Clinal and Allometric Variation in the Skull of Sexually Dimorphic Opossums

Journal of Mammalian Evolution - Three species of sexually-dimorphic opossums are broadly distributed across South America: the habitat generalist Didelphis albiventris, the Atlantic forest-dweller...     

The Role of Sexual Selection and Conflict in Mediating Among-Population Variation in Mating Strategies and Sexually Dimorphic Traits in Sepsis punctum

The black scavenger fly Sepsis punctum exhibits striking among-population variation in the direction and magnitude of sexual size dimorphism, modification to the male forelimb and pre-copulatory behaviour. In some populations, male-biased sexual size dimorphism is observed; in other, less dimorphic, populations males court prior to mating. Such variation in reproductive traits is of interest to evolutionary biologists because it has the potential to limit gene flow among populations, contributing to speciation. Here, we investigate whether large male body size and modified forefemur are associated with higher male mating success within populations, whether these traits are associated with higher mating success among populations, and if these traits carry viability costs that could constrain their response to sexual selection. Flies from five distinct populations were reared at high or low food, generating high and low quality males. The expression of body size, forelimb morphology and courtship rate were each greater at high food, but high food males experienced higher mating success or reduced latency to first copulation in only one of the populations. Among populations, overall mating success increased with the degree of male-bias in overall body size and forelimb modification, suggesting that these traits have evolved as a means of increasing male mating rate. The increased mating success observed in large-male populations raises the question of why variation in magnitude of dimorphism persists among populations. One reason may be that costs of producing a large size constrain the evolution of ever-larger males. We found no evidence that juvenile mortality under food stress was greater for large-male populations, but development time was considerably longer and may represent an important constraint in an ephemeral and competitive growth environment.     

Dominance Genetic Variation Contributes Little to the Missing Heritability for Human Complex Traits

For human complex traits, non-additive genetic variation has been invoked to explain “missing heritability,” but its discovery is often neglected in genome-wide association studies. Here we propose a method of using SNP data to partition and estimate the proportion of phenotypic variance attributed to additive and dominance genetic variation at all SNPs (hSNP2 and δSNP2) in unrelated individuals based on an orthogonal model where the estimate of hSNP2 is independent of that of δSNP2. With this method, we analyzed 79 quantitative traits in 6,715 unrelated European Americans. The estimate of δSNP2 averaged across all the 79 quantitative traits was 0.03, approximately a fifth of that for additive variation (average hSNP2 = 0.15). There were a few traits that showed substantial estimates of δSNP2, none of which were replicated in a larger sample of 11,965 individuals. We further performed genome-wide association analyses of the 79 quantitative traits and detected SNPs with genome-wide significant dominance effects only at the ABO locus for factor VIII and von Willebrand factor. All these results suggest that dominance variation at common SNPs explains only a small fraction of phenotypic variation for human complex traits and contributes little to the missing narrow-sense heritability problem.     

Seeing Dogs: Human Preferences for Dog Physical Attributes

ABSTRACT

This study systematically investigated peoples' preferences for dog physical attributes in images of real-life dogs. Participants (n = 124) completed an aesthetic-preference test wherein they viewed 80 image pairs of mixed-breed adult dogs and were asked which image they “liked best.” In each image pair, the two dog images appeared to be nearly identical, but unbeknownst to participants, the images differed slightly in that one physical characteristic had been manipulated. By altering a single physical characteristic in each image pair, participant preference for each of 14 different physical attributes could be investigated over the course of the study. The feature manipulations examined theories relating to Kindchenschema (an infantile appearance, per Konrad lorenz), ostensive human similarity, the process of domestication, as well as differences in attribute size and symmetry. The results showed that participants preferred some features associated with the infant schema—large eyes and wider-set eyes. They also preferred certain human-like attributes: colored irises and a distinct upturn of the commissure, seeming to capture a smile. By contrast, participants did not reveal a preference for physical characteristics relating to feature size, symmetry or the process of domestication. The findings suggest that identifiable physical attributes of domestic dogs have aesthetic value and, additionally, that human preferences for aesthetic differences can be systematically investigated. Given that people attend to and care about the way dogs look, the effects of particular physical attributes on peoples' preferences merit investigation.     

