Seasonal variation in fertility, fecundity and litter sex ratio in laboratory and wild stocks of house mice (Mus domesticus)

Data compilations were made for three parameters pertaining to reproduction in a domestic strain (14 years) and a wild stock (4 years) of commensal house mice: (a) the percentage of females mated that produced litters; (b) the average number of pups per litter; and (c) the sex ratio of the pups in the litters. Fecundity and fertility varied seasonally in both domestic and wild mice. More females become pregnant and litter sizes were larger in the spring, summer, and fall months than during the winter season. Sex ratios also varied seasonally with more male biased litters produced during the 4 winter months. There appear to be seasonal shifts in productivity for both stocks of mice and these seasonal trends have not been altered by domestication under laboratory conditions. In spite of the fact that house mice are generally opportunistic, it is possible that there has been selection in the mice for shifting rates of production in relation to the best seasons of the year in terms of climate and resource availability. The higher production of males during summer months may be geared toward greater success in dispersal at that season and a higher probability that the males can find a territory and mate successfully in summer rather than winter. These results have potential implications for animal breeders and for those who maintain mouse colonies to produce animals for scientific investigations.     

Are Monomorphic Species Really Sexually Indistinguishable: No Evidence in Wild Long‐Tailed Finches (Poephila acuticauda)

Studies of sexual selection have focused mainly on dimorphic and/or polygynous species, where males, typically possess more exaggerated secondary sexual characters. However in many species, receiving far less attention, the expression of ornamental traits by females matches that in males. Several hypotheses have been proposed to explain sexual monomorphism, including mutual mate choice, genetic correlation, weak sexual selection and sexual indistinguishability. The sexual indistinguishability hypothesis suggests that sexual monomorphism is an adaption to avoid competition in monogamous flock‐living species. Based on measurements of museum skins and domesticated birds in Europe, the Australian long‐tailed finch was classified as a sexually monomorphic species, providing the best empirical support for the sexual indistinguishability hypothesis. Using both domestic and wild long‐tailed finches, we have re‐evaluated the extent to which the sexes are really indistinguishable. Morphological measurements of wing, tail, tail streamers, tarsus, bill and patch size, and colour spectrometric measurements of the yellow upper mandible and grey crown, were compared between the sexes. While the sexes are similar, males and females nonetheless differed in seven of ten traits in wild populations. In domestic populations, the sexes differed to a lesser extent but were still significantly different at three of ten traits, and discriminant analysis showed that 92% of wild individuals and 89% of domestic individuals could reliably be sexed based on just these morphological traits. Contrary to previous work, this study demonstrates that wild long‐tailed finches are sexually dimorphic, and that the similarity between males and females in this species cannot be explained by the sexual indistinguishability hypothesis.     

Variation in body condition of breeding Savi’s Warblers Locustella luscinioides: the reproductive stress and flight adaptation hypothesis revisited

Current theory suggests that mass change in adult birds while breeding may be adaptive (to reduce wing-loading during nestling feeding) or result from physiological stress. To test which might be more important in determining mass loss in breeding Savi’s Warblers (Locustella luscinioides), we used a new approach in which the variation in four indices of body condition was described: weight, fat score, muscle score and lean weight (i.e. excluding fat and muscle). We expected weight variations to be adaptive if they involved changes in fat and lean weight, whereas physiological stress should influence the muscle score to a greater extent. As in other species, females showed a greater variation in weight, and carried more fat, than males during the breeding cycle. During incubation, females had greater weight and fat score than males. The weight remained constant and lean weight declined in both sexes, whereas females increased in muscle, which probably reflects the regression of the reproductive organs. During the nestling stage, both sexes declined significantly in all four indices of condition, showing evidence of physiological stress. However, the greater decline in weight in females than in males is consistent with the flight-adaptation hypothesis, as are the cyclic changes in lean weight associated with the various nesting attempts. The fact that both sexes declined significantly in weight, muscle and lean weight with an increasing number of nesting attempts, but not in fat, which was recovered after each nestling period, also indicates that both reproductive stress and adaptive changes occur during breeding. When the whole breeding season was considered, females showed a greater decline in muscle than males, which we interpret to be evidence for a greater reproductive stress in females. We suggest that the small breast muscle size and depleted protein reserves at the end of the breeding period might influence future survival through impaired flight ability and a compromised post-breeding moult.     

