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PubMed2002

Use of tetracycline in larval diet to study the effect of Wolbachia on host fecundity and clarify taxonomic status of Trichogramma species in cured bisexual lines.

Endosymbionts of the genus Wolbachia were efficiently cured from Trichogramma species by incorporating 0.02% tetracycline into the artificial diet used to rear larvae. Use of this technique yielded stable cured lines (bisexual and arrhenotokous lines) in which no Wolbachia organisms were detected by PCR for up to 14 generations after curing. Four cured strains of Trichogramma pretiosum showed a significantly lower total fecundity compared to their Wolbachia-infected counterpart. However, the fecundity of a single cured strain of Trichogramma evanescens was similar to its Wolbachia-infected counterpart. These differences in the effect on fecundity may be due to differences between the Wolbachia strains infecting T. pretiosum or T. evanescens, providing additional evidence for the hypothesis that a specific interaction exists between some Trichogramma species and their Wolbachia symbionts. Tetracycline in larval diet was also used to generate bisexual strains of Trichogramma oleae and Trichogramma cordubensis so that these species could be crossed with the closely related species, respectively, T. pretiosum and T. evanescens, to test their compatibility. These crosses showed a lack of compatibility, validating maintenance of these as distinct species.

Animals↗
PubMed1998

Effects of stress combinations on the expression of additive genetic variation for fecundity in Drosophila melanogaster.

To test whether stressful conditions altered levels of heritable variation in fecundity in Drosophila melanogaster, parent-offspring comparisons were undertaken across three generations for flies reared in a combined stress (ethanol, cold shock, low nutrition) environment or a control environment. The stressful conditions did not directly influence fecundity but did lead to a reduced fecundity in the offspring generations, perhaps reflecting cross-generation maternal effects. Both the heritability and evolvability estimates were higher in the combined stress treatment, reflecting an apparent increase in the additive genetic variance under stress. In contrast, there were no consistent changes in the environmental variance across environments.

Animal Nutritional Physiological Phenomena↗
PubMed1980

Effects of the host immune response on the longevity, fecundity and position in the intestine of Trichinella spiralis in mice.

In female NIH strain mice, expulsion of a primary infection of the nematode Trichinella spiralis began on day 8 and was virtually complete by day 14 of infection. In secondary and tertiary infections, the number of larvae which established in the intestine was normal, but expulsion began on day 6 and was complete on day 10. In a primary infection the shedding of larvae by female worms began on day 5, reached its peak on days 6--7, began to decrease on day 8 and was minimal by day 10. In secondary and tertiary infections fecundity was depressed. The depression of fecundity occurred slightly in advance of worm loss. During the stable phase of infection, T. spiralis occurred in the anterior half of the small intestine. During expulsion, living worms were found increasingly in more posterior parts of the gut but their fecundity did not vary with position. After direct inoculation into the posterior ileum, adult and larval T. spiralis remained in the posterior half of the small intestine. In this position, larvae established in normal numbers, grew and reproduced normally. Therefore, any part of the small intestine was a suitable site for T. spiralis and expulsion is not merely due to a change in the position of the worms.

Animals↗
PubMed1986

Faecal egg counts and nematode fecundity: Heligmosomoides polygyrus and laboratory mice.

The results are presented of an experimental investigation of the relationship between faecal egg counts and worm burden in outbred MF1 mice infected with Heligmosomoides polygyrus (Nematoda). The sex-ratio of the adult parasites was found to be significantly female biased, but independent of parasite burden. Evidence was also found to suggest a significant association between parasite density and mating success. The linear logarithmic relationship (gradient of approximately 2) between the variance and mean of repeated egg counts from individual mice could not be disrupted by controlled experimental conditions, and is therefore concluded to be an inherent feature of the biology of helminth-host interactions. A significant positive association was detected between host faecal output and parasite fecundity; further investigation of the cause of this association is now required. Average faecal production was found to be inversely related to worm burden. In combination, the above two factors account partly, but not completely, for the observed density dependence in the absolute rate of parasite egg production. Two epidemiological consequences of the relationship between faecal production and parasite fecundity are discussed. First, absolute rates of egg production can only be estimated by temporal egg counts (epd). Secondly, measurements of egg production/g of faecal material (epg) are more reliable indicators of worm burden than measurements of epd. Both faecal output and worm fecundity respond as might be predicted to a period of host food deprivation; faecal egestion and measurements of epd are significantly depressed, and measurements of epg are significantly increased. The data are consistent with the hypothesis that egg production and faecal output are causally associated, but that other factors relating to parasite density also influence egg production. Of the possible causes for the high variability in parasite egg production between mice harbouring low number of worms, the most likely explanation seems to be host heterogeneity (possible genetic in origin). This is discussed in relation to similar patterns observed in data collected from human populations in areas of endemic helminth infection.

