Variation In Female Fecundity Research Articles

Effects of Female and Male Density on their Mating Performance and Female Post-Mating Reproductive Fitness in Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae)

In insects, mating performance and female post-mating reproductive fitness is closely related to female and male density. In nature, females and males of the willow leaf beetle, Plagiodera versicolora (Laicharting), exhibit the phenomenon of swarming damage. This study investigated the effects of female and male density on their mating performance and on female post-mating fecundity, egg hatching rates, and egg-laying patterns. Female and male density had a significant positive effect on the time from pairing to successful mating and on female fecundity, the duration of the egg-laying period, and the number of egg clutches, but it had a significant negative effect on the egg hatching rate. Female and male density had no significant effect on female post-mating longevity and the number of eggs per clutch. Our study shows that variation in female fecundity and egg-laying patterns is an adaptive strategy for P. versicolora at relatively high population densities. This strategy helps to expand the distribution of offspring and lower the competition for food resources among offspring, which, in turn, helps to maintain or increase population abundance.

The significant role of post-pairing male behavior on the evolution of male preferences and female traits

Existing sexual selection theory postulates that a sufficiently large variation in female fecundity or other direct benefits are fundamental for generating male mate choice. In this study, we suggest that, in addition to pre-pairing preferences, choosy males can also have different post-pairing behaviors, a factor which has been comparatively overlooked by previous studies. We found that both male preferences and female traits could evolve much more easily than previously expected when the choosy males that paired with unpreferred females would allocate more efforts to seeking additional post-pairing mating opportunities. Furthermore, a costly female trait could evolve when there was a trade-off between seeking additional mating and paternal care investment within social pair for choosy males. Finally, a costly male preference and a costly female trait might still evolve and reach a stable polymorphic state in the population, which might give rise to a high variability in male choice and female traits in nature. We suggest that male mate choice may be even more common than expected, which needs to be verified empirically.

Female fecundity variation affects reproducibility of experiments on host plant preference and acceptance in a phytophagous insect.

Reproducibility is a scientific cornerstone. Many recent studies, however, describe a reproducibility crisis and call for assessments of reproducibility across scientific domains. Here, we explore the reproducibility of a classic ecological experiment-that of assessing female host plant preference and acceptance in phytophagous insects, a group in which host specialization is a key driver of diversification. We exposed multiple cohorts of Pieris napi butterflies from the same population to traditional host acceptance and preference tests on three Brassicaceae host species. Whereas the host plant rank order was highly reproducible, the propensity to oviposit on low-ranked hosts varied significantly even among cohorts exposed to similar conditions. Much variation could be attributed to among-cohort variation in female fecundity, a trait strongly correlated both to female size and to the size of the nuptial gift a female receives during mating. Small males provide small spermatophores, and in our experiment small females that mated with small males had a disproportionally low propensity to oviposit on low-ranked hosts. Hence, our results provide empirical support to the theoretical prediction that female host utilization is strongly affected by non-genetic, environmental variation, and that such variation can affect the reproducibility of ecological experiments even under seemingly identical conditions.

The evolution of fecundity is associated with female body size but not female-biased sexual size dimorphism among frogs.

Sexual size dimorphism (SSD) is one of the most common ways in which males and females differ. Male-biased SSD (when males are larger) is often attributed to sexual selection favouring large males. When females are larger (female-biased SSD), it is often argued that natural selection favouring increased fecundity (i.e. larger clutches or eggs) has coevolved with larger female body size. Using comparative phylogenetic and multispecies regression model selection approaches, we test the hypothesis that among-species variation in female fecundity is associated with the evolution of female-biased SSD. We also ask whether the hypothesized relationship between SSD and fecundity is relaxed upon the evolution of parental care. Our results suggest a strong relationship between the evolution of fecundity and body size, but we find no significant relationship between fecundity and SSD. Similarly, there does not appear to be a relationship between fecundity and the presence or absence of parental care among species. Thus, although female body size and fecundity coevolve, selection for increased fecundity as an explanation for female-biased SSD is inconsistent with our analyses. We caution that a relationship between female body size and fecundity is insufficient evidence for fecundity selection driving the evolution of female-biased SSD.

