Seasonal aspects of sexual cannibalism in the praying mantis (<Emphasis Type="Italic">Mantis religiosa</Emphasis>)

According to the adaptive foraging hypothesis of sexual cannibalism, females face a trade-off between mating and consuming a courting male. Because male and prey availability can change seasonally, sexual cannibalism may change with season. However, we are not aware of any work examining how sexual cannibalism in insects relates to the time of season. Here, we examined the seasonal pattern of sexual cannibalism and reproductive behaviour in the sexually cannibalistic praying mantis (Mantis religiosa). We repeatedly collected the last instars of praying mantises from the field and brought them up under natural weather and photoperiod, but standardised feeding and socioecological conditions. After the females reached sexual maturity, we allowed all of the females to mate during two mating trials. In comparison to female praying mantises maturing later in the season, early-maturing females were larger but of poorer body condition on the day of a mating trial (20 days after the adult moult). During the first round of mating trials, early-maturing virgin females cannibalised males more frequently than their late-maturing counterparts. In contrast, late-maturing females that mated in the first round of mating trials were more likely than early-maturing, nonvirgin females to be cannibalistic in the second round of mating trials. The latency time until copulation was correlated with a risk of sexual cannibalism and was longer in early-maturing females. Our study suggests that the date of the last (adult) moult plays an important role in the occurrence of sexual cannibalism.     

Reproductive strategies and the influence of date of birth on growth and sexual development of an aseasonally-breeding ungulate: Reeves' muntjac (Muntiacus reevesi)

Unlike most species of deer, Reeves' muntjac does not have a seasonal reproductive cycle. Births are equally distributed throughout the year and, irrespective of season of birth, females start breeding when they have reached a minimum body weight of about 10 kg. A significantly smaller proportion of females is born in the autumn/winter than the spring/summer, but there is no effect of maternal age or condition on foetal sex ratios for first or subsequent pregnancies. Whilst aseasonal breeding increases female productivity, males are only able to hold territories encompassing the ranges of a number of does for a relatively short period of time. It is argued that for muntjac there is much less inter-sexual variation in lifetime reproductive success than for seasonally-breeding polygynous cervids. Hence, although muntjac are sexually dimorphic and polygynous, females do not invest preferentially in male offspring.
Young males can be fertile from 36 weeks of age, when their first antlers are still in velvet. Whilst season of birth has no effect on the rate of sexual development in females, it does for males, with autumn-born male fawns attaining sexual maturity earliest. This accelerated development occurs in the period following independence from the mother, and there is no evidence of a maternal cost in producing male fawns. Since the canine tusks are the main weapons for intra-sexual conflict, there could be clear gains in terms of reproductive success for males that attain sexual maturity, adult weight and adult tusk size quickly, even though their first antlers are much smaller than those of older bucks. The hypothesis is presented that, for muntjac, the majority of a male's lifetime reproductive success is achieved relatively early in life when the canine tusks are in pristine condition, and that bucks lose their territories, and associated access to oestrous does, once the canines are broken.     

Sexual variations in food quality and gastrointestinal features of sika deer (Cervus nippon) in Japan during winter: implications for feeding strategy

We assessed sexual variation in food quality and gut macrostructure in adult male and pregnant female sika deer, Cervus nippon (Temminck, 1838), in Japan during winter. These variations might have important implications relative to sexual differences in habitat use, forage acquisition, and digestive strategy. According to the sexual dimorphism-body size hypothesis the larger males would feed on poorer forage and have heavier stomach contents and heavier intestine contents and longer intestines than smaller females. However, the food quality in rumen contents of males was higher than, or at least similar with, that of pregnant females. In correspondence to food quality, the relative weights of stomach contents and intestines with contents, the relative lengths of intestines to the lengths of body and total intestines in pregnant females were similar to adult males. The relative weights of omasum and abomasum tissues in pregnant females were greater than in males. Our findings suggest sexual differences in feeding strategy in sika deer in Japan during winter. To meet greater nutritional demands of high metabolic rate and gestation, pregnant females seemed to maintain a greater volume of digesta in guts and had more stomach tissues than expected by the sexual dimorphism-body size hypothesis to compensate for poorer forage quality.     

