Testing the hypothesis of adaptive radiation and its eco-phenotypic implications

Abstract

[eng] Without a shadow of a doubt, adaptive radiation processes have played a major role in our current understanding of how species evolved on our planet. Since the original proposal of the theory of evolution by natural selection was published by Charles Darwin and Alfred Wallace more than 150 years ago, examples of adaptive radiations have been extensively studied, particularly in oceanic islands. Because of their well-known geochronology, well defined boundaries, and simpler ecosystems when compared with continental regions, volcanic archipelagos had been referred as natural laboratories to study evolutionary or ecological process. The focus of this thesis is the spider genus Dysdera, which has undergone a remarkable diversification in the Canary Islands—a volcanic archipelago situated off the northwestern coast of Africa. The primary objective of this thesis is to test the hypothesis that the great diversification of the group was the result of an adaptive radiation process and gain insights into the drivers of their ecophenotypic differentiation. First, we conducted an integrative taxonomic revision of the group, employing a combination of molecular and morphological data. Our specific objectives were to determine whether DNA barcodes reveal the presence of previously overlooked lineages and help resolve any conflicts that may arise between different datasets. Additionally, we aimed to investigate whether species that are morphologically distinguishable can potentially be identified using DNA barcodes. Second, using geometric morphometrics, we analysed various morphological structures of the spider body. Our goal was to establish a comprehensive guide for studying variation in the body plan of a non-model system. By integrating different views of similar phenotypic structures, we revealed that the different body parts analysed are interconnected, providing insights into various ecological factors. This research sheds light on the importance of considering multiple morphological characters when studying organismal variation. Third, we have integrated geometric morphometric tools and experimental approaches with a fully resolved phylogeny. With that we have characterized the different cheliceral morphologies present in the archipelago and unveiled their dietary function. Additionally, we tested if they evolved multiple times independently during the diversification of the group and unveil if trophic specialization could be a case of irreversibility in the Dysdera spiders from the Canary Islands. We identified nine different cheliceral morphologies. We confirmed that some of these morphologies were indeed related to either “generalist” or “woodlice-specialized” diets. We provided significant support for the evolutionary convergence of cheliceral morphs in the context of an adaptive radiation. Finally, our results pointed towards the irreversibility of trophic specialization in these spiders. Four, we investigated the diversification patterns and the role that trophic specialization played in this diversification. Additionally, with the use of climatic variables and occurrence data, we unveiled the underlying mode of speciation in the islands. Our results provide support for the hypothesis of adaptive radiation, showing an initial burst of diversification followed by a deceleration in diversification rates. We also found that trophic specialization played a significant role in shaping the diversification patterns within the group. Furthermore, our analysis suggests that speciation primarily occurred in allopatry, followed by secondary contact events. Five, we tested whether species underwent an ecological release process following colonization of low competition environments. With that aim, we employed a multidimensional approach to evaluate various aspects of the species' ecological niche. Specifically, we considered trophic breadth, morphological disparity, and climatic and distributional range. Our findings demonstrate that the potential for experiencing an ecological niche release in Canarian Dysdera is strongly influenced by their trophic specialization. Specialist species exhibit the ability to expand their spatial range and trophic breadth to a greater extent compared to generalist species. The present work provides compelling evidence supporting the Dysdera genus diversification as a case of adaptive radiation in the Canary Islands, and the ecological and evolutionary effects associated with their cheliceral morphology.