Caudal vertebral development and morphology in three salamanders with complex life cycles (Ambystoma jeffersonianum, Hemidactylium scutatum, and Desmognathus ocoee)

Abstract

We describe caudosacral and caudal vertebral morphology across life history stages in three caudate amphibians: Ambystoma jeffersonianum (Ambystomatidae), Desmognathus ocoee (Plethodontidae: Desmognathinae), and Hemidactylium scutatum (Plethodontidae: Plethodontinae). All three species have aquatic larvae, but adults differ in habitat and predator defense strategy. Predator defense includes tail autotomy in D. ocoee and H. scutatum but not A. jeffersonianum. Of the species that autotomize, H. scutatum has a specialized constriction site at the tail base. We investigated whether aquatic larvae exhibit vertebral features similar to those previously described for aquatic adults and examined the effect of metamorphosis, if any, on vertebral morphology and the ontogeny of specialized vertebral features associated with tail autotomy. Interspecific comparisons of cleared-and-stained specimens indicate that vertebral morphology differs dramatically at hatching and that caudosacral and caudal vertebrae undergo continuous ontogenetic change throughout larval, metamorphic, and juvenile periods. Larvae and juveniles of H. scutatum do not exhibit adult vertebral features associated with constricted-base tail autotomy. The pond-type larvae of A. jeffersonianum and H. scutatum have tapering centrum lengths posterior to the sacrum. This pattern is functionally associated with aquatic locomotion. The stream-type larvae of D. ocoee undergo enhanced regional growth in the anterior tail such that the anterior caudal centra become longer than the preceding caudosacral centra. With the exception of the first two caudal vertebrae, a similar growth pattern occurs in H. scutatum adults. We hypothesize that enhanced growth of the anterior caudal segments is associated with tail elongation and autotomy.

Evolutionary implications of hierarchical impacts of nonlethal injury on reproduction, including maternal effects

“…Tail autotomy (active loss) results from a variety of convergent anatomical specializations (Wake & Dresner, 1967; Arnold, 1984, 1988; Wake, 1991; Vaglia, Babcock & Harris, 1997; Babcock & Blais, 2001). Although there are few compelling data from free‐ranging populations of either lizards or salamanders that document causes of tail loss, autotomy has long been viewed as a mechanism for distracting predators, permitting escape (Hubbard, 1903; Wake & Dresner, 1967; Bellairs & Bryant, 1985; Arnold, 1988).…”

Adaptation or exaptation? An experimental test of hypotheses on the origin of salinity tolerance inBufo calamita

“…Development is a highly compartmentalized process (Alberch, 1987;Carroll et al, 2001) and, consequently, organisms with complex life cycles such as amphibians often show certain degree of decoupling between larval and adult traits (Wassersug, 1975;Shaffer et al, 1991;Ebenman, 1992;Moran, 1994;Phillips, 1998). However, trait decoupling across the metamorphic boundary that separates life stages in organisms with complex life cycles is not universal for all traits and organisms (Babcock & Blais, 2001;Watkins, 2001) and sometimes a persistence of a trait in a given stage may be because of its developmental linkage to other trait(s) selected for in a different stage (Cheverud et al, 1983;Cheverud, 1984). Some traits may share a developmental history in spite of metamorphosis, and postmetamorphic traits may be affected by the environment experienced during premetamorphic stages (Goater, 1994;Tejedo et al, 2000;Relyea, 2001;Relyea & Hoverman, 2003;M.…”

Biological controls upon the physical taphonomy of exceptionally preserved salamanders from the Miocene of Rubielos de Mora, northeast Spain

“…Many salamanders possess a weak articulation between the last caudosacral and first caudal vertebra to facilitate tail autotomy (Duellman & Trueb 1986). In salamanders that autotome the entire tail, the anterior caudal vertebrae possess characteristic anterolateral transverse processes (Babcock & Blais 2001). These structures are present in the Rubielos de Mora salamanders, which strongly suggests that they had the capacity for tail autotomy.…”