REPRODUCTION IN THE FEMALE SUBANTARCTIC FUR SEAL, ARCTOCEPHALUS TROPICALIS

The reproductive tracts of 89 female subantarctic fur seals, taken at Gough Island between November 1977 and October 1978, were examined. Females started ovulating at age 4 yr and all 6-yr-old females were sexually mature. They are mono-ovulatory, alternating between ovaries, and only single embryos were found. Females older than 13 yr ( n = 11) showed poor follicular development and some failed to ovulate. The gestation period (first recorded ovulation to first recorded birth) was 360 d, while delayed implantation (first recorded ovulation to first recorded implantation) lasted for 139 days. Follicle numbers in the functional ovary declined sharply after ovulation while the corpus luteum increased in size until at least 1 mo prior to parturition. The number of follicles in the contralateral ovary increased after midwinter (June/July), and the mean size of the largest follicles peaked prior to ovulation in December. The mean size of the largest follicles increased in both ovaries near implantation time, after reaching a low subsequent to, ovulation. The regressing corpus albicans, conspicuous for approximately 3 mo after parturition, could not be detected macroscopically within one year postpartum. Subantarctic fur seals at Gough Island have a distinct postreproductive class of older females. The pregnancy rate for all females ≥4 yr of age was 79%, and it was 84.5% for the sexually mature group of ≥6 yr of age, while the mean age at puberty was 4.80 yr.     

Male and female contributions to heterosis in lifetime performance of mice

Summary Six straightbred lines of mice, some of their F₁ crosses and a synthetic line were used to evaluate male and female contributions to heterosis in lifetime performance measured on females. Females from each straightbred line or F₁ crosses were pair-mated randomly at day 42 with either a male of the corresponding genetic group or from a synthetic line, and pairs were maintained for 155 days (lifetime). Each mother was allowed to rear all young born alive until day 18 when the young were discarded. Data were analyzed using a model in which the group mean of lifetime performance was expressed as the sum of (additive direct) genetic and environmental effects for each of the male and female genetic groups used for mating. Comparison of group means for lifetime performance revealed that estimates of F₁ heterosis due to male and female averaged 10 and 9% for number of parturitions during lifetime, 7 and 28% for total number of young born alive, 6 and 31% for total body weight of young born alive, 8 and 33% for total number of young raised to day 18, 9 and 43% for total body weight of young raised to weaning, and 8 and 8% for days from first mating to last parturition. The male's contribution to heterosis in lifetime performance was smaller than female's contribution for productive traits (total number of young born alive and at day 18, and total body weight of young born alive and at day 18), and was nearly equal in reproductive traits (number of parturitions during lifetime and days from first mating to last parturition).Animal Research Centre Contribution No. 1098     

The influence of female age and host size on the sex ratio of the parasitoid Opius concolor

The sex ratio of the progeny of single females parasitizing large hosts favoured the females (sex ratio=0.26); but on small hosts favoured the males (0.73). No differences in mortality of the sexes were detected. The sex ratio was independent of female age when large hosts were used. The percentage of males observed in the progeny of the first day of female oviposition was significantly greater than the mean, irrespective of the age at which female oviposition began. When females were exposed to small hosts, a greater percentage of females was observed in the progeny from the last days of oviposition.

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Résumé L'influence de la taille de l'hôteret de l'âge de la femelle sur le taux sexuel de la descendance a été étudiée sur le parasitoïde Opius concolor Szépl.Le taux sexuel de la descendance des femelles isolées est favorable aux femelles (t.s.=0,26) quand elles ont à leur disposition des hôtes de grande taille, tandis qu'avec des hôtes petits le taux sexuel est favorable aux mâles (t.s.=0.73). On n'a pas détecté de mortalité différentielle des sexes.Les pourcentage de mâles obtenu le premier jour de ponte des femelles sur les hôtes de grande taille est significativement différent de la moyenne, indépendamment de l'âge de la femelle à ce moment. Cependant, sur des hôtes petits, bien que restant favorable aux mâles dans l'ensemble, une plus grande proportion de femelles à partir des premiers jours de ponte a pu être observée.

