Affect Offspring Sex Ratio Research Articles

Oviposition preference of Ceratitis capitata (Diptera: Tephritidae) at different times after pruning 'Italia' table grapes grown in Brazil.

Studies investigating oviposition preference of Ceratitis capitata (Wiedemann, 1824) in table grapes (Vitis vinifera L.) cultivated in the São Francisco River Valley can provide important information to guide control measures, therefore minimizing damage caused by this species in the region. The aim of this study was to evaluate the oviposition preference of C. capitata females for berries cv. ‘Italia’ collected at five different times (60, 70, 80, 90, and 100 d after production pruning [DAPP]), representing five grapevine growth stages. We also assessed the performance of immature stages of C. capitata regarding the physiological development of the berry. The total soluble solid content was significantly higher in berries at more advanced physiological developmental stages (90 and 100 DAPP). Conversely, these berries showed the lowest values of firmness and titratable acidity. With the onset of physiological development, the average number of punctures per berry increased and reached 5.2 per berry in 100 DAPP berries. The infestation level and pupal weight showed a positive correlation with the growth stage. The highest recovery of pupae was observed in 100 DAPP berries (1.54). Pupal viability values ranged from 50.9 to 64.7% independent of berry maturity stage. The physiological developmental stage of the berry did not affect offspring sex ratio. Results obtained suggest that regardless of the female preference for laying eggs on berries in a more advanced physiological developmental stage, females can initiate the attack to bunches of this cultivar at 60 DAPP, even if the berries have unfavorable physicochemical parameters for oviposition and development of larvae.

Association between extra-pair paternity and nestling sex and condition in the barn swallow

Parents should differentially allocate resources to the production of offspring of either sex depending on their expected fitness return. In sexually promiscuous females, offspring sex ratio should be affected by the sexual attractiveness of biological fathers because sons, but not daughters, will benefit from inheriting genes for sexual attractiveness. Females may acquire benefits for the offspring if the extra-pair male is of superior genetic quality as compared to the social mate, if it carries compatible genes or genes that enhance offspring genetic diversity. If sexually selected ornaments reflect male quality, extra-pair offspring should be more frequently males and of higher quality compared to their half-siblings. Furthermore, the probability of extra-pair offspring to be male should increase with an increasing difference in sexual ornamentation between the extra-pair and the social mate. In this study, we tested if barn swallow offspring sex ratio depends on paternity and on sexual ornamentation of the extra-pair father, and whether paternity predicts offspring phenotypic quality. The results partially fulfilled our prediction. We did not provide support for the hypothesis of a differential sex allocation to the production of male offspring by promiscuous females, both at the individual and at the within-brood level. Moreover, the difference in the ornamentation of the extra-pair and the social male did not affect the sex ratio of individual offspring. However, in accordance with the good genes and the genetic compatibility hypotheses, extra-pair offspring were of superior quality as compared to their half-sibling, in terms of body size and feather growth. In sexually promiscuous species, females should differentially allocate resources to the production of offspring of either sex depending on paternity or sexual ornamentation of the social or the extra-pair mate. Moreover, extra-pair offspring may be of superior quality compared to their within-pair half-siblings. In the present study of the barn swallow, paternity and the differences in sexual ornamentation between the social and the extra-pair mate did not affect offspring sex ratio. In addition, according to the good genes and the genetic compatibility hypotheses, we found that extra-pair offspring are of superior quality as compared to their within-pair siblings. Despite we failed to provide support to the sex allocation theory, the present study emphasizes the importance of “negative” results to better estimate the generality of the occurrence of adaptive sex allocation strategies in the context of sexual selection studies.

Effects of population structure and density on calf sex ratio in red deer (Cervus elaphus)\u2014implications for management

There is ongoing interest to assess what factors affect offspring sex ratio, especially in ungulates. Wildlife managers might be interested in influencing this sex ratio for two reasons: either in order to limit population growth more effectively by reducing the proportion of females born or to increase revenues by a higher proportion of trophy bearing males in the population. While previous studies mostly focused on how maternal traits affect offspring sex ratio, we included here also male traits in our analysis. We achieved this by investigating data from 30 areas covering entire Lower Austria, collected over the past 12 years from both hunted red deer and those killed in road accidents. We focused our analyses on parameters that can be easily assessed by managers on the population and individual level, i.e. the numbers of animals culled in different age/sex classes and their body mass. We found that the proportion of females among calves increased with population density. Furthermore, we found that calf sex ratio (i.e. the proportion males among calves aged between 2 and 7 months) increased with increasing proportions of adult females and males older than 10 years, independent of the density effect. We conclude that wildlife managers interested in the effective reduction of red deer abundance and/or increasing the proportion of males among offspring should select a culling regime leading to a low population density dominated by adult, prime-aged females and males. This can be achieved by over-proportional removal of young females and warranting that a high number of strong males reach an age of at least 10 years.

