Post-reproductive Females Research Articles

Menopause: An evolutionary perspective

Evolutionary biologists classify theories of menopause as either: 1) adaptive, suggesting that female reproductive cessation results from its selective advantage, in that the increased risk of personal reproduction late in life makes it biologically more advantageous to rechannel reproductive energy into helping existing descendents, or 2) nonadaptive, indicating menopause is an artifact of the relatively recent dramatic increase in human longevity. With the possible exception of pilot whales, no mammals studied to date are known to commonly exhibit reproductive cessation in nature. To demonstrate adaptive menopause, one would need to establish both that the longevity of preagricultural humans commonly allowed them to exhibit menopause, and that postreproductive females could assist their descendents sufficiently to compensate for the loss of personal reproduction. The data on longevity of preagricultural humans with respect to the adaptive menopause hypothesis are mixed. Evolutionary models evaluated with data from modern hunting-gathering or agricultural humans fail to find that humans can assist their descendents sufficiently to offset the evolutionary cost of ceasing reproduction. However, assuming the human body has been physiologically adapted to the conditions extant during the vast majority of human history, it may be well worth pursuing how the signs and symptoms of menopause are affected by dietary, exercise, and reproductive hormone regimes mimicking those of the late Paleolithic era.

Biology ofAnastatus biproruli (Hym.: Eupelmidae) a parasitoid ofBiprorulus bibax (Hem.: Pentatomidae)

The effect of temperature on the rate of development ofAnastatus biproruli (Girault) was determined by rearing individuals on eggs ofBiprorulus bibax Breddin under a range of constant temperatures (17.5–40.0°C). Rate of development changed in a linear fashion from 17.5–35.0°C and the lower developmental threshold was estimated to be 12.8°C. An estimated 331.8 degree days were required for development. Survival of developing parasitoids was optimal (72–90%) between 25–35°C. Longevity of virgin adults ranged from 12–26 days at 22.5–35°C but was only 3.6 days at 37.5°C. Mated females produced a mean of 54.6 progeny during an average lifespan of 36.4 days at 30°C. Progeny were produced only during the first 21 days of adulthood but post-reproductive females still attacked and killed hosts. FemaleA. biproruli overwintered successfully, and were able to parasitise host eggs if direct sunlight was available.A. biproruli also overwintered as immature stages in host eggs. The biology ofA. biproruli is discussed with regard to its importance as a natural enemy ofB. bibax.

Gonadotropin-releasing hormone-containing neurons change size with reproductive state in female Haplochromis burtoni

In the preoptico-hypothalamic area (POA) of teleost fish, neurons containing gonadotropin-releasing hormone (GnRH) regulate reproduction through direct projections to pituitary gonadotropes. Here we show that these GnRH-containing cells change size depending on the reproductive and maturational state in female Haplochromis burtoni. We selected animals prior to, during, and after the reproductive portion of their life history, in both brooding and spawning states. Immunocytochemical staining of GnRH-containing neurons in the POA revealed that these cells are up to twice as large in females that have never spawned or are in the act of spawning than they are in females that are carrying broods. Older, postreproductive females have the largest cell sizes. Previous work on male H. burtoni has shown that soma sizes of the homologous neurons change according to social status, with dominant fish having larger cells than subordinates. Since reproductively active females have no apparent social hierarchy and are all exposed to approximately the same external stimuli, the primary factor(s) controlling GnRH-immunoreactive (irGnRH) neuron size appears to be internal reproductive state. Thus, while irGnRH neurons are pleiomorphic in both males and females, cell size change is differently regulated in each.

