Variation in life-history traits of male Japanese fluvial sculpin Cottus pollux in relation to nest abundance along a stream course

Life-history theory predicts the occurrence of variation in the life-history traits of fish populations under different environmental conditions; however, most studies have focused on such variation between geographically separated populations. We compared breeding characteristics and life-history traits of the Japanese fluvial sculpin (Cottus pollux), a bottom-dwelling nest-holding fish, between two adjacent sites sub-divided by a weir along a stream course in central Japan. Males in the area with a lower abundance of nest sites reached sexual maturity at an earlier age and had a shorter life span than males in the area with sufficient nest abundance. Size-dependent male reproduction was found only in areas with a shortage of nest sites, supporting the assumption of competitive exclusion among males for nests. Females matured at the same age in both sites with no differences in age-specific growth rates and mortality. Our results provide evidence for life-history variation in age and size at maturity and age-specific mortality schedule of males in nest-holding fishes in a single stream population via different sexual selection regimes related to differences in nest abundance between sites.     

Female‐biased dimorphism in size and age at maturity is reduced at higher latitudes in lake whitefish Coregonus clupeaformis

Female‐biased sexual dimorphism in size at maturity is a common pattern observed in freshwater fishes with indeterminate growth, yet can vary in magnitude among populations for reasons that are not well understood. According to sex‐specific optimization models, female‐biased sexual size dimorphism can evolve due to sexual selection favouring earlier maturation by males, even when sexes are otherwise similar in their growth and mortality regimes. The magnitude of sexual size dimorphism is expected to depend on mortality rate. When mortality rates are low, both males and females are expected to mature at older ages and larger sizes, with size determined by the von Bertalanffy growth equation. The difference between size at maturity in males and females becomes reduced when maturing at older ages, closer to asymptotic size. This phenomenon is called von Bertalanffy buffering. The predicted relationship between the magnitude of female‐biased sexual dimorphism in age and size at maturity and mortality rate was tested in a comparative analysis of lake whitefish Coregonus clupeaformis from 26 populations across a broad latitudinal range in North America. Most C. clupeaformis populations displayed female‐biased sexual dimorphism in size and age at 50% maturity. As predicted, female‐biased sexual size dimorphism was less extreme among lower mortality, high‐latitude populations.     

Reproductive aspects of male franciscana dolphins (Pontoporia blainvillei) off Argentina

As the first study to investigate reproductive aspects of male franciscana dolphin -Pontoporia blainvillei - in Argentine waters, the aim of this paper was to assess sexual maturity by using histological and morphometric methods. P. blainvillei was labeled as "Vulnerable" by the IUCN in 2008. The specimens analyzed were either incidentally caught in artisanal fishing nets (n=47) or found stranded on the beach (n=3). Testis weight and testicular index of maturity were reliable indicators of sexual maturity, being their values: MTW: 1.14 ± 0.60-4.49 ± 1.94; IM: 0.03 ± 0.01-0.09 ± 0.03, for immature and mature specimens' respectively. It was found that the hierarchical cluster analysis (HCA) might be appropriate for establishing sexual maturity stage, based on both the body morphometric measurements and age. The values for age, standard length and total weight at attainment sexual maturity were 2.92-3.54 years, 126.19-126.27 cm and 23.47-23.75 kg. Considering the extremely low relative testis weight, the reversed sexual length dimorphism, the absence of secondary sexual characteristics, and the lack of scars from intrasexual combats in males, the hypothesis that sperm competition does not occur in the species, and male combats for accessing female reproductive may be rare for P. blainvillei is reinforced. All these features fit the species within a serial monogamous mating system.     

