Molecular systematics and phylogeography of little penguins

Abstract

Biodiversity research has gained considerable momentum in recent decades, perhaps reflecting growing scientific recognition of declining ecosystem and species diversity driven by anthropogenic impacts. Development and advances in genetic and genomic technology have greatly contributed to our understanding and assessment of global and local biodiversity, particularly through the discovery of cryptic species complexes, which are far more common and widespread than previously thought. Studies of temporal demographic and biogeographic trends have revealed dynamic responses of species to human activity. In this thesis I use genetic analyses of subfossil, historic and modern little penguins (Eudyptula minor) to assess the taxonomic status of this species and its dynamic distributional responses to human settlement in New Zealand. Little penguins are the smallest of the extant penguin species, occurring around the coasts of New Zealand and southern Australia. Here I present multilocus genetic evidence for the existence of two cryptic species within the genus Eudyptula, one endemic to New Zealand, the other represented throughout Australia and south-eastern New Zealand. Only moderate levels of hybridization were detected between the two lineages where they co-occur in New Zealand waters. Results of coalescent modelling indicate that the Australian lineage likely expanded into south-eastern New Zealand in recent centuries, concordant with recent anthropogenic turnover events of numerous other vertebrate taxa in coastal New Zealand. This potential human-driven turnover event was further investigated using ancient DNA analysis and radiocarbon dating of pre-human, archaeological and historic Eudyptula remains. Results of these analyses confirm that Australian little penguins were absent from New Zealand prior to human arrival and likely colonised the region between AD 1600 and 1900, following regional anthropogenic declines of the New Zealand endemic species. Finally, comprehensive morphometric comparison of complete Eudyptula skeletons revealed substantial differentiation of skeletal elements, particularly cranial and sternal features, between Australian and New Zealand little penguins, thus further supporting their recognition as two distinct species. The analyses also found some indication that body-size distribution in Eudyptula penguins follows Bergmann’s rule, with smaller individuals inhabiting warmer northern regions and larger individuals found in the colder southern regions. Overall, the results of this thesis highlight the dramatic impacts of human arrival on New Zealand’s coastal ecosystems and how anthropogenic processes can facilitate rapid changes in biogeographic distributions of species. Such biogeographic shifts can potentially remain masked by the existence of cryptic biodiversity within a taxon.