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PubMed2005

Effects of range position, inter-annual variation and density on demographic transition rates of Hornungia petraea populations.

The central-marginal model assumes unfavourable and more variable environmental conditions at the periphery of a species' distribution range to negatively affect demographic transition rates, finally resulting in reduced population sizes and densities. Previous studies on density-dependence as a crucial factor regulating plant population growth have mainly focussed on fecundity and survival. Our objective is to analyse density-dependence in combination with the effect of inter-annual variation and range position on all life stages of an annual plant species, Hornungia petraea, including germination and seed incorporation into the seed bank. As previous studies on H. petraea had revealed a pattern opposite to existing theory with lower population densities at the distribution centre in Italy than at the periphery in Germany, we hypothesised that (1) demographic transition rates are lower, (2) the inter-annual variation in demographic transition rates is higher and (3) the intensity of density-dependence is weaker in Italy than in Germany. To analyse demographic transition rates, we used an autoregressive covariance strategy for repeated measures including density and inter-annual variation. All the three hypotheses were confirmed, but the impact of range position, density-dependence and inter-annual variation differed among the transition steps. All transition rates except fecundity were higher in the German populations than in the Italian populations. Germination rate and incorporation rate into the seed bank were strongly density-dependent. Central populations showed a larger inter-annual variation in fecundity and winter survival rate. Winter survival rate was the only transition step with a stronger density-dependence in peripheral populations. In most cases, these differences between distribution centre and periphery would not have emerged without taking density-dependence and inter-annual variation into account. We conclude that including range position, inter-annual variation and density-dependence in one single statistical model is an important tool for the interpretation of demographic patterns regarding the central-marginal model.

Analysis of Variance↗

PubMed2005

Demographic consequences of age-structure in extreme environments: population models for arctic and alpine ptarmigan.

Organisms living in arctic and alpine environments are increasingly impacted by human activities. To evaluate the potential impacts of global change, a better understanding of the demography of organisms in extreme environments is needed. In this study, we compare the age-specific demography of willow ptarmigan (Lagopus lagopus) breeding at arctic and subalpine sites, and white-tailed ptarmigan (L. leucurus) breeding at an alpine site. Rates of egg production improved with age at the alpine and subalpine sites, but the stochastic effects of nest and brood predation led to similar rates of annual fecundity among 1-, 2-, and 3+-year-old females. All populations had short generation times (T<2.7 years) and low net reproductive rates (R0<1.2). Stable age distributions were weighted towards 1-year-old females in willow ptarmigan (>59%), and to 3+-year-old females in white-tailed ptarmigan (>47%). High damping ratios (rho>3.2) indicated that asymptotic estimates were likely to match natural age distributions. Sensitivity and elasticity values indicated that changes in juvenile survival would have the greatest impact on the finite rate of population change (lambda) in willow ptarmigan, whereas changes to the survival of 3+-year-old females would have a greater effect in white-tailed ptarmigan. High survivorship buffers white-tailed ptarmigan in alpine environments against the potential effects of climate change on annual fecundity, but may make the species more sensitive to the effects of pollutants or harvesting on adult survival. Conversely, processes that reduce annual fecundity would have a greater impact on the population viability of willow ptarmigan in arctic and subalpine environments. If these same demographic patterns prove to be widespread among organisms in extreme environments, it may be possible to develop general recommendations for conservation of the biological resources of arctic and alpine ecosystems.

Age Distribution↗

PubMed2005

Effects of azadirachtin on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae).

Effects of sublethal azadirachtin exposure to the biological performance of Tetranychius urticae Koch was studied under laboratory conditions. Bioassay was used to asses the effect of different concentrations of azadirachtin on longevity, fecundity, fertility, and offspring development. Azadirachtin (64 and 128 ppm) affected fecundity and mortality but had no effect on fertility and offspring development. A subsequent life-table study with 80 ppm of azadirachtin found that the compound caused a reduction of 50% in survival to adult stage. The peak of reproduction was reached at 5 days causing a decrease in the mean fecundity to almost eight times than of untreated females. The net reproductive rate (R0), the intrinsic rate of increase (r(m)), and the finite rate of increase (lambda) of treated females were lower. Treatment showed a negative value of r(m), resulting in a declining population. These results suggest that azadirachtin could be incorporated in Integrated Pest Management (IPM) programmes of T. urticae.

Animals↗

PubMed1983

Chronic intoxication by an herbicide, 2,4,5-trichlorophenoxyacetic acid, in the pond snail, Lymnaea stagnalis L.