Acoustical variations in sexually dimorphic features of distance calls in domesticated zebra finches (Taeniopygia guttata castanotis)

Species-specific distance calls (DCs) were recorded from Zebra finches (Taeniopygia guttata castanotis) obtained from three different breeding stocks: Japanese breeders that use Bengalese finches as fostering parents, and Japanese and American breeders that let natural parents rear Zebra finches. These calls were analyzed for five acoustic parameters that were shown to be sexually dimorphic in wild Zebra finches. Male Zebra finches had DCs that were variable among breeding stocks and among individuals. Female DCs recorded from Bengalese-fostered birds were generally longer in duration and higher in pitch than those recorded from Zebra-finch-reared birds, males and females in each breeding stock differed in at least one acoustic parameter, but that parameter was unique in each of the breeding stocks. These results suggest that although sexual dimorphism in Zebra finch DCs has gradually disappeared during the process of domestication, at least one acoustic attribute which allows discrimination between the calls of the sexes has been preserved.     

A comparative analysis of inherent discrimination and the following reaction in wild and domestic goslings]

Early behavioural reactions playing an important role in obligatory learning were studied in wild and domestic goslings. It was found that domestication did not affect considerably early discrimination but inhibited the development of locomotor activity. As a result, the following reaction was lower in domestic goslings than in wild ones.     

Do age‐specific survival patterns of wild boar fit current evolutionary theories of senescence?

Actuarial senescence is widespread in age‐structured populations. In growing populations, the progressive decline of Hamiltonian forces of selection with age leads to decreasing survival. As actuarial senescence is overcompensated by a high fertility, actuarial senescence should be more intense in species with high reproductive effort, a theoretical prediction that has not been yet explicitly tested across species. Wild boar (Sus scrofa) females have an unusual life‐history strategy among large mammals by associating both early and high reproductive effort with potentially long lifespan. Therefore, wild boar females should show stronger actuarial senescence than similar‐sized related mammals. Moreover, being polygynous and much larger than females, males should display higher senescence rates than females. Using a long‐term monitoring (18 years) of a wild boar population, we tested these predictions. We provided clear evidence of actuarial senescence in both sexes. Wild boar females had earlier but not stronger actuarial senescence than similar‐sized ungulates. Both sexes displayed similar senescence rates. Our study indicates that the timing of senescence, not the rate, is associated with the magnitude of fertility in ungulates. This demonstrates the importance of including the timing of senescence in addition to its rate to understand variation in senescence patterns in wild populations.     

Influence of pregnancy on locomotor and feeding performances of the skink, Mabuya multifasciata: why do females shift thermal preferences when pregnant?

It has been documented in the many-lined sun skink (Mabuya multifasciata) that pregnant females select lower body temperatures (27.6–30.8 °C) than do nonpregnant females and adult males (29.7–35.7 °C). We therefore used the skink to test the hypothesis that the maximization of reproductive benefits should be achieved in pregnant females by shifting thermal preferences towards the levels optimal for embryonic development but entailing relatively small costs of reproduction. Data on adult males showed that temperatures maximizing swimming stamina (indicative of locomotor endurance) fell within the range of body temperatures selected by nonpregnant females and adult males. Data on swimming stamina and feeding performance of pregnant females, nonpregnant females and adult males measured at 26 and 30 °C showed that: (1) pregnancy impaired locomotor and feeding performances, but such impairments did not persist after parturition; (2) the degree of locomotor impairment during pregnancy was greater at 26 °C than at 30 °C, but the degree of feeding impairment during pregnancy was greater at 30 °C than at 26 °C. Pregnant females of M. multifasciata selecting body temperatures at about 29 °C could not only produce good-quality offspring in a relatively short gestation length but also reduce reproductive costs associated with locomotor and feeding impairments to some extent. Thus, data from M. multifasciata validate the above hypothesis.     

Lazy males? Bioenergetic differences in energy acquisition and metabolism help to explain sexual size dimorphism in percids

1. Differences in energy use between genders is a probable mechanism underlying sexual size dimorphism (SSD), but testing this hypothesis in the field has proven difficult. We evaluated this mechanism as an explanation for SSD in two North American percid species--walleye Sander vitreus and yellow perch Perca flavescens. 2. Data from 47 walleye and 67 yellow perch populations indicated that SSD is associated with the onset of maturation: typically, males of both species matured smaller and earlier and attained a smaller asymptotic size than females. Males also demonstrated equal (perch) or longer (walleye) reproductive life spans compared with females. 3. To examine whether reduced post-maturation growth in males was due to lower energy acquisition or higher reproductive costs we applied a contaminant mass-balance model combined with a bioenergetics model to estimate metabolic costs and food consumption of each sex. Mature males exhibited lower food consumption, metabolic costs and food conversion efficiencies compared with females. 4. We propose that slower growth in males at the onset of maturity is a result of decreased feeding activity to reduce predation risk. Our finding that SSD in percids is associated with the onset of maturity is supported by laboratory-based observations reported elsewhere, showing that changes in growth rate, consumption and food conversion efficiency were elicited by oestrogen (positive effects) or androgen (negative effects) exposure in P. flavescens and P. fluviatilis. 5. Researchers applying bioenergetic models for comparative studies across populations should use caution in applying bioenergetic models in the absence of information on population sex ratio and potential differences between the sexes in energetic parameters.     

