Oral presentation- Plenary 12th International Mammalogical Congress

Bats: a macro-evolutionary exception (#385)

Professor Norberto Giannini 1
  1. Unidad Ejecutora Lillo, San Miguel De Tucumán, Tucumán, Argentina

Phylogenies are primary sources for macroevolutionary research. Here I investigate how the two principal aspects of phylogenies, character evolution and taxon relationships, contribute to reveal exceptional evolutionary patterns and processes in one outstanding mammalian lineage, Chiroptera. Bats are the only group of mammals capable of powered flight. Understanding the origin of flight ultimately explains bats as a group, their singularities, and much of their historical and current diversity. Flight enabled bats to reach all continents they inhabit today by the early Eocene. Systematic studies have placed bats among laurasiatherian mammals, with a divergence time estimated near the K-Pg boundary. First (c. 52-my-old) complete fossils exhibit a mosaic of character states but their morphology indicates that these species were accomplished volant mammals. Bats accumulate a large number of un-reversed synapomorphies, including many of the flight apparatus. Detailed morphological and developmental comparisons allow us to identify the homology of all of the aerofoil components. These homologies and their relative ontogenetic timing can help resolve the origin of bat flight. A recent, large-scale supermatrix phylogeny corroborated most of current bat clades, from species groups to superfamilies, albeit some new groups imply considerable biogeographic rethinking of the bat history. Size, a key functional character for volant animals, evolved in that phylogeny in ways that challenge everything we know about evolution of this character in mammals as a group. Neither neutral nor adaptive mammalian models satisfactorily explain the reconstructed pattern of initial nanism, backbone stasis, low-scale size evolution inside subclades and explosive size evolution in a few groups (chiefly pteropodid bats). As proposed two decades ago, various constraints from echolocation parameters emerge as strong candidates to account for body size evolution in bats, from a scaling perspective. Ecological release from echolocation loss may explain megabat size evolution. Size may start acting as a strong evolutionary constraint within a few million years, when the largest megabats of the Recent eventually approach the theoretical maximum size in bats. Thus, a model of nested constraints from echolocation and flight, encompassing the past and the future, is proposed to explain bat evolution. From this point of view, bat evolution is unique among mammals. Beyond exclusively macro-evolutionary patterns, recent analyses of morphological evolution reject drift and compellingly support natural selection acting on correlated cranial characters in all nodes of the phyllostomid phylogeny. Thus, bat phylogenies also help bridge the controversial micro-macro-evolutionary gap.