Brown skuas and South polar skuas from the Antarctic share their gene pools

Abstract

Taxonomic levels of two Catharacta forms from the Antarctica, brown skuas (Catharacta lonnbergi) and south polar skuas (C. maccormicki), are under dispute, although they have been classified as separate species with external morphology. Hybrid zone of brown skuas and south polar skuas has been forming at King George Island (KGI), the Antarctica. Not only hybridization from mixed pairs, but backcross between male hybrid and female brown skuas were observed at KGI. To study the specific difference between two Catharacta forms, we sequenced cytochrome c oxidase I (COI), and Z-chromosome-linked chromo-helicase binding protein gene (CHD1Z, intron A) from the both species and hybrids. COI variation within brown skuas (0-0.293%, 0-2 bp) and south polar skuas (0.440%, 0-3 bp) was similar to that between two forms (0.440%, 0-3 bp), although interspecific variation (0.299-8.474%, 2-55 bp) was higher than intraspecific variation (0.481%, 0-3 bp) for other skua species breeding in the Northern Hemisphere. Interspecific variation of CHD1Z (0-0.662%, 0-4 bp) was not significantly higher than intraspecific variation of brown skuas (0-0.352%, 0-2 bp) and south polar skuas (0-0.828%, 0-5 bp) (ANOVA, F = 0.868, df = 2, p = 0.420). In this study, two Catharacta forms were not clearly distinguished with the sequence data of the COI and CHD1Z. Our data indicate that brown skuas and south polar skuas share their gene pools. The taxonomic issues and genetic variations of Catharacta forms from the Antarctic will be discussed based on their morphological and molecular data.