypic signatures that are consistent with local adaptation. We characterized the genomic basis of this adaptation in both coral hosts and their intracellular symbionts (Symbiodinium sp.) using genome-wide gene expression profiling. Populations differed primarily in their capacity for plasticity: following transplantation to a novel environment, inshore-origin coral expression profiles became significantly more similar to the local population's profiles than those in offshore-origin corals. Furthermore, elevated plasticity of the environmental stress response expression was correlated with lower susceptibility to a natural summer bleaching event, suggesting that plasticity is adaptive in the inshore environment. Our results reveal a novel genomic mechanism of resilience to a variable environment, demonstrating that corals are capable of a more diverse molecular response to stress than previously thought.
Understanding how climate change affects natural populations remains one of the greatest challenges for ecology and management of natural resources. Animals can remodel their physiology to compensate for the effects of temperature variation, and this physiological plasticity, or acclimation, can confer resilience to climate change. The current lack of a comprehensive analysis of the capacity for physiological plasticity across taxonomic groups and geographic regions, however, constrains predictions of the impacts of climate change. Here, we assembled the largest database to date to establish the current state of knowledge of physiological plasticity in ectothermic animals. We show that acclimation decreases the sensitivity to temperature and climate change of freshwater and marine animals, but less so in terrestrial animals. Animals from more stable environments have greater capacity for acclimation, and there is a significant trend showing that the capacity for thermal acclimation increases with decreasing latitude. Despite the capacity for acclimation, climate change over the past 20 years has already resulted in increased physiological rates of up to 20%, and we predict further future increases under climate change. The generality of these predictions is limited, however, because much of the world is drastically undersampled in the literature, and these undersampled regions are the areas of greatest need for future research efforts.
The costs and limits of phenotypic plasticity are thought to have important ecological and evolutionary consequences, yet they are not as well understood as the benefits of plasticity. At least nine ideas exist regarding how plasticity may be costly or limited, but these have rarely been discussed together. The most commonly discussed cost is that of maintaining the sensory and regulatory machinery needed for plasticity, which may require energy and material expenses. A frequently considered limit to the benefit of plasticity is that the environmental cues guiding plastic development can be unreliable. Such costs and limits have recently been included in theoretical models and, perhaps more importantly, relevant empirical studies now have emerged. Despite the current interest in costs and limits of plasticity, several lines of reasoning suggest that they might be difficult to demonstrate.
Although proteins in the green fluorescent protein family (GFPs) have been discovered in a wide array of taxa, their ecological functions in these organisms remain unclear. Many hypothesized roles are related to modifying bioluminescence spectra or modulating the light regime for algal symbionts, but these do not explain the presence of GFPs in animals that are non-luminous and non-symbiotic. Other hypothesized functions are unrelated to the visual signals themselves, including stress responses and antioxidant roles, but these cannot explain the localization of fluorescence in particular structures on the animals. Here we tested the hypothesis that fluorescence might serve to attract prey. In laboratory experiments, the predator was the hydromedusa Olindias formosus (previously known as O. formosa), which has fluorescent and pigmented patches on the tips of its tentacles. The prey, juvenile rockfishes in the genus Sebastes, were significantly more attracted (P<1×10(-5)) to the medusa's tentacles under lighting conditions where fluorescence was excited and tentacle tips were visible above the background. The fish did not respond significantly when treatments did not include fluorescent structures or took place under yellow or white lights, which did not generate fluorescence visible above the ambient light. Furthermore, underwater observations of the behavior of fishes when presented with a brightly illuminated point showed a strong attraction to this visual stimulus. In situ observations also provided evidence for fluorescent lures as supernormal stimuli in several other marine animals, including the siphonophore Rhizophysa eysenhardti. Our results support the idea that fluorescent structures can serve as prey attractants, thus providing a potential function for GFPs and other fluorescent proteins in a diverse range of organisms.
© 2015. Published by The Company of Biologists Ltd.
