Female resistance to sexual coercion can evolve to preserve the indirect benefits of mate choice.

Sexual conflict over the indirect benefits of mate choice may arise when traits in one sex limit the ability of the other sex to freely choose mates but when these coercive traits are not necessarily directly harmful (i.e. forced fertilization per se). Although we might hypothesize that females can evolve resistance in order to retain the indirect, genetic benefits (reflected in offspring attractiveness) of mating with attractive males, up to now it has been difficult to evaluate potential underlying mechanisms. Traditional theoretical approaches do not usually conceptually distinguish between female preference for male mating display and female resistance to forced fertilization, yet sexual conflict over indirect benefits implies the simultaneous action of all of these traits. Here, we present an integrative theoretical framework that draws together concepts from both sexual selection and sexual conflict traditions, allowing for the simultaneous coevolution of displays and preferences, and of coercion and resistance. We demonstrate that it is possible for resistance to coercion to evolve in the absence of direct costs of mating to preserve the indirect benefits of mate choice. We find that resistance traits that improve the efficacy of female mating preference can evolve as long as females are able to attain some indirect benefits of mating with attractive males, even when both attractive and unattractive males can coerce. These results reveal new evolutionary outcomes that were not predicted by prior theories of indirect benefits or sexual conflict.

The influence of developmental environment on courtship song in cactophilic Drosophila.

Closely related species often differ in the signals involved in sexual communication and mate recognition. Determining the factors influencing signal quality (i.e. signal's content and conspicuousness) provides an important insight into the potential pathways by which these interspecific differences evolve. Host specificity could bias the direction of the evolution of sexual communication and the mate recognition system, favouring sensory channels that work best in the different host conditions. In this study, we focus on the cactophilic sibling species Drosophila buzzatii and D. koepferae that have diverged not only in the sensory channel used for sexual communication and mate recognition but also in the cactus species that use as primary hosts. We evaluate the role of the developmental environment in generating courtship song variation using an isofemale line design. Our results show that host environment during development induces changes in the courtship song of D. koepferae males, but not in D. buzzatii males. Moreover, we report for the first time that host rearing environment affects the conspicuousness of courtship song (i.e. song volume). Our results are mainly discussed in the context of the sensory drive hypothesis.

Age-dependent trajectories differ between within-pair and extra-pair paternity success.

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous but genetically polygamous species, this generates the interesting possibility of differential trajectories of within-pair and extra-pair siring success with age in males. We investigate these relationships simultaneously using within-individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within- and extra-pair paternity success increased with age, followed by a senescence-like decline. However, the age trajectories of within- and extra-pair paternity successes differed significantly, with the extra-pair paternity success increasing faster, although not significantly, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within-pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age-dependent pay-offs. Males may partition their reproductive effort between within- and extra-pair matings depending on their current age to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age-specific mortality may explain the variation in rates of extra-pair paternity observed within and between species.

Additive genetic variance in polyandry enables its evolution, but polyandry is unlikely to evolve through sexy or good sperm processes.

Polyandry is widespread despite its costs. The sexually selected sperm hypotheses ('sexy' and 'good' sperm) posit that sperm competition plays a role in the evolution of polyandry. Two poorly studied assumptions of these hypotheses are the presence of additive genetic variance in polyandry and sperm competitiveness. Using a quantitative genetic breeding design in a natural population of Drosophila melanogaster, we first established the potential for polyandry to respond to selection. We then investigated whether polyandry can evolve through sexually selected sperm processes. We measured lifetime polyandry and offensive sperm competitiveness (P2 ) while controlling for sampling variance due to male × male × female interactions. We also measured additive genetic variance in egg-to-adult viability and controlled for its effect on P2 estimates. Female lifetime polyandry showed significant and substantial additive genetic variance and evolvability. In contrast, we found little genetic variance or evolvability in P2 or egg-to-adult viability. Additive genetic variance in polyandry highlights its potential to respond to selection. However, the low levels of genetic variance in sperm competitiveness suggest that the evolution of polyandry may not be driven by sexy sperm or good sperm processes.

Are Indirect Benefits Relevant to Health Care Allocation Decisions?