Natal dispersal in relation to population density and sex ratio in the field vole,Microtus agrestis

Summary In a sample of 240 juvenile field voles 8% of the males and 22% of the females reached sexual maturity within their natal home range. Among individuals retrapped as adults, 58% of males and 23% of females had dispersed, i.e. had moved more than one home range diameter. The mean distance moved for males (58.5 m) exceeded that for females (28.6 m). Male movement distances were negatively associated with total density, and with density of adult females, but not with male density. Female movements were not related to population density. There were no relation between sex ratio and distance moved. The distribution of distances moved for both males and females fit a geometrical distribution, suggesting the importance of competitive processes.     

Reproductive biology of the guitarfish <Emphasis Type="Italic">Rhinobatos hynnicephalus</Emphasis> (Batoidea: Rhinobatidae) in Ariake Bay,Japan

Size at sexual maturity, reproductive cycle, and fecundity of the guitarfish, Rhinobatos hynnicephalus, were examined in Ariake Bay, Japan. Females reached sexual maturity at a larger size than males [total length (TL) at 50% sexual maturity: males, 431 mm; females, 476 mm]. Monthly gonadosomatic indices of males decreased abruptly from July to August. Histological examinations confirmed the presence of mature spermatozoa in the testes in July, with semen in seminal vesicles in July and August. Preovulatory ova were observed in females with near-term embryos in August. Parturition occurred in August, immediately followed by mating, ovulation, and fertilization. Gestation period is approximately 1 year. Fertilized uterine eggs without embryonic development were present throughout the annual reproductive cycle. Embryonic development began in June and ended in August, indicating that R. hynnicephalus undergoes embryonic diapause (9 months). Fecundity increased with TL and ranged from 1 to 9 (mean, 4.4) embryos per litter.     

Consequences of sexual size dimorphism on energetics and locomotor performance of Grammostola rosea (Araneae; Teraphosidae)

Most male spiders are smaller than females; during sexual maturity, males change their behaviour, abandoning their web or nest to seek out receptive females actively, whereas females stalk prey near their web or nest and tend not to move away from it. Considering this behavioural difference to be associated with increased locomotor activity at maturity, it may be hypothesized that males will have traits that increase locomotor performance. The present study examines the kinetics and energetics of the movements of the mygalomorph spider Grammostola rosea Walckenaer, a large spider with sexual size dimorphism. It is found that males have a higher maximum aerobic speed, average speed, distance travelled and critical angle of climbing than females, indicating better performance. Males also have lower costs of transport than females. These results support the hypothesis that sexual dimorphism in wandering spiders with active males, which are characterized by smaller body size and longer legs than the larger and more static females, is associated with low transport cost, high velocity and better locomotor performance.     

Male-male competition and mating success in the orb-web spider,Nephila clavata,with reference to temporal factors

Seasonal occurrence patterns of adults of both sexes, intensity of male-male interactions, and mating success in the spider,Nephila clavata, were examined in the field. Adult males began to attend female webs about 2 weeks before female maturation. Large adult males were abundant in the early breeding season, but small males increased later in the season. From the distribution of males among female webs and size relationship of males within a web, male-male interactions seemed to be more intense when most females were still subadult. This was verified by a field experiment in which males were artificially introduced to female webs that were attended by other males. It was found that the probability of introduced males remaining on subadult female webs was lower than that on adult webs. As mating occurred mostly in the period shortly after the female final molt and first male sperm precedence was known in all spiders reported so far, intense male-male competition on subadult female webs seemed to be reasonable. Male longevity had an important influence on the mating success of males with just-molted females. Mating success was also affected by the relative body size of males present in a given period. Since larger males occupied the position closest to females within a web and stayed there longer, relative body size appeared to influence mating success through male-male competition. Female body size at maturation declined with time; hence, males that attained sexual maturity earlier had the advantage of mating with larger and more fecund females. Therefore, early maturation as well as larger size seem to be two important trairs influencing the reproductive success of males.     

