Gene flow between two non-sister species and perhaps the first record of a particular Honeyeater hybrid.
A few years ago, my sister and her boyfriend travelled around Australia for a year. Occasionally they would send me a picture of the local avifauna. To my knowledge, none of these pictures featured a hybrid. Not that surprising, because hybridization is quite rare on an individual level. There are, however, several Australian species that interbreed, such as parrots and orioles. And the list of Australian hybrids keeps growing: two recent studies report hybrids in the Meliphagidae family (Honeyeaters).
Varied Honeyeater © Jss367 | Wikimedia Commons
Townsville
The first case was documented in eastern Australia. In the 1970s, Julian Ford already noted that there might be a hybrid zone between Varied Honeyeater (Gavicalis versicolor) and Mangrove Honeyeater (G. fasciogularis) around the city of Townsville. Interestingly, these species are not each others closest relatives. Instead, the Mangrove Honeyeater is more closely related to the Singing Honeyeater (G. virescens).
A paper, published in the Biological Journal of the Linnean Society, examined this hybrid zone with genetic data. Leo Joseph and his colleagues compared the DNA of birds within and outside the hybrid zone. They found that both species are clearly distinct, but that some Mangrove Honeyeaters from Townsville contained a bit of Varied Honeyeater DNA (see figure below). This result suggests that there is a some gene flow from Varied into Mangrove Honeyeater.
Another notable finding concerns the genetic markers on the sex-chromosomes (the Z-chromosome to be precise). These markers showed no signs of introgression, indicating that the sex-chromosomes might play an important role in reproductive isolation. You can check out this excellent review by Darren Irwin on this topic.
The genetic structure of Varied Honeyeater (blue) and Mangrove Honeyeater (red) in eastern Australia. (A) For the autosomal markers (i.e. non-sex chromosomes), some Mangrove Honeyeaters contain a bit of Varied Honeyeater DNA. (B) The species are clearly distinct for markers on the sex-chromosomes.
Kensington
For the second hybrid case, we need to travel to western Australia. In Kensington, Geoffrey Groom observed a peculiar Honeyeater that might be a hybrid between New-Holland Honeyeater (Phylidonyris novaehollandiae) and White-cheeked Honeyeater (P. niger). In the journal Australian Field Ornithology, he described several features that support this conclusion.
The bird has characteristics of both species. For example, a dark iris is typical for adult White-cheeked Honeyeaters whereas the black and white throat is only seen in New-Holland Honeyeater. However, a genetic study is needed to confirm the hybrid origin of this bird.
The putative hybrid (middle) between the suggested parental species: White-cheeked Honeyeater (top) and New-Holland Honeyeater (bottom). © Geoffrey Groom
References
Groom, G. N. (2019). A photographic record of a possible New Holland Honeyeater Phylidonyris novaehollandiae longirostris × White-cheeked Honeyeater P. niger gouldii hybrid. Australian Field Ornithology, 36.
Irwin, D. E. (2018). Sex chromosomes and speciation in birds and other ZW systems. Molecular ecology, 27(19):3831-3851.
Joseph, L., Drew, A., Mason, I. J., & Peters, J. L. (2019). Introgression between non-sister species of honeyeaters (Aves: Meliphagidae) several million years after speciation. Biological Journal of the Linnean Society, 128(3):583-591.
The papers have been added to the Meliphagidae page. A big thanks to Leo Joseph for sending me this paper and to Geoffrey Groom for citing my work.
Avian Hybrids 