The complex interplay between macronutrient intake, cuticular hydrocarbon expression and mating success in male decorated crickets.

The condition dependence of male sexual traits plays a central role in sexual selection theory. Relatively little, however, is known about the condition dependence of chemical signals used in mate choice and their subsequent effects on male mating success. Furthermore, few studies have isolated the specific nutrients responsible for condition-dependent variation in male sexual traits. Here, we used nutritional geometry to determine the effect of protein (P) and carbohydrate (C) intake on male cuticular hydrocarbon (CHC) expression and mating success in male decorated crickets (Gryllodes sigillatus). We show that both traits are maximized at a moderate-to-high intake of nutrients in a P:C ratio of 1 : 1.5. We also show that female precopulatory mate choice exerts a complex pattern of linear and quadratic sexual selection on this condition-dependent variation in male CHC expression. Structural equation modelling revealed that although the effect of nutrient intake on mating success is mediated through condition-dependent CHC expression, it is not exclusively so, suggesting that other traits must also play an important role. Collectively, our results suggest that the complex interplay between nutrient intake, CHC expression and mating success plays an important role in the operation of sexual selection in G. sigillatus.

Macronutrient intake regulates sexual conflict in decorated crickets.

Sexual conflict results in a diversity of sex-specific adaptations, including chemical additions to ejaculates. Male decorated crickets (Gryllodes sigillatus) produce a gelatinous nuptial gift (the spermatophylax) that varies in size and free amino acid composition, which influences a female's willingness to fully consume this gift. Complete consumption of this gift maximizes sperm transfer through increased retention of the sperm-containing ampulla, but hinders post-copulatory mate choice. Here, we examine the effects of protein (P) and carbohydrate (C) intake on the weight and amino acid composition of the spermatophylax that describes its gustatory appeal to the female, as well as the ability of this gift to regulate sexual conflict via ampulla attachment time. Nutrient intake had similar effects on the expression of these traits with each maximized at a high intake of nutrients with a P : C ratio of 1 : 1.3. Under dietary choice, males actively regulated their nutrient intake but this regulation did not coincide with the peak of the nutritional landscape for any trait. Our results therefore demonstrate that a balanced intake of nutrients is central to regulating sexual conflict in G. sigillatus, but males are constrained from reaching the optima needed to bias the outcome of this conflict in their favour.

Female choice for male cuticular hydrocarbon profile in decorated crickets is not based on similarity to their own profile.

Indirect genetic benefits derived from female mate choice comprise additive (good genes) and nonadditive genetic benefits (genetic compatibility). Although good genes can be revealed by condition-dependent display traits, the mechanism by which compatibility alleles are detected is unclear because evaluation of the genetic similarity of a prospective mate requires the female to assess the genotype of the male and compare it to her own. Cuticular hydrocarbons (CHCs), lipids coating the exoskeleton of most insects, influence female mate choice in a number of species and offer a way for females to assess genetic similarity of prospective mates. Here, we determine whether female mate choice in decorated crickets is based on male CHCs and whether it is influenced by females' own CHC profiles. We used multivariate selection analysis to estimate the strength and form of selection acting on male CHCs through female mate choice, and employed different measures of multivariate dissimilarity to determine whether a female's preference for male CHCs is based on similarity to her own CHC profile. Female mating preferences were significantly influenced by CHC profiles of males. Male CHC attractiveness was not, however, contingent on the CHC profile of the choosing female, as certain male CHC phenotypes were equally attractive to most females, evidenced by significant linear and stabilizing selection gradients. These results suggest that additive genetic benefits, rather than nonadditive genetic benefits, accrue to female mate choice, in support of earlier work showing that CHC expression of males, but not females, is condition dependent.

Terminal investment in the gustatory appeal of nuptial food gifts in crickets.

Investment in current versus future reproduction represents a prominent trade-off in life-history theory and is likely dependent on an individual's life expectancy. The terminal investment hypothesis posits that a reduction in residual reproductive value (i.e. potential for future offspring) will result in increased investment in current reproduction. We tested the hypothesis that male decorated crickets (Gryllodes sigillatus), when cued to their impending mortality, should increase their reproductive effort by altering the composition of their nuptial food gifts (i.e. spermatophylaxes) to increase their gustatory appeal to females. Using a repeated-measures design, we analysed the amino acid composition of spermatophylaxes derived from males both before and after injection of either a saline control or a solution of heat-killed bacteria. The latter, although nonpathogenic, represents an immune challenge that may signal an impending survival threat. One principal component explaining amino acid variation in spermatophylaxes, characterized by a high loading to histidine, was significantly lower in immune-challenged versus control males. The relevance of this difference for the gustatory appeal of gifts to females was assessed by mapping spermatophylax composition onto a fitness surface derived in an earlier study identifying the amino acid composition of spermatophylaxes preferred by females. We found that immune-challenged males maintained the level of attractiveness of their gifts post-treatment, whereas control males produced significantly less attractive gifts post-injection. These results are consistent with the hypothesis that cues of a survival-threatening infection stimulate terminal investment in male decorated crickets with respect to the gustatory appeal of their nuptial food gifts.

