Litter Sex Ratio Research Articles

Within‐group sex ratios predict growth of social mole‐rats

AbstractGroups of wild animals can vary considerably in their composition, including in the proportion of group members who are male or female, that is the within‐group sex ratio. Variation in within‐group sex ratios can arise from active adjustment of litter sex ratios by mothers, from sex differences in mortality, dispersal and immigration, or from stochastic variation in recruitment. Variation in the within‐group sex ratio can have consequences for within‐group competition and can affect individual life histories throughout development. In this paper, we explore which processes may generate variation in within‐group sex ratios in wild Damaraland mole‐rats (Fukomys damarensis), a singular cooperative breeder. We investigate whether within‐group sex ratios predict the growth, body condition and philopatry of individuals. We show that although the population‐level sex ratio is balanced, skewed within‐group sex ratios are common, particularly among small groups. Our data suggests that stochastic variation in the sex of recruits explains natural variation in the sex ratio of wild groups. Non‐breeding individuals in groups with a sex ratio biased towards their own sex grow more slowly than individuals in groups biased towards the opposite sex, suggesting that intra‐sexual competition may decrease growth rates. We suggest that the costs of competition may contribute to the large variation in growth observed in social mole‐rat groups.

Repeated Exposure to High-THC Cannabis Smoke during Gestation Alters Sex Ratio, Behavior, and Amygdala Gene Expression of Sprague Dawley Rat Offspring.

Because of the legalization of Cannabis in many jurisdictions and the trend of increasing Δ9-tetrahydrocannabinol (THC) content in Cannabis products, an urgent need exists to understand the impact of Cannabis use during pregnancy on fetal neurodevelopment and behavior. To this end, we exposed female Sprague Dawley rats to Cannabis smoke daily from gestational day 6 to 20 or room air. Maternal reproductive parameters, offspring behavior, and gene expression in the offspring amygdala were assessed. Body temperature was decreased in dams following smoke exposure and more fecal boli were observed in the chambers before and after smoke exposure in dams exposed to smoke. Maternal weight gain, food intake, gestational length, litter number, and litter weight were not altered by exposure to Cannabis smoke. A significant increase in the male-to-female ratio was noted in the Cannabis-exposed litters. In adulthood, male and female Cannabis smoke-exposed offspring explored the inner zone of an open field significantly less than control offspring. Gestational Cannabis smoke exposure did not affect behavior on the elevated plus maze test or social interaction test in the offspring. Cannabis offspring were better at visual pairwise discrimination and reversal learning tasks conducted in touchscreen-equipped operant conditioning chambers. Analysis of gene expression in the adult amygdala using RNA sequencing revealed subtle changes in genes related to development, cellular function, and nervous system disease in a subset of the male offspring. These results demonstrate that repeated exposure to high-THC Cannabis smoke during gestation alters maternal physiological parameters, sex ratio, and anxiety-like behaviors in the adulthood offspring.

Maternal pre-conceptional glyphosate exposure impacts the offspring hepatic and ovarian proteome.

Glyphosate (GLY) is an herbicide used for rural and urban weed control. Urinary GLY in women is associated with shortened gestational length yet effects of GLY on offspring due to maternal exposure are unclear. This study tested the hypothesis that maternal chronic pre-conceptional GLY exposure would cause phenotypic and molecular changes in F1 offspring. Female C57BL/6 mice (7-week-old; n = 40) received saline vehicle control (CT; n = 20) or GLY (2 mg/kg; n = 20) daily per os for 10 weeks. At dosing completion, females were housed with unexposed males and divided into Cohort 1 who were euthanized at gestation day 14 (n = 10 per treatment) and Cohort 2 who completed gestation (n = 10 per treatment). F1 female ovarian and liver samples underwent LC-MS/MS and bioinformatic analysis. Maternal exposure did not affect litter (P > .05) sex ratio, or embryonic or neonatal gross phenotypes. In Cohort 2 offspring, no treatment effect on (P > .05) offspring anogenital distance, puberty onset, or ovarian follicular composition was noted. Body weight was increased (P < .05) in male GLY-exposed compared with CT dam offspring. F1 females from GLY-exposed dams had altered (P < .05) abundance of 54 ovarian and 110 hepatic proteins. Pathways altered in the ovary (false discovery rate [FDR] ≤ 0.07) included thermogenesis and phosphatidylinositol-3 kinase-AKT signaling and in liver (FDR ≤ 0.08) included metabolic, glutathione metabolism, oxidative phosphorylation, non-alcoholic fatty liver disease, and thermogenesis. Thus, pre-conceptional GLY exposure affected offspring phenotypic and molecular profiles potentially impacting reproductive health.

