Male Life History Research Articles

No evidence for relationship between paternal post-partum depressive symptoms and testosterone or cortisol in first-time fathers.

Male life history strategies are regulated by the neuroendocrine system. Testosterone (T) and cortisol regulate male behaviors including parenting and facilitate managing tradeoffs at key transitions in development such as first-time fatherhood. Both hormones demonstrate marked fluctuations in the postnatal period, and this presents an opportunity to investigate the role of T and cortisol in postpartum depressive symptoms-comparably less studied in fathers than in mothers in the evolutionary literature. Prior work on depressive symptoms has yet to integrate insights from the "dual hormone hypothesis (DHH)" which has focused on how T and cortisol interact to jointly regulate traits associated with dominance and status-seeking (i.e., mating effort) but has yet to be included in models of parenting effort. In this research, we use secondary data to investigate the relationship between DHH and traits ostensibly opposed to status seeking (i.e., depressive symptoms). First-time fathers (n = 193) provided morning saliva samples 10 months following parturition and reported on the presence of depressive symptoms (BDI-II). Responses were decomposed into three factors: cognitive, affective, and somatic. Using hybrid latent variable structural equation modeling, we did not find evidence that T predicted variability in cognitive, affective, or somatic depressive symptom factors. We found a null effect for cortisol as well. Finally, we could not find evidence that the DHH variable (T × cortisol interaction) predicted any variability in cognitive, affective, or somatic depressive symptoms. While we did not find evidence to support our hypotheses using a secondary data set, this study contributes to research on the neuroendocrinology of depression in fathers. Discussion focuses on the limitations of sample demographics, timing of saliva and self-report collection, and the lack of extant theory specific to paternal postpartum depression.

Is personality and its association with energetics sex‐specific in yellow‐necked mice Apodemus flavicollis?

AbstractFor the last two decades, behavioral physiologists aimed to explain a plausible covariation between energetics and personality, predicted by the “pace‐of‐life syndrome” (POLS) hypothesis. However, the results of these attempts are mixed with no definitive answer as to which of the two most acknowledged models “performance” or “allocation” predicts covariation between consistent among‐individual variation in metabolism and repeatable behavior (animal personality). The general conclusion is that the association between personality and energetics is rather context‐dependent. Life‐history, behavior, and physiology as well as its plausible covariation can be considered a part of sexual dimorphism. However, up to now, only a few studies demonstrated a sex‐specific correlation between metabolism and personality. Therefore, we tested the relationships between physiological and personality traits in a single population of yellow‐necked mice Apodemus flavicollis in the context of a plausible between‐sexes difference in this covariation. We hypothesized that the performance model will explain proactive behavior in males and the allocation model will apply to females. Behavioral traits were determined using the latency of risk‐taking and the open field tests, whereas the basal metabolic rates (BMR) was measured using indirect calorimetry. We have found a positive correlation between body mass‐adjusted BMR and repeatable proactive behavior in male mice, which can support the performance model. However, the females were rather consistent mainly in avoidance of risk‐taking that did not correlate with BMR, suggesting essential differences in personality between sexes. Most likely, the lack of convincing association between energetics and personality traits at the population level is caused by a different selection acting on the life histories of males and females. This may only result in weak support for the predictions of the POLS hypothesis when assuming that only a single model explaining the link between physiology and behavior operates in males and females. Thus, there is a need to consider the differences between sexes in behavioral studies to evaluate this hypothesis.

