Males in many frog families yearly develop keratinized, often spiny nuptial pads on their thumbs and

forearms during the reproductive period, and it is generally accepted that these serve to improve

grip on the female during amplexus. Here we hypothesize that nuptial pads also secrete primer

pheromones that bypass the conventional olfactory system and are injected to directly trigger

physiological changes in the female. This results in accelerated oviposition, which has undeniable

adaptive benefits, since amplectic pairs are restricted in their movements and therefore more

vulnerable to predation. In a transcriptome pilot study, we found that several molecules that are

cosecreted with the primer pheromones may serve to improve pheromone application. Altogether,

we hypothesize that nuptial pads consist of an integrated system of different but additive functions

that is similar to a snake venom apparatus, but for which the secretion changes the physiology of

the female instead of that of the prey. The nuptial pads may combine tools for abrading the skin

(e.g., keratinous spines, in analogy with fangs), molecules acting on neural pathways (primer

pheromones, in analogy with neurotoxins), and proteins that reduce blood coagulation (e.g., fibrino

(geno)lytic proteases, in analogy with haemotoxins) to facilitate pheromone access to the female’

circulatory system. This projects aims at uncovering for the first time the mode of action of a primer

pheromone system in a vertebrate.