Male Traits Research Articles

Environmental conditions and male quality traits simultaneously explain variation of multiple colour signals in male lizards.

Male lizards often display multiple pigment‐based and structural colour signals which may reflect various quality traits (e.g. performance, parasitism), with testosterone (T) often mediating these relationships. Furthermore, environmental conditions can explain colour signal variation by affecting processes such as signal efficacy, thermoregulation and camouflage. The relationships between colour signals, male quality traits and environmental factors have often been analysed in isolation, but simultaneous analyses are rare. Thus, the response of multiple colour signals to variation in all these factors in an integrative analysis remains to be investigated.Here, we investigated how multiple colour signals relate to their information content, examined the role of T as a potential mediator of these relationships and how environmental factors explain colour signal variation.We performed an integrative study to examine the covariation between three colour signals (melanin‐based black, carotenoid‐based yellow–orange and structural UV), physiological performance, parasitism, T levels and environmental factors (microclimate, forest cover) in male common lizards Zootoca vivipara from 13 populations.We found that the three colour signals conveyed information on different aspects of male condition, supporting a multiple message hypothesis. T influenced only parasitism, suggesting that T does not directly mediate the relationships between colour signals and their information content. Moreover, colour signals became more saturated in forested habitats, suggesting an adaptation to degraded light conditions, and became generally brighter in mesic conditions, in contradiction with the thermal melanism hypothesis.We show that distinct individual quality traits and environmental factors simultaneously explain variations of multiple colour signals with different production modes. Our study therefore highlights the complexity of colour signal evolution, involving various sets of selective pressures acting at the same time, but in different ways depending on colour production mechanism.

Nutrient-dependent allometric plasticity in a male-diphenic mite.

Male secondary sexual traits often scale allometrically with body size. These allometries can be variable within species and may shift depending on environmental conditions, such as food quality. Such allometric plasticity has been hypothesized to initiate local adaptation and evolutionary diversification of scaling relationships, but is under‐recorded, and its eco‐evolutionary effects are not well understood. Here, we tested for allometric plasticity in the bulb mite (Rhizoglyphus robini), in which large males tend to develop as armed adult fighters with thickened third legs, while small males become adult scramblers without thickened legs. We first examined the ontogenetic timing for size‐ and growth‐dependent male morph determination, using experimentally amplified fluctuations in growth rate throughout juvenile development. Having established that somatic growth and body size determine male morph expression immediately before metamorphosis, we examined whether the relationship between adult male morph and size at metamorphosis shifts with food quality. We found that the threshold body size for male morph expression shifts toward lower values with deteriorating food quality, confirming food‐dependent allometric plasticity. Such allometric plasticity may allow populations to track prevailing nutritional conditions, potentially facilitating rapid evolution of allometric scaling relationships.

Male Mediterranean fruit flies prefer warmer temperatures that improve sexual performance

Females and males have divergent strategies of energy investment, so the thermal preference of each sex in insects may differ because energetic conversion of metabolic reserves is dependent on temperature. We determined the thermal preference of virgin, sexually mature Mediterranean fruit flies, Ceratitis capitata, and found that males preferred a significantly higher temperature (23.8 ± 0.3 °C) than that of females (22.1 ± 0.3 °C). We then tested predictions for the difference in thermal preference related to the energetic demands of reproduction over a range of temperatures. The frequency and duration of calling bouts by male C. capitata were optimal at 26 °C. Mating propensity and latency, and copula duration, were optimal over the range of 22–28 °C. When mating occurred, temperature had little effect on the incidence of sperm storage by females, but there was a notable decline in the number stored at 28 °C. Female lifespan was highest at 18 °C, but lifetime egg production was optimal at 24 °C. These results illustrate temperature-related differences in the reproductive fitness of the sexes in C. capitata, although the optima for male traits align best with their thermal preference. They also support the theoretical prediction that insect thermal preference should be lower than the optimum for fitness.

