Nooria Al-Wathiqui

Genotype × environment interaction is weaker in genitalia than in mating signals and body traits in Enchenopa treehoppers (Hemiptera: Membracidae)

Theory predicts that selection acting across environments should erode genetic variation in reaction norms; i.e., selection should weaken genotypexa0×xa0environment interaction (Gxa0×xa0E). In spite of this expectation, Gxa0×xa0E is often detected in fitness-related traits. It thus appears that Gxa0×xa0E is at least sometimes sustained under selection, a possibility that highlights the need for theory that can account for variation in the presence and strength of Gxa0×xa0E. We tested the hypothesis that trait differences in developmental architecture contribute to variation in the expression of Gxa0×xa0E. Specifically, we assessed the influence of canalization (robustness to genetic or environmental perturbations) and condition-dependence (association between trait expression and prior resource acquisition or vital cellular processes). We compared Gxa0×xa0E across three trait types expected to differ in canalization and condition-dependence: mating signals, body size-related traits, and genitalia. Because genitalia are expected to show the least condition-dependence and the most canalization, they should express weaker Gxa0×xa0E than the other trait types. Our study species was a member of the Enchenopa binotata species complex of treehoppers. We found significant Gxa0×xa0E in most traits; Gxa0×xa0E was strongest in signals and body traits, and weakest in genitalia. These results support the hypothesis that trait differences in developmental architecture (canalization and condition-dependence) contribute to variation in the expression of Gxa0×xa0E. We discuss implications for the dynamics of sexual selection on different trait types.

Allometric Slopes Not Underestimated by Ordinary Least Squares Regression: A Case Study with Enchenopa Treehoppers (Hemiptera: Membracidae)

ABSTRACT The scaling of traits on body size—allometry—is a subject of broad interest in ecology and evolutionary biology, and one in which studies on insects and spiders have featured prominently. Allometric relationships are described with the slope of regressions of trait size (y) on body size (x). A common method—ordinary least squares (OLS) regression—is often expected to underestimate allometric slopes. The reason for this expectation is that OLS regression assumes that x is determined without error, which is expected to bias slope estimates unless the error in y is much larger than the error in x. However, alternative methods such as reduced major axis (RMA) regression suffer from problems of interpretability. Here, we test the hypothesis that OLS regression will underestimate allometric slopes. We used a natural experiment that arose in the course of training to measure insect genitalia, wherein measurement error for genitalia was larger before training than after training, and also differed by a very large amount between traits. Comparing allometric slopes estimated before and after training, and allometric slopes of traits having very different measurement errors, suggests that OLS regression is robust to measurement error in x and that it does not underestimate allometric slopes.

Using RNA sequencing to characterize female reproductive genes between Z and E Strains of European Corn Borer moth (Ostrinia nubilalis)

BackgroundReproductive proteins often evolve rapidly and are thought to be subject to strong sexual selection, and thus may play a key role in reproductive isolation and species divergence. However, our knowledge of reproductive proteins has been largely limited to males and model organisms with sequenced genomes. With advances in sequencing technology, Lepidoptera are emerging models for studies of sexual selection and speciation. By profiling the transcriptomes of the bursa copulatrix and bursal gland from females of two incipient species of moth, we characterize reproductive genes expressed in the primary reproductive tissues of female Lepidoptera and identify candidate genes contributing to a one-way gametic incompatibility between Z and E strains of the European corn borer (Ostrinia nubilalis).ResultsUsing RNA sequencing we identified transcripts from ~37,000 and ~36,000 loci that were expressed in the bursa copulatrix or the bursal gland respectively. Of bursa copulatrix genes, 8% were significantly differentially expressed compared to the female thorax, and those that were up-regulated or specific to the bursa copulatrix showed functional biases toward muscle activity and/or organization. In the bursal gland, 9% of genes were differentially expressed compared to the thorax, with many showing reproduction or gamete production functions. Of up-regulated bursal gland genes, 46% contained a transmembrane region and 16% possessed secretion signal peptides. Divergently expressed genes in the bursa copulatrix were exclusively biased toward protease-like functions and 51 proteases or protease inhibitors were divergently expressed overall.ConclusionsThis is the first comprehensive characterization of female reproductive genes in any lepidopteran system. The transcriptome of the bursa copulatrix supports its role as a muscular sac that is the primary site for disruption of the male ejaculate. We find that the bursal gland acts as a reproductive secretory body that might also interact with male ejaculate. In addition, differential expression of proteases between strains supports a potential role for these tissues in contributing to reproductive isolation. Our study provides new insight into how male ejaculate is processed by female Lepidoptera, and paves the way for future work on interactions between post-mating sexual selection and speciation.

