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PubMed2003

Maternal effects on offspring depend on female mating pattern and offspring environment in yellow dung flies.

Direct costs and benefits to females of multiple mating have been shown to have large effects on female fecundity and longevity in several species. However, with the exception of studies examining genetic benefits of polyandry, little attention has been paid to the possible effects on offspring of multiple mating by females. We propose that nongenetic effects of maternal matings on offspring fitness are best viewed in the same context as other maternal phenotype effects on offspring that are well known even in species lacking parental care. Hence, matings can exert effects on offspring in the same way as other maternal environment variables, and are likely to interact with such effects. We have conducted a study using yellow dung flies (Scathophaga stercoraria), in which we independently manipulated female mating rate, number of mates and maternal thermal environment and measured subsequent fecundity, hatching success, and offspring life-history traits. To distinguish between direct effects of matings and potential genetic benefits of polyandry we split broods and reared offspring at three different temperature regimes. This allowed us to demonstrate that although we could not detect any simple benefits or costs to matings, there are effects of maternal environment on offspring and these effects interact with female mating regime affecting offspring fitness. Such interactions between female phenotype and the costs and benefits of matings have potentially broad implications for understanding female behavior.

Animals↗
PubMed2003

Natural selection and inheritance of breeding time and clutch size in the collared flycatcher.

Many characteristics of organisms in free-living populations appear to be under directional selection, possess additive genetic variance, and yet show no evolutionary response to selection. Avian breeding time and clutch size are often-cited examples of such characters. We report analyses of inheritance of, and selection on, these traits in a long-term study of a wild population of the collared flycatcher Ficedula albicollis. We used mixed model analysis with REML estimation ("animal models") to make full use of the information in complex multigenerational pedigrees. Heritability of laying date, but not clutch size, was lower than that estimated previously using parent-offspring regressions, although for both traits there was evidence of substantial additive genetic variance (h2 = 0.19 and 0.29, respectively). Laying date and clutch size were negatively genetically correlated (rA = -0.41 +/- 0.09), implying that selection on one of the traits would cause a correlated response in the other, but there was little evidence to suggest that evolution of either trait would be constrained by correlations with other phenotypic characters. Analysis of selection on these traits in females revealed consistent strong directional fecundity selection for earlier breeding at the level of the phenotype (beta = -0.28 +/- 0.03), but little evidence for stabilising selection on breeding time. We found no evidence that clutch size was independently under selection. Analysis of fecundity selection on breeding values for laying date, estimated from an animal model, indicated that selection acts directly on additive genetic variance underlying breeding time (beta = -0.20 +/- 0.04), but not on clutch size (beta = 0.03 +/- 0.05). In contrast, selection on laying date via adult female survival fluctuated in sign between years, and was opposite in sign for selection on phenotypes (negative) and breeding values (positive). Our data thus suggest that any evolutionary response to selection on laying date is partially constrained by underlying life-history trade-offs, and illustrate the difficulties in using purely phenotypic measures and incomplete fitness estimates to assess evolution of life-history trade-offs. We discuss some of the difficulties associated with understanding the evolution of laying date and clutch size in natural populations.

Animals↗
PubMed2003

Inbreeding depression and haplodiploidy: experimental measures in a parasitoid and comparisons across diploid and haplodiploid insect taxa.

It has long been assumed that inbreeding depression in haplodiploid organisms is low due to their ability to purge genetic load in haploid males. It has been suggested that this low genetic load could facilitate the evolution of inbreeding behaviors driven by local mate competition in hymenopteran parasitoids. I have examined inbreeding depression in haplodiploids in two ways. First I show that an outbreeding haplodiploid wasp Uscana semifumipennis (Hymenoptera: Trichogrammatidae) suffers substantial inbreeding depression. Longevity was 38% shorter, fecundity was 32% lower, and sex ratio was 5% more male for experimentally inbred wasps when compared to outbred controls. There were interactions between size and both fecundity and sex ratio for inbred wasps that were not seen for outbred individuals. Second, an analysis of data from the literature suggests that when inbreeding is experimentally imposed on populations, haplodiploid insects and mites as a group do suffer less from inbreeding depression than diploid insects, although substantial inbreeding depression in haplodiploid taxa does exist. The meta-analysis revealed no difference in inbreeding depression between gregarious haplodiploid wasps, which are likely to have a history of inbreeding, and solitary haplodiploid species, which are assumed to be primarily outbred.

