Production Of Male Offspring Research Articles

Stress signaling: coregulation of hemoglobin and male sex determination through a terpenoid signaling pathway in a crustacean

Environmental signals can activate neuro-endocrine cascades that regulate various physiological processes. In the present study, we demonstrate that two responses to environmental stress signaling in the crustacean Daphnia magna--hemoglobin accumulation and male offspring production--are co-elevated by the crustacean terpenoid hormone methyl farnesoate and several synthetic analogs. Potency of the hormones with respect to the induction of both hemoglobin and male offspring was highly correlated, suggesting that both processes are regulated by the same terpenoid signaling pathway. Six clones of the D. pulex/pulicaria species complex that were previously characterized as unable to produce male offspring and five clones that were capable of producing males were evaluated for both hemoglobin induction and male offspring production in response to methyl farnesoate. Four of the five male-producing clones produced both hemoglobin and male offspring in response to the hormone. Five of the six non-male-producing clones produced neither hemoglobin nor males in response to the hormone. These results provide additional evidence that both physiological processes are regulated by the same signaling pathway. Furthermore, the results indicate that the non-male-producing clones are largely defective in some methyl farnesoate signaling component, downstream from methyl farnesoate synthesis but upstream from the genes regulated by the hormone. A likely candidate for the site of the defect is the methyl farnesoate receptor. As a consequence of this defect, non-male-producing clones have lost their responsiveness to environmental signals that are transduced by this endocrine pathway. This defect in signaling would be likely to enhance population growth in stable environments due to the elimination of males from the population, assuming that other processes critical to population growth are not also compromised by this defect.

Juvenile hormone agonists affect the occurrence of male Daphnia

The water flea Daphnia magna reproduces primarily by cyclic parthenogenesis. Environmental stimuli that signal a change to adverse conditions induce the organisms to switch from parthenogenesis to gamogenetic reproduction. During the gamogenetic period, they produce male daphnids and dormant resting eggs, which can survive prolonged periods of environmental adversity. However, little is known about the mechanisms associated with the switch from parthenogenesis to gamogenetic reproduction. We investigated the effects of several juvenoids on sex determination in Daphnia. Females less than 24 h old were exposed to various concentrations of the test substance and were observed for 21 days. It was found that they can trigger the appearance of male daphnids: the percentage of males in the population increases to a level greater than what occurs under ordinary environmental conditions. We found that methylfarnesoate, juvenile hormone III, methoprene, and the phenoxyphenoxy derivatives pyriproxyfen and fenoxycarb (both insecticides) reduced the production of offspring and produced sex ratios dominated by male daphnids. Pyriproxyfen and fenoxycarb showed striking effects at low concentrations. Exposure to either of these chemicals at a concentration of 330 ng l −1 caused adult females to produce almost all male neonates. Methylfarnesoate, juvenile hormone III, and methoprene showed an effect in inducing male production at higher concentrations (3.7 × 10 3, 3.3 × 10 5, and 1.3 × 10 5 ng l −1, respectively). Our findings suggest that juvenile hormone agonists, including some insecticides, affect the chemical signaling responsible for inducing the production of male offspring.

Insecticidal juvenile hormone analogs stimulate the production of male offspring in the crustacean Daphnia magna.

Juvenile hormone analogs (JHAs) represent a class of insecticides that were designed specifically to disrupt endocrine-regulated processes relatively unique to insects. Recently we demonstrated that the crustacean juvenoid hormone methyl farnesoate programs oocytes of the crustacean Daphnia magna to develop into males. We hypothesized that insecticidal JHAs might mimic the action of methyl farnesoate, producing altered sex ratios of offspring. Daphnids were exposed chronically (3 weeks) to sublethal concentrations of methyl farnesoate, the JHA pyriproxyfen, and several nonjuvenoid chemicals to discern whether excess male offspring production is a generic response to stress or a specific response to juvenoid hormones. Only methyl farnesoate and pyriproxyfen increased the percentage of males produced by exposed maternal organisms. As previously reported with methyl farnesoate, acute exposure (24 hr) to either pyriproxyfen or the JHA methoprene caused oocytes maturing in the ovary to develop into males. We performed experiments to determine whether combined effects of a JHA and methyl farnesoate conformed better to a model of concentration addition (indicative of same mechanism of action) or independent joint action (indicative of different mechanisms of action). Combined effects conformed better to the concentration-addition model, although some synergy, of unknown etiology, was evident between the insecticides and the hormone. These experiments demonstrate that insecticidal JHAs mimic the action of the crustacean juvenoid hormone methyl farnesoate, resulting in the inappropriate production of male offspring. The occurrence of such an effect in the environment could have dire consequences on susceptible crustacean populations.

