Abstract:
The burrowing adaptations of the appendicular system of African mole-rats
(Bathyergidae) have been comparatively less investigated than their cranial
adaptations. Because bathyergids exhibit different digging modes (scratchdigging
and chisel-tooth digging) and social systems (from solitary to highly
social), they are a unique group to assess the effects of distinct biomechanical
regimes and social organization on morphology. We investigated the
morphological diversity and intraspecific variation of the appendicular
system of a large dataset of mole-rats (n = 244) including seven species
and all six bathyergid genera. Seventeen morpho-functional indices from
stylopodial (femur, humerus) and zeugopodial (ulna, tibia-fibula) elements
were analyzed with multivariate analysis. We hypothesized that scratchdiggers
(i.e., Bathyergus) would exhibit a more specialized skeletal phenotype
favoring powerful forelimb digging as compared to the chisel-tooth diggers,
and that among chisel-tooth diggers, the social taxa will exhibit decreased
limb bone specializations as compared to solitary taxa due to colony members
sharing the costs of digging. Our results show that most bathyergids have
highly specialized fossorial traits, although such specializations were not
more developed in Bathyergus (or solitary species), as predicted. Most
chisel tooth-diggers are equally, or more specialized than scratch-diggers.
Heterocephalus glaber contrasted significantly from other bathyergids,
presenting a surprisingly less specialized fossorial morphology. Our data
suggests that despite our expectations, chisel-tooth diggers have a suite
of appendicular adaptations that have allowed them to maximize different
aspects of burrowing, including shoulder and neck support for forward force
production, transport and removal of soils out of the burrow, and bidirectional locomotion. It is probably that both postcranial and cranial adaptations in
bathyergids have played an important role in the successful colonization of
a wide range of habitats and soil conditions within their present distribution.
