Effects of aminoglutethimide phosphate on litter size and birth weight in superovulated rats

In this study, litter sizes, birth weights and survival rates of neonates in superovulated rats treated with aminoglutethimide phosphate (AGP) were studied. Young (8- to 9-week old) and adult (14- to 16-week old) rats were treated with 20 or 40 IU PMSG between 1100 and 1300 hours on the day of early diestrus, followed by identical doses of hCG 52 to 54 hours later. These rats received 10 mg AGP on Days 0 to 2 of pregnancy (AGP rats). The duration of pregnancy in the AGP-treated and control rats was about the same. Mean live litter sizes in young and in adult AGP rats treated with 20 IU PMSG and 20 IU hCG were significantly higher (15.5 and 15.4; P<0.01) than in the control rats (11.5 and 12.6). When AGP was given to young and adult rats pretreated with 40 IU PMSG and 40 IU hCG, they produced means of 17.7 and 17.3 live neonates, respectively. The birth weights for young (5.55 to 5.88 g) and adult (5.89 to 5.96 g) AGP rats were smaller than those of respective control rats (6.44 and 6.40 g; P < 0.05-0.01). When the number of neonates was adjusted to 8 per dam for nursing and rearing, all of them were alive at 5 weeks after birth and showed normal growth. However, body weight gains of the progeny of AGP dams were lower than those of controls. These results indicate that rats treated with large doses of gonadotropins and AGP produce larger litter sizes than nontreated controls.     

Sexual dimorphism,body size,bite force and male mating success in tuatara

Sexual dimorphisms in body size and head size are common among lizards and are often related to sexual selection on male fighting capacity (organismal performance) and territory defence. However, whether this is generally true or restricted to lizards remains untested. Here we provide data on body and head size, bite performance and indicators of mating success in the tuatara (Sphenodon punctatus), the closest living relative to squamates, to explore the generality of these patterns. First, we test whether male and female tuatara are dimorphic in head dimensions and bite force, independent of body size. Next, we explore which traits best predict bite force capacity in males and females. Finally, we test whether male bite force is correlated with male mating success in a free‐ranging population of tuatara (Sphenodon punctatus). Our data confirm that tuatara are indeed dimorphic in head shape, with males having bigger heads and higher bite forces than females. Across all individuals, head length and the jaw closing in‐lever are the best predictors of bite force. In addition, our data show that males that are mated have higher absolute but not relative bite forces. Bite force was also significantly correlated to condition in males but not females. Whereas these data suggest that bite force may be under sexual selection in tuatara, they also indicate that body size may be the key trait under selection in contrast to what is observed in squamates that defend territories or resources by biting. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 287–292.     

Male body size and mating success in swarms of the mayfly Epeorus longimanus

Epeorus longimanus is a widely distributed mayfly in the western United States that forms relatively large mating swarms. The operational sex ratio of swarms is highly male biased and males are potentially polygynous, suggesting that male-male competition over mates may be intense. We investigated whether body size influenced male mating success in E. longimanus , as evidence of sexual selection. Males collected as mating pairs had significantly greater body lengths compared with males collected randomly from the swarm on each of six sampling dates examined, and had significantly greater head widths than males from random collections on two dates. There was no indication that large males occupied preferred positions within the swarm, and we suspect that the large male advantage may be due to greater success in pursuing females. We found no evidence of size-assortative mating in E. longimanus indicating that males attempt to male with every female encountered, consistent with the brief copulatory period in mayflies and overall low parental investment of males.     

Plasma progesterone concentrations and length of the first spontaneous oestrous cycle in pubertal rats

The length of the first spontaneous oestrous cycle in pubertal Wistar-Imamichi strain rats determined by vaginal smears varied from 5 to 18 days. The variation was ascribed to the period (3-16 days) of the stage of vaginal smears consisting of leucocytic cells (L stage). Plasma progesterone concentration and the decidual reaction in the uterus were used as indicators of the function of the corpus luteum and the L stage period was categorized as short, lasting for 3-6 days (average 4 days) with non-functional corpora lutea, or long, lasting 9-16 days (average 12 days) and with functional corpora lutea. Rats with the long L stage showed nocturnal and diurnal prolactin surges, but no daily changes in prolactin values were observed in rats with a short L stage. Daily changes in prolactin concentrations were maintained by the administration of progesterone in rats ovariectomized on Day 6 of the L stage. Plasma progesterone values on Day 6 of the L stage decreased with ergocornine treatment on Days 4 and 5 of the L stage and administration of bovine prolactin restored the level. These results indicate that the L stage observed in the first oestrous cycle is maintained by a positive feedback relation between progesterone and prolactin secretions.     