The female Euscepes postfasciatus refractory period is induced by the male but length is determined by the female

Females of many animals mate multiple times during their lives (i.e., polyandry). The period between matings (mating interval) is called the refractory period (RP). In the West Indian sweet potato weevil (Euscepes postfasciatus), males use the ejaculate to induce the RP in females to prevent re-mating. By measuring the RP, a large variation of 1–49 days was observed. This variation may be due to the males (ejaculate quantity and quality) and females (ejaculate sensitivity/degradation ability and body size) and their interactions, but the exact mechanisms are currently unclear. Here, we investigated a tendency towards a particular female RP duration and the associated traits of males and females to test the following three factors responsible for variation in the length of the RP: male manipulation of ejaculate volume, individual differences in male ejaculation substances, and ejaculate sensitivity/degradation ability in females. We prepared virgin males and females to create mating pairs. The following day, another mate was introduced to the females, and the first RP was measured. The same procedure was used for measuring the second RP. The males were also provided with another female (second female), mated, and then the RP of the second female was measured. In addition, the relationship between the length of the RP and female fitness was investigated. The results showed that there was a significant positive correlation between the first and second RP in the focal females, while no significant correlation was observed between the RP of the first and second females induced by the same male. It was also found that the length of the RP did not affect female fitness. This indicated that the males did not adaptively manipulate ejaculation volume depending on the quality of the females, and variance in the length of the RP may be explained by variation in the female physiological ability against ejaculate.

Experimental manipulation of sexual traits in barn swallow populations-No evidence for divergent sexual selection.

Safran et al. (2016a) manipulated two sexual traits (ventral plumage coloration and tail streamer length) in male barn swallows (Hirundo rustica) and reported divergent effects on paternity change between two study populations, in Colorado and Israel. They concluded that geographical variation in the two phenotypic traits is maintained by divergent sexual selection. However, the response variable they used, the longitudinal change in paternity from a pre‐treatment clutch to a post‐treatment clutch, does not reflect an unbiased effect of the treatment. Here, I show that the magnitude of the change in paternity is influenced by variation in the initial paternity score among the treatment groups, which is presumably due to stochastic variation from low sample sizes in the treatment groups. When the bias was accounted for in re‐analyses of the Israeli dataset, the statistical significance of one of two treatment effects disappeared. Similar re‐analyses of the American population were not possible due to inaccessibility of raw data for individual clutches, but an assessment of the mean scores indicates that the two significant treatment effects in this population were similarly biased in their initial paternity scores. The conclusion of divergent sexual selection on male phenotypic traits between the two populations does not seem to be supported.

Evolution of choosiness dictates whether search costs of mate choice enhance speciation by sexual selection

The role of sexual selection in speciation is implicated in both empirical case studies and larger comparative works. However, sexual selection faces two major problems in driving speciation. First, because females with novel preferences search for their initially rare males, search costs are expected to curtail initial sexual divergence. Second, if these populations come back into sympatry, sexual divergence may be erased due to hybridization. A major goal is to understand which conditions increase the likelihood of overcoming these problems. Here we generated a diploid population genetic model of how female search costs and evolution of female 'choosiness' (i.e. preference strength) interact to drive speciation in allopatry and secondary contact. We studied the model using numerical simulations in the context of two different male traits, ecologically 'arbitrary' versus 'magic' traits. First, in allopatry, without female search costs only minor and fluctuating sexual isolation evolved. In contrast, with female search costs, sexual isolation was highly curtailed with arbitrary male traits but was greatly facilitated with magic traits. However, because search costs selected for reduced choosiness, sexual isolation with magic traits was eventually eroded, the rate determined by the genetic architecture of choosiness. These factors also played a key role in secondary contact; with evolvable choosiness and female search costs, pure sexual selection models collapsed upon secondary contact. However, when we added selection against hybrids (i.e. reinforcement) to this model, we found that speciation could be maintained under a wide range of conditions with arbitrary male traits, but not with magic male traits. This surprisingly suggests that arbitrary male traits are in some cases more likely to aid speciation than magic male traits. We discuss these findings and relate them to empirical literature on female choosiness within species and in hybrids.

Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains

Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains

Exploring the interplay between natural and intersexual selection on the evolution of a cognitive trait.

