Dates:
Oct 2015 - Apr 2016
An adaptive radiation is the rapid diversification and divergence of a lineage; these are thought to be caused by invasion of novel continents, acquisitions of key innovations or extinctions of competitors. This project aims to determine whether there is the expected relationship between diversity and disparity, and to determine the best candidate for an adaptive radiation of rodents exhibits the distinctive signature of that evolutionary mode. More specifically, we expect the South American radiation of cricetid rodents, Sigmodontinae to be more disparate than the North American radiation for two reasons. First, no small rodents were on the continent when Sigmodontinae arrived 12 million years, there were small rodents already present when the North American Neotominae arrived around the same time. This is thought to explain the rapid burst of speciation in Sigmodontinae but not in Neotominae To compare diversity and disparity of these clades, we are analyzing the disparity of jaw shape and size by digitizing the coordinates of discrete anatomical loci from photographs of cricetid jaw, and additional points that contain information about curvature of the jaws. Our results show the expected pattern for shape but not for size. The disparity of Neotominae for size is approximately 1.7 times that of Sigmodontinae, in contrast to our expectations. For shape; however, the disparity of Sigmodontinae is 1.4 times that of the North American lineages. Our surprising result needs to be further confirmed by more complete sampling of Sigmodontinae, but it may be these two lineages diverged along different ecological lines.