Levels of gene flow among populations of a wolf spider in a recently fragmented habitat: current versus historical rates |
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Authors: | David H Reed View-Hune Teoh Gail E Stratton and Robert A Hataway |
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Institution: | (1) Department of Biology, University of Mississippi, P.O. Box 1848, University, MS 38677, USA;(2) Present address: Department of Biology, University of Louisville, Louisville, KY 20292, USA |
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Abstract: | Gene flow among populations is important for countering the deleterious effects of random genetic drift and inbreeding, as
well as spreading beneficial mutations. Wind-driven aerial dispersal is known to occur in numerous plants and invertebrates.
Its evolution suggests that historically, suitable habitat patches were dense enough to make such undirected dispersal evolutionarily
advantageous. Using microsatellite markers we assessed the population genetic structure of seven populations of a wolf spider
(Rabidosa rabida) capable of ballooning. Historically, each spider population received a mean of 1.5 migrants per generation from the other
six populations. Over the past several generations the number of migrants reaching a population is only 0.2. This statistically
significant reduction in gene flow coincides with high levels of habitat fragmentation and suggests that undirected aerial
dispersal is ineffective in this fragmented landscape. Further, individuals within populations showed signficantly elevated
levels of homozygosity relative to Hardy–Weinberg expectations, suggesting that cursorial dispersal may be very limited and
genetic structure within populations exists. Inbreeding coefficients averaged 0.18 over all seven populations with very little
variation among populations (s = 0.02). Fitness was lower in smaller populations relative to larger ones. Altered landscapes pose evolutionary dilemmas
for many metapopulations and species that depend on undirected movement for dispersal may be particularly vulnerable to habitat
fragmentation. |
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