Big, Bad, and Beautiful: Phylogenetic Relationships of the Horned Frogs (Anura: Ceratophryidae)

Abstract

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) studying the evolution of polyploidy; (3) studying the evolution of cocoon formation and larval development duration associated with surviving in semiarid environments; and (4) reviewing the ceratophryid fossil record that could be relevant as calibration points in molecular divergence estimations. The analysis included 11 of the 12 extant species and, when possible, multiple exemplars per species, as well as multiple outgroups. Sequence data were obtained on seven mitochondrial and six nuclear genes for up to 8200 bp per specimen. Our results indicate that 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 (Ce. aurita, Ce. cranwelli, Ce. joazeirensis, and Ce. ornata), and another clade composed of Ce. stolzmanni, Ce. calcarata, and Ce. cornuta. Unlike earlier proposals, the octoploid species (Ce. aurita, Ce. joazeirensis, and Ce. ornata) are not monophyletic, as the diploid Ce. cranwelli, and Ce. 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, and 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.

Budgett's frog (Lepidobatrachus laevis): A new amphibian embryo for developmental biology

“…Although the L. laevis genome still awaits sequencing, genome-independent proteomic strategies have recently been shown to be feasible for non-model species (Wuhr et al, 2014). Since L. laevis is a diploid organism (Faivovich et al, 2014), sequencing and assembly of its genomic sequence should be less cumbersome than for the pseudotetraploid X. laevis . Moreover, a draft transcriptome assembly from embryonic organs contains greater than 26,000 predicted L. laevis proteins [including over 10,000 full-length ORFs with significant similarity to human proteins (BLAST e value of less than 10 −5; N.M.A., N.N.-Y.-unpublished data)]; thus, what we learn in this large-egged cannibalistic frog has great potential to provide insight into bio-medically relevant biology.…”

Embryonic ontogeny of three species of Horned Frogs, with a review of early development in Ceratophryidae

“…In Ceratophrys , values range from 20–24 days in wild C. cranwelli to 25–32 days in C. stolzmanni (Fabrezi et al, ; Ortiz, Almeida‐Reinoso, & Coloma, ) and 70 days in C. aurita (Miranda‐Ribeiro, ); in C. ornata , periods from 20 to 32–36 days have been reported (Honegger, Schneider, & Zimmermann, ; Natale et al, ). Faivovich et al () suggested that ceratophryids diversified early in semiarid environments, and three independent transformations resulted in C. aurita , C. ornata , and C. cornuta , which occupy tropical or temperate humid areas. In this context, it seems possible that ancestral short larval periods may have lengthened along with habitat diversification.…”

“…Last, the relationship between ploidy levels and developmental rates should be explored in Ceratophryidae, which is unusual in including multiple polyploid species (Faivovich et al, ). Polyploidy is an important evolutionary phenomenon that causes the whole‐genome multiplication and a consequent genomic redundancy.…”

“…Horned Frogs of the conspicuous anuran family Ceratophryidae include three endemic South American genera. Ceratophrys currently comprises eight species distributed from Colombia and Venezuela to central Argentina and Uruguay (Frost, ), whereas the monotypic Chacophrys and three species of Lepidobatrachus are restricted to some areas of Argentina, Bolivia, Brazil, and Paraguay (Faivovich et al, ; Frost, ). Most ceratophryids inhabit semiarid environments, including xeric areas of the Pacific coasts in Ecuador and Peru ( C. stolzmanni ), the Brazilian Caatinga (e.g., C. joazeirensis ), and the South American Gran Chaco ( C. cranwelli , Chacophrys , and species of Lepidobatrachus ).…”

On the natural history of the Caatinga Horned Frog, Ceratophrys joazeirensis (Anura: Ceratophryidae), a poorly known species of northeastern Brazil

“…Burrowing may be the single most common adaptation for avoiding desiccation among anurans from deserts, savannas, and other dry environments (Main et al 1959, Wells 2007. Additionally, ceratophryids develop a cocoon of dead skin to reduce water loss during aestivation (Faivovich et al 2014). This cocoon has been considered a specialization associated with semiarid environments (McClanahan et al 1976).…”