Offspring Quantity Research Articles

Non-stressful temperature effect on oxidative balance and life history traits in adults fish (Oryzias latipes)

Temperature is well known to affect many biological and ecological traits, especially in ectotherms. From a physiological point of view, temperature is also positively correlated to metabolism and is often associated with an increase in reactive oxygen species (ROS) production. It has recently been suggested that ROS play a role in lifespan and resource allocation. However, only a few authors have attempted to explore the relationships between temperature, resource allocation and oxidative balance in ectotherms. Here, we measured the effect of temperature on growth, reproductive effort, offspring quantity and quality, hatching and survival rates, and the associated proximal costs, which were evaluated through the quantification of oxidative balance elements. We reared adult fish (Oryzias latipes) at two non-stressful temperatures (20 and 30°C) during a relatively long period (4 months, approximately the entire adult life). The results show a trade-off between reproduction and maintenance because investment toward growth could be neglected at the adult stage (confirmed by our results). Intriguingly, ROS-dependent damages did not differ between the two groups, probably because of the higher rate of activation of the antioxidant enzyme superoxide dismutase for warm-acclimated fish. The allocation toward antioxidant defences is associated with an earlier reproduction and a lower quality of offspring. These interesting results bring new perspectives in terms of the prediction of the impact of global warming on biota through the use of ecological theories based on oxidative balance and metabolism.

Evolution of monogamy, paternal investment, and female life history in Peromyscus.

The timing of reproductive development and associated trade-offs in quantity versus quality of offspring produced across the life span are well documented in a wide range of species. The relation of these aspects of maternal life history to monogamy and paternal investment in offspring is not well studied in mammals, due in part to the rarity of the latter. By using five large, captive-bred populations of Peromyscus species that range from promiscuous mating with little paternal investment (P. maniculatus bairdii) to social and genetic monogamy with substantial paternal investment (P. californicus insignis), we modeled the interaction between monogamy and female life history. Monogamy and high paternal investment were associated with smaller litter size, delayed maternal reproduction that extended over a longer reproductive life span, and larger, higher quality offspring. The results suggest monogamy and paternal investment can alter the evolution of female life-history trajectories in mammals.

Early Menarche as an Alternative Reproductive Tactic in Human Females: An Evolutionary Approach to Reproductive Health Issues

The age at which a female reaches sexual maturity is critical in determining her future reproductive health and success. Thus, a worldwide decline in menarcheal age (timing of first menstrual period) may have serious long-term consequences. Early menarcheal timing (first menstrual period before age 12) can have a negative effect on fecundity, as well as the quality and quantity of offspring, and may consequently influence population growth or decline. In this paper, we apply an evolutionary framework to modern human health, and assess both proximate and ultimate consequences of declining menarcheal age. Examination of human reproductive health within an evolutionary framework is innovative and essential, because it illuminates the ultimate consequences of a declining age of menarche and facilitates new ways of thinking about the long-term and intergenerational transmission of health and disease; thus, an evolutionary framework lends itself to innovative public health and policy programs. In this paper, we examine whether or not early menarche is an alternative reproductive tactic that modern human females employ in response to a stressful environment, and whether or not early menarche is ultimately beneficial.

The life-history trade-off between fertility and child survival

Evolutionary models of human reproduction argue that variation in fertility can be understood as the local optimization of a life-history trade-off between offspring quantity and ‘quality’. Child survival is a fundamental dimension of quality in these models as early-life mortality represents a crucial selective bottleneck in human evolution. This perspective is well-rehearsed, but current literature presents mixed evidence for a trade-off between fertility and child survival, and little empirical ground to evaluate how socioecological and individual characteristics influence the benefits of fertility limitation. By compiling demographic survey data, we demonstrate robust negative relationships between fertility and child survival across 27 sub-Saharan African countries. Our analyses suggest this relationship is primarily accounted for by offspring competition for parental investment, rather than by reverse causal mechanisms. We also find that the trade-off increases in relative magnitude as national mortality declines and maternal somatic (height) and extrasomatic (education) capital increase. This supports the idea that socioeconomic development, and associated reductions in extrinsic child mortality, favour reduced fertility by increasing the relative returns to parental investment. Observed fertility, however, falls considerably short of predicted optima for maximizing total offspring survivorship, strongly suggesting that additional unmeasured costs of reproduction ultimately constrain the evolution of human family size.