Analysis of Variance↗
PubMed2003

Breakdown in correlations during laboratory evolution. I. Comparative analyses of Drosophila populations.

We provide evidence from comparisons of populations of Drosophila that evolutionary correlations between longevity and stress resistance break down over the course of laboratory evolution. Using 15 distinct evolutionary regimes, we created 75 populations that were differentiated for early fecundity, longevity, starvation resistance, desiccation resistance, and developmental time. In earlier experiments, selection for postponed aging produced increases in stress resistance, whereas selection for increased stress resistance produced increases in longevity. Direct estimates of correlations also indicated an antagonistic relationship between early fecundity on one hand and longevity or stress resistance on the other. Laboratory evolution of extreme values of stress resistance, however, led to a breakdown in these evolutionary relationships. There was no evidence that these significant changes in correlation resulted from genotype-by-environment interactions or inbreeding. These findings suggest that correlations between functional characters are not necessarily durable features of a species, and that short-term evolutionary responses cannot be extrapolated reliably to longer-term evolutionary patterns.

Animals↗
PubMed2003

Infection success in novel hosts: an experimental and phylogenetic study of Drosophila-parasitic nematodes.

Surprisingly little is known about what determines a parasite's host range, which is essential in enabling us to predict the fate of novel infections. In this study, we evaluate the importance of both host and parasite phylogeny in determining the ability of parasites to infect novel host species. Using experimental lab assays, we infected 24 taxonomically diverse species of Drosophila flies (Diptera: Drosophilidae) with five different nematode species (Tylenchida: Allantonematidae: Howardula, Parasitylenchus), and measured parasite infection success, growth, and effects on female host fecundity (i.e., virulence). These nematodes are obligate parasites of mushroom-feeding Drosophila, particularly quinaria and testacca group species, often with severe fitness consequences on their hosts. We show that the potential host ranges of the nematodes are much larger than their actual ranges, even for parasites with only one known host species in nature. Novel hosts that are distantly related from the native host are much less likely to be infected, but among more closely related hosts, there is much variation in susceptibility. Potential host ranges differ greatly between the related parasite species. All nematode species that successfully infected novel hosts produced infective juveniles in these hosts. Most novel infections did not result in significant reductions in the fecundity of female hosts, with one exception: the host specialist Parasitylenchus nearcticus sterilized all quinaria group hosts, only one of which is a host in nature. The large potential host ranges of these parasites, in combination with the high potential for host colonization due to shared mushroom breeding sites, explain the widespread host switching observed in comparisons of nematode and Drosophila phylogenies.

Animals↗
PubMed2004

The evolution of larval morphology and swimming performance in ascidians.

The complexity of organismal function challenges our ability to understand the evolution of animal locomotion. To meet this challenge, we used a combination of biomechanics, phylogenetic comparative analyses, and theoretical morphology to examine evolutionary changes in body shape and how those changes affected swimming performance in ascidian larvae. Results of phylogenetic comparative analyses suggest that coloniality evolved at least three times among ascidians and that colonial species have a convergent larval morphology characterized by a large trunk volume and shorter tail length in proportion to the trunk. To explore the functional significance of this evolutionary change, we first verified the accuracy of a mathematical model of swimming biomechanics in a solitary (C. intestinalis) and a colonial (D. occidentalis) species and then ran numerous simulations of the model that varied in tail length and trunk volume. The results of these simulations were used to construct landscapes of speed and cost of transport predictions within a trunk volume/tail length morphospace. Our results suggest that the reduction of proportionate tail length in colonial species resulted in improved energetic economy of swimming. The increase in the size of larvae with the origin of coloniality facilitated faster swimming with negligible energetic cost, but may have required a reduction in adult fecundity. Therefore, the evolution of ascidians appears to be influenced by a trade-off between the fecundity of the adult stage and the swimming performance of larvae.

