Conservation genetics of the extinct dusky seaside sparrow Ammodramus maritimus nigrescens

We review the captive breeding program designed for the now-extinct dusky seaside sparrow Ammodramus maritimus nigrescens. The death of the last pure nigrescens, a male, effectively ended hope of preserving the taxon. The captive breeding program inadvertently used females from a subspecies (peninsulae) later shown to be part of a distinct mitochondrial DNA clade of seaside sparrows. The captive breeding program would have produced individuals with nigrescens nuclear genomes and peninsulae mitochondrial DNA genomes. Drawing parallels with a study of mtDNA in the fox sparrow Passerella iliaca we suggest that the captive breeding program might have been acceptable. In particular, fox sparrows of one mtDNA (and plumage) clade hybridize with others equally distinct as those in seaside sparrows, and the hybrids successfully backcross to parental forms. This results in fox sparrows of one plumage clade with a ‘foreign’ mtDNA genome, which is analogous to the projected results of the dusky seaside sparrow captive breeding program. Because hybrid fox sparrows persist naturally for several generations, successfully undergoing several cycles of migration and breeding, we suggest that seaside sparrows with ‘foreign’ mtDNA genomes might have represented a useful, albeit not perfect, captive breeding results.