On the evolution and function of caltrop cornuti in Lepidoptera - potentially damaging male genital structures transferred to females during copulation

Males of many animal groups have spines on their intromittent organs, but cases in which these spines break off during copulation and remain in the female genital tract are rare. Deciduous, star-shaped spines named caltrop cornuti (CC) are known in about 400 species of Lepidoptera and their function is unknown. The evolutionary history of CC is reviewed; these structures have appeared independently several times, in some cases having been lost and regained. Their deciduous design, production cost and potential risk of damage resulting from their acute spines suggest that CC evolved by natural and/or sexual selection. Five functional hypotheses are discussed. Comparative morphological data, obtained from systematic studies, and original observations are used to assess some assumptions and predictions of the hypotheses.