Sex‐specific reproductive investment of summer spawners of Illex argentinus in the southwest Atlantic

Energy investment in reproduction and somatic growth was investigated for summer spawners of the Argentinean shortfin squid Illex argentinus in the southwest Atlantic Ocean. Sampled squids were examined for morphometry and intensity of feeding behavior associated with reproductive maturation. Residuals generated from length‐weight relationships were analyzed to determine patterns of energy allocation between somatic and reproductive growth. Both females and males showed similar rates of increase for eviscerated body mass and digestive gland mass relative to mantle length, but the rate of increase for total reproductive organ weight relative to mantle length in females was three times that of males. For females, condition of somatic tissues deteriorated until the mature stage, but somatic condition improved after the onset of maturity. In males, there was no correlation between somatic condition and phases of reproductive maturity. Reproductive investment decreased as sexual maturation progressed for both females and males, with the lowest investment occurring at the functionally mature stage. Residual analysis indicated that female reproductive development was at the expense of body muscle growth during the immature and maturing stages, but energy invested in reproduction after onset of maturity was probably met by food intake. However, in males both reproductive maturation and somatic growth proceeded concurrently so that energy allocated to reproduction was related to food intake throughout the process of maturation. For both males and females, there was little evidence of trade‐offs between the digestive gland and reproductive growth, as no significant correlation was found between dorsal mantle length‐digestive gland weight residuals. The role of the digestive gland as an energy reserve for gonadal growth should be reconsidered. Additionally, feeding intensity by both males and females decreased after the onset of sexual maturity, but feeding never stopped completely, even during spawning.     

Sexual dimorphism in histological characteristics and contractility of the iliofibularis muscle in the lizard Sceloporus torquatus

The iliofibularis is a hindlimb muscle used in lizard locomotion that is composed of at least three types of fibres: fast‐twitch‐glycolytic (FG), fast‐twitch‐oxidative‐glycolytic fibre (FOG) and slow‐twitch‐oxidative (SO). The striated skeletal muscle is a highly plastic tissue undergoing phenotypic change in response to activity. The lizard Sceloporus torquatus has sexual differences associated with microhabitat use, which can be reflected in the physiology and anatomy of the muscle, and thus, in our study, we analysed the morphological and contractile characteristics of the iliofibularis muscle (IF) of S. torquatus males and females. We found a larger prevalence of FOG compared with FG and SO fibres in the muscle of both sexes. We also found that males show larger areas of the three types of fibres, develop greater strength but also faster fatigue than females, suggesting that strength is a key functional feature that enables males to perform faster movements (but for shorter periods), associated with the demands of territoriality.     

Biochemical composition of the Atlantic bonito Sarda sarda from the Aegean Sea (eastern Mediterranean Sea) in different stages of sexual maturity

The content (% wet mass) in water, ash, lipid, crude protein, DNA and RNA of different tissues was determined during sexual maturation of bonitos Sarda sarda from the Aegean Sea. A total of 220 specimens were collected in the following stages of sexual maturity: immature, resting, developing, mature, spawning and spent. Highest lipid levels in the white muscle, red muscle and liver were measured in immature specimens, while lowest levels were found in spawning bonitos. The gradual percentage of lipid reduction from immature to spawning bonitos was relatively higher in the liver (females 71·2% and males 64·4%) than in the white (females 59·2% and males 53·5%) and red (females 62·1% and males 51·7%) muscle. Lipid levels in the gonads increased gradually from the immature to spawning stage. The decrease of lipid in the somatic tissues was more intense in females than in males, and gonadal lipid content was higher in females than in males. There was a strong reverse correlation between water and lipid percentage in all tissues. Protein content decreased significantly only in spawning bonitos. The percentage of protein reduction from immature to spawning stage was relatively higher in males than in females in both white (females 3·4% and males 4·6%) and red (females 4·6% and males 5·1%) muscles. Protein content in the liver was significantly lower than in the other tissues, being highest in mature females. Gonadal protein content in females increased with maturation and decreased after spawning. The content in ash exhibited considerable stability. The RNA:DNA ratio exhibited a similar pattern of variation in both muscles. The RNA:DNA ratio increased during gonadal development gradually from the developing to spent stage. It was concluded that in S. sarda during gonadal development, there was an increase in gonadal lipid accompanied by a decrease in somatic tissue lipid reserves. Thus, reproductive inactive bonitos have more lipid in their edible part and a higher nutritional value than active ones.     

