Do social environments affect the use of exaggerated traits in the dobsonflyCorydalus bidenticulatus?

Abstract

Male–male competition is strongly affected by female presence. In insects with primitive features such as megalopterans, however, it is not known how aggressiveness is expressed in the context of female presence. Here we examined the effect of social environments on the use of secondary sexual traits in the sexual behavior of the Mexican dobsonfly Corydalus bidenticulatus (Megaloptera: Corydalidae). Males of this species have exaggerated traits such as disproportionally elongated mandibles with no dentition, which is a secondary sexual trait used in competition over female access as well as males of other Corydalus species. We investigated how male–male interactions are carried out, and the scaling relationships of sexual and non‐sexual traits. Our results show that males of C. bidenticulatus are not indiscriminately aggressive. The decision whether to fight or not is affected by their social environments: males are aggressive against other males only when the presence of a female is detected. Results also suggest that mandibles and antennae are sexually dimorphic, being exaggerated and showing positive allometry only in males. In contrast, male genitalia, a sex‐specific trait, show negative allometry.

Allometry and morphological trait relationship in the sexually dimorphic Chinese dobsonfly, Acanthacorydalis asiatica (Wood-Mason, 1884) (Megaloptera, Corydalidae)

“…Thus, mandibles are condition-dependent traits in males (House et al 2015). In Megaloptera, positive allometry between body and weapon sizes is also reported in males of seven species of Corydalus in the Americas, three species of Acanthacorydalis in Asia, and two species of Platyneuromus in Central America (Liu et al 2015; Álvarez et al 2017; Ramírez-Ponce et al 2017). In addition, 22 species of Corydalus in America are suggested to have elongated male mandibles fitting this allometric phenomenon (Contreras-Ramos 1998).…”

“…The molecular phylogenetic tree of all genera of the subfamily Corydalinae of Megaloptera suggests that these three genera are included in the same lineage with the New World Chloronia which lacks any weapons in males, and therefore male weapons are thought to have evolved independently (Liu et al 2015). In Corydalusbidenticulatus , positive allometry is reported between male body size and antenna length (Álvarez et al 2017). In the present study, we cannot examine this, because most specimens were preserved after spending life in a large rearing cage and lost antennae.…”

“…However, this order of insects includes three genera in which the male develops exaggerated traits and conspicuous sexual dimorphism is known. In Corydalus , distributed in North to South America, and Acanthacorydalis , known from Asia, positive allometry is reported between male body size and mandible size (Liu et al 2015; Álvarez et al 2017). These males are known to combat with their mandibles (Liu et al 2015; Álvarez et al 2017).…”

“…In Corydalus , distributed in North to South America, and Acanthacorydalis , known from Asia, positive allometry is reported between male body size and mandible size (Liu et al 2015; Álvarez et al 2017). These males are known to combat with their mandibles (Liu et al 2015; Álvarez et al 2017). In Platyneuromus in Central America, the exaggerated male postocular flanges show the positive allometry with male body size, although the function of this postocular flange is still unknown (Liu et al 2015; Ramírez-Ponce et al 2017).…”

“…We also examined the allometric relationships of male genital size of this species. In Megaloptera, Corydalusbidenticulatus Contreras-Ramos, 1998 is the only species for which the relationship between body and genital size has been studied, and a negative allometry is reported although based on only nine males and statistically marginal at P = 0.05 in correlation analysis (Álvarez et al 2017). Two types of sperm transfer are known in insects; one is ejaculation of sperm or sperm-including spermatophores internally to the female reproductive organs and the other is transfer of sperm via an externally attached spermatophore to the female (Simmons 2001; Chapman 2013).…”