scholarly journals Seasonal Variation in Sex Ratios Provides Developmental Advantages in White-tailed Deer, Odocoileus virginianus

2007 ◽  
Vol 121 (4) ◽  
pp. 412
Author(s):  
Sarah T. Saalfeld ◽  
Stephen S. Ditchkoff ◽  
John J. Ozoga ◽  
Michael S. Mitchell
Keyword(s):  
Reproductive Success ◽  
Odocoileus Virginianus ◽  
Mammalian Species ◽  
Sex Ratios ◽  
Reproductive Potential ◽  
Birth Date ◽  
Male Reproductive Success ◽  
Maternal Condition ◽  
Offspring Sex Ratio ◽  
Offspring Sex

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.

scholarly journals Maternal Condition, Reproductive Investment, and Offspring Sex Ratio in Captive Red Junglefowl (Gallus gallus)

The Auk ◽  
2002 ◽  
Vol 119 (3) ◽  
pp. 840-845 ◽  
Author(s):  
Timothy H. Parker
Keyword(s):  
Reproductive Success ◽  
Egg Size ◽  
Reproductive Investment ◽  
Gallus Gallus ◽  
Male Reproductive Success ◽  
Maternal Condition ◽  
Offspring Sex Ratio ◽  
Red Junglefowl ◽  
Offspring Sex ◽  
The Relationship

Abstract Maternal condition can affect reproductive investment in one or more ways. Captive female Red Junglefowl (Gallus gallus) that were heavier, controlling for tarsus length, produced larger eggs and initiated laying earlier, but did not produce more eggs per clutch. Maternal mass was also a positive predictor of offspring mass. That appears to result from the strong positive relationships between egg size and offspring mass. When the relationship between egg size and offspring mass was statistically controlled, maternal mass no longer predicted offspring mass. Mothers in better condition produced male-biased broods, as predicted when offspring condition depends on maternal condition and when male reproductive success is more dependent than female reproductive success on condition.

Unexpected offspring sex ratios in response to habitat quality in a size-dimorphic bark beetle

1999 ◽  
Vol 77 (4) ◽  
pp. 524-529 ◽  
Author(s):  
Risa D Sargent ◽  
Mary L Reid
Keyword(s):  
Body Size ◽  
Reproductive Success ◽  
Sex Ratio ◽  
Habitat Quality ◽  
Bark Beetle ◽  
Sex Ratios ◽  
Diploid Species ◽  
Differential Mortality ◽  
Male Reproductive Success ◽  
Offspring Sex

Facultative sex ratio manipulation has been examined in a limited number of diploid species, mainly vertebrates. We tested the prediction that mothers would preferentially place males in conditions conducive to large size in the diploid pine engraver bark beetle, Ips pini. In this species, males are the larger sex and therefore male reproductive success was expected to be more dependent on body size than female reproductive success. Because body size is largely environmentally determined in bark beetles, mothers were expected to alter sex ratios in response to habitat quality. Contrary to predictions, offspring sex ratios tended to be more female biased in situations conducive to large offspring size than in situations producing offspring of small size. We were able to rule out nonadaptive explanations such as differential mortality or development times of males and females, suggesting that the observed pattern is adaptive. This study provides a rare example of sex ratio manipulation in diploid insects. However, the unexpected direction of sex ratio biases suggests that daughters gain a yet unknown benefit from being reared in high-quality conditions that surpasses the fitness that would be gained from producing relatively larger sons.

scholarly journals Consistent sex ratio bias of individual female dragon lizards

2006 ◽  
Vol 2 (4) ◽  
pp. 569-572 ◽  
Author(s):  
Tobias Uller ◽  
Beth Mott ◽  
Gaetano Odierna ◽  
Mats Olsson
Keyword(s):  
Genetic Variation ◽  
Sex Ratio ◽  
Incubation Temperature ◽  
Sex Ratios ◽  
Phenotypic Traits ◽  
Female Size ◽  
Offspring Sex Ratio ◽  
Phenotypic Differences ◽  
Sex Ratio Bias ◽  
Offspring Sex

