Poor adult nutrition impairs learning and memory in a parasitoid wasp

Animals have evolved cognitive abilities whose impairment can incur dramatic fitness costs. While malnutrition is known to impact brain development and cognitive functions in vertebrates, little is known in insects whose small brain appears particularly vulnerable to environmental stressors. Here, we investigated the influence of diet quality on learning and memory in the parasitoid wasp Venturia canescens. Newly emerged adults were exposed for 24 h to either honey, 20% sucrose solution, 10% sucrose solution, or water, before being conditioned in an olfactory associative learning task in which an odor was associated to a host larvae (reward). Honey fed wasps showed 3.5 times higher learning performances and 1.5 times longer memory retention than wasps fed sucrose solutions or water. Poor diets also reduced longevity and fecundity. Our results demonstrate the importance of early adult nutrition for optimal cognitive function in these parasitoid wasps that must quickly develop long-term olfactory memories for searching suitable hosts for their progeny.

Poor Adult Nutrition Impairs Learning and Memory in a Parasitoid Wasp

Animals have evolved cognitive abilities whose impairment can incur dramatic fitness costs. While malnutrition is known to impact brain development and cognitive functions in vertebrates, little is known in insects, whose small brain appears particularly vulnerable to environmental stressors. Here, we investigated the influence of diet quality on learning and memory in the parasitoid wasp Venturia canescens. Newly emerged adults were exposed for 24h to either honey, sucrose solution 20%, sucrose solution 10%, or no food, before being conditioned in an olfactory associative learning task in which an odor (orange) was associated to a reward (host larvae). Wasps fed honey showed 3.5 times higher learning performances and 1.5 times longer memory retention times than wasps fed sucrose solutions and starved wasps. Poor diets also reduced longevity and fecundity. Our results demonstrate the importance of early adult nutrition for optimal cognitive function in these parasitoid wasps that must quickly develop olfactory memories for choosing high quality hosts for their progeny.

Identification and RNAi Profile of a Novel Iflavirus Infecting Senegalese Aedes vexans arabiensis Mosquitoes

The inland floodwater mosquito Aedes vexans (Meigen, 1830) is a competent vector of numerous arthropod-borne viruses such as Rift Valley fever virus (Phenuiviridae) and Zika virus (Flaviviridae). Aedes vexans spp. have widespread Afrotropical distribution and are common European cosmopolitan mosquitoes. We examined the virome of Ae. vexans arabiensis samples from Barkédji village, Senegal, with small RNA sequencing, bioinformatic analysis, and RT-PCR screening. We identified a novel 9494 nt iflavirus (Picornaviridae) designated here as Aedes vexans iflavirus (AvIFV). Annotation of the AvIFV genome reveals a 2782 amino acid polyprotein with iflavirus protein domain architecture and typical iflavirus 5’ internal ribosomal entry site and 3’ poly-A tail. Aedes vexans iflavirus is most closely related to a partial virus sequence from Venturia canescens (a parasitoid wasp) with 56.77% pairwise amino acid identity. Analysis of AvIFV-derived small RNAs suggests that AvIFV is targeted by the exogenous RNA interference pathway but not the PIWI-interacting RNA response, as ~60% of AvIFV reads corresponded to 21 nt Dicer-2 virus-derived small RNAs and the 24–29 nt AvIFV read population did not exhibit a “ping-pong” signature. The RT-PCR screens of archival and current (circa 2011–2020) Ae. vexans arabiensis laboratory samples and wild-caught mosquitoes from Barkédji suggest that AvIFV is ubiquitous in these mosquitoes. Further, we screened wild-caught European Ae. vexans samples from Germany, the United Kingdom, Italy, and Sweden, all of which tested negative for AvIFV RNA. This report provides insight into the diversity of commensal Aedes viruses and the host RNAi response towards iflaviruses.

