Evolutionary Mechanisms Affecting the Multivariate Divergence in Some Myotis Species (Chiroptera, Vespertilionidae)

Phenotypic evolutionary rates were measured for 27 craniometric characters in 12 extant OTUs from the bat genus Myotis (Chiroptera, Vespertilionidae). Squared Mahalanobis distance was used as a multivariate measure for amount of divergence, and squared Mahalanobis distance weighted by time was used as a measure for the rate of divergence. Estimates for the rates of divergence were found to be consistent with random walk hypothesis. Thus, the divergence in Myotis could be guided by random drift and mutations. The high dispersion in rate estimates suggests also a possible input of randomly fluctuating selection. The highest rates were recorded for divergence between M. myotis–M. blythii species group and the other OTUs. Rates of divergence between the subspecies of M. blythii occur to be lesser than rates of divergence between the earlier diverged species, their divergence could probably be slowed down by stabilizing selection. Size-adjusted data appeared to be lesser then the initial data, and it can be concluded that both size and shape were involved in divergence of Myotis species. The skeletal characters in bats are known to be extremely conservative during long-term evolution, however, the possibility for random walk at short time interval implies that bat evolution is constrained rather ecologically and biomechanically than genetically or developmentally.