Immune defence,extra-pair paternity,and sexual selection in birds

Secondary sexual characters have been suggested to reliably reflect the ability of individuals to resist debilitating parasites, and females may gain direct or indirect fitness benefits from preferring the most extravagantly ornamented males. Extra-pair paternity provides an estimate of an important component of sexual selection in birds. Species with a high frequency of extra-pair paternity have a variance in realized reproductive success that is greater than the variance in apparent reproductive success, and extra-pair copulations and hence extra-pair paternity by females are often directly associated with the expression of male secondary sexual characters. If sexually dichromatic species have experienced a long period of antagonistic coevolution with their parasites, such species should have evolved larger immune defence organs than sexually monochromatic species. Bird species with sexual dichromatism had larger spleens for their body size than monochromatic species in a comparative analysis. Furthermore, species with a high frequency of extra-pair paternity were sexually dichromatic and had large spleens for their body size. These results are consistent with the hypothesis that females of dichromatic bird species seek extra-pair copulations to obtain indirect fitness benefits in terms of superior resistance of their offspring to virulent parasites.     

MEASURING SELECTION ON A POPULATION OF DAMSELFLIES WITH A MANIPULATED PHENOTYPE

The estimation of the relationship between phenotype and fitness in natural populations is constrained by the distribution of phenotypes available for selection to act on. Because selection is blind to the underlying genotype, a more variable phenotypic distribution created by using environmental effects can be used to enhance the power of a selection study. I measured selection on a population of adult damselflies (Enallagma boreale) whose phenotype had been modified by raising the larvae under various levels of food availability and density. Selection on body size (combination of skeletal and mass at emergence) and date of emergence was estimated in two consecutive episodes. The first episode was survival from emergence to sexual maturity and the second was reproductive success after attaining sexual maturity. Female survival to sexual maturity was lower, and therefore opportunity for selection greater, than males in both years. Opportunity for selection due to reproductive success was greater for males. The total opportunity for selection was greater for males one year and for females the other. Survival to sexual maturity was related to mass gain between emergence and sexual maturity. Females gained more mass and survived less well than males in both years but there was no linear relationship between size at emergence and survival for females in either year. However, females in the tails of the phenotype distribution were less likely to survive than those near the mean. In contrast, small males consistently gained more mass than large males and survived less well in one year. There was significant selection on timing of emergence in both years, but the direction of selection changed due to differences in weather; early emerging females were more successful one year and late emerging males and females the other. The number of clutches laid by females was independent of body size. Because the resources used to produce eggs are acquired after emergence and this was independent of size at emergence, female fitness did not increase with size. Small males may have had lower survival to sexual maturity but they had higher mating success than large males. Resources acquired prior to sexual maturity are essential for reproductive success and may in some species alter their success in inter- and intrasexual competition. Therefore, ignoring the mortality associated with resource acquisition will give an incomplete and potentially misleading picture of selection on the phenotype.     

Seasonal changes in serum metabolites in free-ranging alpine marmots (<Emphasis Type="Italic">Marmota marmota</Emphasis>)

Circannual changes in serum parameters and body mass were studied in free-ranging Marmota marmota that had been shot in Switzerland (Grisons) for management reasons in May, July, and September of 1995, 1996, and 1997; and in April 1996. Markers of lipid (triglycerides, cholesterol), protein (total protein, urea-nitrogen) and mineral (calcium, inorganic phosphate) metabolism were evaluated in 111 haemolysis-free serum samples; the effects of sex, age, reproductive status, season and year were tested. Mean body mass was higher in adult males than in adult females in July and September, and serum cholesterol concentrations were lower in adult males in May. Pregnant females had lower concentrations of total protein than non-pregnant females, and triglyceride concentrations were negatively correlated with the number of uterine ampullae. Inorganic phosphate decreased and total protein increased with age. In adults, triglycerides, cholesterol and urea-nitrogen increased mainly from May to July and decreased between September and May. Total protein, calcium and phosphate did not change throughout the year. This suggests that, during the active season, ingested lipids and amino acids were utilised for metabolic needs or lipid storage, while in winter, lipids were catabolised and protein was spared. Quantitative differences between years, observed for triglycerides and total protein during the active season, were probably due to different climatic conditions in each year.     

浙江南部近海小黄鱼生长和性成熟特征的异质性

鱼类生长和性成熟是渔业资源生物学研究的基础内容.为分析小黄鱼的生物学特征,本文以2015年11月—2018年11月浙江南部近海13个渔业资源季度调查航次获得的4920尾小黄鱼样品为研究对象,使用线性混合效应模型(LMEM),研究了小黄鱼生长和性成熟特征的异质性.结果表明:小黄鱼体长范围为13～215mm,优势体长组为1...     