There has been an increased focus on the role of natural and sexual selection in shaping cognitive abilities, but the importance of the interaction between both forces remains largely unknown. Intersexual selection through female mate choice might be an important driver of the evolution of cognitive traits, especially in monogamous species, where females may obtain direct fitness benefits by choosing mates with better cognitive abilities. However, the importance given by female to male cognitive traits might vary among species and/or populations according to their life‐history traits and ecology. To disentangle the effects of natural and sexual selection, here we use an agent‐based simulation model and compare the model's predictions when females mate with the first randomly encountered male (i.e., under natural selection) versus when they choose among males based on their cognitive trait values (i.e., under natural and intersexual selection). Males and females are characterized, respectively, by their problem‐solving ability and assessment strategy. At each generation, agents go through (1) a choosing phase during which females assess the cognitive abilities of potential mates until eventually finding an acceptable one and (2) a reproductive phase during which all males compete for limited resources that are exploited at a rate, which depends on their cognitive abilities. Because males provide paternal care, the foraging success of mated males determines the breeding success of the pair through its effect on nestling provisioning efficiency. The model predicts that intersexual selection plays a major role in most ecological conditions, by either reinforcing or acting against the effect of natural selection. The latter case occurs under harsh environmental conditions, where intersexual selection contributes to maintaining cognitive diversity. Our findings thus demonstrate the importance of considering the interaction between both selective forces and highlight the need to build a conceptual framework to target relevant cognitive traits.

Health determinants in men of the Bear subculture compared with the MSM population. Literature review.

A number of health problems are more common in the population of men who have sex with men (MSM) as compared with the general population. At the same time, research reveals that the MSM population is far from homogeneous, and that subcultural affiliation is one of the characteristics that should be taken into account in health analyses of this group. One of the subcultures among MSM that has received growing interest from researchers in recent years, is the Bear community. It originated in the USA and comprises men - mostly homosexual or bisexual - who are characterized by larger, massive or muscular figure, and by distinctive male phenotypic traits - especially body hair pattern, including facial hair. The most significant health determinants in this group include a higher prevalence of behaviors contributing to negative health outcomes as compared with other MSM, elevated BMI values, as well as exposure to multiple stigma - both sexual minority and weight stigma. Research to date has shown that these characteristics of Bears have significant implications for their mental and sexual health. The article aims to review the literature, and to discuss the practical and the clinical implications of the studies conducted thus far in this population. The summary gives practical recommendations regarding both the support for Bear men in clinical practice, and the design of adequate and effective health promotion interventions for members of this unique community.

Resource-dependent investment in male sexual traits in a viviparous fish.

Exaggerated and conspicuous sexually selected traits are often costly to produce and maintain. Costly traits are expected to show resource-dependent expression, since limited resources prevent animals from investing maximally in multiple traits simultaneously. However, there may be critical periods during an individual's life where the expression of traits is altered if resources are limited. Moreover, costly sexual traits may arise from sexual selection acting both before (pre-copulatory) and after mating (post-copulatory). Gaining a robust understanding of resource-dependent trait expression therefore requires an approach that examines both episodes of sexual selection after resource limitation during different times in an individual's life. Yet few studies have taken such an approach. Here, we examine how resource restriction influences a set of pre- and post-copulatory traits in male pygmy halfbeaks (Dermogenys collettei), which invest in sexual ornaments and routinely engage in male-male contests and sperm competition. Critically, we examined responses in males when resources were restricted during development and after reaching sexual maturity. Both pre- and post-copulatory traits are resource-dependent in male halfbeaks. Body size, beak size, courtship behavior, and testes size were reduced by diet restriction, while, unexpectedly, the restricted-diet group had a larger area of red color on the beak and fins after diet treatment. These patterns were generally consistent when resources were restricted during development and after reaching sexual maturity. The study reinforces the role of resource acquisition in maintaining variation among sexual traits.

