Biogeography and body size shuffling of aquatic salamander communities on a shifting refuge

Abstract

Freshwater habitats of coastal plains are refugia for many divergent vertebrate lineages, yet these environments are highly vulnerable to sea-level fluctuations, which suggest that resident communities have endured dynamic histories. Using the fossil record and a multi-locus nuclear phylogeny, we examine divergence times, biogeography, body size evolution and patterns of community assembly of aquatic salamanders from North American coastal plains since the Late Cretaceous. At least five salamander families occurred on the extensive Western Interior Coastal Plain (WICP), which existed from the Late Cretaceous through the Eocene. Four of these families subsequently colonized the emergent Southeastern Coastal Plain (SECP) by the Early Oligocene to Late Miocene. Three families ultimately survived and underwent extensive body size evolution in situ on the SECP. This included at least two major size reversals in recent taxa that are convergent with confamilial WICP ancestors. Dynamics of the coastal plain, major lineage extinctions and frequent extreme changes in body size have resulted in significant shuffling of the size structure of aquatic salamander communities on this shifting refuge since the Cretaceous.

Evolutionary insights into the North AmericanNecturus beyericomplex (Amphibia: Caudata) based on molecular genetic and morphological analyses

“…Our inferred gene tree recovers a basal split within the genus Necturus separating the common ancestor of N. punctatus and N. lewisi along the Atlantic Coastal Plain from the common ancestor for all other species from the Gulf Coastal Plain, a pattern also recovered by Bonett, Trujano‐Alvarez, Williams, and Timpe (). The sister taxon relationship of N. lewisi and N. punctatus contradicts previous hypotheses that N. lewisi is the basal Necturus species (Guttman et al., ; Hecht, ; Sessions & Wiley, ).…”

Reduced effects of thyroid hormone on gene expression and metamorphosis in a paedomorphic plethodontid salamander

“…In at least Necturus (Proteidae) it is clear that TRα and TRβ are functional and active in target tissues, and the lack of transformation of external gills may be due to a decoupling of hormone regulation of downstream target genes that presumably completed metamorphosis in ancestral species (Safi et al, ; Vlaeminck‐Guillem et al, ). Obligately paedomorphic families are highly divergent from extant metamorphic species, and each have exhibited this life history since the Cretaceous (Holman, ; Bonett et al, ). There have also been multiple independent instances of paedomorphosis in plethodontid salamanders (Wake, ; Ryan and Bruce, ; Bonett et al, ), which vary in metamorphic responsiveness from nearly complete metamorphosis (facultative metamorphosis; Kezer, ) to very limited changes (obligate paedomorphosis; Dundee, ; this study).…”

“…Most of our knowledge about the genetic and endocrine mechanisms that underlie paedomorphosis is derived from studies of the laboratory model Ambystoma (e.g., axolotls and tiger salamanders; e.g., Galton, ; Voss and Shaffer, ; Voss and Smith, ; Page et al, ; Voss et al, ). However, there is tremendous developmental diversity in salamanders, including many independent instances of paedomorphosis (Wiens et al, ; Bonett et al, ), which could have resulted from a variety of molecular deviations.…”

Larval masquerade: a new species of paedomorphic salamander (Caudata: Plethodontidae: Eurycea) from the Ouachita Mountains of North America

“…Other more recently described paedomorphic salamanders are much more closely related to their sister taxa/clades, which in almost all cases are also paedomorphic (e.g. Netting & Goin 1942;Neill 1964;Chippindale et al 2000;Hillis et al 2001; for divergence times see Bonett et al 2013Bonett et al , 2014. Eurycea subfluvicola also represents an additional independent instance of paedomorphosis within Spelerpini (now with 18 paedomorphic species; AmphibiaWeb 2014).…”