Sex difference in plasma ammonia but not in muscle inosine monophosphate accumulation following sprint exercise in humans

Since accumulation of ammonia in plasma has been shown to be lower in females than in males following sprint exercise, we hypothesised that muscle inosine monophosphate (IMP) accumulation would also be smaller in females, especially in type II fibres. A relationship between plasma ammonia and muscle IMP accumulation was expected, since ammonia and IMP are formed in equimolar amounts during the net breakdown of adenine nucleotides. The sprint-exercise-induced IMP accumulation, measured in biopsies from vastus lateralis muscle, did not differ between males (n = 16) and females (n = 16) either in type I fibres [males 4.6 (SD 3), females 5.7 (SD 2) mmol x kg(-1) dry muscle], type II fibres [males 13.2 (SD 4), females 12.6 (SD 4) mmol x kg(-1) dry muscle] or in mixed muscle [males 8.4 (SD 3), females 8.2 (SD 3) mmol x kg(-1) dry muscle]. The accumulation of plasma ammonia following the sprint was 35% lower in the females than in the males. The inter-individual variation in plasma ammonia accumulation was explained by the sex but not by the muscle IMP accumulation as tested in a multiple regression analysis. In conclusion, the smaller plasma ammonia accumulation following sprint exercise in females than in males would seem not to be explained by a smaller muscle IMP accumulation per unit muscle during sprint exercise.     

Sexual maturation in the black seabream Mylio macrocephalus Teleostei,Sparidae: changes in pituitary gonadotropes,hepatocytes and related biochemical constituents in liver and serum

Summary The black seabream, Mylio macrocephalus, exhibits the phenomenon of sex segregation. Immature fish are developing hermaphrodites, and show a considerable overlap with mature males in their body weights. Mature females tend to be the heaviest group. Fish can be classified into immature, developing and mature groups, with a further division into definitive males or females in the two latter groups. The developing groups still have bisexual gonads, whereas mature males have testes with only a comparatively inconspicuous portion of ovarian tissue, and mature females possess ovaries with vitellogenic oocytes and a greatly regressed testicular component. In the present study, monthly samples were collected over a 3-year period, and changes in pituitary gonadotropes and liver tissue studied by light, and electron microscopy. Seasonal changes in serum constituents were also studied by biochemical techniques.Gonadotropes increased in number and became hypertrophied during sexual maturation, showing an enhanced cytoplasmic vacuolation and degranulation of alcian blue- and periodic acid-Schiff-positive material. The levels of various biochemical constituents in the liver and serum of developing fish tended to be intermediate between those recorded in the immature and mature groups. In mature fish, the serum levels of glucose, sodium and calcium were elevated, but hepatic glycogen content was less than the developing group, and hepatocytes contained activated mitochondria. The seasonal changes in pituitary cytology, hepatic ultrastructure and serum constituents, could be correlated with the metabolic adaptations to sexual maturation.     

Variations in the biochemical composition of the squid Illex argentinus from the South Atlantic Ocean

General condition, biochemical composition changes and fatty acids in several tissues of I. argentinus at different sexual stages were studied. Ovarian maturation involves a simultaneous increase in ovary mass and in protein and lipid levels. Testes weights were modified less than the ovary with maturation and showed a constant biochemical composition during spermatogenesis. The digestive gland grew through most of the maturation process in both sexes. Water level was high in immature squid and low in mature females and males, and varied inversely to that of lipids. Dorsal mantle maintained a constant biochemical composition, between February (immature) and June (fertilized females and mature males). All tissues contained high concentration of polyunsaturated fatty acids followed by saturated fatty acids and monosaturated fatty acids. This digestive gland of the squid is rich in polyenoic fatty acids, 20:5n-3 and 22:6n-3. This tissue could be a cheap raw material, presently discarded, for production of polyunsaturated fatty acids.     

