The Transfer of Male Cuticular Hydrocarbons Provides a Reliable Cue of the Risk and Intensity of Sperm Competition in Decorated Crickets

Theoretically, males should increase their ejaculate expenditure when the probability of sperm competition occurring (or risk) is high but decrease ejaculate expenditure as the number of competing ejaculates (or intensity) increases. Here we examine whether male decorated crickets (Gryllodes sigillatus) use cuticular hydrocarbons (CHCs) transferred to females by rival males at mating to assess the risk and intensity of sperm competition and adjust their ejaculate accordingly. Unmated females and those perfumed with CHCs extracted from one, three, or five males could be distinguished chemically, providing a reliable cue of the risk and intensity of sperm competition. In agreement with theory, males mating with these females increased sperm number with the risk of sperm competition and decreased sperm number with the intensity of sperm competition. Similarly, as the risk of sperm competition increased, males produced a larger and more attractive spermatophylax (an important non-sperm component of the ejaculate) but these traits did not vary with the intensity of sperm competition. Our results therefore demonstrate that both sperm and non-sperm components of the male ejaculate respond to the risk and intensity of sperm competition in different ways and that CHCs provide males with an important cue to strategically tailor their ejaculate

Macronutrient intake and simulated infection threat independently affect life history traits of male decorated crickets.

Nutritional geometry has advanced our understanding of how macronutrients (e.g., proteins and carbohydrates) influence the expression of life history traits and their corresponding trade-offs. For example, recent work has revealed that reproduction and immune function in male decorated crickets are optimized at very different protein:carbohydrate (P:C) dietary ratios. However, it is unclear how an individual's macronutrient intake interacts with its perceived infection status to determine investment in reproduction or other key life history traits. Here, we employed a fully factorial design in which calling effort and immune function were quantified for male crickets fed either diets previously demonstrated to maximize calling effort (P:C = 1:8) or immune function (P:C = 5:1), and then administered a treatment from a spectrum of increasing infection cue intensity using heat-killed bacteria. Both diet and a simulated infection threat independently influenced the survival, immunity, and reproductive effort of males. If they called, males increased calling effort at the low infection cue dose, consistent with the terminal investment hypothesis, but interpretation of responses at the higher threat levels was hampered by the differential mortality of males across infection cue and diet treatments. A high protein, low carbohydrate diet severely reduced the health, survival, and overall fitness of male crickets. There was, however, no evidence of an interaction between diet and infection cue dose on calling effort, suggesting that the threshold for terminal investment was not contingent on diet as investigated here

Genetic covariance in immune measures and pathogen resistance in decorated crickets is sex and pathogen specific

Insects are important models for studying immunity in an ecological and evolutionary context. Yet, most empirical work on the insect immune system has come from phenotypic studies meaning we have a limited understanding of the genetic architecture of immune function in the sexes. We use nine highly inbred lines to thoroughly examine the genetic relationships between a suite of commonly used immune assays (haemocyte count, implant encapsulation, total phenoloxidase activity, antibacterial zone of inhibition and pathogen clearance) and resistance to infection by three generalist insect pathogens (the gram-negative bacterium Serratia marcescens, the gram-positive bacterium Bacillus cereus and the fungus Metarhizium robertsii) in male and female Gryllodes sigillatus. There were consistent positive genetic correlations between haemocyte count, antibacterial and phenoloxidase activity and resistance to S. marcescens in both sexes, but these relationships were less consistent for resistance to B. cereus and M. robertsii. In addition, the clearance of S. marcescens was genetically correlated with the resistance to all three pathogens in both sexes. Genetic correlations between resistances to the different pathogen species were inconsistent, indicating that resistance to one pathogen does not necessarily mean resistance to another. Finally, while there is ample genetic (co)variance in immune assays and pathogen resistance, these genetic estimates differed across the sexes and many of these measures were not genetically correlated across the sexes, suggesting that these measures could evolve independently in the sexes. Our finding that the genetic architecture of immune function is sex and pathogen specific suggests that the evolution of immune function in male and female G. sigillatus is likely to be complex. Similar quantitative genetic studies that measure a large number of assays and resistance to multiple pathogens in both sexes are needed to ascertain if this complexity extends to other species

Evolution of immune function in response to dietary macronutrients in male and female decorated crickets