Seasonal changes in plasma prostaglandin F 2α and sex hormones in the male water frog, Rana esculenta

Prostaglandin F 2α (PGF 2α), progesterone, androgens (testosterone + dihydrotestosterone), and 17β-estradiol were measured in the plasma of male frogs, Rana esculenta, by radioimmunoassays. Plasma concentrations of PGF 2α. were higher from October to December and peaked in March (prereproduction) and in June (postreproduction). Plasma progesterone levels were relatively low but showed an increase from October to December and in June. Plasma androgen titres rapidly increased in early spring, started to fall during the reproductive period (May), and were lowest in July. 17β-Estradiol levels peaked in March and in June. The annual profile of the plasma PGF α levels was positively correlated with those of progesterone and androgens, while it was not correlated to the estradiol plasma pattern, except in March and June. The increase in plasma PGF 2α in the autumn may be related to gonadal recovery. The simultaneous increases in PGF 2α and 17β-estradiol, both in March and June, suggest a PGF 2α dependent estradiol synthesis, a possibility also supported by the increased plasma 17β-estradiol previously observed in PGF 2α treated postreproductive females. The effects of captivity and castration on plasma PGF 2α concentrations were also studied during the annual cycle. Captivity was associated with a reduced PGF 2α titre, while castration did not modify prostaglandin synthesis, which may point to an extragonadal source of plasma PGF 2α.

A TEMPERATURE- AND AGE-DEPENDENT SIMULATION MODEL OF REPRODUCTION FOR THE NORTHERN CORN ROOTWORM, DIABROTICA BARBERI SMITH AND LAWRENCE (COLEOPTERA: CHRYSOMELIDAE)

AbstractBased on data collected at seven constant temperatures, a temperature- and age-dependent model for reproductive development and oviposition by Diabrotica barberi Smith and Lawrence was developed. The model couples temperature-dependent rate and temperature-independent distribution models to represent the observed variability in developmental times for pre-reproductive, reproductive, and post-reproductive females. Using a cohort approach to maintain a physiological age structure, development was coupled with a temperature- and age-dependent model of oviposition. The model was validated at one constant-temperature and three variable-temperature regimes in the laboratory. The time spent in the pre-reproductive stage was slightly underestimated by the model, but the development of mature females and both the timing and magnitude of oviposition under fluctuating-temperature regimes were accurately predicted. The model was relatively insensitive to errors in estimation of the rate of development in the pre-reproductive stage but sensitive to errors in estimation of developmental rate of the reproductive stage and fecundity. Errors in input temperatures were found to be very important, stressing the need for accurately measuring temperature, The major driving variable. The model should be a valuable aid toward understanding oviposition by D. barberi in the field.

Responses of the Skinks, Eumeces fasciatus and E. laticeps, to Airborne Conspecific Odors: Further Appraisal

Approach responses of the skinks E. fasciatus and E. laticeps to sources of airborne conspecific chemical cues were studied in a y-maze olfactometer. At an air speed of 10 km/h, neither postreproductive males, postreproductive females, nor testosterone-treated males approached or avoided conspecific odors significantly more often than a control odor (air). These results differ radically from those obtained in an earlier study at much higher air speed (180 km/h). The appar- ently contradictory results may reflect the induction of alternative motivational states by differ- ences in experimental conditions. At the combination of low temperature and high wind speed in the earlier study, skinks may have responded to an aggregation pheromone. Aggressively or sex- ually motivated skinks may respond primarily to contact pheromones rather than airborne con- specific chemical cues. This hypothesis is suggested by the failure of reproductively active skinks either to approach or avoid airstreams bearing conspecific odors and by direct touching of the bodies and odor trails of conspecifics by the tongue.

The Timing of Reproduction in the Lizard Lacerata vivipara: Differences between Individual Females

During a field study examining the live-bearing lizard Lacerta vivipara, we estimated the timing of mating, ovulation and parturition in individual females. Reproduction was synchro- nized, especially among the larger (older) females. The timing of all reproductive acts was inversely correlated with female size: smaller females have delayed reproductive activities relative to the larger lizards. The timing of copulation and parturition were related to the timing of ovulation in individual females. Thus, females which finished vitellogenesis early tended to mate early and gave birth to their young on an early date. Benefits of early reproduction include: attainment of the highest size-adjusted body weight by the post-reproductive females at the onset of hibernation; early born juveniles reach the largest size at the end of the activity season. The delay of reproduction in the smaller females is coincident with their relatively high growth rates and reduced lipid stores. Allocation of energy to reproduction appears to occur at a slow rate in the smaller adults and probably accounts for the delay in reproductive activities. We therefore consider the postponement of reproduction as a cost of rapid growth. The timing of reproduction in an individual female seems to be the result of an interaction between the benefits of early breeding and the pay-offs of rapid growth.

