Genomic signatures of human adaptation to tropical rainforest habitats

George Perry, The University of Chicago

January 13, 2011 @ 04:00 pm to 05:00 pm

100 Life Sciences Building (Berg Auditorium)

Hosted by the Department of Biology. Abstract For humans, tropical forests are extremely hot and humid, structurally dense, food limited, and harbor a large number and diversity of pathogens. Compared to individuals from other populations, rainforest hunter-gatherers tend to have shorter statures. This observation has prompted hypotheses that small body size - or the pygmy phenotype - might represent an adaptation to one or more of the specificecological challenges of the tropical forest. While these hypotheses assume that the pygmy phenotype is explained (at least in part) by genetic effects, clear empirical support for such an assumption has not been provided. In addition, there is not yet any strong evidence that small body size indeed confers or conferred a fitness benefit in these populations. I will present the complete genome sequences of 10 African rainforest hunter-gatherers, five from each of the Biaka and Mbuti populations of the Central African Republic and DR Congo, respectively. By comparing these genomes to those already available for the Yoruba (a Nigerian agricultural population), I was able to identify high-frequency, rainforest huntergatherer- specific genetic changes that could underlie the pygmy phenotype. Indeed, more than one-third of the genes containing or close to the most differentiated Yoruba versus combined Biaka/ Mbuti genetic variants have roles in anatomical structure development. Separately, the most differentiated variants between the Biaka and Mbuti are found in or nearby genes involved in endochondrial ossification and the growth-critical TGFB and EGFR signaling pathways significantly more often than expected by chance. For a number of these gene regions, an extended haplotype analysis provides evidence of a past history of positive selection in the Biaka or Mbuti. Together, these results suggest a model of an adaptive, genetically-mediated, complex-origin pygmy phenotype, in which the involved genetic variants are comprised of a combination of relatively ancient mutations that arose in an ancestral rainforest hunter-gatherer population and more recent, population-specific mutations that followed the ~20,000 years ago Biaka-Mbuti divergence.

Contact

Stephanie Gookin
sjgookin@psu.edu
814-865-4562