Both sexes suffer increased parasitism and reduced energy storage as costs of reproduction in the brown anole,Anolis sagrei

Sexual selection theory proposes that males suffer reduced immune function and increased parasitism as costs of expressing sexual signals. Life‐history theory proposes that females suffer the same costs because of inherent trade‐offs between reproduction and self‐maintenance. Mechanistically, each theory invokes an energetic trade‐off, although few experiments have directly compared these costs of reproduction between the sexes as a result of fundamental sex differences in the nature of reproductive investment and a tendency for each theory to focus on a single sex. To test whether males and females experience comparable costs of reproduction in terms of energetics, immune function, and parasitism, we used gonadectomy to eliminate most aspects of reproductive investment in wild brown anole lizards (Anolis sagrei) of both sexes. We compared these nonreproductive males and females with intact, reproductive controls with respect to stored energy (fat bodies), immune function (swelling response to phytohemagglutinin), and the prevalence and intensity of infection by four types of parasite (gastric nematodes, intestinal nematodes, faecal coccidia, and ectoparasitic mites). Gonadectomized anoles experienced dramatic increases in fat storage that were accompanied by decreases in the prevalence of intestinal nematodes and in the intensity of coccidia infection. These costs of reproduction were comparable between males and females, although neither sex exhibited the predicted increase in immune function after gonadectomy. Our results suggest that, despite fundamental sex differences in the nature of reproductive investment, both male and female anoles experience similar costs of reproduction with respect to energy storage and some aspects of parasitism.     

长爪沙鼠免疫功能、体脂含量和器官重量的季节变化

小型哺乳动物的体脂含量与免疫功能有关,并受环境条件的影响。为了进一步理解野生长爪沙鼠对环境的生存适应策略,我们于2004 年夏季(7～8月)和2005年冬季(1～3月)测定了野生长爪沙鼠的体重、体脂含量和脏器重量,以及由匙孔血蓝蛋白(KLH)对雄鼠所介导的体液免疫反应。结果发现:雄鼠的胴体干重和体脂含量都显著高于雌鼠,其他各项指标无性别差异。冬季雌雄沙鼠的体重、胴体干重、体脂含量和褐色脂肪组织的湿重,以及雄鼠的睾丸湿重都显著高于夏季。脾脏的重量冬季趋于降低。处理组(注射KLH )动物血清中抗KLH 抗体的含量在冬季和夏季都显著高于对照组(注射生理盐水),且冬季处理组显著高于夏季处理组。本研究结果为动物种群调节的“冬季免疫增强假说”提供了一个新的野外例证。没有检测到免疫器官和产热器官、免疫器官和繁殖器官之间的权衡关系。     

Control of Male and Female Fertility by the Netrin Axon Guidance Genes

The netrin axon guidance genes have previously been implicated in fertility in C. elegans and in vertebrates. Here we show that adult Drosophila lacking both netrin genes, NetA and NetB, have fertility defects in both sexes together with an inability to fly and reduced viability. NetAB females produce fertilized eggs at a much lower rate than wild type. Oocyte development and ovarian innervation are unaffected in NetAB females, and the reproductive tract appears normal. A small gene, hog, that resides in an intron of NetB does not contribute to the NetAB phenotype. Restoring endogenous NetB expression rescues egg-laying, but additional genetic manipulations, such as restoration of netrin midline expression and inhibition of cell death have no effect on fertility. NetAB males induce reduced egg-laying in wild type females and display mirror movements of their wings during courtship. Measurement of courtship parameters revealed no difference compared to wild type males. Transgenic manipulations failed to rescue male fertility and mirror movements. Additional genetic manipulations, such as removal of the enabled gene, a known suppressor of the NetAB embryonic CNS phenotype, did not improve the behavioral defects. The ability to fly was rescued by inhibition of neuronal cell death and pan-neural NetA expression. Based on our results we hypothesize that the adult fertility defects of NetAB mutants are due to ovulation defects in females and a failure to properly transfer sperm proteins in males, and are likely to involve multiple neural circuits.     