Tail Length and Mutual Mate Choice in Bearded Tits (Panurus biarmicus)

Direct sexual selection via mutual mate choice can result in both sexes showing conspicuous traits. We experimentally tested whether this hypothesis can explain tail length in the bearded tit (Panurus biarmicus). In this species, both sexes have a long, graduated tail. Males have, however, a longer tail than females, suggesting perhaps that females are choosier than males in selecting mates. We used two choice set‐ups for each sex: shortened vs. control tail individuals and elongated vs. control tail individuals. We found that direct sexual selection seems to operate differently in the two sexes. In both set‐ups, females spent more time with the male with the longest tail, and they also showed sexual display behaviour only towards these males. Males spent more time with control than with short‐tailed females, but they did not discriminate between control and long‐tailed females. Moreover, males displayed preference towards both short‐ and long‐tailed females. Thus, females preferred long‐tailed males, whereas males did not always prefer long‐tailed females. Our study suggests that mutual mate choice has played a role in the evolution of long tails in bearded tits. It also suggests that the sexual dimorphism in tail length has evolved because mate choice exerts a stronger sexual selection pressure on males than on females.     

Swarming, Delayed Sexual Maturation of Males, and Mating Behavior of Fopius arisanus (Sonan) (Hymenoptera: Braconidae)

Fopius arisanus is unusual among hymenopterous parasitoids in males having an obligatory premating period. We confirmed Hagen's (1953) view that sperm takes several days to migrate from the testes to the seminal vesicles. Males mated for the first time only 4 days after emergence, the time that sperm was first ever recorded in the seminal vesicles. In the field, we studied the sexual maturation of F. arisanus males in relation to their behavior. In general, sexually immature males were found in male-only swarms that persisted over several days in host tree canopies. Mature males were usually found in loose aggregations in the vegetation beneath host trees. Females entered these loose aggregations and were mated, whereas they were generally absent from swarms in the canopy. Swarming is therefore apparently not a primary component of the sexual communication system of the species. We describe, for the first time in F. arisanus, the behavioral sequence that accompanies the intersexual communication that leads to mating. Males probably release a volatile chemical that attracts females from a distance, but we have only circumstantial evidence for this. We also postulate that males may form aggregations to amplify the effects of this distance attractant. In the vicinity of males, females release a pheromone that attracts males, a process we demonstrated with female-baited sticky traps.     

Behavioural development of conspecific odour preferences in bank voles,Clethrionomys glareolus

Biological odours of conspecifics are known to have strong influences on behavioural interaction in bank voles Clethrionomys glareolus. This experiment tested two hypotheses. (1) Olfactory cues from familiar and unfamiliar mature opposite-sex conspecifics differ in their attractiveness to males and females, and their behavioural reactions change with age. (2) A genetically based mechanism is involved in female recognition of kin.In a two-choice preference test, prepubertal males and females were more attracted to familiar than to unfamiliar odours of opposite-sex conspecifics, as manifested by more time spent sniffing familiar voles. As the young reached sexual maturity they shifted their odour preferences. Mature males and females preferred the novel odour of unrelated opposite-sex conspecifics to that of relatives. The results of experiments testing the second hypothesis indicate that females use a genetically based mechanism to recognise their kin. Young and mature females were able to recognise the odour of their biological but socially unknown fathers, and showed the same pattern of behaviour as females in previous experiments.The possible biological functions of kin recognition in bank voles are discussed.     

Deficiencies in sex-regulated expression and levels of two hepatic sterol carrier proteins in a murine model of Niemann-Pick type C disease.

