Host genotype affects the relative success of competing lines of aphid parasitoids under superparasitism

Abstract

1. In solitary parasitoids, only one individual can complete development in a given host. Therefore, solitary parasitoids tend to prefer unparasitised hosts for oviposition, yet under high parasitoid densities, superparasitism is frequent and results in fierce competition for the host's limited resources. This may lead to selection for the best intra-host competitors. 2. Increased intra-host competitive ability may evolve under a high risk of superparasitism if this trait exhibits genetic variation, and if competitive differences among parasitoid genotypes are consistent across environments, e.g. different host genotypes. 3. These assumptions were addressed in the aphid parasitoid Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae) and its main host, the black bean aphid, Aphis fabae (Scopoli) (Hemiptera: Aphididae). Three parthenogenetic lines of L. fabarum were allowed to parasitise three aphid clones singly and in all pairwise combinations (superparasitism). The winning parasitoid in superparasitised aphids was determined by microsatellite analysis. 4. The proportions of singly parasitised aphids that were mummified were similar for the three parasitoid lines and did not differ significantly among host clones. 5. Under superparasitism, significant biases in favour of one parasitoid line were observed for some combinations, indicating that there is genetic variation for intra-host competitive ability. However, the outcome of superparasitism was inconsistent across aphid clones and thus influenced significantly by the host clone in which parasitoids competed. 6. Overall, this study shows that the fitness of aphid parasitoids under superparasitism is determined by complex interactions with competitors as well as hosts, possibly hampering the evolution of improved intra-host competitive ability.

Sequence analysis of mitochondrial ND1 gene can reveal the genetic structure and origin of Bactrocera dorsalis s.s.

“…[42,43]. These phenomena suggest that infection of maternally inherited microorganisms may influence random mating among specific taxa, leading to divergence [39,42,43]. If Wolbachia had a role in population structure observed in the current study has yet to be examined.…”

“…Previous studies have also found similar phenomena in other species, including Dipteran Drosophila melanogaster [36], Drosophila simulans [37], Rhagoletis cerasi [38], mosquitoes [39], Hemipteran Bemisia tabaci [40,41], and Lepidopteran Danaus chrysippus ( L .) [42,43]. These phenomena suggest that infection of maternally inherited microorganisms may influence random mating among specific taxa, leading to divergence [39,42,43].…”

Ample genetic variation but no evidence for genotype specificity in an all-parthenogenetic host–parasitoid interaction

“…But we cannot exclude that there may be genotype‐by‐genotype interactions on fitness‐relevant traits of surviving parasitoids that were not studied here, such as the time until mummification, the rate of emergence from mummies or the body size of emerging parasitoids. In fact, there is some evidence for genotype‐by‐genotype interactions on parasitoid body size (Vorburger et al ., in press). Similarly, we cannot rule out that there may be genotype‐by‐genotype interactions on traits of surviving aphids, e.g.…”

“…, 2007), which is unlikely to be genotype‐specific. However, Henter & Via (1995) have shown that a resistant and a susceptible clone of the pea aphid did not differ in the number of parasitoid ovipositions they suffered, and Vorburger et al. (in press) found that in A. fabae , up to three quarters of individuals on which parasitoid attacks have been observed may survive.…”

Parasitoid bacterial symbionts as markers of within-host competitive outcomes: superparasitoid advantage and sex ratio bias

“…In general, few markers are available for monitoring the outcome of withinhost competition (but see Goubault et al, 2003;Vorburger et al, 2010). In general, few markers are available for monitoring the outcome of withinhost competition (but see Goubault et al, 2003;Vorburger et al, 2010).…”