The Skull Integration Pattern and Internal Constraints in Myotis myotis–Myotis blythii Species Group (Vespertilionidae, Chiroptera) Might be Shaped by Natural Selection During Evolution Along the Genetic Line of Least Resistance

Abstract

Evolutionary dynamics of covariation patterns in craniometric traits was studied for bats from the Myotis myotis–Myotis blythii species group (Mammalia, Chiroptera, Vespertilionidae) namely M.m.myotis, M.b.oxygnathus, M.b.omari, M.b.blythii, and M.b.altaicus. These species evolved towards increasing the size. One more species, M.dasycneme, which is phylogenetically, morphologically, and ecologically rather distant from these OTUs, also was studied for comparison with them. A set of 30 craniometric traits was studied for each of the OTUs using the quantitative genetics approaches. Phenotypic covariance matrices were used as proxies for additive genetic covariance matrices. The analysis has shown that multivariate divergence of the studied Myotis OTUs was governed by selection rather than by random drift and that these OTUs evolved in the direction close to the line of least evolutionary resistance. As overall size increases, the skull integration, respondability, and evolvability increase, while flexibility slightly decreases. Such a pattern can possibly be explained as a consequence of adaptation of M.blythii and especially M.myotis to prey on considerably large hard-shelled insects. A high cohesion of skull structures is needed for the effective functioning of their jaw apparatus. For Myotis bats with other foraging strategies (such as M. dasycneme that catches insects mainly using the claws of hind feet) this cohesion seems to be of lesser importance.