Detection of conspecific odors by the female broad‐headed skink, Eumeces laticeps

AbstractThe potential abilities of adult female E. laticeps to detect conspecific odors and to discriminate between male and female conspecific odors were investigated by comparisons of tongue extrusion rates emitted in response to chemical stimuli presented on moist cotton applicators. Postreproductive females treated with estradiol‐17β to stimulate possible increases in sensitivity to odors associated with the breeding season showed significantly higher tongue‐flick rates to the cloacal odors of both sexes than to distilled water. There was no evidence that the females discerned any difference between male and female odors. Estrogen‐injected females had somewhat higher tongue‐flick rates than did untreated postreproductive females, but the differences were not significant. Tongue extrusion rates of estrogen‐injected females were substantially lower than those of testosterone‐implanted males for all odor stimuli. It is argued, but not demonstrated, that female E. laticeps respond to the cloacal odors as stimuli arising from conspecific or at least closely related skinks.

Fear of Death and Fertility Reconsidered

Kastenbaum raised and examined the hypothesis that fear of death and fertility are directly related phenomena, concluding that procreation was one among several desirable forms of self-continuation. Re-examination of this hypothesis, using Templer's Manifest Death Anxiety Scale and a community sample (N=234) of reproductive and post-reproductive aged males and females, revealed that the hypothesis was confirmed among high school or less educated respondents. Within this subsample, confirmation was found among all females concerning their experienced, desired, and expected fertility. However, their male counterparts exhibited confirmation only with respect to desired and expected fertility, and only if they were within the reproductive age range.

Biology and population dynamics of the intertidal isopod Cirolana harfordi

The distribution of Cirolana harfordi (Lockington) populations is determined largely by the availability of loose boulders on sandy beaches. The isopods swim out from under the rocks at high tide to feed. Their diet consists primarily of minute polychaetes and crustaceans. In addition, the isopods locate and utilize any available dead animal matter in the surf zone. Breeding occurs throughout most of the year, except for a brief lull in the fall. Females produce 1 or 2 broods of 18 to 68 young during their 2-year life-span. Marsupial incubation lasts 3 to 4 months. The population size and structure remained relatively constant from one year to the next. Mortality rates estimated for juveniles, males and females showed that newly emergent young and post-reproductive females suffer the greatest losses (up to 75% mortality per month).

Survival of Spermatozoa in Female Chrysopa carnea During Diapause

Diapause was induced in reproductively active female Chrysopa carnea to determine its effect on sperm stored in the spermatheca. No sperm resorption was found to occur during 3 months of simulated winter conditions. Following diapause termination, oviposition of viable eggs commenced demonstrating that post-diapause mating is not a prerequisite for oviposition in post-reproductive diapausing females. The ecological significance of this reproductive strategy is discussed.

Reproduction and estrogen-induced vitellogenesis in Dipsosaurus dorsalis

1. 1. The ovarian cycle of female Dipsosaurus dorsalis was studied during June through October. A peak of vitellogenesis occurred in late June. 2. 2. Ovarian maturation was accompanied by significant increases in oviduct weight, plasma protein fraction 4 (the “beta-globulin”) and total plasma calcium. 3. 3. Ovulation was followed first by a decrease in calcium and later by a decrease in plasma fraction 4. 4. 4. Oviduct and adrenal weight decreased from peak summer levels by October. 5. 5. A single injection of estradiol 17β in post-reproductive females was followed by significant increases in plasma protein fraction 4 and calcium. 6. 6. This response did not occur in the absence of the pituitary gland.