Male Size Research Articles

The content of reindeer male vocalisations: acoustic cues to age and size

ABSTRACT Some acoustic parameters of animal vocalisations have been shown to reliably indicate male quality and play a role in mate and rival assessment. Reindeer possess a peculiar vocal tract anatomy involving a laryngeal air sac which probably acts as an additional filter, making it a candidate species for novel investigations in the field of bioacoustics. We investigated whether some acoustic parameters of male rutting vocalisations were good indicators of age and body weight (used as an index for body size). We did this by performing acoustic analyses using recordings collected from a semi-domesticated reindeer population in northern Finland. We found the age of subadult males (aged 2.5–4.5 years) to be negatively correlated with formant F3 and formant spacing, suggesting that their vocalisations convey information on the caller’s age. Individual formant frequencies were not affected by male body weight, but formant spacing was lower in heavier males. Despite the presence of the laryngeal air sac, formant spacing seems to be an acoustic parameter influencing mate and rival assessment in reindeer as it gives an honest indication of male body size. We discuss the importance of reliable acoustic cues to quality indices in sexual selection contexts.

Correlating male white‐tailed deer antler size with female body mass across multiple spatial scales

AbstractManagers use morphometric data collected from harvested animals as indicators of nutritional condition. Antler or horn size often are considered in ungulates, but there are problems associated with biased and limited harvest data available from male animals in many populations. Adult female body mass also may be collected, but little information exists on how male antler size scales with female body mass. We evaluated the relationship between property‐specific mature male white‐tailed deer (Odocoileus virginianus) antler size and adult female body mass from harvest data collected at 2 spatial scales. Regression predicted a 4.4‐cm increase in average mature male antler size for every 1‐kg increase in female body mass from 31 properties across the eastern United States, 2015–2023. Adult female mass explained 64% of the variation in mature antler size, and including latitude as a covariate did not improve model fit. When we considered data from 174 properties in Mississippi, USA, 1991–1994, we predicted a 4.7‐cm increase in average mature male antler size for every 1‐kg increase in adult female body mass. Including soil resource region in the Mississippi model explained 48% of the variation in mature male antler size by accounting for differences in average sizes across regions. Our results indicate average female body mass correlates with mature male antler size at multiple spatial scales. We recommend managers collect body mass and age from harvested female deer, as female mass represents a useful metric to track management progress and predict changes in antler size.

Human Male Body Size Predicts Increased Knockout Power, Which Is Accurately Tracked by Conspecific Judgments of Male Dominance

Humans have undergone a long evolutionary history of violent agonistic exchanges, which would have placed selective pressures on greater body size and the psychophysical systems that detect them. The present work showed that greater body size in humans predicted increased knockout power during combative contests (Study 1a-1b: total N = 5,866; Study 2: N = 44 openweight fights). In agonistic exchanges reflective of ancestral size asymmetries, heavier combatants were 200% more likely to win against their lighter counterparts because they were 200% more likely to knock them out (Study 2). Human dominance judgments (total N = 500 MTurkers) accurately tracked the frequency with which men (N = 516) knocked out similar-sized adversaries (Study 3). Humans were able to directly perceive a man’s knockout power because they were attending to cues of a man’s body size. Human dominance judgments—which are important across numerous psychological domains, including attractiveness, leadership, and legal decision-making—accurately predict the likelihood with which a potential mate, ally, or rival can incapacitate their adversaries.

Male proboscis monkey cranionasal size and shape is associated with visual and acoustic signalling

The large nose adorned by adult male proboscis monkeys is hypothesised to serve as an audiovisual signal of sexual selection. It serves as a visual signal of male quality and social status, and as an acoustic signal, through the expression of loud, low-formant nasalised calls in dense rainforests, where visibility is poor. However, it is unclear how the male proboscis monkey nasal complex, including the internal structure of the nose, plays a role in visual or acoustic signalling. Here, we use cranionasal data to assess whether large noses found in male proboscis monkeys serve visual and/or acoustic signalling functions. Our findings support a visual signalling function for male nasal enlargement through a relatively high degree of nasal aperture sexual size dimorphism, the craniofacial region to which nasal soft tissue attaches. We additionally find nasal aperture size increases beyond dental maturity among male proboscis monkeys, consistent with the visual signalling hypothesis. We show that the cranionasal region has an acoustic signalling role through pronounced nasal cavity sexual shape dimorphism, wherein male nasal cavity shape allows the expression of loud, low-formant nasalised calls. Our findings provide robust support for the male proboscis monkey nasal complex serving both visual and acoustic functions.