     

Estrogen-dependent changes in the functional interrelationships among neurons,ependymal cells and glial cells of the arcuate nucleus

Summary The synchronizing effect of ethinylestradiol (4 g/g b.w.) on neurons of the arcuate nucleus 700–950 m caudal to the posterior edge of the optic chiasma was studied by karyometry in 6-week-old albino mice during proestrus.The caudal portion of the arcuate nucleus was identified as the most estrogen-sensitive subdivision; all neurons showed an increase in their nuclear area (mean transect, profile area of the nucleus) 1 h following administration of ethinylestradiol. This hypothalamic region was selected for the subsequent electron-microscopic cytometric study to analyze functional interrelationships among neurons, ependymal cells and glial cells. Six and 12 days after ovariectomy no significant change in the nuclear area of neurons and ependymal cells was found 850–950 m behind the posterior slope of the optic chiasma, but the neurons exhibited a decrease in the number of polyribosomes, the volume fraction (V_Vmi) and the surface density of the inner membrane of mitochondria (S_Vmi). A similar decrease in V_Vmi and S_Vmi was measured in the apical part of ependymal cells and in the pericapillary profiles of ependymal and glial cells, which was accompanied by a reduction in the surface density of ependymal processes extending into the ventricular lumen. In addition, no change of V_Vmi and S_Vmi was seen in the basal subnuclear part of ependymal cells.This bipolar functional reaction of ependymal cells after ovariectomy is discussed as an indicator of ependymal control of neuronal activity by sequestering biologically active agents, e.g., transmitters of neurohormones, in their apical and basal extensions facing the ventricular surface or the pericapillary space.     

Ecdysterone antagonism,mimicry, and synergism of juvenile hormone action on the Monarch butterfly reproductive tract

Previous research on Monarch butterflies has shown that juvenile hormone (JH) stimulates the development of the ovary and certain reproductive glands of both sexes. Ecdysterone injections into intact Monarchs demonstrate that low doses of this hormone inhibit ovarian development, and higher doses stimulate the male and female reproductive glands. In addition, experiments using neckligatured adults show that ecdysterone stimulates the reproductive glands of both sexes, in the apparent absence of JH, with the most pronounced effect being observed on the female colleterial gland. Other studies with neck-ligatured animals demonstrate that ecdysterone also synergizes with JH on the female gland and all three male glands. The feasibility of using Monarch reproductive glands for studies on the mode of action and interaction of JH and ecdysterone, and the possibility of a rôle of ecdysterone in the normal regulation of Monarch oögenesis, are discussed.     

Female resistance behaviour and progeny sex ratio in two Bradysia species (Diptera: Sciaridae) with paternal genome elimination

The relationship between female mating preferences and sex allocation has received considerable theoretical and empirical support. Typically, choosier females adjust their progeny sex ratio towards sons, who inherit the attractive traits of their father. However, in species with paternal genome elimination, where male sperm do not contain the paternal genome, predictions for the direction of progeny sex ratio biases and their relationship with female choosiness are atypical. Paternal genome elimination also creates a potential for male–female conflict over sex allocation, and any influence of female mate choice on sex ratio outcomes have interesting implications for sexually antagonistic coevolution. Within the Sciaridae (Diptera) are species that produce single‐sex progeny (monogenic species) and others in which progeny comprise both sexes (digenic species). Paternal genome elimination occurs in both species. We explore female mate resistance behaviour in a monogenic and digenic species of mushroom gnat from the genus Bradysia. Our experiments confirmed our theoretical predictions, revealing that in the monogenic and digenic species, females producing female‐biased progeny were more likely to have resisted at least one mating attempt.     