Hepatic sterol carrier protein-2 (SCP2) and sterol carrier protein-X (SCPx) levels in normal and in mutant Niemann-Pick Type C mice were determined by immunoblotting with antiserum against rat SCP2. A 14-kDa protein (SCP2) was detected in the cytosol fraction and a 58-kDa protein (SCPx) was found in both cytosolic and organellar fractions. Expression of hepatic SCPx protein was developmentally regulated in a sex-specific pattern. The amounts of organelle-associated SCPx increased 4-fold during sexual development of normal males but decreased dramatically during development of normal females. Levels of hepatic SCP2 increased much less dramatically during sexual maturation of normal males and females. Adult Niemann-Pick Type C mice were deficient in both hepatic SCPx and SCP2. The deficit in SCPx in affected males reflected a failure to increase hepatic SCPx levels during sexual maturation. In affected males SCPx remained at levels found in immature mice. Affected male and female mice were also unable to maintain levels of hepatic SCP2. The level of SCP2 was near normal in affected immature males and subnormal in affected immature females. During sexual maturation hepatic SCP2 declined in affected animals.     

Modulation of behavior in zebrafish,Danio rerio,according to female reproductive status and visual and chemical cues

Zebrafish, Danio rerio, is one of the most studied vertebrate models. However, there are still many aspects of its reproductive behavior to be elucidated. The aim of this work was to clarify whether males and females of this species display different behaviors according to sexual status, and the kind of cues they were exposed to (visual and/or chemical). Females in two different sexual status, pre- (PreS) or post-spawning (PostS), were exposed to single males cues (visual or chemical) or complementary cues (visual and chemical together). PreS females spent more time near the male’s compartment than PostS when they were exposed to complementary cues, but no differences were found when only one cue was present. Males showed a higher proximity to females when they were exposed to visual, and both cues together, but no difference was found according to females’ reproductive status. When no barrier was present, males and PreS females spent more time swimming together than males with PostS females. These results showed that females’ reproductive status, and the kind of cues to which females and males are exposed to, can modulate behaviors related to reproduction. Particularly, both cues together (visual and chemical) are necessary to trigger different behaviors in females according to their reproductive status.     

Reproduction of the Atlantic bobtail squid Sepiola atlantica (Cephalopoda: Sepiolidae) in northwest Spain

Atlantic bobtail squid (Sepiola atlantica) in northwest Spain show seasonal variation in population structure, with juvenile abundance peaking during summer and autumn. However, whether similar patterns exist for reproduction is unknown. Therefore, we describe the reproductive biology of 505 specimens of S. atlantica collected monthly during two consecutive years at two different sites off of Areamilla beach in the Ría de Vigo. Mature males displayed a type of sexual dimorphism previously unknown in members of this species, developing a muscular nodule in the base of each of the ventral arms over ontogeny. Reproductive output of both sexes was similar to that of other bobtail squids. Relative oocyte size (~10% mantle length) appeared to be similar to those of other bobtail squids. Females did not show evidence of having mated before complete maturity. Females of S. atlantica have group‐synchronous ovary maturation, with a positive correlation between female mantle length and ripe oocyte mass, suggesting a terminal investment strategy. Atlantic bobtail squids displayed the same seasonal patterns of reproductive traits at both sampling sites, with significant differences in reproductive activity between males and females. We consider reproductive traits in these small animals as adaptations to the coastal shelf lifestyle.     

Sexual segregation in ungulates: a comparative test of three hypotheses

In most social ungulate species, males are larger than females and the sexes live in separate groups outside the breeding season. It is important for our understanding of the evolution of sociality to find out why sexual segregation is so widespread not only in ungulates but also in other mammals. Sexual body size dimorphism was proposed as a central factor in the evolution of sexual segregation in ungulates. We tested three hypotheses put forward to explain sexual segregation: the predation-risk, the forage-selection, and the activity budget hypothesis. We included in our analyses ungulate species ranging from non-dimorphic to extremely dimorphic in body size. We observed oryx, zebra, bighorn sheep and ibex in the field and relied on literature data for 31 additional species. The predation-risk hypothesis predicts that females will use relatively predator-safe habitats, while males are predicted to use habitats with higher predation risk but better food quality. Out of 24 studies on different species of ungulates, females and their offspring chose poorer quality but safer habitat in only eight cases. The forage-selection hypothesis predicts that females would select habitat based on food quality, while males should prefer high forage biomass. In fact, females selected higher quality food in only six out of 18 studies where males and females segregated, in eight studies there was no difference in forage quality and in four studies males were in better quality habitat. The activity budget hypothesis predicts that with increasing dimorphism in body size males and females will increasingly differ in the time spent in different activities. Differences in activity budgets would make it difficult for males and females to stay in mixed-sex groups due to increased costs of synchrony to maintain group cohesion. The predictions of the activity budget hypothesis were confirmed in most cases (22 out of 23 studies). The heavier males were compared to females, the more time females spent foraging compared to males. The bigger the dimorphism in body mass, the more males spent time walking compared to females. Lactating females spent more time foraging than did non-lactating females or males. Whether species were mainly bulk or intermediate feeders did not affect sexual differences in time spent foraging. We conclude that sexual differences in activity budgets are most likely driving sexual segregation and that sexual differences in predation risk or forage selection are additive factors.     