Effects of litter size on maternal care, body weight and infant development in golden hamsters (Mesocricetus auratus)

The effects of litter size on maternal care, body weight and infant development of golden hamsters were investigated from a longitudinal perspective. Litters were culled to 1,3,6 and 9 pups, and the behavior and body weight of mothers and pups were recorded from the 5th to the 25th postpartum day. We noted that the time spent by mothers in bodily interactions with pups decreased as a function of litter size; maternal pup retrievals reached their maximum around the 13-15th day, which coincided with the increased locomotor activity of pups at this time; the total number of pup retrievals by the mother increased as a function of the litter size, but mothers of larger litters were more 'efficient' (i.e. they failed less frequently in exhibiting a full sequence of retrievals) and exhibited a low litter-size proportional mean number of retrievals. All mothers gradually lost body mass throughout lactation, and decrease in body weight was significantly related to litter size. The mean body weight gain (%) by pups decreased as a function of litter size, but we also noted that single and larger litter pups exhibited a decreased body mass (grams) by the 15th day, suggesting that infant development may be impaired at both extremes of experimental conditions. We concluded that the behavior of mothers and pups was affected by the litter size, and it appeared that the litter had an optimal size-not so large as to overlap the mother's physical capacity, and not so small as to fail to compensate for the parental investment.     

Components of lifetime mating success and body size in males of a scrambling damselfly

Sexual selection is hypothesized to favour small body size in males of scrambling species, that is, those in which males obtain matings by actively searching for females. I tested this hypothesis in a natural population of the scrambling emerald damselfly, Lestes sponsa. Mating efficiency (matings/visit to the pond) was the most important factor explaining variation in male lifetime mating success (LMS; 71%). This suggests a large potential for sexual selection. Path analysis of male LMS suggested a quality factor that positively affected both mating efficiency and life span. In contrast with the small-male mating advantage hypothesis, part of this potential for sexual selection was realized as stabilizing selection on male body size, indicating that there may also be a lower limit to body size for mating efficiency. This also illustrates that the constancy of body size may be explained by sexual selection alone. Survival explained about 20% of the variation in LMS and random processes were potentially important for determining LMS. My results show the problems of using mating efficiency as a measure for the intensity of sexual selection and the need to distinguish between potential and realized selection pressures, especially when comparing the importance of natural and sexual selection. I discuss mechanisms that may have caused the intermediate-male mating advantage in this scrambling species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Sexual size dimorphism and selection in the wild in the waterstrider Aquarius remigis: Body size,components of body size and male mating success

Sexual size dimorphism is assumed to be adaptive and is expected to evolve in response to a difference in the net selection pressures on the sexes. Although a demonstration of sexual selection is neither necessary nor sufficient to explain the evolution of sexual size dimorphism, sexual selection is generally assumed to be a major evolutionary force. If contemporary sexual selection is important in the evolution and maintenance of sexual size dimorphism then we expect to see concordance between patterns of sexual selection and patterns of sexual dimorphism. We examined sexual selection in the wild, acting on male body size, and components of body size, in the waterstrider Aquarius remigis, as part of a long term study examining net selection pressures on the two sexes in this species. Selection was estimated on both a daily and annual basis. Since our measure of fitness (mating success) was behavioral, we estimated reliabilities to determine if males perform consistently. Reliabilities were measured as ? statistics and range from fair to perfect agreement with substantial agreement overall. We found significant univariate sexual selection favoring larger total length in the first year of our study but not in the second. Multivariate analysis of components of body size revealed that sexual selection for larger males was not acting directly on total length but on genital length. Sexual selection for larger male body size was opposed by direct selection favoring smaller midfemoral lengths. While males of this species are smaller than females, they have longer genital segments and wider forefemora. Patterns of contemporary sexual selection and sexual size dimorphism agree only for genital length. For total length, and all other components of body size examined, contemporary sexual selection was either nonsignificant or opposed the pattern of size dimporhism. Thus, while the net pressures of contemporary selection for the species may still act to maintain sexual size dimorphism, sexual selection alone does not.     