Experiments of chronic intoxication with three concentrations (10, 20, and 40 ppm) of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were conducted in the freshwater mollusc Lymnaea stagnalis. Snail survival was concentration dependent. In all cases the growth can be described by the von Bertalanffy pattern (ht = h (1 - e-k(t-to)) and the variations of the k values showed that growth was significantly altered in all the groups treated. The overall fecundity (F) was always reduced; the decrease was due both to a lower number of eggs per egg mass (-7.8 to -12%) and to an earlier death of the intoxicated snails. Fecundity studied in terms of size, according to the law F = ahz, points out the loss of equilibrium between growth and fecundity: in all groups treated the values of the exponent z were increased. The importance of these perturbations can be quantified by the calculation of a "Snail Yield" which is reduced by 72.6% in the 40 ppm group. Egg fertility was also reduced. It can be concluded that 2,4,5-T disturbs the physiological equilibrium of Lymnaea stagnalis leading even to earlier death of the snails.

2,4,5-Trichlorophenoxyacetic Acid↗

PubMed1986

Trichinella spiralis: antifecundity and antinewborn larvae immunity in swine.

The development of antifecundity and antinewborn larvae immunity in swine infected with Trichinella spiralis was investigated. In primary infections, adult female worm fecundity dropped sharply after 3 weeks, although adults could be recovered from the small intestine for at least 7 weeks after infection. In challenge infections of pigs infected previously, adult female worm fecundity was depressed up to 51% and the adults were expelled within 3 weeks. Since immune pigs are almost completely resistant to the secondary establishment of muscle larvae, this suggested the existence of immune effector mechanisms also acting on the newborn larvae. This was supported by observations, using an indirect fluorescent antibody assay, that pig antibody bound to the surface of the newborn larvae. Passive transfer of immune pig serum resulted in a large reduction in muscle larvae burden in both infected pig and rat recipients. Adult female worm fecundity in such immune serum recipients was reduced only by 20% and worm survival in the intestine was unaffected. These results indicate that immunity to the newborn larvae, in addition to antifecundity effects, are responsible for the high levels of acquired resistance to T. spiralis in swine.

Age Factors↗

PubMed1991

Heligmosomoides polygyrus: CD4+ but not CD8+ T cells regulate the IgE response and protective immunity in mice.

Oral inoculation of BALB/c mice with infective larvae of Heligmosomoides polygyrus resulted in chronic infection characterized by the release of parasite eggs in the feces for several months. The actual number of eggs per gram of feces was dependent on the dose of the inoculum. Serum IgE in infected mice peaked at a level of greater than 70 micrograms/ml during Weeks 3 through 6 following inoculation, and high levels of IgE (greater than 40 micrograms/ml) persisted for over 14 weeks. Protective immune responses resulted in reduced egg production and the development of markedly fewer adult worms in the small intestines following a challenge inoculation. The role of CD4+ and CD8+ T cells in these responses was examined by depletion in vivo of either T cell subpopulation with rat mAb specific for the appropriate determinants. Mice treated with anti-CD4 during a primary infection had increased EPG which was due primarily to an increase in worm fecundity (eggs produced per adult female). A challenge inoculation of mice that had been cleared of the primary infection with an anthelmintic drug induced a protective response that reduced development of new adult worms by 70-80% and their fecundity by greater than 90%. This protective response was abrogated by injection of mice with anti-CD4. Serum IgE diminished when adult worms were removed after anthelmintic treatment. A more precipitous drop in serum IgE followed successive treatments of mice with an anthelmintic and anti-CD4. In addition, the anamnestic serum IgE response to a challenge inoculation was reduced by over 80% in anti-CD4-treated mice. Anti-CD8 treatment had no appreciable effect on the immunological or parasitological parameters measured following a challenge inoculation with H. polygyrus. Thus, CD4+ T cells regulate host protective immunity, worm fecundity, and IgE levels in an H. polygyrus infection. This experimental system may be particularly suitable for analysis of chronic nematode infections of humans and livestock because of the responsiveness of the parasite in vivo to changes in host immune function.

Animals↗

PubMed1996

A counterintuitive result in Bell's model of delayed maturity.

