Out of the frying pan into the fire: an ecological perspective on evolutionary reversal in life history in plethodontid salamanders (Amphibia: Plethodontidae)

Abstract

I review and analyze interaction webs involving competition and predation in ensembles of plethodontid salamanders in the southern Appalachian Mountains, USA. The objective is to evaluate hypotheses on interaction webs and population regulation in these ensembles in the context of traditional and recent models of phylogeny and life-history evolution of plethodontids. Two ecological hypotheses evaluated are (1) Hairston's conjecture on differences in the kinds of interactions prevalent among biphasic species with an aquatic larval stage, versus terrestrial species with direct development; and (2) Grover's hypothesis on differences in the factors that limit the distribution of species along the moisture gradient from stream to forest. An evolutionary question concerns the supposition derived from recent phylogenetic reconstructions that the history of one major clade, the supergenus Desmognathus, involved an early transition or reversal from a simple life cycle (direct development) to a biphasic life cycle (larval development, metamorphosis), and that this transition promoted the subsequent adaptive radiation of the taxon. Chippindale et al. proposed that selection for lifehistory reversal in the genus Desmognathus was promoted by competition between direct-developing ancestral desmognathans and other terrestrial plethodontids. Experimental studies of interaction webs in extant ensembles of plethodontids in the southern Appalachians, in concert with data from descriptive studies of feeding and habitat use, demonstrate variation in the relative importance of competition and predation in population regulation of species in the several codistributed lineages of these salamanders. Whereas the existing ecological data do not refute the Chippindale et al. hypothesis, many unresolved questions require additional investigation.

A multigenic perspective on phylogenetic relationships in the largest family of salamanders, the Plethodontidae

“…Phaeognathus, the sister taxon of Desmognathus, displays direct development, as do sequential outgroups to the desmognathines. Furthermore, spelerpines (most having stream larvae) are deeply nested, raising the possibility that stream larvae, so long associated with plethodontid origins (Bruce, 2005(Bruce, , 2007, might have been independently derived in desmognathines and spelerpines. In the first major clade, the plethodontines, parsimony argues in favor of an ancestral condition of direct development.…”

“…They proposed a new taxonomy with four subfamilies: Bolitoglossinae (which included the former Bolitoglossini minus Hydromantes, a taxon not included in their analysis but from results of Mueller et al, 2004, by implication placed in their Plethodontinae), Hemidactyliinae (for Hemidactylium only), Plethodontinae (which included the former Plethodontini plus Desmognathinae), and Spelerpinae (the former Hemidactyliini minus Hemidactylium). This taxonomy was widely adopted (e.g., Bruce, 2007;Frost, 2010).…”

Can Parallel Diversification Occur in Sympatry? Repeated Patterns of Body-Size Evolution in Coexisting Clades of North American Salamanders

“…2; see also Hairston 1949; Burton and Likens 1975; Petranka et al 1993, 1994; Harper and Guynn 1999; Smith and Petranka 2000; Petranka and Murray 2001; Ford et al 2002; Wilson and Dorcas 2003). Although there are some microhabitat differences between species within and between clades, species from these three clades occur microsympatrically in springs, seepages, streams, and adjacent forested habitats in ENA (e.g., Petranka and Smith 2005), and some of the larger, predatory species are even known to feed on species in other clades (reviewed in Bruce 2007).…”

Persistent Plethodontid Themes: Species, Phylogenies, and Biogeography

“…Camp et al (2007) argued that the long-continued uplift of the southern Appalachians during the late Cenozoic provided new habitats to be exploited by the contemporaneously radiating desmognathines. They downgraded the role of interclade competition, disagreeing with Chippindale et al (2004) who suggested that competition avoidance with terrestrial salamanders may have been a major factor promoting re-evolution of larvae and occupation of diverse aquatic habitats (see also Bruce 2007).…”