Genetic study of the production of sexually dimorphic cuticular hydrocarbons in relation with the sex-determination gene transformer in Drosophila melanogaster

In Drosophila melanogaster, the main cuticular hydrocarbons (HCs) are some of the pheromones involved in mate discrimination. These are sexually dimorphic in both their occurrence and their effects. The production of predominant HCs has been measured in male and female progeny of 220 PGa14 lines mated with the feminising UAS-transformer transgenic strain. In 45 lines, XY flies were substantially or totally feminised for their HCs. Surprisingly, XX flies of 14 strains were partially masculinised. Several of the PGa14 enhancer-trap variants screened here seem to interact with sex determination mechanisms involved in the control of sexually dimorphic characters. We also found a good relationship between the degree of HC transformation and GAL4 expression in oenocytes. The fat body was also involved in the switch of sexually dimorphic cuticular hydrocarbons but its effect was different between the sexes.     

Intracerebral Sex Differences in the Vasotocin System in Birds: Possible Implication in Behavioral and Autonomic Functions

The brain vasotocinergic system demonstrates clear sexual dimorphism in birds investigated so far. This paper examines the evidence obtained in studies on gallinaceous (domestic fowl, Japanese quail) and passerine (canary, junco, zebra finch) birds. Vasotocin (VT)-immunoreactive parvocellular neurons are present in the nucleus of stria terminalis of males, but they are less abundant or absent in the corresponding structure of females. A similar difference has been observed in the dorsal paraventricular area of domestic fowl. Sex-related differences in VT-gene expression have been confirmed byin situhybridization. Moreover, overall brain content of VT mRNA in cockerels is about twice that of hens, suggesting that VT synthesis may also be sexually dimorphic in other brain areas where morphological sex differences have not yet been revealed. The vasotocinergic system in birds is implicated in body fluid homeostasis, and during ontogeny it starts to respond to osmotic challenges in a sexually dimorphic way. Photoperiod, aging, or castration—all associated with changes in circulating testosterone levels—affect sexually dimorphic VT pathways and cell clusters. Sexually dimorphic vasotocinergic circuits are distributed in regions containing steroid-concentrating cells and are closely intermingled with aromatase-containing neurons that may mediate activational effects of gonadal steroids on this peptidergic system. However, it remains undetermined whether the observed neuroanatomical sex differences are related to sexually dimorphic autonomic and behavioral effects induced by VT. Most likely, VT in birds has a modulatory rather than a specific regulatory function in control of male sexual behavior and vocalization.     

Hormonal control of behaviour: steroid action in the brain

There have recently been significant advances in our understanding of the cellular action of steroids on brain mechanisms of behaviour. Brain cells contain steroid metabolizing enzymes whose activity is modified by environmental stimuli. Steroids have rapid effects on neurotransmitter receptors via cell membranes and modify the distribution of neuropeptide receptors in areas controlling behaviour. It has been known for some time that oestrogens have an effect on brain structure that can be related to behaviour in the sexually dimorphic avian song system. Recent work suggests that oestrogen may have a similar effect on the developing sexually dimorphic nuclei of the mammalian brain.     

Latitudinal gradients in sexual dimorphism: Alternative hypotheses for variation in male traits

Biological patterns across latitudinal gradients elucidate a number of striking natural clines from which numerous processes can be further explored. The trade‐off between reproduction and somatic maintenance and growth represents a suite of life‐history traits with variable energy allocation and potential latitudinal patterns. Specifically, male sexually dimorphic traits in female choice systems represent one such reproductive investment constrained by resource acquisition and subsequent allocation. Latitudinal variation in sexual dimorphism has been suggested although the relationship between dimorphic traits and latitude are conflicting. Here, we test alternative hypotheses regarding this pattern using two broadly distributed vertebrates exhibiting sexually dimorphic traits. We hypothesized that the exaggeration of dimorphic traits correlates with latitude, with males having exaggerated sexually dimorphic traits at either higher or lower latitudes. Results indicate that male sexually dimorphic traits are exaggerated at lower latitudes while relative gonopodium size in Poecilia latipinna was larger at higher latitudes. This pattern may be a result of lower latitude populations experiencing greater population densities and longer access to resources that could manifest in females more intensively selecting for higher quality males in lower latitudes. Experimental work should address this pattern and investigate mechanistic processes.     