Offspring sex ratio in mammals and the Trivers-Willard hypothesis: In pursuit of unambiguous evidence.

Can mammalian mothers adaptively control the sex of their offspring? The influential Trivers-Willard hypothesis (TWH) proposes that when maternal condition increases the fitness of sons more than that of daughters, the proportion of sons produced should increase with maternal condition. Studies of mammals, however, often fail to support this hypothesis. This article highlights recent advances, including studies on the assumptions of the TWH and physiological mechanisms for sex-ratio manipulation. Particular emphasis is placed on how factors such as paternal quality, maternal reproductive costs and environmental conditions experienced by mothers early in life can mask/alter the expected relationship between maternal condition and offspring sex ratio or lead to apparent support for the TWH. While there is growing evidence that sex ratio around conception may be maternally and paternally manipulated, a challenge for future studies on sex allocation is to integrate how multiple and potentially opposite selective pressures affect offspring sex ratio.

Morphological features, development and reproduction of Melittobia acasta on Bombus terrestris

AbstractMorphological features, development and reproduction behavior of the parasite Melittobia acasta (Walker) were studied when reared on the pupae of the bumblebee Bombus terrestris L. in the laboratory under 23°C, 50% relative humidity and 12 h light : 12 h dark conditions. The parasites laid transparent white and elongated eggs. Newly hatched larval size and shape were very similar to eggs but they were identified by their body segments. Larvae increased their body size through moulting and transformed into a vermiform shape. Male pupae were shiny brown with dots. The female pupae were distinguished by their black shiny color, shorter size and the presence of compound eyes. Adult male pupae were dark brown and dwarf‐winged, whereas female pupae were macropterous and brachypterous. Reproduction took place by fertilization and also parthenogenetically. Mean fecundity within 5 days by mated (47.9 ± 30.5 female−1) and virgin (7.4 ± 6.8 female−1) females were statistically different. Mated females laid fertilized eggs that produced adult males or females, whereas virgin females laid unfertilized eggs that produced males. Development durations of the virgin female originated eggs, larvae, pupae and adults were statistically identical with those of mated females. The parasites were female‐biased and foundress number did not affect offspring sex ratio. This study shows that both mated and virgin females of M. acasta can produce many offspring on B. terrestris pupae within a short period, indicating that they are dangerous parasites of the bumblebee in a mass rearing system.

An adaptive annual rhythm in the sex of first pigeon eggs.

When the reproductive value of male and female offspring varies differentially, parents are predicted to adjust the sex ratio of their offspring to maximize their fitness (Trivers and Willard, Science 179:90–92, 1973). Two factors have been repeatedly linked to skews in avian offspring sex ratio. First, laying date can affect offspring sex ratio when the sexes differ in age of first reproduction, such that the more slowly maturing sex is overproduced early in the season. Second, position of the egg in the laying sequence of a clutch may affect sex ratio bias since manipulating the sex of the first eggs may be least costly to the mother. We studied both factors in two non-domesticated pigeon species. Both the Wood pigeon (Columba palumbus) and the Rock pigeon (Columba livia) have long breeding seasons and lay two-egg clutches. In the field, we determined the sex of Wood pigeon nestlings. In Rock pigeons, housed in captivity outdoors, we determined embryo sex after 3 days of incubation. On the basis of their sex-specific age of first reproduction, we predicted that males, maturing at older age than females, should be produced in majority early and females later in the year. This was confirmed for both species. The bias was restricted to first eggs. Rock pigeons produced clutches throughout the year and show that the sex of the first egg followed an annual cycle. To our knowledge, this study presents the first evidence of a full annual rhythm in adaptive sex allocation in birds. We suggest that this reflects an endogenous seasonal program in primary sex ratio controlled by a preovulatory mechanism.