Density-related reproductive costs and natal conditions predict male life history in a highly polygynous mammal

Density-related reproductive costs and natal conditions predict male life history in a highly polygynous mammal

Sex-Biased Differences in Infant Mortality and Life Expectancy at Síi Túupentak , an Ancestral Ohlone Village in Central California (ca. 540–145 cal. BP)

ABSTRACT: Síi Túupentak (CA-SCA-565/H) is a late precontact ancestral Ohlone village and cemetery site in Central California (ca. 540–145 cal. BP). Integration of proteomic, genomic, and osteological analyses provided highly confident biological sex estimates for remains of most individuals at this site (65 of 76), spanning all age groups, from perinatal infants to aged adults. Based on these relatively comprehensive data, it was possible to generate sex-specific Kaplan-Meier survival curves for this burial population of sedentary hunter-gatherers. As was common among societies predating modern Western medicine and antibiotics, infant mortality was high for both males and females. However, male infants (from birth to 5 years of age) appear to have died at nearly twice the rate of female infants (10 of 33 males vs. 5 of 32 females) and had a mean age of survival at birth of only 19 years, compared to 30 years for females. The difference in male and female survival was statistically significant by log-rank test ( p = 0.005). Compared to survival curves for other societies predating modern Western medicine and antibiotics, including American-era historical deaths recorded for a cemetery in San Francisco, this bias is larger than might be expected. We suspect the pattern of sex-biased infant mortality at Síi Túupentak could relate to an intrinsic survival advantage for female infants, combined with extrinsic factors such as environmental pathogens, nutritional stress, and gendered differences in weaning patterns detected through stable isotope analyses. Using isotopic data on weaning ages and ethnographic accounts of gendered foraging activities, we focus on the potential role of sex-biased differences in weaning patterns and highlight potential demographic and social implications. Broader application of proteomic and genomic sex estimation would allow sex-biased differences in nutrition and health, as well as social and cultural aspects of male and female life histories, to be compared across a wide range of archaeologically known hunter-gatherer societies.

Contrasting Male and Female Dietary Life Histories: A Case Study at an Ancestral Muwekma Ohlone Heritage Site in San Jose, California

ABSTRACT: Stable carbon and nitrogen isotope analyses of bones and teeth at the ancestral heritage Muwekma Ohlone site of Yakmuy ́Ooyákma-tka (“Place of the East Ridge Site”; CA-SCL-215) reveal significant differences in the dietary life history of males and females. Overall, isotope data indicate that site inhabitants were primarily dependent on low-trophic-level foods, likely plants, and minor amounts of marine food for their main source of dietary protein. From tooth dentin serial samples, we found that males and females were similar for δ13C in early childhood (age 1–9 years), but boys were elevated in δ15N by 0.6–1.0‰ relative to girls, indicating boys were accessing slightly greater amounts of higher-trophic-level foods, such as meat from game. The sex-biased difference in δ15N diminishes during the second decade of life, as female δ15N values increase and become equal to males. However, a difference in δ13C emerges during the second decade: female δ13C values are elevated relative to males. This could indicate that teenage females consumed higher amounts of low-trophic-level, marine-derived protein, such as shellfish. During later adult years the difference in δ13C disappears, while males again show an increase in δ15N relative to females. Although these differences are small, they reveal important sex-biased life history patterns during childhood and adulthood in this ancient community.

Social correlates of androgen levels and dispersal age in juvenile male geladas

Androgens offer a window into the timing of important male life history events such as maturation. However, when males are the dispersing sex, piecing together normative androgen profiles across development is challenging because dispersing males are difficult to track. Here, we examined the conditions that may be associated with male androgen status (via fecal androgen metabolites, fAMs) and age at dispersal in wild male geladas (Theropithecus gelada). Gelada male life histories are highly variable — dispersal may occur before sexual maturation, dispersal itself can be immediate or drawn out, and, due to their multi-leveled society, social conditions affecting dispersal can vary for juveniles living in different reproductive units within the same band. Using longitudinal data from known natal males, we examined how androgen levels and age at dispersal were associated with: (1) access to maternal resources (i.e., maternal rank, birth of a younger sibling, experiencing maternal loss), and (2) access to male peers (i.e., number of similar-aged males in their unit). We found that androgens were significantly lower in males with high-ranking mothers (in males >2.5 years of age; infant androgens were unrelated) and that having more male peers in their social group and larger groups overall predicted an earlier age at dispersal. Moreover, dispersal in geladas was not preceded or followed by a surge in androgen levels. Taken together, results suggest that social environments can cause individual variation in androgens and dispersal age. Whether this variation leads to differences in male fitness in later life remains to be determined.