Maternal cortisol level around conception is associated with offspring sex ratio in captive European wild rabbit (Oryctolagus cuniculus)

The sex ratio of the offspring at birth is usually 1: 1 established by natural selection. The sex allocation model predicts that if parents have adequate resources, they would benefit from differentially allocating maternal investment to that sex having higher fittness under the particular environmental conditions. However, little is known about what mechanisms would result in biased sex ratio. One such mechanism could be the interaction of of stress reactivity and progesterone levels in the mothers around conception. In the present investigation the fecal cortisol and progesterone levels at the day of conception were measured in fifteen European wild rabbit does kept in cages. The does were clustered to low and high cortisol response groups and the sex ratio of their progeny was determined. We found a significant correlation between the progesterone levels of mothers and their stress status measured at the mating. This correlation was also reflected in the sex ratio bias in their litters. Even though the litter size was not different, we found higher progesterone levels and more female offspring in the does with higher cortisol levels indicating that maternal status around conception may affect the litter sex ratio.

Maternal survival costs in an asocial mammal.

Maternal characteristics, social dynamics, and environmental factors can all influence reproduction and survival and shape trade‐offs that might arise between these components of fitness. Short‐lived mammals like the golden‐mantled ground squirrel (GMGS; Callospermophilus lateralis) tend to maximize effort toward current reproduction at the expense of survival but may be complicated by other aspects of the species’ life history and environment. Here, we use 25 years of data (1995–2020) collected from a population of GMGS at the Rocky Mountain Biological Research Laboratory in Gothic, Colorado, to test the effect of several maternal characteristics (e.g., age, experience, and timing of litter emergence), social context (e.g., litter sex ratio and kin density), and environmental context (e.g., date of bare ground and length of vegetative growing season) on survival of reproductive female GMGS using Cox proportional hazard models. Our results indicated that social dynamics (i.e., density) and environmental conditions (i.e., standardized first day of permanent snow cover and length of growing season) explained significant variation in annual maternal survival, while maternal characteristics did not. A higher density of related breeding females and the total number of females (both related and unrelated to the focal mother) were associated with an increase in the mortality hazard. A later standardized date of the first day of permanent snow cover and a shorter growing season both reduced the maternal mortality hazard. Together, our results suggest that factors extrinsic to the squirrels affect maternal survival and thus may also influence local population growth and dynamics in GMGS and other short‐lived, territorial mammal species.

Sexual dimorphism in placental development and function: Comparative physiology with an emphasis on the pig.

Across mammalian species, it has been demonstrated that sex influences birth weight, with males being heavier than females; a characteristic that can be observed from early gestation. Male piglets are more likely to be stillborn and have greater preweaning mortality than their female littermates, despite the additional maternal investment into male fetal growth. Given the conserved nature of the genome between the sexes, it is hypothesized that these developmental differences between males and females are most likely orchestrated by differential placental adaptation. This review summarizes the current understanding of fetal sex-specific differences in placental and endometrial structure and function, with an emphasis on pathways found to be differentially regulated in the pig including angiogenesis, apoptosis, and proliferation. Given the importance of piglet sex in agricultural enterprises, and the potential for skewed litter sex ratios, it is imperative to improve understanding of the relationship between fetal sex and molecular signaling in both the placenta and endometria across gestation.

Progestogen metabolites for use in pregnancy monitoring of 13-lined ground squirrels (Ictidomys tridecemlineatus).

This research was conducted to discover whether pregnancy prediction is possible in female 13-lined ground squirrels (TLGS; a small hibernating ground squirrel named for their number of stripes). Pregnancy status in this species, we postulated, could be anticipated by generating profiles for individuals via a non-invasive technique known as fecal endocrine hormone profiling. Fecal samples were collected from 13 females thrice weekly for 4 weeks post-hibernation in the breeding season of 2016. Fecal samples were then processed and run through an assay known as an ELISA giving concentrations of hormone metabolites excreted through feces. We then set these samples against time points to develop a profile for each female. We have ascertained that elevated progesterone (potential pregnancy) can be detected by a commercially available assay kit. Understanding hormone patterns in animals gives researchers a better idea of best husbandry practices, including breeding in managed care.

