Testis Mass Research Articles

SEXUAL SELECTION CAN REMOVE AN EXPERIMENTALLY INDUCED MUTATION LOAD

Sexual selection is argued to be important for the removal of deleterious mutations, promoting population fitness, accelerating adaptation, and compensating for the two-fold cost of sex. Here we induced mutations in the dung beetle Onthophagus taurus using ionizing radiation, and tested the efficacy of sexual selection in their removal. Mutations reduced male precopulatory (strength) and postcopulatory (testes mass) sexual traits. Two generations of sexual selection were sufficient to remove mutations that affected male strength, but not testes mass. Induced mutations did not affect female productivity, which was elevated by sexual selection. Our results provide empirical support for the hypothesis that condition-dependent traits offer a large target for mutational variation, and that sexual selection can purge the genome of deleterious mutations and promote population fitness.

Song evolution in Maluridae: influences of natural and sexual selection on acoustic structure

Many factors may influence the evolution of acoustic signals, including sexual selection, morphological constraints and environmental variation. These factors can play simultaneous and interacting roles in determining signal phenotypes. Here, we assess the evolution of song features in the Maluridae, a passerine family with significant variation among taxa in levels of sperm competition, morphological features and breeding habitats ranging from arid grasslands in Australia to tropical rainforests in New Guinea. We used phylogenetic comparative methods and a robust molecular phylogeny to compare song characteristics with a variety of other measures, including testes mass, body-size and latitude. Several aspects of the temporal and frequency structure of song were associated with relative testes mass, suggesting that sexual selection may influence some song characteristics in this family. The lowest frequencies of song were strongly predicted by body-size, indicating that morphological constraints have also likely influenced acoustic phenotypes. Song versatility, reflecting the diversity of note types in a song, was positively correlated with latitude, suggesting that complexity may increase in association with more temperate or variable environments. Variation in song structure across the family appears to reflect a complex interaction between natural and sexual selection.

Effects of thyroxine treatment during lactation on the testicular function of rats across different ages

Thyroid hormones are involved in the development of several tissues and organs and are essential for the normal growth and reproductive function. The aim of this study was to determine the effects of thyroid hormones on the development of testis and progression of spermatogenesis. Lactating mothers were treated with oral thyroxine (T4; 20 μg/100 g) for 20 days after parturition. The pups were decapitated at the age of 20, 40 and 60 days post partum. Neonatal hyperthyroidism resulted in a decrease in body and testis mass, an increase of free thyroxine and a decrease of testosterone concentrations in plasma of treated rats. The treatment was associated with a significant decrease of the diameter of seminiferous tubules and a slowdown in spermatogenesis, following a delay in the maturation of germ cells. We conclude that thyroid hormones affect the progression of postnatal spermatogenesis.

Annual Reproductive Cycle in the Scincid LizardChalcides viridanusfrom Tenerife, Canary Islands

Chalcides viridanus is a small skink endemic to Tenerife, the Canary Islands. This paper describes its annual reproductive cycle and sexual dimorphism by use of data from external measurements, dissection, and histological observation of gonads from monthly samples. Males were significantly larger than females in head-forelimb length, distance between forelimbs and hind limbs, tail width, and body mass. Male testes were largest in March, when most individuals showed active spermiogenesis, although no spermiation was observed. In April, the testes were somewhat smaller but showed seminiferous tubules and epididymis ducts with abundant sperm. In this month, female gonads and ovarian follicles were significantly enlarged, and vitellogenesis was evident. Oviductal embryos were found in May and June, and parturition took place at the beginning of August. Both testis mass in males and diameter of the largest oocyte in females were significantly correlated to abdominal fat body mass. We conclude that in C. viridanus both sexes exhibit seasonal changes in gonadal activity with synchronous development of both male and female gonads in the spring months.

