In the Light of Evolution Volume X: Comparative Phylogeography (2017) / Chapter Skim
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14 Evolutionary Lessons from California Plant Phylogeography - Victoria L. Sork, Paul F. Gugger, Jin-Ming Chen, and Silke Werth
14 Evolutionary Lessons from California Plant Phylogeography - Victoria L. Sork, Paul F. Gugger, Jin-Ming Chen, and Silke Werth
Pages 275-294
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From page 275... ...
Because most phylogeographic studies have used neutral markers, the role of selection may have been under valued. In this paper, we contend that plants provide a useful evolution ary lesson about the impact of selection on spatial patterns of neutral genetic variation, when the environment affects which individuals can colonize new sites, and on adaptive genetic variation, when environ mental heterogeneity creates divergence at specific loci underlying local adaptation.
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From page 276... ...
However, the focus on commonality has overlooked the fact that, ultimately, phylogeography is the result of the interaction between organisms and their environment. Because species respond individualistically to climate fluctuations across the physical landscape, co-occurring species often show discordant phylogeographic patterns (e.g., Soltis et al., 2006)
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From page 277... ...
For example, algae photosynthesize, corals and many marine invertebrates are sessile, and fungi exhibit high reproductive output with leptokurtic dispersal. Nonetheless, our goal here is to explore how key characteristics found in plants illustrate an evolutionary lesson about the role of natural selection in shaping migration patterns and demographic history over space and time.
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From page 278... ...
Thus, the sessile nature of plants may, at a minimum, better document the spatial signature of adaptive versus neutral processes, which provides a lesson on the importance of this trait for phylogeographic studies. Most Plant Species Exhibit a Leptokurtic Pattern of Gene Flow An obvious difference between plants and animals is their dispersal biology.
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From page 279... ...
In contrast, the lesson from plants is that they often have a distribution of dispersal distances and that the interaction between dispersal and selection for local adaptation can promote divergence at smaller scales for adaptive genetic variation and less divergence among neutral markers. High Reproductive Output Most plant species have high fecundity and much higher offspringto-parent ratios than animal species.
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From page 280... ...
When combined with the leptokurtic dispersal kernel for pollen and seeds, it enhances the potential for the evolution of local adaptation within the vast majority of locally dispersed propagules and the opportunity for long-distance dispersal events to transport the seeds somewhere that an individual can survive. This life history trait would enhance the ability of plants or other sessile organisms to have large species distributions.
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From page 281... ...
In the literature, we also find other examples of environmental effects on the phylogeography of plants. For example, in a study of the Sonoran desert succulent Euphorbia lomelii in Baja California, temperature variables affecting phenological synchrony of flowering significantly affected geographic patterns of genetic variation after controlling for phylogeographic history (Dyer et al., 2010)
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From page 282... ...
Thus, we see many tree species with widespread distributions whose longevity may have prevented population contractions from resulting in complete extinction before environ mental conditions would allow expansion. CASE STUDIES OF PLANT PHYLOGEOGRAPHY Evolutionary Lessons from a California Endemic Oak, Quercus lobata Study Region California is a species-rich biogeographic region that simultaneously offers a multifaceted history of geological change, complex geographical structure, and historic climatic fluctuations (Calsbeek et al., 2003)
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From page 283... ...
. Thus, California provides an opportunity to examine phylogeographic patterns that can be distinct from the postglacial population expansion dynamics reflected by species in Europe (Petit et al., 2003)
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From page 284... ...
. The phylogeographic analyses of chloroplast DNA variation support the inference that valley oak's distribution was stable and that migration was local (Fig.
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From page 285... ...
. Species distribution models based on climate data indicate that valley oak habitat has been largely stable throughout its current distribution since at least the last interglacial period over 100 ka (Gugger et al., 2013)
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From page 286... ...
Phylogeographic studies use neutral genetic markers to study migration and demographic history, but a growing body of research investigates geographic patterns of adaptive genetic variation. In valley oak, landscape genomic analyses to test for natural selection identify a number of candidate genes for local adaptation to climate (Gugger et al., 2016; Sork et al., 2016)
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From page 287... ...
On the other hand, high reproductive output, effective gene flow, and large effective population sizes may enhance adaptive responses. Evolutionary Lessons from California's State Lichen, Ramalina menziesii Study Region The widely distributed lace lichen R
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From page 288... ...
(A) Closeup photography of lace lichen thallus (photograph taken by S.W.)
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From page 289... ...
(B) Bayesian Markov Chain Monte Carlo tree generated in BEAST on the basis of four nuclear genes, with ecoregion-specific clades colorcoded as indicated in the figure.
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From page 290... ...
For this particular lichen, high dispersal capability and high reproductive output of the microscopic spores are essential, given that the photobiont is not codispersed in these propagules. An interesting feature of the lace lichen is that it can persist in a broad range of habitats and ecoregions, most likely due to local adaptation of the photosynthetic green alga, rather than the mycobiont.
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From page 291... ...
. Lace lichen's widespread dispersal capability, along with its high reproductive output, and its ability to associate with locally adapted algal strains have allowed it to occupy an exceptionally wide geographic range across multiple climate zones, encompassing tropical/subtropical dry-to-humid temperate conditions.
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From page 292... ...
The fact that they show incongruent phylogeographic structure within ecoregions and lack of comigration among ecoregions is a dramatic illustration of how selection by habitat, generation time, and dispersal abilities can create different histories and different evolutionary trajectories, even for taxa sharing the same environment. CONCLUSIONS The overarching evolutionary lesson from plants and these two case studies that occupy regions with high environmental heterogeneity and high species diversity is the contribution of natural selection in the response of species to climate fluctuations and the presence of major physical barriers.
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From page 293... ...
Future studies that use the new genomic tools that include neutral and adaptive genetic markers, incorporate information about adaptive and demographic responses, and include the contribution of life history traits will more accurately model species-specific shifts in species distributions due to climate change. ACKNOWLEDGMENTS We thank the organizers of this symposium, Francisco Ayala and John Avise, its participants, and two anonymous referees.
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