Male-biased sex ratio increases female egg laying and fitness in the housefly, Musca domestica

A biased operational sex ratio (OSR) can have multiple, confounding effects on reproductive fitness. A biased OSR can increase harassment and mating activity directed towards potential mates but may also increase the ability of potential mates to choose a good partner if lower quality mates are screened out through competitive interactions. Additionally, a biased OSR may affect reproductive fitness through changes in male ejaculate content or in female reproductive response. We quantified how a male-biased OSR (1:1, 2:1, or 5:1 male to female) affected the size of a female??s first egg clutch and her offspring??s survivorship in the housefly, Musca domestica. A male-biased OSR increased female fitness: females laid more eggs in their first clutch, had increased offspring survivorship at a 2:1 versus 1:1 OSR, and had equivalent fitness with a 5:1 male to female OSR. Courtship activity increased when the OSR was male-biased but was not a significant predictor of female fitness. Trials where females chose their mates versus trials where a random male was chosen for them had equivalent first clutch sizes and offspring survivorship. These results suggest that there are cryptic effects from a male-biased OSR on female fitness that are most likely driven by pre-copulatory social environment.     

Biological assessment of Tetrastichus brontispae,a pupal parasitoid of coconut leaf beetle Brontispa longissima

To control coconut leaf beetle, Brontispa longissima (Gestro), the pupal parasitoid Tetrastichus brontispae Ferrière was imported from Taiwan and its biology was studied in quarantine in Hainan, China. The parasitoid development includes an egg, three larval instars and three pupal stages. Its developmental time from egg to adult was 19.5±0.5 days under conditions of 24±2°C and 75±5% relative humidity (RH). Temperature had no effect on the sex ratio of offspring, but significantly affected the parasitism rate and reproduction. The parasitism rates were 98.07, 97.97 and 95.03% at 28, 24 and 20°C, respectively, whereas the parasitism rate was 52.18% at 18°C and 69.48% at 30°C, respectively. Furthermore, the parasitoids reared at 18 and 30°C produced fewer offspring than those at 20, 24 and 28°C, respectively. With the increase in temperature, developmental time decreased linearly from 46.19 days at 18°C to 17.10 days at 28°C. RH significantly influenced development, parasitism rate and the reproduction of T. brontispa. With the decrease of RH, developmental time increased from 22.94 days at 20% RH to 18.84 days at 95% RH. In contrast, parasitism rate and the number of offspring per female increased with the increase of RH. Though emergence rates between 50 and 95% RH were much higher than those between 20 and 35% RH, the sex ratios between 20 and 95% RH were not different. Photoperiod had no effect on parasitism, the number of offspring per female, emergence and the sex ratio of T. brontispae, but developmental time was significantly different for different photoperiods. Sucrose, honey and glucose significantly enhanced adult longevity, parasitism and the number of offspring per female of T. brontispae, but had no effect on the sex ratio and survival. Females of T. brontispae only parasitized fourth to fifth larval instars and 1–5-day-old pupae, but there was a significant difference in the number of offspring per female, development time, emergence and the sex ratio of offspring in different instars. These results showed that 1-day-old pupae, a temperature of 24–28°C and 65–95% RH were optimal for T. brontispae. These findings should be helpful in developing a production system to rear and release T. brontispae in large enough quantities to effectively control coconut leaf beetle.     

Food restricting young hamsters (Mesocricetus auratus) affects sex ratio and growth of subsequent offspring

Trivers and Willard (1973) predicted that stressed adult female mammals may enhance their fitness by skewing offspring sex ratios and maternal investment to favor daughters. The present study investigated whether stressing young hamsters might also influence sex ratio and growth of subsequent offspring. Control females received food ad libitum (A) on Days 1-50 postpartum (AA). Experimental females were food-restricted (R) either on Days 1-25 (RA), Days 26-50 (AR), or Days 1-50 (RR) postpartum. Subjects were mated when 91-95 days old. Litter sizes and survivorship (= % litters within a treatment that contained at least one pup), sex ratio (= % males), and pup weights in the next generation were recorded every fifth day from parturition until Day 25 postpartum. Control litters contained significantly more offspring at birth than did RR litters. Sex ratio was significantly higher at birth for AA litters than for the other treatments. Postpartum sex ratio within each group remained similar to that recorded at birth. RR litters contained significantly fewer pups compared to the other three treatments from Days 5-25. RR female pups weighed significantly more at birth than their counterparts in the other treatments. Weights of males at birth were similar in all treatments. By Day 25, both male and female RR pups weighed significantly less than control, AR, and RA pups. Food restriction early in life may have long-term consequences on sex ratio and pup growth in golden hamsters.     

