Figure 1 - uploaded by Geoff S Oxford
Content may be subject to copyright.
Map of the Stockholm archipelago showing sampling sites: for island names see Table 1. The approximate boundary of Stockholm is shown in darker shading. For analyses of geographical trends (see text), islands were grouped as follows: (1, 2, 3); (5, 6, 7, 8); (10, 11); (12, 13); (14, 15, 16, 17). The inset shown the locations of the more detailed Stockholm (S) and Go¨teborgGo¨teborg (G) maps (Figures 1 and 2, respectively).
Source publication
The selective significance, if any, of many invertebrate visible polymorphisms is still not fully understood. Here we examine colour- and black spotting-morph frequencies in the spider Enoplognatha ovata in populations on two Swedish archipelagos with respect to different spatial scales and, in one archipelago, against the background of variation a...
Contexts in source publication
Context 1
... archipelago, v 2 (24) = 155.6, p < < 0.001). Where more than one sample (n ‡ 20) was taken on an island a one-way ANOVA was run on arcsine-transformed fre- quencies for each colour-morph comparing varia- tion within and between islands for each of the two archipelagos. Neither was significant. Similar analyses were made of the variation within and between single islands or island groups, as defined in the legends to Figures 1 and 2, for each of the Stockholm and Go¨teborgGo¨teborg archipelagos to check for geographical trends in morph frequencies. Again, none was found. Finally, one-way ANOVA was used to compare colour-morph frequencies within and between the two archipelagos. The results were also non-significant, suggesting that for colour there is no larger-scale pattern in variation over and above that found between local ...
Context 2
... frequency of individuals possessing at least some black spots in samples from the Stockholm archipelago was very high (97.7%, total sample size, n = 915, Table 1) and the proportions varied sig- nificantly between populations (for n ‡ 20, exact R Â C test, p = 0.006). Of those individuals with spots most (98.8%) possessed 10-12 with the majority of the remainder showing four (the 023000 configuration -see Figure 1d in Oxford, 1989). Spotting frequencies were not scored for the Ido¨population Ido¨population because the sample size was small and all spiders were frozen for allozyme analyses. The presence of spots in samples from the Go¨teborgGo¨teborg archipelago was also high (90.5%, n = 1576, Table 1) of which 94.5% of individuals possessed 10-12 spots, and the remainder usually four (as above). The frequency of spotting between popu- lations was marginally significant (for n ‡ 20, exact R Â C test, p = 0.043). Because the presence of spots was fixed in five of the samples from the Stockholm islands, one-way ANOVA on arcsine transformed frequencies (all samples with n ‡ 20) was performed on only those populations contain- ing some spiders without spots, in order to investi- gate variation within and among island groups. There was no among-island-group variation over and above that within island groups. A similar result was found in the Go¨teborgGo¨teborg island groups. However, comparisons between the archipelagos (again using only samples containing both spotted and none- spotted morphs with n ‡ 20) showed them to be highly significantly different with respect to spotting frequencies (F (1,20) = 15.7, p = 0.001). This is de- spite the fact that excluding fixed populations, all of which were on the Stockholm islands, will have the effect of making the two archipelagos more similar with respect to spotting; i.e., the test performed is conservative. Within spotted spiders, as noted above, there was a very clear bi-modal distribution of total spot numbers on both archipelagos. The proportion with 10 or 12 spots ('full' spots, Table 1) versus the rest within the spotted class was not significantly different between populations for the Stockholm archipelago (for n ‡ 20, exact R Â C test, p = 0.055) but was marginally significant for the Go¨teborgGo¨teborg islands (for n ‡ 20, exact R Â C test, p = 0.047). ANOVAs were performed on the frequencies (arcsine transformed) of 'full' spots within the spotted class, again ignoring samples in which 'full' spotting was fixed. There were no significant differences among island groups within the two archipelagos but a significant difference between them (F (1,17) = 5.86, p = 0.027). Thus the Go¨teborgGo¨teborg islands had spiders with lower fre- quencies of spotted individuals and, within this group, lower numbers with the 'full' spot com- plement, compared with those on the Stockholm islands. Taking all samples (n ‡ 20) together, there is a significant correlation between the arcsine- transformed frequencies of total spotting and fre- quencies of 'full' spots within the spotted class (r = 0.58, p = 0.001, df = 25) (Figure 3). Ten samples are fixed for one or both of these variables and these might unduly affect the correlation coefficient. Repeating the calculation with these 10 points omitted also yielded a significant correla- tion (r = 0.60, p = 0.011, df = 15). A positive association between the frequency of spotted morphs, and the proportion of fully spotted indi- viduals within this class, is also found in combined data from three UK populations with a wider range of spotting frequencies; Nidderdale (north- ern, central England), Pembrokeshire (south-west Wales) and Ainsdale (north-west England) (r = 0.40, p = 0.011, df = 38, frequencies arc- sine transformed) (Oxford, unpubl. ...