Global warming is increasing the overheating risk for many organisms, though the potential for plasticity in thermal tolerance to mitigate this risk is largely unknown. In part, this shortcoming stems from a lack of knowledge about global and taxonomic patterns of variation in tolerance plasticity. To address this critical issue, we test leading hypotheses for broad-scale variation in ectotherm tolerance plasticity using a dataset that includes vertebrate and invertebrate taxa from terrestrial, freshwater and marine habitats. Contrary to expectation, plasticity in heat tolerance was unrelated to latitude or thermal seasonality. However, plasticity in cold tolerance is associated with thermal seasonality in some habitat types. In addition, aquatic taxa have approximately twice the plasticity of terrestrial taxa. Based on the observed patterns of variation in tolerance plasticity, we propose that limited potential for behavioural plasticity (i.e. behavioural thermoregulation) favours the evolution of greater plasticity in physiological traits, consistent with the 'Bogert effect'. Finally, we find that all ectotherms have relatively low acclimation in thermal tolerance and demonstrate that overheating risk will be minimally reduced by acclimation in even the most plastic groups. Our analysis indicates that behavioural and evolutionary mechanisms will be critical in allowing ectotherms to buffer themselves from extreme temperatures.
© 2015 The Author(s) Published by the Royal Society. All rights reserved.
Understanding the ecology and evolution of the cnidarian-algal symbiosis is of major scientific interest as it is sensitive to temperature and strong light and may therefore be susceptible to climate change. The stability of this mutualism is often mediated by host color pigments that influence photosynthetic activity in symbiotic dinoflagellates either by providing the photosystem with irradiance of suitable wavelength or by protecting it from much too much and potentially damaging light. Like scleractinian corals, the upside-down jellyfish, Cassiopea andromeda, relies heavily on the nutrients provided by its symbionts of the dinoflagellate genus Symbiodinium. It occurs in several conspicuously different color morphs and is found in habitats with high levels of irradiation. We tested whether the color morphs of Cassiopea were correlated with the Symbiodinium distribution in the host and whether host color was associated with different clades of Symbiodinium. We found that the presence of color pigment did not correlate with the distribution of Symbiodinium in the host. Symbiodinium was found in both the colored tentacles of the jellyfish and the colorless feeding tentacles. At least six different color morphs co-occurred in the very shallow waters of the Red Sea, but they all hosted a single Symbiodinium clade (clade A1). Therefore, no correlation of host color morph and Symbiodinium clade could be found. Photoaccumulative or photoprotective functions of host pigments, as proposed for some scleractinian corals, thus seem unlikely in the colored tentacles (vesicles) of the upside-down jellyfish Cassiopea andromeda.
The food and beverage industry is seeking to broaden the palette of naturally derived colorants. Although considerable effort has been devoted to the search for new blue colorants in fruits and vegetables, less attention has been directed towards blue compounds from other sources such as bacteria and fungi. The current work reviews known organic blue compounds from natural plant, animal, fungal, and microbial sources. The scarcity of blue colored metabolites in the natural world relative to metabolites of other colors is discussed and structural trends common among natural blue compounds are identified. These compounds are grouped into seven structural classes and evaluated for their potential as new color additives.
Reef corals are highly sensitive to heat, yet populations resistant to climate change have recently been identified. To determine
the mechanisms of temperature tolerance, we reciprocally transplanted corals between reef sites experiencing distinct temperature
regimes and tested subsequent physiological and gene expression profiles. Local acclimatization and fixed effects, such as
adaptation, contributed about equally to heat tolerance and are reflected in patterns of gene expression. In less than 2 years,
acclimatization achieves the same heat tolerance that we would expect from strong natural selection over many generations
for these long-lived organisms. Our results show both short-term acclimatory and longer-term adaptive acquisition of climate
resistance. Adding these adaptive abilities to ecosystem models is likely to slow predictions of demise for coral reef ecosystems.
Cassiopea xamachana were bleached by elevated temperature or held in complete darkness. Wet weight was measured over several weeks in bleached and unbleached individuals with or without addition of dissolved organic matter (DOM) and/or particulate organic matter (POM) in a three-factor experiment. Wet weight decreased to a greater extent in temperature-bleached individuals compared to unbleached individuals. Bleaching by darkness produced differences that took longer to manifest themselves compared with temperature bleaching suggesting more than just loss of photosynthetic capability results from heat bleaching. No differences were found between jellyfish based on DOM and/or POM treatments. Heat stress combined with loss of zooxanthellae negatively effects C. xamachana over short time spans indicating the potential for this species to be impacted by natural bleaching events. Cassiopea xamachana could also be a useful model for further study of the effects of bleaching and the recovery.
