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Offspring Sex (offspring + sex)

Distribution by Scientific Domains
Life Sciences100%

Terms modified by Offspring Sex

  • offspring sex ratio
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    Selected Abstracts

    Seasonal change in offspring sex and size in Dawson's burrowing bees (Amegilla dawsoni) (Hymenoptera: Anthophorini)

    ECOLOGICAL ENTOMOLOGY, Issue 3 2005
    John Alcock
    Abstract., 1.,Nesting females of Dawson's burrowing bees, Amegilla dawsoni, produce a large size class of offspring, which includes daughters and major sons, and a small size class, which consists entirely of minor sons averaging half the weight of their larger siblings. Female allocation patterns change over the flight season such that the initial pattern of producing daughters shifts toward the production of both daughters and major sons in the middle of the season, and then the production of primarily minor sons in the latter part of the nesting season. 2.,In Dawson's burrowing bees, this pattern is correlated with declines in pollen and nectar availability as the nesting season progresses as well as a heightened risk of dying before the final brood cell is completed. Here, the relation between these factors and the provisioning tactics of nesting Dawson's burrowing bees is discussed. [source]

    THE ADAPTIVE SIGNIFICANCE OF TEMPERATURE-DEPENDENT SEX DETERMINATION: EXPERIMENTAL TESTS WITH A SHORT-LIVED LIZARD

    EVOLUTION, Issue 10 2005
    Daniel A. Warner
    Abstract Why is the sex of many reptiles determined by the temperatures that these animals experience during embryogenesis, rather than by their genes? The Charnov-Bull model suggests that temperature-dependent sex determination (TSD) can enhance maternal fitness relative to genotypic sex determination (GSD) if offspring traits affect fitness differently for sons versus daughters and nest temperatures either determine or predict those offspring traits. Although potential pathways for such effects have attracted much speculation, empirical tests largely have been precluded by logistical constraints (i.e., long life spans and late maturation of most TSD reptiles). We experimentally tested four differential fitness models within the Charnov-Bull framework, using a short-lived, early-maturing Australian lizard (Amphibolurus muricatus) with TSD. Eggs from wild-caught females were incubated at a range of thermal regimes, and the resultant hatchlings raised in large outdoor enclosures. We applied an aromatase inhibitor to half the eggs to override thermal effects on sex determination, thus decoupling sex and incubation temperature. Based on relationships between incubation temperatures, hatching dates, morphology, growth, and survival of hatchlings in their first season, we were able to reject three of the four differential fitness models. First, matching offspring sex to egg size was not plausible because the relationship between egg (offspring) size and fitness was similar in the two sexes. Second, sex differences in optimal incubation temperatures were not evident, because (1) although incubation temperature influenced offspring phenotypes and growth, it did so in similar ways in sons versus daughters, and (2) the relationship between phenotypic traits and fitness was similar in the two sexes, at least during preadult life. We were unable to reject a fourth model, in which TSD enhances offspring fitness by generating seasonal shifts in offspring sex ratio: that is, TSD allows overproduction of daughters (the sex likely to benefit most from early hatching) early in the nesting season. In keeping with this model, hatching early in the season massively enhanced body size at the beginning of the first winter, albeit with a significant decline in probability of survival. Thus, the timing of hatching is likely to influence reproductive success in this short-lived, early maturing species; and this effect may well differ between the sexes. [source]

    Body size, locomotor speed and antipredator behaviour in a tropical snake (Tropidonophis mairii, Colubridae): the influence of incubation environments and genetic factors

    FUNCTIONAL ECOLOGY, Issue 5 2001
    J. K. Webb
    Summary 1,The physical conditions experienced by reptile embryos inside natural nests can influence the size, shape and behaviour of the resultant hatchlings. Although most reptiles are tropical, the effects of incubation temperatures on offspring phenotypes have received little attention in tropical species. 2,The consequences of differences in thermal variance during incubation on offspring were studied in a tropical natricine snake (the Keelback Tropidonophismairii), which lays eggs in soil cracks of varying depths. Some 253 eggs from 19 clutches were incubated under two thermal regimes with identical mean temperatures (25·6 °C), but temperatures in the ,variable' treatment fluctuated more (21·8,29·6 °C) than those in the ,constant' temperature treatment (25·2,26·5 °C). These thermal regimes were similar to those of shallow (20 cm deep) and deep (40 cm deep) soil cracks, respectively, and represent thermal conditions inside natural nests and potential nest sites. 3,Incubation temperatures affected body size, shape and antipredator behaviour of hatchling snakes. Snakes from constant temperature incubation were longer and thinner than snakes from high variance incubation. Clutch effects influenced all offspring traits, with significant interactions between clutch of origin and incubation treatment for body size, but not swimming speed or behaviour. 4,There was a significant interaction between incubation treatment and offspring sex on neonate swimming speed. Incubation under cycling thermal regimes significantly increased swimming speeds of females, but had little effect on males. Such sex differences in phenotypic responses of hatchling snakes support a major assumption of the Charnov,Bull hypothesis for the evolution of temperature-dependent sex determination. [source]

    Should males come first?

    JOURNAL OF AVIAN BIOLOGY, Issue 6 2005
    The relationship between offspring hatching order, sex in the black-headed gull Larus ridibundus
    In birds with hatching asynchrony and sexual size dimorphism, chicks hatched earlier and later in the laying sequence usually suffer different mortalities due to uneven abilities to compete for food, especially in poor years. If sexes differ in vulnerability to environmental conditions, e.g., by having different food requirements due to differential growth rates, mothers can increase fitness by allocating sex according to the laying order, producing less vulnerable sex later rather than early in the clutch. By analysing variation in primary sex ratio using a PCR-based DNA technique, we tested this prediction in black-headed gull Larus ridibundus chicks where males may be the less viable sex under adverse conditions. The overall primary sex ratio of the population did not depart from parity. However, first hatched chicks were more likely to be males whereas last hatched chicks were more likely to be females. Both egg volume and hatchling body mass decreased with laying order irrespective of sex. Time of breeding had no effect on offspring sex or hatchling sex ratios. [source]

    Multiple pathways of maternal effects in black-headed gull eggs: constraint and adaptive compensatory adjustment

    JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2006
    T. G. G. GROOTHUIS
    Abstract We investigated in the black-headed gull whether female deposition of antioxidants and immunoglobulins (enhancing early immune function), and testosterone (suppressing immune function and increasing early competitive skills) correlate suggesting that evolution has favoured the mutual adjustment of different pathways for maternal effects. We also took egg mass, the position of the egg in the laying sequence and offspring sex into account, as these affect offspring survival. Yolk antioxidant and immunoglobulin concentrations decreased across the laying order, while yolk testosterone concentrations increased. This may substantially handicap the immune defence of last-hatched chicks. The decrease in antioxidant levels was greater when mothers had a low body mass and when the increase in testosterone concentrations was relatively large. This suggests that female black-headed gulls are constrained in the deposition of antioxidants in last-laid eggs and compensate for this by enhanced testosterone deposition. The latter may be adaptive since it re-allocates the chick's investment from costly immune function to growth and competitive skills, necessary to overcome the consequences of hatching late from an egg of reduced quality. [source]