Analysis of Variance↗
PubMed1980

The influence of Hymenolepis diminuta on the survival and fecundity of the intermediate host, Tribolium confusum.

An experimental study of the effects of parasitism by H. diminuta on the intermediate host, Tribolium confusum, is described. No density-dependent constraints on parasite establishment within individual hosts are evident, although a reduction in cysticercoid size at high parasite burdens is demonstrated. The relationship between parasite burden, host mortality and host fecundity is investigated. Host mortality is linearly related to parasite burden, whereas the relationship between parasite burden and host fecundity is non-linear. There is no difference in viability between eggs from infected and uninfected females. The generative causes of these effects are not investigated experimentally, although it is postulated that survival is related to the degree of damage to the midgut wall caused by parasite penetration, and fecundity to the biomass of parasites harboured by the host. The significance of these effects is discussed in relation to the overall dynamics of the host-parasite association.

Animals↗
PubMed1989

The role of parasite fecundity and longevity in the success of Trichostrongylus tenuis in low density red grouse populations.

The prevalence of the caecal threadworm Trichostrongylus tenuis in red grouse in the north of Scotland was high despite low grouse densities. Prevalence, intensity and aggregation of threadworms was higher in old than in young grouse. Infections were long-lasting: populations of adult worms could survive for over 2 years in grouse, with little mortality. Parasite egg output decreased with the age of a worm population, largely as a result of a decrease in the fecundity of ageing female worms. Seasonal variations in worm fecundity were also evident. However, there was no evidence of an intensity-dependent decrease of worm fecundity with increasing worm numbers in either captive or wild grouse. The long life and high reproductive capacity of T. tenuis probably contribute to its effective transmission and high prevalence.

Animals↗
PubMed1991

Trichobilharzia ocellata: influence of infection on the fecundity of its intermediate snail host Lymnaea stagnalis and cercarial induction of the release of schistosomin, a snail neuropeptide antagonizing female gonadotropic hormones.

Subadult and adult specimens of the pond snail Lymnaea stagnalis were infected with the schistosome Trichobilharzia ocellata. Egg production and growth of the snails were monitored over an 8-week period post-infection (p.i.). Snail haemolymph was collected and analysed for the presence of schistosomin, a neuropeptide which antagonizes the action of the snails' female gonadotropic hormones. Snails infected as subadults showed an increase in fecundity during the first 4 weeks p.i. compared with non-infected controls. The possibility is discussed that this increase is caused by an accelerated maturation of the female sex organs due to elevated levels of Dorsal Body Hormone, a female gonadotropic hormone. No difference in fecundity was found between snails infected as adults and control snails during the first 4 weeks p.i. Snails infected as subadults and as adults showed a decrease in fecundity from week 5 p.i. and onwards. This decrease coincided with the appearance of schistosomin in the haemolymph of the snails and with that of differentiating cercariae in the daughter sporocysts. Cercariae are probably involved in the induction of schistosomin release from the snails' CNS into the haemolymph. Snails infected as subadults or as adults grew at approximately the same rate as uninfected snails.

Animals↗
PubMed1989

Density dependence in establishment, growth and worm fecundity in intestinal helminthiasis: the population biology of Trichuris muris (Nematoda) infection in CBA/Ca mice.