Questions: Does sexual selection operate on locomotor performance? Which taxa are likely to have locomotor performance influenced by sexual selection? Methods: We reviewed recent literature. Conclusions: Theory and empirical evidence support the hypothesis that sexual selection operates on locomotor performance, but tests of alternative hypotheses are rare. We provide a general framework for developing testable hypotheses. Many animal taxa show potential for sexual selection as a strong force acting on locomotor performance. These include species with male aerial display or territory defence, such as numerous bird species, gliding lizards, and flying insects, but also terrestrial ones, among which lizards have been studied the most. Locomotor performance may be an important component of female choice via its direct or indirect benefits to females.
Fiji is a distribution of the popular open-source software ImageJ focused on biological-image analysis. Fiji uses modern software engineering practices to combine powerful software libraries with a broad range of scripting languages to enable rapid prototyping of image-processing algorithms. Fiji facilitates the transformation of new algorithms into ImageJ plugins that can be shared with end users through an integrated update system. We propose Fiji as a platform for productive collaboration between computer science and biology research communities.
Choosing appropriate primers is probably the single most important factor affecting the polymerase chain reaction (PCR). Specific amplification of the intended target requires that primers do not have matches to other targets in certain orientations and within certain distances that allow undesired amplification. The process of designing specific primers typically involves two stages. First, the primers flanking regions of interest are generated either manually or using software tools; then they are searched against an appropriate nucleotide sequence database using tools such as BLAST to examine the potential targets. However, the latter is not an easy process as one needs to examine many details between primers and targets, such as the number and the positions of matched bases, the primer orientations and distance between forward and reverse primers. The complexity of such analysis usually makes this a time-consuming and very difficult task for users, especially when the primers have a large number of hits. Furthermore, although the BLAST program has been widely used for primer target detection, it is in fact not an ideal tool for this purpose as BLAST is a local alignment algorithm and does not necessarily return complete match information over the entire primer range.
We present a new software tool called Primer-BLAST to alleviate the difficulty in designing target-specific primers. This tool combines BLAST with a global alignment algorithm to ensure a full primer-target alignment and is sensitive enough to detect targets that have a significant number of mismatches to primers. Primer-BLAST allows users to design new target-specific primers in one step as well as to check the specificity of pre-existing primers. Primer-BLAST also supports placing primers based on exon/intron locations and excluding single nucleotide polymorphism (SNP) sites in primers.
We describe a robust and fully implemented general purpose primer design tool that designs target-specific PCR primers. Primer-BLAST offers flexible options to adjust the specificity threshold and other primer properties. This tool is publicly available at http://www.ncbi.nlm.nih.gov/tools/primer-blast.
The upside-down jellyfish Cassiopea is a globally distributed, semi-sessile, planktonically dispersed scyphomedusa. Cassiopea occurs in shallow, tropical inshore marine waters on sandy mudflats and is generally associated with mangrove-dominated habitats. Controversy over the taxonomy of upside-down jellyfishes precedes their introduction to the Hawaiian Islands during the Second World War, and persists today. Here we address the global phylogeography and molecular systematics of the three currently recognized species: Cassiopea andromeda, C. frondosa, and C. xamachana. Mitochondrial cytochrome c oxidase I (COI) sequences from Australia, Bermuda, Fiji, the Florida Keys, the Hawaiian Islands, Indonesia, Palau, Panama, Papua New Guinea, and the Red Sea were analyzed. Highly divergent COI haplotypes within the putative species C. andromeda (23.4% Kimura 2-parameter molecular divergence), and shared haplotypes among populations of two separate putative species, C. andromeda and C. xamachana from different ocean basins, suggest multiple anthropogenic introductions and systematic confusion. Two deeply divergent Oahu haplotypes (20.3%) from morphologically similar, geographically separate invasive populations indicate long-term (14–40million years ago) reproductive isolation of phylogenetically distinct source populations and cryptic species. Data support at least two independent introductions to the Hawaiian Islands, one from the Indo-Pacific, another from the western Atlantic/Red Sea. Molecular phylogenetic results support six species: (1) C. frondosa, western Atlantic (2) C. andromeda, Red Sea/western Atlantic/Hawaiian Islands (3) C. ornata, Indonesia/Palau/Fiji (4) Cassiopea sp. 1, eastern Australia (5) Cassiopea sp. 2, Papua New Guinea and (6) Cassiopea sp. 3, Papua New Guinea/Hawaiian Islands.