Influence of prey availability on the movement pattern of breeding saker falcons (Falco cherrug) in Mongolia

Abstract As an apex predator in arid steppe, saker falcon plays a crucial role in maintaining ecosystem balance. Understanding their movement patterns concerning conspecific competition and prey availability is important for their conservation. We aim to understand how movement pattern of breeding saker falcons relates to prey availability. Twelve adult sakers were tracked during the breeding seasons, using satellite transmitters. Throughout the breeding season, sakers exhibited territorial behaviour, with minimal overlap in range use among neighbouring conspecifics. Males occupied larger areas (mean = 2,397 ha, median = 1,221 ha), compared to females (mean = 1,241 ha, median = 554 ha), and it remained consistent throughout breeding season. Female home range size increased notably during late nestling stage and post-fledging dependence periods, indicating release from brooding constraints. Notably, we found a negative relationship between male home range size and prey availability. In high rodent density areas, males occupied smaller areas (mean = 1,135 ha, median = 1,034 ha), contrasting with low rodent density areas (mean = 6,815 ha, median = 6,516 ha). However, no significant relationship was observed between female home range size and prey availability. We also noted instances of nest abandonment and early dispersal behaviour in some females, potentially influenced by a handicapping effect of tagging. Our findings offer valuable insight into how prey availability shapes saker falcon space use and defines their spatial requirements for successful breeding. This knowledge is crucial for the conservation and management of globally endangered saker falcons, informing targeted habitat protection and resource management strategies.

The relationship of the male's proctodeal gland size to sperm-egg interaction and the duration of fertility in Japanese quail

In avian species, male fertility significantly impacts reproductive success. This study investigates the relationship between proctodeal gland size in male Japanese quails and sperm function, as well as female fertility duration. Six hundred adult Japanese quails were selected and housed in individual cages. Males (n = 300) were divided into 6 groups (50/group) based on the size of their proctodeal glands. Females (n = 300) were randomly assigned to corresponding groups. After acclimatization, sperm kinematics and the frequency and weight of foam discharge were evaluated. Males were paired with females for 24 h, and eggs were collected for 20 d postcopulation. Eggs were incubated to assess fertility duration. Fresh eggs (n = 20/group/d) were used to assess sperm penetration into the perivitelline membrane on the 2nd, 9th, and 16th d postinsemination. Plasma testosterone levels and the testes' relative weight were determined. The results indicated a significant increase (p < 0.0001) in sperm concentration, total and progressive motility, and nearly all sperm kinematic parameters such as VSL, VCL, VAP, LIN, WOB, and STR values as the size of the proctodeal gland increased. Quails copulated with males having a small and average proctodeal gland area (<400 mm2) laid fertile eggs for a shorter period and had significantly fewer sperm penetration holes than those mated with males having a larger proctodeal gland area (>400 mm2). The proctodeal gland size was positively correlated with testicular weight, plasma testosterone concentrations, and sperm kinetic variables. The results indicate that the size of the proctodeal gland in males can be used to predict sperm function and the duration of fertility in Japanese quail.

The influence of the post-autotomy regeneration of a sexual trait and mating tactics in a fiddler crab

Abstract Male fiddler crabs own an enlarged claw which is a weapon and an ornament. The enlargement of this claw begins from the juvenile stage and continues throughout life. Males may voluntarily lose (i.e., autotomize) this claw. After several molts males may regenerate a new claw, called leptochelous, which acquires a similar length but a lower muscle mass area than the original one, called brachychelous. In some species, regenerated claws develop permanently as leptochelous, the population having 2 discrete claw morphologies. Other species present morphological variations with leptochelous and brachychelous being 2 ends of a continuum. In the species Leptuca uruguayensis, we studied the morphological variation of this enlarged claw, whether it may be caused by its regeneration at different male sizes, and its consequences on mating success. We found that claws could not be discriminated as discrete morphs, suggesting a morphological continuum from brachychelous to leptochelous. Regenerated claws in the laboratory were initially small and proportional to body size, although a field experiment confirmed that claw size is recovered after several molts. Morphological variation may be caused by energetic limitations where males of different sizes must differently trade-off between restitution of claw length (ornament function) or claw muscle area (weapon function). Fiddler crabs use 2 mating tactics with different levels of female choice. However, regardless of the mating tactic, leptochelous males were at a disadvantage at high densities, although not at low densities, suggesting that the consequences of autotomy and regeneration on mating success may depend on the social context.

