Minisatellite DNA markers reveal hybridisation between the endangered black robin and tomtit

Abstract

We have used multilocus minisatellite DNA profiling to assess genetic variation in the endangered and highly inbred black robins and the closely related tomtits. These species are restricted to wild populations on the Chatham Islands, off the east coast of New Zealand. DNA profiles revealed a remarkable degree of genetic similarity among black robins, as well as among the tomtits sampled, although the typical profiles of these two species were clearly distinct. The parentage of two putative hybrid chicks and one putative hybrid adult was established for a 'black robin' adult male and an adult tomtit female which were found nesting together. The 'black robin' male, despite being morphologically a typical black robin, was found to possess a number of minisatellite-containing restriction fragments not recorded from the black robin population (n = 103). These fragments were however detected in tomtits. Consequently, this bird appeared to be an F1 hybrid and his three offspring were F2 hybrids. Mitochondrial DNA sequencing of members of this family showed that the 'black robin' male had cytochrome b and 16S of black robin, rather than tomtit, haplotypes. This indicates that the black robin adult male hybrid was the result of a black robin female mating with a tomtit male. These findings are particularly important since tomtits had been used as cross-foster parents for black robins, as part of an earlier conservation recovery program. The existence of any hybrids thus detected would have important implications for cross-fostering programs generally, since may such programs are now being implemented in conservation programs worldwide.