Offspring Sex Ratio Research Articles

Using Feathers for Molecular Sexing of Straw-headed Bulbul (<i>Pycnonotus zeylanicus</i>) Offsprings

Sex determination of of straw-headed bulbul offspring was carried out from 27 offspring’s plucked feather samples in a captive breeding program. Using direct PCR, this study provided more evidences that feather samples are reliable as a source of DNA for non-invasive and effective molecular sexing. The study also revealed that the offspring sex ratio of straw-headed bulbul was slightly inclined towards males, but there was no significant difference from the value of 0.5.

The influence of environmental conditions on sex determination in the blue mussel Mytilus edulis

Abstract The factors affecting sex determination remain largely unknown for most bivalve species. Environmental factors, such as temperature, are known to influence sex determination in some species, and this has been hypothesized for the mussel Mytilus edulis, but not experimentally validated yet. Adult exposure to different environmental conditions during gametogenesis, which occurs seasonally, may also affect offspring phenotype, including sex determination. Intergenerational carryover effects have been reported in bivalves, but the impact of parental exposures on offspring sex determination has not been examined so far. To address these questions, artificial fertilizations were performed on individuals collected in three different years and their embryos were reared at three different temperatures to specifically test if the environment influences offspring sex ratio through effects on parental developing gametes and/or on developing embryos. The analysis of 1938 embryos from 25 crosses revealed a significant effect of both temperature treatments and sampling years on the proportion of females. However, the overall variation is mostly explained by the “temperature treatment × sampling years” interaction. Taken together, our results suggested that interannual environmental variations experienced by the parents (during gametogenesis) and embryo (during development) can influence the sex of the offspring in M. edulis.

Adjustment of fecundity and sex ratio in response to social environments in a haplodiploid mite

Animals can adjust reproductive strategies in favour of corporation or competition in response to local population size and density, the two key factors of social environments. However, previous studies usually focus on either population size or density but ignore their interactions. Using a haplodiploid spider mite, Tetranychus ludeni Zacher, we carried out a factorial experiment in the laboratory to examine how ovipositing females adjust their fecundity and offspring sex ratio during their early reproductive life under various population size and density. We reveal that females laid significantly more eggs with increasing population size and significantly fewer eggs with increasing population density. This suggests that large populations favour cooperation between individuals and dense populations increase competition. We demonstrate a significant negative interaction of population size and density that resulted in significantly fewer eggs laid in the large and dense populations. Furthermore, we show that females significantly skewed the offspring sex ratio towards female-biased in small populations to reduce the local mate competition among their sons. However, population density incurred no significant impact on offspring sex ratio, while the significant positive interaction of population size and density significantly increased the proportion of female offspring in the large and dense populations, which will minimise food or space competition as females usually disperse after mating at crowded conditions. These results also suggest that population density affecting sex allocation in T. ludeni is intercorrelated with population size. This study provides evidence that animals can manipulate their reproductive output and adjust offspring sex ratio in response to various social environments, and the interactions of different socio-environmental factors may play significant roles.

Maternal influence on the skewing of offspring sex ratio: a review

Sex pre-selection of the progeny to suit the livestock production system aids in greatly increasing the efficiency and profitability of the livestock enterprise to meet the demand for animal meat and dairy products. Individual animals can skew the sex ratio in response to various social and environmental stipulations. These social and environmental factors include the composition of the maternal diet, maternal hormonal levels, maternal stress, and the time of insemination. Hence, this present review focuses on these approaches and their success rate as premises for the alterations of offspring sex ratio in different animal species. Numerous studies have linked maternal nutrition and its influence on offspring sex ratio. A maternal diet rich in calcium and magnesium favoured the production of more females, while diets rich in sodium and potassium favoured more males. Furthermore, feeding animals with a particular type of fat diet, including omega-3, omega-6, or omega-9 fatty acids, assists in sex pre-selection. The circulating hormone level in females during conception is associated with the skewing of sex ratio. In addition, maternal stress during the conception period is also found to be associated with the skewing of the sex ratio in favour of female offspring. The timing of insemination relative to the ovulation period has been identified as a promising approach for the pre-selection of offspring sex; however, proper detection of oestrus is crucial. Among all the approaches reported, dietary manipulation could be regarded as the most affordable and stands a better chance of being optimised for commercial livestock production. Reduction in the cost of desired sex production by adopting sex pre-selection techniques will lead to the improvement of the economy and minimise the culling of the undesired sex. However, further research is necessary to focus on the understanding of the underlying molecular mechanisms for the production of animals of the desired sex.

