Abstract
The cattle egret (Bubulcus ibis) has recently colonized Brazil. This process offers an excellent opportunity for the study of colonization and dispersal patterns across extensive areas by non-native birds. The aims of the present investigation were a) to determine the genetic diversity of the cattle egret in Brazil and Africa, b) evaluate genetic differentiation between populations in different regions of Brazil and Africa, and c) detect genetic signs of demographic expansion in these two areas. Mitochondrial DNA (mtDNA) Control Region (CR) sequences were obtained from 112 cattle egrets in four Brazilian and four African (Kenya, Ghana and Nigeria) populations. Genetic diversity (H, h, θ s ) and population structure (AMOVA, Fst) were assessed and the populations were tested for signs of recent demographic expansion. A total of 35 haplotypes were found: 22 exclusive to Africa, 10 exclusive to Brazil and three shared by both samples. The degree of genetic diversity, determined by mtDNA analysis, was similar between Brazil and Africa, demonstrating that the successful colonization of the non-native area occurred with no significant loss of diversity. The pairwise Fst values among the Brazilian and African populations were all significantly different. The population in southern Brazilian exhibited the lowest degree of differentiation with respect to the African population, followed by the southeastern and northeastern populations of the country. The genetic differentiation data suggest that the colonization of Brazil by the cattle egret began in the southern region and expanded to the southeastern and northeastern regions of the country. This genetic differentiation pattern is in accordance with the higher number of cattle per grazing area in southern Brazil, which may have favored the onset of the successful establishment of the species. The findings indicate that mtDNA genetic diversity was retained during the colonization process and colonization began in the southern region of the country. Moreover, signs of demographic expansion were detected in the African sample.
Highlights
The cattle egret (Bubulcus ibis Linnaeus, 1758) primarily inhabits grassland habitats and forages in close association with grazing animals, such as cattle and other livestock, and it is classified in three subspecies
The present findings revealed no signs of demographic expansion in Brazil, as expected for a recent colonization process
The cattle egret has retained most of the Mitochondrial DNA (mtDNA) genetic diversity during the colonization process in Brazil
Summary
The cattle egret (Bubulcus ibis Linnaeus, 1758) primarily inhabits grassland habitats and forages in close association with grazing animals, such as cattle and other livestock, and it is classified in three subspecies. The cattle egret is known to have established and expanded to the Americas without such intervention (Telfair 1983). This bird is considered an invasive species according to the International Union for Conservation of Nature’s Invasive Species Specialist Group (ISSG) and is listed among the invasive alien vertebrate species in the Galapagos Islands (Phillips et al 2012). Many details of its expansion are unknown, cattle egret populations from West Africa or southern Europe are thought to be the origin of populations in the Americas (Telfair 1983, Valverde 2003). Egrets that probably crossed the Atlantic Ocean were first recorded in coastal areas of northern South America (Palmer 1962, Wetmore 1963). By 1973, its occurrence was reported in the state of Rio Grande do Sul (southern Brazil) (Belton 1974)
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