Sensitivity to ocean warming is generally expected to be lower in populations from more heterogeneous thermal environments, owing to greater phenotypic plasticity and/or genotype selection. While resilience of benthic populations from thermally fluctuating environments has been investigated at a variety of spatial scales, this has received limited attention across depths and has remained unresolved for Antipatharian corals, key habitat-forming species across a wide bathymetric range in all of the world oceans. In this study, we aimed at addressing the thermal sensitivity of Antipatharian corals across depths characterized by different levels of temperature fluctuations. We used an acute ramping experimental approach to compare the thermal sensitivity of colonies of (1) the branched Antipatharian Antipathella wollastoni (Gray, 1857) from two distinct depths (25 and 40 m) in Gran Canaria (Canary Islands, Spain); and of (2) unbranched mesophotic (80 m) Stichopathes species, from Lanzarote (Canary Islands, Spain; S. gracilis (Gray, 1857)), and Stichopathes sp. clade C from Mo'orea, French Polynesia. Results showed that the daily temperature range in Gran Canaria was larger at mesophotic depths (3.9 °C vs. 2.8 °C at 40 and 25 m, respectively) and this coincided with lower thermal sensitivity in mesophotic colonies of A. wollastoni. Second, S. gracilis from Lanzarote showed a lower thermal sensitivity than the previously studied Stichopathes sp. clade C from Mo'orea (French Polynesia) inhabiting a less variable habitat. These results are in line with the climate variability hypothesis, which states that populations under more variable thermal conditions have a lower sensitivity to warming than those from more stable environments, as they have adapted/acclimated to these higher levels of temperature fluctuations.
Upside-down jellyfish (Cassiopea spp.) are predominantly tropical, but there have been recent reports of medusae in temperate environments. In 2017 they were recorded in temperate Lake Macquarie, Australia, where they have a tendency to disappear from this area through late winter (Austral, August). This raises questions about the role of temperature as a controlling factor of their abundance, and future density increases with warming oceans as a result of climate change. Here we test the degree to which temperature may drive winter die-offs of the medusa stage in temperate environments, and how this may change with altered thermal regimes. We assessed the physiological response of Cassiopea (via measurement of bell pulsation rate, bell diameter, and routine metabolic rate) under a regime mirroring Lake Macquarie's seasonal temperature drop (autumn into winter) compared to three other temperature profiles: 1) seasonal profile with predicted climate change (+ 2 °C), 2) stable temperatures equivalent to the end of autumn (20 °C) and, 3) a profile that mimicked the increasing temperatures from winter into summer (20 °C increasing to 24 °C). Overall, the results indicate that, compared to the ambient state, elevated temperatures can have positive effects on performance of Cassiopea medusae as evidenced by greater bell pulsation rate and bell diameter. The rate of bell diameter decline was lower in all elevated temperature treatments relative to the ambient profile. This highlights the capacity for elevated temperatures in the future to slow the rate of bell degradation, contributing to an increased probability of overwinter survival, thus increasing the size and duration of Cassiopea blooms in temperate waterways such as Lake Macquarie.
