Genetic diversity and population structure of North America’s rarest heron, the reddish egret (Egretta rufescens)

Abstract

The global distribution of the reddish egret is characterized by disjunct colonies occurring from the Pacific side of Northwest Mexico to the Caribbean. We examined distantly isolated colonies of reddish egret to determine global population genetic structure. We used seven polymorphic microsatellites to accomplish five goals: (1) to assess range wide population differentiation among reddish egret (Egretta rufescens) populations, (2) identify extent of gene flow, (3) determine any historical occurrence of bottlenecks, (4) assess genetic differentiation between color morphs, (5) clarify subspecies status of E. r. dickeyi, a completely dark morph population located in and around the Baja California peninsula, Mexico. Genetic differentiation was dramatic (global Fst = 0.161) throughout the reddish egrets range extending from Baja California, Mexico to Great Inagua, Bahamas. Differentiation occurred among three distinct regions (Fst = 0.238) but not among colonies/islands within regions suggesting regional philopatry. Genetic diversity (alleles per locus, and heterozygosity) in Baja California Sur, Mexico and Great Inagua, Bahamas populations is lower than in the Texas/Mexico population due to minimal dispersal between regions and smaller population sizes. Dark and white color morphs when present within the same region showed no differentiation. Patterns of recent population bottlenecks are not evident in each of the three regional populations. With evidence of limited gene flow in addition to low genetic diversity and prospects of habitat loss we recommend that reddish egrets be managed as three distinct or evolutionary significant units.