Annual patterns in reproduction and perirenal fat of hares (Lepus europaeus) in sub-alpine Canterbury, New Zealand

The aim of this paper was to describe how the age, sex and reproductive state of hares affected the amount of fat found around their left kidney. A total of 2208 hares ( Lepus europaeus ) was shot and autopsied over 13 years from sub-alpine grasslands in Canterbury, South Island, New Zealand. Adult females may be pregnant from July to mid-March. Adult males' testis weights were highest from July to January, and some fertile males may have been present in all months but April. The amount of perirenal fat in adults increased in autumn, peaked in early winter, and decreased thereafter to low levels through spring and summer. Autumn fat deposition in males was not clearly related to reproductive state in individuals, although it coincided with seasonal testicular development. Autumn fat deposition in females may have been caused in part by the cessation of lactation, but, like that in males, the increase was also part of an endogenous pattern. Fat utilization in winter was related to breeding. In males, utilization coincided with reproductive activity and the amount of perirenal fat remained consistently low throughout the breeding season. In females, net fat utilization was associated with lactation but this was balanced to some extent by fat deposition induced by pregnancy. Females simultaneously lactating and pregnant were in finer balance between utilization and deposition. Other factors, such as the number of embryos and the stage of gestation, altered the fat balance in these hares. Fat was also deposited as a 'yolk-sac' in embryos.     

Observations on the reproductive cycle of cultures white sturgeon, Acipenser transmontanus

Males and females of cultured white sturgeon, Acipenser transmontanus, mature at an average age of 4 and 8 years, respectively. However, the onset of ovarian vitellogenesis and puberty are highly asynchronous in the female stock. Gonadal cycles are annual in males and biennial in females, and gametogenesis is influenced by season. Neuroendocrine regulation of reproduction appears to involve a dual gonadotropin system controlling gonadal development and spawning. Labile puberty and sex-specific duration of the gonadal cycle are distinct characteristics of cultured and wild sturgeon. Photoperiod and temperature play a significant role in environmental regulation of the reproductive cycle, but further studies are necessary to elucidate the roles of endogenous and environmental factors in sturgeon reproduction which is critically important for both aquaculture and conservation of endangered wild stocks.     

Meek Males and Fighting Females: Sexually-Dimorphic Antipredator Behavior and Locomotor Performance Is Explained by Morphology in Bark Scorpions (Centruroides vittatus)

Sexual dimorphism can result from sexual or ecological selective pressures, but the importance of alternative reproductive roles and trait compensation in generating phenotypic differences between the sexes is poorly understood. We evaluated morphological and behavioral sexual dimorphism in striped bark scorpions (Centruroides vittatus). We propose that reproductive roles have driven sexually dimorphic body mass in this species which produces sex differences in locomotor performance. Poor locomotor performance in the females (due to the burden of being gravid) favors compensatory aggression as part of an alternative defensive strategy, while male morphology is coadapted to support a sprinting-based defensive strategy. We tested the effects of sex and morphology on stinging and sprinting performance and characterized overall differences between the sexes in aggressiveness towards simulated threats. Greater body mass was associated with higher sting rates and slower sprinting within sexes, which explained the greater aggression of females (the heavier sex) and, along with longer legs in males, the improved sprint performance in males. These findings suggest females are aggressive to compensate for locomotor costs of reproduction while males possess longer legs to enhance sprinting for predator evasion and mate finding. Sexual dimorphism in the metasoma (“tail”) was unrelated to stinging and sprinting performance and may best be explained by sexual selection.     

Food deprivation effects on the running-wheel activity of wild and domestic Norway rats

Increases in activity typically accompany the food deprivation of Norway rats housed in activity wheels. The hypothesis that domestication has reduced the intensity of this response to food deprivation was tested by comparing the wheel-running scores of adult male wild (laboratory-reared) and domestic Norway rats when food-deprived and satiated.Wild rats were more active in the wheels than domestic subjects, irrespective of the presence or absence of food. However, the proportional increase in wheel-running when food deprived was the same for both stocks. It is hypothesized that the process of domestication has had little influence on the wheel-running response of rats to food deprivation.     