When allocating scarce healthcare resources, the expected benefits of alternative allocations matter. But, there are different kinds of benefits. Some are direct benefits to the recipient of the resource such as the health improvements of receiving treatment. Others are indirect benefits to third parties such as the economic gains from having a healthier workforce. This article considers whether only the direct benefits of alternative healthcare resource allocations are relevant to allocation decisions, or whether indirect benefits are relevant too. First, we distinguish different conceptions of direct and indirect benefits and argue that only a recipient conception could be morally relevant. We analyze four arguments for thinking that indirect benefits should not count and argue that none is successful in showing that the indirectness of a benefit is a good reason not to count it. We conclude that direct and indirect benefits should be evaluated in the same way.

Genetic diversity does not explain variation in extra-pair paternity in multiple populations of a songbird.

Many songbirds are socially monogamous but genetically polyandrous, mating with individuals outside their pair bonds. Extra-pair paternity (EPP) varies within and across species, but reasons for this variation remain unclear. One possible source of variation is population genetic diversity, which has been shown in interspecific meta-analyses to correlate with EPP but which has limited support from intraspecific tests. Using eight populations of the genetically polyandrous red-winged blackbird (Agelaius phoeniceus), including an island population, we investigated whether population-level differences in genetic diversity led to differences in EPP. We first measured genetic diversity over 10 microsatellite loci and found, as predicted, low genetic diversity in the island population. Additional structure analyses with multilocus genotypes and mtDNA showed the island population to be distinct from the continental populations. However, the island population's EPP rate fell in the middle of the continental populations' distribution, whereas the continental populations themselves showed significant variation in EPP. This result suggests that genetic diversity by itself is not a predictor of EPP rate. We discuss reasons for the departure from previous results, including hypotheses for EPP that do not solely implicate female-driven behaviour.

Sexual conflict over mating in Gnatocerus cornutus? Females prefer lovers not fighters.

Female mate choice and male-male competition are the typical mechanisms of sexual selection. However, these two mechanisms do not always favour the same males. Furthermore, it has recently become clear that female choice can sometimes benefit males that reduce female fitness. So whether male-male competition and female choice favour the same or different males, and whether or not females benefit from mate choice, remain open questions. In the horned beetle, Gnatocerus cornutus, males have enlarged mandibles used to fight rivals, and larger mandibles provide a mating advantage when there is direct male-male competition for mates. However, it is not clear whether females prefer these highly competitive males. Here, we show that female choice targets male courtship rather than mandible size, and these two characters are not phenotypically or genetically correlated. Mating with attractive, highly courting males provided indirect benefits to females but only via the heritability of male attractiveness. However, mating with attractive males avoids the indirect costs to daughters that are generated by mating with competitive males. Our results suggest that male-male competition may constrain female mate choice, possibly reducing female fitness and generating sexual conflict over mating.

Maternal sexual interactions affect offspring survival and ageing.

In many species, females exposed to increased sexual activity experience reductions in longevity. Here, in Drosophila melanogaster, we report an additional effect on females brought about by sexual interactions, an effect that spans generations. We subjected females to a sexual treatment consisting of different levels of sexual activity and then investigated patterns of mortality in their offspring. We found reduced probabilities of survival, increases in the rate of senescence and a pattern of reduced mean longevities, for offspring produced by mothers that experienced higher levels of sexual interaction. We contend that these effects constitute trans-generational costs of sexual conflict--the existence or implications of which have rarely been considered previously. Our results indicate that ongoing exposure by mothers to male precopulatory interactions is itself sufficient to drive trans-generational effects on offspring mortality. Thus, we show that increases in maternal sexual activity can produce trans-generational effects that permeate through to latter life stages in the offspring. This helps to elucidate the complex interplay between sex and ageing and provides new insights into the dynamics of adaptation under sexual selection.

The impact of indirect benefits (reduced travel time, fuel use and emissions) in cost benefit analysis of road safety countermeasures.

OBJECTIVE: In cost benefit analysis of road safety countermeasures, all relevant effects on safety, travel time and environment have a substantial impact during economic appraisal. However, in the most widely used road safety appraisal tools such as SafetyAnalyst and International Road Assessment Programme (iRAP), indirect effects related to travel time and environment are not considered. Most economic appraisal studies conducted for road safety countermeasures consider only the safety benefits and ignore the indirect benefits due to lack of models to evaluate them. This study attempts to document the quantitative impact of indirect benefits during economic appraisal of road safety infrastructure investments particularly from the angle of reduced crashes. METHODS: To this effect, data from 9 European countries and the 20-year infrastructure improvement programme developed for the Netherlands are applied to demonstrate the impact of these indirect benefits through a quantitative study. RESULTS: The results show that indirect benefits increase the value of benefits by 7%, which improves the cost effectiveness of countermeasures. Consequently, the number of countermeasures selected for implementation are increased due to addition of these benefits. Travel time benefits constitute the largest share of indirect benefits with a contribution of 6% to the overall benefits due to countermeasure implementation. CONCLUSION: In conclusion, indirect benefits have a substantial impact on the computation of benefits and countermeasure selection process. In order to present improved business cases for road safety infrastructure investments, there is need to include these benefits during economic appraisal process. Travel time benefits have the highest portion of all indirect benefits compared to vehicle operating costs (VOCs) and emission benefits. The study recommends conducting more research related to travel time benefits due to countermeasure implementation.