Constraints Affecting Fertility of Sex Sorted Semen: An Overview

In most mammals, the male to female sex ratio of offspring is about 50% because half of the sperm contains either the Y chromosome or the X chromosome. Desired sex either male or female which is produced from semen having X or Y bearing sperm is known as sexed semen. Flow cytometry is the only proven method for semen sexing to be commercially viable with more than 90% accuracy to produce calves of desirable sex. The sexed semen technology has several advantages, the production of more female calves and more milk, and lowered risk of dystocia. Increased efficiency of progeny testing, embryo transfer and in-vitro fertilization program has proposed a demand of feasible technology for sex sorting of spermatozoa. In India, this revolutionary technology is in its budding stage. This paper aimed to review the constraints affecting the fertility of sex sorted semen.

Association between occupational testicular radiation exposure and lower male sex ratio of offspring among orthopedic surgeons.

Exposure to occupational radiation can lower the male sex ratio. However, specific radiation exposure to the testes has not been evaluated. This study aimed to examine the association between testicular radiation exposure and lower male sex ratio in children. A comprehensive questionnaire survey was administered to 62 full-time male doctors with children aged < 10 years at 5 hospitals. Based on the possibility of testicular radiation exposure 1 year before the child's birth, participants were assigned to 3 groups as follows: RT (orthopedic surgery), RNT (cardiology/neurosurgery), and N (others). Intergroup differences in the proportion of female children were ascertained, and the female sex ratio (number of female/total number) of each group was compared against the standard value of 0.486. Multivariate logistic regression analysis with a generalized estimating equation was used to model the effects on the probability of female birth while controlling for the correlation among the same fathers. The study population included 62 fathers and 109 children, 49 were female: 19/27, 11/30, and 19/52 in the RT, RNT, and N group, respectively; the RT group had the highest proportion of females (p = 0.009). The p values for comparisons with the standard sex ratio (0.486) were 0.02, 0.19, and 0.08 for the RT, RNT, and N groups, respectively. Based on the N group, the adjusted odds ratios for the child to be female were 4.40 (95% confidence interval 1.60-2.48) and 1.03 (0.40-2.61) for the RT and RNT groups, respectively. Our results imply an association between testicular radiation exposure and low male sex ratio of offspring. Confirmatory evidence is needed from larger studies which measure the pre-conceptional doses accumulated in various temporal periods, separating out spermatogonial and spermatid effects.

Impact of a nonnative parasitoid species on intraspecific interference and offspring sex ratio

In an assemblage of multiple predators sharing a single prey species, the combined effects of the component species may scale unpredictably because of emergent interspecific interactions. Prior studies suggest that chaotic but persistent community dynamics are induced by intra-/interspecific interactions between native and nonnative parasitoids competing over a shared host. Here, we test the impact of the nonnative parasitoid Heterospilus prosopidis (Hymenoptera: Braconidae) on the intraspecific interference and offspring sex ratio of the native parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae). We found that the nonnative parasitoid reduced intraspecific interference among native parasitoids and decreased the proportion of female offspring produced by the native parasitoid (predicted under conditions of reduced host availability). At higher host densities, the nonnative parasitoid contributed less to the total proportion of hosts parasitized, as its innate saturating Type II response changed to a dome-shaped Type IV response with increasing density of the native parasitoid, while the native parasitoid retained its increasing Type I response. This inverse host-density-dependent response between the two parasitoids and associated competitive superiority can explain the observed changes in parasitism; at high host densities, the searching efficiency of the native parasitoid increases via host feeding while the nonnative parasitoid experiences egg limitation. These results highlight the importance of the complementary top-down effects of multiple consumers on a single resource.

Fluctuating heat stress during development exposes reproductive costs and putative benefits.