Sexual Dimorphism in the Hindlimb Muscles of the Asiatic Toad(Bufo gargarizans)in Relation to Male Reproductive Success

In many anurans, the forelimb muscles of males are used to grasp females and are often heavier than those of females despite the larger female body size. Such sexual dimorphism in forelimb musculature is thought to result from sexual selection. In addition, the hindlimbs of frogs and toads play an important role in the reproductive process as amplectant males can expel rivals with robust hindlimbs through kicking. In this study, the sexual dimorphism in dry mass for six hindlimb muscles of the Asiatic toad(Bufo gargarizans) was investigated. The results showed that, when controlled for body size, the hindlimb muscle mass of males significantly exceeded that of females for every muscle. The hindlimb muscle mass of amplectant males was also significantly larger than that of non-amplectant males. These results suggested that if strong hindlimb muscles could improve mating success of males, sexual selection would promote the evolution of dimorphism in this character.     

Male Mate Preferences in the Mosquitofish Gambusia holbrooki

Although male mosquitofish invest little in their progeny, the simultaneous availability of many potential mates and the large variance in their quality are expected to favour the evolution of mechanisms of male mate choice. Males of Gambusia holbrooki were shown to exhibit sexual preferences when presented simultaneously with two potential mates. When females differed in size, males showed more sexual activity directed at the larger of the two and the time spent with this female increased with the difference between the two females. This preference, however, was lower than expected if males spent time in direct proportion to the difference in fertility between females. In the second part of the study, females which had just delivered were found to be clearly preferred over gravid females. Attractiveness of females dropped after the third day, and disappeared in the sixth day after parturition. The results are discussed in relation to the probable occurrence of sperm competition and sperm displacement in this species.     

Olfactory Communication and Neighbor Recognition in Giant Kangaroo Rats

We hypothesized that olfactory communication facilitates neighbor recognition in the giant kangaroo rat, Dipodomys ingens , and is therefore influential in coordinating social interactions in this solitary, desert rodent. We tested whether (i) D. ingens can discriminate between odors of same- and opposite-sex conspecifics; and (ii) the kangaroo rats exhibit scent preferences based on familiarity. In habituation-discrimination tests, we found that both genders distinguish differences between the scent of individuals of the same- and opposite-sex. In olfactory preference tests, both males and females spent significantly more time investigating the scent of their familiar cagemate than the scent of an unfamiliar conspecific. Giant kangaroo rats may be able to recognize familiar neighbors from olfactory cues, thus supporting a hypothesis of neighbor recognition. Neighbor recognition may be an important mechanism of social interactions in this endangered species.     

幼小鼠对种内几种化学信息的识别和反应

50年代以来,国际上相继开展了一些关于化学信息在小家鼠繁殖中作用的研究,并在实验室中揭示了一些反应:如集群雌鼠气味使雌鼠性周期延长的Lee-Boot效应,雌鼠气味能解除集群雌鼠对性周期的抑制、并促使它们同期发情的Whitten效应,以及陌生雄鼠气味中断妊娠的Bruce效应等等。但是,在成鼠间起作用的几种化学信息,是否能被幼鼠感受,对幼鼠的发育和性成熟是否产生影响,还是一个未知的问题。 影响小鼠发育的因素很多,除环境因子外,近来还出现了有关社群因素中外激素对小鼠性成熟影响的报道,发现雄鼠或给予雄激素的雌鼠有促进幼雌鼠性成熟的作用,范志勤发现父本气味和陌生雄鼠气味对幼雌鼠性成熟均有促进作用。但是,目前关于种内雌鼠气味、集群雌鼠气味、幼鼠气味影响性成熟的研究尚不多见。有关各种气味对性成熟效应的比较的报道亦少。本文的目的在于通过实验方法,阐明种内的几种化学信息,诸如父本、陌生雄性、雌性、集群雌性、幼雌等几种气味,对幼雌小鼠性成熟的影响,并据此了解幼鼠识别这几种信息的能力。     

