PUB - Publikationen an der Universität Bielefeld

Interspecific introgression can occur between species that evolve rapidly within an adaptive radiation.Pachyptilapetrels differ in bill size and are characterised by incomplete reproductive isolation, leading to interspecific gene flow. Salvin’s prion (Pachyptila salvini), whose bill width is intermediate between broad-billed (P. vittata) and Antarctic (P. desolata) prions, evolved through homoploid hybrid speciation. MacGillivray’s prion (P. macgillivrayi), known from a single population on St Paul (Indian Ocean), has a bill width intermediate betweensalviniandvittataand could also be the product of interspecies introgression or hybrid speciation. Recently, another prion population phenotypically similar tomacgillivrayiwas discovered on Gough (Atlantic Ocean), where it breeds 3 months later thanvittata. The similarity in bill width between the medium-billed birds on Gough andmacgillivrayisuggest that they could be closely related. In this study, we used genetic and morphological data to infer the phylogenetic position and evolutionary history ofP. macgillivrayiand the Gough medium-billed prion relative otherPachyptilataxa, to determine whether species with medium bill widths evolved through common ancestry or convergence. We found that Gough medium-billed prions belong to the same evolutionary lineage asmacgillivrayi, representing a new population of MacGillivray’s prion that originated through a colonisation event from St Paul. We show thatmacgillivrayi’s medium bill width evolved through divergence (genetic drift) and independently from that ofsalvini, which evolved through hybridisation (gene flow). This represents the independent convergence towards a similarly medium-billed phenotype. The newly discovered MacGillivray’s prion population on Gough is of utmost conservation relevance, as the relictmacgillivrayipopulation in the Indian Ocean is very small.