The results are presented of an experimental study of the population biology of chronic Trichuris muris (Nematoda) infection in cortisone-treated CBA/Ca mice. Attention is focused upon both the validity of the common use of faecal egg counts to demonstrate density dependence in helminth fecundity, and the identification of other possible density-dependent mechanisms that may regulate worm numbers in chronic trichuriasis. The results show that faecal egg counts, although demonstrating high daily variation, are not an artefact of host faecal output but a significant density-dependent function of worm burden. This finding contrasts with the observations on Heligmosomoides polygyrus infection in outbred MFI mice, but accords with similar studies in a wide variety of host - helminth systems. Worm establishment in the murine host is found to be a density related function of infection dose. This is attributed to the probable existence of a physical gut-carrying capacity in the murine host for T. muris. Worm distribution in the gut is also shown to the density dependent, with worms being displaced from the caecum to the colon at increasing intensities of infection. The sex ratio of the adult parasites, however, is found to be both unitary and independent of worm burden. Evidence for a significant density-dependent decline in female T. muris growth or size is presented. The results also show a significant positive association between female T. muris weight and per capita fecundity. These findings indicate that the stunted growth of individual worms at high parasite densities may be a potential mechanism underlying density dependence in helminth fecundity.

Animals↗
PubMed2001

Contrasting regulation of fecundity in two abomasal nematodes of Svalbard reindeer (Rangifer tarandus platyrhynchus).

Stability of trichostrogylid populations indicates that some form of density-dependent regulation occurs which could act through fecundity. We present evidence for intraspecific density-dependent effects in 1 of 2, dominant, abomasal nematodes species (Ostertagia gruehneri) of Svalbard reindeer (Rangifer tarandus platyrhynchus). We found evidence in O. gruehneri, for density-dependent regulation of female worm length in April, July and October 1999. However, it is only in July that female worm length explains the variation in the number of eggs in utero which is also related to egg production per female worm only in this month and not at other times of the year. The seasonal pattern in faecal egg output in this species focuses egg production in the summer months when conditions are favourable to transmission. In contrast, we found no evidence in the other common species (Marshallagia marshalli) for density-dependent regulation of female worm length during or the number of eggs in utero. Faecal egg output in M. marshalli was positively related to worm burden but not to the mean number of eggs in utero. Neither inter-specific interactions nor host body condition appeared to influence worm fecundity. The contrasting patterns of density-dependent regulation of fecundity provides further evidence for divergent life-histories in this nematode community.

Abomasum↗
PubMed2003

Effects of plant flavonoids on fecundity, survival, and feeding of the Formosan subterranean termite.

Fecundity, mortality, and food consumption of the Formosan subterranean termite, Coptotermes formosanus Shiraki, were evaluated in response to five plant flavonoids (genistein, biochanin A, apigenin, quercetin, and glyceollin). Apigenin fed at 50 microg/primary reproductive pair proved to be the most toxic flavonoid. Biochanin A was most effective in reducing fecundity. Subsequently, these two flavonoids were tested through oral feeding and topical application at 100-microg dose. Significant reduction in the numbers of progeny was evident for biochanin A in both treatment methods. Choice feeding tests with termite workers showed that initially termites were attracted to filter paper treated with biochanin A, but over a period of 72 hr, consumed significantly less material when compared to controls. Biochanin A is a promising phytochemical with ability to reduce fecundity in primary reproductives of the Formosan subterranean termite, but it does not elicit phagostimulant activity.

Animals↗
PubMed2003

Effect of active immunization with the C-terminal 67-94 (R-28) region of human seminal plasma inhibin on the fecundity of adult male rabbits.

PROBLEM: To characterize the specificity of antibodies to the synthetic C-terminal 67-94 (R-28) peptide of human seminal plasma inhibin (hSPI), and to examine the effect of active immunization on the fecundity of adult male animals. METHOD OF STUDY: The specificity of R-28-DT antibodies was tested using enzyme-linked immunosorbent assay, immunohistochemical and immunofluorescence staining, and Western blotting. For fertility studies, adult male rats and rabbits were immunized and mated with females of the same strain. RESULTS: Rabbit antibodies to R-28-DT recognized native hSPI, as demonstrated by sperm agglutination in vivo and in vitro, on the sperm head by immunofluorescence staining, and in the columnar epithelial cells of the prostate by immunohistochemical staining. Immunization with the R-28-DT conjugate elicited a poor antibody response in male rats and their fecundity remained unaffected, while in male rabbits it elicited a good immune response with reduction in their fertility. CONCLUSION: R-28-DT antibodies recognized the native hSPI in the prostatic epithelium and agglutinated washed rat, rabbit, monkey, and human spermatozoa in vitro. Immunization of rabbits caused agglutination of spermatozoa resulting in a decrease in their fecundity. The conjugated R-28 peptide of hSPI offers promise as a male contraceptive.

