Colonization of the American Continent by African populations of cattle egret (Bubulcus ibis) and its parasites (Plasmodium and Haemoproteus): genetics revealing the bioinvasion process

Abstract

The Cattle Egret (Bulbucus ibis), native to tropical Africa, invaded the American continent in the end of the 19th Century. The most commonly accepted hypothesis assumes that birds flew over the Atlantic ocean, established initially in the Northeast of South America, and from there they dispersed all over the continent, approximately 50-60 years ago. Nowadays, the species is one of the most abundant in the American continent and, in spite of its expansion have been well documented demographically; the genetics of its introduction has remained unexplored. The main goals of this study are: to use molecular genetic tools to clarify the historic of the invasion process; to identify the African source region from where founder egrets came to colonize the American continent, and to estimate the number of invasion events that took place as well as the actual date in which the process started. Samples from fifteen populations of the Cattle Egret spanning a range from near the supposed introduction region (extreme North of Brazil, in Amapá state) to the extreme South of Brazil will be collected. Also, eight samples from countries in the African Atlantic coast (Senegal, Guine-Bissau, Ghana and Angola), situated near the region probable source of invasive populations will be collected. MtDNA (control region and cyt-b) and microsatellites (eight polymorphic loci to be prospected in the species) will be used to analyze native and invasive populations. Comparison between levels of genetic diversity and its distribution in the native and colonized ranges will aid to test the hypothesis about the number of invasion entrances. Lower levels of genetic differentiation and higher indexes of population assignment are expected between the most ancient Brazilian populations, in the North-Northeast of the country, and the African samples. The phylogeographic analysis with base in mtDNA haplotypes will help identifying the source population in Africa and the extent of the invasive events. In addition, we will analyze mtDNA sequences of Plasmodium and Haemoproteus present in B. ibis samples from Brazilian populations and from some of the African populations with the aim of identifying their lineages and to check the diagnostic of introduction obtained through analysis of host's (B. ibis) DNA. (AU)