Reproductive Characteristics and Performance of the Florida Panther: A Retrospective Examination of Long-Term Data

AbstractKnowledge of reproductive characteristics and performance (RCP) is necessary to estimate a species' breeding output and provide indicators to evaluate population health. Long-term data are important because they provide insight into the roles of intrinsic and extrinsic factors in determining RCP and lifetime breeding output of individuals and productivity of populations. Here, I examine the RCP of the Florida panther Puma concolor coryi by using an extensive data set collected from 1981 to 2019. My objective is to establish baseline RCP parameters and to determine the factors that affect lifetime breeding output. Briefly, the results from a variety of data analyses show the following: 1) Florida panthers exhibit a spring (March–May) birth pulse; 2) minimum age at sexual maturity does not differ between sexes; 3) mean annual proportion of females reproducing, litter size, and birth rate progressively decrease with increasing maternal age; 4) mean litter sex ratio is male biased; 5) mean birth interval differs between successful and unsuccessful litters; 6) proportion of kittens that recruited into the breeding population is small; and 7) distribution of parentage and mating partners among individuals in litters of known mothers and fathers is right skewed. The results indicate that breeding output is limited both by low birth rate and small proportion of offspring recruiting into the breeding population. The decreasing RCP with increasing maternal age suggests that costs of reproduction and progressive body condition senescence are important factors limiting lifetime breeding output. Despite these inhibiting factors, the data came from a period of substantial population growth and expansion since 1995, so the RCP shown is productive for this species. Outcomes from this study provide important RCP information for wildlife managers to implement measurable criteria to assess trends in Florida panther breeding output and population health.

Stereotypic behaviour predicts reproductive performance and litter sex ratio in giant pandas

Breeding and welfare problems confront many conservation breeding programs. Stereotypies—repetitive, unvarying, functionless behaviours —are common abnormal behaviours that often arise in suboptimal conditions. While the role of stereotypies in welfare assessment is well studied, few investigations address the relationship between stereotypic behaviour and reproduction. We examined the correlation between stereotypic behaviour and reproductive performance in 101 giant pandas (Ailuropoda melanoleuca). High stereotyping males copulated more and produced more cubs, suggesting that highly sexually motivated males were prone to stereotypy but also had high reproductive competence. Female stereotypies were negatively associated with all reproductive measures closely tied to behavioural competence: high stereotyping females were less likely to copulate, less likely to mother-rear cubs, and—probably a result of poor maternal care—had lower cub survival. However, females that exhibited stereotypies were more likely to produce a cub, suggesting stereotypies are tied to behavioural but not physiological competence. High stereotyping female pandas also displayed strong and consistent bias toward production of female offspring while paternal relationship to sex allocation was the reverse. These results are consistent with stress-mediated sex allocation theory. Our findings raise concern about differential reproductive success among high and low stereotyping pandas, and possible genetic adaptation to captivity.

Effect of feeding male mice with palm, fish, and sunflower oils on sperm characteristics and sex ratio of offspring.

Several studies have indicated that feeding female animal with fatty acids could result in alteration of offspring sex ratio; however, there is little information available regarding the effect of feeding male animal with fatty acids on sex ratio of offspring. The aim of current study was to investigate the effect of paternal feeding with n-3 and n-6 polyunsaturated fatty acids (PUFAs) on sperm characteristics and sex ratio of offspring in mice. Male mice received 2.50% of palm oil (control), fish oil (n-3 PUFAs) or sunflower oil (n-6 PUFAs) for two months. Sperm kinematics and viability were assessed using computer-assisted sperm analyzer and eosin-Y staining, respectively. Additionally, female mice were randomly introduced to males of three experimental groups to determine reproductive parameters including litter size, conception rate and sex ratio. Fish oil enhanced sperm concentration, motility and viability, whereas sunflower oil decreased sperm concentration. Nevertheless, progressive motility, velocity, linearity and straightness of sperms were not affected by source of fatty acids. Although supplementation with fish oil resulted in male-biased sex ratio, palm and sunflower oils did not impact sex ratio. Besides, source of fatty acids failed to influence conception rate and litter size. In conclusion, the present study provided evidence for the impact of paternal fish oil consumption on sex ratio of offspring for the first time. Moreover, it showed beneficial effect of n-3 PUFAs and adverse effects of n-6 PUFAs on seminal parameters.