Variable mate-guarding time and sperm allocation by male snow crabs (Chionoecetes opilio) in response to sexual competition, and their impact on the mating success of females.

Two laboratory experiments investigated mate guarding and sperm allocation patterns of adult males with virgin females of the snow crab, Chionoecetes opilio, in relation to sex ratio. Although females outnumbered males in treatments, operational sex ratios were male-biased because females mature asynchronously and have a limited period of sexual attractiveness after their maturity molt. Males guarded females significantly longer as the sex ratio increased: the mean time per female was 2.9 d in a 2 males:20 females treatment compared to 5.6 d in a 6 males:20 females treatment. Female injury and mortality scaled positively to sex ratio. Males that guarded for the greatest number of days were significantly larger, and at experiment's end had significantly smaller vasa deferentia, suggesting greater sperm expense, than males that guarded for fewer days. In both experiments, the spermathecal load (SL)--that is, the quantity of ejaculate stored in a female's spermatheca--was independent of molt date, except in the most female-biased treatment, where it was negatively related. The SL increased as the sex ratio increased, mainly because females accumulated more ejaculates. However, similarly sized males had smaller vasa deferentia and passed smaller ejaculates, such that, at a given sex ratio, the mean SL was 55% less in one experiment than in the other. Some females extruded clutches with few or no fertilized eggs, and their median SL (3-4 mg) was one order of magnitude smaller than that of females with well-fertilized clutches (31-50 mg), indicating sperm limitation. Males economized sperm: all females irrespective of sex ratio were inseminated, but to a varying extent submaximally; each ejaculate represented less than 2.5% of male sperm reserves; and no male was fully exhausted of sperm. Sperm economy is predicted by sperm competition theory for species like snow crab in which polyandry exists, mechanisms of last-male sperm precedence are effective, and the probability that one male fertilizes a female's lifetime production of eggs is small.     

Offspring sex ratio in the sequentially polygamous Penduline Tit Remiz pendulinus

Despite the growing literature on facultative sex-ratio adjustment in chromosomal sex-determining vertebrate taxa (birds, mammals), the consistency of results is often low between studies and species. Here, we investigate the primary and secondary offspring sex ratio of a small passerine bird, the Eurasian Penduline Tit (Remiz pendulinus) in three consecutive years. This species has a uniquely diverse breeding system, in which the male (and/or the female) abandons the nest during egg-laying, and starts a new breeding attempt. This allowed us to test (1) whether patterns of parental care, i.e., male-only care, female-only care or biparental desertion, influence offspring sex ratio, and (2) whether the offspring sex ratio is repeatable between successive clutches of males and females. Using molecular markers to sex 497 offspring in 176 broods, we show that (1) offspring sex ratio does not depend on which parent provides care, and (2) the offspring sex ratio is not repeatable between clutches of a given individual. The overall primary and secondary offspring sex ratio at a population level is not different from parity (54 ± 6% males, and 50 ± 3% (mean ± SE), respectively). We suggest that ecological and phenotypic factors, rather than individual traits of parents, may influence offspring’s sex, and conclude that there is currently no evidence for a facultative adjustment of offspring sex ratio in the Penduline Tit.     

Low Numbers of Sperm Retained in the Spermatheca May Explain the High Values of Sperm Precedence in the Migratory Locust, Locusta migratoria (Latr.)