Patterns of male parentage in the fungus-growing ants

Ant queens from eight species, covering three genera of lower and two genera of higher attine ants, have exclusively or predominantly single mating. The ensuing full-sib colonies thus have a strong potential reproductive conflict between the queen and the workers over male production. This is because, all other things being equal, relatedness incentives should favour traits expressed in both workers and the queen to monopolise the production of the colony's male offspring. Microsatellite genotyping of males from these attine species shows that workers in queenless colonies are able to produce males, but that no worker-produced males were found in queenright colonies. Our results suggest that worker reproduction is rare or even absent in colonies with a fertile queen. This indicates that either the queen directly prevents the workers from raising their own sons, or that worker reproduction is absent in the presence of a fertile queen due to high ergonomic costs of this behaviour.

An inclusive fitness-based exploration of the origin of soldiers: The roles of sex ratio, inbreeding, and soldier reproduction

I present an inclusive fitness model for the origin of soldiers that incorporates soldier production of males and females, in haplodiploids and diploids. In this paper, the term soldier refers to an individual that is morphologically and/or behaviorally specialized for defense. However, the model presented here can usefully be extended to other helping behaviors that are episodic in nature and that impact the colony as a whole rather than helping behavior that is directed to specific individuals. In general, the results of the model show that proto-soldier reproduction via sib-mating increases the ease with which soldiering evolves. Male haplodiploids appear the most apt to evolve soldier behavior compared to female haplodiploids and diploids. Haplodiploid females are expected to produce a greater proportion of male dispersers relative to their production of female dispersers and thereby increase the predilection in females to evolve soldiering compared to diploid populations. Application of the model to gall-forming thrips in Australia reveals that species basal to the phylogenetic branch where soldiers are inferred to have evolved show a lower threshold for soldier evolution than more derived species. This phylogenetic pattern is consistent with soldier production of male and female offspring facilitating the origin of soldiering in the social gall-forming thrips.

Temporal and quantitative changes in sexual reproductive cycling of the cladoceran Daphnia magna by a juvenile hormone analog.

Cyclic parthenogens, such as the cladoceran, Daphnia magna, utilize both asexual (parthenogenetic) and sexual reproduction in order to maximize population fitness in variable environments. Parthenogenetic reproduction is the default strategy among D. magna, while various environmental cues trigger cycles of sexual reproduction. Experiments were conducted with the juvenile hormone analog methoprene to test the hypothesis that members of the insect juvenile hormone/vertebrate retinoic acid family of transcription factors are involved in the regulation of sexual reproduction in daphnids. Neither methoprene, food reduction, or crowding independently stimulated entry into the sexual reproductive phase of the daphnids. However, the combination of food deprivation and crowding stimulated entry into the sexual reproductive phase characterized by an initial high production of males and the subsequent intermittent production of haploid egg-containing ephippia. Exposure to 160 nM methoprene along with food deprivation and crowding caused a significant reduction in the percentage of males produced during the early phase of the sexual cycle and significantly increased the percentage of males produced during the later stages of the cycle. Methoprene concentrations as low as 6.4 nM significantly reduced the number of resting eggs produced and proportionately increased the production of parthenogenetically-produced neonates. These experiments demonstrate that methoprene uncouples the coordinate production of males and resting eggs during the sexual reproductive period of D. magna. Methoprene stimulates male offspring production and defers their production to latter stages of the sexual reproductive period, while inhibiting the production of resting eggs and promoting the continuance of parthenogenetic reproduction. J. Exp. Zool. 290:148-155, 2001.