The presence of stable color polymorphisms within populations begs the question of how genetic variation is maintained. Consistent variation among populations in coloration, especially when correlated with environmental variation, raises questions about whether environmental conditions affect either the fulcrum of those balanced polymorphisms, the plastic expression of coloration, or both. Color patterns in male bluefin killifish provoke both types of questions. Red and yellow morphs are common in all populations. Blue males are more common in tannin‐stained swamps relative to clear springs. Here we combined crosses with a manipulation of light to explore how genetic variation and phenotypic plasticity shape these patterns. We found that the variation in coloration is attributable mainly to two axes of variation: (1) a red‐yellow axis with yellow being dominant to red, and (2) a blue axis that can override red‐yellow and is controlled by genetics, phenotypic plasticity, and genetic variation for phenotypic plasticity. The variation among populations in plasticity suggests it is adaptive in some populations but not others. The variation among sires in plasticity within the swamp population suggests balancing selection may be acting not only on the red‐yellow polymorphism but also on plasticity for blue coloration. This article is protected by copyright. All rights reserved
Morphological variability within Cassiopea is well documented and has led to inaccuracies in the establishment of species boundaries in this taxon. Cassiopea medusae specimens from the Western Pacific (Japan and the Philippines) were analysed using multiple lines of complementary evidence, including types of cnidae, macro-morphology and molecular data. These observations lead to the recognition of two distinct species: Cassiopea mayeri, sp. nov. and a previously synonymised variety now raised to species level (Cassiopea culionensis, stat. nov.). These species can be distinguished from each other using morphological features. Herein, sexually dimorphic traits are included for the first time in the descriptions of Cassiopea species. Nematocyst types not previously observed in the genus are also reported. Molecular analyses, based on individual and combined markers (16S + cytochrome c oxidase I, COI), also support two distinct species; they are not sister taxa, and both are nested together within a clade of other Cassiopea members from the Australian and Indo-Pacific regions. Species richness is underestimated in the Western Pacific region, and integrative approaches are helpful to reveal and describe species. The systematics of Cassiopea is far from completely understood, but the present study represents an important further step.
Exposure to high‐frequency temperature variability often but not always enhances coral heat tolerance, raising the question of whether this depends on the type of variability regime and past vs. current exposure. We collected corals from a macrotidal, highly fluctuating temperature environment and preconditioned them to either constant or variable daily temperatures for ~ 1.5 yr. Corals were then exposed to three new temperature variability regimes for ~ 1 month (constant control, symmetric variability, and tidal variability) to assess the effect of short‐term environmental history, followed by a 12‐d heat stress test. Measurements of visual coral health, photophysiology, photosynthesis, respiration, and calcification rates showed that preconditioning to constant vs. variable temperatures for 1.5 yr did not significantly impact coral physiology and heat tolerance. In contrast, environmental history experienced in the month prior to the heat stress test significantly influenced the physiological responses, with corals exposed to both types of variability having lower heat tolerance. Interestingly, corals in the tidal variability regime suffered greater health declines than in the symmetric variability regime although both treatments had the same cumulative heat exposure. Since heating rate and temperature amplitude were higher in the tidal variability regime (but time spent above the bleaching threshold was shorter), this suggests that short, extreme heat pulses may be more deleterious than longer but more moderate ones, though other factors likely also played a role. Overall, our findings demonstrate that daily temperature variability has significant potential to alter coral heat tolerance but only certain types of variability may enhance coral adaptive capacity.
1. Species introductions provide insights into how populations respond to new environments and selection pressures through rapid adaptation and adaptive phenotypic plasticity. However, maladaptive responses are increasingly recognised to also be common in nature. The spotted-wing drosophila, Drosophila suzukii, has rapidly invaded divergent environments providing the opportunity to examine adaptive and maladaptive phenotypic and evolutionary responses to its introduced range.
2. We studied how population density in the field and wing size of individuals varied over an elevational gradient on Hawaii. We then conducted a reciprocal common garden experiment to evaluate how temperature influenced wing size and other correlates of fitness. We did this by reciprocally rearing D. suzukii collected from low and high elevations in temperatures representative of low and high elevation.
3. We observed a wing size increase with elevation. Additionally, flies were more abundant at higher elevation. In the reciprocal common garden experiment, flies emerged faster in the warm, low-elevation temperature and developed larger wings in the cool, high-elevation temperature. Emergence of flies from high- and low-elevation sites showed a pattern suggesting maladaptation to the temperature representing their home environment.
4. We suggest that opposing selection pressures, the high vagility of flies, and extreme plasticity in body size constrain adaptation to temperature along an elevational gradient. Although successful invasive species such as D. suzukii often exhibit local adaptation, this research demonstrates that invasive species can be successful even without such adaptation.