Effect of early shearing during gestation on the productive and reproductive behavior of female sheep offspring in their first 18 months of age

The research has shown the interesting contributions of shearing in mid-gestation on the performance of lambs from birth to weaning. Other studies have reported that shearing at early pregnancy influences the development of the placenta and lamb live weight at birth. However, there was a lack of information on the effect of early-prepartum shearing on the behavior of the offspring from weaning onward. This study evaluated the effect of shearing ewes at 50 days of gestation on the growth, reproductive behavior and response to a gastrointestinal parasite challenge in the female offspring from weaning to 18 months old. Fifty-seven Polwarth female lambs were used, 22 being singles and 35 twins born to ewes either shorn at 50 days of pregnancy (PS, n = 23) or shorn at 62 days postpartum (U, control, n = 34) resulting in four subgroups: single lambs born to PS ewes (n = 8), born to U ewes (n = 14), twin lambs born to PS ewes (n = 15) or born to U ewes (n = 20). All progeny were managed together under improved pasture with a minimum forage allowance of 6% live weight on dry basis. Body weight, body condition score and fecal eggs count were recorded every 14 days from weaning to 18 months of age. Concentrations of progesterone were measured weekly (from 4 to 10 months of age and from 14 to 18 months of age) to establish the onset of puberty. Ovulation rate at an induced and a natural heat (545 ± 1.0 and 562 ± 1.0 day old) was recorded. Prepartum shearing did not affect the age at puberty or the ovulation rate of female offspring, but those born as singles were more precocious ( P = 0.03) and heavier ( P = 0.02) at puberty than twin born lambs. Both the average value of parasite egg count ( P = 0.0 7) and the Famacha index ( P = 0.02) for the entire study period were lower in lambs born to prepartum shorn ewes than those born to postpartum shorn ewes. In conclusion, shearing at 50 days of gestation did not affect the growth or the reproductive behavior of female offspring. However, female lambs born from ewe shorn during gestation showed a better response to the parasitic challenge, and further research is required to confirm this.     

Genotypes and their interaction effects on reproduction and mating‐induced immune activation in Drosophila melanogaster

Mating causes considerable alterations in female physiology and behaviour, and immune gene expression, partly due to proteins transferred from males to females during copulation. The magnitude of these phenotypic changes could be driven by the genotypes of males and females, as well as their interaction. To test this, we carried out a series of genotype‐by‐genotype (G × G) experiments using Drosophila melanogaster populations from two distant geographical locations. We expected lines to have diverged in male reproductive traits and females to differ in their responses to these traits. We examined female physiological and behavioural post‐mating responses to male mating traits, that is behaviour and ejaculate composition, in the short to mid‐term (48 hr) following mating. We then explored whether a sexually transferred molecule, sex peptide (SP), is the mechanism behind our observed female post‐mating responses. Our results show that the genotypes of both sexes as well as the interaction between male and female genotypes affect mating and post‐mating reproductive traits. Immune gene expression of three candidate genes increased in response to mating and was genotype‐dependent but did not show a G × G signature. Males showed genotype‐dependent SP expression in the 7 days following eclosion, but female genotypes showed no differential sensitivity to the receipt of SP. The two genotypes demonstrated clear divergence in physiological traits in short‐ to mid‐term responses to mating, but the longer‐term consequences of these initial dynamics remain to be uncovered.     

Egg‐induced changes to sperm phenotypes shape patterns of multivariate selection on ejaculates

Sperm cells exhibit extraordinary phenotypic diversity and rapid rates of evolution, yet the adaptive value of most sperm traits remains equivocal. Recent findings suggest that to understand how selection targets ejaculates, we must recognize that female‐imposed physiological conditions often alter sperm phenotypes. These phenotypic changes may influence the relationships among sperm traits and their association with fitness. Here, we show that chemical substances released by eggs (known to modify sperm physiology and behaviour) alter patterns of selection on a suite of sperm traits in the mussel Mytilus galloprovincialis. We use multivariate selection analyses to characterize linear and nonlinear selection acting on sperm traits in (a) seawater alone and (b) seawater containing egg‐derived chemicals (egg water). Our analyses revealed that nonlinear selection on canonical axes of multiple traits (notably sperm velocity, sperm linearity and percentage of motile sperm) was the most important form of selection overall, but importantly these patterns were only evident when sperm phenotypes were measured in egg water. These findings reveal the subtle way that females can alter patterns of selection, with the implication that overlooking environmentally moderated changes to sperm, may result in erroneous interpretations of how selection targets phenotypic (co)variation in sperm traits.