Research and utilization of mixed seed production technology for two-line hybrid wheat

<p indent="0mm">China’s Two-line Hybrid Wheat Technology System is an important achievement resulting from novel domestic use of sterile lines to realize agroindustrial application of hybrid wheat. However, compared with hybrid rice and maize, the industrial application level of hybrid wheat is still in its early stage. The unstable production of hybrids, as well as their high cost and the large sowing amount of seeds required for their cultivation, have always limited the rapid industrialization of two-line hybrid wheat. Two-line hybrid wheat research and cultivation show that high-efficiency seed production is the core key technology for the successful industrialization of hybrid wheat. Moreover, the outcrossing performance of wheat photo-thermo sensitive sterile lines is the key to the success of seed production. Wheat photo-thermo sensitive sterile lines can change from selfing to outcrossing under seed production conditions, and their seed production characteristics are affected by various factors of both sterile lines and restorer lines. Breeding sterile lines and restorer lines with high combining ability and excellent outcrossing traits can effectively improve the seed setting rate and yield of outcrossing in seed production and also greatly reduce the cost of wheat hybrid seed production. In our study, the influencing factors and results of the seed production process were assessed based on related seed production experiments with two-line hybrid wheat conducted from 2016 to 2020. Outcrossing traits, such as female bloom traits of floret opening size and stigma exposure rate and male fertility traits of pollen dispersal distance, anther size, anther exposure rate, and pollen amount were significantly correlated with outcrossing performance. In the pollination stage, larger pollen amounts, shorter pollen dispersal distances, longer pollination durations of the restorer line, higher stigma exposure rates, and larger floret opening angles of the sterile line can greatly improve the outcrossing seed setting rate, production yield, and quality of the sterile line. The flowering period of male parents was 2–3 days later than that of female parents, which could be utilized to realize the effective preparation of temporal-spatial and physiological synergy. With the male parent comprising 5% of a mixed population, the yield of mixed seed production was significantly increased by 28.2% compared with even row ratio seed production. From 2019 to 2021, large-scale mixed seed production in the Nanyang area has achieved excellent results with large-scale seed production of BS1453/JS1 reaching 5273.4 kg/hm². The establishment of a simple, scientific, safe, and efficient technology system for large-scale mixed seed production has solved the technical bottleneck of large-scale seed production of two-line hybrid wheat, providing theoretical and technical support for the popularization and widespread application of two-line hybrid wheat.

Morphometric and Phylogenetic analysis of morphotypes in Artemia franciscana Kellogg, 1906 (Crustacea: Anostraca)

We document morphology and genetic relatedness of morphotypes within the Artemia franciscana that has colonized Covelong saltern in Kelambakkam (South India). They exhibits high phenotypic plasticity and intra-population variation in a supposedly panmictic population. Morphometric analysis was carried out on 18 traits in males and 15 in females and subjected to multivariate analysis. Three types each in males (M1, M3 and M4) and females (F1, F2 and F3) were singled out. The axes in the plot explain 77.9% in males and 73.9% in females of the variation through discriminant function analysis. The sequence divergence of the population was evaluated through mtDNA (16S rRNA) and nDNA (p26 gene) markers. The substantial sequence divergence was observed between the morphotypes through nDNA and appearing sequence divergence was recognized by mtDNA. Likewise, phylogenetic analyses of maximum likelihood and Bayesian analysis through nDNA revealed a maximum similarities between M1, M4 with F1 & F2 and M3 with F3. Further, haplotype distribution of nDNA revealed unique haplotype between M1 and M4 with F1 and F2 morphotypes. This study thus confirms the occurrence of morphotypes with specific characteristics inside a seemingly homogeneous population.

Male reproductive potential in the Black Sea turbot (Scophthalmus maximus) spawning populations

The combined analysis of biological characteristics and sperm traits of wild turbot males during spawning periods from mid-April to mid-June 2008, 2010, 2012–2014 in the local populations at the depths 50–95 m in the Northern Black Sea was carried out on the basis of the gillnet catches. Only mature males were observed during all sampling months and years. Gonadosomatic index of mature males with total body length 36–64 cm (aged 3–13-years-old) varied within 0.2–2.6. Sperm volume stripped from spermiating males ranged from 0.3 to 7.5 ml; sperm density and relative stripped production of spermatozoa fall in the range of 0.2–11 × 109 ml−1 and 0.4–46 × 109 per male, correspondingly. Principal component analysis indicated that neither biological characteristics of males, nor the phase of the spawning season impact the percentage of motile spermatozoa and сurvilinear velocity VCL in activated sperm. However, the best sperm traits (significantly higher, p < 0.05, than that of the sperm traits of males in other years) with average percentage of motile spermatozoa 95% (73 – 99.8%), average VCL 140 µm.s−1 (92–222 µm.s−1) was determined for males in 2010.