Simultaneous failure of two sex-allocation invariants: implications for sex-ratio variation within and between populations.

Local mate competition (LMC) occurs when male relatives compete for mating opportunities, and this may favour the evolution of female-biased sex allocation. LMC theory is among the most well developed and empirically supported topics in behavioural ecology, clarifies links between kin selection, group selection and game theory, and provides among the best quantitative evidence for Darwinian adaptation in the natural world. Two striking invariants arise from this body of work: the number of sons produced by each female is independent of both female fecundity and also the rate of female dispersal. Both of these invariants have stimulated a great deal of theoretical and empirical research. Here, we show that both of these invariants break down when variation in female fecundity and limited female dispersal are considered in conjunction. Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers. Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.

Male mate preference for female eyespan and fecundity in the stalk-eyed fly, Teleopsis dalmanni

Traditional views of sexual selection view males as the indiscriminate sex, competing for access to choosy females. It is increasingly recognized that mating can also be costly for males and they are therefore likely to exhibit choice in order to maximize their reproductive success. Stalk-eyed flies are model species in sexual selection studies. Males are sperm limited and constrained in the number of matings they are able to partake in. In addition, variation in female fecundity has been shown to correlate positively with female eyespan, so eyespan size could provide males with a reliable signal of female reproductive value. We examined male mate preference in the wild in the stalk-eyed fly, Teleopsis dalmanni. In addition, we set up experiments in the laboratory allowing males a choice between females that varied in 1) eyespan (a proxy for fecundity) and/or 2) fecundity (manipulated through diet). We found that males exhibited preference for large eyespan females, both in the wild and laboratory studies. As well as using female eyespan as a mating cue, males were also able to assess female fecundity directly. Changes in fecundity among large eyespan females caused corresponding changes in male mate preference, whereas changes in the fecundity of small eyespan females had limited effect on their attractiveness. These results show that male mate preferences are a prevalent feature of a canonical example of female mate choice sexual selection and that males use multiple cues when they assess females as potential mates.

Small and poor females change sex: A theoretical and empirical study on protogynous sex change in a triggerfish under varying resource abundance

Sex change is known from various fish species. In many polygynous species, the largest female usually changes sex to male when the dominant male disappeared, as predicted by the classical size-advantage model. However, in some fishes, the disappearance of male often induces sex change by a smaller female, instead of the largest one. The halfmoon triggerfish Sufflamen chrysopterum is one of such species. We conducted both field investigation and theoretical analysis to test the hypothesis that variation in female fecundity causes the sex change by less-fertile females, even if they are not the largest. We estimated the effect of body length and residual body width (an indicator of nutrition status) on clutch size based on field data. Sex-specific growth rates were also estimated from our investigation and a previous study. We incorporated these estimated value into an evolutionarily stable strategy model for status-dependent size at sex change. As a result, we predict that rich females change sex at a larger size than poor ones, since a rich fish can achieve high reproductive success as a female. In some situations, richer females no longer change sex (i.e. lifelong females), and poorer fish changes sex just after maturation (i.e. primary males). We also analyzed the effect of size-specific growth and mortality.

