Meeting Abstract
Bipedalism is a relatively unique mode of locomotion and it is often accompanied by specialized morphological features. Within rodents, the most well-supported hypothesis is that bipedalism initially evolved to enhance vertical jumping ability for predator evasion. In previous research, we found that kangaroo rats (Dipodomys spp.) are exceptional evaders when dodging rattlesnake strikes. However, few studies have directly compared the evasive abilities of bipedal and quadrupedal rodents, and those that have rely on indirect measures (e.g. predator diet studies) or focus on running ability rather than jumping ability. Thus, the hypothesis of predator avoidance has yet to be directly tested in an ecologically meaningful way. We used hind limb muscle dissections and field-based attack simulations to measure muscle morphology and jump performance for three kangaroo rat species and a quadrupedal heteromyid rodent, the desert pocket mouse (Chaetodipus penicillatus). Reaction time and take-off velocity significantly differed among the rodent species; interestingly, there was not a significant difference between pooled bipedal and quadrupedal rodents, with larger kangaroo rat species performing more similarly to the pocket mice than to smaller kangaroo rat species. We will combine our morphology and performance data to determine which aspects of the hind limb morphology contribute most to the observed differences in performance. These results will have implications for understanding the selective pressures that drove the evolution of bipedalism in small mammals.