Patrilineal segmentary systems provide a peaceful explanation for the post-Neolithic Y-chromosome bottleneck

Studies have found a pronounced decline in male effective population sizes worldwide around 3000–5000 years ago. This bottleneck was not observed for female effective population sizes, which continued to increase over time. Until now, this remarkable genetic pattern was interpreted as the result of an ancient structuring of human populations into patrilineal groups (gathering closely related males) violently competing with each other. In this scenario, violence is responsible for the repeated extinctions of patrilineal groups, leading to a significant reduction in male effective population size. Here, we propose an alternative hypothesis by modelling a segmentary patrilineal system based on anthropological literature. We show that variance in reproductive success between patrilineal groups, combined with lineal fission (i.e., the splitting of a group into two new groups of patrilineally related individuals), can lead to a substantial reduction in the male effective population size without resorting to the violence hypothesis. Thus, a peaceful explanation involving ancient changes in social structures, linked to global changes in subsistence systems, may be sufficient to explain the reported decline in Y-chromosome diversity.

On features of the life cycle of humpback shrimp Pandalus hypsinotus (Decapoda, Pandalidae) in the Tatar Strait

The study is based on biological analyses of &gt; 80,000 ind. of Pandalus hypsinotus collected in trawl surveys and trap fishery in the Tatar Strait in 2010–2022. Due to the lack of age-recording structures, the size-age structure of shrimp is usually determined by various statistical methods, each of which has some limitations and drawbacks. The modal analysis of size-sex composition dynamics is used in this study, including tracing the growth of strong year-classes. The analysis takes into account the dynamics of major seasonal events such as group molting, spawning, and larval hatching. The reproductive cycle of females is assumed to be 2 years. Based on results of the analysis, the life cycle of humpback shrimp in the Tatar Strait is as follows. After the larvae hatch from eggs in April-May, immature shrimp spend the first year of their life at the depths &lt; 70 m, where they reach the carapace length of 9–15 mm, with a modal size of 11–12 mm. In the second year, they grow to the length of 20–22 mm, on average, then become males and migrate to deeper layer where join the adults. Further growth is described on the data for the strong year-class of 2010: the modal size of males reaches 26–27 mm at age 3 years, 29–30 mm — at age 4, 32–33 mm — at age 5, and 35–36 mm — at age 6. Gender transition of shrimp begins at age 5+, but most males become hermaphroditic at the age 6+. The modal size of intersex hermaphrodites ranges from 37 to 39 mm. At the age of 6 years and 9 months, the intersexes spawn en masse and transform into females. The first larval hatching of new females occurs after 15 months, i.e. at exactly 8 years of age. At least three cycles of spawning (larvae release) are assumed for females, taking into account their polymodal size composition and dynamics of their size increments per molt by age. In assumption of 2-year reproductive cycle, the female stage lasts 6 years. Thus, the total life span for the most of humpback shrimps is estimated to be 12 years (6 years before gender transition and 6 years after). Apparently, a small number of them live 14 years and spawn four times, and some can live up to 16 years and spawn five times.

