On the function of cornuti, sclerotized structures of the endophallus of Lepidoptera

Abstract

The genitalia of many male insects include structures whose functions are unknown or poorly understood. The endophallus of many Lepidoptera bears sclerotized structures known as cornuti, which in some species break off during copulation and remain within the female genital tract ("deciduous" cornuti). I describe previous and original hypotheses on the role of cornuti, identify the selective pressures invoked by these hypotheses, propose different ways of testing them and briefly review pertinent evidence. I describe ten functional hypotheses for non-deciduous cornuti and four for deciduous cornuti; six hypotheses invoke natural selection and eight involve sexual selection. In some cases more than one of the proposed functions could be performed by cornuti; evolutionary change from one function to another is also possible. I suggest that the wide morphological variation observed in non-deciduous cornuti across taxa supports hypotheses invoking sexual selection. I propose that the function and evolution of cornuti can be revealed with a combination of descriptive studies, cornuti removal experiments and comparative tests.

Sexual Selection Within the Female Genitalia in Lepidoptera

“…12.4b-d, f), which could provide internal stimulation to the female during copulation. If this is the case, CFC could favor males whose cornuti provide the best stimulation because they are located in the proper positions and have the appropriate size and shape (Cordero 2010). Female stimulation could be influenced by properties of the female genitalia, such as the degree of sclerotization and the distribution of sensory structures on different portions of the bursa copulatrix (Rogers and Wells 1984;Lincango et al 2013), which in turn could evolve to improve the ability of females to choose the males that provide the best stimulation (i.e., the best copulatory courtship).…”

“…For example, the star-shaped caltrop cornuti, shed by males during copulation in many Notodontidae species (Miller 1991(Miller , 2009Miller et al 1997), could pierce the bursa copulatrix if the female receives further spermatophores and thus prevent female remating (Cordero and Miller 2012). Since monandry could be detrimental for females (for example, by reducing the amount of spermatophore-derived nutrients), sclerotized shieldlike structures in areas of contact with cornuti could evolve in the female's bursae copulatrix (Cordero 2010;Cordero and Miller 2012). Female structures that damage the male genitalia could also evolve.…”

“…Although the controversy about the relative importance of female choice and sexual conflict has attracted the most attention (Hosken and Stockley 2004;Eberhard 2010;Arnqvist and Rowe 2002;Schilthuizen 2014;Simmons 2014), determining the relative importance of the different mechanisms is an empirical problem that needs to take into account the fact that more than one mechanism could influence the evolution of a particular genital structure and that the different mechanisms could interact in complex ways (Cordero 2005(Cordero , 2010Cordero and Eberhard 2005;Simmons 2014). We illustrate these ideas with some speculations about the evolution of cornuti (Fig.…”

“…For example, the cornuti could provide internal stimulation to the female (Cordero 2010) and cryptic female choice (of a different nature than the one considered above) would be responsible for the maintenance and further elaboration of cornuti. Other possibility is that males used their cornuti to pierce the female genital tract to delay female remating, until the female is able to heal the damage provoked by cornuti, in which case sexual conflict (also of a different nature than the one considered above) would be responsible for the maintenance and elaboration of cornuti.…”

“…The cornuti not only operate as attachment devices. Cordero (2010) reviewed all the potential functions of cornuti including caltrop cornuti (Cordero and Miller 2012) (see next section). They are diverse structures even within a single family (e.g., see recent analysis of cornuti in Tortricinae by Anzaldo et al 2014).…”