The increased occurrence of extreme climate events, such as marine heatwaves (MHWs), has resulted in substantial ecological impacts worldwide. To date metrics of thermal stress within marine systems have focussed on coral communities, and less is known about measuring stress relevant to other primary producers, such as seagrasses. An extreme MHW occurred across the Western Australian coastline in the austral summer of 2010/2011, exposing marine communities to summer seawater temperatures 2‐5 °C warmer than average. Using a combination of satellite imagery and in situ assessments, we provide detailed maps of seagrass coverage across the entire Shark Bay World Heritage Area (ca. 13,000 km2) before (2002, 2010) and after the MHW (2014, 2016). Our temporal analysis of these maps documents the single largest loss in dense seagrass extent globally (1,310 km2) following an acute disturbance. Total change in seagrass extent was spatially heterogenous, with the most extensive declines occurring in the Western Gulf, Wooramel Bank and Faure Sill. Spatial variation in seagrass loss was best explained by a model that included an interaction between two heat stress metrics, the most substantial loss occurring when degree heat weeks (DHWm) was ≥ 10 and the number of days exposed to extreme sea surface temperature during the MHW (DaysOver) was ≥ 94. Ground‐truthing at 622 points indicated that change in seagrass cover was predominantly due to loss of Amphibolis antarctica rather than Posidonia australis, the other prominent seagrass at Shark Bay. As seawater temperatures continue to rise and the incidence of MHWs increase globally, this work will provide a basis for identifying areas of meadow degradation, or stability and recovery; and potential areas of resilience.
Aim
To test if physiological acclimation can buffer species against increasing extreme heat due to climate change.
Location
Global.
Time period
1960 to 2015.
Major taxa studied
Amphibians, arthropods, brachiopods, cnidarians, echinoderms, fishes, molluscs, reptiles.
Methods
We draw together new and existing data quantifying the warm acclimation response in 319 species as the acclimation response ratio (ARR): the increase in upper thermal limit per degree increase in experimental temperature. We develop worst‐case scenario climate projections to calculate the number of years and generations gained by ARR until loss of thermal safety. We further compute a vulnerability score that integrates across variables estimating exposure to climate change and species‐specific tolerance through traits, including physiological plasticity, generation time and latitudinal range extent.
Results
ARR is highly variable, but with marked differences across taxa, habitats and latitude. Polar terrestrial arthropods show high ARRs [95% upper confidence limit (UCL95%) = 0.68], as do some polar aquatic invertebrates that were acclimated for extended durations (ARR > 0.4). While this physiological plasticity buys 100s of years until thermal safety is lost, combination with long generation times leads to decreased potential for evolutionary adaptation. Additionally, 27% of marine polar invertebrates have no capacity for acclimation and reptiles and amphibians have minimal ARR (UCL95% = 0.16). Low physiological plasticity, long generations times and restricted latitudinal ranges combine to distinguish reptiles, amphibians and polar invertebrates as being highly vulnerable amongst ectotherms.
Main conclusions
In some taxa the combined effects of acclimation capacity and generation time can provide 100s of years and generations before thermal safety is lost. The accuracy of assessments of vulnerability to climate change will be improved by considering multiple aspects of species’ biology that, in combination may increase persistence under extreme heat events, and increase the probability for evolutionary rescue.
Scleractinian corals occur in tropical regions near their upper thermal limits and are severely threatened by rising ocean temperatures. However, several recent studies have shown coral populations can harbor genetic variation in thermal tolerance. Here we have extended these approaches to study heat tolerance of corals in the Persian/Arabian Gulf, where heat‐tolerant local populations experience extreme summer temperatures (up to 36°C). To evaluate whether selection has depleted genetic variation in thermal tolerance, estimate potential future adaptive responses and understand the functional basis for these corals’ unusual heat tolerance, we conducted controlled crosses in the Gulf coral Platygyra daedalea. Heat tolerance is highly heritable in this population (h²=0.487‐0.748), suggesting substantial potential for adaptive responses to selection for elevated temperatures. To identify genetic markers associated with this variation, we conducted genome‐wide SNP genotyping in parental corals and tested for relationships between paternal genotype and offspring thermal tolerance. Resulting multilocus SNP genotypes explained a large fraction of variation in thermal tolerance in these crosses (69%). To investigate the functional basis of these differences in thermal tolerance, we profiled transcriptional responses in tolerant and susceptible families, revealing substantial sire effects on transcriptional responses to thermal stress. We also studied sequence variation in these expressed sequences, identifying alleles and functional groups of differentially expressed genes associated with thermal tolerance. Our findings demonstrate that corals in this population harbor extensive genetic variation in thermal tolerance, and heat‐tolerant phenotypes differ in both gene sequences and transcriptional stress responses from their susceptible counterparts.
