Abstract
BackgroundEfficient transfer of chemical signals is important for successful mating in many animal species. Multiple evolutionary lineages of animals evolved direct sex pheromone transmission during traumatic mating—the wounding of the partner with specialized devices—which helps to avoid signal loss to the environment. Although such direct transmission modes of so-called allohormone pheromones are well-documented in invertebrates, they are considered rare in vertebrates. Males of several species of the frog genus Plectrohyla (Hylidae, Anura) have elongated teeth and develop swollen lips during the breeding season. Here we investigated the possibility that these structures are used to scratch the females’ skin and apply allohormone pheromones during traumatic mating in several Plectrohyla species.ResultsOur behavioural observations revealed that males press their upper jaw onto the females’ dorsum during amplexus, leaving small skin scratches with their teeth. Histological examinations of the males’ lips identified specialized mucus glands, resembling known amphibian pheromone glands. Whole-transcriptome sequencing of these breeding glands showed high expression of sodefrin precursor-like factor (SPF) proteins, which are known to have a pheromone function in multiple amphibian species.ConclusionsOur study suggests SPF delivery via traumatic mating in several anuran species: the males have specialized breeding glands in the lips for production and secretion and use their elongated teeth as wounding devices for application. We hypothesize that these SPF proteins end up in the females’ circulatory system, where understanding their exact function will require further molecular, physiological and behavioural testing.
Highlights
Efficient transfer of chemical signals is important for successful mating in many animal species
Mating behaviour and extra‐genital wounding structures During field work in Mexico, we kept a couple of P. sagorum in amplexus in captivity for 24 h and observed their mating behaviour
In the lips of all three examined species, we identified specialized mucus glands (SMGs), a type of sexually dimorphic skin gland, that has been described in various amphibian species
Summary
Efficient transfer of chemical signals is important for successful mating in many animal species. Animals developed different solutions to this problem, such as long living carrier proteins which slowly release volatile pheromones (e.g. major urinary proteins in mice [5]), by properly navigating air- and water currents towards a pheromone source (e.g. in moths, crabs, and lobsters; for review see [6]), or by fanning pheromones in the direction of the receiver (e.g. in aquatic newts [7]) Another option is the direct transmission of pheromones, avoiding any signal loss to the environment. Some of these proteins have been shown to have originated early in amphibian evolution and can be found among several urodele and anuran families [8, 25, 26], their transmission via traumatic mating using extra-genital wounding structures [9] is currently only known from these salamanders
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