The role and mechanism of growth hormone in the regulation of sexually dimorphic P450 enzymes in rat liver

The determination of sexually dimorphic hepatic steroid metabolism in rat liver has been shown to involve growth hormone. However, the mechanisms by which growth hormone controls the cytochrome P450 enzymes responsible for this dimorphic steroid metabolism is largely unknown. In this review we discuss different levels of growth hormone signal transduction, including receptor binding, signal transduction and activation of target genes by growth hormone.     

Comparative application of the coefficient of variation and range-based statistics for assessing the taxonomic composition of fossil samples

Dental variation has been used commonly to assess taxonomic composition in morphologically homogeneous fossil samples. While the coefficient of variation (CV) has been used traditionally, range-based measures of variation, such as the range as a percentage of the mean (R%) and the maximum/minimum index (I_max/min) have recently become popular alternatives. The current study compares the performance of these statistics when applied to single- and pooled-species dental samples of extant Cercopithecus species. A common methodology for such problems of species discrimination has been to simply compare the maximum value of a variation statistic observed in extant samples with that observed in the fossil sample. However, regardless of what statistic is used, this approach has an unknowable Type I error rate, and usually has low power to detect multiple species. A more appropriate method involves a formal hypothesis test. The null hypothesis is that the level of variation in the fossil sample does not exceed what might be expected in a sample drawn randomly from a reference population, taking into account sampling error and the size of the fossil sample. Previous research using this method with the CV has indicated that it offers considerable power at an acceptable Type I error rate. In the current study, the data of primary interest were posterior dental dimensions for single- and pooled species samples from extant Cercopithecus species. In addition, the study also investigated the relative performance of variation statistics when applied to highly dimorphic canine dimensions, since much recent work has employed sexually dimorphic dental dimensions for assessing single-species hypotheses. The results indicate that the CV consistently out-performed the range-based statistics when using posterior dental dimensions to test a single-species hypothesis. Regardless of which statistic was used, tests on sexually dimorphic dimensions offered minimal power. In consideration of these results and the problem of studywise Type I error rates, we recommend against the use of multiple measures of variation to test for multiple species composition, and advocate the CV as the statistic of choice when using the method of Cope & Lacy (1992). For similar reasons, we argue for careful selection of dental variables for inclusion in such analyses, and in particular recommend against including sexually dimorphic dimensions when testing for multiple species composition.     

Sexual Dimorphisms in the Dermal Denticles of the Lesser-Spotted Catshark,Scyliorhinus canicula (Linnaeus, 1758)

The dermal layers of several elasmobranch species have been shown to be sexually dimorphic. Generally, when this occurs the females have thicker dermal layers compared to those of males. This sexual dimorphism has been suggested to occur as a response to male biting during mating. Although male biting as a copulatory behaviour in Scyliorhinus canicula has been widely speculated to occur, only relatively recently has this behaviour been observed. Male S. canicula use their mouths to bite the female’s pectoral and caudal fins as part of their pre-copulatory behaviour and to grasp females during copulation. Previous work has shown that female S. canicula have a thicker epidermis compared to that of males. The structure of the dermal denticles in females may also differ from that of males in order to protect against male biting or to provide a greater degree of friction in order to allow the male more purchase. This study reveals that the length, width and density of the dermal denticles of mature male and female S. canicula are sexually dimorphic across the integument in areas where males have been observed to bite and wrap themselves around females (pectoral fin, area posterior to the pectoral fin, caudal fin, and pelvic girdle). No significant differences in the dermal denticle dimensions were found in other body areas examined (head, dorsal skin and caudal peduncle). Sexually dimorphic dermal denticles in mature S. canicula could be a response to male biting/wrapping as part of the copulatory process.     

Is sexual selection driving diversification of the bioluminescent ponyfishes (Teleostei: Leiognathidae)?