Single-trait and antagonistic index selection for litter size and body weight in mice

Individual selection based on female performance only was conducted in four lines of mice: L⁺ for increased litter size, W⁺ for increased 6-week body weight, L^-W⁺ for a selection index aimed at decreasing litter size and increasing 6-week body weight and L⁺W^- for a selection index aimed at increasing litter size and decreasing 6-week body weight. A fifth line (K) served as an unselected control. All litters were standardized to eight mice at one day of age. Expected heritability was based on twice the regression of offspring on dam (h²_d), which contains additive genetic variance due to direct (σ²_Ao) and maternal (σ²_Am) effects and their covariance (σ_AoAm). Responses and correlated responses were measured either deviated (method 1) or not deviated (method 2) from the control line. Realized heritabilities (h²_R) for litter size were 0.19 ± 0.04 (1) and 0.16 ± 0.03 (2), which were similar to h ²_d of 0.17 ± 0.04. The h² _R for 6-week body weight of 0.55 ± 0.07 (1) and 0.44 ± 0.07 (2) agreed with h²_d of 0.42 ± 0.02. Realized genetic correlations (r*_GR) between litter size and 6-week body weight calculated from the double-selection experiment were 0.52 ± 0.10 (1) and 0.52 ± 0.13 (2), which were not significantly different from the base population estimate of r* _Gd = 0.63 ± 0.14. Divergence (L^-W ⁺ minus L⁺W^-) in the antagonistic index selection lines was 0.21 ± 0.01 index units (I = 0.305 P_W - 0.436 P_L, where P _W and P_L are the phenotypic values for 6-week body weight and litter size, respectively.). The h² _R of index units of 0.14 ± 0.02 calculated from divergence agreed with h²_d of 0.14 ± 0.04. Divergences in litter size (-0.19 ± 0.07) and 6-week body weight (0.46 ± 0.10) were in the expected direction. Antagonistic index selection yielded about one-half the expected divergence in litter size, while divergence in 6-week body weight was only slightly less than expected. Realized genetic correlations indicated that litter size, 6-week body weight and index units each showed positive pleiotropy with 3-week body weight, postweaning gain and weight at vaginal introitus and negative pleiotropy with age at vaginal introitus. Sex ratio and several components of fitness (days from joining to parturition, percent fertile matings and percent perinatal survival) did not change significantly in the selected lines.     

The role of body size in mating success of Sphenarium purpurascens in Central Mexico

1. The effect of body size on the assortative mating and reproductive behaviour of the univoltine grasshopper Sphenarium purpurascens (Charpentier) was studied in Central Mexico. 2. Assortative mating by size was observed in the field. Evidence of positive assortative mating in relation to body size was found in laboratory experiments. Female fecundity and male success in contests were also correlated with body size. 3. Larger females had a higher number of eggs per pod. Larger males usually won fights and were able to take over females from other males, and to resist takeovers by other males while guarding. 4. Individuals of both sexes were observed copulating with more than one sexual partner in the field, suggesting polygamy. Male–male contests determined access to females, and males exhibited a postcopulatory prolonged mate-guarding behaviour lasting up to 18 days. 5. In a 2-year study, sex ratio was male-biased at the beginning of the reproductive season and decreased to 1:1 by the end of the season, suggesting that the population is protandrous. 6. The results of this study indicate that assortative mating results from male–male competition and female availability, and suggests that body size is a potential target of natural and sexual selection.     

Physiological pineal effects on female reproductive function of laboratory rats: prenatal development of pups, litter size and estrous cycle in middle age