Male and female reproductive toxicity induced by sub-chronic ethanol exposure in CF-1 mice

Since genetic damage induced by ethanol exposure is controversial and incomplete and because germ and somatic cells constitute bioindicators for monitoring reproductive toxicity and genotoxic actions of ethanol consumption, the purpose of the present investigation was to evaluate morphological sperm, oocyte alterations and parental genotoxic effects after sub-chronic ethanol intake in the CF-1 outbred mouse strain. Ethanol 10% was administered to CF-1 adult male (treated males, TM) and female (treated females, TF) mice for 27 days, whereas water was given to controls from both sexes too (CM and CF). Post-treatment micronucleus frequency (MN-PCE/1,000/mouse) and gamete morphology were evaluated. To test whether change of female reproductive status results in maternal genotoxicity, CF-1 females received ethanol 10% (exposed group, periconceptionally treated females (PTF)) or water (control group, pregnant control females (PCF)) in drinking water for 17 days previous and up to 10 days of gestation. TM had a high percentage of abnormal spermatozoa vs CM (p < 0.001) and elevated parthenogenetic activated oocyte frequency appeared in TF vs CF (p < 0.001). Sub-chronic ethanol ingestion induced increased MN frequency in TM and TF (p < 0.01). In PTF, where blood alcohol concentrations were between 19–28 mg/dl, very significantly increased MN frequency was found vs PCF (p < 0.01), whereas MN values were similar to TF. These results show that sub-chronic alcohol ingestion in CF-1 mice produces sperm head dysmorphogenesis and oocyte nuclear anomalies, suggesting that morphological abnormalities in germ cells are probably related to parental genotoxicity after ethanol consumption.     

Reproductive behavior of the honeydew moth,Cryptoblabes gnidiella

Summary

The reproductive behavior of the honeydew moth, Cryptoblabes gnidiella (Millière) (Lepidoptera: Pyralidae), was studied in the laboratory. The sex ratio was 1.1:1, males to females, in both laboratory and field stocks. Most of the females that mated did so during the first night after emergence; males began mating on the following night. Mating occurred 1–2 h before dawn and averaged 100 min. Both sexes mated only once in one night. Most females mated only once in their lifetime, a few mated 2–4 times, whereas males mated up to six times per lifetime. Insects that lived longer also mated more times. When the sex ratio was altered from 3:1 to 1:3, males to females, the percentage of females that mated in one night dropped from 90 to 65, whereas the number of matings per male rose from 0.32 to 2.25. When fresh one-day-old females were provided daily at a ratio of three per male, the males averaged 1.4 matings per lifetime vs. 2.6 with 2- to 3-day-old females. A delay in mating did not affect the percentages of males and females that mated; highest percentages were obtained with 2- to 4-day-old males and females, but a delay in mating resulted in egg fertility dropping from 91 % to 73 %. The preoviposition period lasted a full day after mating, and then most of the eggs were laid during the first night. Average fecundity was 105 eggs per female (maximum: 230).     

Sexual behaviour and reproductive competition in male wild and domestic Norway rats

The copulatory behaviour of male wild Norway rats (Rattus norvegicus) exposed individually to females in hormone-induced oestrus is characterized by fewer mounts and intromissions per ejaculatory series, shorter ejaculation latencies, and longer ejaculatory clasps than the copulatory behaviour of domestic males. Competition between wild and domestic males tested simultaneously in pairs produced only minor changes in copulatory behaviour. The reproductive success of wild and domestic male pairs simultaneously exposed to naturally cycling females was nearly equal in both the laboratory and an outdoor enclosure. Genotype of the female had little effect on male copulatory behaviour. The copulatory behaviour of sexually naive and experienced domestic rats did not differ. However, most sexually naive wild males failed to exhibit copulatory behaviour under the test conditions employed.     

Influence of sex, body size, and reproduction on overwinter lipid depletion in brook trout

Expressed as percentages of total fresh body weight, lipids of brook trout Salvelinus fontinalis declined between October and April: reproductive males from 2·89 to 1·22%, reproductive females from 3·19 to 1·84%, and non-reproductive males and females from 2·75 to 2·08%. The absolute and proportional overwinter reduction in lipids among reproductive trout was more than twice that of non-reproductive trout, with reproductive males losing significantly more lipids than reproductive females. Larger reproductive individuals lost more lipids during winter, relative to body size, than smaller individuals, although such an effect was not evident among non-reproductive trout. The average overwinter reduction in lipids for reproductive males (58%), females (42%), and non-reproductive trout (24%) was negatively associated with mark-recapture estimates of overwinter survival probabilities of 0·27, 0·36, and 0·58, respectively, providing support for the hypothesis that energy is allocated to reproduction to the detriment of post-reproductive survival. Our emergent hypothesis that reproductive costs differ between sexes, and the life history consequences thereof, merit further study.