Is promiscuity the key? Multiple paternity in the garden dormouse (Eliomys quercinus)

Many mammals have a promiscuous mating system with multiple sired litters. Promiscuity can increase the genetic variability, reduce the risk of inbreeding, and increase the effective population size, and is therefore crucial for preventing genetic loss and maintaining adaptability. This is particularly true for small and threatened populations. The garden dormouse (Eliomys quercinus) is a threatened species, which exhibited a drastic decline over the last 20–30 years. The aim of this study was therefore to investigate the mating system of the garden dormouse in mountain forest habitat by parentage analyses using 5 polymorphic microsatellite markers combined with morphometric data and information about the nesting behavior. Genetic parentage analyses revealed that 64% (9 of 14) of the litters were sired by at least two males, suggesting that garden dormice have a promiscuous mating system. The genetic findings were further supported by indirect indicators of promiscuity, such as testes, that were nearly four times larger than predicted for a rodent of its body mass and only slight male biased sexual size dimorphism. The finding of a promiscuous mating system in garden dormice should be taken into account in future conservation efforts. Due to its habitat preferences and limited dispersal potential garden dormice are vulnerable to forest fragmentation. The connection of suitable habitats facilitates dispersal and promotes access to potential mating partners, which could be especially important for populations colonizing new habitats. Access to potential mates may also reduce inbreeding, loss of genetic variability which is crucial for populations viability and survival.

Multiple invasions and predation: The impact of the crayfish Cherax quadricarinatus on invasive and native snails

AbstractThe pace of biological invasions has increased in recent decades, leading to multiple invasions and the potential dominance of invasive species, destabilizing local ecological networks. This provides opportunities to study new ecological species interactions, including predation. Tropical freshwaters have been particularly concerned by aquatic invasions and we focused here on the Martinique island (Lesser Antilles). We examined the predator–prey relationships involving invasive Thiarid snails (Tarebia granifera and Melanoides tuberculata) and the native Neritina punctulata, both confronted with a newcomer predator, the redclaw crayfish (Cherax quadricarinatus). We conducted several mesocosm experiments to assess the impact of crayfish predation on snail survival and the passive and active antipredator responses of snails. A first experiment indicated snail survival rates between 50% and 80%, depending on crayfish size and sex. Notably, there was a negative correlation between snail survival and male crayfish size and the predation method (shell crushing vs. “body sucking”) varied with crayfish size. The second experiment suggested no refuge size for snails, with both very small (&lt;5 mm) and very large (&gt;5 mm) unable to escape predation, regardless of crayfish size (from 77 to 138 mm) or sex. Finally, we investigated the escape behavior of Thiarids regarding three crayfish cues. Melanoides tuberculata tend to bury in the substrate and T. granifera to climb up aquarium walls, what was expected from their shell morphologies, and both responding to crayfish cues within minutes. Overall, C. quadricarinatus proves to be an efficient snail predator with limited escape options for snails, potentially contributing to the decline of certain snail populations in Martinique. This omnivorous predator might impact other native species across different groups, including shrimps and fish. Our study underscores the urgent need for monitoring efforts, solidifying the redclaw crayfish reputation as a dangerous invasive species for freshwater macrobenthic faunas worldwide.

Potential strategic allocation of nuptial gift proteins of the neotropical katydid Conocephalus ictus (Orthoptera Tettigoniidae)

In many katydids, the male feeds his mate with a large gelatinous spermatophore. While providing large spermatophores can increase female fecundity and lifespan, it may also decrease their sexual receptivity, benefiting male fitness. Allocating resources to these edible gifts may entail a lower apportionment of them to other functions, generating a trade-off between somatic and reproductive functions. Despite their effect on male and female fitness, little is known of the compounds associated with katydid spermatophores. Our study found 177 different putative proteins in the spermatophore of Conocephalus ictus, with no correlation between male body size with spermatophore mass, number, concentration and mass of proteins. However, we did observe a negative relationship between male forewing length and protein concentration, and a negative relationship between the mass of the spermatophore transferred to the females and their body size, suggesting a resource allocation trade-off in males, but also strategic transference of resources based on female quality.

Aesthetic preference for artificially selected color variant affects mate choice copying behavior in female Poecilia latipinna.