Reproduction in the East African root rat (Tachyoryctes splendens; Rodentia: Spalacidae) from Tanzania: the importance of rainfall

AbstractThe East African root rat Tachyoryctes splendens (Rüppell, 1835) is a solitary subterranean rodent mole. The present study investigated breeding patterns in both sexes of T. splendens from data collected at monthly intervals over an entire calendar year. The study focused on the analyses from post‐mortem examination of male and female East African root rats to assess the presence of foetuses, gonadal histology, reproductive tract morphometrics, measurement of gonadal steroids (plasma progesterone and oestradiol‐17β in females and testosterone in males) and field observations (i.e. the presence of infants, juveniles, subadults and lactating females). The objective of this study was to assess if the reproductive biology of root rats reflected the bimodal pattern of rainfall that is characteristic of East Africa. Rainfall has been suggested to trigger breeding in many subterranean rodents and as a consequence, this study aimed to assess the relationship between rainfall and reproductive characteristics of T. splendens. Peaks in mean gonadal mass, increases in concentration of reproductive hormones and the presence of graafian follicles and corpora lutea in the ovaries of females, and testes mass, seminiferous tubule diameter and testosterone titre mirrored the annual peaks of precipitation at the study area. Together with field observations of the temporal occurrence of pregnancies, infants, juveniles and subadults, the data show that T. spendens cues its breeding with the patterns of rainfall, such that offspring are born in the latter half of each rainy season, from April to July and November to December.

Variation in Apical Hook Length Reflects the Intensity of Sperm Competition in Murine Rodents

BackgroundPost-copulatory sexual selection has been shown to shape morphology of male gametes. Both directional and stabilizing selection on sperm phenotype have been documented in vertebrates in response to sexual promiscuity.MethodologyHere we investigated the degree of variance in apical hook length and tail length in six taxa of murine rodents.ConclusionsTail sperm length and apical hook length were positively associated with relative testis mass, our proxy for levels of sperm competition, thus indicating directional post-copulatory selection on sperm phenotypes. Moreover, our study shows that increased levels of sperm competition lead to the reduction of variance in the hook length, indicating stabilizing selection. Hence, the higher risk of sperm competition affects increasing hook length together with decreasing variance in the hook length. Species-specific post-copulatory sexual selection likely optimizes sperm morphology.

Polyandry Has No Detectable Mortality Cost in Female Mammals

In several taxonomic groups, females mate with several males during a single reproductive cycle. Although there is evidence that polyandry provides some benefits to females, it often involves mortality costs. However, empirical evidences of mortality costs of polyandry have so far been reported only in invertebrates. Whether polyandry has mortality costs in vertebrates is currently unknown. In the present study, we aimed to fill the gap by investigating the relationships between the level of polyandry (measured either by male relative testes mass or the percentage of multiple paternities) and female patterns of mortality across mammals. While we found that the two metrics of female mortality co-varied with pace of life, we did not find any evidence that polyandry leads to either decreased median lifespan or increased aging rate in mammals. We discuss such an absence of detectable mortality costs of polyandry in female mammals in light of recent advances in the study of mammalian reproductive biology and life-history tactics.

Within population variation in testis size in the mole-shrew (Anourosorex squamipes) (Mammalia: Soricidae)

Sperm competition is recognized as a key event occurring during postcopulatory sexual selection. The evolutionarily stable strategy (ESS) predicts that males in poor condition should invest more heavily in sperm compared with males in good condition. We explored the effects of body condition and season on testes mass in the mole-shrew (Anourosorex squamipes). We used the “scaled mass index” as body condition to analyze the effects of season, body condition and body length on testis size. The results showed that testes mass was greatest in summer. Head body-length also significantly affected testis size in the four seasons. In addition, males in good conditions had relatively heavier testes than those in poor conditions in spring, summer and autumn, but not in winter, suggesting that the finding contradicts the prediction of the evolutionarily stable strategy.

EJACULATE QUALITY AND CONSTRAINTS IN RELATION TO SPERM COMPETITION LEVELS AMONG EUTHERIAN MAMMALS

The outcome of sperm competition is influenced by the relative quantity and quality of sperm among competing ejaculates. Whereas it is well established that individual ejaculate traits evolve rapidly under postcopulatory sexual selection, little is known about other factors that might influence the evolution of ejaculates. For example, the metabolic rate is likely to affect the sperm production rate and the cellular activity or metabolism of sperm, and it has recently been suggested to constrain the evolution of sperm length in large but not small mammals. I thus examined in eutherian mammals how ejaculate quality traits vary with one another and with testis mass, body size, and metabolism. I found all ejaculate traits to covary positively with one another and to increase with relative testis mass. When controlling for testis mass, small-bodied species showed superior sperm quality (but not sperm number). Furthermore, sperm motility and viability were positively associated with the mass-corrected metabolic rate, but the percentage of morphologically normal and acrosome-intact sperm were not. These results indicate that body size and the energy budget may also influence the evolution of ejaculate quality, although these influences appear to vary among traits.