Sex ratio evolution relies on genetic variation in either the phenotypic traits that influence sex ratios or sex-determining mechanisms. However, consistent variation among females in offspring sex ratio is rarely investigated. Here, we show that female painted dragons ( Ctenophorus pictus ) have highly repeatable sex ratios among clutches within years. A consistent effect of female identity could represent stable phenotypic differences among females or genetic variation in sex-determining mechanisms. Sex ratios were not correlated with female size, body condition or coloration. Furthermore, sex ratios were not influenced by incubation temperature. However, the variation among females resulted in female-biased mean population sex ratios at hatching both within and among years.

scholarly journals Reproduction and Offspring Sex Ratios Differ Markedly among Closely Related Hyperparasitoids Living in the Same Microhabitats

2019 ◽  
Vol 32 (3) ◽  
pp. 243-251 ◽  
Author(s):  
Jeffrey A. Harvey ◽  
Lucas de Haan ◽  
Oriol Verdeny-Vilalta ◽  
Bertanne Visser ◽  
Rieta Gols
Keyword(s):  
Reproductive Success ◽  
Sex Ratios ◽  
Reproductive Traits ◽  
Female Offspring ◽  
Forest Edge ◽  
Cotesia Glomerata ◽  
Small Scale ◽  
Lifetime Reproductive Success ◽  
Closely Related Species ◽  
Offspring Sex

Abstract Closely related species in nature usually exhibit very similar phylogenetically conserved traits, such as reproduction, behavior and development. Here, we compared fecundity schedules, lifetime reproductive success and offspring sex ratios in three congeneric facultative hyperparasitoid wasps that exhibit several overlapping traits and which co-occur in the same small-scale habitats. Gelis agilis, G. proximus and G. hortensis are abundant in meadows and forest edge habitats in the Netherlands. Gelis agilis is asexual (all female), whereas the other two species reproduce sexually. Here they developed on cocoons of the primary parasitoid Cotesia glomerata. When provided with unlimited hosts, lifetime reproductive success was three times higher in G. proximus than in G. agilis with G. hortensis producing intermediate numbers of offspring. All three species depleted their teneral reserves during their lives. Females of G. proximus and G. hortensis lived significantly longer than females of G. agilis. Offspring sex ratios in young G. proximus mothers were female-biased and marginally male-biased in G. hortensis. As mothers aged, however, the ratio of male:female progeny produced rapidly increased until no daughters emerged later in life. Our results reveal significant differences in reproductive traits among the three species despite them co-occurring in the same microhabitats, being very closely related and morphologically similar. The increase in the production of male progeny by Gelis mothers over time suggests a depletion in sperm number or viability with age. This is especially interesting, given that Gelis species are among the least fecund parasitoids thus far studied. It is likely that in the field most Gelis mothers are probably only able to parasitize a few hosts and to maintain the production of female offspring.

Host size-dependent sex allocation behaviour in a parasitoid: implications forCatolaccus grandis(Hymenoptera: Pteromalidae) mass rearing programmes

1998 ◽  
Vol 88 (1) ◽  
pp. 37-45 ◽  
Author(s):  
K.M. Heinz
Keyword(s):  
Biological Control ◽  
Sex Ratio ◽  
Sex Allocation ◽  
Sex Ratios ◽  
Boll Weevil ◽  
Mass Rearing ◽  
Host Size ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Control Programmes

AbstractAn often encountered problem associated with augmentative and inundative biological control programmes is the high cost of producing sufficient numbers of natural enemies necessary to suppress pest populations within the time constraints imposed by ephemeral agroecosystems. In many arrhenotokous parasitoids, overproduction of males in mass-rearing cultures inflates costs (per female) and thus limits the economic feasibility of these biological control programmes. Within the context of existing production technologies, experiments were conducted to determine if the sex ratio ofCatolaccus grandis(Burks), an ectoparasitoid of the boll weevilAnthonomous grandisBoheman, varied as a function of boll weevil larval size. Results from natural and manipulative experiments demonstrate the following behavioural characteristics associated with C.grandissex allocation behaviour: (i) femaleC. grandisoffspring are produced on large size hosts and male offspring are produced on small hosts; (ii) whether a host is considered large or small depends upon the overall distribution of host sizes encountered by a female parasitoid; and (iii) female parasitoids exhibit a greater rate of increase in body size with host size than do male parasitoids. The observed patterns cannot be explained by sex-specific mortality of immature parasitoids developing on the different host size categories. In subsequent experiments, laboratory cultures ofC. grandisexposed daily to successively larger sizes ofA. grandislarvae produced successively greater female biased offspring sex ratios, cultures exposed daily to successively smaller sizes of host larvae produced successively greater male biased offspring sex ratios, and cultures exposed daily to equivalent host size distributions over time maintained a uniform offspring sex ratio. By increasing the average size ofA. grandislarval hosts exposed toC. grandisby 2.5 mg per day in mass rearing cultures, the percentage of male progeny can be reduced from 33% to 23% over a period of four consecutive exposure days.