Offspring in Response to Parental Female Densities in the Fruit Fly Parasitoid DIACHASMIMORPHA LONGICAUDATA (Hymenoptera: Braconidae: Opiinae)

As part of an evaluation of the braconid parasitoid Diachasmimorpha longicaudata (Ashmead) as a biocontrol agent of Ceratitis capitata (Wiedemann) in Brazil, the aims in the current study were to find the best parental ratio of females to males in the rearing cages in order to get the highest female biased offspring in the parasitoid rearing process, and to verify the parasitism efficiency on C. capitata according to parental female densities. Three treatments were assessed: T1 (20 females: 20 males), T2 (60 females: 20 males) and T3 (100 females: 20 males). Ten late-third instars of C. capitata were offered daily to each female parasitoid from the 1st to the 12th d of age. The parental female productivity, fecundity, offspring sex ratio, percentage of parasitoid emergence, and daily mortality of parental females and males at different female/male densities were evaluated. The results indicated that numbers higher than 20 parental females did not affect offspring sex ratio, overall offspring production, nor the percent parasitism. Female biased offspring occurred in all three parental female/male ratios analyzed in this study, except that predominately males developed from parasitoid eggs laid in the age interval 1-2 d post emergence. Higher parasitoid female productivity and fecundity were found at the 1:1 female/male per cage density whereas lower productivity and fecundity were recorded at the 5:1 female/male ratio. Higher female/male ratio in the parental cages increased the mortality rate of females but did not influence the number of parental male deaths. The results may facilitate advancement of an optimum mass-rearing system to aid in control of C. capitata in Brazil.

Seasonal Variation in Sex Ratios Provides Developmental Advantages in White-tailed Deer, <em>Odocoileus virginianus</em>

Since Trivers and Willard first proposed their hypothesis concerning the adaptive advantages of producing a particular offspring sex in relation to maternal condition in 1973, it has been at the forefront of scientific research concerning sex ratios with most subsequent studies focusing on maternal condition as a key contributor to variations in sex ratios. Another factor that could greatly influence sex ratios, although has been only infrequently examined in mammalian species, is birth date. We investigated how birth date influenced offspring sex ratios in White-tailed Deer (Odocoileus virginianus). Since date of birth can greatly influence an individual’s fitness and reproductive success, we suggest that birth date may be an alternative strategy in determining offspring sex ratios. Since it has been shown that the lifetime reproductive fitness of a mother can be increased by producing a particular sex during a particular time, we hypothesized that more male offspring should be born earlier in the season due to their increased reproductive potential from being born at this time. Offspring born earlier will have a head start in development and therefore have greater potential for increased body size and dominance later in life, traits that greatly influence male reproductive success. In this study, we found that maternal condition did not affect offspring sex ratio in a captive population of White-tailed Deer in Michigan; however, birth date did. We found that more males tended to be born during the second and fourth birthing periods, while more females were born during the first, third and fifth periods. In addition, we found that males born earlier in the season had greater mass the following spring than those born later, a trend that was not as dramatic in females. These results lend moderate support to our hypothesis that in White-tailed Deer offspring sex will tend to vary according to timing of birth and relative reproductive advantages gained by a particular sex being born at that time.

Maternal size and age affect offspring sex ratio in the solitary egg parasitoid Anaphes nitens

AbstractIn this study, the effects of maternal age, diet, and size on offspring sex ratio were investigated for the solitary egg parasitoid, Anaphes nitens Girault (Hymenoptera: Mymaridae), both outdoors, during the winter, and inside a climatic chamber under favourable constant conditions. During the winter of 2005–2006, each of seven groups containing 40 1‐day‐old females was mated and randomly distributed among two treatments: (treatment 1) a droplet of undiluted honey ad libitum + one fresh egg capsule of the snout beetle Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae) as host; (treatment 2) drops of water + one fresh egg capsule of G. scutellatus. We recorded the lifetime fecundity, the daily sex allocation, and the lifetime offspring sex ratio to study the existence of a relationship with maternal characteristics. Moreover, we assessed the effect of location (outdoors vs. indoors) and group (groups are representative of early, mid, and late winter) on sex ratio. The most important factor that biased the sex ratio was maternal body size: larger females of both treatments produced more female offspring. As females of A. nitens could gain more advantage than males from body size, larger mothers have a higher fitness return if they produce more daughters. The effect of the treatment was significant: starved females produced more females. Location and group were not significant. Fecundity and sex ratio were age dependent. Old mothers that received honey (treatment 1) had fewer offspring and a more male‐biased offspring sex ratio, probably due to reproductive senescence and sperm depletion. Starved females (treatment 2) experienced reproductive decline earlier, perhaps because they invested more energy in maintenance rather than in reproduction.

