Allometric, Phylogenetic, and Adaptive Components of Climbing Performance in Seven Species of Didelphid Marsupials

Abstract

Didelphid marsupials specialized in arboreal locomotion have morphological features convergent with primates, and hence are an ideal group to test hypotheses about the evolution of arboreality. We analyzed the relative contributions of allometric, phylogenetic, and adaptive aspects to the climbing performance of 7 species of didelphid marsupials of the Atlantic Forest of Brazil. These species encompass a diversity of body sizes, use of the vertical strata, and lineages within didelphid marsupials. Climbing performance was evaluated by measuring the velocity in climbing 3 nylon ropes of 0.6, 0.9, and 1.25 cm diameter. The cycle of maximum velocity was chosen to measure relative stride length, frequency, and relative velocity. As expected, arboreal species (Gracilinanus microtarsus, Marmosops incanus, Micoureus paraguayanus, and Caluromys philander) had higher relative climbing velocities than more terrestrial species (Didelphis aurita, Philander frenatus, and Metachirus nudicaudatus). Stride frequency was mostly associated with phylogeny and vertical use of the forest, but relative velocities generally were determined by a combination of stride length and frequency. Differences in climbing performance originated early in the diversification of the group, but continued to evolve because significant differences also were detected at the subfamily, tribe, and genus levels, which seems to parallel the evolution of grasping abilities in primates.