Temperature and thermal variability are increasing worldwide, with well-known survival consequences. However, effects on other potentially more thermally sensitive reproductive traits are less understood, especially when considering thermal variation. Studying the consequences of male reproduction in the context of climate warming and ability to adapt is becoming increasingly relevant. Our goals were to test how exposure to different average temperatures that either fluctuated or remained constant impacts different male reproductive performance traits and to assess adaptive potential to future heat stress. We took advantage of a set of Drosophila melanogaster isogenic lines of different genotypes, exposing them to four different thermal conditions. These conditions represented a benign and a stressful mean temperature, applied either constantly or fluctuating around the mean and experienced during development when heat stress avoidance is hindered because of restricted mobility. We measured subsequent male reproductive performance for mating success, fertility, number of offspring produced and offspring sex ratio, and calculated the influence of thermal stress on estimated heritability and evolvability of these reproductive traits. Both costs and benefits to different thermal conditions on reproductive performance were found, with some responses varying between genotypes. Mating success improved under fluctuating benign temperature conditions and declined as temperature stress increased regardless of genotype. Fertility and productivity were severely reduced at fluctuating mean high temperature for all genotypes, but some genotypes were unaffected at constant high mean temperature. These more thermally robust genotypes showed a slight increase in productivity under the fluctuating benign condition compared to constant high temperature, despite both thermal conditions sharing the same temperature for 6hr daily. Increasing thermal stress resulted in higher heritability and evolvability. Overall, the effects of temperature on reproductive performance depended on the trait and genotype; performance of some traits slightly increased when high temperatures were experienced for short periods but decreased substantially even when experiencing a benign temperature for a portion of each day. While thermal stress increased genetic variation that could provide adaptive potential against climate warming, this is unlikely to compensate for the overall severe negative effect on reproductive performance as mean temperature and variance increase.

No room for males in caves: Female-biased sex ratio in subterranean amphipods of the genus Niphargus.

Sex allocation theory predicts that the proportion of daughters to sons will evolve in response to ecological conditions that determine the costs and benefits of producing each sex. All else being equal, the adult sex ratio (ASR) should also vary with ecological conditions. Many studies of subterranean species reported female-biased ASR, but no systematic study has yet been conducted. We test the hypothesis that the ASR becomes more female-biased with increased isolation from the surface. We compiled a data set of ASRs of 35species in the subterranean amphipod Niphargus, each living in one of three distinct habitats (surface-subterranean boundary, cave streams, phreatic lakes) representing an environmental gradient of increased isolation underground. The ASR was female-biased in 27 of 35species; the bias was statistically significant in 12species. We found a significant difference in the ASR among habitats after correction for phylogeny. It is most weakly female-biased at the surface-subterranean boundary and most strongly female-biased in phreatic lakes. Additional modelling suggests that the ASR has evolved towards a single value for both surface-subterranean boundary and cave stream-dwelling species, and another value for 9 of 11 phreatic lake dwellers. We suggest that a history of inbreeding in subterranean populations might lower inbreeding depression such that kin selection favours mating with siblings. This could select for a female-biased offspring sex ratio due to local mate competition among brothers. The observed patterns in sex ratios in subterranean species make them a group worthy of more attention from those interested in sex allocation theory.

Pregnancy and offspring sex ratio following insemination with SexedULTRA and conventional semen in cows in a commercial beef operation.

Pregnancy rate per AI (PR/AI) and breeding season pregnancy rates between insemination with sexed semen (SS; at 18hr after the onset of oestrus) and conventional semen (CS; at 12hr after the onset of oestrus,) and offspring gender ratio between two groups were compared. Angus cross cows (n=686, during 2019 and 2020 breeding seasons) were oestrus-synchronized using Select-Synch + CIDR protocol and were observed thrice daily for oestrus until 72hr after PGF2α administration. Cows expressed oestrus (n=513) were inseminated with either SS (n=246; SexedULTRA 4M™; y chromosome-bearing sperm) or CS (n=267). Cows (n=173) that failed to express oestrus at 72hr after PGF2α received 100μg of GnRH and CS insemination concomitantly. Two weeks later, cows were penned with natural service sires (bull:cow ratio 1:25) for 45days. Pregnancy was diagnosed 30days after bull removal. Calves' gender was determined at birth. For cows that expressed oestrus, PR/AI did not differ (p>.1) between SS (65.0%) and CS (66.7%) groups. The overall PR/AI differed (p<.05) between SS (65.0%) and CS (56.4%) groups. The natural service PR differed (p<.001) but breeding season PR (p>.05) did not differ between SS vs. CS groups. Bull:heifer gender ratio following AI was 88:12 and 52:48 for SS and CS groups, respectively, with an overall 66:34 ratio. Bull:heifer gender ratio for the two breeding seasons was 79:21 and 52:48 for SS and CS groups, respectively, with an overall 62:38 ratio. In conclusion, the fertility of SS insemination at 18hr after onset of oestrus was 97% of CS insemination at 12hr after onset of oestrus. Though breeding season pregnancy did not differ between SS and groups, preferred calf gender was 25 percentage points greater for SS over CS application. The gender accuracy was 88%.