Adaptive Fetal Sex Allocation in Elk: Evidence and Implications

Population managers of large ungulates often assume that approximately even numbers of male and female offspring are produced. In contrast, evolutionary theory predicts that maternal investment in polygynous mammals should depend on the relative resource status of the female in relation to sex-specific demands of the offspring (i.e., females should bias sex allocation depending on their body condition). Examination of elk (Cervus elaphus) reproductive tracts from Oregon revealed that fetal sex ratios vary with maternal body condition (kidney fat index [KFI] Females with low maternal body condition were more likely to produce daughters than females with high KFI levels. Adult females with high KFIs conceived earlier and produced significantly more sons than daughters in the first 2 weeks of the reproductive season than females with lower body condition. Because reproductive data from elk in Oregon support the hypothesis of adaptive sex ratios according to the Trivers and Willard hypothesis, I evaluated the effects of adaptive sex ratios on offspring production in a hypothetical elk population. Using the observed relations between body condition, pregnancy, and fetal sex ratio, I examined the effects of maternal body condition on the production of male and female offspring in a population. I used a gamma distribution to simulate different maternal body condition (KFI) distributions and estimated the resultant fetal sex ratios. These simulations indicated that equality of sex ratios in offspring is a rare occurrence and is limited to average environmental conditions. With increasing body condition in the herd, the model predicted that more sons were conceived and that fetal sex ratios increasingly deviated from unity. Fetal sex ratios from annual and regional samples in Oregon supported this result and were positively correlated with mean KFI at the population level. If females in populations at or near carrying capacity suffer from generally low body condition, intrauterine and neonatal mortality may further reduce the number of sons produced and produce a significant bias toward daughters. Thus, adaptive sex ratio adjustment in elk may have significant importance for elk population management and the production of males.

Environmental influences on male courtship and implications for female choice in a lekking HawaiianDrosophila

This study examined how variation in a critical environmental variable, protein content in the adult diet, influenced male mating signals, mating success and male ‘quality’ in a lekking Hawaiian Drosophila, D. grimshawi . Specifically, the effects of low- and high-protein-containing diets on male physical condition, courtship behaviour, copulation success and adult offspring production were investigated. Potential differences in attractiveness to females were investigated by recording times to mating. Males fed high-protein diets were in better physical condition, courted more vigorously, and mated more often and sooner than males fed low-protein diets. Matings involving males fed a high-protein diet resulted in more eclosing offspring than matings involving low-protein-fed males. Because females control when mating occurs in this species, these results indicate that females may have preferred males fed high-protein diets. The results are discussed in light of recent questions regarding female choice and the possible benefits that females of lekking species might gain by discriminating between males.

Climate change and temperature-dependent sex determination in reptiles.

Despite increasing concern over the possible impact of global temperature change, there is little empirical evidence of direct temperature effects on biotic interactions in natural systems. Clear assessment of the ecological and evolutionary impact of changing climatic temperature requires a natural system in which populations exhibit a direct unambiguous fitness response to thermal fluctuation. I monitored nests of a population of painted turtles (Chrysemys picta) with temperature-dependent sex determination to investigate the causal relationship between local climatic variation in temperature and offspring sex ratio. Consistent with theoretical predictions, annual offspring sex ratio was highly correlated with mean July air temperature, validating concerns about the effect of climate change on population demography. This correlation implies that even modest increases in mean temperature (< 2 degrees C) may drastically skew the sex ratio. Statistical evaluation of the variance in climate change indicates that an increase in mean temperature of 4 degrees C would effectively eliminate production of male offspring. Quantitative genetic analyses and behavioral data suggest that populations with temperature-dependent sex determination may be unable to evolve rapidly enough to counteract the negative fitness consequences of rapid global temperature change. Populations of species with temperature-dependent sex determination may serve as ideal indicators of the biological impact of global temperature change.

Sex ratios in field populations of Epidinocarsis lopezi, an exotic parasitoid of the cassava mealybug, in Africa

Abstract. In cassava fields in Africa, population sex ratios of Epidinocarsis fopezi vaned from 0.44 (males to total parasitoids) at low host densities to highly male‐biased ratios of 0.70 at high host densities. This variability is caused by the difference in allocation of sons and daughters to hosts of different sizes, through the following mechanisms: (a) small, i.e. second instar, hosts are mainly used for the production of male offspring, whereas in large, i.e. third instar, hosts a variable, female‐biased sex ratio is produced; (b) E.fopezi does not selectively oviposit into large hosts but always accepts both small and large hosts for oviposition upon encountering; (c) in the field, this parasitoid is time‐limited, and not egg‐limited. On the basis of an optimal diet model, such general host acceptance is shown to be the best strategy. Thus, sex ratio increases with host density for three reasons: the proportion of small hosts encountered in the field increases with increasing host density, small hosts are used for male production, and hosts are always accepted when encountered.