Quick guideNuptial gifts

What’s in it for the females? Male spermatophores often provide limiting resources, like amino acids or sodium, that enhance a female’s lifetime egg production and longevity. Some spermatophores also contain defensive chemicals that protect females and their eggs against predators. Gifts that females ingest, such as a male’s spermatophylax, salivary mass or scavenged prey, have also been shown to provide a net benefit to females in terms of lifetime fitness.

Molecular characterization of firefly nuptial gifts: a multi-omics approach sheds light on postcopulatory sexual selection.

Postcopulatory sexual selection is recognized as a key driver of reproductive trait evolution, including the machinery required to produce endogenous nuptial gifts. Despite the importance of such gifts, the molecular composition of the non-gametic components of male ejaculates and their interactions with female reproductive tracts remain poorly understood. During mating, male Photinus fireflies transfer to females a spermatophore gift manufactured by multiple reproductive glands. Here we combined transcriptomics of both male and female reproductive glands with proteomics and metabolomics to better understand the synthesis, composition and fate of the spermatophore in the common Eastern firefly, Photinus pyralis. Our transcriptome of male glands revealed up-regulation of proteases that may enhance male fertilization success and activate female immune response. Using bottom-up proteomics we identified 208 functionally annotated proteins that males transfer to the female in their spermatophore. Targeted metabolomic analysis also provided the first evidence that Photinus nuptial gifts contain lucibufagin, a firefly defensive toxin. The reproductive tracts of female fireflies showed increased gene expression for several proteases that may be involved in egg production. This study offers new insights into the molecular composition of male spermatophores, and extends our understanding of how nuptial gifts may mediate postcopulatory interactions between the sexes.

Linking larval nutrition to adult reproductive traits in the European corn borer Ostrinia nubilalis

Throughout an organisms lifetime, resources are strategically allocated to many different functions, including reproduction. Reproduction can be costly for both sexes; females produce nutrient‐rich eggs, whereas males of many species produce large and complex ejaculates. In capital breeding insects, nutrients are mainly acquired during the larval period, yet allocation decisions impact the reproductive fitness of adults. The present study examines the effect of larval dietary nitrogen on both male and female reproductive traits in the European corn borer moth Ostrinia nubilalis Hübner, whose adults do not feed and whose males transfer a large, nitrogen‐rich spermatophore. One day post‐eclosion, O. nubilalis adults reared on one of three different diets (3.0%, 1.6%, or 1.1% nitrogen) are mated and two experiments are undertaken: one to measure nitrogen and carbon content of male ejaculates, and the other to determine female fecundity and fertility. Although male larval diet does not alter the percentage nitrogen content of adult somatic tissue, males reared on the higher nitrogen diet (3.0%) produce spermatophores with increased nitrogen relative to somatic nitrogen. Furthermore, females raised on the 3.0% nitrogen diet receive spermatophores with lower carbonu2009:u2009nitrogen ratios and thus more nitrogen. Overall, females lay more eggs as their larval dietary nitrogen increases, although they lay fewer eggs when their mates are raised on the higher (3.0%) nitrogen diet. This suggests that O. nubilalis females may use male‐derived nitrogen not to supplement egg production, but rather for somatic maintenance. Overall, the present study furthers our understanding of how larval diet can affect adult fitness in Lepidoptera.