Caste, Sex, and Parasitism Influence Brain Plasticity in a Social Wasp

Brain plasticity is widespread in nature, as it enables adaptive responses to sensory demands associated with novel stimuli, environmental changes and social conditions. Social Hymenoptera are particularly well-suited to study neuroplasticity, because the division of labor amongst females and the different life histories of males and females are associated with specific sensory needs. Here, we take advantage of the social waspPolistes dominulato explore if brain plasticity is influenced by caste and sex, and the exploitation by the strepsipteran parasiteXenos vesparum.Within sexes, male wasps had proportionally larger optic lobes, while females had larger antennal lobes, which is consistent with the sensory needs of sex-specific life histories. Within castes, reproductive females had larger mushroom body calyces, as predicted by their sensory needs for extensive within-colony interactions and winter aggregations, than workers who frequently forage for nest material and prey. Parasites had different effects on female and male hosts. Contrary to our predictions, female workers were castrated and behaviorally manipulated by female or male parasites, but only showed moderate differences in brain tissue allocation compared to non-parasitized workers. Parasitized males maintained their reproductive apparatus and sexual behavior. However, they had smaller brains and larger sensory brain regions than non-parasitized males. Our findings confirm that caste and sex mediate brain plasticity inP. dominula, and that parasitic manipulation drives differential allocation of brain regions depending on host sex.

Mother's curse is pervasive across a large mitonuclear Drosophila panel.

The maternal inheritance of mitochondrial genomes entails a sex‐specific selective sieve, whereby mutations in mitochondrial DNA can only respond to selection acting on females. In theory, this enables male‐harming mutations to accumulate in mitochondrial genomes as long as they are neutral, beneficial, or only slightly deleterious to females. Ultimately, this bias could drive the evolution of male‐specific mitochondrial mutation loads, an idea known as mother's curse. Earlier work on this hypothesis has mainly used small Drosophila panels, in which naturally sourced mitochondrial genomes were coupled to an isogenic nuclear background. The lack of nuclear genetic variation in these designs has precluded robust generalization. Here, we test the predictions of mother's curse using a large Drosophila mitonuclear genetic panel, comprising nine isogenic nuclear genomes coupled to nine mitochondrial haplotypes, giving a total of 81 different mitonuclear genotypes. Following a predictive framework, we tested the mother's curse hypothesis by screening our panel for wing size. This trait is tightly correlated with overall body size and is sexually dimorphic in Drosophila. Moreover, growth is heavily reliant on metabolism and mitochondrial function, making wing size an ideal trait for the study of the impact of mitochondrial variation. We detect high levels of mitonuclear epistasis, and more importantly, we report that mitochondrial genetic variance is larger in male than female Drosophila for eight out of the nine nuclear genetic backgrounds used. These results demonstrate that the maternal inheritance of mitochondrial DNA does indeed modulate male life history traits in a more generalisable way than previously demonstrated.

Individuality meets plasticity: Endocrine phenotypes across male dominance rank acquisition in guinea pigs living in a complex social environment

The time of dominance rank acquisition is a crucial phase in male life history that often affects reproductive success and hence fitness. Hormones such as testosterone and glucocorticoids can influence as well as be affected by this process. At the same time, hormone concentrations can show large individual variation. The extent to which such variation is repeatable, particularly in dynamic social settings, is a question of current interest. The aim of the present study was therefore to investigate how dominance rank and individual differences contribute to variance in hormone concentrations during male rank acquisition in a complex social environment. For this purpose, dominance rank as well as baseline testosterone, baseline cortisol, and cortisol responsiveness after exposure to a novel environment were determined in colony-housed guinea pig males from late adolescence through adulthood. Hormone-dominance relationships and repeatability of hormone measures beyond their relation to rank were assessed. There was a significant positive relationship between baseline testosterone and rank, but this link became weaker with increasing age. Baseline cortisol or cortisol responsiveness, in contrast, were not significantly related to dominance. Notably, all three endocrine parameters were significantly repeatable independent of dominance rank from late adolescence through adulthood. Baseline testosterone and cortisol responsiveness showed a significantly higher repeatability than baseline cortisol. This suggests that testosterone titres and cortisol responsiveness represent stable individual attributes even under complex social conditions.