Sex‐specific effects of developmental environment on reproductive trait expression in Drosophila melanogaster

Variation in the expression of reproductive traits provides the raw material upon which sexual selection can act. It is therefore important to understand how key factors such as environmental variation influence the expression of reproductive traits, as these will have a fundamental effect on the evolution of mating systems. It is also important to consider the effects of environmental variation upon reproductive traits in both sexes and to make comparisons with the environment to which the organism is adapted. In this study, we addressed these issues in a systematic study of the effect of a key environmental factor, variation in larval density, on reproductive trait expression in male and female Drosophila melanogaster. To do this, we compared reproductive trait expression when flies were reared under controlled conditions at eight different larval densities that covered a 20-fold range. Then, to place these results in a relevant context, we compared the results to those from flies sourced directly from stock cages. Many reproductive traits were surprisingly insensitive to variation in larval density. A notable exception was nonlinear variation in female fecundity. In contrast, we found much bigger differences in comparisons with flies from stock cages—including differences in body size, latency to mate, copulation duration, fecundity, and male share of paternity in a competitive environment. For a number of traits, even densities of 1000 larvae per vial (125 larvae per mL of food) did not phenocopy stock cage individuals. This study reveals novel patterns of sex-specific sensitivity to environmental variation that will influence the strength of sexual selection. It also illustrates the importance of comparisons with the environment to which individuals are adapted.

Fine-Scale Mapping of Natural Variation in Fly Fecundity Identifies Neuronal Domain of Expression and Function of an Aquaporin

To gain insight into the molecular genetic basis of standing variation in fitness related traits, we identify a novel factor that regulates the molecular and physiological basis of natural variation in female Drosophila melanogaster fecundity. Genetic variation in female fecundity in flies derived from a wild orchard population is heritable and largely independent of other measured life history traits. We map a portion of this variation to a single QTL and then use deficiency mapping to further refine this QTL to 5 candidate genes. Ubiquitous expression of RNAi against only one of these genes, an aquaporin encoded by Drip, reduces fecundity. Within our mapping population Drip mRNA level in the head, but not other tissues, is positively correlated with fecundity. We localize Drip expression to a small population of corazonin producing neurons located in the dorsolateral posterior compartments of the protocerebrum. Expression of Drip–RNAi using both the pan-neuronal ELAV-Gal4 and the Crz-Gal4 drivers reduces fecundity. Low-fecundity RILs have decreased Crz expression and increased expression of pale, the enzyme encoding the rate-limiting step in the production of dopamine, a modulator of insect life histories. Taken together these data suggest that natural variation in Drip expression in the corazonin producing neurons contributes to standing variation in fitness by altering the concentration of two neurohormones.

Strategic mating effort in a simultaneous hermaphrodite

Sexual selection theory for simultaneously hermaphroditic animals predicts an overall preference for inseminating partners that have a relatively higher female fecundity. Previous work on the link between male mating decisions and female fecundity has primarily focused on the effect of the partners’ body size using existing variation in this trait within a study population. On the assumption that the body size is positively correlated with female fecundity, sperm donors should preferentially inseminate relatively larger individuals to obtain a higher fitness gain through their male sex function. However, empirical evidence for such size-dependent mate choice in simultaneous hermaphrodites is equivocal, possibly because of confounding variables. We studied the mating behavior of the simultaneously hermaphroditic flatworm Macrostomum lignano and tested for a strategic mating effort in response to the feeding status of the partner. We experimentally manipulated the feeding status of potential mating partners in order to generate variation in female fecundity among them and tested whether this affected the copulation number and the number of sperm that the focal worm managed to store in the partner’s sperm storage organ. We found that the manipulation of the feeding status had a strong effect on the body size of the potential mating partners and that focal worms copulated more frequently with, and stored more sperm in well-fed partners compared to unfed partners. Our results suggest that M. lignano adjusts its mating effort in response to the feeding status of the mating partner.

