CULLEY, THERESA M. Department of Ecology & Evolutionary Biology, University of California-Irvine, Irvine CA 92697. - Genetic effects of forest fragmentation in woodlot populations of an understory herb, Viola pubescens (Violaceae).
Habitat fragmentation has become an important concern in the
midwestern United States due to conversion of temperate deciduous
forests to agricultural land during the past two centuries. The
genetic effect of forest fragmentation in these areas was examined in
a common understory herb, Viola pubescens, a species that
produces self-pollinated cleistogamous (CL) flowers and potentially
outcrossing chasmogamous (CH) flowers. Using allozymes, genetic
variation was measured in populations inhabiting woodlots of differing
sizes (0.5 - 40.5 ha) and distances from one another (0.3 - 11.4 km)
within the agricultural landscape of central Ohio. Woodlot size was
significantly and positively correlated with all measures of genetic
variation (A, P, Ho, and He), with variation
highest in the larger woodlot populations (e.g., P = 0.88,
Ho = 0.39) and lowest in the smaller woodlots (P = 0.25,
Ho = 0.03). Overall, populations were genetically
differentiated from one another (q = 0.34),
but there was no relationship between genetic and geographic distance.
More likely, limited gene flow in this species may reflect a reduction
in pollinators in the fragmented woodlots, leading to an increase in
selfing rates through automatic selfing in CL flowers and delayed
selfing in CH flowers. Despite the commonality of V. pubescens
and the reproductive advantage it has through the CH/CL system,
fragmented populations still experience genetic erosion. This study
highlights the need for conserving the remaining populations of this
species, along with other less common taxa in the temperate deciduous
forest.
Key words: cleistogamy, genetic effects, habitat fragmentation, Viola pubescens