In a series of articles, I will discuss recent advances in hybridization genomics – the fundamentals of adaptive introgression, “islands of speciation”, differential gene flow, and linked selection have been discussed in my previous posts (here, here, and also at the Social Evolution Forum). I will focus this series on applications/support/fallibilities of theories in recent literature, and incidentally, also the focus of a new special issue of Molecular Ecology.
Hybridization following secondary contact in Myzomela honeyeaters – Sardell and Uy, 2016, Evolution
Clockwise from left, Myzomela cardinalis, M. tristrami and a putative hybrid (note red feathers on nape/collar) of Makira. Image courtesy: Uy Lab @ http://www.bio.miami.edu/uy/Research/Myzo.jpg
Studying a hybrid zone of Myzomela honeyeater songbirds (M. tristrami – sexually monochromatic, black, and M. cardinalis – sexually dichromatic, black and red) in the Solomon Islands, Sardell and Uy (2016) reveal a scenario of incomplete reproductive isolation, recent secondary contact, and their evolutionary consequences through analyses of nuclear and mitochondrial haplotypes of >200 birds sampled across six sites. One mitochondrial and six nuclear markers were then amplified, sequenced, and phased. Divergence time between the two species was then estimated using BEAST to be around 5.8 mya (95% CI: 3.1-9.3 mya). Hybridization was quantified by comparing identifying haplotypes present exclusively in allopatry in sympatric heterospecifics – showing exclusive mitochondrial introgression (sex biased), and nuclear introgression from M. cardinalis into M. tristrami. Both mitochondrial and nuclear diversities were larger in M. tristrami, indicative of larger effective population sizes. Similar admixture patterns were also determined using estimation of population structure. Further characterization of hybridization using more markers, and population genetic models in the species will reveal a better understanding of the genomics of hybrid zones
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