Balancing the benefits of vaccination: An envy-free strategy.

The Covid-19 pandemic revealed the difficulties of vaccinating a population under the circumstances marked by urgency and limited availability of doses while balancing benefits associated with distinct guidelines satisfying specific ethical criteria. We offer a vaccination strategy that may be useful in this regard. It relies on the mathematical concept of envy-freeness. We consider finding balance by allocating the resource among individuals that seem heterogeneous concerning the direct and indirect benefits of vaccination, depending on age. The proposed strategy adapts a constructive approach in the literature based on Sperner's Lemma to point out an approximate division of doses guaranteeing that both benefits are optimized each time a batch becomes available. Applications using data about population age distributions from diverse countries suggest that, among other features, this strategy maintains the desired balance, throughout the entire vaccination period. We discuss complementary aspects of the method in the context of epidemiological models of age-stratified Susceptible - Infected - Recovered (SIR) type.

Condition-dependent male copulatory courtship and its benefits for females.

Postcopulatory sexual selection has shaped the ornaments used during copulatory courtship. However, we know relatively little about whether these courtship ornaments are costly to produce or whether they provide indirect benefits to females. We used the mealworm beetle, Tenebrio molitor, to explore this. We challenged males using an entomopathogenic fungus and compared their courtship (frequency of leg and antennal contacts to the female), copulation duration, number of eggs laid, and hatching rate against control males. Infected males copulated for longer yet they reduced their leg and antennal contacts compared to control males. However, there was no obvious relation between infection, copulation duration, and courtship with egg production and hatching success. In general, our results indicate that the ornaments used during postcopulatory courtship are condition-dependent. Moreover, such condition dependence cannot be linked to male fitness.

It's Not about Him: Mismeasuring 'Good Genes' in Sexual Selection.

What explains preferences for elaborate ornamentation in animals? The default answer remains that the prettiest males have the best genes. If mating signals predict good genes, mating preferences evolve because attractive mates yield additive genetic benefits through offspring viability, thereby maximizing chooser fitness. Across disciplines, studies claim 'good genes' without measuring mating preferences, measuring offspring viability, distinguishing between additive and nonadditive benefits, or controlling for manipulation of chooser investment. Crucially, studies continue to assert benefits to choosers purely based on signal costs to signalers. A focus on fitness outcomes for choosers suggests that 'good genes' are insufficient to explain the evolution of mate choice or of sexual ornamentation.

Communicating Benefits from Vaccines Beyond Preventing Infectious Diseases.

Despite immunisation being one of the greatest medical success stories of the twentieth century, there is a growing lack of confidence in some vaccines. Improving communication about the direct benefits of vaccination as well as its benefits beyond preventing infectious diseases may help regain this lost confidence. A conference was organised at the Fondation Merieux in France to discuss what benefits could be communicated and how innovative digital initiatives can used for communication. During this meeting, a wide range of indirect benefits of vaccination were discussed. For example, influenza vaccination can reduce hospitalisations and deaths in older persons with diabetes by 45% and 38%, respectively, but the link between influenza and complications from underlying chronic non-communicable diseases such as diabetes is frequently underestimated. Vaccination can reduce antimicrobial resistance (AMR), which is growing, by reducing the incidence of infectious disease (though direct and indirect or herd protection), by reducing the number of circulating AMR strains, and by reducing the need for antimicrobial use. Disease morbidity and treatment costs in the elderly population are likely to rise substantially, with the ageing global population. Healthy ageing and life-course vaccination approaches can reduce the burden of vaccine-preventable diseases, such as seasonal influenza and pneumococcal diseases, which place a significant burden on individuals and society, while improving quality of life. Novel disease surveillance systems based on information from Internet search engines, mobile phone apps, social media, cloud-based electronic health records, and crowd-sourced systems, contribute to improved awareness of disease burden. Examples of the role of new techniques and tools to process data generated by multiple sources, such as artificial intelligence, to support vaccination programmes, such as influenza and dengue, were discussed. The conference participants agreed that continual efforts are needed from all stakeholders to ensure effective, transparent communication of the full benefits and risks of vaccination.