Four hypotheses about the temporal variation of the number of spermatozoa in the spermatheca of once-mated females were tested in the migratory locust, Locusta migratoria. The best fit provided a regression model that assumed a sudden drop in sperm numbers being indicative of sperm ejection by females. Thereafter, one-fifth of an average ejaculate is stored. Low numbers of sperm stored do not lead to female sperm limitation, as none of the fitness parameters measured, fertilization success, hatching success, and offspring sex ratio, were correlated with the number of sperm present. Fertilization success decreased with successive egg pods. The offspring sex ratio was slightly male biased and tended to increase throughout the laying period. By applying our sperm ejection model to an independent data set of Parker and Smith (1975), we show that the low numbers of sperm retained by the female and subsequent sperm mixing rather than direct replacement may explain the high P₂ values found in this species.     

Spatial dynamics in breeding performance of a predator: the connection to prey availability

Using nationwide long-term data on goshawk and grouse populations in Finland we study the spatial dynamics of the numbers of breeding northern goshawk ( Accipiter gentilis ) pairs, goshawk brood size and offspring sex ratio and their connection to the abundance of grouse. Our first large-scale data comprise of observations on goshawk nests during 1986–2001 pooled to 21 different regions. The second set are annual (1989–1998) observations of brood size and offspring sex ratio (females over the sum of females and males) in goshawk nests all over the country, aggregated to 50 km grid level (n=28 grid units). The third set comprises counts (1989–2001) of four species of woodland grouse, split to adults and juveniles, also given in the same 50 km grid units. Using these data, we show that the annual numbers of northern goshawk nests in the different regions fluctuate in synchrony. Synchrony is also found in long-term fluctuations of northern goshawk brood size and offspring sex ratio. Moreover, synchrony is found in annual numbers of grouse juveniles and adults, the main prey for the northern goshawk. In the brood size and offspring sex ratio of the goshawk, as well as in the annual numbers of grouse juveniles and adults the degree of synchrony falls off with increasing distance. However, only in sex ratios and in grouse dynamics are the slopes of synchrony vs distance roughly matching. We also found that sex ratio either vs grouse juveniles or grouse adults has a more matching spatial dimension (50 km radius) that sex ratio vs brood size. These observation lend support to the hypothesis that goshawk offspring sex ratio and grouse abundance are interconnected. Despite the reason, consequences of spatial coupling in sex ratio could have repercussions on other life history events.     

Causes and consequences of adaptive seasonal sex ratio variation in house sparrows

1. Here we examine how sex ratio variation in house sparrow broods interacts with other demographic traits and parental characteristics to improve the understanding of adaptive significance and demographic effects on variation in sex ratio. 2. The sex ratio in complete broods did not deviate significantly from parity (54.9% males). 3. There was sex-specific seasonal variation in the probability of recruitment. Male nestlings that hatched late in the breeding season had larger probability of surviving than early hatched males. 4. An adaptive adjustment of sex ratio should favour production of an excess of males late in the breeding season. Accordingly, the proportion of male offspring increased throughout the breeding season. 5. A significant nonlinear relationship was present between sex ratio and age of the female. However, there was no relationship between parental phenotype and standardized hatch day that could explain the observed seasonal change in sex ratio. 6. The sex-specific number of offspring recruited by a pair to subsequent generations was closely related to the brood sex ratio. 7. These results indicate an adaptive adjustment of sex ratio to seasonal variation in environmental conditions that affects the offspring fitness of the two sexes differently. Our results also suggest that such a sex ratio variation can strongly influence the demography and structural composition of small passerine populations.     

Acute corticosterone treatment prior to ovulation biases offspring sex ratios towards males in zebra finches Taeniopygia guttata

