Genetic insights into the range expansion of the cattle egret (Pelecaniformes: Ardeidae) in Brazil and population differentiation between the native and colonized areas

Abstract

Bubulcus ibis ibis expanded its range by flying across the Atlantic Ocean from Africa or Europe to South America. To provide insights into the source of migrant birds, we genotyped cattle egret sampled in Central and southern Africa (N = 129, 13 sites, five countries) and Brazil (N = 166, six sites) at 14 microsatellites. Expected heterozygosity was high in all colonies, but significantly lower in Brazilian samples. Population-genetic analyses based on different assumptions concurrently found significant genetic differentiation between Brazil and Africa. The genetic homogeneity among African populations did not enable us to identify the source of the invasive birds. Among Brazilian populations, the highest proportion of the African allelic ancestry was found in Fernando de Noronha. This archipelago on the north-eastern coast of Brazil could be an important stopover site for migrating birds coming from Africa. Bayesian demographic analyses supported population growth in Africa with subsequent expansion to Brazil and migration from Africa to Brazil at the time of colonization. We discuss our findings in light of previous colonization trajectories suggested by meteorological models and the anthropogenic changes that may promote the expansion of the cattle egret in Brazil.