Effects of cocoa tree phenology and canopy microclimate on the performance of the mirid bug Sahlbergella singularis

Populations of the cocoa mirid, Sahlbergella singularis Haglund (Hemiptera: Miridae), on cocoa, Theobroma cacao L. (Malvaceae), display sharp seasonal fluctuations in population size. To better understand factors and mechanisms involved in seasonal variation, we studied the life history traits of 10 successive generations of a caged population under field conditions. Nymphal survival and development were assessed on pods stored under cocoa canopy, whereas female survival and fecundity were evaluated on sleeved pods in cocoa trees. At the same time, cocoa phenology and cocoa canopy microclimate were characterized. A life table analysis was conducted with survival and fecundity temporal data. Reproductive parameters showed far more variation than nymphal development parameters, both within and among generations. We obtained low intrinsic rates of natural increase (about 0.04), the variation of which was mainly linked to the decrease in fecundity. Fecundity as well as life table parameters varied in accordance with natural population fluctuations, suggesting that S. singularis seasonal variation might be mainly linked to variation in female fecundity. A multiple regression analysis showed that variation in female fecundity was first correlated with the presence of young fruits on cocoa trees. Fecundity was also weakly affected by daily minimum r.h. and daily mean temperature. The usefulness of our results for modeling of S. singularis population dynamics and for the improvement of IPM strategies is discussed.

Effect of exposure to short-term heat stress on survival and fecundity in Drosophila ananassae

In ectothermic organisms, temperature plays a vital role in survival and reproductive success. Founding isofemale lines from wild-collected females is a basic tool for characterizing quantitative traits in a natural population. The effects of heat shock, i.e., short exposure to heat stress, on survival and reproductive success in 10 recently collected isofemale lines of Drosophila ananassae Doleschall, 1858 were compared. Flies were treated as follows: (i) unstressed control; (ii) placed at 37 °C for 90 min (pre-treatment); (iii) placed at 40 °C for 60 min 24 h before the fecundity test; and (iv) placed at 40 °C for 60 min with pre-treatment 16 h before they were exposed to 40 °C. The heat stress strongly affected survival. However, there was no significant difference between the survival of males and females. Furthermore, the female fecundity, measured as F1 offspring produced over the next 12 days, was also reduced. Heat pre-treatment improved survival of both male and female and also improved female productivity. We found significant variation in female fecundity among isofemale lines, and intraclass correlations increased for stress treatments. The results suggest that a small increase in environmental stress may affect fitness traits, and there is enough genetic variation for thermal adaptation in D. ananassae.

Cryptic male choice: sperm allocation strategies when female quality varies

Abstract We examined evolutionary stable sperm allocation and included stochastic variation in male mating frequency, not included in previous models examining sperm allocation strategies. We assumed sperm mixing and variation in female quality and used a genetic algorithm to analyse the evolution of male sperm allocation. Our results show that males should invest more sperm in initial copulations than in subsequent copulations as a male might fail to mate again. The inclusion of variation in female fecundity had no influence on the evolutionary stable sperm allocation strategy if males were unable to recognize female quality. If males were assumed to allocate sperm in response to female quality, the proportion of sperm allocated was positively correlated with female quality. Moreover, with increasing variance in female quality, males conserved more sperm for later copulations. Literature data on sperm allocation from diverse taxa show a good fit with the predictions given by our model.

The influence of variation in female fecundity on effective population size

Understanding the relationship between effective population size (Ne) and the number of adults in a population (N) is important for predicting genetic change in small populations. In general, Ne is expected to be close to N/2, i.e. in the range N/4-3N/4, provided that the powerful effect of population bottlenecks on reducing Ne is factored out (using the harmonic mean of N). However, some very low published estimates of Ne/N(<; 0.1) raise the possibility that other factors acting to reduce Ne have been underestimated. Here one such factor, variation in female fecundity, is investigated. Its effect on Ne depends on the standardized variance in fecundity (per breeding season), a measure that is generally independent of mean fecundity. Empirical estimates of this standardized variance from 16 animal studies yielded an average value of 0.44, and a maximum value less than 1.5. To investigate the effect of such values, three kinds of fecundity variation were modelled: random (seasonal): individual; and age-related. Fixed individual differences among females reduce Ne the most. However, to reduce Ne to N/10, the resulting standardized variance must usually be 10 or more. Random differences need to be even larger to achieve the same reduction. One possible mechanism, the random loss of whole families, requires very high family mortality (90% or more). The third model, fecundity that increases linearly with age, is ineffective at causing a marked decrease in Ne. Given the finding that very unusual conditions are required to reduce Ne below Ne/10, low estimates of Ne/N need to be examined critically: the lowest published ratio, for a natural population of oysters, was found to be questionable because of possible immigration into the population by cultivated oysters.