Researchers have documented significant skews in the primary sex ratios of avian offspring in relation to a variety of environmental and social cues. Zebra finches Taeniopygia guttata, in particular, adjust offspring sex ratio according to both the quality and quantity of available food, as well as male attractiveness. The mechanisms behind such manipulation of offspring sex remain elusive. Recent studies suggest that females with chronically elevated corticosterone levels (both naturally and artificially) produce significantly female biased offspring sex ratios. We tested the effects of a pharmacological dose of corticosterone or progesterone administered at the time of sex chromosome segregation on the primary sex ratio of zebra finch offspring to determine whether one or both hormones act on offspring sex at this critical period. Females were injected with 20 μg of corticosterone or 20 μg of progesterone five hours prior to the predicted time of ovulation of the 3^rd or 4th ovulating follicle. A third group of females were unmanipulated. The corticosterone treated group produced 72% males while the control group produced 37.5% in the 3rd or 4th ovulation of the sequence. Progesterone injections disrupted ovulation and oviposition in 90% of females. Corticosterone administration did not adversely affect oviposition or ovulation. Females injected with corticosterone had significantly elevated levels of corticosterone 20 min, 1 h and 2.5 h post‐injection and produced significantly more males compared to untreated females. Our results suggest that offspring sex ratios may be influenced at the time of meiotic division by acute exposure to corticosterone and provides evidence for the timing of this effect.     

Effect of the hereditary characteristics of male blue foxes Alopex lagopus L. on the sex ratio of their offspring

Family analysis of a commercial population of the blue fox (the Pushkinskoe Breeding Fur Farm, Moscow oblast) with respect to secondary sex ratio has been performed. The offspring of each individual male or female involved in crossing between 1984 and 1988 was analyzed. The study of all families formed by every male and every female has made it possible to determine a group of "outstanding" fathers (23 out of 287 males), whose offspring was predominantly male (62.1% of the offspring were males, versus 53.9% in the total population). The results of subsequent detailed study on the pedigrees of male blue foxes in whose offspring the sex ratio significantly deviates from 1:1 indicate that this character is transmitted from fathers to sons without the deterioration of other commercially valuable characters. It is presumed that the significant deviation of sex ratio from 1:1 in the offspring of some male blue foxes is determined by genetic factors.     

Parental age,birth order and tertiary sex ratio in the human population of Punjab,Pakistan

The data of this study, an extension of a previous study on secondary sex ratio in the human population of Muridke, Punjab, Pakistan, are based on the population of Muridke, 27 km north of Lahore, Punjab, Pakistan. Records of deaths of children, at later stages of birth, for different birth ranks, and that of maternal and paternal ages were made. 1000 families were scored for this study. Families providing the required information were included. Data for paternal age and maternal age combination consisted of 4807 total number of children of which 2586 were male. Paternal age and birth order combination was comprised of a total of 4405 children, containing 2316 males. Maternal age and birth order combination consisted of 4658 children, of which 2458 were males. The discrepancy in the number of children in the 3 types of combinations was due to the lack of required information in different groups. Sex ratio based on total number of males in relation to paternal age and maternal age was 0.54. Younger fathers (15-19 years) showed higher sex ratio (0.69). This dropped in paternal age groups 20-24 years (0.59) and 25-29 years (0.51). Younger mothers (15-19 years) showed higher sex ratio (0.62), declines in the age groups 20-24 years (0.52) and 25-29 years (0.51) and rise in age groups 35-39 years (0.55) and 40-44 years (0.54). Chi-square tests were carried out to compare the number of male and female offspring in the paternal age groups 15-19, 20-24, and 25-29 years. These showed highly significant deviation from the expected number. The higher age groups showed nonsignificant differences in the number of male and female offspring. Maternal age groups 15-19, 20-24, and 25-29 years showed highly significant differences in the male and female offspring and nonsignificant results in the higher age groups. Maternal age in relation to paternal age showed positive simple and partial correlations. Sex ratio for the total number of males based on paternal age and birth order was 0.52. 1st birth order showed higher sex ratio (0.55) and decreased in the 2nd (0.50) and 3rd birth orders (0.51), showed increase in the 4th birth order (0.53) and declines in the higher birth ranks. The number of male and female offspring in the birth orders 1, 2, and 3 showed significant differences, but in higher birth ranks the difference was insignificant. Paternal age and birth order indicated positive simple and partial correlations. Higher sex ratio (0.58) was seen in the 1st birth order and then it decreased in the 2nd (0.50) and 3rd (0.51) birth order. Chi-square tests carried out to compare the number of male and female offspring in borth orders 1, 2, and 3 showed highly significant differences but in higher birth ranks the difference was insignificant.     