Animals↗
PubMed2004

Evolutionary potential of Chamaecrista fasciculata in relation to climate change. II. Genetic architecture of three populations reciprocally planted along an environmental gradient in the great plains.

Climate change will test the evolutionary potential of populations. Information regarding the genetic architecture within and among populations is essential for prediction of evolutionary outcomes. However, little is known about the distribution of genetic variation for relevant traits in natural populations or alteration of genetic architecture in a changing environment. In this study, pedigreed families from three populations of the annual prairie legume Chamaecrista fasciculata were reciprocally transplanted in three environments across a broad latitudinal range in the Great Plains. The underlying premise of this work is that northern populations will in the future experience climates similar to current-day climates further south. Estimates of narrow-sense heritability ranged from 0.053 to 0.481, suggesting the potential for evolutionary change is possible for most traits. In general, the northern population harbored less genetic variation and had lower heritability for traits than the southern population. This population also experienced large reductions in fitness, as measured by estimated lifetime fecundity, when raised in either the intermediate or the southern climate, whereas the difference between the intermediate and southern population was less extreme. For fecundity, the pattern of cross-environment additive genetic correlations was antagonistic to evolutionary change in four of six cases when native and nonnative sites were compared. Six additional antagonistic positive correlations were found for the rate of phenological development and leaf thickness. Overall, the data suggest that if climate changes as predicted, the northern population will face a severe evolutionary challenge in the future because of low heritabilities, cross-environment genetic correlations antagonistic to selection, and demographic instability due to lower seed production in a hotter and drier climate.

Adaptation, Physiological↗
PubMed1997

Reproductive biology of the mosquitofish in a permanent natural lagoon in south-west Spain: two tactics for one species

Introduced Gambusia holbrooki in a natural lagoon of southern Spain consisted of two age groups: 1992 cohort, 7-11 months old and 1993 cohort, <4 months old. In the 1992 cohort, females grew even during the gestation period at about 0.30 mm day-1. In the 1993 cohort, females displayed a high growth rate (0.55 mm day-1) and reached reproductive size in a few weeks, but stopped growing when they matured. All the 1992 cohort reproduced from mid-May to mid-June, but only 50% of the 1993 cohort reproduced, from mid-August to mid-September. Reproducing females were significantly larger in the 1992 cohort (39.8 mm) than in the 1993 one (34.8 mm). The largest 1992 females cohort had reproduced previously; the 1993 cohort had not. The mean dry weight of intra-ovarian embryos decreased to a minimum immediately before birth. These metabolic costs represented 29.8 and 31.4% of the initial weights of the 1992 and 1993 embryos, respectively. Mean dry weight of full-term embryo was significantly higher in the 1992 cohort (0.80+/-0.129 mg; 95% CL) than in the 1993 one (0.70+/-0.086 mg; 95% CL). With more females in 1992, cohort fecundity was considerably higher (number of embryos=7151; 63%) than in the 1993 (4193; 37%) cohort. The population completed two generations each year (spring and summer). The spring stock grew slower than the summer one but continued to grow during the gestation period, reaching larger final lengths, with more synchronous reproduction and clearer evidence of a second reproductive event. Each reproductive stock displayed its own life-history characteristics, with significant differences between mean length of reproducing females, growth rate, mean brood size, offspring size, standard fecundity and minimum length at reproduction.

Journal Article↗
PubMed1995

Early onset of autoimmunity in MRL/++ mice following immunization with beta 2 glycoprotein I.