Adaptations to different habitats in sexual and asexual populations of parasitoid wasps: a meta-analysis

BackgroundCoexistence of sexual and asexual populations remains a key question in evolutionary ecology. We address the question how an asexual and a sexual form of the parasitoidVenturia canescenscan coexist in southern Europe. We test the hypothesis that both forms are adapted to different habitats within their area of distribution. Sexuals inhabit natural environments that are highly unpredictable, and where density of wasps and their hosts is low and patchily distributed. Asexuals instead are common in anthropic environments (e.g., grain stores) where host outbreaks offer periods when egg-load is the main constraint on reproductive output.MethodsWe present a meta-analysis of known adaptations to these habitats. Differences in behavior, physiology and life-history traits between sexual and asexual wasps were standardized in term of effect size (Cohen’sdvalue; Cohen, 1988).ResultsSeeking consilience from the differences between multiple traits, we found that sexuals invest more in longevity at the expense of egg-load, are more mobile, and display higher plasticity in response to thermal variability than asexual counterparts.DiscussionThus, each form has consistent multiple adaptations to the ecological circumstances in the contrasting environments.

Insects and incest: sib-mating tolerance in natural populations of a parasitoid wasp

This preprint has been reviewed and recommended by Peer Community In Evolutionary Biology (http://dx.doi.org/10.24072/pci.evolbiol.100047) 1. Sib-mating avoidance is a pervasive behaviour that likely evolves in species subject to inbreeding depression. Laboratory studies have provided elegant demonstrations of sib-mating avoidance, but small-scale bioassays often minimize the costs associated with mate finding and choice, which could lead to spurious findings. 2. We used the hymenopteran parasitoid wasp Venturia canescens as a model organism, because previous laboratory studies revealed that sib-mating led to a 25% decrease in fertile offspring, and that sib-mating was partially avoided. 3. Our study consisted of a mate choice experiment in laboratory cages to determine if kin discrimination occurs in this species. We further performed a field study in which 86 wild-caught males, 155 wild-caught females and their 226 daughters were genotyped at eighteen microsatellite loci. With these data, we reconstructed the genotype of each female ′s mate and estimated the relatedness of each mating pair. 4. Mate choice experiments confirmed that females are capable of discriminating kin. Time to mating depended on the frequency of female encounters with related and unrelated males. Contrary to previously published results, however, no sib-mating avoidance was detected. In the field, the effective rate of sib-mating did not differ from the probability that sibs encounter one other at random, which corroborates the absence of sib-mating avoidance. We also detected a weak but significant male bias in dispersal, which could reduce encounters between sibs. 5. Our results suggest that, despite kin discrimination, V. canescens tolerates sib-mating in the field. The weak male-biased dispersal cannot explain entirely this pattern. This raises the question as to why kin discrimination is maintained in this species. It further calls into question the idea that inbreeding depression occurs in most species with single-locus complementary sex determination.

The recurrent domestication of viruses: major evolutionary transitions in parasitic wasps

Several lineages of endoparasitoid wasps, which develop inside the body of other insects, have domesticated viruses, used as delivery tools of essential virulence factors for the successful development of their progeny. Virus domestications are major evolutionary transitions in highly diverse parasitoid wasps. Much progress has recently been made to characterize the nature of these ancestrally captured endogenous viruses that have evolved within the wasp genomes. Virus domestication from different viral families occurred at least three times in parasitoid wasps. This evolutionary convergence led to different strategies. Polydnaviruses (PDVs) are viral gene transfer agents and virus-like particles of the waspVenturia canescensdeliver proteins. Here, we take the standpoint of parasitoid wasps to review current knowledge on virus domestications by different parasitoid lineages. Then, based on genomic data from parasitoid wasps, PDVs and exogenous viruses, we discuss the different evolutionary steps required to transform viruses into vehicles for the delivery of the virulence molecules that we observe today. Finally, we discuss how endoparasitoid wasps manipulate host physiology and ensure parasitism success, to highlight the possible advantages of viral domestication as compared with other virulence strategies.