scholarly journals Does sex-ratio selection influence nest-site choice in a reptile with temperature-dependent sex determination?

2013 ◽  
Vol 280 (1772) ◽  
pp. 20132460 ◽  
Author(s):  
Timothy S. Mitchell ◽  
Jessica A. Maciel ◽  
Fredric J. Janzen
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Nest Site ◽  
Sex Ratios ◽  
Temperature Dependent ◽  
Dioecious Species ◽  
Offspring Sex Ratio ◽  
Nest Sites ◽  
Offspring Sex ◽  
Nest Site Choice

Evolutionary theory predicts that dioecious species should produce a balanced primary sex ratio maintained by frequency-dependent selection. Organisms with environmental sex determination, however, are vulnerable to maladaptive sex ratios, because environmental conditions vary spatio-temporally. For reptiles with temperature-dependent sex determination, nest-site choice is a behavioural maternal effect that could respond to sex-ratio selection, as mothers could adjust offspring sex ratios by choosing nest sites that will have particular thermal properties. This theoretical prediction has generated decades of empirical research, yet convincing evidence that sex-ratio selection is influencing nesting behaviours remains absent. Here, we provide the first experimental evidence from nature that sex-ratio selection, rather than only viability selection, is probably an important component of nest-site choice in a reptile with temperature-dependent sex determination. We compare painted turtle ( Chrysemys picta ) neonates from maternally selected nest sites with those from randomly selected nest sites, observing no substantive difference in hatching success or survival, but finding a profound difference in offspring sex ratio in the direction expected based on historical records. Additionally, we leverage long-term data to reconstruct our sex ratio results had the experiment been repeated in multiple years. As predicted by theory, our results suggest that sex-ratio selection has shaped nesting behaviour in ways likely to enhance maternal fitness.

scholarly journals Drivers of sex ratio bias in the eastern bongo: lower inbreeding increases the probability of being born male

2019 ◽  
Vol 286 (1902) ◽  
pp. 20190345 ◽  
Author(s):  
Aurelio F. Malo ◽  
Tania C. Gilbert ◽  
Philip Riordan
Keyword(s):  
Sex Ratio ◽  
Inbreeding Depression ◽  
Sex Ratios ◽  
Reproductive Traits ◽  
Genetic Effects ◽  
Equal Proportion ◽  
Paternal Effects ◽  
Offspring Sex Ratio ◽  
Genetic Quality ◽  
Offspring Sex

Parent sex ratio allocation has consequences for individual fitness, population dynamics, and conservation. Theory predicts that parents should adjust offspring sex ratio when the fitness returns of producing male or female offspring varies. Previous studies have assumed that only mothers are capable of biasing offspring sex ratios, but have neglected fathers, given the expectation of an equal proportion of X- and Y-chromosome-bearing (CBS) sperm in ejaculates due to sex chromosome segregation at meiosis. This assumption has been recently refuted and both paternal fertility and paternal genetic quality have been shown to bias sex ratios. Here, we simultaneously test the relative contribution of paternal, maternal, and individual genetic quality, as measured by inbreeding, on the probability of being born a son or a daughter, using pedigree and lifelong offspring sex ratio data for the eastern bongo ( Tragelaphus eurycerus isaaci ). Our models showed first, that surprisingly, as individual inbreeding decreases the probability of being born male increases, second, that paternal genetic effects on sex ratio were stronger than maternal genetic effects (which were absent). Furthermore, paternal effects were opposite in sign to those predicted; father inbreeding increases the probability of having sons. Previous paternal effects have been interpreted as adaptive due to sex-specific inbreeding depression for reproductive traits. We argue that in the eastern bongo, the opposite sign of the paternal effect on sex ratios results from a reversed sex-specific inbreeding depression pattern (present for female but not male reproductive traits). We anticipate that this research will help stimulate research on evolutionary constraints to sex ratios. Finally, the results open a new avenue of research to predict sex ratio allocation in an applied conservation context. Future models of sex ratio allocation should also include the predicted inbreeding level of the offspring and paternal inbreeding levels.