Sexual selection may facilitate genetic isolation among populations and result in increased rates of diversification. As a mechanism driving diversification, sexual selection has been invoked and upheld in numerous empirical studies across disparate taxa, including birds, plants and spiders. In this study, we investigate the potential impact of sexual selection on the tempo and mode of ponyfish evolution. Ponyfishes (Leiognathidae) are bioluminescent marine fishes that exhibit sexually dimorphic features of their unique light-organ system (LOS). Although sexual selection is widely considered to be the driving force behind ponyfish speciation, this hypothesis has never been formally tested. Given that some leiognathid species have a sexually dimorphic LOS, whereas others do not, this family provides an excellent system within which to study the potential role of sexual selection in diversification and morphological differentiation. In this study, we estimate the phylogenetic relationships and divergence times for Leiognathidae, investigate the tempo and mode of ponyfish diversification, and explore morphological shape disparity among leiognathid clades. We recover strong support for a monophyletic Leiognathidae and estimate that all major ponyfish lineages evolved during the Paleogene. Our studies of ponyfish diversification demonstrate that there is no conclusive evidence that sexually dimorphic clades are significantly more species rich than nonsexually dimorphic lineages and that evidence is lacking to support any significant diversification rate increases within ponyfishes. Further, we detected a lineage-through-time signal indicating that ponyfishes have continuously diversified through time, which is in contrast to many recent diversification studies that identify lineage-through-time patterns that support mechanisms of density-dependent speciation. Additionally, there is no evidence of sexual selection hindering morphological diversity, as sexually dimorphic taxa are shown to be more disparate in overall shape morphology than nonsexually dimorphic taxa. Our results suggest that if sexual selection is occurring in ponyfish evolution, it is likely acting only as a genetic isolating mechanism that has allowed ponyfishes to continuously diversify over time, with no overall impact on increases in diversification rate or morphological disparity.     

Sex differences in cannabinoid pharmacology: A reflection of differences in the endocannabinoid system?

Marijuana is the most widely used illicit drug in the U.S., and marijuana use by women is on the rise. Women have been found to be more susceptible to the development of cannabinoid abuse and dependence, have more severe withdrawal symptoms, and are more likely to relapse than men. The majority of research in humans suggests that women are more likely to be affected by cannabinoids than men, with reports of enhanced and decreased performance on various tasks. In rodents, females are more sensitive than males to effects of cannabinoids on tests of antinociception, motor activity, and reinforcing efficacy. Studies on effects of cannabinoid exposure during adolescence in both humans and rodents suggest that female adolescents are more likely than male adolescents to be deleteriously affected by cannabinoids. Sex differences in response to cannabinoids appear to be due to activational and perhaps organizational effects of gonadal hormones, with estradiol identified as the hormone that contributes most to the sexually dimorphic effects of cannabinoids in adults. Many, but not all sexually dimorphic effects of exogenous cannabinoids can be attributed to a sexually dimorphic endocannabinoid system in rodents, although the same has not yet been established firmly for humans. A greater understanding of the mechanisms underlying sexually dimorphic effects of cannabinoids will facilitate development of sex-specific approaches to treat marijuana dependence and to use cannabinoid-based medications therapeutically.     

Prostaglandin-E2: a point of divergence in estradiol-mediated sexual differentiation

The preoptic area of the mammalian forebrain is a critical substrate for the development and maintenance of many sexually dimorphic behaviors relevant to reproduction. Normal development of the male rodent brain requires completion of two processes: (1) masculinization-induction of the male phenotype, and (2) defeminization-removal of the female phenotype. Both processes, although distinct, are largely directed by the same steroid, estradiol. Whether estradiol achieves both ends via the same or separate mechanisms has been unknown. Here, we report that prostaglandin-E(2) (PGE(2)) acting downstream of estradiol, is necessary and sufficient to masculinize sexual behavior but does not affect defeminization of sexual behavior or maternal behavior. Moreover, the volume of the sexually dimorphic nucleus of the preoptic area predicts defeminization of sexual behavior, but not masculinization of sexual behavior. Another sexually dimorphic cellular endpoint regulated by estradiol, spinophilin protein expression in the mediobasal hypothalamus, was not affected by PGE(2). Thus, PGE(2) is a key divergence point in the downstream actions of estradiol to simultaneously masculinize and defeminize sexual behavior.     