Context 3
... were collected from islands in the Stockholm (samples 1-17) and Go¨teborgGo¨teborg (samples 18-30) archipelagos (Figures 1 and 2) between 5 and 15 August, 1997. They were sought in road- side patches of broad-leaved vegetation and sam- ples were obtained within as short a linear distance as possible (up to c. 30 m), depending on density. In August mature females are established within rolled leaves; searching for leaves rather than spi- ders directly ensured that sampling was random with respect to visible morphs. Sampled leaves were sought in adjacent stretches of vegetation by the two authors and collected into separate bags. After a sufficient number had been gathered the first c.50 animals drawn equally from both bags were placed live into individual Eppendorf tubes for subsequent electrophoresis. The lids of the tubes were perforated for ventilation and the spi- ders placed in a cool box. The remaining individ- uals were preserved in 70% ethanol and sorted into separate tubes according to colour morph within 24 h (Oxford & Reillo, 1993). Live spiders were stored under cool conditions through the fieldwork period, transported to the University of York in a cool box and preserved at )80°C until required. Table 1. The approximate boundary of Stockholm is shown in darker shading. For anal- yses of geographical trends (see text), islands were grouped as follows: (1, 2, 3); (5, 6, 7, 8); (10,11); (12,13); (14,15,16,17). The inset shown the locations of the more detailed Stockholm (S) and Go¨teborgGo¨teborg (G) maps (Figures 1 and 2, respectively). Table 1. The approximate bound- ary of Go¨teborgGo¨teborg is shown in darker shading. For analyses of geographical trends (see text), islands were grouped as fol- lows: (18,19); (20,21,22); (23,24); (25,26,27); (28,29,30). See inset to Figure 1 for the location of the study area ...
Context 4
... were collected from islands in the Stockholm (samples 1-17) and Go¨teborgGo¨teborg (samples 18-30) archipelagos (Figures 1 and 2) between 5 and 15 August, 1997. They were sought in road- side patches of broad-leaved vegetation and sam- ples were obtained within as short a linear distance as possible (up to c. 30 m), depending on density. In August mature females are established within rolled leaves; searching for leaves rather than spi- ders directly ensured that sampling was random with respect to visible morphs. Sampled leaves were sought in adjacent stretches of vegetation by the two authors and collected into separate bags. After a sufficient number had been gathered the first c.50 animals drawn equally from both bags were placed live into individual Eppendorf tubes for subsequent electrophoresis. The lids of the tubes were perforated for ventilation and the spi- ders placed in a cool box. The remaining individ- uals were preserved in 70% ethanol and sorted into separate tubes according to colour morph within 24 h (Oxford & Reillo, 1993). Live spiders were stored under cool conditions through the fieldwork period, transported to the University of York in a cool box and preserved at )80°C until required. Table 1. The approximate boundary of Stockholm is shown in darker shading. For anal- yses of geographical trends (see text), islands were grouped as follows: (1, 2, 3); (5, 6, 7, 8); (10,11); (12,13); (14,15,16,17). The inset shown the locations of the more detailed Stockholm (S) and Go¨teborgGo¨teborg (G) maps (Figures 1 and 2, respectively). Table 1. The approximate bound- ary of Go¨teborgGo¨teborg is shown in darker shading. For analyses of geographical trends (see text), islands were grouped as fol- lows: (18,19); (20,21,22); (23,24); (25,26,27); (28,29,30). See inset to Figure 1 for the location of the study area ...