scholarly journals Maternal condition and previous reproduction interact to affect offspring sex in a wild mammal

2016 ◽  
Vol 12 (8) ◽  
pp. 20160510 ◽  
Author(s):  
Mathieu Douhard ◽  
Marco Festa-Bianchet ◽  
Fanie Pelletier
Keyword(s):  
Sex Ratio ◽  
Empirical Studies ◽  
Good Condition ◽  
Ovis Canadensis ◽  
Maternal Condition ◽  
Paternal Effects ◽  
Offspring Sex Ratio ◽  
Fitness Consequences ◽  
Offspring Sex ◽  
Dimorphic Species

Trivers and Willard proposed that offspring sex ratio should vary with maternal condition when condition, meant as maternal capacity to care, has different fitness consequences for sons and daughters. In polygynous and dimorphic species, mothers in good condition should preferentially produce sons, whereas mothers in poor condition should produce more daughters. Despite its logical appeal, support for this hypothesis has been inconsistent. Sex-ratio variation may be influenced by additional factors, such as environmental conditions and previous reproduction, which are often ignored in empirical studies. We analysed 39 years of data on bighorn sheep ( Ovis canadensis ) that fit all the assumptions of the Trivers–Willard hypothesis. Production of sons increased with maternal condition only for mothers that weaned a son the previous year. This relationship likely reflects a mother's ability to bear the higher reproductive costs of sons. The interaction between maternal condition and previous weaning success on the probability of producing a son was independent of the positive effect of paternal reproductive success. Maternal and paternal effects accounted for similar proportions of the variance in offspring sex. Maternal reproductive history should be considered in addition to current condition in studies of sex allocation.

Endogenous Corticosterone Elevations Five Hours Prior to Ovulation do not Influence Offspring Sex Ratios in Zebra Finches

2016 ◽  
Vol 9 (3) ◽  
pp. 131-138 ◽  
Author(s):  
A.E. Gam ◽  
K.J. Navara
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Zebra Finches ◽  
Meiotic Segregation ◽  
Offspring Sex Ratio ◽  
Handling Stress ◽  
Offspring Sex ◽  
Baseline Corticosterone ◽  
Underlying Mechanisms ◽  
Heterogametic Sex

Previous research suggests that environmental and social factors can drive female birds to bias offspring sex ratios. The underlying mechanisms controlling these adjustments remain unclear. Results from experimental and correlative research suggest that maternal corticosterone plays an important role in this process. Since females are the heterogametic sex in birds, corticosterone may potentially bias offspring sex ratios during meiotic segregation, through non-random segregation of sex chromosomes. In a previous study, we showed that pharmacological elevations of corticosterone near the time of meiotic segregation exerted an effect on offspring sex ratio, causing female Zebra Finches ( Taeniopygia guttata) to produce significantly more males. Here, we aimed to determine whether endogenous elevations in the physiological range have similar effects on offspring sex. First we examined offspring sex ratio in relation to baseline corticosterone levels to determine if natural variation in circulating corticosterone near the time of meiotic segregation is related to offspring sex ratio. Next, we used a 5-minute bag handling protocol to induce corticosterone elevations 5 hours prior to ovulation. Maternal baseline corticosterone levels did not correlate with average clutch sex ratios. In addition, the sex ratios produced by females exposed to handling stress did not differ from sex ratios produced by unmanipulated females. Together these results suggest that physiological levels of endogenous corticosterone, both baseline and acutely elevated near the time of sex determination may not be involved in the adjustment of primary sex ratios in Zebra Finches.

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