Parental investment in the Columbian ground squirrel: empirical tests of sex allocation models

Parental allocation of resources into male or female offspring and differences in the balance of offspring sexes in natural populations are central research topics in evolutionary ecology. Fisher (Fisher, R. A. 1930. The genetical theory of natural selection, Clarendon Press, Oxford, UK) identified frequency-dependent selection as the mechanism responsible for an equal investment in the sexes of offspring at the end of parental care. Three main theories have been proposed for explaining departures from Fisherian sex ratios in light of variation in environmental (social) and individual (maternal condition) characteristics. The Trivers-Willard model (Trivers, R., and D. Willard. 1973. Natural selection of parental ability to vary the sex ratio of offspring. Science 179:90-92) of male-biased sex allocation by mothers in the best body condition is based on the competitive ability of male offspring for future access to mates and thus superior reproduction. The local resource competition model is based on competitive interactions in matrilines, as occur in many mammal species, where producing sons reduces future intrasexual competition with daughters. A final model invokes advantages of maintaining matrilines for philopatric females, despite any increased competition among females. We used 29 yr of pedigree and demographic data to evaluate these hypotheses in the Colombian ground squirrel (Urocitellus columbianus), a semisocial species characterized by strong female philopatry. Overall, male offspring were heavier than female offspring at birth and at weaning, suggesting a higher production cost. With more local kin present, mothers in the best condition biased their offspring sex ratio in favor of males, and mothers in poor condition biased offspring sex ratio in favor of females. Without co-breeding close kin, the pattern was reversed, with mothers in the best condition producing more daughters, and mothers in poor condition producing more sons. Our results do not provide strong support for any of the single-factor models of allocation to the sexes of offspring, but rather suggest combined influences of relative maternal condition and matriline dominance on offspring sex ratio.

Evolutionary dynamics of the Trivers-Willard effect: A nonparametric approach.

The Trivers–Willard hypothesis (TWH) states that parents in good condition tend to bias their offspring sex ratio toward the sex with a higher variation in reproductive value, whereas parents in bad condition favor the opposite sex. Although the TWH has been generalized to predict various Trivers–Willard effects (TWE) depending on the life cycle of a species, existing work does not sufficiently acknowledge that sex‐specific reproductive values depend on the relative abundances of males and females in the population. If parents adjust their offspring sex ratio according to the TWE, offspring reproductive values will also change. This should affect the long‐term evolutionary dynamics and might lead to considerable deviations from the original predictions.In this paper, I model the full evolutionary dynamics of the TWE, using a published two‐sex integral projection model for the Columbian ground squirrel (Urocitellus columbianus). Offspring sex ratio is treated as a nonparametric continuous function of maternal condition. Evolutionary change is treated as the successive invasion of mutant strategies. The simulation is performed with varying starting conditions until an evolutionarily stable strategy (ESS) is reached.The results show that the magnitude of the evolving TWE can be far greater than previously predicted. Furthermore, evolutionary dynamics show considerable nonlinearities before settling at an ESS. The nonlinear effects depend on the starting conditions and indicate that evolutionary change is fastest when starting at an extremely biased sex ratio and that evolutionary change is weaker for parents of high condition. The results show neither a tendency to maximize average population fitness nor to minimize the deviation between offspring sex ratio and offspring reproductive value ratio.The study highlights the importance of dynamic feedback in models of natural selection and provides a new methodological framework for analyzing the evolution of continuous strategies in structured populations.

Impact of feeding experiences on oviposition and sex allocation of Neoseiulus californicus (Acari: Phytoseiidae)

Feeding experiences of predators during immature and adult stages may impact females’ reproduction. In the present study, we investigated reproductive performances of Neoseiulus californicus when both parents had different feeding experiences on Tetranychus urticae and Frankliniella occidentalis. Female and male immatures fed on either prey species. Each newly emerged female adult individually mated with a male had either the same or different feeding experience. Prey for mated females were either same as or different from that consumed during their immature stages. Therefore, eight reproductive treatments were created. The highest cumulative fecundity (57.5±3.3 eggs/female) was observed when both female and male fed on T. urticae with the lowest fecundity (34.2±2.7 eggs/female) observed when the parents fed on F. occidentalis. Daily fecundity and oviposition duration were mainly affected by prey of mated females. Mated females preyed on T. urticae had 56.6% higher daily fecundity and 22.3% shorter oviposition duration than those preyed on F. occidentalis. No significant difference in offspring sex ratio and egg hatch rate was detected between treatments. About 88% of the first-laid eggs developed to males. Impact of prey species consumed by male immatures was only observed on pre-oviposition duration. The average pre-oviposition duration of females who mated with males fed on T. urticae in their immaturity was 33.0% shorter than those females who mated with males fed on F. occidentalis in their immaturity. Results of the present study are valuable in optimizing N. californicus field release strategies, and will help further investigations into the nutritional requirements of this species.

