Imminent extinction of the guanay cormorant on the Atlantic South American coast: a conservation concern?

Guanay cormorants Phalacrocorax bougainvilli aredistributed mostly on the Pacific coast of Peru and northern Chile. A smallpopulation of around 50 pairs was described on the Patagonian Atlantic coast inthe late 1960s. Further records have revealed a progressive decrease of thispopulation. During 1999 we looked for guanay cormorants at those Atlanticcolonies where the species was recorded in the past. Only four individuals weredetected in one colony (Punta Lobería), and all of them were mated withking cormorants P. albiventer. In addition, we recordedhybrids between guanay and king cormorants mated with pure king and imperialcormorants P. atriceps. Causes of the population declineare unknown. Since guanay cormorants inhabiting the Atlantic coast could be agenetically differentiated population, we emphasize the need for molecularstudies. If genetic polymorphism is detected, the capture of remnant individualsin order to constitute a genetic stock should be considered.     

Admixture analysis of a rural population of the state of Guerrero, Mexico

We studied 156 individuals of Native American descent from the city of Tlapa in the state of Guerrero in western Mexico. Most individuals' ethnicity was either Nahua, Mixtec, or Tlapanec, but self-identified Mestizos and individuals of mixed ethnicities were also included in the sample. We typed 24 autosomal, one Y-chromosome, and four mitochondrial ancestry-informative markers (AIMs) to estimate group and individual admixture proportions, and determine whether the admixture process involved directional gene flow between parental groups. When genetically defined (GD) Mestizos were excluded from the analysis, Native American ancestry represented approximately 98% of the population's gene pool, while European and West African ancestry represented approximately 1% each. Maternally inherited markers also showed an exceptionally high Native American contribution (98.5%), as did the paternally inherited marker, DYS199 (90.7%). We did not detect genetic structure in this population using these AIMs, which appears consistent with the homogeneity of the sample in terms of admixture proportions. The addition of GD Mestizos to the sample did not produce a considerable change in admixture estimates, but it had a major effect on population structure. These results show that the population of Tlapa in Guerrero, Mexico, has experienced little admixture with Europeans and/or West Africans. They also show that the impact of a small number of admixed individuals on an otherwise homogeneous population might have profound implications on subsequent ancestry/phenotype analysis and mapping strategies. We suggest that heterogeneity is a major characteristic of Mexican populations and, as a consequence, should not be disregarded when designing epidemiological studies of Mexican and Mexican American populations.