New data on sexual dimorphism and reproductive biology of Alaska skate <Emphasis Type="Italic">Bathyraja parmifera</Emphasis> from the northwestern Pacific Ocean

New data on sexual dimorphism and features of reproductive biology of Alaska skate Bathyraja parmifera from the western Bering Sea and the northern Sea of Okhotsk are presented. Based on comparative analysis of 11 external morphological characters, the males differ from the females in the length of the disc and snout length (to the eyes, to the mouth, and to the nostrils). In the western Bering Sea, 50% of the females and 50% of the males reach the first sexual maturity at 84.5 cm TL and 85.2–90.2 cm TL, respectively; in the Sea of Okhotsk, 50% of the males reach their first sexual maturity at 80.8–83.8 cm TL (the assessment depends on the features of the method). Among smaller skates (less than 45 cm TL), the males prevail, but the proportion of the females increases in larger size groups; the sex ratio becomes equal in the exemplars 60–80 cm TL, but the males prevail again among the largest fishes (more than 80 cm TL).     

Sexual dimorphism of body size and shell shape in European tortoises

Adult body size and shape were examined in almost 1400 individuals of the tortoises Testudo graeca , T. hermanni and T. marginata from Greece. The size at maturity was greater in females than in males in all three species. Maximum and mean adult sizes were also greater in females than in males in T. graeca and T. hermanni . Males grew to a larger size than females in T. marginata , and mean adult size was similar in the sexes in this species. Sexual dimorphism of shape (adjusted for size covariate) was shown in most of the characters examined, and the degree of this dimorphism differed significantly among the three species. Differences were related to their contrasting courtship behaviours: horizontal head movements and severe biting in T. marginata , vertical head bobs and carapace butting in T. graeca , and mounting and tail thrusting in T. hermanni . There was no difference in the frequency of observations of courtship or fighting among the three species, but courtship was about 10 times more common than combat in males. All species showed greatest courtship activity in autumn; copulation was rarely observed in T. hermanni (only 0.36% of courting males) and not seen in the other species in the field. Observations made throughout the activity season indicated that feeding was equally common in males and females in all three species. Differences in shape were more likely to be the result of sexual selection than of natural selection for fecundity. Detailed predictions are made for sexual dimorphism of other characters in these species.     

Sexual and vegetative reproduction in the aboveground part of a dioecious clonal plant, <Emphasis Type="Italic">Dioscorea japonica</Emphasis> (Dioscoreaceae)

In dioecious clonal plants, the reproductive effort required to set seeds will be responsible for the larger investment in sexual reproduction by females. If there will be a trade-off in resource allocation between sexual and clonal reproduction, this differential sexual reproduction will lead to sexual differentiation in the relative amount of clonal reproduction. To test this prediction, we studied differences between the sexes in their phenologies and investments in sexual and vegetative reproduction (clonal reproduction by means of bulbils) with respect to ramet size in a dioecious clonal plant, Dioscorea japonica Thunb. The period of bulbil production overlapped the period during which infructescences developed. Females flowered later, produced heavier inflorescences, and fewer flowers per inflorescence than did males. Regression analysis using the size of the individual plants demonstrated that large females made smaller investments in inflorescences and larger investments in sexual reproduction than did large males. In contrast, females invested fewer resources in vegetative reproduction than did males. However, the total investments in sexual and vegetative reproduction did not differ between the sexes. These results supported our hypothesis on the sexual differentiation in sexual and clonal reproduction.     

Spawning season and size at sexual maturity of <Emphasis Type="Italic">Kyphosus bigibbus</Emphasis> (Kyphosidae) from northwest Kyushu,Japan

The reproductive characteristics of Kyphosus bigibbus were examined using individuals collected between June 2004 and February 2009 off Nagasaki Peninsula in northwest Kyushu, Japan. The spawning season and size at sexual maturity of this species were characterized based on a gonad index and histological examination of the gonads. The spawning season extends from June to October. This species is assumed to be an indeterminate, multiple-batch spawner. Females reached sexual maturity at larger size than males (fork length at 50% sexual maturity: males 284 mm, females 360 mm).     

