HOST-RANGE EVOLUTION INAPHIDIUSPARASITOIDS: FIDELITY, VIRULENCE AND FITNESS TRADE-OFFS ON AN ANCESTRAL HOST

Abstract

The diversity of parasitic insects remains one of the most conspicuous patterns on the planet. The principal factor thought to contribute to differentiation of populations and ultimately speciation is the intimate relationship parasites share with hosts and the potential for disruptive selection associated with using different host species. Traits that generate this diversity have been an intensely debated topic of central importance to the evolution of specialization and maintenance of ecological diversity. A fundamental hypothesis surrounding the evolution of specialization is that no single genotype is uniformly superior in all environments. This "trade-off" hypothesis suggests that negative fitness correlations can lead to specialization on different hosts as alternative stable strategies. In this study we demonstrate a trade-off in the ability of the parasitoid, Aphidius ervi, to maintain a high level of fitness on an ancestral and novel host, which suggests a genetic basis for host utilization that may limit host-range expansion in parasitoids. Furthermore, behavioral evidence suggests mechanisms that could promote specialization through induced host fidelity. Results are discussed in the context of host-affiliated ecological selection as a potential source driving diversification in parasitoid communities and the influence of host species heterogeneity on population differentiation and local adaptation.

Host adaptation of a gregarious parasitoid Sclerodermus harmandi in artificial rearing

“…At times, artificial rearing can have some negative effects on host searching and parasitization rates of parasitoids (Chambers 1977;Gandolfi et al 2003). Such effects may be a consequence of behavioral or physiological alterations of parasitoids arising when parasitoids are reared on a substitute host rather than the target host (Gandolfi et al 2003;Shimoji and Miyatake 2002;Henry et al 2008).…”

Assortative mating and the role of phenotypic plasticity in male competition: implications for gene flow among host-associated parasitoid populations

“…Eight F-line populations were maintained on A. solani feeding on Capiscum annuum (Solanaceae) and 12 P-line populations were maintained on A. pisum on Vicia fabae (Fabaceae). For more information on the initiation and maintenance of host selection lines, please refer to Henry et al (2008).…”

“…However, when multiple males are present, as is often the case with Aphidius parasitoids, they frequently compete for copulatory privileges. Laboratory-reared populations of Aphidius ervi (Haliday) were maintained on pea Acyrthosiphon pisum (Harris) or foxglove aphids Aulacorthum solani (Kaltenbach) for a period of 2 years, by which time the populations diverged in several traits including reproductive fitness (Henry et al 2008). Furthermore, parasitoids maintained plasticity in traits such as adult body size.…”

Spatiotemporal variations in aphid‐parasitoid relative abundance patterns and food webs in agricultural ecosystems

“…The fitness of parasitoids is linked to the availability of the host species they are able to exploit (Henry et al 2008). Therefore, one can expect the specific composition of the community of hosts and their relative abundance to be a major factor explaining the relative abundances of parasitoids.…”