Beware the F-test (or, how to compare variances)

This is the author accepted manuscript. The final version is available from Elsevier Masson via the DOI in this record.Biologists commonly compare variances among samples, to test whether underlying populations have equal spread. However, despite warnings from statisticians, incorrect testing is rife. Here we show that one of the most commonly employed of these tests, the F-test, is extremely sensitive to deviations from Normality. The F-test suffers greatly elevated false-positive errors when the underlying distributions are heavy-tailed, a distribution feature which is very hard to detect using standard Normality tests. We highlight and assess a selection of parametric, jackknife and permutation tests, consider their performance in terms of false positives, and power to detect signal when it exists, then show correct methods to compare measures of variation among samples. Based on these assessments, we recommend using Levene’s Test, Box-Anderson Test, Jackknifing or Permutation Tests to compare variances when Normality is in doubt. Levene’s and Box-Anderson tests are the most powerful at small sample sizes, but the Box-Anderson test may not control Type I error for extremely heavy-tailed distributions. As noted previously, do not use F-tests to compare variances.DHod is supported by NERC standard grant NE/L007770/1 and by NERC International Opportunities Fund NE/N006798/1 and DHos by the Leverhulme Trust (RF-2015-001)

The problem of measuring trait-preference correlations without disrupting them

This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this record.A key element at the heart of the Fisher-Lande-Kirkpatrick model of the sexual selection process is the genetic correlation between (male) trait and (female) preference. The strength of this association is critical in determining a population’s evolutionary trajectory, which is why estimating its magnitude is so important. In the Lande model, the trait-preference correlation is solely established and maintained by mate choice, and although it is unclear how exclusively mate choice does this in nature, the experimental designs typically employed to measure trait-preference genetic correlations could be systematically weakening estimates by not allowing free mate-choice (similarly with husbandry practices). The precise impact of the problem is unknown, and possibly unknowable, but simple solutions can be applied to ensure the accuracy of trait-preference correlation estimates is maximized

Longevity and developmental stability in the dung fly Sepsis cynipsea, as affected by the ectoparasitic mite, Pediculoides mesembrinae

This is the final version of the article. Available from [Oxford University Press via the DOI in this record.Fluctuating asymmetry (FA) is a widely employed measure of developmental stability. It has been found to increase with many stressors including parasite infection. Associations between parasites and FA may exist for several reasons in addition to parasites being the direct cause of increased FA. Developmentally stable individuals may have superior immune systems, and be less susceptible to parasite infection, and/or may be less exposed to parasites than developmentally unstable ones. Mites negatively impact host fitness in a number of insects, and if FA is a reflection of general genetic quality, as has been proposed, associations between mite number and FA are predicted. Potential relationships were investigated between an ectoparasitic mite, Pediculoides mesembrinae (Canestrini) (Phthiraptera: Menoponidae) and FA in the common dung fly Sepsis cynipsea (L.) (Diptera: Sepsidae). While it was found that mite infested flies died much faster than flies without mites, indicating that mites indeed stress their hosts, counter to expectations, no associations between mites and FA were found in any analyses. Additionally, FA in mite-infected flies generally did not differ from previously published FA data from uninfected S. cynipsea. Nevertheless, parasitized males tended to be somewhat less asymmetrical than non-parasitized males, but based on our data, it does not appear that mite infestation is generally associated with developmental stability in S. cynipsea.We thank Hansueli Ochs, Bundesamt für Veterinärwesen BVET, Switzerland, for identification of the mites and for information on their behaviour and habits and Marco Demont for kindly supplying mites for the experimental infection experiment. Thanks also to Thomas Gut and Regina Schwilch for help measuring flies and counting mites, John Hunt and numerous other colleagues for discussion, and to the SNF, ESF and NERC for financial support

Peacock flies

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.A quick guide on peacock flies, a species of insect where, unusually, both males and females perform dances apparently to attract mates

Conflict on the sex chromosomes: cause, effect, and complexity

Intralocus sexual conflict and intragenomic conflict both affect sex chromosome evolution and can in extreme cases even cause the complete turnover of sex chromosomes. Additionally, established sex chromosomes often become the focus of heightened conflict. This creates a tangled relationship between sex chromosomes and conflict with respect to cause and effect. To further complicate matters, sexual and intragenomic conflict may exacerbate one another and thereby further fuel sex chromosome change. Different magnitudes and foci of conflict offer potential explanations for lineage-specific variation in sex chromosome evolution and answer long-standing questions as to why some sex chromosomes are remarkably stable, whereas others show rapid rates of evolutionary change.J.E.M. is supported by the European Research Council (grant agreement 260233) and a short-term fellowship from the Wissenschaftskolleg zu Berlin. D.J.H. is supported by the University of Exeter, and N.W. by the University of Exeter and The Royal Society (Wolfson Award)

Genotype-by-environment interactions for female mate choice of male cuticular hydrocarbons in Drosophila simulans

This is the final version of the article. Available from Public Library of Science via the DOI in this record.Recent research has highlighted the potential importance of environmental and genotype-by-environment (G×E) variation in sexual selection, but most studies have focussed on the expression of male sexual traits. Consequently, our understanding of genetic variation for plasticity in female mate choice is extremely poor. In this study we examine the genetics of female mate choice in Drosophila simulans using isolines reared across two post-eclosion temperatures. There was evidence for G×Es in female choosiness and preference, which suggests that the evolution of female mate choice behaviour could differ across environments. However, the ranked order of preferred males was consistent across females and environments, so the same males are favoured by mate choice in spite of G×Es. Our study highlights the importance of taking cross-environment perspectives in order to gain a more comprehensive understanding of the operation of sexual selection.This work was funded by the Association for the Study of Animal Behaviour (DJH), the ESF and NERC (DJH and JH), and a Royal Society Fellowship and Equipment grant (JH). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Complex interactions between sperm viability and female fertility

