The Evolution of Body Size in Noctilionoid Bats

Norberto P. Giannini, Lucila I. Amador, and R. Leticia Moyers Arévalo

Body mass is the single most important factor affecting the biology of animals. Small size is generally highly favorable for flying vertebrates; in addition to this constraint, echolocating bats are also restricted by the physics of call parameters. However, we find in a single group, the Noctilionoidea, virtually the entire size range found across all echolocating bats. Here we examine the evolutionary significance of this variation. We explore how the reconstructed body mass of the ancestral phyllostomid was inherited from noctilionoid ancestors, how size changed along the branches of the phyllostomid tree, and how size co-varied with characteristic evolutionary shifts in the ecology of phyllostomid bats. We found little change along the backbone of the phylogenetic tree and across major dietary transitions, many scattered increases and decreases of variable magnitude, and most variation concentrated in phyletic change in a few groups, especially vertebrate-specialized and frugivorous phyllostomids. These trends imply sustained selection acting over millions of years in a consistent direction, principally towards an increase in size. Initial stasis may have facilitated ecological transitions, while capacity for size change may have fueled intense directional selection within highly specialized lineages. Finally, diverging trends appear to reflect past character displacement.