Microsatellite DNA Analysis of Breeding Behaviour and Evolution in Buller's Albatross (Thalassarche Bulleri)

Abstract

Albatrosses belong to the order Procellariiformes, and are the largest of the seabirds. They have characteristic life histories, including delayed age of maturity and low reproductive rate, laying one egg per breeding season. Many species do this annually on remote islands in New Zealand and Australian waters. In the last few decades, several albatross species have experienced population declines, due largely to commercial longline fishing operations, which may catch many albatrosses accidentally on hooks. Presently, little is known about albatross population genetic structure, as most studies rely on field observations, including mark/recapture methods and satellite telemetry. The aims of this study are to examine levels of genetic variation in three Buller's albatross (Thalassarche bulleri) breeding colonies on The Snares and one on Solander Island, and across six different species of the genus Thalassarche using microsatellite DNA analysis, and to evaluate patterns of molecular evolution in albatrosses by mapping microsatellite sequence data onto a partial albatross phylogeny. Sufficient amounts of genomic DNA were extracted from feathers, and liver and blood samples to allow endangered albatross species to be genotyped reliably. Microsatellite genotype data for six polymorphic loci from 126 T. bulleri chicks suggest that the four geographically distinct breeding colonies are genetically homogeneous, due to substantial levels of gene flow (Nm ≈5) between them. The results are the first to show that the high natal philopatry observed in Buller's albatross is not enough to develop and maintain genetically distinct breeding colonies. Microsatellite DNA analyses of an additional 103 individual Thalassarche birds representing six species at the same six loci suggest close evolutionary relationships between present-day albatross species. Two pairs of especially closely related species are Buller's albatross (T. bulleri) and Pacific albatross (T. nov. sp.), and Chatham albatross (T. eremita) and Salvin's albatross (T. salvini). Nonetheless, assignment tests were able to assign individuals correctly to their source species, suggesting that microsatellite markers can offer a reliable molecular tool for the species identification of albatross corpses recovered from longline fishing vessels. A total of 111 complete DNA sequences across six loci from albatross species from three genera reveal that the correct microsatellite loci are PCR amplified, and that microsatellite allele size differences are most often the result of repeat number changes of long (> 5 repeats) dinucleotide arrays, meeting expectations of a stepwise mutation model (Kimura and Ohta, 1978). The most variable DNA regions suggest more complex mutational patterns, including size homoplasy. In a phylogenetic context, these data support the division of albatrosses into various well-recognized discrete genera, including Diomedea, Phoebetria, and Thalassarche. This study is the first to use this novel approach in albatrosses, and achieved at the same time an increased understanding regarding general pattern of microsatellite evolution.