Bell formulated a model with constant parameters in which he applied the commonsense argument that delayed maturity would be favored in iteroparous species if fecundity at first episode increased with age at a rate greater than the rate of decline in survival. However, analysis of his model reveals a flaw leading to the counterintuitive result that a geometric increase in fecundity with age cannot be made large enough to offset even a small geometric decline in survival so that population growth rate could increase with age of maturity. Thus, favorable selection of delayed maturity is unlikely in Bell's model. Some age-dependent models are described that avoid this flaw. This analysis extends the models of Sibly and Calow to include the counterintuitive result that an exponential increase in fecundity cannot offset an exponential decline in survival to favor delayed reproduction at any age.

Age Factors↗

PubMed1992

Frozen algae as food for Daphnia magna Straus in toxicity testing.

As EC validity criteria for the production of Daphnia magna neonates in standard toxicity tests set fecundity minima which must be attained, it is important that culture conditions provide an adequate ration of high quality food. Maintaining a steady supply of fresh algae can be problematical so the possibility of using frozen food was investigated. The performance of three generations of D. magna fed on diets of fresh or frozen Chlorella was compared. There were no significant effects on fecundity due to food type or generation. Cumulative fecundity (over 21 days) on fresh or frozen food exceeded 120 neonates per female and satisfied that EC validity criterion (60 neonates per female). In addition criteria relating to survival and variability were met. We conclude that frozen Chlorella are an acceptable substitute for fresh algae.

Animals↗

PubMed1984

The effect of light, dark or altered circadian cycle on the lifespan of the rotifer Asplanchna brightwelli.

Rotifers were maintained in various light conditions for at least 20 generations. In the first set of experiments lifespan and fecundity data were compared for groups of rotifers maintained under LL (continuous light), DD (continuous dark) or LD 12:12 (control, 12 hr. light 12 hr. dark). The mean lifespan of the rotifers cultured in DD conditions was significantly increased as compared to the LL or LD 12:12 groups but there were no fecundity differences. There was no alteration in lifespan or fecundity of the LL group as compared to the LD 12:12 control. In a second set of experiments, an LD 6:18 cycle was imposed to determine whether a shift in the circadian cycle would influence lifespan. Rotifers exposed to the LD 6:18 cycle and to the DD conditions showed an 18% and 22% increase in mean lifespan respectively. The results are interpreted to demonstrate that lifespan is influenced by the circadian cycle.

Animals↗

PubMed2005

Sex and death: what is the connection?

A cost of reproduction, where lifespan and fecundity are negatively correlated, is of widespread occurrence. Mutations in insulin/IGF signaling (IIS) pathways and dietary restriction (DR) can extend lifespan in model organisms but do not always reduce fecundity, suggesting that the link between lifespan and fecundity is not inevitable. Understanding the molecular basis of the cost of reproduction will be informed by elucidation of the mechanisms by which DR and IIS affect these two traits.

Animals↗

PubMed2006

Analysis of the cycle of reproduction of Sardina pilchardus (Walbaum, 1792) off the Moroccan Atlantic coast.

This work focuses on aspects of reproductive biology of Sardina pilchardus from the Atlantic coast of Morocco. The mean values of batch fecundity estimated for the species is 23150(+/-1301) oocytes for a mean size of 19.5(+/-0.49) cm, the mean relative fecundity being 346(+/-7.34) oocytes per gram of female without ovary. Batch fecundity increases with total length and body weight without ovary. Sizes at first sexual maturity (L50) are reached for males and females at 15.8(+/-0.29) cm and 15.8(+/-0.35) cm, respectively. The spawning period for the population extends between October and July and the spawning peak occurs from October to February. However, the small sardines (14.5-17 cm) in their first reproduction spawn between November and June, whereas larger fish (17.5-25 cm) spawn between October and July. The factor of condition (K) increased in summer during the sexual resting phase. It is weak in winter during the period of reproduction. Regarding, the sex ratio, there was no significant difference in the number of males and females.

Aging↗

PubMed2005

Sexual cooperation: mating increases longevity in ant queens.

Divergent reproductive interests of males and females often cause sexual conflict . Males of many species manipulate females by transferring seminal fluids that boost female short-term fecundity while decreasing their life expectancy and future reproductivity . The life history of ants, however, is expected to reduce sexual conflict; whereas most insect females show repeated phases of mating and reproduction, ant queens mate only during a short period early in life and undergo a lifelong commitment to their mates by storing sperm . Furthermore, sexual offspring can only be reared after a sterile worker force has been built up . Therefore, the males should also profit from a long female lifespan. In the ant Cardiocondyla obscurior, mating indeed has a positive effect on the lifetime reproductive success of queens. Queens that mated to either one fertile or one sterilized male lived considerably longer and started laying eggs earlier than virgin queens. Only queens that received viable sperm from fertile males showed increased fecundity. The lack of a trade-off between fecundity and longevity is unexpected, given evolutionary theories of aging . Our data instead reveal the existence of sexual cooperation in ants.