Sex ratio, spawning season and size at maturity of red bandfish in the western Aegean Sea

The red bandfish Cepola rubescens is characterized by a normal gonochoristic sexual organization. The overall male: female ratio did not differ significantly ( x ²=4.57, P <0.05) from the theoretical 1: 1. However, the male: female ratio differed with season and length class and these differences are most probably related to sexual differences in growth rate, natural mortality rate and energetic cost of reproduction. Red bandfish spawns over an extended period, from late spring to mid autumn, with larger females spawning earlier than smaller ones. Males reach maturity at a larger total length, 299 mm, and age, 2.6 years, than females, 219 mm and 1.9 years respectively, a fact most probably indicating the existence of social structure in red bandfish. Finally, red bandfish matures at a comparatively smaller length and age than other fish species.     

Maturational changes in patterns of association in male and female humpback whales, Megaptera novaeangliae

The patterns of association of juvenile male and female humpback whales, Megaptera novaeangliae , in the southern Gulf of Maine were studied for evidence of maturational changes. Both males and females became less solitary with age. In males, time spent alone changed from a mean of 55.8% of observations at age one to 26.8% at age six. Females were alone in a mean of 49.9% of observations at age one, but in only 20.5% by age six. However, females that produced calves at five, six or seven were associated with no whales but the calf in 73.8% of observations. Males exhibited a clear age-related trend of increasing associations with adults, notably with adult females which constituted approximately 80% of the associates of males aged six years or more. Females showed a similar trend of increasing associations with adults of both sexes. Tests of association data for whales of known age with similar data for adults of the same sex showed that the association patterns of young males and females became statistically indistinguishable from those of adults by the ages of five and four, respectively. The data suggest that the observed changes in social behaviour are closely linked to the attainment of sexual maturity and preparation for adult roles. The different patterns of males and females after maturity may reflect differing reproductive and life-history strategies.     

Alternative life histories in Xiphophorus multilineatus: evidence for different ages at sexual maturity and growth responses in the wild

In order to examine potential trade-offs in alternative life histories of the high-backed pygmy swordtail Xiphophorus multilineatus, otoliths were used from wild-caught males to determine if sneaker males had the advantage of maturing earlier in natural environments. The sneakers matured significantly earlier than courters, but there was no difference among the three courter variants. In addition, analyses suggested that the effect of the pituitary locus on size at sexual maturity and growth rates was a consequence of age at sexual maturity. Finally, one of the courter variants had a significantly different relationship between age and size at sexual maturity than the other variants, suggesting that in this variant, age at sexual maturity may be more closely related to size and therefore may be less plastic in its growth responses.     

Seasonal effects on sexual maturation of male bank voles (Clethrionomys glareolus)

The weights of the testes and accessory glands, and the degree of morphological and functional development of the seminiferous tubules, were used as indicators of sexual maturation in male bank voles. Males reared under constant laboratory conditions showed a significant relationship between the seasons and sexual maturation. Young males reached maturity most rapidly in the reproduction season (mid-April to mid-October), while adult males matured earlier, in the spring season (mid-January to mid-April). The influence of season on animals reared in outdoor cages was much more pronounced. One of the important factors was the photoperiod: animals reared from 3 to 12 weeks of age in a short photoperiod (8L:16D) matured less rapidly than did those reared in 16L:8D.     

Chronic treatment of male tammar wallabies with deslorelin implants during pouch life: effects on development, puberty, and reproduction in adulthood

The present study evaluated the effects of chronic GnRH agonist (deslorelin) treatment on sexual maturation in the male tammar wallaby. Slow-release deslorelin or placebo implants were administered to male pouch young (n = 10/group) when they were between 180 and 200 days old, to determine if disruption of the pituitary-testicular axis during development altered the timing of sexual maturation or had long-term effects on adult reproductive function. Deslorelin treatment caused retardation of testicular growth and reduced the serum FSH and testosterone concentrations between 12 and 24 mo of age. Maturation of the hypothalamic-pituitary-testicular axis was also delayed in treated animals at 13 and 19 mo of age. Despite these alterations in the pattern and timing of neuroendocrine development, sexual maturation was not permanently blocked in these animals and deslorelin-treated animals reached sexual maturity at the same age as treated animals, as evidenced by a fully functional pituitary-testicular axis and proven fertility at 25 mo of age. The ability of the treated animals to reach puberty at the same time as control animals, despite delayed maturation of the hypothalamic-pituitary-testicular axis, suggests that puberty in the male tammar wallaby is additionally regulated by other, gonadotropin-independent factors.     