Mitochondria as the powerhouses of sexual selection: Testing mechanistic links between development, cellular respiration, and bird song

The developmental environment can affect the expression of sexually selected traits in adulthood. The physiological mechanisms that modulate such effects remain a matter of intense debate. Here, we test the role of the developmental environment in shaping adult mitochondrial function and link mitochondrial function to expression of a sexually selected trait in males (bird song). We exposed male zebra finches (Taeniopygia guttata) to corticosterone (CORT) treatment during development. After males reached adulthood, we quantified mitochondrial function from whole red blood cells and measured baseline CORT and testosterone levels, body condition/composition, and song structure. CORT-treated males had mitochondria that were less efficient (FCRL/R) and used a lower proportion of maximum capacity (FCRR/ETS) than control males. Additionally, CORT-treated males had higher baseline levels of CORT as adults compared to control males. Using structural equation modelling, we found that the effects of CORT treatment during development on adult mitochondrial function were indirect and modulated by baseline CORT levels, which are programmed by CORT treatment during development. Developmental treatment also had an indirect effect on song peak frequency. Males treated with CORT during development sang songs with higher peak frequency than control males, but this effect was modulated through increased CORT levels and by a decrease in FCRR/ETS. CORT-treated males had smaller tarsi compared to control males; however, there were no associations between body size and measures of song frequency. Here, we provide the first evidence supporting links between the developmental environment, mitochondrial function, and the expression of a sexually selected trait (bird song).

Intersexuality in a natural population of the terrestrial isopod Porcellioscaber.

Intersex phenotypes are rarely observed in natural isopod populations and their expression is typically associated with infection of Wolbachia, a reproductive parasite that manipulates arthropod reproduction. During an intensive sampling effort of a natural population of the isopod Porcellioscaber, an adult individual was isolated that expressed both male and female traits. The intersex individual exhibited clearly developed external male genitalia and carried multiple eggs in its brood pouch. No Wolbachia infection could be identified in this individual, a result that needs to be approached with caution due to suboptimal DNA preservation for diagnostic PCR assays. Wolbachia were, however, detected in two adult females of the same population, and appear closely related to isolates that infect other terrestrial isopod species. This is the first demonstration that intersex phenotypes can arise under natural conditions in P.scaber.

Effects of genetic vs. environmental quality on condition-dependent morphological and life history traits in a neriid fly.

Condition is assumed to reflect both genes and environment, enabling condition‐dependent signals to reveal genetic quality. However, because the phenotypic effects of variation in genetic quality could be masked by environmental heterogeneity, the contribution of genetic quality to phenotypic variation in fitness‐related traits and condition‐dependent signals remains unclear. We compared effects of ecologically relevant manipulations of environmental quality (nutrient dilution in the larval diet) and genetic quality (one generation of inbreeding) on male and female morphology, life history and reproductive performance in the neriid fly Telostylinus angusticollis. We found that larval diet quality had strong, positive effects on male and female body size, male secondary sexual traits, and aspects of male and female reproductive performance. By contrast, inbreeding had weak effects on most traits, and no trait showed clear and consistent effects of both environmental and genetic quality. Indeed, inbreeding effects on body size and male competitive performance were of opposite sign in rich vs. poor larval diet treatment groups. Our results suggest that environmental quality strongly affects condition, but the effects of genetic quality are subtle and environment‐dependent in this species. These findings raise questions about the genetic architecture of condition and the potential for condition‐dependent traits to function as signals of genetic quality.

The spatial and temporal distribution of females influence the evolution of testes size in Australian rodents.

Male-male competition after mating (sperm competition) favours adaptations in male traits, such as elevated sperm numbers facilitated by larger testes. Ultimately, patterns of female distribution will affect the strength of sperm competition by dictating the extent to which males are able to prevent female remating. Despite this, our understanding of how the spatial and temporal distributions of mating opportunities have shaped the evolutionary course of sperm competition is limited. Here, we use phylogenetic comparative methods to explore interspecific variation in testes size in relation to patterns of female distribution in Australian rodents. We find that as mating season length (temporal distribution of females) increases, testes size decreases, which is consistent with the idea that it is difficult for males to prevent females from remating when overlap among oestrous females is temporally concentrated. Additionally, we find that social species (spatially clustered) have smaller testes than non-social species (spatially dispersed). This result suggests that males may be effective in monopolizing reproduction within social groups, which leads to reduced levels of sperm competition relative to non-social species where free-ranging females cannot be controlled. Overall, our results show that patterns of female distribution, in both space and time, can influence the strength of post-mating sexual selection among species.

