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Monday, January 25 • 11:20am - 11:40am
Gene Flow From An Adaptively Divergent Source Causes Genetic Rescue, Not Outbreeding Depression, In Two Wild Populations of Trinidadian Guppies

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AUTHORS: Sarah W. Fitzpatrick, Michigan State University; Lisa M. Angeloni, Colorado State University; W. Chris Funk, Colorado State University

ABSTRACT: Interplay between genetic variation and demography can determine the ultimate fate of wild populations. Genetic factors associated with small populations such as loss of genetic variation and inbreeding may cause population decline and an inability to adapt to changing environments. Genetic rescue (GR), defined as an increase in population growth owing to the infusion of new alleles via gene flow, is one way to reverse a genetically induced population decline. However, its use is limited largely due to current poor understanding of the fitness effects of gene flow. Theory predicts that gene flow can boost fitness when recipient populations are small and inbred, but too much gene flow may homogenize populations, constrain local adaptation, and reduce fitness. Experimental introduction experiments using Trinidadian guppies set up an ideal opportunity to monitor demographic and genetic effects of gene flow from an adaptively divergent immigrant source on two small native populations. I monitored population dynamics using capture-mark-recapture analysis for 29 months (3 months before gene flow and 26 months after) and genotyped all individuals for 17 months (3 months before gene flow and 14 months after) at microsatellite loci to classify individuals by their genetic ancestry: native, immigrant, F1 hybrid, or F2 hybrid. I then reconstructed a pedigree for both wild populations to compare estimates of total fitness (i.e., lifetime reproductive success) among individuals of different genetic ancestry. In total I monitored 9,590 guppies from two streams and genotyped 3,298 guppies for individual fitness estimates. My study captures the initial and sustained effects of gene flow in detail, over 6-8 generations, under fully natural conditions. I documented substantial and long-term net positive effects on population fitness that can be attributed to gene flow (i.e., genetic rescue) in two natural populations. Immigration and subsequent hybridization with genetically and phenotypically divergent individuals led to a dramatic increase in within-population genetic variation, individual fitness, abundance, and population vital rates, though dynamic differences were observed between streams, sexes, and over time. My results suggest that adaptive divergence should not, in itself, preclude the use of assisted gene flow for inducing fitness benefits, and also that low levels of migration can result in genetic rescue without the loss of native genetic signature. Indeed, low levels of gene flow can provide a substantial demographic boost to small populations, and may provide the buffer needed to withstand environmental stochasticity.

Monday January 25, 2016 11:20am - 11:40am EST