Provisioning behavior and the estimation of investment ratios in a solitary bee, Calliopsis (Hypomacrotera) persimilis (Cockerell) (Hymenoptera: Andrenidae)

One aspect of behavioral ecology that has received considerable attention, especially by students of social insects, is the relative amount of energy invested by parents in the rearing of male versus female offspring. Sexual selection theory makes predictions about how individuals should allocate their total investment in the sexes. To test these predictions we must accurately quantify the relative “cost” incurred by a parent in the production of an average individual of either sex. Body weight ratios are the most common estimate of cost ratio, but the correspondence between offspring body weight and energetic investment on the part of the parent has rarely been determined. Calliopsis (Hypomacrotera) persimilis is a solitary, ground-nesting bee whose natural history makes it particularly convenient for studies of investment patterns and foraging behavior. Each day females construct and provision from 1 to 6 cells in linear, closely-spaced series. Each cell is provisioned with pollen from Physalis Wrightii flowers, which is collected on two or three foraging trips. However, the temporal sequence in which two- and three-trip foraging bouts occur is not random. Females invariably begin each day provisioning cells with three trips worth of pollen and usually switch to provisioning the latter cells of the day with just two trips worth of pollen. The sex of the offspring within the same co-linear series of cells also varies non-randomly — female offspring predominate in the first cells of each series and male offspring in the latter cells. The correspondence between the number of foraging trips to provision a cell, the total time spent foraging, and offspring sex was determined for 36 cells. The data indicate a close, though not absolute, relationship between the number of foraging trips and the sex of the offspring: males usually received two trips of pollen, though some received three, whereas female offspring invariably received three trips worth of pollen. A number of potential estimates of the relative cost of female and male offspring production were calculated. Estimates of the cost ratio based on the amount of time spent foraging, adult dry body weight, and pollen ball dry weight all give similar values. Female offspring receive an energetic investment of from 1.3 to 1.5 times that of males. These results support the use of adult dry body weight ratios in the estimation of cost ratios.

The evolution of polyandry by queens in social Hymenoptera: the significance of the timing of removal of diploid males

Multiple mating by queens in social Hymenoptera with single locus sex determination may be an adaptation to reduce the effect of genetic load caused by the production of diploid males, if there is a concave relationship between queen fitness and the proportion of diploid male offspring in the colony. In this situation queens should be selected to reduce the variance in the production of diploid male offspring by multiple mating. It has been suggested that this concave relationship occurs in species such as the honey bee, Apis mellifera, in which reproduction occurs near the peak of colony population. This paper suggests that the timing of diploid male removal may influence mating frequency, with early removal of diploid males favoring multiple mating and late removal of diploid males favoring single mating. This idea is explored in two ways. A mathematical model shows that cell use in the brood area of species that rear young in cells will be more efficient with multiple mating. This would favor multiple mating in species, such as the honey bee, in which brood rearing is constrained by the usable area of the brood chamber. Secondly, comparison of polyandrous honey bees (early removal of diploid males as young larvae) with monandrous fire ants, Solenopsis invicta, and Melipona bees (non-removal of immature diploid males) suggests that in the species without diploid male removal, variance reduction may reduce queen fitness. Suggestions are made for testing this hypothesis.

Is there an optimal sex ratio for insect mass rearing?

The optimal sex ratio ( sr) for insect mass rearing depends upon the use to which the insects will be put. Mass rearing for release in control programs and for producing insects for experimental purposes may require sr values in the breeding population that optimize the production of male offspring, female offspring, or some combination of both. We have developed a number of models to guide those in mass rearing in their choice of strains to be used in the rearing facility. We have considered the cases of both prezygotic and postzygotic determination of sr, as well as whether or not there is a limit to the resources and time available to raise the insects. In general the number of females or males and females together produced is maximized for a sr in which there is a maximum possible number of females in the breeding population. When males alone are required the optimal sr in the rearing facility lies between 0.1 and 0.5 its actual value being dependent upon a variety of parameters such as the number of generations available and the number of eggs laid per female.

The Genetic Demography of the Gainj of Papua New Guinea. 2. Determinants of Effective Population Size

The Hill-Emigh-Pollak model of effective population size for dioecious species with overlapping generations is subjected to a sensitivity analysis designed to measure the relative importance of the model's parameters. According to this analysis, effective size appears to be most sensitive to changes in the parameters related to reproductive heterogeneity (the variances and covariances in the net lifetime production of male and female offspring) and less sensitive to changes in parameters related to demographic recruitment (the mean generation length and the number of males and females reaching reproductive age each year). The recruitment parameters, however, are more likely to vary among populations and, on balance, are probably more important as causes of interpopulation variation in effective size. Since the model's covariance terms are new to population genetics, analytical expressions are derived for them under the Poisson and negative binomial birth processes. The model is applied to demographic data on the Gainj, a tribal population of highland New Guinea. The reproductive output of Gainj females follows a Poisson distribution, whereas that of males follows a negative binomial distribution with a variance three times that of females. This increased reproductive heterogeneity in males is attributable to polygyny. Demographic recruitment is slow, largely because of slow sexual maturation and late marriage. In consequence, the mean generation time is long and the number of individuals initiating reproduction each year is small. The net effect of these factors is to reduce the effective size of the Gainj population to about one-half of the total population size.