TLR7/8 signalling affects X-sperm motility via the GSK3 \u03b1/\u03b2-hexokinase pathway for the efficient production of sexed dairy goat embryos

BackgroundGoat milk is very similar to human milk in terms of its abundant nutrients and ease of digestion. To derive greater economic benefit, farmers require more female offspring (does); however, the buck-to-doe offspring sex ratio is approximately 50%. At present, artificial insemination after the separation of X/Y sperm using flow cytometry is the primary means of controlling the sex of livestock offspring. However, flow cytometry has not been successfully utilised for the separation of X/Y sperm aimed at sexing control in dairy goats.ResultsIn this study, a novel, simple goat sperm sexing technology that activates the toll-like receptor 7/8 (TLR7/8), thereby inhibiting X-sperm motility, was investigated. Our results showed that the TLR7/8 coding goat X-chromosome was expressed in approximately 50% of round spermatids in the testis and sperm, as measured from cross-sections of the epididymis and ejaculate, respectively. Importantly, TLR7/8 was located at the tail of the X-sperm. Upon TLR7/8 activation, phosphorylated forms of glycogen synthase kinase α/β (GSK3 α/β) and nuclear factor kappa-B (NF-κB) were detected in the X-sperm, causing reduced mitochondrial activity, ATP levels, and sperm motility. High-motility Y-sperm segregated to the upper layer and the low-motility X-sperm, to the lower layer. Following in vitro fertilisation using the TLR7/8-activated sperm from the lower layer, 80.52 ± 6.75% of the embryos were XX females. The TLR7/8-activated sperm were subsequently used for in vivo embryo production via the superovulatory response; nine embryos were collected from the uterus of two does that conceived. Eight of these were XX embryos, and one was an XY embryo.ConclusionsOur study reveals a novel TLR7/8 signalling mechanism that affects X-sperm motility via the GSK3 α/β-hexokinase pathway; this technique could be used to facilitate the efficient production of sexed dairy goat embryos.

The effect of temperature on host patch exploitation by an egg parasitoid.

The effect of temperature during host patch exploitation by parasitoids remains poorly understood, despite its importance on female reproductive success. Under laboratory conditions, we explored the behaviour of Anaphes listronoti, an egg parasitoid of the carrot weevil, Listronotus oregonensis, when foraging on a host patch at five temperatures. Temperature had a strong effect on the female tendency to exploit the patch: A. listronoti females parasitized more eggs at intermediate temperature (20 to 30°C) compared to those foraging at the extreme of the range (15.9°C and 32.8°C). However, there was no difference in offspring sex-ratio and clutch size between temperature treatments. Mechanisms of host acceptance within a patch differed between temperatures, especially at 32.8°C where females used ovipositor insertion rather than antennal contact to assess whether a host was already parasitized or not, suggesting that host handling and chemical cues detection were probably constrained at high temperature. Females spent less time on the host patch with increasing temperatures, but temperature had no effect on patch-leaving rules. Our results show that foraging A. listronoti females behave better than expected at sub-optimal temperatures, but worse than expected at supra-optimal temperatures. This could impair parasitoid performance under ongoing climate change.

Offspring sex ratio and partially asynchronous hatching in the Little Bittern (Ixobrychus minutus) population in south-western Slovakia

Birds are one of the best-studied animal groups in Europe. Despite this, there are several bird species, including the Little Bittern (Ixobrychus minutus), of which the breeding biology is still little known. Here, I examine the sex of offspring in relation to hatching order, the degree of hatching asynchrony and some other aspects of nesting biology (such as breeding phenology, clutch size, egg and nestling survival) of the Little Bittern in the south-western Slovakian population. Egg-laying occurred from 5 May to 10 July, but the majority of clutches were initiated in May. Mean clutch size was 5.2 ± 0.92 (SD) eggs. Parents initiated full incubation predominantly after laying the third egg (86.4% of cases) of the clutch, which led to only partially asynchronous hatching of eggs. However, no evidence was found for offspring sex ratio adjustment according to hatching order. Nevertheless, survival rates of eggs and nestlings were relatively high (80.9% and 94.3 %, respectively). The possible causes of observed patterns are discussed.