Animals↗

PubMed2004

Assisted reproduction may change birth intentions.

OBJECTIVE: To determine whether the development and expansion of assisted reproductive technology (ART) between 1982 and 1995 raised the birth intentions of subfecund people relative to fecund people. DESIGN: Comparison of birth intention rates among fecund and subfecund women in the 1982, 1988, and 1995 rounds of the National Survey of Family Growth, standardized by age, parity, and education. SETTING: No clinical setting. PARTICIPANT(S): Nationally representative samples of married women who were 20 to 44 years old. INTERVENTION(S): None. RESULT(S): Between 1982 and 1995, birth intentions rose at least 2.5 times faster among subfecund women than among fecund women. This rise was not due to increasing average age at maternity over the period. CONCLUSION(S): The development of ART and expansion of services may well have increased birth intentions among subfecund women between 1982 and 1995.

Adult↗

PubMed2006

Association of obesity with treatment outcomes in ovulatory infertile women undergoing superovulation and intrauterine insemination.

OBJECTIVE: To evaluate the association between obesity and the outcome of superovulation and intrauterine insemination (IUI) in infertile ovulatory women. DESIGN: Retrospective chart review. SETTING: University-based infertility clinic. PATIENT(S): Three hundred thirty-three ovulatory women, grouped by body mass index (BMI) categories, who received superovulation and IUI for treatment of infertility. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S) PRIMARY OUTCOME: cycle fecundity. SECONDARY OUTCOMES: total dose of gonadotropins, serum level of E(2), and number of follicles >or=17 mm on the day of hCG injection. RESULT(S): Adjusted cycle fecundity was not different among BMI groups (underweight: 0.14 [95% CI: {0.07, 0.29}], normal weight: 0.12 [95% CI: {0.09, 0.16}], overweight: 0.17 [95% CI: {0.12, 0.24}], and obese: 0.14 [95% CI: {0.08, 0.23}]). Adjusted total gonadotropin dose (IU/cycle) was greater in obese women than in underweight or normal-weight women. Although the numbers of large follicles were not different, E(2) levels (pg/mL) were lower in obese women than in normal-weight and overweight women. CONCLUSION(S): Our sample of ovulatory infertile women demonstrated that treatment-related cycle fecundity is unaffected by obesity. We conclude that obese, infertile ovulatory women require a greater dose of gonadotropins to achieve similar levels of superovulation than normal, underweight or overweight women.

Adult↗

PubMed2006

Successful pregnancies after transplantation of frozen-thawed mouse ovaries into chimeric mice that received lethal-dose radiation.

OBJECTIVE: To study whether fecundity was recovered in mice into which umbilical cord blood cells (UCBCs) were transfused after lethal-dose radiation, followed by transplantation of frozen-thawed ovaries. DESIGN: Prospective basic research study. SETTING: Academic research laboratory. ANIMAL(S): Female C57BL/6 mice as recipients of UCBCs and ovaries, male B6C3F1 mice for mating, and green fluorescent protein (GFP)-transgenic mice: 18.5-day-old fetuses (-/+) for UCBCs and adult GFP mice (+/+) for ovarian tissues. INTERVENTION(S): The UCBCs were transfused into each irradiated mouse, with GFP+ ovaries transplanted 4 weeks later. The chimeric mice were mated 3 weeks after ovarian transplantation and were examined 14 to 16 weeks after the transfusion of UCBCs. MAIN OUTCOME MEASURE(S): Percentage of chimerism, number of GFP+ pups. RESULT(S): The percentage of chimerism in these mice tends to increase with the radiation dose. The recovery of fecundity was observed in the chimeric mice that were transplanted with fresh and previously vitrified ovaries after exposure to radiation. CONCLUSION(S): Even when the exposure dose of radiation administered as pretreatment is lethal, the fecundity of recipients can be maintained if their ovaries are cryopreserved before they are exposed to radiation.

Animals↗

PubMed2006

Fish consumption and time to pregnancy in Japanese women.

