Using effects of parasitoid size on fitness to test a host quality model assumption with the parasitoid wasp Spalangia endius

Abstract

How body size affects fitness of males relative to females is relevant to understanding the evolution of sexual size dimorphism and maternal sex-ratio manipulation. In most parasitoid wasps, mothers oviposit a greater proportion of daughters in larger hosts. The host-quality model describes how this may be adaptive. A major assumption of the model is that host size has a greater effect on the fitness of daughters than of sons. The assumption has often been tested indirectly by examining the effects of parasitoid size on fitness, because a parasitoid's size generally increases with the size of the host on which it develops. The validity of this indirect method is examined here for the parasitoid wasp Spalangia endius Walker, 1839 parasitizing Musca domestica L., 1758. If the method is valid, effects of parasitoid size on fitness should match the effects of host size on fitness that were shown in a previous study. The effects matched in that both parasitoid size and host size affected the fitness of females but not of males. However, the aspects of female fitness that were affected differed. That female size but not male size affected fitness was consistent with the female-biased sexual size dimorphism of S. endius.Résumé : L'effet de la taille corporelle sur la fitness des mâles par rapport à celle des femelles est un facteur important pour la compréhension de l'évolution du dimorphisme sexuel de la taille et de la manipulation maternelle du rapport mâles:femelles. Chez la plupart des guêpes parasitoïdes, les mères pondent un pourcentage plus élevé de rejetons femelles dans les hôtes de plus grande taille. Le modèle de la qualité de l'hôte décrit de quelle manière ce phénomène peut être adaptatif. Une présupposition majeure du modèle est que la taille de l'hôte a un effet plus important sur la fitness des rejetons femelles que sur celle des mâles. Cette présupposition a souvent été vérifiée indirectement par l'examen des effets de la taille du parasitoïde sur sa fitness, parce que la taille du parasitoïde augmente généralement en fonction de la taille de l'hôte sur lequel il se développe. Nous examinons la validité de cette méthode indirecte chez la guêpe parasitoïde Spalangia endius Walker, 1839 vivant sur Musca domestica L., 1758. Si la méthode est valide, les effets de la taille du parasitoïde sur sa fitness devraient être semblables à ceux de la taille de l'hôte sur la fitness qui ont été observées dans une étude antérieure. Les effets concordent en ce que tant la taille du parasitoïde que celle de l'hôte affectent la fitness des femelles, mais pas celle des mâles. Cependant, il y a des différences dans les aspects de la fitness des femelles qui sont affectés. Le fait que la taille des femelles, mais non celle des mâles, ait des effets sur la fitness est en accord avec dimorphisme sexuel de la taille qui favorise les femelles chez S. endius.[Traduit par la Rédaction]

Cascading effects of host size and host plant species on parasitoid resource allocation

“…Host size, which is a proxy for the developmental stage of the herbivorous host, is likely to be a primary cue for foraging parasitoids due to Correspondence: Teresa M. Stoepler, Department of Biological Sciences, The George Washington University, 2023 G St. NW, Suite 340, Washington, DC 20052, U.S.A. E-mail: teresa.stoepler@gmail.com its potential influence on offspring development time, the risk of multiparasitism, and host immunocompetence (King, 1987;Bukovinszky et al, 2009). Lampson et al, 1996;Fidgen et al, 2000;Teder & Tammaru, 2002, but see Kouamé & Mackauer, 1991), and evidence for a positive relationship between parasitoid size and fitness in a number of parasitoid groups suggests that parasitoid host choice should be under strong selection (Godfray, 1994;Visser, 1994;Nakamura, 1995;Allen & Hunt, 2001;King & Napoleon, 2006). Lampson et al, 1996;Fidgen et al, 2000;Teder & Tammaru, 2002, but see Kouamé & Mackauer, 1991), and evidence for a positive relationship between parasitoid size and fitness in a number of parasitoid groups suggests that parasitoid host choice should be under strong selection (Godfray, 1994;Visser, 1994;Nakamura, 1995;Allen & Hunt, 2001;King & Napoleon, 2006).…”

“…A number of studies have found that host size is positively correlated with adult parasitoid size (e.g. Lampson et al, 1996;Fidgen et al, 2000;Teder & Tammaru, 2002, but see Kouamé & Mackauer, 1991), and evidence for a positive relationship between parasitoid size and fitness in a number of parasitoid groups suggests that parasitoid host choice should be under strong selection (Godfray, 1994;Visser, 1994;Nakamura, 1995;Allen & Hunt, 2001;King & Napoleon, 2006). Larger hosts, or hosts with the potential to grow large, are assumed to be superior to small hosts because they represent greater resource quantity for parasitoid development (Charnov, 1982;Charnov & Skinner, 1985).…”

Benefit of polyandry in a highly monandrous species when females mate with already mated males

“…A third explanation is that the frequency at which females encounter and mate with males that have already mated four times may be low. Given the sex ratio in this species, males are expected to mate one and a half to three times on average (King and Fischer 2010), and reproductive success is highly variable among males even in the laboratory (King and Napoleon 2006). Thus, some males will have more success than average.…”

Inhibition of male sexual behavior after interacting with a mated female

“…This was done to match an earlier study and because the male that is first to mount a female is usually also the first to contact, court, and attempt copulation ; Figures 1-3c below). Wasps were 0 -2 d old, and each male was tested against a male that was the same number of days old and the same size to our eyes, although even very obvious differences in male size do not appear to affect mating success in this species (King & Napoleon, 2006). The males were assigned to treatments (e.g., virgin versus experienced) at random.…”