Vitellogenin levels in male and female rainbow trout (Salmo gairdneri Richardson) at various stages of the reproductive cycle

The immunoassayable vitellogenin (VTG) in plasma from male rainbow trout had the same molecular weight as authentic VTG from female fish. The VTG level in male trout was low (usually nanograms, occasionally up to a few micrograms, per ml) and did not correlate with the stage of sexual maturity. The plasma VTG level of female trout that were two years from first spawning was 200-fold higher than males of the same strain and age. The plasma VTG level of female rainbow trout rose approximately a million-fold during the two or three years required to attain sexual maturity.     

Sex ratio and sexual dimorphism in the dioecious Borderea pyrenaica (Dioscoreaceae)

Sex ratio and sexual dimorphism of Borderea pyrenaica, a long-lived dioecious geophyte endemic to the Pyrenees (north-east Iberian Peninsula), were examined in three alpine populations. In this species, age can be estimated and the sex of nonreproductive adult plants identified. Male plants attain sexual maturity earlier, flower more frequently and grow faster than female plants, whereas females allocate a higher biomass to reproduction than males. These results support the hypothesis that female plants incur a higher cost of sexual reproduction and that this higher cost is measurable as reduced vegetative growth and lower flowering frequency. Variation of sex ratio among young, intermediate and old adults within populations suggests, however, that this higher female reproductive investment does not result in sexual differences in mortality. The overall male-biased sex ratio in B. pyrenaica is mainly a consequence of the tendency of males to reproduce at an earlier age and more frequently than females.     

Influence of age at mating on the reproductive performance of Parthenium beetle,Zygogramma bicolorata (Coleoptera: Chrysomelidae)

Abstract Age-specific mating incidence, sexual maturation and effect of age at mating on reproductive performance of the Parthenium beetle, Zygogramma bicolorata Pallister, was studied. Based on 50% mating incidence the calculated age of sexual maturation of males and females was 10.5 and 11.1 days, respectively, which was not statistically significant. However, on the basis of age at first mating, that is, sexual maturity, females matured 2 days earlier than males. Fecundity, pre-oviposition, oviposition and post-oviposition period and female longevity appear to be influenced by female age at mating with reproductive performance peaking at 30 days. On the other hand, egg viability was influenced by male age and was highest when males mated at the age of 40 days. To summarise, egg production and timing of egg deposition was female age-dependent, whereas egg fertility was male age-dependent. It was also observed that females mated at a later age and laid a higher number of eggs immediately after mating than did earlier mated females. This was ostensibly in a bid to increase fitness by maximizing reproductive output in the reduced life span available. This is the first investigation on the effect of age of females at mating on reproduction in this beetle.     

Growth differences and dimorphic expression of growth hormone (GH) in female and male Cynoglossus semilaevis after male sexual maturation

Half-smooth tongue sole, Cynoglossus semilaevis, is an ideal model to investigate the regulatory mechanisms of sexual growth dimorphism in fish species. The aim of the study was to investigate the effect of differential age of sexual maturity for females and males on growth and GH mRNA expression in C. semilaevis. The body weight differences between the sexes were not significant in C. semilaevis at age 5 months when females and males were all immature. Significant differences in body weight between the sexes were found after early sexual maturation of males at the age of 9 months. The body weight of 21-month-old females (621.4 ± 86.4g), still not immature, was even 3.28 times higher than that of the males (189.7 ± 14.4g). The cDNAs encoding GH in C. semilaevis was cloned. The GH gene is 2924bp long and consists of six exons and five introns. The results of qRT-PCR showed that GH mRNA levels of the immature females were not significantly different from that of immature males at age 5 months. However, GH mRNA levels of the immature females were significantly higher compared with those of the mature males at age 9 months (P<0.05). At age 11 months, GH mRNA levels of females were even 6.4-fold higher than that of males. In conclusion, for the first time we show that early sexual maturity of males is the main cause of sexual growth dimorphism in C. semilaevis and exert significant effect on GH mRNA expression.     

