Lipid Dynamics, Identification, and Expression Patterns of Fatty Acid Synthase Genes in an Endoparasitoid, Meteorus pulchricornis (Hymenoptera: Braconidae)
Abstract:In insect parasitoids, fatty acid synthases (FASs) have received less attention and their roles associated with lipogenesis loss are far from clear. Meteorus pulchricornis is a solitary endoparasitoid wasp of many larvae of lepidopteran pests. The lipid content during developmental stages of M. pulchricornis was measured; it was higher in the larval and pupal stages but declined from six-day-old pupae. Lipid accumulation constantly decreased in the adult stage, even after feeding on honey solutions. To investi… Show more
“…No stop codons were found in any of the protein domains and ACC and FAS amino acid sequences of all these species aligned (Supplementary Texts 1 and 2 ), suggesting that these two critical genes for fat synthesis have been conserved throughout the repeated evolution of parasitism in insects. Further tests on these and other parasitoids are now needed to confirm plasticity of fat synthesis at the phenotypic level, but emerging results in other parasitoid systems, e.g., Nasonia species 23 and Meteorus pulchricornis 33 strengthen the notion that plasticity of fat synthesis may be the rule rather than the exception in parasitoids. Figure 2 Conservation of two genes crucial for fatty acid synthesis in four parasitoid insects that supposedly had lost lipogenic activity.…”
Numerous cases of evolutionary trait loss and regain have been reported over the years. Here, we argue that such reverse evolution can also become apparent when trait expression is plastic in response to the environment. We tested this idea for the loss and regain of fat synthesis in parasitic wasps. We first show experimentally that the wasp Leptopilina heterotoma switches lipogenesis on in a fat-poor environment, and completely off in a fat-rich environment. Plasticity suggests that this species did not regain fat synthesis, but that it can be switched off in some environmental settings. We then compared DNA sequence variation and protein domains of several more distantly related parasitoid species thought to have lost lipogenesis, and found no evidence for non-functionality of key lipogenesis genes. This suggests that other parasitoids may also show plasticity of fat synthesis. Last, we used individual-based simulations to show that a switch for plastic expression can remain functional in the genome for thousands of generations, even if it is only used sporadically. The evolution of plasticity could thus also explain other examples of apparent reverse evolution.
“…No stop codons were found in any of the protein domains and ACC and FAS amino acid sequences of all these species aligned (Supplementary Texts 1 and 2 ), suggesting that these two critical genes for fat synthesis have been conserved throughout the repeated evolution of parasitism in insects. Further tests on these and other parasitoids are now needed to confirm plasticity of fat synthesis at the phenotypic level, but emerging results in other parasitoid systems, e.g., Nasonia species 23 and Meteorus pulchricornis 33 strengthen the notion that plasticity of fat synthesis may be the rule rather than the exception in parasitoids. Figure 2 Conservation of two genes crucial for fatty acid synthesis in four parasitoid insects that supposedly had lost lipogenic activity.…”
Numerous cases of evolutionary trait loss and regain have been reported over the years. Here, we argue that such reverse evolution can also become apparent when trait expression is plastic in response to the environment. We tested this idea for the loss and regain of fat synthesis in parasitic wasps. We first show experimentally that the wasp Leptopilina heterotoma switches lipogenesis on in a fat-poor environment, and completely off in a fat-rich environment. Plasticity suggests that this species did not regain fat synthesis, but that it can be switched off in some environmental settings. We then compared DNA sequence variation and protein domains of several more distantly related parasitoid species thought to have lost lipogenesis, and found no evidence for non-functionality of key lipogenesis genes. This suggests that other parasitoids may also show plasticity of fat synthesis. Last, we used individual-based simulations to show that a switch for plastic expression can remain functional in the genome for thousands of generations, even if it is only used sporadically. The evolution of plasticity could thus also explain other examples of apparent reverse evolution.
“…No stop codons were found in any of the protein domains and ACC and FAS amino acid sequences of all these species aligned (Supplementary Texts 1 and 2), suggesting that these two critical genes for fat synthesis have been conserved throughout the repeated evolution of parasitism in insects. Further tests on these and other parasitoids are now needed to confirm plasticity of fat synthesis at the phenotypic level, but emerging results in other parasitoid systems, e.g., Nasonia species 24 and Meteorus pulchricornis 34 strengthen the notion that plasticity of fat synthesis may be more widespread in parasitoids.…”
Dollo's law of irreversibility states that once a complex adaptation has been lost in evolution, it will not be regained. Recently, various violations of this principle have been described. Here, we argue that the logic underlying Dollo's law only applies to traits that are constitutively expressed, while it fails in case of 'plastic' traits that are up- or downregulated according to needs. We tested this hypothesis for an archetypal violation of Dollo's law, the loss and regain of fat synthesis in parasitic wasps. Wasps from lineages that supposedly had lost lipogenic ability more than 200 million years ago were grown under various conditions. In line with our hypothesis, it turned out that fat synthesis had not been lost but was only switched on in low-fat environments. Such plasticity cannot only explain supposed violations of Dollo's law, but also the maintenance of adaptations to rarely occurring extreme events.
“…With regard to the focus of studies on lack of lipid accumulation and parasitoid life histories, a key result of the study by Ruther et al ( 2021) is that their labeling experiments show very low isotope traces in the fatty acid fraction, suggesting that the Fatty Acid Synthase enzyme is functional in several parasitoids. This finding is not novel, however, because previous studies already showed that the fatty acid synthase (fas) gene is intact in several parasitoid species (Kraaijeveld et al, 2019;Visser et al, 2012Visser et al, , 2021 and its multiple paralogs are constitutively expressed in other species (Lammers et al, 2019;Visser et al, 2012;Wang et al, 2020), suggesting that fas plays a functional role in several aspects of the parasitoid's biology. The real conundrum, however, is the fact that while parasitoids may be capable of synthesizing fatty acids, the accumulation of storage lipids is not induced by sugar-feeding as it is in non-parasitoid insects.…”
Ruther et al (2021) evaluated fatty acid synthesis in several parasitic wasp species to test if the general finding that lipogenesis in parasitoids is lacking is upheld (Visser et al 2010 PNAS). As proposed by Visser & Ellers (2008), parasitoids can readily assimilate the triglyceride stores produced by their host. When large triglyceride stores are carried over from larval feeding into adulthood (i.e., up to 30 to 40% of the parasitoid’s dry body weight; Visser et al., 2018, 2021), de novo lipid synthesis from adult feeding is either unnecessary or too costly to maintain, leading to trait loss (Ellers et al., 2012). To test the hypothesis that many parasitoids do not synthesize substantial quantities of fat stores as adults, a previous study used feeding experiments on a wide taxonomic range of insects, including parasitoid wasps, parasitoid flies, a parasitoid beetle, and 65 non-parasitoid species (Visser et al., 2010 and references therein). What is striking is that when compared to non-parasitoid insects, 24 out of 29 evolutionarily distinct parasitoid lineages (Coleoptera, Diptera and Hymenoptera; Visser et al., 2010) did not accumulate significant lipid quantities in adulthood even when fed surplus carbohydrates. When little to no lipids are synthesized de novo by adult parasitoid wasps, this can lead to significant constraints on energy allocation toward key adult functions, such as maintenance, dispersal, and reproduction (Jervis et al., 2008). To our minds, the most important question is ‘why don’t parasitoids accumulate substantial quantities of fat as adults like other insects do, and what does this mean for their life histories?’
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