Three experiments were conducted examining whether an artificially selected "gold" color variant in female "models" affects mate choice copying behavior in sailfin mollies (Poecilia latipinna). Experiment I consisted of a pair of female preference assays, first assessing preference for male body size, followed by a mate choice copying assay that paired a model female with the smaller, non-preferred male from the initial preference test. Female subjects were divided into three groups that used either a wildtype female model, an artificially selected "gold" variant (cultivated within the aquarium fish trade) model, or control wherein no model was presented. Results showed females consistently copied the model's choice, switching preferences from the larger to smaller male when paired with a model regardless of color. In the second experiment wildtype females were presented with a pair of size-matched dummy males both of which paired with model females (one gold and the other wild type). Subjects consistently preferred the male previously paired with the gold- over the male with the wildtype-model, suggesting pre-existing sensory/perceptual biases may have affected their mate choice copying behavior. Previous studies have offered evidence for the spread of novel traits in males via sensory exploitation. However, these results indicate such biases may influence courtship behavior in circumstances where the novel trait is expressed in females as well. For the third experiment, wildtype females were presented with a choice between gold vs wildtype dummy males, the results of which revealing significant preferences for gold. In a follow-up assay pairing a wild type model with the non-preferred wildtype male, females maintained their preference for gold males despite the conflicting social driver of mate choice copying. These data offer evidence for the existence of a perceptual/cognitive bias in the context of mate choice copying, favoring the gold phenotype and/or novelty in general.

Filling the gaps in ecology of tropical tiger beetles (Coleoptera: Cicindelidae): first quantitative data of sexual dimorphism in semi-arboreal Therates from the Philippine biodiversity hotspot.

Sexual dimorphism, driven by sexual selection, leads to varied morphological distinctions in male and female insects, providing insights into selection pressures across species. However, research on the morphometric variability within specific taxa of tiger beetles (Coleoptera: Cicindelidae), particularly arboreal and semi-arboreal species, remains very limited. We investigate sexual dimorphism in six semi-arboreal Therates tiger beetle taxa from the Philippines, focusing on morphological traits. We employed morphometric measurements and multivariate analyses to reveal patterns of sexual dimorphism between sexes within the taxa. Our results indicate significant sexual dimorphism in elytra width, with females consistently displaying broader elytra, potentially enhancing fecundity. Notable sexual size dimorphism was observed in Therates fulvipennis bidentatus and T. coracinus coracinus, suggesting heightened sexual selection pressures on male body size. Ecological factors, mating behavior, and female mate choice might contribute to the observed morphological variation. These findings emphasize the need for further studies to comprehend mating dynamics, mate choice, and ecological influences on morphological variations in semi-arboreal and arboreal tiger beetles.

(267) Penile Length and Circumference in Vietnamese Men

Abstract Introduction Penile size has long been an important fixation in men's lives. Establishing what the normal size of the penis is very important to have a yardstick for men, which is a challenge and depends on the culture, race, and form of measurement applied. Objective To evaluate the size of the penis in flaccidity, erection, and stretch of Vietnamese men. Methods A total of 259 men who visited the Andrology and Fertility Hospital of Hanoi, VietNam were involved in the study between October 2022 and April 2023. Penile measurements (flaccid, erect length/circumference, stretched length) were predominantly taken by 1 investigator using a tape measure and the same measurement technique. All statistical analyses were completed using STATA 17.0. Statistical analysis was performed with the Spearman correlation as tested by the Kolmogorov–Smirnov test (p&amp;lt;0.05). Results The mean age of 259 patients was 29,24 (range: 15–48). The mean penile lengths were: flaccid length 9.21 cm (SD 1.71 cm), flaccid circumference at the middle of the shaft 8.25 cm (SD 0.96 cm), erect length 13.22 (SD 1.46cm), erect circumference at the middle of the shaft 10.42 cm (SD 0.94 cm), and stretched length 12.47 cm (SD 1.61 cm). The mean testicular volume was 12.47 mL (SD 6.37 mL) and 12.65 (SD 4.03 mL) for the left and right testicles, respectively. Stretched length is most closely correlated with erect length with r=0.68. We also observed that the testicular volume, erect length was a significant inverse correlation with age, which ranged from r = -0.14 to -0.21. Conclusions The results of this study help to establish a reference range for male genital size in Vietnam, which should be helpful for urologists and andrologist in counseling patient Disclosure No.

The condition-dependence of male genital size and shape.