Context 5
... were collected from islands in the Stockholm (samples 1-17) and Go¨teborgGo¨teborg (samples 18-30) archipelagos (Figures 1 and 2) between 5 and 15 August, 1997. They were sought in road- side patches of broad-leaved vegetation and sam- ples were obtained within as short a linear distance as possible (up to c. 30 m), depending on density. In August mature females are established within rolled leaves; searching for leaves rather than spi- ders directly ensured that sampling was random with respect to visible morphs. Sampled leaves were sought in adjacent stretches of vegetation by the two authors and collected into separate bags. After a sufficient number had been gathered the first c.50 animals drawn equally from both bags were placed live into individual Eppendorf tubes for subsequent electrophoresis. The lids of the tubes were perforated for ventilation and the spi- ders placed in a cool box. The remaining individ- uals were preserved in 70% ethanol and sorted into separate tubes according to colour morph within 24 h (Oxford & Reillo, 1993). Live spiders were stored under cool conditions through the fieldwork period, transported to the University of York in a cool box and preserved at )80°C until required. Table 1. The approximate boundary of Stockholm is shown in darker shading. For anal- yses of geographical trends (see text), islands were grouped as follows: (1, 2, 3); (5, 6, 7, 8); (10,11); (12,13); (14,15,16,17). The inset shown the locations of the more detailed Stockholm (S) and Go¨teborgGo¨teborg (G) maps (Figures 1 and 2, respectively). Table 1. The approximate bound- ary of Go¨teborgGo¨teborg is shown in darker shading. For analyses of geographical trends (see text), islands were grouped as fol- lows: (18,19); (20,21,22); (23,24); (25,26,27); (28,29,30). See inset to Figure 1 for the location of the study area ...
Similar publications
The candy-stripe spider, Enoplognatha ovata, exhibits a striking color polymorphism comprising three morphs. A number of lines of evidence strongly suggest that this polymorphism is maintained by natural selection: its presence in a sister species, E. latimana; the physical nature of the variation; the virtual lack of monomorphic populations; the h...
Citations
... electrophoresis has proven very useful for the analysis of geographic structure of arachnids. Some early studies focused specifically on population structure (Porter & Jakob 1990;Steiner et al. 1992;Smith & Engel 1994;Hudson & Adams 1996;Smith & Hagen 1996;Boulton et al. 1998), but allozymes have also been used to examine questions of relatedness among colonies of social spiders (Johannesen et al. 1998;Johannesen & Lubin 1999, 2001Johannesen & Veith 2001;Evans & Goodisman 2002;Yip et al. 2012), paternity (Schafer & Uhl 2002), species boundaries and speciation (Piel & Nutt 2000;Ramirez & Chi 2004), dispersal (Pedersen & Loeschcke 2001;Schafer et al. 2001), the effects of forest fragmentation, whether natural (Vandergast et al. 2004) or manmade (Ramirez & Haakonsen 1999;Gurdebeke et al. 2000), and to estimate selection on color polymorphisms (Tso et al. 2002;Oxford 2005;Oxford & Gunnarsson 2006;Croucher et al. 2012) as well as patterns of diversification within rapidly diversifying lineages (Pons & Gillespie 2004;Baert et al. 2008;De Busschere et al. 2010). ...
Particularly intriguing examples of adaptive radiation are those in which lineages show parallel or convergent evolution, suggesting utilization of similar genetic or developmental pathways. The current study focuses on an adaptive radiation of Hawaiian “spiny-leg” spiders in which diversification is associated with repeated convergent evolution leading to similar sets of ecomorphs on each island. However, two species on the oldest islands in the archipelago exhibit variability, occurring as two different ecomorphs. More derived species on the younger islands show much less variability, any one species displaying a single ecomorph. We measured ecomorphological features within individuals over time to determine the nature of the variability. Then, using transcriptomes, we conducted lineage-based tests for selection under varying models and analyses of gene tree versus species tree incongruencies. Our results provide strong evidence that variability in color in T. kauaiensis and T. polychromata is associated with development within individuals (polyphenism). Moreover, a total of 28 loci showed a signature of selection associated with loss of the color-changing phenotype, and 37 loci showed a signature of selection associated with the colonization of a new environment. The results illustrate how developmental polyphenism might provide an avenue for the repeated evolution of ecomorphs during adaptive radiation.This article is protected by copyright. All rights reserved.
... electrophoresis has proven very useful for the analysis of geographic structure of arachnids. Some early studies focused specifically on population structure (Porter & Jakob 1990;Steiner et al. 1992;Smith & Engel 1994;Hudson & Adams 1996;Smith & Hagen 1996;Boulton et al. 1998), but allozymes have also been used to examine questions of relatedness among colonies of social spiders (Johannesen et al. 1998;Johannesen & Lubin 1999, 2001Johannesen & Veith 2001;Evans & Goodisman 2002;Yip et al. 2012), paternity (Schafer & Uhl 2002), species boundaries and speciation (Piel & Nutt 2000;Ramirez & Chi 2004), dispersal (Pedersen & Loeschcke 2001;Schafer et al. 2001), the effects of forest fragmentation, whether natural (Vandergast et al. 2004) or manmade (Ramirez & Haakonsen 1999;Gurdebeke et al. 2000), and to estimate selection on color polymorphisms (Tso et al. 2002;Oxford 2005;Oxford & Gunnarsson 2006;Croucher et al. 2012) as well as patterns of diversification within rapidly diversifying lineages (Pons & Gillespie 2004;Baert et al. 2008;De Busschere et al. 2010). ...