Animals↗
PubMed2000

Highly fecund mothers sacrifice offspring survival to maximize fitness.

Why do highly fecund organisms apparently sacrifice offspring size for increased numbers when offspring survival generally increases with size? The theoretical tools for understanding this evolutionary trade-off between number and size of offspring have developed over the past 25 years; however, the absence of data on the relation between offspring size and fitness in highly fecund species, which would control for potentially confounding variables, has caused such models to remain largely hypothetical. Here we manipulate egg size, controlling for maternal trait interactions, and determine the causal consequences of offspring size in a wild population of Atlantic salmon. The joint effect of egg size on egg number and offspring survival resulted in stabilizing phenotypic selection for an optimal size. The optimal egg size differed only marginally from the mean value observed in the population, suggesting that it had evolved mainly in response to selection on maternal rather than offspring fitness. We conclude that maximization of maternal fitness by sacrificing offspring survival may well be a general phenomenon among highly fecund organisms.

Animals↗
PubMed2002

Increased fecundity of malathion-specific resistant beetles in absence of insecticide pressure.

Despite that resistance frequency is assumed to decline when selective pressure is relaxed, the stability of resistance frequency has been observed in some insects in the absence of insecticide. In the red flour beetle, Tribolium castaneum, the first case of malathion-resistance was reported in the early 1960s. The malathion-specific resistant phenotype has now almost completely replaced the susceptible one in red flour beetle populations. In the present study, several life-history traits that could influence the fitness of the insects were compared between insecticide-susceptible and malathion-specific resistant populations of the red flour beetle. On average, egg fertility and egg-to-adult development time did not differ between susceptible and resistant populations. However, the fecundity of resistant females was greater than that of susceptible ones. Generally, differences in development time between insecticide resistant and susceptible populations are considered as having more effect on fitness than do differences in fecundity. However, the observed increased female fecundity may participate, in combination with the previously observed increased male reproductive success, to the development and the stability of malathion-specific resistance in T. castaneum.

Animals↗
PubMed2003

Blockade of macrophage migration inhibitory factor (MIF) in Schistosoma japonicum-infected mice results in an increased adult worm burden and reduced fecundity.

Macrophage migration inhibitory factor (MIF), a cytokine produced by many cell types, modulates cellular and humoral immune responses. In schistosomiasis, ova in the portal circulation induce a delayed type hypersensitivity (DTH) that results in formation of hepatic granulomas (HG) which secrete MIF activity. Therefore, we hypothesized that endogenous MIF modulates immune responses in schistosomiasis. To test this hypothesis, Schistosoma japonicum-infected mice were injected with rabbit IgG or neutralizing rabbit IgG antibody to MIF 4.5-6.5 week post infection when HG form and female worms are laying eggs. Compared with controls, 6.5-7-week post-infection, antibody-treated mice had 1.7-3 times as many adult worms and half as many ova per worm pair in their livers. In contrast, antibody introduced before infection or 6-8 week post infection did not affect worm burden or fecundity. Thus, for the first time there is evidence that 4.5-6 week post-infection endogenous MIF somehow mediates reduction of adult worm burden and promotes fecundity. Splenocytes and HG cells from antibody-treated mice showed reduced intracellular expression of TNFalpha and/or IL-10. We hypothesize that endogenous MIF enhances adult worm attrition by up-regulating innate and adaptive immune responses by increasing expression of MHC-II, co-stimulatory, adhesion, receptor and cytokine molecules, and promotes fecundity by up-regulating TNFalpha expression.

Animals↗
PubMedDate not supplied

[Influence of some medium factors on the fecundity of Biomphalaria glabrata (Say, 1818) Mollusca, Pulmonata) in laboratory conditions].