Demographic consequences of harvesting: a case study from a small and isolated moose population

Harvesting can have a substantial impact on population dynamics and individual performance in wild populations. While the direct consequences of harvest on individual survival and population growth rate are often apparent, harvesting can also have indirect and more subtle demographic consequences. Disentangling these consequences, however, requires in-depth knowledge of individual life histories of both females and males in the population. Here, we summarise demographic research on a population where such data exist: the Vega moose population in northern Norway. In this population, vital rates vary considerably among both females and males, and harvesting increases this variation by generating positive covariation between reproductive performance and survival. The skewed age and sex structure, which is typical of many harvested populations, also has demographic consequences: it reduces the ratio of effective to total population size and influences variation in vital rates in males and females. The moose harvest at Vega is structured by age- and sex-specific quotas, but it is not intentionally selective regarding size or other phenotypic characteristics. Still, harvest selection for earlier birth rates and larger calves was apparent, likely due to habitat-performance relationships and habitat-specific harvest mortality. Together, the bulk of research on this population shows that harvesting impacts population demography through many different pathways, with some being more subtle than others. These complex pathways influence the demographic variance and affect stochastic processes such as population growth, genetic drift, and rates of evolutionary change, and they must therefore be acknowledged in management plans to achieve sustainable harvesting.

Evolutionary and Life History Insights into Masculinity and Warfare

In this paper I present, evaluate, and discuss evidence that evolutionary and life history theory can inform our understanding of violence and warfare as well as how these human challenges are influenced by the evolution of male life histories and our perceptions of masculinity. While other anthropological perspectives have interrogated the evolution of war from human and comparative contexts, few have addressed the influence of male life history variables such as age-specific mortality and reproductive constraints on the emergence and conduct of war. Other evolutionary factors worthy of consideration include sexual dimorphism, phenotypic plasticity, and paternity uncertainty. I initially present a contextual examination of the evolutionary science that underlies the engagement of human males with violence and warfare, casting particular attention on the opportunities and constraints of deploying evolutionary and life history theory. I later incorporate other variables including human variation, behavioral endocrinology, and comparative perspectives. In the latter half of this paper I suggest a novel perspective for understanding males, war, and violence by drawing on male-specific patterns of mortality, paternity uncertainty, and the evolution of male aging. While evolutionary and life history theory can provide an informative perspective to understand how males contribute to violence and warfare, there are limitations that set the stage for intellectual partnership opportunities with cultural anthropologists, psychologists, and other social scientists.

Weak relationships of parasite infection with sexual and life‐history traits in wild‐caught Texas field crickets (Gryllus texensis)

Sex differences in immune investment and infection rate are predicted due to the divergent life histories of males and females, where females invest more toward immunity due to the fitness consequences of a reduced lifespan and males allocate less toward immunity due to increased resource investment in traits critical to sexual selection. Consequently, males are expected to fight infection less adeptly, resulting in higher parasite loads relative to females across all taxa. Wild animals rarely face a single parasite within their given environment, yet nearly all studies on sex‐biased infection rates have focused on a single host–parasite relationship. Here, we investigate how simultaneous natural infections of ecto‐ and endosymbionts (i.e. both parasitic and phoretic taxa) correlate with sex biases in host immune response and reproductive investment in a field‐caught cricket, Gryllus texensis. Our comprehensive analysis found no significant sex differences in two measures of immune response (melanization and nodulation), and found no strong evidence of a sex bias in the prevalence or intensity of parasitism by the three most common parasites infecting wild G. texensis field crickets (Eutrombidiidae, gregarines, and nematodes). Two traits related to female fitness, egg number and egg size, showed no relation to parasitic infection; however, males having wider heads and poorer body condition were significantly more infected by eutrombidiid mites, gregarines, and nematodes. Despite frequent predictions of male‐biased parasitism in the literature, our results concur with many other studies indicating that the divergent life histories of males and females alone are not sufficient to explain natural infection rates in wild insects.