The male genitals of internal fertilisers evolve rapidly and divergently, and sexual selection is generally responsible for this. Many sexually selected traits are condition-dependent-with their expression dependent upon the resources available to be allocated to them-as revealed by genetic or environmental manipulations of condition. However, it is not clear whether male genitals are also condition-dependent. Here we manipulate condition in two ways (via inbreeding and diet) to test the condition-dependence of the genital arch of Drosophila simulans. We found that genital size but not genital shape suffered from inbreeding depression, whereas genital size and shape were affected by dietary manipulation of condition. The differential effects of these treatments likely reflect underlying genetic architecture that has been shaped by past selection: inbreeding depression is only expected when traits have a history of directional selection, while diet impacts traits regardless of historical selection. Nonetheless, our results suggest genitals can be condition-dependent like other sexually selected traits.

Investigating the Effects of Male Size and Pronotal Glowspots on Female Courtship Behaviour of the Glowspot Cockroach (Lucihormetica verrucosa)

Investigating the Effects of Male Size and Pronotal Glowspots on Female Courtship Behaviour of the Glowspot Cockroach (Lucihormetica verrucosa)

The origins and drivers of sexual size dimorphism in sharks.

While sexual size dimorphism (SSD) is abundant in nature, there is huge variation in both the intensity and direction of SSD. SSD results from a combination of sexual selection for large male size, fecundity selection for large female size and ecological selection for either. In most vertebrates, it is variation in the intensity of male-male competition that primarily underlies variation in SSD. In this study, we test four hypotheses regarding the adaptive value of SSD in sharks-considering the potential for each of fecundity, sexual, ecological selection and reproductive mode as the primary driver of variation in SSD between species. We also estimate past macroevolutionary shifts in SSD direction/intensity through shark phylogeny. We were unable to find evidence of significant SSD in early sharks and hypothesise that SSD is a derived state in this clade, that has evolved independently of SSD observed in other vertebrates. Moreover, there is no significant relationship between SSD and fecundity, testes mass or oceanic depth in sharks. However, there is evidence to support previous speculation that reproductive mode is an important determinant of interspecific variation in SSD in sharks. This is significant as in most vertebrates sexual selection is thought to be the primary driver of SSD trends, with evidence for the role of fecundity selection in other clades being inconsistent at best. While the phylogenetic distribution of SSD among sharks is superficially similar to that observed in other vertebrate clades, the relative importance of selective pressures underlying its evolution appears to differ.

Study on Rachis Characters of Different Cultivars of Banana

Banana is one of the most important staple food around tropics. Bananas can be eaten as green when it is starchy. These crops are the most important components for food security around world by providing income to the farming community through local trade. This experiment was conducted to study the rachis behaviour and male bud characteristics of ABB genomic group and AAB genomic group banana cultivars. Here 5 cultivars under ABB genomic group (Behula, Bara Beglo, Bluggoe, Green Bombay, Pantharaj) and 5 cultivars of AAB genomic group (Dudhsagar, Martaman, Manohar, Desi Malbhog, Kalibhog) were observed. All of these 10 cultivars showed different characteristics in case of male bud, like male bud shape, male bud size, colour of the bract (external face), male bract lifting, wax on the bract, male flower behaviour, compound tepal basic colour, anther colour, stigma colour, ovary shape and dominant colour of male flower, all these were explained in details in this study.

Sexual dimorphism in the Neotropical snakes genus Chironius (Serpentes: Colubridae)

Abstract Sexual dimorphism is a common phenomenon among snakes, with female snakes being larger than male snakes as a recurrent pattern . However, species that show male-male combat behaviour may impose a selective advantage by developing larger bodies in male specimens, like the diurnal Chironius snakes, which display courtship and male-male combat behaviours. In this study, we analysed sexual dimorphism in body, tail, and head size, and skull size and shape in twelve species of Chironius. We investigated whether sexual dimorphism patterns could be a result of allometric growth. The absence of sexual dimorphism regarding body and head length was the main pattern revealed by our analyses. Sexual dimorphism characterized by larger body and head sizes in males was observed in Chironius bicarinatus, Chironius foveatus, and Chironius fuscus. Only females of Chironius exoletus exhibited larger body and head sizes than males. Regarding the shape of the head, six species showed sexual divergences, with enlarged or robust heads. Sexual dimorphism in skull shape seems related to selection in Chironius flavolineatus, with no allometric influences. Larger tails in males of C. fuscus, C. flavolineatus, and Chironius quadricarinatus may represent an advantageous defensive strategy. Finally, the lack of divergence in tail length in the remaining species probably evolved due to arboreal habits in Chironius.