Opportunistic predation and offspring sex ratios of cicada-killer wasps (Sphecius speciosus Drury)

Abstract.  1. The way in which hunting of prey affects the sex ratio of the predator's offspring is not well understood. Female cicada-killer wasps are convenient for study because they specialise in capturing cicadas to provision their offspring. Cicada prey are nearly twice as heavy as the wasps that carry them, hence some degree of prey selectivity by the wasps is to be expected. It has been suggested that wasps bias their offspring towards females by foraging selectively for female prey, whereas there is some evidence that sex ratios are actually male-biased. This study was designed to establish the connection between foraging and offspring sex ratio.
2. Three, non-exclusive, hypotheses of selective predation were tested. The frequency of predation on different classes of prey in conjunction with their availability was estimated by intercepting the wasps on their way to their nests and by sampling cicadas in the environment. The hypothesis of selective predation was not supported; predation appears to be opportunistic and non-selective. Cicada prey weight was not a simple linear function of wasp weight, although the smallest wasps were constrained to carry small prey.
3. Wasp offspring (larvae) were excavated from subterranean nests and found to be male-biased (3 : 1 or 4 : 1) in 2 years. The observed ratios are close to expectation from Fisher's equal-investment model, taking account of sexual size dimorphism, and are evidently unrelated to the sex of the prey. A simple binomial probability rule of sex allocation provides a behavioural mechanism for producing the observed sex ratio of offspring.     

Collection frequency affects percent Y-chromosome bearing sperm,sperm head area and quality of bovine ejaculates

This study evaluated the percentage of Y-chromosome bearing spermatozoal (%Y-CBS) variation from ejaculates within individual males using two experiments. In the first experiment, six ejaculates were taken from each of five sexually rested (>30 days) Holstein bulls. Ejaculates were processed separately and stored in liquid nitrogen. From each ejaculate, five straws were thawed and equal sperm number, pooled samples were constructed using hemacytometer counts. Individual ejaculate DNA samples were extracted and quantified by spectroscopy. AY-chromosome specific segment was amplified by polymerase chain reaction (PCR) and the product separated by gel electrophoresis. Ethidium bromide stained bands were detected by image analysis and equated to a 50 %Y-CBS pool. In the second experiment (91 days), two ejaculates were collected from sexually rested (>21 days) bulls weekly and two ejaculates were collected from bulls every 21 days. Specific Y-chromosome (SRY) and X-chromosome (factor IX, F9) sperm DNA was amplified by PCR and the products separated by gel electrophoresis. Ethidium bromide stained bands were detected by image analysis and compared to a standard curve constructed from pure SRY and F9 PCR product. The log ratio (SRY/F9) of the corrected intensity densities were used to estimate the percent Y-chromosome DNA bearing spermatozoa (%Y-CDBS) in each ejaculate using inverse regression procedures. In Experiment 1, ejaculate differences for the first collection ranged from 17 to 71 %Y-CBS. Differences remained large for the second ejaculates and lessened for the third and fourth collections. Differences were least for the last two collections. Sperm head area also fluctuated. In Experiment 2, collection frequency affected the pattern of %Y-CDBS response. In bulls collected weekly, %Y-CDBS changed in a sinusoid fashion with a period of about 13.5 days. For bulls collected on a 21-day interval, %Y-CDBS ejaculate differences were high in the first ejaculate after sexual rest. Maximization of %Y-CDBS variation between ejaculate and its identification by PCR would allow ejaculate selection to be used to the alter the sex ratio in producers' calf crops.     