Y-linked variation for autosomal immune gene regulation has the potential to shape sexually dimorphic immunity

Sexually dimorphic phenotypes arise from the differential expression of male and female shared genes throughout the genome. Unfortunately, the underlying molecular mechanisms by which dimorphic regulation manifests and evolves are unclear. Recent work suggests that Y-chromosomes may play an important role, given that Drosophila melanogaster Ys were shown to influence the regulation of hundreds of X and autosomal genes. For Y-linked regulatory variation (YRV) to facilitate sexually dimorphic evolution, however, it must exist within populations (where selection operates) and influence male fitness. These criteria have seldom been investigated, leaving the potential for dimorphic evolution via YRV unclear. Interestingly, male and female D. melanogaster differ in immune gene regulation. Furthermore, immune gene regulation appears to be influenced by the Y-chromosome, suggesting it may contribute to dimorphic immune evolution. We address this possibility by introgressing Y-chromosomes from a single wild population into an isogenic background (to create Y-lines) and assessing immune gene regulation and bacterial defence. We found that Y-line males differed in their immune gene regulation and their ability to defend against Serratia marcescens. Moreover, gene expression and bacterial defence were positively genetically correlated. These data indicate that the Y-chromosome has the potential to shape the evolution of sexually dimorphic immunity in this system.     

Components of phenotypic variation in the morphometrics of shearwater (Puffinus) species

Coefficients of variation were used to examine the variability of bill, wing and foot measurements of 11 sexually size dimorphic and seven monomorphic shearwater ( Puffinus ) species, and to investigate the selective regimes that may be acting on these traits. The effects of phylogeny can lead to a lack of statistical independence among interspecies data, so randomization tests were performed in addition to standard statistical approaches, which assume independence. However, the results obtained from the two approaches always agreed. Among the 18 species, bill measurements were significantly more variable than those of the wing or foot; furthermore, bill depth dimensions exhibited the greatest amount of phenotypic variation. Both sexually monomorphic and sexually dimorphic species exhibited the same patterns of phenotypic variation. In the sexually dimorphic species, patterns of trait variation did not differ significantly between sexes. The findings suggest that variation in the bill of dimorphic Puffinus species is not due to sexual selection. More probably, variability among the traits is due to differences in the strength of natural selection, with those traits under strong stabilizing selection (e.g. wing, tarsus and mid-toe) exhibiting reduced variability, as optimum physical dimensions are being selected for.     

Sexual dimorphism and species differences in the neurophysiology and morphology of the acoustic communication system of two neotropical hylids

We examined auditory tuning and the morphology of the anatomical structures underlying acoustic communication in female Hyla microcephala and H. ebraccata and compared our findings to data from a previous study (Wilczynski et al. 1993) in which we showed species differences in the traits that in males relate to differences in the species-typical calls. Female species differences in the best excitatory frequency (BEF) of the basilar papilla (BP) were similar to the differences seen in males, and females had a significantly lower BEF in H. ebraccata, but not H. microcephala. In both species, females had lower BP thresholds. Snout-vent length, head width, and tympanic membrane diameters were sexually dimorphic in both species and larger in females, whereas laryngeal components were sexually dimorphic and larger in males. Middle and inner ear volumes were not sexually dimorphic. Despite the significant species differences in laryngeal morphology seen in males, female larynges are not significantly different. Furthermore, the interaction of species and sex differences resulted in significantly different degrees of sex dimorphism in the species, particularly for the larynx, which is more sexually dimorphic in H. microcephala, and measures of body size, which are more dimorphic in H. ebraccata. Accepted: 6 December 1996     

Ultrastructure of the sexually dimorphic tarsal glands and tegumental glands in gonyleptoid harvestmen (Opiliones,Laniatores)