The present study investigates whether and how the pineal or its hormone melatonin influences female reproductive functions, namely the litter size, prenatal development of offsprings, and estrous cyclicity, especially its age-related cessation in a non-seasonal breeder, the laboratory rat. Wistar rats were maintained under a 24 h light-dark (12Lratio12D) cycle. Female rats were divided into 3 groups: non-operated (NO), sham-operated (SX), and pinealectomized (PX). Surgeries were performed in 35-40 day-old females. Starting at an age between 70 days and 7 months, female rats of all 3 groups were repeatedly mated with intact males. PX mothers more frequently delivered pups with malformations (e.g., taillessness, hydronephrosis, 7 out of 1263 pups) than control rats (0/1323; p<0.007). In the first delivery at 3 months of age, but not at later ages, PX mothers delivered more pups of lower body weight than control animals (p<0.001). Examination of vaginal smears showed that almost all female rats of the NO, SX, and PX groups had 4-day estrous cyclicity when they were young-between 60 days and 5 months of age. At an age of 17 to 18 months, most female rats of the NO and SX groups showed irregular, continuously diestrous or pseudopregnancy-like patterns, and 4-day estrous cyclicity was found in only 10% of the NO or SX animals. In contrast, about 50% of the PX rats showed 4-day estrous cyclicity at this older age (p< 0.001). Melatonin, when added to drinking water (0.4 mg/L) for 16 days during the dark phase increased the frequency of diestrous phase, except in continuously diestrous rats and very few others. This melatonin effect was strong in PX rats but relatively weak in SX rats. In conclusion, the pineal hormone appears to influence various reproductive functions and developmental processes, especially pregnancy and the timing of reproductive aging in rats. The effects of pinealectomy are more prominent at an age of 60 to 80 days (i.e., shortly after puberty) and at the beginning of the cessation of cycles in middle-aged females.     

Testes weight, body weight and mating systems in marsupials and monotremes

Relationships between testes weight, body weight and mating systems were examined in 40 marsupial species and in the extant monotremes. Relationships between relative testes weight and mating systems in marsupials resemble those previously described for primates. Thus relative testes weights are greatest in those marsupials where females mate with multiple males during the fertile period, i.e. polyandrous species (e.g. Antechinus ftavipes, Isoodon obesulus, Perameles nasuta, Potorous tridactylus, Macropus eugenii and M. agilis) and smallest in monandrous forms (e.g. Petauroides volans and Petaurus breviceps ) where females usually mate with a single male. These findings are consistent with effects of sperm competition upon the evolution of relative testes sizes in marsupials. Where field studies on marsupial mating systems are lacking, we make predictions based upon examination of their relative testes weights. Tarsipes rostratus, Acrobates pygmaeus, Macropus rufogriseus and Sarcophilus harrisii are predicted to engage in multiple matings and sperm competition. Conversely, Lasiorhinus latifrons, Cercatetus concinnus and Pseudoantechinus macdonnellensis are predicted to be monandrous in their mating behaviour. The monotremes ( Ornithorhynchus anatinus, Tachyglossus aculeatus and Zaglossus bruijnii ) are characterized by possession of very large testes; monotremes are shown to have significantly greater relative testes weights than marsupials, primates or avian species. This taxonomic difference is unlikely to be related lo the occurrence of oviparity or to the abdominal position of the testes in the Monotremata. Their mating systems are not known in detail, but some evidence for multiple matings (and hence for sperm competition) exists for Tachyglossus aculeatus so that their large testes may be adaptive in this context.     

Male mating success in a North American pitviper: influence of body size,testosterone, and spatial metrics

Males with enhanced traits relative to conspecifics often show increased mating and reproductive success and thus have a fitness advantage. The opportunity or potential for sexual selection is predicted to occur under these conditions. Here, we investigated proximate determinants of mating success in male copperhead snakes (Agkistrodon contortrix), a medium‐sized pitviper of North America. Specifically, we investigated the relationships of body size (snout‐vent length, body mass), body condition index, spatial metrics (total distance moved, home range size), and plasma testosterone concentration on mating success in males. The single mating season lasts from August through September. We compared a set of candidate linear mixed models and selected the best‐fitting one using the adjusted Akaike Information Criterion (AICc). The AICc‐selected model (model 2), with testosterone, body condition index, and home range size as predictor variables, showed that male mating success was positively correlated with testosterone. To our knowledge, this is the first report to show the relationship of testosterone and individual mating success in any snake species. A parallel study conducted on male fitness in A. contortrix of the same population used microsatellite markers to assign parentage of fathers (known mothers). Unlike our study, they found that snout‐vent length was positively correlated with reproductive success and that males were experiencing greater sexual selection. This relationship has been detected under natural conditions in other species of snakes. Although behavioural data are important in any mating system analysis, they should not stand alone to infer parentage, relationships or selection metrics (e.g. Bateman gradients). Long‐term sperm storage by females, female cryptic choice, and other factors contribute to the complexity of mating success of males. Accordingly, we thus conclude that estimates of reproductive success and fitness in cryptic species, such as copperheads and other snakes, require robust molecular methods to draw accurate conclusions regarding proximate and evolutionary responses. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 185–194.     