Interaction Between Sexually Antagonistic Selection and Mate Choice in the Evolution of Female Responses to Male Traits

Theoretical analyses of selection on mutations affecting female responsiveness to male traits suggested that sexually antagonistic selection and traditional female choice are not exclusive alternatives. They can act simultaneously on the same female traits, and can either reinforce or act against each other. These analyses do not yield theoretical predictions regarding the relative frequency and importance of the two types of selection on female responsiveness, as the balance between them is affected by complex factors, including the frequency distribution of male traits, and the mechanisms of male action. Male–female interactions differ from many other evolutionary interactions involving potential evolutionary conflict, in that male and female genomes are irretrievably mixed in their offspring, thus increasing the possibility of indirect payoffs to one participant from the traits of its partner.     

Environmental Predictors of Geographic Variation in Human Mating Preferences

Sexual selection theory classically posits consistent and directional mate-preferences for male traits that provide benefits to females. However, flexible mate-choice tactics may persist within a species when males display multiple desirable features that confer different benefits to females under variable environmental conditions. Ecological factors such as population density, resource demand, and sex ratio can influence the value that female animals place on certain male characteristics across mating environments. In this study, I used human mate-preference data from `lonely hearts' advertisements in the newspapers of 23 cities in the USA to assess geographic differences in female preferences for male traits (e.g. physical attributes, resource-holding potential, emotional characteristics, personal interests) in relation to these ecological parameters. I found that females placed more emphasis on the resource-accruing ability of prospective mates in densely populated cities and cities having greater resource demands (higher cost of living). In contrast, women from densely populated or resource-demanding cities placed less emphasis on the emotional aspects or personal interests of males. Preferences for physical features were not environmentally linked, but instead were a function of the degree to which females advertised their own physical attractiveness. Collectively, these results suggest that certain mate-choice criteria employed by women are sensitive to variation in local environmental conditions and that variable levels of resource or mate availability may favor different mating tactics across human populations.     

Sexually Dimorphic and Sex-Independent Left-Right Asymmetries in Chicken Embryonic Gonads

Female birds develop asymmetric gonads: a functional ovary develops on the left, whereas the right gonad regresses. In males, however, testes develop on both sides. We examined the distribution of germ cells using Vasa/Cvh as a marker. Expression is asymmetric in both sexes: at stage 35 the left gonad contains significantly more germ cells than the right. A similar expression pattern is seen for expression of ERNI (Ens1), a gene expressed in chick embryonic stem cells while they self-renew, but downregulated upon differentiation. Other pluripotency-associated markers (PouV/Oct3/4, Nanog and Sox2) also show asymmetric expression (more expressing cells on the left) in both sexes, but this asymmetry is at least partly due to expression in stromal cells of the developing gonad, and the pattern is different for all the genes. Therefore germ cell and pluripotency-associated genes show both sex-dependent and independent left-right asymmetry and a complex pattern of expression.     

Mutual Mate Choice for Colorful Traits in King Penguins

While studies of mate choice based on male color pattern are ubiquitous, studies of mate choice based on ornamental color traits in sexually monomorphic species are less common. We conducted manipulative field experiments on two color ornaments of king penguins (Aptenodytes patagonicus), the size of auricular patches of orange feathers and degree of UV reflectance from beak spots, to determine how the degree of ornamentation influenced pairing rate. In a reduction of auricular patch size, females paired significantly more quickly than males in both control and experimental samples. When this bias was taken into account statistically, pairing of individuals with reduced auricular patches was significantly delayed. We also reduced, but did not eliminate, UV reflectance from beak spots by applying a UV filter; no sex difference in pairing rate was evident in this experiment. Treated birds paired significantly more slowly than untreated control individuals, taking more than a week longer to pair on average than their unmanipulated counterparts, a result that was significant for males and approached significance for females. Our results may indicate mutual mate choice via UV reflectance of the beak spot. Given that this is a species where breeding is extremely slow and considerable investment by both males and females is required for successful reproduction, our results support the hypothesis that in such species, sexual selection might act on the same ornament in both sexes.     

Male Mate Preferences in the Mosquitofish Gambusia holbrooki

Although male mosquitofish invest little in their progeny, the simultaneous availability of many potential mates and the large variance in their quality are expected to favour the evolution of mechanisms of male mate choice. Males of Gambusia holbrooki were shown to exhibit sexual preferences when presented simultaneously with two potential mates. When females differed in size, males showed more sexual activity directed at the larger of the two and the time spent with this female increased with the difference between the two females. This preference, however, was lower than expected if males spent time in direct proportion to the difference in fertility between females. In the second part of the study, females which had just delivered were found to be clearly preferred over gravid females. Attractiveness of females dropped after the third day, and disappeared in the sixth day after parturition. The results are discussed in relation to the probable occurrence of sperm competition and sperm displacement in this species.     