Mechanisms affecting litter sex ratio and embryo quality

Mechanisms affecting litter sex ratio and embryo quality

Influence of Βeta-Cryptoxanthin Supplementation on Ovarian Reserve and Fertility Status in Aged Wistar Rats

Previous observational studies have suggested that β-cryptoxanthin, a micronutrient present in yellow and orange fruit and vegetables, may help delay the onset of menopause. Given the widespread social trend of delaying pregnancy, the possibility that β-cryptoxanthin supplementation may delay age-related loss of fertility and onset of menopause is of significant interest. In a parallel study, either saline or β-cryptoxanthin (5 µg/kg rat/day) was delivered to Wistar albino rats via an osmotic pump from 4 to 7 months of age. All control and β-cryptoxanthin-treated dams were fertile at 7 months of age, with no differences in litter size, sex ratio, or pup viability at the time of mating at 7, 9, 11, and 15 months of age (p ≥ .05 for all). As expected, over time there was a pronounced decrease in litter size and serum anti-Müllerian hormone (AMH), but with no significant differences between the two groups at any time point. Overall, there was a positive correlation between litter size and AMH (r = 0.324, p = .012), confirming a link between this serum marker of ovarian reserve status and fertility potential. At 16 months, bilateral oophorectomies were performed at necropsy, before conducting follicle density assessments of ovarian reserve. The total number and stage of follicle development were similar between the β-cryptoxanthin and control groups (13.8 ± 3.2 cf 10.2 ± 4.8, respectively, p > .05). β-cryptoxanthin supplementation for 3 months early in reproductive life was not effective in delaying ovarian senescence or enhancing fertility in rats later in life, contrary to the association suggested by observational studies in humans.

Effects of glyphosate on the ovarian function of pregnant mice, the secretion of hormones and the sex ratio of their fetuses

Glyphosate is the active ingredient of the commercial formulation Roundup®, which is used worldwide. This study aimed to investigate the toxic effects of pure glyphosate or Roundup® on pregnant mice and their fetuses during pregnancy. From gestation days (GDs) 1–19, ICR mice were orally administered distilled water, 0.5% glyphosate solution or 0.5%-glyphosate Roundup® solution. The ovaries and serum were collected at GD19. The results showed decreases in body weight gain and, ovary and liver weight in glyphosate-treated mice. Additionally, histopathological alterations in the ovary including increased atretic follicles, interstitial fibrosis and decreased mature follicles were observed in the groups treated with glyphosate. The serum concentrations of both progesterone and estrogen were markedly altered after glyphosate exposure, and there were also changes in the expression of GnRH, LHR, FSHR, 3β-HSD and Cyp19a1 genes at the hypothalamic-pituitary-ovarian axis. Furthermore, oxidative stress was observed in the treated mice, increasing the activity of T-AOC, CAT and GSH-Px, as well as the MDA content in both the serum and ovary. With regard to litters, the sex ratio was significantly altered by pure glyphosate. These results show that glyphosate is able to cause several effects on pregnant mice, such as ovarian failure, interference with hormone secretion by affecting the steroidogenesis-related gene expression, and oxidative stress. The sex ratio of litters was also influenced by prenatal exposure to pure glyphosate.

The sex ratio in farmed American mink (&amp;lt;i&amp;gt;Neovison&amp;lt;/i&amp;gt; &amp;lt;i&amp;gt;vison&amp;lt;/i&amp;gt;)

Abstract. The aim of the study was to analyse the sex ratio of American mink litters in relation to dam's age, gestation length, and time interval between the first and second mating. The observations were carried out on a mink farm located in northern Poland. The analysis involved litters of 207 females, aged 1 (n=107) and 2 years (n=100), which successfully raised all the born kits. The sex of the offspring was identified on weaning. The kits were assigned to groups according to their dam's gestation length, mating date, and first-to-second mating interval. It was found that female kits quantitatively predominated over male offspring. Longer pregnancies, delayed mating time, and greater interval between the first and second mating was accompanied by a higher number of female births in relation to male births.