Molecular genetic tools have been a boon to arachnologists for decades and used to study many unique aspects of arachnid biology including genomics, phylogenetics, population genetics, and biogeography. These tools have evolved over time and now provide myriad methods for exploring evolutionary questions. Early tools, while still useful under the proper circumstances, are giving way to a new generation of DNA sequencing technologies. These new platforms yield impressive amounts of data at a fraction of the cost of traditional techniques. Herein, we discuss the history and future of molecular evolutionary arachnology in terms of available genetic/genomic tools and their potential applications, strengths, weaknesses, and relative costs. Next-generation sequencing (NGS) platforms are varied in their methods and potential uses, making high-throughput sequencing studies focusing on a wide array of questions tractable. To date, relatively few studies have employed NGS technologies using arachnids, but many could benefit from using them. Because no model species exist within the class Arachnida, we have a limited understanding of arachnid genomics. With the ever-advancing nature of sequencing technologies and bioinformatics, arachnologists can relatively easily implement NGS studies to bridge the gaps in our understanding and open avenues for deeper and more powerful experiments. To this end, we discuss examples of applications of NGS technologies focusing on arachnid taxa. Despite the allure of acquiring massive quantities of sequence data, we should recognize the limitations of existing NGS technologies and not forsake pre-NGS methods when these technologies could adequately address our questions.
... Perhaps the best known examples of intra-specific mimicry arise as a component of male polymorphisms, with territorial and femalelike males (sneakers), presenting two different sexual strategies (Shuster & Wade, 2003). Intra-specific mimicry also occurs in the form of female phenotypes resembling conspecific males, e.g. in butterflies (Cook et al., 1994), spiders (Oxford & Gunnarsson, 2006) and especially in damselflies (Van Gossum et al., 2008b). The question then arises as to whether the extent of mimetic fidelity also increases with the population-specific mimic/model ratio, as observed for Batesian mimicry. ...
The coexistence of two or more heritable morphs within species’ populations is commonly observed in nature, a phenomenon known as polymorphism. Intriguingly, such polymorphisms are often restricted to only the male or only the female sex (intra-sexual polymorphisms). The phenomenon is paradoxical to evolutionary biologists because selection is expected to favor not more than only a single phenotype. Hence, questions related to whether and how different morphs can be maintained are subject to classic and long-standing debates. Theory posits that longterm maintenance of polymorphisms is possible only under a restricted set of conditions, but exact mechanisms remain poorly understood in many cases.
The overall objective of my PhD thesis is to explore several mechanisms that may help to explain maintenance of intra-sexual polymorphism. I selected female polymorphic damselflies as my model system, in which two or three female morphs can easily be distinguished based on their body coloration, while only a single male type occurs. The coexistence of these female morphs is commonly explained as a counter adaptation to reduce costly male sexual harassment. However, observations in several species indicate extreme and often gradually varying morph frequencies across populations. As it appears from recent work, social interactions alone appear insufficient to thoroughly explain this geographic variation in female morph frequencies, thus questioning the exact mechanisms underlying this polymorphism. Additional mechanisms have been suggested, including divergent selection. Specifically, one morph may be favored over the others depending on a given set of environmental conditions like solar radiation, ambient temperature or precipitation
regimes.
In my thesis, I first ask to what extend geographic variation in morph frequencies is related to numerous of investigated biotic and abiotic variables and to the genetic variability across populations. Given the lack of spatial organization in morph frequencies along a continuous 1100 km transect, the limited explanatory power by the investigated ecological variables and the extremely low genetic variation in a region characterized by atypical morph frequencies across sites, I suggest that historical and present-day stochastic processes may play a more prominent role than previously acknowledged in shaping biogeographical patterns in morph frequencies.
Next to the above described exploration of biogeographical patterns and covarying factors, the observed frequency and density variation across sites itself offers ample opportunity to evaluate and test predictions based on social interactions. Besides body coloration, I found that female morphs differ in multiple traits like behavior, morphology, immune function, energy reserves and fecundity. This made me suggest that correlational selection may favor optimal trait combinations in which female morphs maximize fitness in alternative ways. When including the entire range of female morph frequencies, I show under experimental and natural conditions that males bias their mating preference towards the most common morph within a given population. This biased mating behaviour most likely translates into dissimilar harassment levels between female morphs, causing negative frequency-dependent costs in terms of female morph fecundity. I further show geographic variation in morph-specific behavioral harassment resistance strategies, which may as well be related to the social environment.
