Non-reproductive male cane toads (Rhinella marina) withhold sex-identifying information from their rivals

A male cane toad (Rhinella marina) that mistakenly clasps another male (rather than a female) in a sexual embrace (amplexus) can be induced to dismount by a male-specific “release call”. Although that sex-identifying system can benefit both males in that interaction, our standardised tests showed that one-third of male cane toads did not emit release calls when grasped. Most of those silent males were small, had small testes relative to body mass, and had poorly-developed secondary sexual characteristics. If emitting a release call is costly (e.g., by attracting predators), a non-reproductive male may benefit by remaining silent; other cues (such as skin rugosity) will soon induce the amplexing male to dismount, and the “opportunity cost” to being amplexed (inability to search for and clasp a female) is minimal for non-reproductive males. Hence, male toads may inform other males about their sexual identity only when it is beneficial to do so.