This article is protected by copyright. All rights reserved.
Do all animals sleep? Sleep has been observed in many vertebrates, and there is a growing body of evidence for sleep-like states in arthropods and nematodes. Here we show that sleep is also present in Cnidaria, an earlier-branching metazoan lineage. Cnidaria and Ctenophora are the first metazoan phyla to evolve tissue-level organization and differentiated cell types, such as neurons and muscle. In Cnidaria, neurons are organized into a non-centralized radially symmetric nerve net that nevertheless shares fundamental properties with the vertebrate nervous system: action potentials, synaptic transmission, neuropeptides, and neurotransmitters . It was reported that cnidarian soft corals and box jellyfish exhibit periods of quiescence, a pre-requisite for sleep-like states, prompting us to ask whether sleep is present in Cnidaria. Within Cnidaria, the upside-down jellyfish Cassiopea spp. displays a quantifiable pulsing behavior, allowing us to perform long-term behavioral tracking. Monitoring of Cassiopea pulsing activity for consecutive days and nights revealed behavioral quiescence at night that is rapidly reversible, as well as a delayed response to stimulation in the quiescent state. When deprived of nighttime quiescence, Cassiopea exhibited decreased activity and reduced responsiveness to a sensory stimulus during the subsequent day, consistent with homeostatic regulation of the quiescent state. Together, these results indicate that Cassiopea has a sleep-like state, supporting the hypothesis that sleep arose early in the metazoan lineage, prior to the emergence of a centralized nervous system.
It has been 55 years since Hugo Freudenthal described Symbiodinium microadriaticum (Dinophyceae), the type species of this large and important dinoflagellate genus found commonly in mutualistic symbiosis with cnidarians, other invertebrates, and certain protists. However, no type specimen was designated by Freudenthal, thus S. microadriaticum was invalid, as was Symbiodinium and every species subsequently assigned to the genus. The original culture was lost, but since 1977, a different culture, CCMP2464/rt-061, had been considered to represent S. microadriaticum. From this culture a preserved specimen is herein designated the holotype of S. microadriaticum, validating the binomial and Symbiodinium. All binary designations previously considered to belong in Symbiodinium also are validated herein. This article is protected by copyright. All rights reserved.
Bright colouration in animals has long attracted the attention of physicists, chemists
and biologists. As such, studies on the functions of colours are interdisciplinary,
focusing on the mechanisms of colour production and maintenance, the
physical and chemical properties of the colour-producing elements, and visual
systems and behaviour of potential receivers. Blue colouration has received a large
share of research attention and is fascinating for several reasons: blue has been
attributed to a very broad range of functions, blue is achieved by a great variety of
mechanisms (although their production and maintenance costs are currently
unclear), and the blue part of the spectrum (450–490 nm) can be perceived by most
taxa. This review explores the breadth of studies that propose a function for blue
colouration. In so doing, it discusses the diversity of ways in which blue colours
are produced both as pigments and structural colours, and that blue visual pigments
are common across a broad range of taxa. This analysis of the current
literature emphasizes the importance of multidisciplinary hypothesis testing when
attempting to elucidate the function of colours, the need for manipulative over
correlative evidence for the function of colours, and, as colour research becomes
evermore interdisciplinary, the need for well-defined consistent terminology
Quantitative genetic models of evolution of phenotypic plasticity are used to derive environmental tolerance curves for a population in a changing environment, providing a theoretical foundation for integrating physiological and community ecology with evolutionary genetics of plasticity and norms of reaction. Plasticity is modelled for a labile quantitative character undergoing continuous reversible development and selection in a fluctuating environment. If there is no cost of plasticity, a labile character evolves expected plasticity equalling the slope of the optimal phenotype as a function of the environment. This contrasts with previous theory for plasticity influenced by the environment at a critical stage of early development determining a constant adult phenotype on which selection acts, for which the expected plasticity is reduced by the environmental predictability over the discrete time lag between development and selection. With a cost of plasticity in a labile character, the expected plasticity depends on the cost and on the environmental variance and predictability averaged over the continuous developmental time lag. Environmental tolerance curves derived from this model confirm traditional assumptions in physiological ecology and provide new insights. Tolerance curve width increases with larger environmental variance, but can only evolve within a limited range. The strength of the trade-off between tolerance curve height and width depends on the cost of plasticity. Asymmetric tolerance curves caused by male sterility at high temperature are illustrated. A simple condition is given for a large transient increase in plasticity and tolerance curve width following a sudden change in average environment.