Testicular germ cell-specific lncRNA, Teshl, is required for complete expression of Y chromosome genes and a normal offspring sex ratio.

Heat shock factor 2 (HSF2) regulates the transcription of the male-specific region of the mouse Y chromosome long arm (MSYq) multicopy genes only in testes, but the molecular mechanism underlying this tissue specificity remains largely unknown. Here, we report that the testicular germ cell-specific long noncoding RNA (lncRNA), NR_038002, displays a characteristic spatiotemporal expression pattern in the nuclei of round and elongating spermatids. NR_038002-knockout male mice produced sperm with abnormal head morphology and exhibited reduced fertility accompanied by a female-biased sex ratio in offspring. Molecular analyses revealed that NR_038002 interacts with HSF2 and thereby activates expression of the MSYq genes. We designate NR_038002 as testicular germ cell-specific HSF2-interacting lncRNA (Teshl). Together, our study is the first to demonstrate that the testis specificity of HSF2 activity is regulated by the lncRNA Teshl and establishes a Teshl-HSF2-MSYq molecular axis for normal Y-bearing sperm qualities and consequent balanced offspring sex ratio.

On the virulence of the entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae (Ascomycota: Hypocreales), against the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae)

BackgroundThe diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a noxious pest of cruciferous crops all over the world causing serious economic damage. Management of insect pest generally depends on chemical control; however, due to development of resistance against all types of insecticides, alternative approaches especially utilization of a microbial agent is inevitable.ResultsPotential of 2 entomopathogenic fungi (EPF), viz., Beauveria bassiana and Metarhizium anisopliae, was evaluated against 2nd and 3rd larval instars of P. xylostella by adopting leaf dip and direct spraying methods under laboratory conditions. Significant mortality rate was achieved by each fungus under adopted methodologies. However, B. bassiana was found to be more effective in both conditions than M. anisopliae. Highest mean corrected mortality (77.80%) was recorded, when spores of B. bassiana were sprayed on the 2nd instar larvae (LC50=1.78×104/ml) after the 6th day of treatment. Similarly, incase of M. anisopliae LC50 for the 2nd instar at the same methodology was 2.78×104/ml with a mortality percentage of 70.0%. Offspring sex ratio was non-significantly related to treatment concentration and methodology, except for the control.ConclusionBeauveria bassiana and M. anisopliae had potential to suppress P. xylostella infestations when applied appropriately. Present findings suggested that B. bassiana and M. anisopliae when sprayed on immatures of host insect had more effect as compared to leaf dip procedure. Furthermore, no significant effect of concentrations was observed on sex ratio.

Lifespan decreases with proportion of sons in males but not females of zoo-housed tigers and lemurs.

Several studies have shown higher costs of rearing sons than daughters in mammals where males are larger than females. These studies typically focus on females by examining how the offspring sex ratio during a single reproductive event affected mothers' subsequent reproduction or survival probability. Here, we examine relationships between offspring sex ratio during single or multiple reproductive events and several survival metrics in mothers and fathers, using data from zoo-housed tigers (Panthera tigris) and ruffed lemurs (Varecia sp.). Our analyses failed to reveal an overall cost of reproduction or a higher cost of sons to mothers. In male ruffed lemurs, the proportion of sons produced during early life (before 10years old) was negatively correlated with lifespan later in life. In tigers, males with a higher proportion of sons during their lifetime had shorter lifespans. One likely mechanism is the difference in testosterone levels between males: a high concentration of testosterone can increase the proportion of sons and compromise immune function. Our results suggest studies in wild populations should address the outstanding challenge of understanding consequences of sex allocation for males, and open an opportunity to predict lifespan in an applied conservation context.

The role of maternal preconception vitamin D status in human offspring sex ratio

Evolutionary theory suggests that some animal species may experience shifts in their offspring sex ratio in response to maternal health and environmental conditions, and in some unfavorable conditions, females may be less likely to bear sons. Experimental data in both animals and humans indicate that maternal inflammation may disproportionately impact the viability of male conceptuses; however, it is unknown whether other factors associated with both pregnancy and inflammation, such as vitamin D status, are associated with the offspring sex ratio. Here, we show that among 1,228 women attempting pregnancy, preconception 25-hydroxyvitamin D concentrations are positively associated with the live birth of a male infant, with notably stronger associations among women with elevated high sensitivity C-reactive protein, a marker of systemic low-grade inflammation. Our findings suggest that vitamin D may mitigate maternal inflammation that would otherwise be detrimental to the implantation or survival of male conceptuses in utero.