Drosophila Sexual Attractiveness in Older Males Is Mediated by Their Microbiota.

Age is well known to be a basis for female preference of males. However, the mechanisms underlying age-based choices are not well understood, with several competing theories and little consensus. The idea that the microbiota can affect host mate choice is gaining traction, and in this study we examine whether the male microbiota influences female preference for older individuals in the fruit fly Drosophila pseudoobscura. We find that an intact microbiota is a key component of attractiveness in older males. However, we found no evidence that this decrease in older male attractiveness was simply due to impaired microbiota generally reducing male quality. Instead, we suggest that the microbiota underlies an honest signal used by females to assess male age, and that impaired microbiota disrupt this signal. This suggests that age-based preferences may break down in environments where the microbiota is impaired, for example when individuals are exposed to naturally occurring antibiotics, extreme temperatures, or in animals reared in laboratories on antibiotic supplemented diet.

Genetic variation in male attractiveness: It is time to see the forest for the trees.

Female choice based on multiple male traits, rather than on any single one, has been reported in many species and may well be a rule rather than an exception. However, the implications this has for selection acting on choosiness itself remain underappreciated. We argue that this constitutes one of the important impediments to our understanding of the evolution of mate choice. We discuss this issue primarily in the context of the Fisherian model of sexual selection. We review theory and empirical data, showing how the crucial parameter of the model-genetic variation in male attractiveness-can be estimated when attractiveness is a function of multiple traits. Based on the reviewed theory, we show how relying on individual male traits, instead of overall attractiveness, can produce biased estimates of Fisherian benefits of female choice. This bias can be substantial, especially when many traits contribute to male attractiveness. We discuss a number of methodological issues that, we hope, will stimulate future studies and help resolving the long-standing mystery of mate choice.

No evidence for female discrimination against male house mice carrying a selfish genetic element.

Meiotic drivers distort transmission to the next generation in their favor, with detrimental effects on the fitness of their homologues and the rest of the genome. Male carriers of meiotic drivers commonly inflict costs on their mates through genetic incompatibility, reduced fecundity, or biased brood sex ratios. Given these costs, evidence for female discrimination against male carriers is surprisingly rare. One of few examples is the t haplotype in house mice, a meiotic driver that shows strong transmission distortion in males and is typically homozygote lethal. As a consequence, mating between 2 t heterozygous (+/t) mice leads to high embryo mortality. Previous experiments showing that +/t females avoid this incompatibility cost by preferring +/+ versus +/t males have inferred preference based on olfactory cues or brief social interactions. Evidence from mating contexts in laboratory settings and semi-natural populations has been inconclusive. Here, we investigated female choice from a large number of no-choice mating trials. We found no evidence for discrimination against +/t males based on mating, remating, and copulatory behavior. Further, we found no evidence for avoidance of incompatibility through selective interactions between gametes. The likelihood of mating showed significant effects of female weight and genotype, suggesting that our test paradigm enabled females to exhibit mate choice. We discuss the strengths and limitations of our approach. By explicitly considering selection at both the individual and gene level, we argue why precopulatory female discrimination by +/t females may be less evolutionarily stable than discrimination by all females based on postcopulatory mechanisms.

Benefits of extra-pair mating may depend on environmental conditions-an experimental study in the blue tit (Cyanistes caeruleus).

Extra-pair mating constitutes a relatively common reproductive strategy in many socially monogamous bird species. This strategy may considerably improve reproductive success of males, but female benefits from extra-pair matings still remain unclear and empirical evidence is scarce. This may be because genetic benefits of extra-pair mating are not always revealed. It is possible that they are shown only in unfavourable environmental conditions and hence problems arise with detecting differences between within- and extra-pair offspring whose performance is measured under favourable conditions. In order to test this prediction, we manipulated environmental conditions by altering brood sizes of blue tits and compared phenotypic characteristics of within- and extra-pair offspring in mixed-paternity broods. We found that extra-pair young exhibited a higher response to phytohemagglutinin in comparison to within-pair young, but this was only observed among nestlings from experimentally enlarged broods. These results indicate that genetic benefits may interact with the environment, and thus benefits of extra-pair mating are likely to become visible only when conditions are relatively unfavourable.