Fisheries-induced evolution of alternative male life history tactics in Coho salmon.

Fisheries‐induced evolution (FIE) can result when harvest imposes artificial selection on variation in heritable phenotypic traits. While there is evidence for FIE, it remains difficult to disentangle the contributions of within‐generation demographic adjustment, phenotypic plasticity, and genetic adaption to observed changes in life history traits. We present evidence for FIE using dozens of Coho salmon (Oncorhynchus kisutch) populations in which males adopt one of two age‐invariant, heritable life history tactics: most mature as large three‐year‐old “hooknose” and typically fight for spawning opportunities, while some mature as small two‐year‐old “jacks” and fertilize eggs through sneaking. The closure of a fishery targeting three‐year‐old fish provided an experimental test of the prediction that fishery‐imposed selection against hooknose males drives an evolutionary increase in the proportion of males adopting the jack tactic. The data support the prediction: 43 of 46 populations had higher jack proportions during than after the fishery. The data further suggest that changes in jack proportion were not solely the result of demographic adjustments to harvest. We suggest that systems where fisheries differentially exploit phenotypically discrete, age‐invariant life histories provide excellent opportunities for detecting FIE.

Trade-offs between age-related breeding improvement and survival senescence in highly polygynous elephant seals: Dominant males always do better.

Life history trade-off theory predicts that current reproduction can negatively affect survival and future reproduction. Few studies have assessed breeding costs for males of polygynous species compared to females, despite substantial variation in breeding success among individual males (e.g. subordinate cf. dominant breeders). Specifically, differentiating between the cost of attending breeding seasons, and the additional cost of successfully securing and mating females is lacking. We investigated whether trade-offs are present in the highly polygynous male southern elephant seal (Mirounga leonina) using 34-years of individual-level data. We compare age-specific survival, recruitment and future breeding success probabilities of pre-breeders (males yet to recruit) and breeders (subordinate and dominant social ranks) using multievent models. Pre-breeders and breeders of overlapping ages had similar survival probabilities, suggesting that there was no attendance cost for early recruits. In addition, the probability of recruiting as a dominant breeder never exceeded recruitment probability as a subordinate breeder of the same age. Therefore, older pre-breeders that delayed attendance costs generally did not improve their breeding success (probability of being dominant) at recruitment more than younger recruits. Rather, recruitment age may be a function of individual quality, with lower quality individuals requiring more time to socially mature. When comparing subordinate and dominant breeders, we found clear evidence for survival senescence, with subordinate breeders having a higher baseline mortality. In contrast, age-specific future breeding success (probability of being dominant at t+1) increased with age, with dominant breeders maintaining higher subsequent breeding success than subordinate breeders. The opposite trends in survival and future breeding success for both subordinate and dominant breeders may indicate a lifetime, population-level trade-off. However, we found no evidence to suggest that being a dominant breeder consecutively (and having a higher accumulated breeding cost) accelerated the rate of senescence when compared to individuals that were previously subordinate. Thus, males experienced actuarial senescence regardless of social rank, with dominant (and possibly high quality) breeders showing a reduced trade-off between survival and future breeding success. We make several novel contributions to understanding polygynous male life histories and southern elephant seal demography.

