Big, bad, and beautiful: phylogenetic relationships of the horned frogs (Anura: Ceratophryidae)

FAIVOVICH, J.; NICOLI, L.; BLOTTO, B.L.; PEREYRA, M.O.; BALDO, D.; BARRIONUEVO, J.S.; FABREZI, M.; WILD, E.R.; HADDAD, C.F.B.

SOUTH AMERICAN JOURNAL OF HERPETOLOGY

Sociedade Brasileira de Herpetologia

Lugar: São Paulo; Año: 2014 vol. 9 p. 207 - 227

1937-2418

The horned frog family, Ceratophryidae, currently comprises three genera and 12 extant species, distributed from the Caribbean lowlands to the Pampean grasslands. Horned frogs are fossorial species that are remarkable in terms of their adult and larval morphology, karyotype, behavior and other aspects of their biology. In this paper we present a molecular phylogenetic analysis with the goals of (1) exploring the relationships among the species of Ceratophryidae, (2) study the evolution of polyploidy, (3) study the evolution of cocoon formation and larval development duration associated with surviving in semiarid environments. The analysis included 11 of the 12 extant species and, when possible, included multiple exemplars per species, and multiple outgroups. Sequence data were obtained on seven mitochondrial and six nuclear genes for up to 8200 bp per specimen. Our results support a sister group relationship of Ceratophryidae and Telmatobiidae, as some previous analyses have also reported. The individual monophyly of Ceratophrys and Lepidobatrachus is well corroborated. The monotypic Chacophrys is recovered as the sister taxon of Lepidobatrachus, but with Jackknife frequency < 50%. Lepidobatrachus asper is the sister taxon of L. laevis + L. llanensis. Relationships within Ceratophrys are congruent with an earlier proposal, with a clade composed of the species possessing a dorsal bony shield (C. aurita, C. cranwelli, C. joazeirensis, and C. ornata), and another clade composed of C. stolzmanni, C. calcarata, and C. cornuta. Unlike earlier proposals, the octoploid species (C. aurita, C. joazeirensis, and C. ornata) are not monophyletic, as the diploid C. cranwelli, and C. ornata are sister taxa. This result implies an ambiguous optimization of ploidy levels, with either a single origin of octoploidy with a subsequent reversal to diploidy, or two independent origins of octoploidy being equally parsimonious; both alternatives are quite unusual from the perspective of chromosome evolution. Our results suggest that ceratophryids diversified in semiarid environments and three independent events resulted in three species subsequently occupying temperate or tropical humid areas. This early diversification in semiarid areas explains the retention of characteristics associated with these environments (like the production of a cocoon of dead skin during estivation, or possibly an accelerated larval period and development) in species present in humid areas. A revision of the fossil record of this family of frogs indicates that there are only two fossil remains that could serve as calibration points for molecular clock estimation, but a number of issues associated with them preclude their use.