Although dietary macronutrients are known to regulate insect immunity, few studies have examined their evolutionary effects. Here, we evaluate this relationship in the cricket Gryllodes sigillatus by maintaining replicate populations on four diets differing in protein (P) to carbohydrate (C) ratio (P- or C-biased) and nutritional content (low- or high-nutrition) for >37 generations. We split each population into two; one maintained on their evolution diet and the other switched to their ancestral diet. We also maintained populations exclusively on the ancestral diet (baseline). After three generations, we measured three immune parameters in males and females from each population. Immunity was higher on P-biased than C-biased diets and on low- versus high-nutrition diets, although the latter was most likely driven by compensatory feeding. These patterns persisted in populations switched to their ancestral diet, indicating genetic divergence. Crickets evolving on C-biased diets had lower immunity than the baseline, whereas their P-biased counterparts had similar or higher immunity than the baseline, indicating that populations evolved with dietary manipulation. Although females exhibited superior immunity for all assays, the sexes showed similar immune changes across diets. Our work highlights the important role that macronutrient intake plays in the evolution of immunity in the sexes

Active and covert infections of cricket Iridovirus and Acheta domesticus Densovirus in reared Gryllodes sigillatus crickets

Interest in developing food, feed, and other useful products from farmed insects has gained remarkable momentum in the past decade. Crickets are an especially popular group of farmed insects due to their nutritional quality, ease of rearing, and utility. However, production of crickets as an emerging commodity has been severely impacted by entomopathogenic infections, about which we know little. Here, we identified and characterized an unknown entomopathogen causing mass mortality in a lab-reared population of Gryllodes sigillatus crickets, a species used as an alternative to the popular Acheta domesticus due to its claimed tolerance to prevalent entomopathogenic viruses. Microdissection of sick and healthy crickets coupled with metagenomics-based identification and real-time qPCR viral quantification indicated high levels of cricket iridovirus (CrIV) in a symptomatic population, and evidence of covert CrIV infections in a healthy population. Our study also identified covert infections of Acheta domesticus densovirus (AdDNV) in both populations of G. sigillatus. These results add to the foundational research needed to better understand the pathology of mass-reared insects and ultimately develop the prevention, mitigation, and intervention strategies needed for economical production of insects as a commodity

Intralocus sexual conflict over optimal nutrient intake and the evolution of sex differences in life span and reproduction

Despite widespread variation in lifespan across species, three clear patterns exist: sex differences in lifespan are ubiquitous, lifespan is commonly traded against reproduction, and nutrition has a major influence on these traits and how they trade-off. One process that potentially unites these patterns is Intralocus Sexual Conflict (IASC) over the optimal intake of nutrients for lifespan and reproduction. If nutrient intake has sex-specific effects on lifespan and reproduction and nutrient choice is genetically linked across the sexes, IASC will occur and may prevent one or both sexes from feeding to their nutritional optima. Here we determine whether this process is operating in the cricket Gryllodes sigillatus. We show that protein and carbohydrate intake have contrasting effects on lifespan and reproduction in the sexes and that there are strong positive intersexual genetic correlations for the intake of these nutrients under dietary choice. This divergence in nutrient effects, combined with the genetic architecture for nutrient choice is predicted to accelerate the evolutionary response of nutrient intake in males but constrain it in females, suggesting they are losing the conflict. Supporting this view, males and females were shown to regulate nutrient intake to a common ratio that was not perfectly optimal for lifespan or reproduction in either sex, especially in females. Our findings show that IASC over the optimal intake of nutrients is likely to be an important process generating sex differences in lifespan and reproduction and may help explain why females age faster and live shorter than males in G. sigillatus.The data from the 3 experiments are presented as separate worksheet in the Hunt et al_data file. In each worksheet, we used the following abbreviations for the variables measured: P = protein, C = carbohydrate, LS= lifespan, DRE = daily reproductive effort, LRE = lifetime reproductive effort. For each variable, if a "Z" is presented in front of the abbreviation it signifies that the variable underwent a Z – transformation prior to analysis. Funding provided by: Royal SocietyCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000288Award Number: UF0762844Funding provided by: Natural Environment Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000270Award Number: NE/G00949X/1Funding provided by: Australian Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000923Award Number: DP180101708Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: IOS-1118160Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: IOS-1654028This work consists of 3 main experiments. In Experiment 1, we examine how the intake of protein and carbohydrates influences lifespan and reproduction in male and female crickets. The data is analysed using response surface analysis and comparisons between the sexes (and across traits within the sexes) are characterised using sequential models and the calculation of angles between vectors and distances between nutritional optima. In Experiment 2, we examine the quantitative genetic basis of protein and carbohydrate intake in males and females using 9 inbred lines of crickets. These crickets were given the choice between two diets differing in the ratio of protein:carbohydrate but with the same caloric content. Genetic estimates were obtained using a Bayesian analysis. In Experiment 3, we examined the regulated intake point of males and females when given the choice between a broader range of diets differing the ratio of protein:carbohydrates and total caloric content. This data was analysed using multivariate analysis of variance (MANOVA) and analysis of covariance (ANCOVA). Data from Experiments 1 and 2 were used to estimate the strength of intralocus sexual conflict over the optimal intake of nutrients for lifespan. Data from Experiments 1 and 3 were used to examine how well male and female crickets regulated their intake of nutrients relative to the optima for lifespan and reproduction