In at least four closely related families of the diverse harvestmen lineage Gonyleptoidea, males may possess sexually dimorphic tarsal glands in the swollen tarsomeres of the basitarsus and/or metatarsus of leg I. The first histological and ultrastructural examination of the sexually dimorphic tarsal glands in leg I focused only on Manaosbiidae. In this study, we examine the morphology and ultrastructure of the sexually dimorphic glands, and their associated glandular openings, found in the basitarsus and/or metatarsus of leg I of males representing Cosmetidae, Gonyleptidae, and Cranaidae (glandular openings only). In cosmetids and gonyleptids, the tarsal glands are made up of 20–60 glandular units that form distinct groups within the prolateral and retrolateral half of the tarsomere. Each glandular unit consists of a pair of terminal secretory cells, an intercalary cell wrapped around the receiving canal, and a canal cell tightly wrapped around the length of the conducting canal. Cosmetidae, Gonyleptidae, and Cranaidae exhibit remarkably similar tarsal glands and gland openings although the location of the glands in the leg differs slightly among them. Males of these three families exhibit markedly different glands and glandular openings compared to males of the family Manaosbiidae. The sexually dimorphic tarsal glands may provide an important morphological character for determining phylogenetic relationships among gonyleptoid families. Finally, we provide morphological and ultrastructural data for the common tegumental glands. These data indicate that the sexually dimorphic tarsal glands are strikingly similar to, and may possibly be derived from, the tegumental glands. J. Morphol. 274:1203–1215, 2013. © 2013 Wiley Periodicals, Inc.     

Sexually and Developmentally Dimorphic Grooming: A Comparative Survey of the Ungulata

Grooming is effective in removing fitness‐compromising ectoparasites, such as ticks. Tick‐removal grooming is regulated both by a central control mechanism (programmed grooming model) and by cutaneous stimulation from tick bites (stimulus‐driven model). The programmed grooming model predicts that organismic factors that impact the cost‐benefit ratio of grooming (e.g., sex and body size) will influence the rate of grooming. The ‘vigilance principle’ predicts that breeding males of sexually dimorphic species will groom less than females to maintain high levels of vigilance for rival males and oestrus females. The intraspecific body size principle predicts that juveniles will engage in more frequent grooming than larger‐bodied adults to compensate for the higher cost of tick infestation for smaller animals. To examine the generalizability of these predictions, we surveyed the grooming rate of 53 species/subspecies of ungulates (primarily Bovidae and Cervidae) in tick‐free zoological parks in which stimulus‐driven grooming was controlled for. Matched‐pair analysis supported both predictions. Males delivered fewer oral grooming episodes per hour than females in 85% of sexually dimorphic species (n = 40), but only 56% of monomorphic species (n = 11) exhibited sexually dimorphic grooming, which was not different from random. Juvenile oral episodes per hour exceeded that of adult females in 74% of surveyed species (n = 36). As predicted by the body size principle, the grooming rate of juveniles declined as juveniles grew larger and less vulnerable to tick infestation. In separate analyses of Bovidae and Cervidae to control for common ancestry, both families supported sexually dimorphic grooming, but developmentally dimorphic grooming was supported only for Bovidae. Our results indicate that sexually dimorphic grooming is widespread in the ungulate species surveyed, suggesting that programmed grooming evolved at least as early as the common ancestor to the Artiodactyla.     

No evidence for sexual dimorphism of facial width-to-height ratio in four large adult samples

Sexual dimorphism in physical appearance may be an important cue in both intra- and intersex competition. Recently, the facial width-to-height ratio (fWHR) has been proposed as a novel sexually dimorphic morphologic measure, with men suggested to have a higher fWHR than women. Currently, however, the status of fWHR as a sexually dimorphic trait is unclear. Here we tested for sexual dimorphism in fWHR, as well as in three additional, previously reported facial measures, in four (three Caucasian and one African) independent samples. In three of the four samples, no significant sex differences in fWHR were observed. In one sample, males showed a significantly lower (rather than higher) fWHR than females (this effect was no longer significant after controlling for body mass index). By contrast, significant and large sex differences were observed in all four samples for each of the three previously validated facial metrics, namely, (a) lower face/face height, (b) cheekbone prominence, and (c) face width/lower face height. These results provide strong evidence against the claim that fWHR, at least as measured from the surface of the face, is sexually dimorphic.     