Large-Scale Age-Dependent Skewed Sex Ratio in a Sexually Dimorphic Avian Scavenger

Age-dependent skewed sex ratios have been observed in bird populations, with adult males generally outnumbering females. This trend is mainly driven by higher female mortality, sometimes associated with anthropogenic factors. Despite the large amount of work on bird sex ratios, research examining the spatial stability of adult sex ratios is extremely scarce. The Andean condor (Vultur gryphus) is the only bird of prey with strong sexual dimorphism favouring males (males are 30% heavier than females). By examining data from most of its South-American range, we show that while the juvenile sex ratio is balanced, or even female-skewed, the sex ratio becomes increasing male-skewed with age, with adult males outnumbering females by >20%, and, in some cases by four times more. This result is consistent across regions and independent of the nature of field data. Reasons for this are unknown but it can be hypothesized that the progressive disappearance of females may be associated with mortality caused by anthropogenic factors. This idea is supported by the asymmetric habitat use by the two sexes, with females scavenging in more humanized areas. Whatever the cause, male-skewed adult sex ratios imply that populations of this endangered scavenger face higher risks of extinction than previously believed.     

Neurosteroid Biosynthesis Regulates Sexually Dimorphic Fear and Aggressive Behavior in Mice

The neurosteroid allopregnanolone is a potent positive allosteric modulator of GABA action at GABA_A receptors. Allopregnanolone is synthesized in the brain from progesterone by the sequential action of 5α-reductase type I (5α-RI) and 3α-hydroxysteroid dehydrogenase (3α-HSD). 5α-RI and 3α-HSD are co-expressed in cortical, hippocampal, and olfactory bulb glutamatergic neurons and in output neurons of the amygdala, thalamus, cerebellum, and striatum. Neither 5α-RI nor 3α-HSD mRNAs is expressed in glial cells or in cortical or hippocampal GABAergic interneurons. It is likely that allopregnanolone synthesized in principal output neurons locally modulates GABA_A receptor function by reaching GABA_A receptor intracellular sites through lateral membrane diffusion. This review will focus on the behavioral effects of allopregnanolone on mouse models that are related to a sexually dimorphic regulation of brain allopregnanolone biosynthesis. Animal models of psychiatric disorders, including socially isolated male mice or mice that receive a long-term treatment with anabolic androgenic steroids (AAS), show abnormal behaviors such as altered fear responses and aggression. In these animal models, the cortico-limbic mRNA expression of 5α-RI is regulated in a sexually dimorphic manner. Hence, in selected glutamatergic pyramidal neurons of the cortex, CA3, and basolateral amygdala and in granular cells of the dentate gyrus, mRNA expression of 5α-RI is decreased, which results in a downregulation of allopregnanolone content. In contrast, 5α-RI mRNA expression fails to change in the striatum medium spiny neurons and in the reticular thalamic nucleus neurons, which are GABAergic. By manipulating allopregnanolone levels in glutamatergic cortico-limbic neurons in opposite directions to improve [using the potent selective brain steroidogenic stimulant (SBSS) S-norfluoxetine] or induce (using the potent 5α-RI inhibitor SKF 105,111) behavioral deficits, respectively, we have established the fundamental role of cortico-limbic allopregnanolone levels in the sexually dimorphic regulation of aggression and fear. By selectively targeting allopregnanolone downregulation in glutamatergic cortico-limbic neurons, i.e., by improving the response of GABA_A receptors to GABA, new therapeutics would offer appropriate and safe management of psychiatric conditions, including impulsive aggression, irritability, irrational fear, anxiety, posttraumatic stress disorders, and depression. Special issue article in honor of Dr. Ji-Sheng Han.     

