Much more than a clasp: Evolutionary pattern of amplexus diversity in anurans

Abstract

18The evolution and diversification of animal reproductive modes have been pivotal questions 19 in behavioral ecology. Amphibians present the highest diversity of reproductive modes 20 among vertebrates, involving various behavioral, physiological and morphological traits. One 21 of such features is the amplexus, the clasp or embrace of males on females during 22 reproduction, which is almost universal to anurans. Hypotheses about the origin amplexus are 23 limited and have not been thoroughly tested, nor had they taken into account evolutionary 24 relationships in most comparative studies. However, these considerations are crucial to 25 understand the evolution of reproductive modes. Here, using an evolutionary framework, we 26 reconstruct the ancestral state of amplexus in 686 anuran species; investigate whether the 27 amplexus type is a conserved trait; and test whether sexual size dimorphism (SSD) could have 28 influenced the amplexus type or male performance while clasping females. Overall, we found 29 evidence of at least 35 evolutionary transitions in amplexus type across anurans. We also 30 found that amplexus exhibits a high phylogenetic signal (it is conserved across Anura 31 evolutionary history) and the amplexus type does not evolve in association with SSD. We 32 discuss the implications of our findings on the diversity of amplexus types across anurans. 33 Keywords: Amphibia -ancestral reconstruction -frogs -reproductive modes -sexual 34 dimorphism. 35 36Understanding the evolution and diversification of reproductive modes in animals has been a 37 shared interest among evolutionary biologists over decades (e.g.