Spring temperatures influence selection on breeding date and the potential for phenological mismatch in a migratory bird

Climate change has affected the seasonal phenology of a variety of taxa, including that of migratory birds and their critical food resources. However, whether climate-induced changes in breeding phenology affect individual fitness, and how these changes might, therefore, influence selection on breeding date remain unresolved. Here, we use a 36-year dataset from a long-term, individual-based study of House Wrens (Troglodytes aedon) to test whether the timing of avian breeding seasons is associated with annual changes in temperature, which have increased to a small but significant extent locally since the onset of the study in 1980. Increasing temperature was associated with an advancement of breeding date in the population, as the onset of breeding within years was closely associated with daily spring temperatures. Warmer springs were also associated with a reduced incubation period, but reduced incubation periods were associated with a prolonged duration of nestling provisioning. Nest productivity, in terms of fledgling production, was not associated with temperature, but wetter springs reduced fledging success. Most years were characterized by selection for earlier breeding, but cool and wet years resulted in stabilizing selection on breeding date. Our results indicate that climate change and increasing spring temperatures can affect suites of life-history traits, including selection on breeding date. Increasing temperatures may favor earlier breeding, but the extent to which the phenology of populations might advance may be constrained by reductions in fitness associated with early breeding during cool, wet years. Variability in climatic conditions will, therefore, shape the extent to which seasonal organisms can respond to changes in their environment.Peer reviewedIntegrative Biolog

No direct or indirect benefits to cryptic female choice in house crickets (Acheta domesticus)

Cryptic female choice in crickets occurs through the premature removal of a male's spermatophore after copulation, which terminates sperm transfer. Although it is known that this behavior can directly influence the paternity of offspring, its effects on female fitness have not been directly assessed. We tested the hypothesis that spermatophore removal by female house crickets (Acheta domesticus) confers fitness benefits on females, by randomly assigning mates to females but permitting some females to freely remove spermatophores after mating (cryptic-choice treatment) while forcing others to accept complete ejaculates (no-choice treatment). Although there was about a two-fold difference in the volume of ejaculate received by females of the two treatments, there were no significant differences in female longevity, reproductive output, or offspring quality, as measured by offspring mass and developmental time. Although differential spermatophore removal by females imposes strong sexual selection on males, the absence of a clear treatment effect suggests that females obtain no direct or indirect genetic benefits through their postcopulatory mating preferences. Copyright 2004.Acheta domesticus; crickets; cryptic female choice; indirect genetic benefits; offspring fitness; spermatophore; sexual selection

Mate choice

Much progress has been made over the last 30 years showing the complexity of female mate choice. There is now a better understanding of why females choose certain males over others, as well as the various mechanisms used to make mate choice decisions. It is also known that female mate choice can exert significant sexual selection on male sexual traits and that there is likely to be a strong genetic basis to mate choice, as well as significant positive genetic covariance between mate choice and the expression of the preferred sexual trait. However, female mate choice does not always drive the evolutionary divergence of male sexual traits in a predictable way, and the role of female mate choice in facilitating reproductive isolation and speciation is likely to be even more complex. More research on mate choice in insects is still needed and this chapter outlines some future directions