In the Light of Evolution Volume X: Comparative Phylogeography (2017) / Chapter Skim
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11 Phenotypes in Phylogeography: Species' Traits, Environmental Variation, and Vertebrate Diversification - Kelly R. Zamudio, Rayna C. Bell, and Nicholas A. Mason
11 Phenotypes in Phylogeography: Species' Traits, Environmental Variation, and Vertebrate Diversification - Kelly R. Zamudio, Rayna C. Bell, and Nicholas A. Mason
Pages 215-234
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From page 215... ...
With new methods and markers, the focus in phylogeography shifted to previously unrecognized geographic genetic variation, thus reducing the attention paid to phenotypic variation in those same diverging lineages. Although phenotypic differences among lineages once provided the main data for studies of evolutionary change, the mechanisms shaping phenotypic differentiation and their integra tion with intraspecific genetic structure have been underexplored in phylogeographic studies.
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. If most species show phylogeographic structure caused by landscape features that impede gene flow, then the geographic distribution of divergent lineages should coincide among species that coinhabit those landscapes.
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Finally, we emphasize the importance of natural history and field collections for the successful integration of organismal phenotypes and phylogeographic studies. SPECIES-SPECIFIC TRAITS AND IDIOSYNCRATIC PHYLOGEOGRAPHIC PATTERNS Comparative phylogeography seeks to characterize concordant phylogeographic breaks or contact zones, biogeographic "hotspots" for understanding mechanisms shaping genetic structure within and among species with shared distributions (Rissler and Smith, 2010; Moritz et al., 2009)
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For example, phenotypes that directly affect dispersal or persistence in new environments, such as those related to locomotor efficiency, physiological tolerance, or body size, can influence the frequency of migration and gene flow among subdivided populations. Others, such as recruitment rate, life span, and time to maturity will affect population size and turnover and thus the amount of genetic variation in subdivided populations.
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. A second study in the tropics confirmed that topographic complexity and especially macro habitat preferences had strong effects on population divergence, so that species occupying forests and topographically complex regions showed deeper phylogeographic structure (Rodríguez et al., 2015)
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Just as common responses to phylogeographic barriers became a null hypothesis early in the history of the field (Papadopoulou and Knowles, Chapter 8, this volume) , an understanding of how organismal traits mediate responses to variable environments and demography will be necessary for a complete picture of the expected mode and rate of phylogeographic diversification (Papadopoulou and Knowles, 2015b)
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, and DNA sequencing technologies (Edwards et al., 2015) Phenotypic variation Detectable Undetectable Geographically clustered Geographically dispersed A C E 1 4 1 4 1 4 2 5 2 5 2 5 3 6 3 6 3 6 Present 1 1 1 2 2 2 Phylogeographic structure 3 3 3 4 4 4 7 7 7 5 5 5 6 8 6 8 6 8 7 7 7 9 9 9 8 8 8 9 9 9 B D F 1 4 1 4 1 4 2 5 2 5 2 5 3 6 3 6 3 6 Absent 2 2 2 5 5 5 6 6 6 4 4 4 7 7 7 8 8 8 9 8 9 8 9 8 7 7 7 9 9 9 3 3 3 1 1 1 FIGURE 11.1 Potential patterns of phylogeographic structure and phenotypic diversity among populations (A–F)
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TABLE 11.1 Patterns of Phylogeographic Structure and Phenotypic Diversity in Vertebrates Geographic Variation in Phylogeographic Biological Mechanisms Phenotypes Structure or Processes Empirical Examples Clustered Present Neutral divergence, Neotropical oscines local adaptation, (Winger and Bates, divergent sexual 2015) ; treefrogs selection (Warwick et al., 2015)
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of genetic and phenotypic variation within a phylogeographic framework. Geographically Clustered Phenotypes with Phylogeographic Structure Phylogeographic structure often coincides with phenotypic variation (Fig.
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. This pattern likely reflects subtle phylogeographic structure resulting from recent, rapid genetic isolation or adaptive divergence with ongoing gene flow among subspecies.
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Nonetheless, combining high-throughput sequencing with experimental studies to disentangle phenotypic plasticity and adaptive genetic divergence within a phylogeographic context is an exciting area of ongoing research. Geographically Dispersed Phenotypes with Phylogeographic Structure Many species are polymorphic with discrete or continuous phenotypic variation shared among phylogeographically structured populations (Fig.
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. Furthermore, rapid adaptation and phenotypic plasticity in response to regional conditions also can induce geographically clustered phenotypic variation without perceivable phylogeographic structure at larger spatial scales, especially if gene flow reduces genetic isolation among populations (Fig.
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Dispersed polymorphism among populations that lack phylogeographic structure is more likely in vagile than dispersal-limited taxa, and the maintenance of phenotypic diversity will depend on the strength of selection acting on phenotypic variants among populations connected by high levels of gene flow. Uniform Phenotypes with Phylogeographic Structure Many lineages exhibit phylogeographic structure with little or no detectable phenotypic variation (Fig.
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, may display phenotypic uniformity and little to no phylogeographic structure among populations. A phylogeographic framework can disentangle cases in which continued gene flow homogenizes genetic and phenotypic variation among populations and cases in which historical demographic events, such as recent and/or rapid range expansions, have limited the time for phenotypic differences to accumulate (Marko and Hart, 2011)
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From page 229... ...
Thus, a phylogeographic approach that encompasses phenotypic and environmental variation within species and contextualizes the demographic history of functional traits can provide exceptional insights into how organismal diversity evolves. Identifying the role of extrinsic barriers in shaping the geographic distribution of functional phenotypic variation is an essential first step for investigating local adaptation.
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Phylogeographic studies of functional traits can identify the processes that shape adaptive variation and estimate the strength of selection acting on phenotypic variation by building links between locally adapted genotypes/phenotypes, population demography, and environmental variation in selective regimes. The challenge of this approach, however, is that it requires identifying and quantifying adaptive phenotypes, obtaining samples that encompass relevant environmental and phenotypic variation across the species' range, and characterizing functional genetic variation underlying adaptive phenotypes as well as neutral variation to estimate population demographic history.
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Just as phylogeography initially formalized conceptual links among heredity, population divergence, and phylogenetic relationships among species, an analytical framework that advocates genealogical and spatially explicit analyses of intraspecific functional genetic and phenotypic variation will bridge microevolutionary processes acting on individual populations and macroevolutionary patterns at larger spatial and temporal scales. These integrative and rigorous approaches have been possible only in select systems to date, but identifying the underlying genetic basis of phenotypic variation within species is becoming increasingly tractable in vertebrates.
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FIELD STUDIES AND NATURAL HISTORY COLLECTIONS: SOURCES OF PHENOTYPIC DATA Organismal phenotypes, many of which are the target of selection and play important roles in species performance in variable environments, are important components of how we identify and categorize biodiversity. We have argued that, despite the clear benefits of integrating patterns of phenotypic evolution into phylogeographic predictions and inferences, this integration has yet to be fully realized.
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Meanwhile, our ability to quantify genetic and phenotypic variation also has expanded; thus, the field of phylogeography now is poised for another integration, this time by incorporating data on phenotypic variation in diverging lineages, understanding the selective and genetic basis for that variation, and quantifying the role that phenotypes play in diversification. This integration has the potential to unify once again disparate fields in evolutionary biology, and address how interactions among abiotic landscape features and biological features of species shape biodiversity (Greene, 2005)
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