Reproductive biology of the male Cape porcupine, Hystrix africaeaustralis

The reproductive tract of the male Cape porcupine is morphologically and histologically similar to that of New World hystricomorph rodents. Males are reproductively active throughout the year and attained sexual maturity (complete spermatogenesis) at an age of 8-18 months. Testes weight, epididymides weight and seminiferous tubule diameter attained asymptotic values at the age of 23-30 months. A tendency towards seasonality in the activity of accessory glands, preceded and accompanied by an increase in circulating plasma testosterone values, may be considered as a factor enforcing seasonal breeding in females. Testosterone concentrations in pubertal males were significantly higher than those recorded in sexually mature males.     

Growth and sexual maturation of the male house musk shrew (Suncus murinus)

The sexual maturation in the male house musk shrew, Suncus murinus, was investigated by weighing gonads, accessory sexual organs and various other organs, and measuring testosterone concentrations in the plasma from birth to 50 days of age. The histological and histochemical studies of the testis were also carried out. Testicular weight increased markedly from 10 days of age. On 15 days of age, the activity of delta 5-3 beta-Hydroxysteroid dehydrogenase (HSD) was detected in Leydig cells. In accordance with an increase of HSD activity, the concentrations of plasma testosterone raised rapidly from 15 days of age and reached a peak on Day 30. Growth of prostate glands and seminal vesicles showed a sigmoidal pattern and their significant growth began from Day 25. Sperms were detected first in the seminiferous tubules on Day 28, and most tubules were filled with many sperms on Day 33. From these results, the beginning of sexual maturation, i.e. puberty, of the male shrew is considered to be around Day 25. The weight gain of testes, accessory sexual organs and the body became slower on Day 40. The male animal of Day 40 could mate and impregnate the female. Therefore, the male shrew seems to attain to the sexual maturity between days 35 and 40.     

Reproduction in the male sub-Antarctic fur seal Arctocephalus tropicalis

The reproductive tracts of male sub-Antarctic fur seals Arctocephalus tropicalis ( n = 123), taken at Gough Island (40° 20'S, 9° 54'W) between November 1977 and October 1978, were examined. The presence of spermatozoa in the epididymal tubules showed that all males ≥4 years old had reached puberty, and the marked slower increase in mean testis weight and baculum length suggested that sexual (social) maturity was approached by 8-year-olds. Full adulthood was attained at 10–11 years of age based on the peak in mean testis and prostate weights, and mean baculum length. Secondary sexual characteristics were only fully developed in males ≥9 years old. A significant decline in mean testosterone concentration, and in testis, epididymis and prostate weights showed that adult males were reproductively quiescent during winter from May to July when seminiferous and epididymal tubules had lowest mean diameters with no spermatozoa present. Both the mean plasma testosterone concentration and mean testis weight peaked twice during the austral summer. The first peak coincided with the breeding season, and the second peak with the moulting period when adult males were impotent. Photoperiodic cueing might explain this seasonal trend.     

The evolutionary significance and social perception of male pattern baldness and facial hair

Both male facial hair and male pattern baldness are genetically based, suggesting that they contributed to fitness. The multiple fitness model provides an evolutionary interpretation of the social perception of male pattern baldness and beardedness in terms of the multidimensional meaning of physical maturational stages. Male facial beardedness is associated with the sexual maturation stage and is hypothesized to signal aggressive dominance. Male pattern baldness, by contrast, is associated with the next stage of physical maturation, termed senescence. Pattern baldness may signal social maturity, a non-threatening form of dominance associated with wisdom and nurturance. We tested these hypotheses on social perceptions using manipulated male facial stimuli. We presented faces with three levels of cranial hair, including full, receding, and bald, and two levels of facial hair, beard with moustache and clean shaven. Consistent with the model, a decrease in the amount of cranial hair was associated with increased perceptions of social maturity, appeasement, and age, and decreased perceptions of attractiveness and aggressiveness. Targets with facial hair were perceived as more aggressive, less appeasing, less attractive, older, and lower on social maturity than clean shaven faces.     