Dominant Genetic Variation and Missing Heritability for Human Complex Traits: Insights from Twin versus Genome-wide Common SNP Models

In order to further illuminate the potential role of dominant genetic variation in the “missing heritability” debate, we investigated the additive (narrow-sense heritability, h²) and dominant (δ²) genetic variance for 18 human complex traits. Within the same study base (10,682 Swedish twins), we calculated and compared the estimates from classic twin-based structural equation model with SNP-based genomic-relatedness-matrix restricted maximum likelihood [GREML(d)] method. Contributions of δ² were evident for 14 traits in twin models (average δ²_twin = 0.25, range 0.14–0.49), two of which also displayed significant δ² in the GREMLd analyses (triglycerides δ²_SNP = 0.28 and waist circumference δ²_SNP = 0.19). On average, the proportion of h²_SNP/h²_twin was 70% for ADE-fitted traits (for which the best-fitting model included additive and dominant genetic and unique environmental components) and 31% for AE-fitted traits (for which the best-fitting model included additive genetic and unique environmental components). Independent evidence for contribution from shared environment, also in ADE-fitted traits, was obtained from self-reported within-pair contact frequency and age at separation. We conclude that despite the fact that additive genetics appear to constitute the bulk of genetic influences for most complex traits, dominant genetic variation might often be masked by shared environment in twin and family studies and might therefore have a more prominent role than what family-based estimates often suggest. The risk of erroneously attributing all inherited genetic influences (additive and dominant) to the h² in too-small twin studies might also lead to exaggerated “missing heritability” (the proportion of h² that remains unexplained by SNPs).     

幼林期黄梁木生长性状的种源间变异

以黄梁木Neolamarckia cadamba 11个种源为材料,在广东雷州、海南东方和海南海口3个试验点开展种源试验,调查2年生幼林的胸径、树高、材积等生长性状。结果表明,在3个试验点,所有性状在地点间、种源间、地点内区组间、种源与地点内区组交互项以及地点与种源交互项的差异均达极显著水平。根据稳定性分析可将参试的11个种源划分为3大类。     

Genetic Analysis of Variation in Human Meiotic Recombination

The number of recombination events per meiosis varies extensively among individuals. This recombination phenotype differs between female and male, and also among individuals of each gender. In this study, we used high-density SNP genotypes of over 2,300 individuals and their offspring in two datasets to characterize recombination landscape and to map the genetic variants that contribute to variation in recombination phenotypes. We found six genetic loci that are associated with recombination phenotypes. Two of these (RNF212 and an inversion on chromosome 17q21.31) were previously reported in the Icelandic population, and this is the first replication in any other population. Of the four newly identified loci (KIAA1462, PDZK1, UGCG, NUB1), results from expression studies provide support for their roles in meiosis. Each of the variants that we identified explains only a small fraction of the individual variation in recombination. Notably, we found different sequence variants associated with female and male recombination phenotypes, suggesting that they are regulated by different genes. Characterization of genetic variants that influence natural variation in meiotic recombination will lead to a better understanding of normal meiotic events as well as of non-disjunction, the primary cause of pregnancy loss.     

Gene Expression in Peripheral Immune Cells following Cardioembolic Stroke Is Sexually Dimorphic

Aims

Epidemiological studies suggest that sex has a role in the pathogenesis of cardioembolic stroke. Since stroke is a vascular disease, identifying sexually dimorphic gene expression changes in blood leukocytes can inform on sex-specific risk factors, response and outcome biology. We aimed to examine the sexually dimorphic immune response following cardioembolic stroke by studying the differential gene expression in peripheral white blood cells.

Methods and Results

Blood samples from patients with cardioembolic stroke were obtained at ≤3 hours (prior to treatment), 5 hours and 24 hours (after treatment) after stroke onset (n = 23; 69 samples) and compared with vascular risk factor controls without symptomatic vascular diseases (n = 23, 23 samples) (ANCOVA, false discovery rate p≤0.05, |fold change| ≥1.2). mRNA levels were measured on whole-genome Affymetrix microarrays. There were more up-regulated than down-regulated genes in both sexes, and females had more differentially expressed genes than males following cardioembolic stroke. Female gene expression was associated with cell death and survival, cell-cell signaling and inflammation. Male gene expression was associated with cellular assembly, organization and compromise. Immune response pathways were over represented at ≤3, 5 and 24 h after stroke in female subjects but only at 24 h in males. Neutrophil-specific genes were differentially expressed at 3, 5 and 24 h in females but only at 5 h and 24 h in males.

Conclusions

There are sexually dimorphic immune cell expression profiles following cardioembolic stroke. Future studies are needed to confirm the findings using qRT-PCR in an independent cohort, to determine how they relate to risk and outcome, and to compare to other causes of ischemic stroke.