Effects of norgestomet-implants and fluorogestone acetate-impregnated sponges on oestrous cycle length and luteal function of ewes

Plasma progesterone profiles were used to assess luteal function and length and synchronization of oestrous cycles in ewes after insertion of subcutaneous ear implants containing Norgestomet or intravaginal sponges impregnated with fluorogestone acetate (FGA) for 12 or 14 days. Insertions were made 2, 9 or 16 days after synchronization of the oestrous cycle with FGA-sponges. An i.m. injection of 500 IU pregnant mares' serum gonadotrophin was given at the time of sponge or implant removal. Norgestomet- implants inserted 9 or 16 days after FGA-sponge treatment had no effect on luteal function but delayed the onset of a new oestrous cycle for the duration of treatment. Following withdrawal of implants, oestrus was effectively synchronized. When Norgestomet-implants were inserted 2 days after FGA-sponge treatment, luteal function was normal. At the time of implant removal, plasma progesterone levels were elevated suggesting the presence of functional corpora lutea. In contrast, insertion of FGA-sponges early in the oestrous cycle shortened the luteal phase and a new oestrous cycle was initiated within 48 h after sponge removal. These results indicate that Norgestomet- implants can artificially prolong the length of the oestrous cycle and do not affect the functional lifespan of corpora lutea in cycling ewes. However, when Norgestomet-implants are inserted early in the oestrous cycle, they are unable to cause premature regression of corpora lutea.     

Genetic parameters for feed intake,litter weight,body condition and rebreeding success in primiparous Norwegian Landrace sows

The aim of this study was to estimate genetic parameters for feed intake recorded as farmers’ perception of young sows’ appetite for the first 3 weeks of lactation (APP) and feed intake recorded for one day in the 3rd week of lactation (FEED), litter weight (LW) at 3 weeks, sow body condition at weaning (BC) and the following five reproduction traits: weaning-to-service interval of 1 to 7 days (WSI7), weaning-to-service interval of 1 to 50 days (WSI50), delayed service or not (DELAYED), pregnant on first service or not (PREGNANT) and litter size in 2nd parity (NBT2). The analyses included data on 4606 Norwegian Landrace 1st-parity sows and their litters. The Gibbs sampling method was used. The traits DELAYED and PREGNANT were analysed as threshold traits and APP, FEED, LW, BC, WSI7, WSI50 and NBT2 were analysed as linear traits. The heritability estimates for APP and FEED were low (<0.1), whereas the estimates for DELAYED and PREGNANT were rather high (0.4 and 0.3). The heritability estimate for BC was 0.2. The genetic correlations confirmed the complexity of breeding for sow performance; selection for heavy 1st litters may lead to lower body condition at weaning, which in turn leads to lower reproductive performance and smaller litters in 2nd parity. Selection for higher sow feed intake would improve body condition, but the simple way of measuring feed intake tested in this study (APP and FEED) cannot be recommended because of the low heritability obtained for these traits.     

Male mating success in the Azorean rock-pool blenny: the effects of body size, male behaviour and nest characteristics

Larger male Azorean rock-pool blennies Parablennius sanguinolentus parvicornis received more female visits, were courted more often by females and received more spawnings. Larger males also received a higher number of male intrusions, attacked more conspecifics and defended larger territories. Larger males showed more nest cleaning behaviour and a marginally non-significant trend for higher egg fanning rate. Male courtship, male attack rate against conspecifics and parental behaviour were all correlated with the frequency of female spawnings received by each male even when controlling for male size, suggesting that these behaviour patterns influence male mating success. On the other hand, a positive partial correlation was found between female courtship and the frequency of female spawnings, controlling for the number of female visits, which suggests a role for female mate choice on male mating success. Finally, males nesting in chambers in the bottom of pools received more spawnings than males nesting either in crevices or under boulders. However, nest opening area was associated significantly negatively with male mating success, when controlling for male size. Thus, the present data suggest strongly that male characteristics overrule nest characteristics in determining male mating success in the Azorean rock-pool blenny.