Range expansion and hybridization in Round Island petrels (Pterodroma spp.): evidence from microsatellite genotypes

Abstract

Historical records suggest that the petrels of Round Island (near Mauritius, Indian Ocean) represent a recent, long-distance colonization by species originating from the Atlantic and Pacific Oceans. The majority of petrels on Round Island appear most similar to Pterodroma arminjoniana, a species whose only other breeding locality is Trindade Island in the South Atlantic. Using nine microsatellite loci, patterns of genetic differentiation in petrels from Round and Trindade Islands were analysed. The two populations exhibit low but significant levels of differentiation in allele frequencies and estimates of migration rate between islands using genetic data are also low, supporting the hypothesis that these populations have recently separated but are now isolated from one another. A second population of petrels, most similar in appearance to the Pacific species P. neglecta, is also present on Round Island and observations suggest that the two petrel species are hybridizing. Vocalizations recorded on the island also suggest that hybrid birds may be present within the population. Data from microsatellite genotypes support this hypothesis and indicate that there may have been many generations of hybridization and back-crossing between P. arminjoniana and P. neglecta on Round Island. Our results provide an insight into the processes of dispersal and the consequences of secondary contact in Procellariiformes.

Genetic Introgression: An Integral but neglected component of speciation in birds

“…A special case of this process was demonstrated on Round Island in the Indian Ocean, which was recently invaded by an Atlantic and a Pacific species of petrel (Pterodroma), leading to a petrel population that possesses genetic affinities to both species (Brown et al 2010). More typically, however, immigration waves are associated with a classical hybrid-zone scenario in which one species slowly pushes back the other in geographic space (e.g., Rohwer et al 2001, Haig et al 2004, Secondi et al 2006, Gay et al 2008.…”

On the role played by the carrying capacity and the ancestral population size during a range expansion

“…Episodes of REs have been postulated for many species (Rendine et al, 1986;Ibrahim et al, 1996;Cavalli-Sforza and Feldman, 2003;Klopfstein et al, 2006;Boessenkool et al, 2009;Brown et al, 2010) but they have been quantitatively tested in a spatially explicit framework only in few studies (Barbujani et al, 1995;Hamilton et al, 2005;Ray et al, 2005;Francois et al, 2008;Neuenschwander et al, 2008;Gaggiotti et al, 2009;Schneider et al, 2010;Mona et al, 2013). REs leave distinct signatures in the genetic diversity of populations (Barbujani et al, 1995;Ray et al, 2003;Edmonds et al, 2004;Travis et al, 2007;Sousa et al, 2014), proceeding as a series of founder events followed by continuous migrations among neighboring demes (Austerlitz et al, 1997;Ray et al, 2003).…”

Phylogenetic Relationships in Pterodroma Petrels Are Obscured by Recent Secondary Contact and Hybridization

“…Field observations on Round Island indicate that mixed-species pairs are not uncommon. Pairs of dark-shafted and white-shafted birds have been observed on a number of occasions, and at least one of these pairs has successfully hatched a chick [22]. The bird identified as P. heraldica from its band number was caught whilst rearing a chick, and appeared to be paired with a dark-shafted bird resembling P. arminjoniana .…”