Male‐specific mortality biases secondary sex ratio in Eurasian tree sparrows Passer montanus

Sex allocation theory predicts that parents bias the offspring sex ratio strategically. In avian species, the offspring sex ratio can be biased at multiple growth stages, although the mechanisms are not well known. It is crucial to reveal a cause and timing of biased offspring sex ratio. We investigated (i) offspring sex ratio at multiple growth stages, from laying to fledging; and (ii) the stage at which offspring sex ratio became biased; and (iii) the cause of biased offspring sex ratio in Eurasian tree sparrows Passer montanus. Sex determination of 218 offspring, including hatchlings and unhatched eggs from 41 clutches, suggested that the offspring sex ratio was not biased at the egg‐laying stage but was significantly female‐biased after the laying stage due to higher mortality of male embryos. Half of the unhatched eggs showed no sign of embryo development (37/74, 50.00%), and most undeveloped eggs were male (36/37, 97.30%). Additional experiments using an incubator suggested that the cause of embryo developmental failure was a lack of developmental ability within the egg, rather than a failure of incubation. This study highlights the importance of clarifying offspring sex ratio at multiple stages and suggests that offspring sex ratio is adjusted after fertilization.     

Allocation of maternal- and ejaculate-derived proteins to reproduction in female crickets, Teleogryllus oceanicus

Female fitness has traditionally been thought to be maximized with one or a few matings. More recent research suggests that polyandry, mating with two or more males, can generate an increase in the viability of offspring females produce. However, the mechanism(s) underlying enhanced offspring viability remain largely unknown. The Australian field cricket Teleogryllus oceanicus has proved a useful model for examining the evolutionary significance of polyandry. Embryo viability appears to be associated with a male's investment in accessory gland tissue, implicating a role for seminal fluid. Here, I used amino acids labelled with different radio isotopes to identify proteins manufactured by males and females before they engaged in reproduction. Males incorporated 95% of the radiolabel into the testes, accessory glands and the ejaculate that was transferred to the female at mating. Male ejaculate compounds were incorporated predominantly into the female's somatic tissue. Relatively more female compounds were incorporated into the ovaries and into laid eggs than ejaculate compounds, and relatively fewer female compounds were sequestered in the somatic tissue than ejaculate compounds. The patterns observed suggest that while ejaculate compounds may be incorporated directly into eggs, they are likely to have a larger effect on maternal allocation to offspring.     

Females of the grasshopper Chorthippus parallelus (Zett.) do not remate for fresh sperm

The evolution of female multiple mating is still a largely debated field. Among the benefits that have been proposed to explain this risky behaviour is the replenishment of sperm reserves. Apart from an increase in total sperm number, it can be an expression of post-copulatory mate choice or can be directed towards the uptake of fresh sperm. Using fresh sperm for fertilization instead of sperm aged by storage in the female genital tract may avoid a lowered fertilization capacity, an increase in deleterious effects or a skewed offspring sex ratio. We investigated the influence of sperm age on female fitness in the grasshopper Chorthippus parallelus, a species where females mate multiply. After copulation, females store sperm over the course of weeks until fertilization. An average ejaculate of 250 000 spermatozoa exponentially declined with time within the female''s spermatheca. The number of days since copulation better explained the variation in actual sperm number than the number of pods or eggs laid. We investigated differences in female fitness parameters in two treatments. In the first, females were mated only once, while in the second, females always had freshly ejaculated sperm available. Although in our experiment, multiply mated females had heavier offspring than singly mated females, egg number per pod, hatching and fertilization success, their composite effects and offspring sex ratio did not vary with respect to season or sperm age. We therefore reject the hypothesis that the reason for remating in females of this species is the uptake of fresh sperm.     

Sex ratios of Spalangia endius (Hymenoptera: Pteromalidae), in relation to current theory

Abstract. 1. Spulungiu endius Walker is a solitary parasitoid of house fly puparia.
2. The sex and size of S.endius was not related to host size.
3. In the laboratory the mean sex ratio of all offspring of nine groups, each comprising twenty females, was consistently female-biased (x = 83.5%, range 79–87%). The sex ratio in the field was less female-biased and showed greater fluctuation (61–75%). This may be a consequence of females laying male eggs before mating, some females remaining unmated, possible shorter adult life expectancy in the field than in the laboratory, and, perhaps, the presence of conspecific females.
4. The sex ratio of offspring of individual females varied from 66% to 100% females, and males were deposited early in the oviposition sequence.
5. Although a large number of fly puparia died before adult flies or parasitoids emerged (64.5%; n = 5874), there was no differential mortality of either sex.
6. Our results fit no general sex ratio hypothesis and we conclude that (i) the genetic nature of sex ratios in these insects needs careful examination, and (ii) the prevalence of female-biased sex ratios in solitary parasitoids needs investigation.     

