Brown Skua and south polar Skua (Aves: Stercorariidae) a hybridization case or same species?

Abstract

Brown Skua (Stercorarius antarctica-lonnbergi) and South Polar Skua (Stercorarius maccormicki) aoccur in the Antarctic Peninsula and are sympatric in distribution over about 500km. In this region hybridization between a male of South Polar Skua and a female Brown Skua producing a viable and fertile offspring has been reported. The present study aims to review the evolutionary history of South Polar Skua and Brown Skua to better understand the hybridization process between these species. To assess the evolutionary history between these species, 67 DNA samples were sequenced for AK1 locus, 70 samples for RAG1 locus and 96 samples for Cytb locus, sampling in King George and Elephant Island. Cytb and RAG1 loci showed greater genetic diversity in samples from hybrid birds than those of non-hybrid individuals and may re ect the outcome of the heterosis. Overall Brown Skua had higher genetic diversity than South Polar Skua. In addition, South Polar Skua showed probable populational expansion signals, in contrast to Brown Skua that showed population stability through time. However, our phylogenetic analysis did not corroborate the reciprocal monophyly between these species. Thus, South Polar Skua and Brown Skua show incomplete lineage sorting, indicating these species are a single taxonomic group.