Maternal body condition and plasma hormones affect offspring sex ratio in peafowl

In theory, females that can afford to do so may increase their fitness by investing in offspring of the sex with the greater probability of attaining high reproductive success. This has been observed in a wide variety of mammalian, reptilian and avian species although the proximate mechanism remains a mystery. Using a captive population of peafowl, Pavo cristatus, we investigated the relation between maternal quality, offspring sex ratio and plasma concentrations of the reproductive hormones testosterone and 17β-oestradiol and the principal avian stress hormone corticosterone. Each peacock was paired with three peahens that differed with respect to their relative body condition, creating a condition and dominance hierarchy within each pen and thus a situation in which we would predict investment in offspring to vary between hens. We found significant intercorrelations between maternal body condition (but not dominance rank or clutch size), maternal plasma levels of corticosterone and testosterone (but not 17β-oestradiol) and clutch sex ratio, such that good maternal condition, low plasma corticosterone and high levels of testosterone were associated with male biases in the sex ratio and increased investment in male eggs. The observed biases were probably present at laying, and thus add to the growing number of studies showing primary sex ratio adjustment in response to maternal body condition, and furthermore may indicate a role for corticosterone and testosterone in the avian sex manipulation process.

Temperature‐induced changes in spider mite fitness: offsetting effects of development time, fecundity, and sex ratio

AbstractTemperature affects many life history parameters in poikilotherms. Temperature clearly affects development time and fecundity, which affect the intrinsic rate of increase. In haplodiploid mites, ambient temperature may also affect offspring sex ratio which, in turn, affects intrinsic rate of increase. The combined effect of all these processes determines the fitness of individual females. However, sex ratio also affects mating structure and, potentially, rate of local adaptation. We investigated the direct effect of temperature variation on sex ratio, development time, and fecundity in the twospotted spider mite (Tetyranychus urticae), and calculated the effect of their interaction on mite intrinsic rate of increase. We conducted experiments at 2 temperatures and designed the experiment to separate pre‐adult and adult sensitivity to temperature variation. Mites were reared from eggs to adult ecdysis at either 22 °C or 32 °C. Upon emergence as adults, these 2 groups were each split between 22 °C and 32 °C and allowed to oviposit. Not surprisingly, development from egg to adult was accelerated when mites were exposed to the higher temperature during offspring development, regardless of the temperature experienced by the mother during her development. Fecundity and the proportion of female offspring were affected by temperature only when mothers were exposed during both development and oviposition. About 12 offspring were gained and female bias was increased by 26% when the mother's development occurred at 22 °C, whereas oviposition at 22 °C added only 6 more offspring and increased female bias by only 7%. There was no correlation between sex ratio and fecundity; both were related to temperature but not to each other. Furthermore, development time, not fecundity or sex ratio, appeared to the main factor affecting the intrinsic rate of increase. Our results support other evidence that sex ratio varies independently of development time and fecundity.

Dominance Rank, Secondary Sex Ratio, and Reproduction of Offspring in Polygynous Primates

One question in evolutionary biology which is central to understanding reproductive strategies and parental efforts at rearing offspring is why organisms produce certain offspring sex ratios (Trivers and Willard 1973; Charnov 1982). Fisher (1930) argued that since each individual has a mother and a father, both sexes contribute genes equally to the next generation. All else being equal, if members of one sex were overproduced, their ability to reproduce would be limited by the availability of members of the less abundant sex and natural selection would favor any predisposition to produce offspring of the less abundant sex. In this fashion, Fisher reasoned, selection would adjust the offspring sex ratio in an outbreeding population until total parental investment (PI, Trivers 1972) in the two sexes was equal. Fisher (1930) assumed, but did not clearly state, that all parents were alike in their ability to rear reproductively successful sons and daughters (Patterson and Emlen 1980). A model proposed by Trivers and Willard (1973), however, specified how deviations from equal PI may be favored by natural selection according to the influence of maternal condition on the reproduction of offspring. The TriversWillard model proposed that in polygynous species if some condition of mothers (e.g., dominance rank) influences the condition and, as a result, the reproductive success (RS) of sons more than daughters, then selection should result in the evolution and maintenance of mechanisms by which females in poor condition invest less in sons than daughters and/or females in good condition invest more in sons than daughters. This model is particularly relevant for primates, since the majority of species are polygynous (Clutton-Brock and Harvey 1977). Since the dominance rank of a monkey's social group and family has a strong