In different samples of fresh waters we studied the fecundity of Biomphalaria glabrata. We tested, too, the influence of different concentrations of Na, Ca, Mg, and K-salts. The snail, B. glabrata, is not affected by very high rates of those salts but eggs laying is getting down when the amount of NaCl is between 2000 and 4000 mg/1, of MgCl2 between 410 and 763 mg/1 and KCl between 330 and 760 mg/1. The rate in Ca seems inactive in the field of fecundity but, in an other hand, high concentrations of Ca suppressed the inhibiting effect of the high rates in Mg. B. glabrata is not affected by high rates in Mg, when Mg/Ca is Low. The inhibiting effect of Mg begins when Mg/Ca is around 30. The importance of different kinds of substratum for eggs lying on fecundity was also studied.

Animals↗
PubMed1992

Eggs, enzymes, and evolution: natural genetic variants change insect fecundity.

Phosphoglucose isomerase genotypes in the butterfly Colias differ dramatically in biochemical properties. These differences were evaluated earlier, using metabolic network theory, to predict, successfully, their effects on glycolytic metabolism and hence on Colias flight capacity and several consequent fitness components in the wild. Female egg-laying, not previously studied, also depends on flight, so female fecundity is now predicted to differ among these genotypes. An experimental design incorporating the thermal ecology of Colias confirms these predictions in a cool habitat. Thus female fecundity differences among animal enzyme polymorphs have now been found. Quantitative reconstruction of the selection regime for phosphoglucose isomerase genotypes in Colias can now begin. The most heat-stable genotypes are the least fecund, suggesting that global warming, if it occurs, may have severe impacts, through population genetics, on demography of thermally sensitive creatures.

Analysis of Variance↗
PubMed1999

Fecundity above the Species Level: Ovule Number and Brood Size in the Genisteae (Fabaceae: Papilionoideae).

Per-fruit components of fecundity (ovules per ovary, seeds per fruit, seed : ovule ratio, and patterns of seed maturation within pods) were studied in 33 species of the Genisteae, a legume tribe of mostly Mediterranean shrubs, e.g., Cytisus, Ulex, that also includes more widespread herbs such as Lupinus. Species identity explained most variance in both potential (ovules) and realized (seeds per fruit and seed : ovule ratio) fecundity, and although significant population-specific effects existed, these were relatively small, indicating that estimates of fecundity were not particularly prone to environment-induced changes. Average seed : ovule ratios varied between 20% (for a few species in which fixed rates of embryo abortion result into single seeded pods) and 100% (annuals), but most taxa were in the 40%-60% range. The probability that an ovule near the base of the ovary matured into a seed was significantly lower than the pod average in the majority of species. As indicated by the large size of stigmatic pollen loads, this was unlikely to result from insufficient pollination but rather from preferential embryo abortion. High abortion rates next to pod base occurred in both presumed selfers and obligate outcrossers. Evidence points to relatively stereotyped reproductive ways and high reproductive coherence in the tribe, with major departures from the norm being high seed : ovule ratios exhibited by annual Lupinus (associated with selfing), and low ratios shown by species with single seeded pods (associated with fixed rates of embryo abortion).

Journal Article↗
PubMed2003

A new version of the size-advantage hypothesis for sex change: incorporating sperm competition and size-fecundity skew.

Traditional sex-change theory cannot explain the existence of protogynous species in which the largest females do not change sex when provided an opportunity. We present an expected reproductive success threshold model that incorporates previously unconsidered factors (size-fecundity skew and sperm competition) that can strongly affect reproductive expectations. The model predicts a variety of circumstances when the largest females remaining in a social group should not change sex in the absence of the dominant male, yet it also predicts that these same conditions should promote sex change in smaller females. If a large female's fecundity is markedly higher than the aggregate of the other members of her social group (i.e., there exists a skew in the size-fecundity distribution that raises a large female's expected reproductive success threshold), she should defer from sex change. Sperm competition can strongly lower the expectation of paternity obtained as a sex-changed male, and this also raises the threshold. The model suggests that deferral of sex change should be more common in species in which intense sperm competition is prevalent (such as fishes living in seagrass beds). This prediction appears consistent with patterns seen in nature.

Animals↗