Anogenital distance reflects the sex ratio of a gilt's birth litter and predicts her reproductive success1.

Anogenital distance (AGD) has been used to reflect masculinization in litter-bearing species. As masculinization affects behavior and reproduction, AGD could be measured to assist in selecting gilts with a temperament more suited to commercial production and greater reproductive potential. We hypothesized that gilts from a male-biased litter would have a longer AGD and poorer reproductive performance. In Exp. 1, AGD and weight were measured at day 1, day 21, and week 16 of age for gilts from male-biased litters (≥60% males; n = 51) and female-biased litters (≥60% females; n = 51). Sow AGD was measured 3 d after farrowing. In Exp. 2, AGD was measured at gilt selection at approximately 24 wk of age and gilts followed to second parity. Litter sex ratio affected AGD at 16 wk of age, with gilts from female-biased litters having longer AGD (mean ± SEM, 9.1 ± 0.7 mm vs. 11.0 ± 0.6 mm, P = 0.013). Anogenital distance was not different on day 1 or day 21. There was no effect of sex ratio on weight at any time, and sow AGD was not associated with the sex ratio of her litter. Gilts with an AGD longer than the mean of 11.55 mm were heavier (mean ± SEM, 118.8 ± 0.4 kg vs. 117.7 ± 0.4 kg, P = 0.023), were achieved puberty earlier (179.6 ± 0.6d vs. 182.2 ± 0.6 d, P = 0.001), were mated younger (200.6 ± 0.6 d vs. 203.2 ± 0.6 d, P = 0.001), and were more likely to be mated (91% vs. 83%, P = 0.005) than gilts with an AGD shorter than the mean. Gilts with an AGD greater than 11.55 mm had a greater born alive litter size (11.79 ± 0.20 vs. 11.20 ± 0.19, P = 0.018) compared with gilts with an AGD shorter than 11.55 mm. At 16 wk, AGD was associated with sex bias and could be used as a selection tool to predict reproductive success of the first parity, with a longer AGD being associated with gilts that had been born into a female-biased litter and that had better reproductive performance.

Costs of Franklin’s ground squirrel (Poliocitellusfranklinii) ectoparasitism reveal adaptive sex allocation

Parasite infestation may impose direct costs of blood, nutrient, and energy depletion, along with indirect costs of increased immune response upon hosts. We investigated how ectoparasitism influences body mass and reproduction in a free-living population of Franklin’s ground squirrels (Poliocitellus franklinii (Sabine, 1822)) located near Delta Marsh, Manitoba, Canada. We experimentally reduced ectoparasite burden by treating seven reproductive females with an insecticide following breeding and contrasted body mass and reproductive performance of those individuals to seven sham-treated control females. Insecticide-treated dams did not differ from sham-treated dams in body mass, litter size, or juvenile mass, and thus, dam growth and reproduction were not compromised by ectoparasite defense at the infestation levels experienced in this study. However, litter sex ratio differed significantly between insecticide-treated and control females, with a higher proportion of male offspring produced among females with reduced ectoparasite load. Our findings are thus consistent with the Trivers–Willard model for adaptive sex allocation, yet they provide novel comparative insight into how sociality may modulate the expression of adaptive sex allocation among small mammals given the differential payoff associated with the production of high-quality female versus male offspring in more social versus less social species.

Efek Ekstrak Air Biji Pepaya (Carica papaya L.) terhadap Fertilitas Mencit (Mus musculus L.) Betina

Papaya seeds were known as medicinal plant which have anti-fertility potencies. So it could be used as a herbal contraceptive. The purpose of this study was to test the anti-fertility effect of Papaya seed water extract on mice (Mus musculus L.) fertility which proved by pregnancy rate, litters number and sex ratio of litters. This study was designed by Completely Randomized Design, using 15 female Swiss Webster mice that were divided into 5 treatment groups with triplicates. The K(-) group were treated by distilled water; K(+) group were treated by contraceptive pills; P1, P2, P3 groups that were treated by papaya seeds extract with 1.4, 3.5 and 7 mg/animal/day respectively. Each treatment was given orally with 0.5 ml in volume for 21 days. At the end of treatment, mice was mated. The observed parameters were pregnancies occurence, litters number and sex ratio of the litters. The litters number data were analyzed by Analysis of Variance. The results showed there was differences in pregnancy time and sex ratio between control and treatment groups, but there was not significantly different in litters number. It could be concluded that the fertility of mice was inihibited by water extract of papaya seeds.