Male-limited evolution suggests no extant intralocus sexual conflict over the sexually dimorphic cuticular hydrocarbons of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Sexually dimorphic traits are likely to have evolved through sexually antagonistic selection. However, recent empirical data suggest that intralocus sexual conflict often persists, even when traits have diverged between males and females. This implies that evolved dimorphism is often incomplete in resolving intralocus conflict, providing a mechanism for the maintenance of genetic variance in fitness-related traits. We used experimental evolution in Drosophila melanogaster to directly test for ongoing conflict over a suite of sexually dimorphic cuticular hydrocarbons (CHCs) that are likely targets of sex-specific selection. Using a set of experimental populations in which the transmission of genetic material had been restricted to males for 82 generations, we show that CHCs did not evolve, providing experimental evidence for the absence of current intralocus sexual conflict over these traits. The absence of ongoing conflict could indicate that CHCs have never been the target of sexually antagonistic selection, although this would require the existing dimorphism to have evolved via completely sexlinked mutations or as a result of former, but now absent, pleiotropic effects of the underlying loci on another trait under sexually antagonistic selection. An alternative interpretation, and which we believe to be more likely, is that the extensive CHC sexual dimorphism is the result of past intralocus sexual conflict that has been fully resolved, implying that these traits have evolved genetic independence between the sexes and that genetic variation in them is therefore maintained by alternative mechanisms. This latter interpretation is consistent with the known roles of CHCs in sexual communication in this species and with previous studies suggesting the genetic independence of CHCs between males and females. Nevertheless, direct estimates of sexually antagonistic selection will be important to fully resolve these alternatives.     

Does gestational temperature or prenatal sex ratio influence development of sexual dimorphism in a viviparous skink?

Prenatal sex ratio (through exposure to hormones from siblings in utero) can influence sexually dimorphic traits of many mammals; but research on viviparous reptiles has contrasting outcomes, which have yet to be resolved. The thermal environment experienced during gestation has a strong effect on the phenotype of reptiles, but whether this thermal effect overrides that of prenatal sex ratio has yet to be explored. We experimentally investigated whether the gestation temperature, or litter sex ratio, influences sexually dimorphic traits (head width and axilla-groin length) in a viviparous skink (Oligosoma maccanni). We found that gestation temperature had a significant influence on sexually dimorphic traits of neonates, and at 3 months of age still influenced head width. We found no evidence that traits in either sex were masculinized or feminized in response to litter sex ratio. The development of external sexual dimorphisms increased gradually (all thermal regimes pooled), with neonates showing no sexual dimorphism, 3-month-old juveniles showing some sexual dimorphism in head width, and adults having stronger, but incompletely separated, sexual dimorphism for both traits. We suggest that the overlap in sexually dimorphic traits of adult O. maccanni (and perhaps other reptiles) may be better explained by natural variation in temperatures experienced during embryonic development, rather than hormonal effects arising from litter sex ratio. The interaction of hormones and temperature during gestation and the effect of these factors on sexual dimorphism within reptiles deserve further exploration.     

Sexual differentiation and the Kiss1 system: hormonal and developmental considerations

The nervous system (both central and peripheral) is anatomically and physiologically differentiated between the sexes, ranging from gender-based differences in the cerebral cortex to motoneuron number in the spinal cord. Although genetic factors may play a role in the development of some sexually differentiated traits, most identified sex differences in the brain and behavior are produced under the influence of perinatal sex steroid signaling. In many species, the ability to display an estrogen-induced luteinizing hormone (LH) surge is sexually differentiated, yet the specific neural population(s) that allows females but not males to display such estrogen-mediated "positive feedback" has remained elusive. Recently, the Kiss1/kisspeptin system has been implicated in generating the sexually dimorphic circuitry underlying the LH surge. Specifically, Kiss1 gene expression and kisspeptin protein levels in the anteroventral periventricular (AVPV) nucleus of the hypothalamus are sexually differentiated, with females displaying higher levels than males, even under identical hormonal conditions as adults. These findings, in conjunction with accumulating evidence implicating kisspeptins as potent secretagogues of gonadotropin-releasing hormone (GnRH), suggest that the sex-specific display of the LH surge (positive feedback) reflects sexual differentiation of AVPV Kiss1 neurons. In addition, developmental kisspeptin signaling via its receptor GPR54 appears to be critical in males for the proper sexual differentiation of a variety of sexually dimorphic traits, ranging from complex social behavior to specific forebrain and spinal cord neuronal populations. This review discusses the recent data, and their implications, regarding the bi-directional relationship between the Kiss1 system and the process of sexual differentiation.