Bats: A macroevolutionary exception

GIANNINI, NP

Perth

Congreso; 12th International Mammalogical Congress; 2017

International Federation of Mammalogists

Phylogenies areprimary sources for macroevolutionary research. Here I investigate how the twoprincipal aspects of phylogenies, character evolution and taxon relationships, contributeto reveal exceptional evolutionary patterns and processes in one outstanding mammalianlineage, Chiroptera. Bats are the only group of mammals capable of poweredflight. Understanding the origin of flight ultimately explains bats as a group,their singularities, and much of their historical and current diversity. Flightenabled bats to reach all continents they inhabit today by the early Eocene. Systematicstudies have placed bats among laurasiatherian mammals, with a divergence timeestimated near the K-Pg boundary. First (c. 52-my-old) complete fossils exhibita mosaic of character states but their morphology indicates that these specieswere accomplished volant mammals. Bats accumulate a large number of un-reversedsynapomorphies, including many of the flight apparatus. Detailed morphologicaland developmental comparisons allow us to identify the homology of all of the aerofoilcomponents. These homologies and their relative ontogenetic timing can helpresolve the origin of bat flight. A recent, large-scale supermatrix phylogenycorroborated most of current bat clades, from species groups to superfamilies,albeit some new groups imply considerable biogeographic rethinking of the bathistory. Size, a key functional character for volant animals, evolved in[JAF1]  thatphylogeny in ways that challenge everything we know about evolution of thischaracter in mammals as a group. Neither neutral nor adaptive mammalian models satisfactorilyexplain the reconstructed pattern of initial nanism, backbone stasis, low-scalesize evolution inside subclades and explosive size evolution in a few groups (chieflypteropodid bats). As proposed two decades ago, various constraints fromecholocation parameters emerge as strong candidates to account for body sizeevolution in bats, from a scaling perspective. Ecological release fromecholocation loss may explain megabat size evolution. Size may start acting as a strong evolutionaryconstraint within a few million years, when the largest megabats of the Recent eventuallyapproach the theoretical maximum size in bats.[JAF2]  Thus, a modelof nested constraints from echolocation and flight, encompassing the past andthe future, is proposed to explain bat evolution. From this point of view, batevolution is unique among mammals. Beyond exclusively macro-evolutionarypatterns, recent analyses of morphological evolution reject drift andcompellingly support natural selection acting on correlated cranial characters inall nodes of the phyllostomid phylogeny. Thus, bat phylogenies also help bridgethe controversial micro-macro-evolutionary gap.