Antiphospholipid antibodies (aPL) are associated with thrombosis, thrombocytopenia and recurrent fetal loss in humans and in some animal models. Immunization with beta 2 glycoprotein I (beta 2GPI) induced aPL production in normal rabbits and mice. However, the association of these antibodies with disease manifestations remains controversial. To determine whether induction of aPL by beta 2GPI immunization in an autoimmune strain of mice (MRL/++) would result in acceleration of clinical and serological autoimmune disease manifestations, three groups of 8-week-old female mice were studied. One group was immunized with beta 2GPI, and one with ovalbumin (OVA); the third was not immunized. After two booster injections, sera were analysed for the presence of anticardiolipin (aCL) and anti-DNA by ELISA and anti-nuclear antibody (ANA) by immunofluorescence. Mice were studied for thrombocytopenia, proteinuria, fecundity rates, litter sizes and the development of central nervous system dysfunction. Elevated levels of aCL, anti-DNA and ANA were detected in all beta 2GPI-immunized, in three OVA-immunized, and in none of the unimmunized mice. The anti-DNA antibodies were inhibited by CL micelles, suggesting cross-reactivity between aCL and anti-DNA. Platelet counts, fecundity rates and litter size were reduced in beta 2GPI-immunized but not in OVA-immunized or unimmunized mice. None of the mice developed neurological dysfunction or significant proteinuria over a 10-week period post-immunization. These findings suggest that beta 2GPI immunization induces aPL in MRL/++ mice associated with accelerated autoimmune manifestations resembling the antiphospholipid syndrome.

Animals↗
PubMed2006

Recruitment pulses induce cannibalistic giants in Arctic char.

1. Recent theoretical studies on the population dynamic consequences of cannibalism have focused on mechanisms behind the emergence of large cannibals (giants) in size-structured populations. Theoretically, giants emerge when a strong recruiting cohort imposes competition induced mortality on stunted adults, but also provides a profitable resource for a few adults that accelerate in growth and reach giant sizes. 2. Here the effects of a recruitment pulse on the individual and population level in an allopatric Arctic char population have been studied over a 5-year period and these results were contrasted with theoretical model predictions for the conditions necessary for the emergence of cannibalistic giants. 3. The recruitment pulse had negative effects on invertebrate resource abundance, and the decrease in body condition and increase in mortality of adult char suggested that strong intercohort competition took place. 4. The frequency of cannibalism increased and a few char accelerated in growth and reached 'giant' sizes. 5. The main discrepancy between model predictions and field data was the apparently small effect the recruited cohort had on resources and adult char performance during their first summer. Instead, the effects became pronounced when the cohort was 1 year old. This mismatch between model predictions and field observations was suggested to be due to the low per capita fecundity in char and the restricted nearshore habitat use in young-of-the-year (YOY) char. 6. This study provides empirical evidence that the emergence of giants is associated with the breakthrough of a strong recruiting cohort and also suggests that the claimed stable char populations with large cannibals may instead be populations with dynamic size structure that results in intermittent breakthroughs of recruitment pulses, providing the conditions necessary for char to enter the cannibalistic niche. 7. The data suggest that increased recruit survival through restricted habitat use may destabilize dynamics and cause the emergence of giants. However, they also suggest that this does not necessarily develop into populations with bi-modal size structure in populations with low per capita fecundity and size- and density-dependent habitat use of recruiting cohorts.

Animals↗
PubMed1988

Anti-mosquito antibodies decrease the reproductive capacity of Aedes aegypti.

Aedes aegypti (L.) fed on rabbits immunized with mosquito antigens showed a reduction in fecundity in the first oviposition and decreased viability of the progeny. Feeding behaviour of mosquitoes was not affected and no significant mortality was observed due to the presence of anti-mosquito antibodies in the bloodmeal. Antibodies were detected in the oocytes of mosquitoes 48 h after the bloodmeal. The role of specific antibodies in influencing fecundity is discussed.

Aedes↗
PubMed1988

Tsetse: the limits to population growth.