Lack of gonadal control of the dorsal gland and sandbathing in male and female bannertail kangaroo rats (Dipodomys spectabilis)

Previous studies have demonstrated gonadal control of mammalian scent glands; castration leads to reduced scent-marking rates and smaller gland sizes. I investigated whether gonadal hormones control the size of the dorsal gland (a specialized sebaceous gland) and sandbathing as a scent-marking behavior in adult male and female bannertail kangaroo rats (Dipodomys spectabilis). Gland sizes of males and females were similar in all age classes, except adult males with larger body weights had proportionately larger glands than females. Male gland sizes declined 18% following castration but were not significantly smaller than those of intact males; females showed no change in dorsal gland size either as a result of ovariectomy or after estradiol benzoate implants. Sandbathing rates also did not decline as a result of gonadectomy. Rather, castrated males and overiectomized females sandbathed at higher frequencies than intact males and ovariectomized females with estradiol benzoate implants, respectively. Gonadal hormones apparently have little influence on the function of a specialized scent gland and may inhibit sandbathing as a scent-marking behavior in adult D. spectabilis.     

Serum biochemical values in fallow deer (<Emphasis Type="Italic">Dama dama</Emphasis> L.) from different habitats in Croatia

Serum biochemical values were determined in blood samples collected from 48 shot fallow deer from the Brijuni islands and 45 sedated fallow deer (Dama dama L.) from hunting grounds in the continental part of Croatia. The parameters were compared with regard to age, sex and habitat. Statistically significant differences were found for serum total protein concentration, alkaline phosphatase, aspartate aminotransferase and alanine aminotransferase activity between young and adult island deer, as well as for total protein, triacylglyceride, cholesterol concentration and alkaline phosphatase activity between young and adult continental deer. In young animals, island males had higher albumin concentrations, while continental males had higher alkaline phosphatase values than females. In adult animals, island males had a higher blood urea nitrogen concentration, while continental males had higher albumin and cholesterol concentrations, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and creatine kinase activities. In this group, males exhibited lower bilirubin and triacylglyceride concentrations than females. Our results indicate that besides age, sex and sampling method, nutritional and environmental factors should be considered when evaluating serum biochemical parameters of fallow deer     

Life-history characteristics of a wild population of vervets (Cercopithecus aethiops sabaeus) in Barbados,West Indies

Life history data are presented for a population of vervets, Cercopithecusaethiops sabaeus, in Barbados, West Indies. The data were obtained from two habituated troops and from vervets captured during a large-scale trapping program. Individuals of known age from one troop were weighed periodically, and separate growth curves generated for males and females. The mean weight of captured adult females was 3.3 kg; that of adult males, 5.3 kg. The average age at sexual maturity is estimated at 34 months for females and 60 months for males. Vervets give birth throughout the year, but most infants are born between April and July. The average interbirth interval following a surviving infant is 11.8 months. The mortality of juveniles is heaviest between birth and 2 years of age and decreases thereafter. Males emigrate from their natal troops at sexual maturity and one incident of a juvenile female emigrating is reported.     

池塘中斑索蟾的种群结构、个体生长与存活率

在澳大利亚新南威尔士南部沿海,作者搜集了一个池塘繁殖的斑索蟾(Crinia signifera)的种群统计资料。通过捕捉进出池塘的1 612只个体,获得种群大小、结构、生长率、性成熟时的大小和年龄、死亡率及寿命资料。迁移高峰从6月持续到11月,蛙的最高、最低遇见数量分别出现在春季和秋季。但第2年,该池塘蛙的数量明显减少,可能是由于补充到种群中的幼体数量很少的缘故。6个月后个体的重捕率很低;但距第一次捕获18个月以后,仍有个别个体再次被捕获。性成熟时,雌性比雄性的身体大一些。生长曲线显示,雌性比雄性的生长更快,所以更早地达到性成熟。研究种群的数量、结构和死亡率趋势等与已知的其它Crinia signifera种群基本一致。但研究种群迁移活动的高峰出现较晚,并且夏季的活动水平明显很高。这种长的活动时间可能会导致存活率的下降,同时有利于选择迅速性成熟的雌性[动物学报51 (3) : 393 -400 , 2005]。