The role of the environmental niche in fostering ecological divergence during adaptive radiation remains enigmatic. In this study, we examine the interplay between environmental niche divergence and conservatism in the context of adaptive radiation on oceanic islands, by characterizing the niche breadth of four Hawaiian arthropod radiations: Tetragnatha spiders (Tetragnathidae Latreille, 1804), Laupala crickets (Gryllidae Otte, 1994), a clade of Drosophila flies (Drosophilidae Fallén, 1823) and Nesosydne planthoppers (Delphacidae Kirkaldy, 1907). We assembled occurrence datasets for the four lineages, modelled their distributions and quantified niche overlap. All four groups occupy the islands in distinct ways, highlighting the contrasting axes of diversification for different lineages. Laupala and Nesosydne have opposite environmental niche extents (broad and narrow, respectively), whereas Tetragnatha and Drosophila share relatively intermediate tolerances. Temperature constrains the distributions of all four radiations. Tests of phylogenetic signal suggest that, for Tetragnatha and Drosophila, closely related species exhibit similar environmental niches; thus, diversification is associated with niche conservatism. Sister species comparisons also show that populations often retain similar environmental tolerances, although exceptions do occur. Results imply that diversification does not occur through ecological speciation; instead, adaptive radiation occurs largely within a single environment.
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Reinforcement and the Proliferation of Species
Adaptive radiations are characterized by the rapid proliferation of species. Explaining how adaptive radiations occur therefore depends, in part, on identifying how populations become reproductively isolated––and ultimately become different species. Such reproductive isolation could arise when populations adapting to novel niches experience selection to avoid interbreeding and, consequently, evolve mating traits that minimize such hybridization via the process of reinforcement. Here, we highlight that a downstream consequence of reinforcement is divergence of conspecific populations, and this further divergence can instigate species proliferation. Moreover, we evaluate when reinforcement will––and will not––promote species proliferation. Finally, we discuss empirical approaches to test what role, if any, reinforcement plays in species proliferation and, consequently, in adaptive radiation. To date, reinforcement’s downstream effects on species proliferation remain largely unknown and speculative. Because the ecological and evolutionary contexts in which adaptive radiations occur are conducive to reinforcement and its downstream consequences, adaptive radiations provide an ideal framework in which to evaluate reinforcement’s role in diversification.
more » « less- PAR ID:
- 10127744
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Journal of Heredity
- ISSN:
- 0022-1503
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Some of the most important insights into the ecological and evolutionary processes of diversification and speciation have come from studies of island adaptive radiations, yet relatively little research has examined how these radiations initiate. We suggest that
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Abstract Adaptive radiation plays a fundamental role in our understanding of the evolutionary process. However, the concept has provoked strong and differing opinions concerning its definition and nature among researchers studying a wide diversity of systems. Here, we take a broad view of what constitutes an adaptive radiation, and seek to find commonalities among disparate examples, ranging from plants to invertebrate and vertebrate animals, and remote islands to lakes and continents, to better understand processes shared across adaptive radiations. We surveyed many groups to evaluate factors considered important in a large variety of species radiations. In each of these studies, ecological opportunity of some form is identified as a prerequisite for adaptive radiation. However, evolvability, which can be enhanced by hybridization between distantly related species, may play a role in seeding entire radiations. Within radiations, the processes that lead to speciation depend largely on (1) whether the primary drivers of ecological shifts are (a) external to the membership of the radiation itself (mostly divergent or disruptive ecological selection) or (b) due to competition within the radiation membership (interactions among members) subsequent to reproductive isolation in similar environments, and (2) the extent and timing of admixture. These differences translate into different patterns of species accumulation and subsequent patterns of diversity across an adaptive radiation. Adaptive radiations occur in an extraordinary diversity of different ways, and continue to provide rich data for a better understanding of the diversification of life.more » « less
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ABSTRACT Adaptive radiations are rich laboratories for exploring, testing, and understanding key theories in evolution and ecology because they offer spectacular displays of speciation and ecological adaptation. Particular challenges to the study of adaptive radiation include high levels of species richness, rapid speciation, and gene flow between species. Over the last decade, high‐throughput sequencing technologies and access to population genomic data have lessened these challenges by enabling the analysis of samples from many individual organisms at whole‐genome scales. Here we review how population genomic data have facilitated our knowledge of adaptive radiation in five key areas: (1) phylogenetics, (2) hybridization, (3) timing and rates of diversification, (4) the genomic basis of trait evolution, and (5) the role of genome structure in divergence. We review current knowledge in each area, highlight outstanding questions, and focus on methods that facilitate detection of complex patterns in the divergence and demography of populations through time. It is clear that population genomic data are revolutionising the ability to reconstruct evolutionary history in rapidly diversifying clades. Additionally, studies are increasingly emphasising the central role of gene flow, re‐use of standing genetic variation during adaptation, and structural genomic elements as facilitators of the speciation process in adaptive radiations. We highlight hybridization—and the hypothesized processes by which it shapes diversification—and questions seeking to bridge the divide between microevolutionary and macroevolutionary processes as rich areas for future study. Overall, access to population genomic data has facilitated an exciting era in adaptive radiation research, with implications for deeper understanding of fundamental evolutionary processes across the tree of life.more » « less
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Abstract Species interactions drive diverse evolutionary outcomes. Speciation by cascade reinforcement represents one example of how species interactions can contribute to the proliferation of species. This process occurs when the divergence of mating traits in response to selection against interspecific hybridization incidentally leads to reproductive isolation among populations of the same species. Here, we investigated the population genetic outcomes of cascade reinforcement in North American chorus frogs (Hylidae:
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