Growth rates of tsetse populations were estimated by calculating the dominant eigenvalues of appropriate Leslie matrices. The individual effects of four variables (pre-adult and adult survival probability, interlarval period and pupal duration), have been investigated by varying each one over a wide range of values, while the other three are held constant. R, the log of the growth rate, was found to vary approximately linearly with adult and pre-adult death rate; a 1% change in the adult death rate causes approximately a 10-fold change in R. R varies linearly with the log of fecundity and of the pupal duration. An increase in the pupal duration results in a decrease in the growth rate for populations which have a positive growth rate, but an increase for populations which have a negative growth rate. For a population at equilibrium, a change in the pupal duration has no effect. Small changes in fecundity have less effect on the growth rate than small changes in the death rate; this fact is advanced as an important contributor to the generally very cautious nature of female tsetse, and their aversion to man, particularly as a potential host. A simple linear model is described which relates R to all four variables and their first order interactions. The model is used to produce a set of graphs which encapsulate the relationship between the growth rate and the vital parameters over a wide range of values. It is also used to draw the loci on one side of which tsetse populations grow, and on the other of which they decline. Population resilience is discussed in relation to the problem of tsetse eradication; it is concluded that if one can impose and sustain an added mortality of 4% per day on any female tsetse population then it must go extinct, regardless of the strength of the density dependent processes; and it seems likely that in most field conditions only an added 2-3% is required. It is pointed out that ground and aerial spraying techniques produce much higher daily mortalities than this, but they may often not be sustained for sufficiently long to achieve eradication. When odour-baited targets are used the increased death rate is much smaller, but it can be sustained as required; recent work in Zimbabwe shows that there is a good correspondence between the calculated imposed death rate and the observed rate of decline of tsetse populations.

Animals↗
PubMed2006

Bayesian selection of predictors of conception probabilities across the menstrual cycle.

There is increasing interest in identifying predictors of human fertility, including environmental exposures, behavioural factors, and biomarkers, such as mucus or reproductive hormones. Epidemiological studies typically measure fecundability, the per menstrual cycle probability of conception, using time to pregnancy data. A critical predictor, which is often ignored in the design or analysis, is the timing of non-contracepting intercourse in the menstrual cycle. In order to limit confounding by behavioural differences between exposure groups, it may be preferable to base inferences on day-specific conception probabilities in relation to intercourse timing. This article proposes Bayesian methods for selection of predictors of day-specific conception probabilities. A particular focus is the case in which data on ovulation timing are not available. We focus on the selection of fertile days in the cycle during which conception probabilities are non-negligible and predictors may play a role. Data from recent European and Italian prospective studies of daily fecundability are presented, and the proposed approach is used to estimate cervical mucus effects within a mid-cycle potentially fertile window using data from the Italian study.

Bayes Theorem↗
PubMed1981

Immunity to Strongyloides ratti in rats. 1. Adoptive transfer with mesenteric lymph node cells.

Adoptive transfer of immunity against the enteral phase of Strongyloides ratti was monitored using four parameters; namely, number of worms recovered, position occupied in the host's small intestine, worm length and fecundity. When immune mesenteric lymph node cells (IMLNC) were transferred from donors infected for 20, 26 or 32 days into recipients infected for 3 days, a marked acceleration of worm expulsion was evident by day 16 post-infection (p.i.). IMLNC from day-16 p.i. donors did not transfer expulsion. In an experiment in which recipients were given 2 x 10(8) or 1 x 10(8) IMLNC from donors infected for 26 days, accelerated worm expulsion occurred only with the higher inoculum, although manifestations of direct worm immunity, i.e. altered position and reduced length and fecundity, were evident in both cases. Transfer of IMLNC appeared to have no effect upon worm establishment; when cells were transferred on the day of infection a period of 16 days was necessary to effect both direct anti-worm immunity and expulsion, although the former was evident on day 14 p.i. However, when IMLNC were transferred to rats already infected for 6 days, a very significant reduction of their worm burden was apparent 10 days after IMLNC transfer.

Animals↗
PubMed2004

Plant-like mating in an animal: sexual compatibility and allocation trade-offs in a simultaneous hermaphrodite with remote transfer of sperm.