Male reproductive traits of full-sibs of different age classes in three-spined sticklebacks (Gasterosteus aculeatus)

The process of ageing is associated with negative effects of mutations acting late in life, which range from those affecting cells to those affecting the whole organism. In many animal taxa, the deterioration of the phenotype with age also affects traits such as males’ primary and secondary sexual characteristics. In three-spined sticklebacks (Gasterosteus aculeatus), males usually reproduce at one or two years of age. To see whether sexual selection has the potential to differ between young and old males, full-sib brothers of different age classes were compared, which were bred and raised under standardised laboratory conditions. During two simulated, successive breeding seasons males were allowed to build their nest in single tanks either in the first (“young males”) or in the second (“old males”) breeding season. A comparison of reproductively active brothers of the first and second breeding season showed that older males produce more but smaller sperm, which might be of lower quality. The fact that older males stored more sperm is size dependent as the results show that larger males possess a greater absolute testis mass, which is inextricably linked to sperm number. However, independent of body size, old males had a lower intensity of red/orange and UV breeding coloration as well as a reduced testis melanisation, which might have consequences in female mate choice and sperm competition.

Physiological and neuroendocrine responses to chronic variable stress in male California mice (Peromyscus californicus): Influence of social environment and paternal state

Social environment and parental state affect stress responses in mammals, but their impact may depend on the social and reproductive strategy of the species. The influences of cohabitation with a male or female conspecific, and the birth of offspring, on the physiological and endocrine responses to chronic variable stress were studied in the monogamous and biparental California mouse (Peromyscus californicus). Adult male California mice were housed either with a male cage mate (virgin males, VM), a female cage mate (pair-bonded males, PBM), or a female cage mate and their first newborn litter (new fathers, NF). VM, PBM and NF underwent a 7-day chronic variable stress paradigm (CVS, three stressors per day at semi-random times, n=7-8 per housing condition). Compared to control males (CON, n=6-7 per housing condition), CVS caused loss of body mass, increased basal plasma corticosterone concentrations, and increased basal expression of arginine vasopressin (AVP) mRNA in the paraventricular nucleus of the hypothalamus (PVN). These effects were independent of housing condition. Neither CVS nor housing condition altered novel-stressor-induced corticosterone release, spleen or testis mass, or basal expression of corticotropin-releasing hormone (CRH) mRNA in the PVN. Although CVS appeared to increase adrenal mass and reduce thymus mass specifically in NF, these effects were explained by the lower adrenal mass and higher thymus mass of NF compared to PBM and VM under control conditions. These results suggest that neither engaging in a pair bond nor becoming a father attenuates typical responses to CVS, but that fatherhood may provide a buffer against transient mild stressors (i.e., weighing and blood sampling in the control groups) in this monogamous and biparental rodent.

Evolution of mating systems and sexual size dimorphism in North American cyprinids

Mating systems evolve with sexual size dimorphism (SSD) in many animals. Mating systems with males larger than females occur when males compete for female access or guard territories, while mating systems with group mating tend to occur in species where females are the same size or larger than males. In addition to variation in SSD with mating system, sperm competition varies among mating systems in predictable patterns. We examined the evolution of mating systems with SSD and testes mass in 111 North American Cyprinidae fishes using phylogenetic comparative methods. Our results demonstrate that the evolution of mating systems in Cyprinidae fishes is from ancestral taxa that are group spawners with females the same size or larger than males to pair spawning systems where males tend to be larger than females. We used an additive model to predict male and female body size from testes mass and mating system. Only mating system varied predictably with SSD. Our results for analyses of hyperallometry (Rensch’s rule) were that individual species of Cyprinidae can have hyperallometry for SSD, but the pattern is not present across all taxa.

Perturbation of male sexual behavior in mice (Mus musculus) within a discrete range of perinatal bisphenol-A doses in the context of a high- or low-phytoestrogen diet

Differentiation of masculine and feminine behavior in mammals depends on perinatal sex steroids. As bisphenol-A (BPA) can be estrogenic and anti-androgenic, we examined impacts of perinatal exposure upon adult sexual behavior and morphology of male mice. In Experiment 1, dams were fed either a high- or low-phytoestrogen diet and received daily oral doses of 0, 0.175, 1.75, or 17.5μg BPA from gestation day 10 through post-partum day 9. Male offspring from the high-phytoestrogen plus 17.5μg BPA condition showed reduced mass of vesicular-coagulating but not other male glands, and showed increased latency to insemination when paired with females. In Experiment 2, these procedures were replicated but with all animals fed the high-phytoestrogen diet and perinatal BPA doses of 0, 17.5, 175, or 1750μg/day. Adult masses of testes and male-accessory glands and levels of urinary steroids were not significantly affected. When males each encountered a sexually receptive female, there were fewer intromissions among those given 17.5 or 175μg and fewer ejaculations among those given 17.5μg, but the 1750μg dose had no effect. Perinatal BPA dosages thus influenced male sexual behavior non-monotonically, with impairment evident in a discrete dose range among males on a high-phytoestrogen diet.

