Concurrence in the ability for lipid synthesis between life stages in insects

Authors: VISSER, BERTANNE - Universite Catholique; Willett, Denis; Alborn, Hans; HARVEY, JEFFREY - Netherlands Institute Of Ecology

Submitted to: Royal Society Open Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2017
Publication Date: 3/22/2017
Citation: Visser, B., Willett, D.S., Alborn, H.T., Harvey, J.A. 2017. Concurrence in the ability for lipid synthesis between life stages in insects. Royal Society Open Science. 4:160815.

Interpretive Summary: Scientists at the chemistry group, ARS CMAVE, Gainesville Florida in collaboration with a scientist at Louvain Catholic University, Belgium, investigated lipid production in larvae and adults of three parasitic wasp species from two different lineages and in the vinegar fly Drosophila melanogaster and discovered that the ability to synthesize lipids is consistent between adults and larvae of the same species. Parasitic wasps have become more and more important in agriculture where native as well as introduced species are used for biological control of pest insects. The loss and reacquisition of lipogenesis in parasitic wasps might be more common than currently appreciated and thus, might have far-reaching consequences for species dynamics and interactions with host insects as well as for mass rearing on artificial diet. Previous collaborative research provided preliminary evidence for such an evolutionary trajectory in adult parasitoids. Traditionally, evolutionary trajectories have been thought to be unidirectional: organisms acquire traits that confer fitness benefits. However, evidence is mounting that resource compensation also can drive evolutionary trait loss. Evolutionary studies indicate that ability to produce lipids (lipogenesis) have been lost but also reacquired in certain parasitic wasp lineages where the loss of lipogenesis evolved as a consequence of the parasitic larvae acquiring sufficient lipids from their insect hosts and regained with parasitism of less ideal insects. Additionally, it was found that adults and larvae of a specialist parasitoid with a dependable lipid rich host remain unable to synthesize lipids while the generalist parasitoids, likely to encounter an unstable supply of lipids across variable hosts, had regained lipogenic abilities. Collectively, these results support the hypothesis that lipid synthesis was lost and regained as a consequence of host resource compensation and selection on larvae.

Technical Abstract: Trait loss results from (relaxed) selection on unnecessary or costly traits, but the phenotypic function of a lost trait may persist when it is compensated for by the environment. Compensated trait loss frequently occurs in symbiotic species, where resource provisioning by one partner fuels trait loss in the other partner. The majority of parasitoid insects lack the ability for lipid synthesis, a trait that was lost presumably because their host supplies sufficient fat stores to the developing parasitoid larva. Some generalist parasitoid species have, however, regained the ability for lipid synthesis under the premise that unpredictable or low lipid availability from the host fuels the regain of this trait. Lipid synthesis was thus assumed to have been lost and regained as a consequence of resource provisioning and selection on parasitoid larvae. Despite clear comparative data available for adult parasitoids, it has remained elusive whether parasitoid larvae are able to synthesize lipids. Here, we use feeding experiments and topical application of stable isotopes to determine lipogenic ability in larvae and adults of three ectoparasitoid species that either lost or regained lipgenic ability, as well as the more distantly related vinegar fly Drosophila melanogaster that synthesizes lipids. We provide conclusive evidence of concurrence in lipogenic strategies between larval and adult life stages in all species. Our results support the hypothesis that lipid synthesis was lost and regained as a consequence of resource compensation and selection on parasitoid larvae and increase our understanding of the evolution of lipid synthesis in insects.