Much more than a clasp: evolutionary patterns of amplexus diversity in anurans

Abstract

The evolution and diversification of animal reproductive modes have been pivotal questions in behavioural ecology. Amphibians present the highest diversity of reproductive modes among vertebrates, involving various behavioural, physiological and morphological traits. One such feature is the amplexus, which is the clasp or embrace of males on females during reproduction and is found almost universally in anurans. Hypotheses about the origin of amplexus are limited and have not been tested thoroughly, nor have they taken into account evolutionary relationships in most comparative studies. However, these considerations are crucial to an understanding of the evolution of reproductive modes. Here, using an evolutionary framework, we reconstruct the ancestral state of amplexus in 685 anuran species. We investigate whether the type of amplexus has a strong phylogenetic signal and test whether sexual size dimorphism could have influenced amplexus type or male performance while clasping females. Overall, we found evidence of ≥34 evolutionary transitions in amplexus type across anurans. We found that amplexus type exhibits a high phylogenetic signal and that amplexus type does not evolve in association with sexual size dimorphism. We discuss the implications of our findings for the diversity of amplexus types across anurans.

A taxonomic revision of the genus Phrynoglossus in Indochina with the description of a new species and comments on the classification within Occidozyginae (Amphibia, Anura, Dicroglossidae)

“…The inguinal amplexus mode that we documented in P. magnapustulosus and P. myanhessei is supported as an autapomorphy of the genus Phrynoglossus by the observation of an inguinal amplexus mode also in P. sumatranus by Eto and Matsui (2012). According to a large-scale analysis of the amplexus mode across all groups of anuran amphibians, reveal the inguinal amplexus as the basal state to all Anura (Carvajal-Castro et al 2020). However, the latter authors gave the axillary amplexus as the only mode found within the family Dicroglossidae obviously not being aware of the inguinal amplexus mode in Phrynoglossus.…”

Novel reproductive behavior in an Asian frog: sex‐reversed inguinal amplexus

“…We were unable to determine the function of this novel reproductive behavior exhibited by Lau’s leaf litter toad. This period of amplexus could be part of courtship (e.g., Carvajal‐Castro et al 2020), a signal by the female that she will mate with the male, which is then followed by another form of amplexus during oviposition and fertilization. This is not an unlikely scenario, as other species of frogs engage in different forms of amplexus prior to and during oviposition (e.g., Pombal et al 1994, Bourne et al 2001, Willaert et al 2016).…”

“…Diversity in amplexus has foundations in phylogeny and the environment, with axillary and inguinal amplexus being the two most common forms (Carvajal‐Castro et al 2020). Inguinal amplexus, in which the male grasps the female around the waist, is considered the ancestral condition.…”

“…In the past few decades, other forms of positioning for egg deposition and fertilization have been discovered. To date, nine different forms of amplexus have been described for frogs, all involving the male on top of or in line horizontally (cloacal apposition) with the female, but not all involving clasping (Carvajal‐Castro et al 2020). For example, in cloacal apposition, the male and the female face in opposite directions with their cloacas either adpressed or in close proximity.…”

Exploring the global animal biodiversity in the search for new drugs -Amphibians

“…Fertilization in Anura mainly occurs externally, taking place by amplexus, involving the male grasping the female with its front legs and covering the eggs with sperm as they are released from the female's body [51]. After fertilization, the life cycle of most anurans starts in water when the eggs hatch into limbless larvae with gills.…”