Erratum to: Life histories of anadromous salmon males reveal a trade-off between primary and secondary sexual traits

Erratum to: Life histories of anadromous salmon males reveal a trade-off between primary and secondary sexual traits

Effects of larval diets and temperature regimes on life history traits, energy reserves and temperature tolerance of male Aedes aegypti (Diptera: Culicidae): optimizing rearing techniques for the sterile insect programmes

BackgroundProducing high quality sterile males is vital in Aedes aegypti rear-and-release birth control strategies. Larval diets, rearing temperatures, and their interactions determine the accumulation rates of essential nutrients in larvae, but these factors have been understudied in relation to mass-rearing techniques for producing eminent males.MethodsWe compared the effects of two larval diets, a cereal-legume-based diet (Khan’s diet) and a standard larval diet developed in the FAO/IAEA Insect Pest Control Laboratory (IAEA 2 diet). Diets were tested at selected temperatures for both larval and male adult life history traits, adult extreme temperature tolerance, and mating capacity relative to energy reserves of reared male adult Ae. aegypti.ResultsKhan’s diet resulted in shorter immature development time at each test temperature (except for 25 °C) than an IAEA 2 diet. Larvae reared at 28 °C and 32 °C with Khan’s diet demonstrated low pupation rates (c.80%). We accounted for these phenomena as secondary sex ratio manipulation, because a higher proportion of male adults emerged at 28 °C and 32 °C than that for the IAEA 2 diet. In general, the pupal development time shortened as temperature increased, resulting in higher teneral energy reserves in male mosquitoes. High energy reserves allowed male mosquitoes reared with Khan’s diet to have higher adult longevity (5–6 days longer when sugar-fed and 2–3 days longer when water-fed) and tolerance of heat stress than those fed on the IAEA 2 diet. The IAEA 2 diet produced larger male mosquitoes than Khan’s diet did: mosquitoes fed on Khan’s diet were 1.03–1.05 times smaller than those fed on the IAEA 2 diet at 28 °C and 32 °C. No evidence indicated reduced mating capacity for small mosquitoes fed on Khan’s diet.ConclusionsLarvae reared at 28 °C and 32 °C with Khan’s diet were characterized by shorter immature development time compared with those fed on the IAEA 2 diet. Adult mosquitoes produced from that larval rearing condition exhibited a significant male bias, long lifespan, and better endurance against extreme temperatures relative to energy reserves. Thus, the larval diet at rearing temperature of 28 °C and 32 °C optimized rearing techniques for the sterile insect programmes. However, mating competitiveness and flight performance of adult males require further investigation.

The Viking and the Farmer: Alternative Male Life Histories Portrayed in the Romantic Poetry of Erik Gustaf Geijer

Abstract This article applies a life history model to advance the evolutionary understanding of poetry that inspired nineteenth-century Swedish National Romanticism. We show that the characters featured in two of Erik Gustaf Geijer’s poems, “The Viking” and “The Yeoman Farmer” (1811), display patterns of time perspective, mating effort, and parental invest­ment that are now recognized as central life history attributes: a fast strategy and a slow strategy, respectively. These patterns were identified by undergraduate participants (N = 427) who read excerpts of the poems that had been stripped of identifying information and mentions of romantic or sexual relationships. Participants read each poem and rated each character on validated scales of the life history dimensions of mating effort and paren­tal investment, relationship interests and attractiveness, characteristics of his developmen­tal environment, and physiological characteristics. Results are consistent with generally accepted associations in life history theory and also inform current theoretical develop­ments and debates. Geijer had an intuitive understanding of life history patterns, which he used to create recognizable characters for his Romantic depiction of Swedish history.

Life histories of anadromous salmon males reveal a trade-off between primary and secondary sexual traits

Abstract The life-history trade-off between investment in somatic growth and gonadal tissue is caused by individual energy limitations and results in individuals that adopt specific tactics to achieve reproduction. Allocation in primary and secondary sexual traits in Atlantic salmon males was studied by assessing life history traits (smolt size, sea age, growth rate) based on back-calculation of scales, ejaculate energy content (sperm ATP content, mass and density) and the size of secondary sexual traits. We found that males investing less in secondary sexual traits produce ejaculates with a higher energy content. Differences were found in the investment into primary and secondary sexual traits between fish that spent one year in the sea before returning to their spawning grounds (grilse) and multi-sea-winter adults, suggesting that different energy allocation patterns in reproductive effort reflect alternative developmental pathways. These findings are consistent with the pattern where multi-sea-winter male ejaculate investment relies principally on the resource acquisition in the ocean, whereas grilse ejaculate investment relies chiefly on the resource allocation of available surplus energy, thus representing alternative male reproductive tactics.