The importance of sexual compatibility between mates has only recently been realized in zoological research into sexual selection, yet its study has been central to botanical research for many decades. The reproductive characteristics of remote mating, an absence of precopulatory mate screening, internal fertilization and embryonic brooding are shared between passively pollinated plants and a phylogenetically diverse group of sessile aquatic invertebrates. Here, we further characterize the sexual compatibility system of one such invertebrate, the colonial ascidian Diplosoma listerianum. All 66 reciprocal pairings of 12 genetic individuals were carried out. Fecundities of crosses varied widely and suggested a continuous scale of sexual compatibility. Of the 11 animals from the same population c. 40% of crosses were completely incompatible with a further c. 20% having obvious partial compatibility (reduced fecundity). We are unaware of other studies documenting such high levels of sexual incompatibility in unrelated individuals. RAPD fingerprinting was used to estimate relatedness among the 12 individuals after a known pedigree was successfully reconstructed to validate the technique. In contrast to previous results, no correlation between genetic similarity and sexual compatibility was detected. The blocking of many genotypes of sperm is expected to severely modify realized paternity away from 'fair raffle' expectations and probably reduce levels of intra-brood genetic diversity in this obligatorily promiscuous mating system. One adaptive benefit may be to reduce the bombardment of the female reproductive system by outcrossed sperm with conflicting evolutionary interests, so as to maintain female control of somatic : gametic investment.

Animals↗
PubMed2004

Sources of stochasticity in models of sex allocation in spatially structured populations.

There are many ways to include stochastic effects in models of sex allocation evolution. These include variability in the number of mating partners and fecundity in a rich literature that goes back 20 years. The effects of variance in the fecundity and number of mating partners have typically been considered separately from the stochastic effects of mortality. However, I show that these processes produce mathematically equivalent models with subtly different biological details. These scenarios differ in the way that information becomes available to individuals because the parents often have information on mating partners while they are making sex allocation decisions, but must make these decisions before brood mortality takes place. This makes it possible to test which mechanism, stochastic mortality or variation in mating partners, is responsible for observed sex ratios. Alternatively, asymmetric variance between sexual functions can cause skewed sex allocation, even in the absence of local mate competition. This allows the evolution of either female- or male-biased sex ratios depending on which sexual function is more variable.

Animals↗
PubMed2004

Constrained sex allocation in a parasitoid due to variation in male quality.

The theory of constrained sex allocation posits that when a fraction of females in a haplodiploid population go unmated and thus produce only male offspring, mated females will evolve to lay a female-biased sex ratio. I examined evidence for constrained sex ratio evolution in the parasitic hymenopteran Uscana semifumipennis. Mated females in the laboratory produced more female-biased sex ratios than the sex ratio of adults hatching from field-collected eggs, consistent with constrained sex allocation theory. However, the male with whom a female mated affected her offspring sex ratio, even when sperm was successfully transferred, suggesting that constrained sex ratios can occur even in populations where all females succeed in mating. A positive relationship between sex ratio and fecundity indicates that females may become sperm-limited. Variation among males occurred even at low fecundity, however, suggesting that other factors may also be involved. Further, a quantitative genetic experiment found significant additive genetic variance in the population for the sex ratio of offspring produced by females. This has only rarely been demonstrated in a natural population of parasitoids, but is a necessary condition for sex ratio evolution. Finally, matings with larger males produced more female-biased offspring sex-ratios, suggesting positive selection on male size. Because the great majority of parasitic hymenoptera are monandrous, the finding of natural variation among males in their capacity to fertilize offspring, even after mating successfully, suggests that females may often be constrained in the sex allocation by inadequate number or quality of sperm transferred.

Analysis of Variance↗
PubMed2005

Sex-specific selective pressures on body mass in the greater white-toothed shrew, Crocidura russula.

The direction, intensity and shape of viability-, sexual- and fecundity selection on body mass were investigated in a natural population of the greater white-toothed shrew (Crocidura russula), combining parentage assignment through molecular techniques and mark-recapture data over several generations. A highly significant stabilizing viability selection was found in both sexes, presumably stemming from the constraints imposed by their insectivorous habits and high metabolic costs. Sexual selection, directional in both sexes, was twice as large in males than in females. Our results suggest that body mass matters in this context by facilitating the acquisition and defense of a breeding territory. No fecundity selection could be detected. The direction of sexual size dimorphism (SSD) was in agreement with the observed pattern of selective pressures: males were heavier than females, because of stronger sexual selection. SSD intensity, however, was low compared with other mammals, because of the low level of polygyny, the active role of females in territory defense and the intensity of stabilizing viability selection.

Animals↗