Furthermore, one female morph (andromorph) shows remarkable phenotypic resemblance with conspecific males. In line with ideas on intra-specific mimicry, I show that andromorphs share more morphological similarities with males compared with other females. Moreover, consistent with expectations based on signal detection theory, this mimetic similarity increases with the proportion of andromorphs (mimics) to the males (models). Because investigated short- and long-term weather parameters did not differently affect behavioral and physiological traits of female morphs and because of the low predictive power of such parameters in explaining geographic morph frequency variation, I indicate a minor role for abiotic conditions in explaining the maintenance of this polymorphism. Instead, I conclude that frequency- and densitydependent selection imposed by male harassment acting within populations may, at least in part, keep this polymorphism in balance. In addition, I point at underestimated stochastic effects that may cancel out effects of selection under some conditions.
... Perhaps the best-known examples of intraspecific mimicry arise as a component of male polymorphisms, with territorial and female-like males (sneakers), presenting two different sexual strategies [9]. Intraspecific mimicry also occurs in the form of female phenotypes resembling conspecific males (e.g. in butterflies [10], spiders [11] and especially in damselflies [12]). The question then arises as to whether the extent of mimetic fidelity also increases with the population-specific mimic/model ratio, as observed for Batesian mimicry. ...
Contemporary theory predicts that the degree of mimetic similarity of mimics towards their model should increase as the mimic/model ratio increases. Thus, when the mimic/model ratio is high, then the mimic has to resemble the model very closely to still gain protection from the signal receiver. To date, empirical evidence of this effect is limited to a single example where mimicry occurs between species. Here, for the first time, we test whether mimetic fidelity varies with mimic/model ratios in an intraspecific mimicry system, in which signal receivers are the same species as the mimics and models. To this end, we studied a polymorphic damselfly with a single male phenotype and two female morphs, in which one morph resembles the male phenotype while the other does not. Phenotypic similarity of males to both female morphs was quantified using morphometric data for multiple populations with varying mimic/model ratios repeated over a 3 year period. Our results demonstrate that male-like females were overall closer in size to males than the other female morph. Furthermore, the extent of morphological similarity between male-like females and males, measured as Mahalanobis distances, was frequency-dependent in the direction predicted. Hence, this study provides direct quantitative support for the prediction that the mimetic similarity of mimics to their models increases as the mimic/model ratio increases. We suggest that the phenomenon may be widespread in a range of mimicry systems.
... Such colour variation can result from any number of factors ranging from diet to genes (see Oxford & Gillespie (1998), for review). Colour polymorphism is well studied in only very few theridiid species, such as the Hawaiian 'happy face spider', Theridion grallator Simon, 1900 (Oxford & Gillespie 1998, 2001 ), Theridion californicum (Oxford 2009) and Enoplognatha (Oxford 2005; Oxford & Gunnarsson 2006 ). While completely unknown, Anelosimus represents another promising lineage for understanding the mechanics of colour variation in theridiid spiders. ...
Madagascar is a biodiversity hotspot, thought to be colonized mostly via Cenozoic dispersal from Africa, followed by endemic radiation of multiple lineages. Anelosimus spiders are diverse in Madagascar, and, like their congeners in the Americas, are most diverse in wet montane forests. Most Anelosimus species are social in that they cooperate in web building and prey capture either during a part of their life cycles (subsocial), including hitherto studied Malagasy species, or permanently (quasisocial). One Central American coastal species, Anelosimus pacificus, has secondarily switched to solitary living, and available evidence suggests that its closest relatives from S. America and Europe are likely also solitary. Here, we show that the only known coastal Anelosimus species in Madagascar and Comoros -Anelosimus decaryi and Anelosimus amelie sp. n. - are also solitary. Using a phylogenetic approach, we test two competing hypotheses: (i) that Malagasy Anelosimus are monophyletic and thus represent a second example of reversal to solitary living in a littoral habitat or (ii) that solitary and subsocial lineages independently colonized Madagascar. We find that solitary Malagasy Anelosimus are closely related to their solitary counterparts from Europe and the Americas, while subsocial Malagasy species nest sister to Anelosimus nelsoni from S. Africa. This finding suggests that (i) the two Anelosimus lineages colonized Madagascar independently and (ii) a reversal to solitary behaviour has occurred only once in Anelosimus. Thus, solitary littoral Malagasy species did not descend from Malagasy mountains, but arrived from much further afar. African and possibly American origin of the two lineages is implied by our findings. To restore natural classification of Anelosimus, Seycellocesa Koçak & Kemal is synonymized with it.