The sex ratio of a gilt’s birth litter can affect her fitness as a breeding female

Lifetime reproductive performance and behaviour are established in utero driven by genetics and the steroidal milieu of the uterine environment. Developing males synthesise androgens that can be absorbed by females in the litter. Consequently, the proportion of males in a litter has the potential to affect both lifetime reproductive performance and behaviour of female littermates. Although reproductive potential is understandably important for gilt selection, behaviour is becoming progressively more important as group housing of sows increases. Aggression can be a cause for removal from the breeding herd, and can also negatively affect reproductive performance and herd longevity. This review covers existing evidence of masculinisation in rodents and sheep, the mechanism causing masculinisation, and the knowledge gaps surrounding masculinisation in pigs. Premature culling of gilts is an economic and animal welfare issue in the pork industry resulting in low retention of gilts and reduced productivity. The selection of gilts needs to be improved to incorporate both lifetime reproductive potential and behaviour. We determined that there is cause to investigate the effect of the birth litter sex ratio of a gilt on her suitability for selection into the breeding herd.

The sex ratio of a litter affects the behaviour of its female pigs until at least 16 weeks of age

There are sex differences in behaviour with males tending to be more aggressive and less fearful than females. When females are treated with androgens they display more aggressive, male like, behaviours and this suggests that androgen exposure has a role in the development of aggression. Female pigs born into litters that are more than 60% male (male biased) are likely exposed to greater androgen concentrations in utero than female pigs born into litters that are greater than 60% female (female biased). We hypothesise that the proportion of males in the litter in utero affects female pig behaviour. We predict that gilts from male biased litters will be more aggressive and less anxious than gilts from female biased litters. The behaviour of females from male biased (n=24) and female biased (n=30) litters was assessed at day 11 and day 21 of life with an arena test, at weaning (28days of life) by assessing fight number and duration as well as injury scores and at 16 weeks of age with a resident intruder test. In the day 21 arena test, the pigs from female biased litters took longer to emerge into the arena than pigs from male biased litters (1.13±0.05 (42.2s) vs. 1.32±0.09 (15.5s) respectively, P=0.016). At weaning there was a higher scratch score for piglets from male biased litter (0.84±0.2 vs 0.69±0.15, P=0.015) and this continued as a trend on the day following weaning (1.76±0.10 vs 1.57±0.13, P=0.080). At 16 weeks of age in the resident intruder test 48% of gilts from male biased litters initiated a fight compared to 24% of gilts from female biased litters (P=0.08). Our data suggest that the sex ratio of the birth litter can affect behaviour of gilts, potentially having long term implications for sow aggression.

Female kin density affects offspring sex ratio in an asocial mammal, the golden-mantled ground squirrel, Callospermophilus lateralis

Evolutionary theory predicts that parents should bias investment in offspring towards the sex that will yield the higher fitness returns, and one outcome may be biased offspring sex ratios. Bias in offspring sex ratios has been proposed to vary with specific social, maternal and environmental conditions that alter the fitness returns of each sex, but empirical evidence is conflicting both within and across taxa. We used 18 years of pedigree and demographic data to investigate variation in offspring sex ratios in a population of golden-mantled ground squirrels. Despite overall parity in offspring sex ratio, we found predictable changes in offspring sex ratio in response to female density at the population level: squirrels produced more daughters when female density was low and more sons when female density was high. At the individual level, females adjusted litter sex ratios similarly, but only in response to high densities of kin, and not in response to density of nonkin. This effect was reversed for older females (≥3 years) in dense kin neighbourhoods, which were more likely to produce daughters, perhaps because older females had the behavioural dominance necessary to recruit daughters at high densities. By contrast, litter sex ratios did not vary with maternal condition or food availability. Our results support the local resource competition theory of offspring sex allocation for this species. Knowledge of female relatedness revealed patterns of sex ratio adjustment that otherwise would have been obscured, highlighting the importance of interactions with kin in an asocial species.