Offspring sex ratio in sheep,cattle, goats and pigs: influence of season and lunar phase at conception

This study assessed the relationship between season and lunar phase at conception on offspring sex ratio of four livestock species (sheep, cattle, goats and pigs). The sex of 66,830 lambs (1995–2015); 25,546 calves (2011–2015); 5671 kids (2002–2007) and 1916 piglets was recorded. Moon phases were categorized as either new moon, crescent moon, full moon or decrescent moon. Sex ratio, expressed as proportion of males (males/males + females), was tested against the expected value of 1:1. In sheep, offspring sex ratio and lunar phase were not correlated; season had a significant (p = 0.002) effect on offspring sex ratio. The proportion of males born of spring and winter matings was significantly higher than it was among offspring born of summer (p < 0.05) or autumn (p < 0.01) conceptions. Offspring sex ratios in spring (p < 0.05), autumn (p < 0.01) and winter (p < 0.05) differed significantly from the expected. In cattle, moon phase and season did not affect the offspring sex ratio; however, the interaction effect was highly significant (p = 0.001). The overall piglet sex ratio (0.522), and the sex ratios among piglets conceived during a crescent moon and those conceived in summer differed significantly (p < 0.05) from 1:1. Research including additional factors such as hormonal treatments prior to insemination, food availability, weather and maternal and paternal factors might provide the underlying reasons for the effects of season and moon phase on offspring sex ratio in some livestock species.     

Offspring sex is not related to maternal allocation of yolk steroids in the lizard Bassiana duperreyi (Scincidae)

The eggs of birds and reptiles contain detectable levels of several steroid hormones, and experimental application of such steroids can reverse genetically determined sex of the offspring. However, any causal influence of maternally derived yolk steroids on sex determination in birds and reptiles remains controversial. We measured yolk hormones (dihydrotestosterone, testosterone, and 17 beta-estradiol) in newly laid eggs of the montane scincid lizard Bassiana duperreyi. This species is well suited to such an analysis because (1) offspring sex is influenced by incubation temperatures and egg size as well as by sex chromosomes, suggesting that yolk hormones might somehow be involved in the complex pathways of sex determination, and (2) experimental application of either estradiol or fadrozole to such eggs strongly influences offspring sex. We obtained yolk by biopsy, before incubating the eggs at a temperature that produces a 50:50 sex ratio. Yolk steroid levels varied over a threefold range between eggs from different clutches, but there were no significant differences in yolk steroids, or in relative composition of steroids, between eggs destined to become male versus female. Further, yolk steroid concentrations were not significantly related to egg size. Thus, yolk steroid hormones do not appear to play a critical role in sex determination for B. duperreyi.     

Pollinating fig wasp Ceratosolen solmsi adjusts the offspring sex ratio to other foundresses

Abstract Local mate competition theory predicts that offspring sex ratio in pollinating fig wasps is female‐biased when there is only one foundress, and increased foundress density results in increased offspring sex ratio. Information of other foundresses and clutch size have been suggested to be the main proximate explanations for sex ratio adjustment under local mate competition. Our focus was to show the mechanism of sex ratio adjustment in a pollinating fig wasp, Ceratosolen solmsi Mayr, an obligate pollinator of the functionally dioecious fig, Ficus hispida Linn., with controlled experiments in the field. First, we obtained offspring from one pollinator and offspring at different oviposition sequences, and found that offspring sex ratio decreased with clutch size, and pollinators produced most of their male offspring at the start of bouts, followed by mostly females. Second, we found that offspring sex ratio increased with foundress density, and pollinators did adjust their offspring sex ratio to other females in the oviposition patches. We suggest that when oviposition sites are not limited, pollinators will mainly adjust their offspring sex ratio to other foundresses independent of clutch size changes, whereas adjusting clutch size may be used to adjust sex ratio when oviposition sites are limited.