Sexual size dimorphism in species with asymptotic growth after maturity

If animals mature at small sizes and then grow to larger asymptotic sizes, many factors can affect male and female size distributions. Standard growth equations can be used to study the processes affecting sexual size dimorphism in species with asymptotic growth after maturity. This paper first outlines the effects of sex differences in growth and maturation patterns on the direction and degree of sexual dimorphism. The next section considers the effects of variation in age structure or growth rates on adult body sizes and sexual size dimorphism. Field data from a crustacean, fish, lizard and mammal show how information on a species' growth and maturation patterns can be used to predict the relationships between male size, female size and sexual size dimorphism expected if a series of samples from the same population simply differed with respect to their ages or growth rates. The last section considers ecological or behavioural factors with different effects on the growth, maturation, survival or movement patterns of the two sexes. This study supports earlier suggestions that information on growth and maturation patterns may be useful, if not essential, for comparative studies of sexual size dimorphism in taxa with asymptotic growth after maturity.     

Green swordtails alter their age at maturation in response to the population level of male ornamentation

Effects of the social environment on age at sexual maturation are assumed to require direct interactions, such as suppression of subordinates through aggression from dominants. Using green swordtails (Xiphophorus helleri), we demonstrate for the first time that females and males adjust their age at maturation in response to visual cues of male sexual ornamentation in the current environment: females matured earlier, whereas males matured later if all the mature males seen had large ornaments. Thus, age at maturation shifted in accordance with the perceived quality of mates (females) or mating competitors (males), demonstrating a capability to use visual cues from the environment to strategically adjust rates of sexual development.     

Retroviruses and sexual size dimorphism in domestic cats (Felis catus L.).

Hochberg and co-workers have predicted that an increase in host adult mortality due to parasites is balanced by an earlier age at first reproduction. In polygynous species we hypothesize that such a pattern would lead to diverging selection pressure on body size between sexes and increased sexual size dimorphism. In polygynous mammals, male body size is considered to be an important factor for reproductive success. Thus, under the pressure of a virulent infection, males should be selected for rapid growth and/or higher body size to be able to compete successfully as soon as possible with opponents. In contrast, under the same selection pressure, females should be selected for lighter adult body size or rapid growth to reach sexual maturity earlier. We investigated this hypothesis in the domestic cat Felis catus. Orange cats have greater body size dimorphism than non-orange cats. Orange females are lighter than non-orange females, and orange males are heavier than non-orange males. Here, we report the extent to which orange and non-orange individuals differ in infection prevelance for two retroviruses, feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV). FIV is thought to be transmitted almost exclusively through aggressive contacts between individuals, whereas FeLV transmission occurs mainly through social contacts. The pattern of infection of both diseases is consistent with the higher aggressiveness of orange cats. In both sexes, orange cats are significantly more infected by FIV, and tend to be less infected by FeLV than other cats. The pattern of infection is also consistent with an earlier age at first reproduction in orange than in non-orange cats, at least for females. These results suggest that microparasitism may have played an important role in the evolution of sexual size dimorphism of domestic cats.     

Effect of individual and group rearing on age and size at maturity of male mosquitofish, Gambusia affinis

Age and size at sexual maturity were significantly greater for male mosquitofish, Gambusia affinis Baird and Girard, reared in sib-groups than for their sibs reared individually. Age at sexual maturity averaged 43.3 and 62.1 days for individually- and group-reared males, respectively, a 43% difference; final length and weight at maturity were 7.7 and 34.2% greater, respectively, for group-reared males than for their individually-reared sibs. The results were consistent among 30 families that represented the progeny of 30 wild-caught females. The observed differences may be attributable to behavioural interactions affecting the neuroendocrine control of the maturation process, as suggested by previous studies of Xiphophorus .