Визначення біологічного віку сірих нориць за допомогою багатовимірного фенотипування (на прикладі Microtus arvalis Pallas, 1779 і M. socialis Pallas, 1773)

Factor analysis of common and social voles morphological variability was given for 17 morphological features. According to the results of such analysis in vole samples, it was found that 85.4% variability of the majority morphological features for common vole and 88.6% the same one in case of social vole have been described by three first’s principal components (PC 1 –PC 3 ). In both vole species first principal component characteri­zes the age variability by general size of the body, and second and third components – body proportions. A definition of voles biological age might be used of the body general size and proportions, mass of testes (reproductive status) and thymus (capacity for subsequent growth). 2 groups of males common vole and 8 groups of males of social vole of different biological age was identified by the multidimensional phenotyping. It was shown that biodiversity of social vole males is significantly higher in comparison with the common vole. This could be explained by the fact that physiological and reproductive activity was higher in Microtus socialis comparing with M . arvalis. Keywords : Microtus socialis , M. arvalis, voles, general size and proportions of body, method of multidimensional phenotyping, biological age.

Indication of Density‐Dependent Changes in Growth and Maturity of the Barndoor Skate on Georges Bank

AbstractDrastic increases or decreases in biomass often result in density‐dependent changes in life history characteristics within a fish population. Acknowledging this phenomenon and in light of the recent biomass increase in Barndoor Skate Dipturus laevis, the current study re‐evaluated the growth rate and sexual maturity of 244 specimens collected from 2009–2011within closed areas I and II on Georges Bank, USA. Ages were estimated using vertebral band counts from skate that ranged from 21 to 129 cm TL. The von Bertalanffy growth function was applied to pooled age‐at‐length data. Parameter estimates from the current study of L∞ = 155 cm TL and k = 0.10 represent a significant decrease from previously reported parameters of L∞ = 167 cm TL and k = 0.14. In addition to changes in growth parameters, age at 50% maturity for both males (based on clasper length, testes mass, and percent mature spermatocytes) and females (based on data from shell gland mass, ovary mass, and follicle diameter) increased by 3 years and 4 years, respectively. Based on our results and the 10‐ to 12‐year gap in the collection of samples, it is likely that Barndoor Skate within this region have exhibited pliability in life history parameters.Received January 21, 2013; accepted July 9, 2013

Long-day photoperiod interacts with vasopressin and food restriction to modulate reproductive status, and vasopressin receptor expression of male Golden spiny mice

We tested the effects of photoperiod, water and food availability on body mass, reproductive status and arginine vasopressin receptor 1A (Avpr1a) mRNA expression in males of desert-adapted golden spiny mice, Acomys russatus. In Experiment 1, males were acclimated to short-day (SD; 8 h:16 h light:dark) or long-day (LD; 16 h:8 h light:dark) photoperiods with either saline (control) or vasopressin treatment for 3 weeks. The results of this experiment revealed that under control conditions, SD mice increased body mass by ~5% while LD mice decreased it by ~4%. SD photoperiod had no effect on reproductive status and leptin levels, whereas LD males increased testes mass and serum testosterone, but the photoperiod had no effect on leptin levels. Vasopressin administration decreased LD-induced reproductive enhancement. Because no consistent effect of SD treatment was found on reproductive status, Experiment 2 was carried out only on LD-acclimated males kept under 75% food restriction (decrease from ad libitum) with saline or leptin treatment. Body mass, testes mass, serum testosterone, leptin concentrations and Avpr1a mRNA expression were measured. Food restriction remarkably decreased body mass, with a more potent effect in leptin-treated males, showing enhanced reproductive status and a significant increase in serum leptin compared with controls. Avpr1a expression was significantly upregulated in LD, vasopressin-treated and food-restricted males, with higher levels in the hypothalamus compared with the testes. We conclude that in A. russatus, LD photoperiod interacts with water and food availability to advance reproductive responses. Avpr1a is suggested to integrate nutritional and osmotic signals to optimize reproduction by modulating reproductive and energetic neuroendocrine axes at the central level. The interaction between photoperiod and other environmental cues is of an adaptive value to desert-adapted small rodents for timing reproduction in unpredictable ecosystems such as extreme deserts.

