Effect of Winning Experience on Aggression Involving Dangerous Fighting Behavior in Anastatus disparis (Hymenoptera: Eupelmidae)

Abstract

Aggressive behavior is widely observed in animal species for acquiring important resources and usually includes both dangerous and nondangerous fighting patterns. Only a few species show dangerous fighting patterns that are defined by fights ending with contestants being severely injured or killed. Prior experience, an important factor in many species, has been demonstrated to affect a contestant's subsequent fighting behavior. Few studies have focused on the effect of experience on aggression involving dangerous fighting patterns. Here, an egg parasitoid wasp, Anastatus disparis, which shows extreme and dangerous fighting behavior to acquire mating opportunities, was used as an experimental model. Our results showed that the fighting intensity of the winning males significantly decreased subsequent fighting behavior, which was inconsistent with general predictions. Transcriptomic analyses showed that many genes related to energy metabolism were downregulated in winners, and winners increased their fighting intensity after dietary supplementation. Our study suggested that fighting in A. disparis is a tremendous drain on energy. Thus, although males won at combat, significant reductions in available energy constrained the intensity of subsequent fights and influenced strategic decisions. In addition, winners might improve their fighting skills and abilities from previous contests, and their fighting intensity after dietary supplementation was significantly higher than that of males without any fighting experience. Generally, in A. disparis, although winners increased their fighting ability with previous experience, the available energy in winners was likely to be a crucial factor affecting the intensity and strategic decisions in subsequent fights.

Keywords: aggressive behavior; dangerous fighting pattern; energy; parasitoid wasp; transcriptomic analyses.

Fig. 1.

Effect of winning experience on aggression. Aggression in our studies was described with intensity of fighting. Fight intensity was assessed by the proportion of males (A), the proportion severely injured (B), and the mean score of injuries per wasp (C) after 3 h. The error bars indicate standard errors. The same letter on the column indicates no significant difference; however, different letters indicate significant difference.

Fig. 2.

Expression of annotated genes involved in sugar transporter (A and B) and dopamine synthesis (C). The expression of genes determined through qRT-PCR was calculated by the 2^−ΔΔCt method using the housekeeping gene EF1A as a reference to eliminate sample-to-sample variations in the initial cDNA samples. The error bars indicate standard errors. The same letter on the column indicates no significant difference; however, different letters indicate significant difference.

Fig. 3.

Effect of dietary supplementation on winner aggression. Aggression in our studies was described with intensity of fighting. Fight intensity was assessed by the proportion of males (A), the proportion severely injured (B), and the mean score of injuries per wasp (C) after 3 h. The error bars indicate SEs. The same letter on the column indicates no significant difference; however, different letters indicate significant difference.