An opportunity to explore the effects of fluctuating temperatures on tropical scleractinian corals arose when diurnal warming (as large as 4.7°C) was detected over the rich coral communities found within the back reef of Moorea, French Polynesia. In April and May 2007, experiments were completed to determine the effects of fluctuating temperature on Pocillopora meandrina and Porites rus, and consecutive trials were used to expose them for 13days to 26°C, 28°C (ambient conditions), 30°C, or a fluctuating treatment ranging from 26 to 30°C over 24h. The multivariate response was assessed using maximum dark-adapted quantum yield of PSII (FV/FM), Symbiodinium density, chlorophyll-a content, and calcification. In trial 1, multivariate physiology of both species was significantly affected by treatments, with the fluctuating temperature resulting in a 17–45% decline in Symbiodinium density (relative to the ambient) matching that occurring at a constant 30°C; FV/FM, chlorophyll-a content, and calcification, did not differ between the fluctuating and the steady treatments. In contrast, in trial 2 that utilized corals collected two weeks after those used in trial 1, the corals were unaffected by the treatments, likely due to an environment×trial interaction caused by seasonal declines in Symbiodinium density. Together, these results demonstrate that short transgressions to ecologically relevant high and low temperatures can elicit a potentially detrimental response equivalent to that occurring upon exposure to a constant high temperature. The dissimilar responses among dependent variables and consecutive trials underscore the importance of temporal replication and multivariate approaches in coral ecophysiology. It is likely that recent history has a stronger effect on the response of corals to treatments than is currently recognized.
The evolutionary and environmental stability of character correlations has increasingly been the focus of ecological and quantitative genetic studies. Although the genetic stability of character correlations is a central assumption of quantitative genetic models of phenotypic evolution, theoretical considerations suggest that both the genetic and the phenotypic architecture should change in response to selection and to environmental heterogeneity. We investigate genetic (population) differences and plasticity to nutrient availability of the phenotypic architecture describing the whole-plant phenotype of Arabidopsis thaliana (Brassicaceae). We found significant genetic differences among early and late flowering ecotypes in the relationships between several traits, when a path-analytical model was used to estimate character correlations. Furthermore, we found significant plasticity of several path coefficients when nutrient levels were altered. A whole-plant analysis considering all paths in the model simultaneously confirmed that populations of A. thaliana are characterized by distinct phenotypic architectures, and that these are altered in different ways by environmental changes. We discuss the implications of these findings for our understanding of selective pressure on and response by multivariate phenotypes.
We explore the effects of linear and quadratic reaction norms on heritability and directional selection. Genetic variation for reaction norm parameters can alter the heritability of traits; the magnitude of the heritability depends upon both the environment and the correlation among the parameters. Genetic variation for reaction norm parameters can alter the response to directional selection. Selection on a trait in one environment can shift both the mean of the trait measured across environments and the plasticity of the trait; the signs and magnitudes of these responses depend on the correlations among the parameters of the reaction norm. Our model is consistent with the results of ten experiments for selection on a trait in a single environment. In all experiments, selection towards the overall mean of the population always resulted in a relatively lower plasticity than selection away from the overall mean. Our model was able to predict the results of two experiments for selection on a trait index calculated over more than one environment. Predictions were good for the direct response to selection but poorer for the correlated response to selection. Our results indicate the need for more data on the effects of environment on genetic parameters, especially correlations among reaction norm parameters.