Parental care and testosterone in males of the bank vole (Myodes glareolus): Sensitization and androgenic stimulation of paternal behavior

The relationship between parental responsiveness of bank vole males and their body weight, testes mass, and plasma and gonadal testosterone levels were examined. Two groups of voles were studied: Group I consisted of 14 breeding pairs where females gave birth to young within a month after formation of pairs, and Group II represented 13 pairs without offspring and signs of pregnancy in females. Males in Group I, unlike those in Group II, had contact with pups before the tests on parental responsiveness. In Group I, males were found to have larger testes and to exhibit a higher level of care-giving activity (pup retrieval) as compared to males in Group II. Both the plasma and gonadal testosterone levels in males exhibiting pup retrieval were revealed to be significantly higher than those for males exhibiting infanticide. Thus, promiscuity, competition for receptive females, and a higher level of testosterone secretion, which are characteristic of bank vole males during the breeding season, are not out of the realm of possibility of the males that care for young. Our findings suggest that factors promoting parental responsiveness in bank vole males are sensitization due to contact with pups and an increase in testosterone secretion. Obviously, there is a need to reexamine the role that testosterone plays in regulating rodent parental behavior.

Epithelioid hemangioma of the testis

Testicular hemangioma is a very rare benign vascular neoplasm, there are only less than 30 cases of testicular hemangiomas reported in the literature. We report a case of epithelioid hemangioma of the testis in a 53-year-old man who presented with painless mass in the right testis. An orchiectomy was performed, The 1 cm tumor was composed of prominent proliferation of small, capillary-sized vessels lined by plump, epithelioid endothelial cells. Immunohistochemically, the epithelioid endothelial cells reacted with antibodies to factor VIII-related antigen, CD31, CD34 and Vimentin, but not CK, EMA, CEA, S-100 and CD68. Although it is a rare tumor, we should be aware of it and avoid confusion with other vascular neoplasm.

Reproduction of the greater bulldog bat Noctilio leporinus (Chiroptera: Noctilionidae) in a mangrove area in southern Brazil

The reproductive pattern of the greater bulldog bat (Noctilio leporinus) was studied in southern Brazil from January to December 1999. The morphological characteristics of their reproductive organs were recorded monthly, through histological analysis of testes and ovaries. Those data were correlated with forearm size and body mass, as well as with external reproductive characteristics. The diameter of the seminiferous tubule increased proportionately to testis mass and body weight, and larger males had greater testis mass. Sexually mature males were recorded throughout the year. Ovary histology revealed that females ovulate between July and December. Lactating females were recorded in nearly every month of the year. Noctilio leporinus has a bimodal polyestrous pattern, with an increase in the recruitment of juveniles between January and May.

Male survival patterns do not depend on male allocation to sexual competition in large herbivores

Understanding causes of between-sex differences in survival patterns is a long-standing challenge in evolutionary biology. Interspecific differences in male allocation to sexual competition have been suggested to shape species-specific patterns of male adult survival and actuarial senescence, and thereby the extent of between-sex differences in these parameters. Sexual competition is complex and involves both competition for gaining mating (i.e., precopulatory competition) and competition for fertilization opportunities (i.e., postcopulatory competition). However, to date, studies seeking for a relationship between allocation to precopulatory competition and male absolute adult survival have led to contrasting results and the influence of postcopulatory competition on these parameters has never been yet investigated. To fill the gap, we performed a comparative study in large herbivores using median lifespan (i.e., age at which only half of the initial cohort is still alive) and actuarial intensity of senescence (i.e., number of years elapsed between the median lifespan and the age where only one-tenth of the initial cohort is still alive). As expected, we found a lower adult survival and a stronger actuarial intensity of senescence in males than in females. Conversely, we did not find any evidence that variation in male allocation to pre- and/or postcopulatory traits explain between-species differences of both absolute and relative adult survival and intensity of actuarial senescence. These results challenge the idea that allocation to specific traits associated with sexual competition is responsible for between-sex differences in survival and senescence patterns generally reported in mammals. Key wor ds: actuarial senescence, aging, sexual selection, sexual size dimorphism, testes mass, ungulates, weapon size. [Behav Ecol]