Population boundaries and genetic diversity in the endangered Mariana crow(Corvus kubaryi)

The Mariana crow (Corvus kubaryi) is an endangered species that is restrict ed to the islands of Guam and Rota in the Mariana archipelago. Predation by the introduced brown tree snake (Boiga irregularis) has decimated bird pop ulations on Guam, and the crow population there is the last wild remnant of the endemic forest avifauna. The population on Guam is critically endanger ed and, despite intensive management, the population has continued to decli ne. Additional management options include intermixing the Guam and Rota pop ulations, but such options are best evaluated within a population genetics framework. We used three types of molecular markers to assay genetic variat ion in the Mariana crow: mitochondrial DNA (mtDNA) sequences, minisatellite s and microsatellites. The two populations could be differentiated by mtDNA sequencing and they differed in allele frequencies at nuclear markers. Thu s, the populations could be designated as evolutionarily significant units. However, the Guam population is genetically more diverse than the Rota pop ulation, and its survival probability if managed separately is very low. Al l markers did indicate that the two populations are closely related and sep arated by a shallow genealogical division. Intermixing the populations is j ustified by two rationales. First, the apparent population differences may result from recent human activities. Second, a greater amount of genetic in formation may be preserved by joint management. The translocation of birds from Rota to Guam has begun, but strategies that will ensure maintenance of the variation in the Guam population warrant further exploration.