The work described in this paper examined the possible relationship between fish consumption and human fecundity among Japanese women using hair mercury level and time to pregnancy (TTP) as indicators of fish consumption and fecundity. We hypothesized that hair mercury concentrations reflect the level of fish consumption and, consequently, can also be taken to indicate the level of intake of organochlorine compounds (OCs) such as dioxins and polychlorinated biphenyls (PCBs) for which fish are the primary source, and which can disrupt normal human reproductive processes. TTP was obtained by a self-administered questionnaire from women who had been delivered of a baby at either of two hospitals in Sendai, Japan, during the period of January 2002-March 2004. Total mercury concentration in their hair (0-3cm from the scalp) was determined by cold vapor atomic absorption spectrometry. Of the 298 women approached, 193 (65%) reported their TTP. The subjects were classified into two groups according to their TTP: group 1, 0-12 months TTP; and Group 2, >12 months TTP. A step-down procedure backward binominal logistic regression analysis was performed by using age, BMI, parity, frequency of intercourse, life-style parameters (smoking, drinking and dietary habits) and hair mercury level of the female subjects and their partners as independent variables. Two separate analyses were performed by including/excluding information on the partners of the subjects. The analyses did not extract hair mercury concentration as significant indicating that fish consumption did not prolong TTP, which was not consistent with the results of our previous study, i.e., in that study frequent fish eaters showed prolonged TTP. Possible reasons of the negative result are discussed and it is suggested that the hair mercury levels in the present study were not an appropriate indicator of fish consumption of the subjects or of their exposure to OCs. Further study on the relationship between fish consumption (and, ultimately, of OCs intake) and fecundity with more appropriate indicators of fish consumption and/or fish-mediated pollutants intake are warranted to characterize the health risk posed by fish consumption.

Adult↗

PubMed2005

Dietary restriction in Drosophila.

The fruit fly Drosophila is a useful organism for the investigation of the mechanisms by which dietary restriction (DR) extends lifespan. Its relatively short generation time, well-characterised molecular biology, genetics and physiology and ease of handling for demographic analysis are all major strengths. Lifespan has been extended by DR applied to adult Drosophila, by restriction of the availability of live yeast or by co-ordinate dilution of the whole food medium. Lifespan increases to a maximum through DR with a progressive dilution of the food and then decreases through starvation as the food is diluted further. Daily and lifetime fecundities of females are reduced by food dilution throughout the DR and starvation range. Standard Drosophila food ingredients differ greatly between laboratories and fly stocks can differ in their responses to food dilution, and a full range of food concentrations should therefore be investigated when examining the response to DR. Flies do not alter the time that they spend feeding in response to DR. Both mean and maximum lifespan are extended by DR. The nutrients critical for the response to DR in Drosophila require definition. The extension of lifespan in response to DR is very much greater in females than in males. Two nutrient-sensing pathways, the insulin/IGF-like and TOR pathways, have been implicated in mediating this response of lifespan to DR in Drosophila, as have two protein deacetylases, dSir2 and Rpd3, although the precise nature of this interaction remain to be characterised. Although female fecundity is reduced by DR, the response of lifespan to DR appears normal in sterile females, possibly implying that reduced fecundity is not necessary for extension of lifespan by DR. There is no reduction in metabolic rate or in the rate of generation of superoxide and hydrogen peroxide from isolated mitochondria in response to DR. DR acts acutely and rapidly (within 48 h) to reduce the mortality of flies that are fully fed to the level found in animals exposed to DR throughout life. This rapid mortality rate recovery provides a powerful framework within which to further investigate the mechanisms by which DR extends lifespan.

Age Factors↗

PubMed2004

How do sessile dioecious species cope with their males?

In terrestrial plants the segregation of male and female reproductions on different individuals results in the seed-shadow handicap: males do not disperse any seed so that the number of local patches reached by seeds is potentially reduced in dioecious populations in comparison to hermaphrodite populations. An analytical model, incorporating a lottery-based recruitment and dispersal stochasticity, was built. The spatially mediated cost of the seed-shadow handicap has been assessed considering the criterions for the invasion of a resident hermaphrodite species by a dioecious species and the reverse invasion, both species having the same demographic parameters but assuming a likely higher fecundity for dioecious females. The reciprocal invasion of a dioecious and hermaphrodite species differing only by their fecundity is never possible. The seed-shadow handicap disappears when the dispersal or survival rate is high enough. This latter point is due to dispersal stochasticity, which allows for the existence of empty patches. A low fecundity and an aggregated seed distribution increase dispersal stochasticity and increase the positive impact of a low mortality rate on the relative competitivity of dioecy and hermaphroditism. Adding a dispersal cost has a comparable effect but also requires higher dispersal rates for the dioecious invasion.

Plant Physiological Phenomena↗