Species and sex specific chemical composition in a concealed gland from an internal gland-like tissue of an African frog family

Intraspecific chemical communication in frogs is understudied and the few
published cases are limited to externally visible and male-specific
breeding glands. Frogs of the family Odontobatrachidae, a West African
endemic complex of five morphologically cryptic species, have large, fatty
gland-like strands along their lower mandible. We investigated the general
anatomy of this strand and analyzed its chemical composition. We found the
strand to be present in males and females of all species. The strand
varies in markedness, with well-developed strands usually found in
reproductively active individuals. Although the strands are situated under
the skin, they are connected to particular skin sections, the vocal sac in
male frogs and a respective area in females. Gas-chromatography/mass
spectrometry and multivariate analysis revealed, that the strands contain
sex- and species-specific chemical profiles, which are consistent across
geographically distant populations. The profiles varied between
reproductive and non-reproductive individuals. Our results indicate that
the gland-like strand in the Odontobatrachidae comprise a so far
overlooked type of breeding related organ, potentially a gland, that most
likely plays a role in the mating and/or breeding behavior of the five
Odontobatrachus species. Our results highlight the relevance of multimodal
signaling in anurans, and indicate that chemical signaling may not be
restricted to sexually dimorphic, apparent skin glands.