Molecular Genetic Assessment of Population Structure, Paternity, and Sex Ratios for the Reddish Egret

Abstract

We examined distantly isolated colonies of Reddish Egret to determine global population genetic structure. We analyzed 13 polymorphic satellites and used nine of them to accomplish seven goals: 1) to assess range wide population differentiation among Reddish Egret (Egretta rufescens) populations, 2) identify extent of gene flow and immigration among populations, 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 Baja, Mexico, 6) assess paternity of nest mates, 7) determine offspring sex ratio. We collected blood samples of244 nestlings, each from a separate nest, from colonies in Texas, Baja California, Bahamas, and Florida. Genetic differentiation was dramatic (global Fst = .257) throughout the Reddish Egret's range extending from Baja California, Mexico to Great Inagua, Bahamas. Differentiation occurred between 3 distinct regions but not between colonies/islands within regions. Genetic diversity (Alleles per locus, and heterozygosity) is less in Baja, Mexico and Great Inagua populations than the Texas/Florida population due to minimal immigration between regions and historical population reductions. Dark and white color morphs when present within the same region showed little to no differentiation. Patterns of recent population bottlenecks are evident in each of the 3 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 3 distinct or evolutionary significant units (Baja, Texas/Florida, and Inagua). Furthermore, our results do not refute the current subspecies status of E. r .dickeyi. In nests where all offspring were sampled, possible multiple paternity was identified 15.4% of the time. Offspring sex ratio did not deviate significantly from expected.