Variation in the fecundity of roe deer in Britain: effects of age and body weight

This paper investigates variation in female fecundity in relation to effects of age and body weight within and between 15 populations of roe deer Capreolus capreolus (Linnaeus, 1758) in Britain. Analyses were based on carcass material and fecundity was assessed from the presence/absence and number fertilised ovulations (corpora lutea) and implanted foetuses. A significant proportion (>10%) of does ovulated in their first year in some populations, but such precocious reproductive activity rarely resulted in successful implantation of a foetus.

Protandry in Aedes Sierrensis: The Significance of Temporal Variation in Female Fecundity

Protandry, the early emergence of males into a seasonally breeding population, has been described mathematically as a mating strategy resulting from sexual selection on both sexes. A key implicit assumption in protandry models is that all matings contribute equally to a male's reproductive success. We build a simulation model of protandry based on field censuses and investigate the consequences of size—specific temporal variation in female fecundity for the optimal timing of protandry in the western treehole mosquito, Aedes sierrensis. We show that theoretical predictions of protandry are robust when differential female fecundity is incorporated into a model of protandry in A. sierrensis. In addition, we utilize field data and laboratory experiments to elucidate the selective forces acting on both sexes of this mosquito. Under conditions of reduced per capita resources, males minimized development time by pupating at lower mass; females maximized mass by delaying pupation. These gender—specific, homeostatic adjustment to food and density, which result in density—dependent protandry, indicate that protandry is the result of selection on independent fitness criteria in each sex.

Male preference for large females and assortative mating for body size in the sand lizard (Lacerta agilis)

Male sand lizards (Lacerta agilis) are polygynous and guard individual females for several hours to days after copulation. Even though the copulation itself only lasts 2–4 min, the total time that a male invests per female is considerably more and may constitute a substantial investment during a mating season. In such situations, when male copulation frequency is constrained, or when variation in female fecundity is high, mate choice by males may be adaptive. Large body size in female sand lizards is correlated with higher fecundity. In choice experiments performed in the laboratory, male sand lizards preferred to court large females rather than small females. In addition, when there was little difference in size between the females in the experiment, the males visited the two females more often before they started to court the preferred female. The results from a field study during 1984 and 1987–1990 showed that females are non-aggressive, have small neighboring home ranges (c. 100 m2) and may share burrows and sites for thermoregulation. This means that females can be found close together and thus gives males the opportunity to choose a mate. Assortative mating with respect to size was observed in a natural population, as well as a limited number of direct choices of females by males. These results support the results of the choice experiment.

Male choice and competition in Tetraopes tetraophthalmus: effects of local sex ratio variation

Male milkweed beetles (Tetraopes tetraophthalmus) are shown to exhibit choice between potential mates. Males, however, also exhibit direct competition for access to potential mates. These differences in male behavior are dependent on the local sex ratio, with males becoming increasingly choosy when the sex ratio is female-biased, and more competitive when the sex ratio is malebiased. Females show neither choice nor competition. In both the laboratory and in the field, body size is important in determining patterns of competition and choice. Larger males win most aggressive encounters, and males generally prefer large females as mates. The combination in a single sex, of competition for mates and mate choice is not predicted by classical sexual selection theory. Male choice and competition may have evolved in T. tetraophthalmus due to the combination of (1) the mating system (2) the pattern of variation in female fecundity, and (3) the spatially and temporally variable operational sex ratios. This explanation is not dependent on high heritability of body size.