Parallels between sexual strategies and other allocation strategies.

Allocation strategies in which a limited resource is apportioned among alternative activities are applicable to diverse structural, genetical and behavioral topics, including male versus female investments. In a model of sex allocation strategies, the absolute fitnesses of individuals are calculated by summing the production of male and female gametes or offspring, each weighted by its reproductive value. The ESS is obtained by examining the fitness advantage of one phenotype over another. An analogous method is used to obtain a general model of allocation strategies that incorporates some widespread features. Allocation strategies are affected by the sizes and shapes of the reward curves, stochastic factors, and constraints on the allocations permitted. A number of parallels among diverse types of allocation strategies, including the occurrence of fixed, conditional and mixed strategies, and matching rules, are discussed.

Parallels between sexual strategies and other allocation strategies.

Allocation strategies in which a limited resource is apportioned among alternative activities are applicable to diverse structural, genetical and behavioral topics, including male versus female investments. In a model of sex allocation strategies, the absolute fitness of individuals are calculated by summing the production of male and female gametes or offspring, each weighted by its reproductive value. The ESS is obtained by examining the fitness advantage of one phenotype over another. An analogous method is used to obtain a general model of allocation strategies that incorporates some widespread features. Allocation strategies are affected by the sizes and shapes of the reward curves, stochastic factors, and constraints on the allocations permitted. A number of parallels among diverse types of allocation strategies, including the occurrence of fixed, conditional and mixed strategies, and matching rules, are discussed.

Intra-sex and inter-sex sibling interactions as sex ratio determinants

Fisher1 produced the first general argument that a random-mating sexually-reproducing population should devote equal reproductive resources to the production of male and female offspring, while Hamilton2 considered several unusual situations in which the expenditure of reproductive resources should be biased towards one sex or the other. His ‘host’ model has been widely cited3–6 and at least three factors proposed as the cause of the sex ratio bias: local mate competition, sib-mating and inbreeding. The problem of which of these factors is the real cause of the biased sex ratio seems important in view of the large number of apparently different but often closely related sex ratio models which are now being proposed. It would be useful to have ways of classifying them according to the presence of different factors which affect the equilibrium sex ratio. Here, I present a general equation (equation (2)) for differential change in fitness which exhibits the equilibrium sex ratio as achieving a balance between the factor contained in Fisher's standard grandchild argument1 and a second factor resulting from intra-sex sibling interactions over reproductive resources. In particular, I analyse Hamilton's host model2 for the presence of these different factors.

Production of male and female offspring in the strictly monogenic fly Chrysomya rufifacies after ovary transplantation.

Production of male and female offspring in the strictly monogenic fly Chrysomya rufifacies after ovary transplantation.

Sex ratios in laboratory and field populations of the old field mouse, Peromyscus polionotus

SummaryMales outnumbered females as juveniles but not as adults among mice captured by hand in their burrows. The higher production of male offspring together with their higher mortality rate resulted in a 1∶1 sex ratio for the adult mice. Despite the equal abundance of each sex, more males than females were caught in traps. Males must have a higher chance of encountering a trap and/or of entering a trap after finding it.

Factors Involved in Male Production by Crowded Moina macrocopa Mothers.

The writers, , have extended the earlier observations of Grosvenor and Smith and others on the association between crowding of Moina macrocopa mothers and the production of male offspring. We also noted an association between retardation in the time of production of the parthenogenetic young and the percentage of male young produced. Within limits the percentage of male young produced is roughly proportional both to the degree of crowding and to the amount of retardation in the time of their production. Excessive retardation, however, whether induced by crowding or by other treatments, is accompanied by a reduced percentage of male young. We have interpreted this retardation and this male production as due to the accumulation of the mothers' excretory products. Stuart and Banta have shown that quantity of bacteria available as food for Moina mothers appears, under certain appropriate experimental set-ups, to be the determining factor in sex control in this species. This finding might raise the question as to whether quantity of available food is the principal or sole influential factor involved in male causation in crowding or other experiments, by Moina mothers. In certain experiments involving aeration of mothers during the critical period male production was reduced or eliminated, in which case quantity of food apparently cannot be considered the determining factor in sex control. But the results of crowding might seem readily interpretable on this basis. This note records the results of experiments designed to differentiate between (1) the quantity of available food and (2) some other factor associated with crowding (presumably “the accumulation of excretory products”) as factors in influencing male production.