Multi-scale predictors of parasite risk in wild male savanna baboons (Papio cynocephalus)

Several factors are thought to shape male parasite risk in polygynous and polygynandrous mammals, including male-male competition, investment in potentially immunosuppressive hormones, and dispersal. Parasitism is also driven by processes occurring at larger scales, including host social groups and populations. To date, studies that test parasite-related costs of male behavior at all three scales—individual hosts, social groups, and the host population—remain rare. To fill this gap, we investigated multi-scale predictors of helminth parasitism in 97 male savanna baboons (Papio cynocephalus) living in the Amboseli ecosystem in Kenya over a 5-year span. Controlling for multi-scale processes, we found that many of the classic indicators of male mating effort—high dominance rank, testosterone, and glucocorticoids—did not predict helminth infection risk. However, we identified two parasite-related costs associated with male behavior: (i) socially connected males exhibited higher Trichuris trichiura egg counts and greater parasite species richness than socially isolated males and (ii) males with stable group residency exhibited higher parasite species richness than males who frequently dispersed to new social groups. At the population level, males harbored more parasites following periods of drought than rainfall. Lastly, parasites exhibited positive covariance suggesting that infection risk increases if a host already harbors one or more parasite taxa. These results indicate that multi-scale processes are important in driving male parasite risk and that some aspects of male behavior are costly. Together, our results provide an unusually holistic perspective on the drivers of parasite risk in the context of male behaviors and life histories. Infection by gastrointestinal helminths can have major consequences for host fitness, especially in the context of male mating effort. Multi-scale processes—from the host to its social group and population—are important for understanding key drivers of parasitism. We leveraged long-term data from one of the longest running behavioral ecology studies of a wild primate population in the world, the well-studied Amboseli baboon population in Kenya. We found that traditional indicators of male mating effort (attaining high dominance rank, high testosterone and glucocorticoids) did not predict parasitism. However, male social connectedness to females, competitive group demography, and harsh weather were all associated with higher parasitism. Because socially connected males faced the highest parasite risk, males may face a tradeoff between male-female relationships and parasitism. Our results show how processes at multiple scales contribute to variation in male parasite risk.

Sex, Energy, Well-Being and Low Testosterone: An Exploratory Survey of U.S. Men’s Experiences on Prescription Testosterone

Prescription testosterone sales in the United States have skyrocketed in the last two decades due to an aging population, direct-to-consumer advertising, and prescriber views of the benefits and risks to testosterone, among other factors. However, few studies have attempted to directly examine patient experiences on prescription testosterone therapy. The present exploratory study involved an online self-report survey of U.S. testosterone patients who were at least 21 years of age. The primary focus was on patient perspectives concerning motivations leading to the initiation of testosterone therapy and the perceived effects of treatment. Responses to open-ended questions drew upon a coding scheme incorporating both inductive and deductive approaches, influenced by the clinical, male life history theory, and behavioral endocrinology literature. Results indicated that the most frequent reasons men gave for taking prescription testosterone were low testosterone (37.1%), well-being (35.2%), energy (28.7%), libido (21.9%), and social energy (19.4%); older men claimed libido as a motivation for testosterone initiation more frequently than younger men (p < 0.001). Men most frequently claimed testosterone improved their energy (52.3%), libido (41.9%), and muscle (28.5%). Results are interpreted in the context of medical, life history theoretical and behavioral endocrinology approaches, including an emphasis on sex and energy.