Self-grooming induced by sexual chemical signals in male root voles (Microtus oeconomus Pallas)

Sniffing is one-way animals collect chemical signals, and many males self-groom when they encounter the odor of opposite-sex conspecifics. We tested the hypothesis that sexual chemical signals from females can induce self-grooming behavior in male root voles (Microtus oeconomus Pallas). Specifically, we investigated the sniffing pattern of male root voles in response to odors from the head, trunk, and tail areas of lactating and non-lactating females. The self-grooming behavior of males in response to female individual odorant stimuli was documented, and the relationship between self-grooming and sniffing of odors from the head, trunk, and tails areas were analyzed. Sniffing pattern results showed that males are most interested in odors from the head area, and more interested in odors from the tail as compared to the trunk area. Males displayed different sniffing and self-grooming behaviors when they were exposed to odors from lactating females as compared to non-lactating females. Males also spent more time sniffing and engaged in more sniffing behaviors in response to odors from the lactating females’ tail area as compared to the same odors from non-lactating females. Similarly, males spent more time self-grooming and engaged in more self-grooming behaviors in the presence of individual odors from lactating females as compared to individual odors from non-lactating females. Partial correlation analyses revealed that the frequency of self-grooming was significantly correlated with the frequency of tail area sniffs. Results from this experiment suggest that sexual attractiveness of lactating females is stronger than that of non-lactating females. Furthermore, the partial correlation analysis demonstrated that self-grooming in males is induced by odors from the tail area of females. Collectively, these results support the hypothesis that sexual chemical signals from females can induce self-grooming behavior in male root voles. Self-grooming may also reflect the groomer's sexual motivation and facilitate sexual interactions.     

Changes in the dominance rank and reproductive behaviour of male bonnet macaques (Macaca radiata)

The dominance rank of male bonnet macaques influenced their associations and sexual interactions with cycling and conceiving females. Only high-ranking males formed exclusive associations with high-ranking females, and high-ranking males copulated with these females more often than did other males. Changes in male dominance rank were directly related to changes in male mating behaviour, as males who rose in rank spent increasing amounts of time in exclusive proximity to conceiving high-ranking females, and males whose ranks declined spent decreasing amounts of time in proximity to such females. The year of the study in which dominance relationships were most stable was also the year in which the top-ranking male most successfully monopolized access to conceiving high-ranking females.     

Female Reproductive Seasonality and Male Influxes in Wild Mandrills (<Emphasis Type="Italic">Mandrillus sphinx</Emphasis>)

The correlates of variation in the number of males in primate groups form a long-standing question in primatology. We investigated female reproductive seasonality and the numbers of males in groups of wild mandrills (Mandrillus sphinx) in a 25-month camera-trap survey with 160 camera locations in Moukalaba-Doudou National Park, Gabon. We used 1760 videos to analyze group composition, including the presence of females with newborn infants and with sexual swellings, the number of males present in groups, and male spatial positioning in groups. Female reproduction was seasonal, with a peak in the number of newborns in the mid-rainy season and a peak in the number of females with sexual swellings in the early dry season. The number of males in the group increased in the dry season, with a much greater increase in the number of mature males (sevenfold) than in submature males (twofold). The peak number of mature males, but not submature males, in the group lagged significantly behind the peak in the number of females with sexual swellings, suggesting that submature males enter groups before mature males and/or that mature males stay in the group longer after the peak of females with sexual swellings. Mature, but not submature, males appeared frequently near females with sexual swellings. In conclusion, we found a clear relationship between the presence of receptive females and the number of males in the group, and evidence that male competitive ability influences male strategies.