Evolutionary processes in communally breeding Mexican Jays (Aphelocoma ultramarina).
I am currently investigating the genetic structure of populations of Mexican jays, communally nesting birds that live on “sky island” in Arizona and northern Mexico. The amount and pattern of differentiation among populations can result from many factors. A particularly important issue in the study of population structure in birds is the ways in which social systems and fine-scale demography affect population subdivision. Mexican Jays are an excellent subject for the study of genetic structure because of their unique social behavior and their geographic distribution. Mexican Jays have one of the most extreme examples of sociality and one of the best studied social systems among birds. The species is distributed in an assemblage of contiguous populations in the southern part of its range in Mexico, with disjunct relict populations to the north, in Arizona and Texas. Based on our knowledge of social behavior, dispersal, geological history, and classical taxonomy, there are reasons to expect substantial genetic differentiation among populations of Mexican Jays. Their tendency to breed in or near their natal groups, their long lives, and their sedentary nature suggest that gene flow may be reduced relative to other species. The isolation of populations on “sky islands” at the northern end of the range could further reduce gene flow among those populations and may have resulted in founder effects when they were first isolated.The geographic distribution of the Mexican Jay contains an assemblage of contiguous populations in the southern part of its range, the Sierra Madre Occidental, Sierra Madre Oriental, and Transvolcanic ranges in Mexico, and disjunct relict populations to the north, in Arizona and Texas. Classical taxonomy of Mexican Jays suggests differentiation among populations throughout the species range. Based on our knowledge of social behavior, dispersal, geological history, and classical taxonomy there are reasons to expect to find substantial genetic differentiation among populations of Mexican Jays. Using morphological variation, Pitelka (1951) described seven subspecies of Mexican Jays. Phylogenetic analysis of allozymes by Peterson (1992) suggested there were three major groups, eastern (Sierra Madre Oriental), western (Sierra Madre Occidental), and southern (Transvolcanic Belt). Peterson found that a population from an Arizona sky island, at the northwestern limit of the species range, clustered with the southern populations from the Transvolcanic Belt. I assayed polymorphic nuclear microsatellite loci from samples representing all seven subspecies. The microsatellite data support the existence of eastern, western, and southern groups. Samples from the Arizona sky islands cluster with the western populations, not those from the south. Populations in the Transvolcanic Belt share no alleles with the other populations at one microsatellite locus, indicating they are a distinct evolutionary lineage. This research was supported by an NSF POWRE (Professional Opportunities for Women in Research and Education) award, “Microsatellites as markers of evolutionary processes in a social bird.” I am currently preparing manuscripts for publication.
I also studied parentage in Mexican jays (formerly called gray-breasted jays), using allozymes to detect evidence for extra-pair fertilizations. Although allozymes are not as powerful a technique as newer techniques based on DNA, such as microsatellites, we were able to find evidence for multiple mating by females in this species.
Bowen, B. S., R. R. Koford, and J. L. Brown. 1995. Genetic evidence for undetected alleles and unexpected parentage in the gray-breasted jay. Condor 97:503-511. pdf coming soon.
Bhagabati, N. K., J. L., Brown, and B. S. Bowen. 2004. Geographic variation in Mexican Jays (Aphelocoma ultramarina): Local differentiation, polyphyly, or hybridization? Molecular Ecology 13:2721-2734.