Tracking the Diversity and Chromosomal Distribution of the Olfactory Receptor Gene Repertoires of Three Anurans Species.

Olfaction is a crucial capability for most vertebrates and is realized through olfactory receptors in the nasal cavity. The enormous diversity of olfactory receptors has been created by gene duplication, following a birth-and-death model of evolution. The olfactory receptor genes of the amphibians have received relatively little attention up to now, although recent studies have increased the number of species for which data are available. This study analyzed the diversity and chromosomal distribution of the OR genes of three anuran species (Engystomops pustulosus, Bufo bufo and Hymenochirus boettgeri). The OR genes were identified through searches for homologies, and sequence filtering and alignment using bioinformatic tools and scripts. A high diversity of OR genes was found in all three species, ranging from 917 in B. bufo to 1194 in H. boettgeri, and a total of 2076 OR genes in E. pustulosus. Six OR groups were recognized using an evolutionary gene tree analysis. While E. pustulosus has one of the highest numbers of genes of the gamma group (which detect airborne odorants) yet recorded in an anuran, B. bufo presented the smallest number of pseudogene sequences ever identified, with no pseudogenes in either the beta or epsilon groups. Although H. boettgeri shares many morphological adaptations for an aquatic lifestyle with Xenopus, and presented a similar number of genes related to the detection of water-soluble odorants, it had comparatively far fewer genes related to the detection of airborne odorants. This study is the first to describe the complete OR repertoire of the three study species and represents an important contribution to the understanding of the evolution and function of the sense of smell in vertebrates.

Larval chondrocranial and internal oral morphology of the neotropical treefrog Boana crepitans (Wied-Neuwied, 1824; Amphibia, Anura, Hylidae).

We describe the internal oral morphology and chondrocranial anatomy for Boana crepitans tadpoles, and compare them with available descriptions for other species in the subfamily Cophomantinae. Among species of the Boana faber group, the chondrocranial anatomy has been reported only for one species internal oral morphology and cranial anatomy are similar to other described species of Boana and Cophomantinae. B. crepitans lacks unique features in the oral cavity and chondrocranium that would distinguish it from other congeneric species. We identify six characters from the internal oral anatomy of tadpoles unique for Cophomantinae. In addition, Boana has infralabial papillae projections, buccal floor arena papillae, and lateral ridge papillae projections shorter than those described for Aplastodiscus and Bokermannohyla.