Abstract
Multiple factors are thought to cause limb abnormalities in amphibian populations by altering processes of limb development and regeneration. We examined adult and juvenile axolotls (Ambystoma mexicanum) in the Ambystoma Genetic Stock Center (AGSC) for limb and digit abnormalities to investigate the probability of normal regeneration after bite injury. We observed that 80% of larval salamanders show evidence of bite injury at the time of transition from group housing to solitary housing. Among 717 adult axolotls that were surveyed, which included solitary‐housed males and group‐housed females, approximately half presented abnormalities, including examples of extra or missing digits and limbs, fused digits, and digits growing from atypical anatomical positions. Bite injury probably explains these limb defects, and not abnormal development, because limbs with normal anatomy regenerated after performing rostral amputations. We infer that only 43% of AGSC larvae will present four anatomically normal looking adult limbs after incurring a bite injury. Our results show regeneration of normal limb anatomy to be less than perfect after bite injury.
Highlights
Salamanders are renowned for their ability to regenerate limbs
While we can only speculate about the origin of limb regeneration, it seems likely to have evolved in response to bite injury
Limb regeneration probably evolved because limbs are essential organs for completing a biphasic lifecycle, which is the ancestral lifecycle among salamanders
Summary
Salamanders are renowned for their ability to regenerate limbs. This ability presumably originated hundreds of millions of years ago, perhaps tracing back to the evolution of tetrapod limbs. Salamander larvae inflict conspecific bite injuries during early development while feeding within productive aquatic habitats that support high densities (Walls & Jaeger 1987; Semlitsch & Reichling 1989; Wildy et al 2001). Such habitats contain arthropod and fish predators that are capable of biting or grasping salamander limbs, causing injury (Gamradt & Kats 1996; Johnson et al 2006; Bowerman et al 2010). Limb regeneration probably evolved because limbs are essential organs for completing a biphasic lifecycle, which is the ancestral lifecycle among salamanders
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