Environmental heterogeneity, multivariate sexual selection and genetic constraints on cuticular hydrocarbons in Drosophila simulans.

Sexual selection is responsible for the evolution of many elaborate traits, but sexual trait evolution could be influenced by opposing natural selection as well as genetic constraints. As such, the evolution of sexual traits could depend heavily on the environment if trait expression and attractiveness vary between environments. Here, male Drosophila simulans were reared across a range of diets and temperatures, and we examined differences between these environments in terms of (i) the expression of male cuticular hydrocarbons (CHCs) and (ii) which male CHC profiles were most attractive to females. Temperature had a strong effect on male CHC expression, whereas the effect of diet was weaker. Male CHCs were subject to complex patterns of directional, quadratic and correlational sexual selection, and we found differences between environments in the combination of male CHCs that were most attractive to females, with clearer differences between diets than between temperatures. We also show that genetic covariance between environments is likely to cause a constraint on independent CHC evolution between environments. Our results demonstrate that even across the narrow range of environmental variation studied here, predicting the outcome of sexual selection can be extremely complicated, suggesting that studies ignoring multiple traits or environments may provide an over-simplified view of the evolution of sexual traits.

Genotype-by-environment interactions for cuticular hydrocarbon expression in Drosophila simulans.

Genotype-by-environment interactions (G × Es) describe genetic variation for phenotypic plasticity. Recent interest in the role of these interactions in sexual selection has identified G × Es across a diverse range of species and sexual traits. Additionally, theoretical work predicts that G × Es in sexual traits could help to maintain genetic variation, but could also disrupt the reliability of these traits as signals of mate quality. However, empirical tests of these theoretical predictions are scarce. We reared iso-female lines of Drosophila simulans across two axes of environmental variation (diet and temperature) in a fully factorial design and tested for G × Es in the expression of cuticular hydrocarbons (CHCs), a multivariate sexual trait in this species. We find sex-specific environmental, genetic and G × E effects on CHC expression, with G × Es for diet in both male and female CHC profile and a G × E for temperature in females. We also find some evidence for ecological crossover in these G × Es, and by quantifying variance components, genetic correlations and heritabilities, we show the potential for these G × Es to help maintain genetic variation and cause sexual signal unreliability in D. simulans CHC profiles.

Digital fundus imaging of subretinal neovascularization.

Digital fundus imaging was used for fluorescein angiography in patients with subretinal neovascularization. After laser treatment, digital red-free photographs were obtained and compared against pretreatment angiogram frames to determine the margins of treatment. This technique allowed instant review of images and confirmation of complete laser treatment of the lesions. Of 15 eyes treated and followed for at least one year, there were two eyes with early recurrences (13%). A total of five eyes had recurrences during the follow-up period (33%). Digital imaging is a useful tool for treating subretinal neovascularization.

Digital fundus imaging: a comparison with photographic techniques.

Fluorescein angiographic images from digital and photographic systems were obtained simultaneously from consecutive patients and examined in a side-by-side manner for evaluation of graininess, contrast, focus, and overall image quality. Digital fundus images showed superior contrast and overall image quality compared with photographic images obtained in this manner. These images were rated as somewhat grainier than photographic images. Patients had fewer complications undergoing digital fluorescein angiography versus photographic fluorescein angiography. Digital fundus imaging is a legitimate alternative to photographic imaging and offers the potential advantage of fewer complications compared with photographic techniques.

Pneumatic retinopexy: experience in southwest Oklahoma.

Pneumatic retinopexy is a procedure which can be utilized as an alternative to scleral buckling to repair retinal detachment. It offers the advantages of being less invasive and is easily performed under local anesthesia on an outpatient basis. We enjoyed an initial success rate of reattachment in five of six eyes with this procedure. One case experienced late redetachment, and a subsequent case experienced early redetachment from development of new retinal breaks. Six cases were successfully reattached in one or two procedures, and all cases were reattached in three procedures. All patients experienced stable or improved vision with pneumatic retinopexy.

The effect of daily wear time on contact lens complications.

Complications of contact lens wear include limbal neovascularization, corneal edema, keratitis, and spectacle blur. The incidence of complications was studied in a population of new clinic patients previously fitted for contact lenses. Patients whose daily wear time was greater than 12 hours had a significantly greater incidence of complications. Factors that are presumed to contribute to this difference include hypoxic effects, mechanical trauma, and hygiene. Patient education is stressed for the treatment and prevention of contact lens related complications.