Selection for male stamina can help explain costly displays with cost-minimizing female choice

In many species, male lifespan is shorter than that of females, often attributed to sexual selection favouring costly expression of traits preferred by females. Coevolutionary models of female preferences and male traits predict that males can be selected to have such life histories; however, this typically requires that females also pay some costs to express their preferences. Here we show that this problem diminishes when we link coevolutionary models of costly mate choice with the idea of stamina. In our model, the most successful males are those who can combine high attendance time on a lek — or, more generally, tenacious effort in their display time budgets — with high viability such that they are not too strongly compromised in terms of lifespan. We find that an opportunistic female strategy, that minimizes its costs by mating with highly visible (displaying) males, often beats other alternatives. It typically resists invasion attempts of genotypes that mate randomly in the population genetic sense, as well as invasion of stricter ways of being choosy (which are potentially costly if choice requires e.g. active rejection of all males who do not presently display, or risky travel to lekking sites). Our model can produce a wide range of male time budgets (display vs. self-maintenance). This includes cases of alternative mating tactics where males in good condition spend much time displaying, while those in poor condition never display yet, importantly, gain some mating success due to females not engaging in rejection behaviours should these be very costly to express.Significance statementIn many species, males spend much time and energy on displaying to attract females, but it is not always clear what females gain from paying attention to male displays. The tradition in mathematical models attempting to understand the situation is to assume that random mating is the least costly option for females. However, random mating in the population genetic sense requires females to behave in a manner that equalizes mating success between displaying and non-displaying males, and here we point out that this is biologically unlikely. Opportunistically mating females can cause males to spend much of their time budgets displaying and will shorten male lifespans in a quality-dependent manner.

P679. Testing for Sex Differences in Callous-Unemotional Traits and Fear Reactivity

There is a longstanding view that youth with callous-unemotional traits are fearless, and fearlessness plays a critical role in the development of callous-unemotional traits. Yet, biological evidence supporting this link is lacking, and even fewer studies explore if this is true for both males and females. This study tested if callous-unemotional traits in adolescent males and females were related to sympathetic nervous system (SNS) reactivity during a fear induction task.

When Older Males Sire More Offspring—Increased Attractiveness or Higher Fertility?

In birds with extrapair mating, older males usually have higher fertilization success than younger males. Two hypotheses can potentially explain this pattern: 1) females prefer older, and often more ornamented males, or 2) older males invest more in reproduction and fertility than younger males. Here we studied factors associated with age-related male fertilization success in a population of barn swallows Hirundo rustica in Canada. We document that male fertilization success increased gradually up to a minimum age of four-year old. The age effect was especially strong for the number of extrapair offspring obtained and the occurrence of a second brood. The higher fertilization success of older males was also associated with an early start of breeding in spring. The length of the elongated outermost tail feathers, a postulated male ornament preferred by females, also increased with age (in both sexes), but it was not a significant predictor of male fertilization success within age classes. Male fertility traits, especially testis size, but also sperm motility and sperm velocity, increased significantly across age groups. Our results suggest that the higher fertilization success by older males is due to their higher reproductive investments and that their longer tails are an adaptation to early arrival on the breeding grounds.Significance statementThe barn swallow is a socially monogamous passerine with extensive extrapair mating. We found that males become more successful in siring both withinpair and extrapair offspring as they become older. Their increased fertilization success was associated with a higher reproductive effort as indicated by larger testes, more motile sperm, and an earlier start of breeding in spring. The length of the outer tail feathers increased with age in both sexes, but long tails did not enhance male fertilization success among males of the same age. Long tails are probably an adaptation to rapid migration and earlier arrival on the breeding grounds. Our findings suggest that the commonly observed age-related increase in male fertilization success in passerine birds is better explained by life history theory than by sexual selection theory.