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Invasive species often exhibit rapid evolution in their introduced ranges despite the genetic bottlenecks that are thought to accompany the translocation of small numbers of founders; however, some invasions may not fit this “genetic paradox.” The invasive cane toad (Rhinella marina) displays high phenotypic variation across its environmentally het...
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Invasive species often evolve rapidly following introduction despite genetic bottlenecks that may result from small numbers of founders; however, some invasions may not fit this “genetic paradox”. The invasive cane toad (Rhinella marina) displays high phenotypic variation across its introduced Australian range. Here, we used three genome-wide datas...
The Journal of Human Evolution (JHE) was founded 50 years ago when much of the foundation for how we think about human evolution was in place or being put in place, providing the main framework for how we consider our origins today. Here, we will explore historical developments, including early JHE outputs, as they relate to our understanding of th...
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... In Australia, the range of this species has expanded rapidly over the last eight decades (Urban, Phillips, Skelly, & Shine, 2008). A reduction in genetic diversity after the introduction does not seem to have affected ecologically relevant traits in cane toads (Selechnik et al., 2019); instead, the up-regulation of a suite of genes related to metabolism, energetics, and immune function may hold the key to increased invasiveness in this species (Rollins, Richardson, & Shine, 2015). The spread of toads in Australia has resulted in the appearance of a range-expansion phenotype manifested in dispersal-prone behavior, faster growth rates, longer leg lengths, and greater stamina in toads at the invasion front (Lindström, Brown, Sisson, Phillips, & Shine, 2013;Phillips, Brown, Webb, & Shine, 2006). ...
The Anthropocene has witnessed catastrophic amphibian declines across the globe. A multitude of new, primarily human‐induced drivers of decline may lead to extinction, but can also push species onto novel evolutionary trajectories. If these are recognized by amphibian biologists, they can be engaged in conservation actions. Here, we summarize how principles stemming from evolutionary concepts have been applied for conservation purposes, and address emerging ideas at the vanguard of amphibian conservation science. In particular, we examine the consequences of increased drift and inbreeding in small populations and their implications for practical conservation. We then review studies of connectivity between populations at the landscape level, which have emphasized the limiting influence of anthropogenic structures and degraded habitat on genetic cohesion. The rapid pace of environmental changes leads to the central question of whether amphibian populations can cope by either adapting or by shifting their ranges. We gloomily conclude that extinction seems far more likely than adaptation or range shifts for most species. That said, conservation strategies employing evolutionary principles, such as selective breeding, introduction of adaptive variants through translocations, ecosystem interventions aimed at decreasing phenotype‐environment mismatch or genetic engineering may effectively counter amphibian decline in some areas or for some species. The spread of invasive species and infectious diseases has often had disastrous consequences, but has also provided some premier examples of rapid evolution with conservation implications. Much can be done in terms of setting aside valuable amphibian habitat that should encompass natural and agricultural areas, as well as designing protected areas to maximize the phylogenetic and functional diversity of the amphibian community. We conclude that an explicit consideration and application of evolutionary principles, although certainly not a silver bullet, should increase effectiveness of amphibian conservation in both the short and long term.
... The invasive range of cane toads in Australia includes highly varied environments; climatic conditions in the range core are similar to those in the native range (Central and South America), but intermediate areas and the invasion front receive much less annual rainfall (2,000-3,000 mm in QLD, 400-1,000 mm in NT and WA) and have higher annual mean temperatures (21-24°C in QLD, 24-27°C in NT and WA; Bureau of Meteorology A.G., 2018). Toads cluster genetically based on these environmental patterns: Toads from the range core are genetically distinct from those from intermediate areas and the invasion front (Selechnik, Richardson, & Shine, 2019). Furthermore, loci putatively under selection are involved in tolerance of temperature extremes and dehydration (Selechnik et al., 2019). ...
... Toads cluster genetically based on these environmental patterns: Toads from the range core are genetically distinct from those from intermediate areas and the invasion front (Selechnik, Richardson, & Shine, 2019). Furthermore, loci putatively under selection are involved in tolerance of temperature extremes and dehydration (Selechnik et al., 2019). Traits such as locomotor performance at high temperatures also follow this pattern (Kosmala, Brown, Christian, Hudson, & Shine, 2018), but others do not. ...
... Spleens were collected from toads in the range core (QLD: Gordonvale and Daintree, N = 5 each), intermediate areas (NT: Cape Crawford and Timber Creek, N = 4 each), and invasion front (WA: Caroline Pool and Durack River, N = 5 each). Soft clustering was performed to visualize differential expression patterns between different phases of the invasion (Figure 2) be under selection) have previously been found in a gene involved in blood clotting ( Selechnik et al., 2019). However, if lowering blood clotting rates is indeed an adaptation to aridity in toads from intermediate areas and the front, then one might expect that transcripts promoting blood clotting would be downregulated in these individ- ...
Host–pathogen associations change rapidly during a biological invasion and are predicted to impose strong selection on immune function. It has been proposed that the invader may experience an abrupt reduction in pathogen‐mediated selection (“enemy release”), thereby favoring decreased investment into “costly” immune responses. Across plants and animals, there is mixed support for this prediction. Pathogens are not the only form of selection imposed on invaders; differences in abiotic environmental conditions between native and introduced ranges are also expected to drive rapid evolution. Here, we use RNA‐Seq to assess the expression patterns of immune and environmentally associated genes in the cane toad (Rhinella marina) across its invasive Australian range. Transcripts encoding mediators of costly immune responses (inflammation, cytotoxicity) showed a curvilinear relationship with invasion history, with highest expression in toads from oldest and newest colonized areas. This pattern is surprising given theoretical expectations of density dynamics in invasive species and may be because density influences both intraspecific competition and parasite transmission, generating conflicting effects on the strength of immune responses. Alternatively, this expression pattern may be the result of other evolutionary forces, such as spatial sorting and genetic drift, working simultaneously with natural selection. Our findings do not support predictions about immune function based on the enemy release hypothesis and suggest instead that the effects of enemy release are difficult to isolate in wild populations, especially in the absence of information regarding parasite and pathogen infection. Additionally, expression patterns of genes underlying putatively environmentally associated traits are consistent with previous genetic studies, providing further support that Australian cane toads have adapted to novel abiotic challenges.
Non‐invasive sampling methods for studying intestinal microbiome are widely applied in studies of endangered species and in those conducting temporal monitoring during manipulative experiments. Although existing studies show that non‐invasive sampling methods among different taxa vary in their accuracy, to date, no studies have been published comparing non‐lethal sampling methods in adult amphibians. In this study, we compare microbiomes from two non‐invasive sample types (faeces and cloacal swabs) to that of the large intestine in adult cane toads, Rhinella marina. We use 16S rRNA sequencing to investigate how microbial communities change along the digestive tract and which non‐lethal sampling method better represents large intestinal microbiota. We found that cane toads’ intestinal microbiota was dominated by Bacteroidetes, Proteobacteria, Firmicutes and, interestingly, we also saw a high proportion of Fusobacteria, which has previously been associated with marine species and changes in frog immunity. The large and small intestine of cane toads had a similar microbial composition, but the large intestine showed higher diversity. Our results indicate that cloacal swabs were more similar to large intestine samples than were faecal samples, and small intestine samples were significantly different from both non‐lethal sample types. Our study provides valuable information for future investigations of the cane toad gut microbiome and validates the use of cloacal swabs as a non‐lethal method to study changes in the large intestine microbiome. These data provide insights for future studies requiring non‐lethal sampling of amphibian gut microbiota.