Male Enchenopa treehoppers (Hemiptera: Membracidae) vary mate-searching behavior but not signaling behavior in response to spider silk

Finding and attracting mates can impose costs on males in terms of increased encounters with, and attraction of, predators. To decrease the likelihood of predation, males may modify mate-acquisition efforts in two main ways: they may reduce mate-searching efforts or they may reduce mate-attraction efforts. The specific behavior that males change in the presence of predator cues should depend upon the nature of risk imposed by the type of predator present in the environment. For example, sit-and-wait predators impose greater costs to males moving in search of mates. Here, we test whether cues of the presence of a sit-and-wait predator lead to a reduction in mate-searching but not mate-acquisition behavior. We used a member of the Enchenopa binotata complex of treehoppers—a clade ofxa0vibrationally communicating insects in which males fly in search of mates and produce mate-attraction signals when they land on plant stems. We tested for changes in mate-searching and signaling behaviors when silk from a web-building spider was present or absent. We found that males delayed flight when spider silk was present but only if they were actively searching for mates. These results suggest that males have been selected to reduce predation risk by adjusting how they move about their environment according to the cues of sit-and-wait predators.

Postmating transcriptional changes in the female reproductive tract of the European corn borer moth

Mating triggers a cascade of physiological and behavioural responses in females that persist after copulation. In insects, seminal fluid proteins contained within male ejaculates are known to initiate some responses, but our understanding of how females mediate these reactions remains limited. Few studies have examined postmating transcriptional changes within ejaculate‐receiving organs within females or how these changes might depend on the identity of the male. Furthermore, whereas males of many insects transfer packaged ejaculates, transcriptional dynamics have mainly been examined in dipterans, in which males transfer a free ejaculate. To identify genes that may be important in mediating female physiological responses in a spermatophore‐producing species, we sequenced the transcriptomes of the ejaculate‐receiving organs and examined postmating gene expression within and between pheromone strains of the European corn borer (ECB) moth, Ostrinia nubilalis. After within‐strain mating, significant differential expression of 978 transcripts occurred in the female bursa or its associated bursal gland, including peptidases, transmembrane transporters, and hormone processing genes; such genes may potentially play a role in postmating male–female interactions. We also identified 14 transcripts from the bursal gland that were differentially expressed after females mated with cross‐strain males, representing candidates for previously observed postmating reproductive isolation between ECB strains.

Molecular dissection of nuptial gifts in divergent strains of O strinia moths: Nuptial gifts in O strinia moths

Seminal fluid proteins (SFPs) produced in the male accessory glands and ejaculatory duct are subject to strong sexual selection, often evolve rapidly and therefore may play a key role in reproductive isolation and species formation. However, little is known about reproductive proteins for species in which males transfer ejaculate to females using a spermatophore package. By combining RNA sequencing and proteomics, we characterize putative SFPs, identify proteins transferred in the male spermatophore and identify candidate genes contributing to a one‐way gametic incompatibility between Z and E strains of the European corn borer moth Ostrinia nubilalis. We find that the accessory glands and ejaculatory duct secrete over 200 highly expressed gene products, including peptidases, peptidase regulators and odourant‐binding proteins. A comparison between Ostrinia strains reveals that accessory gland and ejaculatory duct sequences with hormone degradation and peptidase activity are among the most extremely differentially expressed. However, most spermatophore peptides lack reproductive tissue bias or canonical secretory signal motifs and aproximately one‐quarter may be produced elsewhere before being sequestered by the male accessory glands during spermatophore production. In addition, most potential gene candidates for postmating reproductive isolation do not meet standard criteria for predicted SFPs and almost three‐quarters are novel, suggesting that both postmating sexual interactions and gametic isolation likely involve molecular products beyond traditionally recognized SFPs.