Male soldiers are functional in the Japanese strain of a polyembryonic wasp

Abstract

Polyembryonic parasitoids clonally produce sterile soldier larvae in both sexes. Female soldier larvae of Copidosoma floridanum defend their siblings and host resources against heterospecific competitors as well as conspecific male embryos that results in female biased sex ratios. However, the male soldiers of the USA strain exhibit no aggressive behaviors against them, suspected to be a secondary loss of male defense function in the course of evolution. From vitro and vivo experiments, we have found functional male soldiers in the Japanese strain of C. floridanum. In vitro experiments, male soldiers exhibit aggressions against four larval competitors, though aggressiveness is much weaker than that of female soldiers. In vivo experiments, heterospecific competitors are equivocally excluded in both male and female broods. Our findings support the idea that male soldiers have evolved primarily to defend against heterospecific competitors. Further experiments against conspecific embryos may be able to confirm this hypothesis.

Effects of heat shock and ambient temperature on female soldier production in a polyembryonic parasitic wasp

“…In C. floridanum, unfertilized eggs produce males, fertilized eggs produce females and soldier larvae are produced in both sexes. Female soldier larvae exhibit aggression against both conspecific and heterospecific competitors (Grbic et al 1992;Harvey et al 2000;Giron et al 2004;Dunn et al 2014), whereas male soldier larvae exhibit aggression only against heterospecific competitors (Uka et al 2013). There are also several differences between the sexes in terms of the development of soldier larvae (Grbic et al 1992;Ode & Strand 1995), the level of aggression (Giron et al 2007;Uka et al 2013) and the ability to increase the production of soldier larvae in response to multiparasitism (Yamamoto et al 2007), as noted above.…”

“…However, the results of the present study do not correspond with those by reported by Smith et al (2017), who show that heat shock does not affect the number of female soldiers. Differences in soldier production and function are reported between populations of C. floridanum that originated in the U.S.A. and Japan (Grbic et al 1992;Ode & Strand 1995;Grbic et al 1997;Uka et al 2013). Such differences in the nature of soldier larvae between geographical strains may be a reason for the lack of agreement.…”

Two types of embryos with different functions are generated in the polyembryonic wasp Macrocentrus cingulum (Hymenoptera: Braconidae)

“…In C. floridanum caste ratios shift in response to interspecific competition (Gordon and Harvey et al, 2000;Watanabe et al, 2012). Other studies with C. floridanum have examined the molecular mechanisms underlying caste formation (Donnell et al, 2004;Gordon and Strand, 2009;Smith et al, 2010;Uka et al, 2013;Zhurov et al, 2004). In contrast, much less is known about polyembryony in other species and families of wasps.…”

“…For example, the embryos of the polyembryonic wasp, Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) develop into two functionally different larval castes referred to as reproductive and precocious (¼soldier) larvae (Ivanova-Kasas, 1972;. Reproductive larvae consume the host, pupate and form adult wasps, whereas precocious larvae never molt and have functions that include manipulating the sex ratios of the reproductive caste and defending the brood against interspecific competitors (Giron et al, 2007;Smith et al, 2010;Uka et al, 2013). In C. floridanum caste ratios shift in response to interspecific competition (Gordon and Harvey et al, 2000;Watanabe et al, 2012).…”

Sex differences in the protection of host immune systems by a polyembryonic parasitoid

“…Previous studies have shown that C. floridanum usually kills and eliminates the larvae of its competitor, Glyptapanteles pallipes (Braconidae) by attacking them with soldier larvae and a unique toxic humoral factor [12]. There are distinctive differences between male and female broods of C. floridanum in the numbers, behaviours and competitive abilities of the soldiers [13,14]. In addition, in a mixed brood where one male egg and one female egg are laid on a host egg, many male offspring are killed by female soldiers, but surviving males typically mate with most of the female reproductives [14].…”