This is the final version. Available from Nature Research via the DOI in this record.The datasets generated and analysed during the current study have been uploaded on Dryad and are available for download: https://doi.org/10.5061/dryad.n8pk0p2qz.Sperm viability is a major male fitness component, with higher sperm viability associated with enhanced sperm competitiveness. While many studies have focussed on sperm viability from the male fitness standpoint, its impact on female fitness is less clear. Here we used a panel of 32 isogenic Drosophila simulans lines to test for genetic variation in sperm viability (percentage of viable cells). We then tested whether sperm viability affected female fitness by mating females to males from low or high sperm viability genotypes. We found significant variation in sperm viability among genotypes, and consistent with this, sperm viability was highly repeatable within genotypes. Additionally, females mated to high sperm viability males laid more eggs in the first seven hours after mating, and produced more offspring in total. However, the early increase in oviposition did not result in more offspring in the 8 hours following mating, suggesting that mating with high sperm-viability genotypes leads to egg wastage for females shortly after copulation. Although mating with high sperm-viability males resulted in higher female fitness in the long term, high quality ejaculates would result in a short-term female fitness penalty, or at least lower realised fitness, potentially generating sexual conflict over optimal sperm viability.European Union’s Horizon 202

Sexual conflict

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Evolutionary conflict arises from differences in the fitness interests of replicating entities and has its roots in relatedness asymmetries. Every replicator is related to itself by 100%, but in most cases is less related to other replicators, which generates selfishness and conflicts of interest. Since this basic condition is the norm at many levels of biological organization, conflict is rife in biological systems. Sexual conflict, on which we focus here, is the evolutionary conflict that occurs between males and females because of their divergent fitness interests. Sexual conflict occurs despite sexual reproduction requiring some level of cooperation between males and females because the fitness interests of the sexes are nevertheless never perfectly aligned. In other words, males and females may agree on where they are going, but not necessarily on how to get there. Sexual conflict is a vast topic with relevance to many areas of biology and so here we restrict our focus to matters we think are of broadest interest. Hosken et al. introduce sexual conflict

Pre and Post-copulatory Selection Favor Similar Genital Phenotypes in the Male Broad Horned Beetle.

PublishedJournal ArticleSexual selection can operate before and after copulation and the same or different trait(s) can be targeted during these episodes of selection. The direction and form of sexual selection imposed on characters prior to mating has been relatively well described, but the same is not true after copulation. In general, when male-male competition and female choice favor the same traits then there is the expectation of reinforcing selection on male sexual traits that improve competitiveness before and after copulation. However, when male-male competition overrides pre-copulatory choice then the opposite could be true. With respect to studies of selection on genitalia there is good evidence that male genital morphology influences mating and fertilization success. However, whether genital morphology affects reproductive success in more than one context (i.e., mating versus fertilization success) is largely unknown. Here we use multivariate analysis to estimate linear and nonlinear selection on male body size and genital morphology in the flour beetle Gnatocerus cornutus, simulated in a non-competitive (i.e., monogamous) setting. This analysis estimates the form of selection on multiple traits and typically, linear (directional) selection is easiest to detect, while nonlinear selection is more complex and can be stabilizing, disruptive, or correlational. We find that mating generates stabilizing selection on male body size and genitalia, and fertilization causes a blend of directional and stabilizing selection. Differences in the form of selection across these bouts of selection result from a significant alteration of nonlinear selection on body size and a marginally significant difference in nonlinear selection on a component of genital shape. This suggests that both bouts of selection favor similar genital phenotypes, whereas the strong stabilizing selection imposed on male body size during mate acquisition is weak during fertilization.This work was supported by a Leverhulme Early Career Fellowship (ECF/2010/0067) [to C.M.H.] and a NERC and a Leverhulme Research Fellowship (NE/G005303/1) [to D.J.H.]. The Society for Integrative and Comparative Biology provided assistance for attending the symposium at which this research was presented

Operational sex ratio and density predict the potential for sexual selection in the broad-horned beetle

This is the final version. Available from Elsevier Masson via the DOI in this record.Sexual selection can act on all aspects of the phenotype and the opportunity for selection (I s ) sets its maximal strength. Popular approaches to alter I s include the manipulation of the operational sex ratio (OSR) and/or density, with an increase in I s predicted with a male-biased OSR and at higher density. However, debate continues regarding the utility of I s to measure meaningful changes in the strength of selection, as changes in I s with OSR and density may only reflect stochastic processes. Here we tested whether the manipulation of OSR and density alters I s in the broad-horned flour beetle, Gnatocerus cornutus, a species where males are under intense sexual selection and the targets of selection are known. We also recorded the average number of fights and mating behaviour of individuals in our competitive arenas. We found significant main effects of OSR and density on I s , with the opportunity for selection being highest in male-biased high-density treatments. There were also significant effects of OSR and density on the average number of matings, whereas only density influenced the average number of fights. These results suggest that manipulation of OSR and density influence the opportunity for sexual selection in G. cornutus and our observations of fighting and mating behaviour provide a proximate mechanism for the change in I s .NERCAR