Male-male lethal combat in the quasi-gregarious parasitoid Anastatus disparis (Hymenoptera: Eupelmidae)

Abstract

Most animals employ aggressive behaviours to acquire resources such as food, territory and mates. Although mating is important for males, which typically exhibit competitive behaviours to gain mating opportunities, they generally tend to avoid conflict escalation; while extreme combat also occurs in some species and results in death. In this study, male-male lethal combat behaviour in Anastatus disparis was examined (Hymenoptera: Eupelmidae) by investigating the characteristics of fighting and the factors that influence fighting intensity in this species. Male fight intensity in A. disparis increased with both competitor density and female presence, while it was not influenced by the relatedness among male competitors. By comparing the frequency of received attacks between injured and non-injured males, we found that the former were more vulnerable to attack. In contrast to death due to lethal attack, death that occurs as a result of A. disparis combat may be the cumulative effect of injuries sustained over repeated competitive encounters. Combined with the biological characters of A. disparis, we discuss potential factors contributing to the evolution of fatal conflict in this species.

Sexual dimorphism and sex-biased gene expression in an egg parasitoid species, Anastatus disparis

“…Our transcriptome data are consistent with this observation, with the functions of some annotated genes highly expressed in males being associated with aggression, as widely studied in D. melanogaster [68] [69]. Male ghting in A. disparis is high intensity and dangerous, with contestants commonly being severely injured or killed [48] [49]. The annotated gene muscleblind ( Figure 6: c70505.graph_c4) was highly expressed in males and might play a role in the high-intensity male ghting in A. disparis (qRT-PCR: t=7.244, df=4, p<0.05).…”

Effects of female body size and age and male mating status on male combat in Anastatus disparis (Hymenoptera: Eupelmidae)

“…Many factors have been shown to influence the occurrence and intensity of fights, such as the fighting ability of each contestant (termed resource-holding potential, RHP) (Parker, 1974), the value of the resource (Enquist & Leimar, 1987, 1990Innocent et al, 2011;Stockermans & Hardy, 2013;Liu & Hao, 2019a), the density of competitors (Murray & Gerrard, 1984, 1985Murray, 1987Murray, , 1989Innocent et al, 2011;Liu et al, 2017), the relatedness of the combatants (Hamilton, 1979;Reinhold, 2003;Innocent et al, 2011;Sato et al, 2013;Kapranas et al, 2016;Liu et al, 2017), and the fighting experience of the combatants (Parker, 1974;Hsu et al, 2006;Schwartzer et al, 2013). These influences have been extensively studied in terms of both dangerous and nondangerous fighting patterns.…”

“…Typically, the sex ratio (male %) in A. disparis is 10-20%, and the males of A. disparis are polygynous, while females mate only once in their lifetime (Li & Lou, 1992;Liu et al, 2015). Mates are always a valuable resource and to acquire mating opportunities, the males of A. disparis frequently engage in dangerous fighting behaviour near their emergence site (Liu et al, 2017;Liu & Hao, 2019a).…”

“…Although male-male chasing near the emergence site is frequently observed, injury is mainly caused by severing of the opponent's feet and antenna via the contestant's mouthparts. Injured individuals are more vulnerable to attack, and the severe injury and death that occur as a result of A. disparis combat may be the cumulative effect of injuries sustained over repeated competitive encounters (Liu et al, 2017). Here, A. disparis was used as an experimental model to identify the factors that influence and change the resource value, causing a subsequent adjustment of fighting behaviour.…”

“…In the wild, male fighting behaviour near the emergence site is most pronounced during the peak eclosion period. Therefore, in this study, the aggression experiments lasted 3 h. The number of males reared on field-collected egg masses of L. dispar ranges from 4 to 28, and male fight intensity in A. disparis increases with competitor density (Liu et al, 2017). Thus, in each aggression experiment, to control for the effect of competitor density on male aggression, we introduced four males into a cylindrical arena (height: 5 cm, diameter: 10 cm).…”