Evolutionary Inferences on the Chromosomal Diversity of Anseriformes (Neognathae; Galloanseres) by Microsatellite Mapping

Anseriformes represent a basal order in the phylogeny of neognath birds and are of particular interest in cytogenetic research due to their distinctive chromosomal features. However, aspects of their chromosomal evolution, such as the distribution and organization of microsatellite sequences, remain poorly understood. Given the role of these dynamic repetitive sequences in chromosome organization, differentiation, and evolution, we analyzed microsatellite distribution in three Anatidae species, each representing a different subfamily: Amazonetta brasiliensis-Brazilian Teal (Anatinae), Coscoroba coscoroba-Coscoroba Swan (Anserinae), and Dendrocygna viduata-White-faced Whistling Duck (Dendrocygninae). This is the first karyotypic description for White-faced Whistling Duck (2n = 78) and Brazilian Teal (2n = 80), whereas Coscoroba Swan, previously analyzed, exhibits a notably high diploid number (2n = 98). Despite sharing a similar macrochromosome morphology, the three showed differences in diploid numbers and microsatellite distribution. Extensive microsatellite accumulation was found in both autosomal and sex chromosomes (Z and W) of Brazilian Teal and Coscoroba Swan, while White-faced Whistling Duck displays minimal hybridization signals and an absence of microsatellites on the sex chromosomes. The accumulation of specific microsatellites, such as (CAC)10 and (GAG)10, in centromeric and pericentromeric regions suggests an association with transposable elements, potentially driving chromosomal evolution. Notably, the substantial accumulation of these sequences on the Z and W chromosomes of Brazilian Teal and Coscoroba Swan, but not White-faced Whistling Duck, supports the hypothesis that repetitive sequence expansion occurs in a species-specific manner, contributing to sex chromosome differentiation. These findings highlight microsatellite mapping as a valuable tool for understanding chromosomal evolution and genomic differentiation in Anseriformes.