Economic Growth and Evolution: Parental Preferences for Quality and Quantity of Offspring

This paper presents a quantitative analysis of the model developed in Galor and Moav, Natural Selection and the Origin of Economic Growth (2002), in which agents vary genetically in their preference for quality and quantity of children. The simulation produces a pattern of income and population growth that resembles the period of Malthusian stagnation before the Industrial Revolution and the take-off into a modern growth era. We also investigate the possibility that the economy will regress to Malthusian conditions after the modern growth era and show the susceptibility of the modern high-growth state to an increasing prevalence of a strongly quantity-preferring genotype.

Trust and r-K life history adaptation

In this paper, the relationship between human fertility and trust is investigated. The concept of r-K life history – the traits in organisms that trade-off between the quantity and quality of offspring – is integrated with the quadratic population growth model. The results show a negative correlation between the fertility rate and generalised trust. Key word: r-k life history, generalized trust, population studies, quadratic population growth, evolution

Mink with Divergent Activity Levels have Divergent Reproductive Strategies

AbstractStable individual differences in activity levels within populations have been linked to differences in reproductive rate or parental care in several species, including American mink (Neovison vison). Fur‐farmed mink are good models for studying such effects because they yield large sample sizes and readily allow investigations into maternal behaviour, reproductive success, offspring performance and the relationships between these factors. On farms, very inactive individuals generally have smaller litters, and this held true in our study populations. We tested two competing hypotheses to explain this: (1) inactive individuals are failing to cope with a challenging environment and experiencing chronic stress and/or depression‐like ‘apathy’; this predicts female‐skewed litters, poorer maternal care, higher infant mortality and poorer infant growth and (2) inactive individuals do not have reduced fitness but instead employ an alternative adaptive reproductive strategy, trading off offspring quantity for quality; this predicts enhanced maternal care, reduced infant mortality and enhanced infant growth. Inactive females’ kits, especially their sons, grew faster than active females’, even after statistically controlling for litter size; and by 21 d, inactive and active dams’ litters no longer differed in total biomass, despite the former’s smaller litter sizes. In kit retrieval tests, inactive females were faster than active dams to reach their sons (as well as more likely to contact their sons than their daughters: a bias towards male kits not evident in the active dams). Furthermore, kit growth rates and dam latencies to touch them co‐varied, suggesting the existence of consistent differences in maternal style across inactive and active dams. Hypothesis 2 was thus supported: inactive females favour offspring quality over quantity, investing more resources in fewer kits, particularly males. This potentially boosts their sons’ adult fitness. More broadly for laboratory‐based studies, possible ‘captivity effects’ on the fitness correlates of activity and other personality traits are discussed.

Promoting effects on reproduction increase population vulnerability of Daphnia magna

Environmental risk assessment of chemicals is based on single species tests at the individual level with single compounds. However, the protection goal is the sustainability of a population, which faces several natural stressors and mixtures of chemicals in the environment. Therefore, experiments were undertaken to quantify the combined effects of chemicals with different modes of action on Daphnia magna populations. Populations continuously exposed to dispersogen A and at abundance equilibrium were treated with a 2-d pulse of p353-nonylphenol. In previous studies, dispersogen A was shown to act as a natural info-chemical, promoting the reproduction of daphnids (higher offspring quantity) coupled with reduced offspring fitness, whereas nonylphenol in pulsed-exposure caused size-selective mortality. Dispersogen A caused accelerated population growth to maximum abundance, shifted the population structure towards smaller individuals, and increased the population sensitivity to nonylphenol. The authors showed that a positive effect observed at the individual level can be transposed to a negative effect when monitored at the population level. So far, positive effects are not addressed in environmental risk assessment, and even in higher-tier testing, population structure is not quantified. Both factors indicate a potential mismatch between protection aim and risk assessment practice.

Intercarpellary growth of pollen tubes in the extragynoecial compitum and its contribution to fruit set in an apocarpous species, Schisandra sphenanthera (Schisandraceae)

Apocarpous plants possess carpels that are separated in the gynoecium. Extragynoecial compita, commonly occurring in basal angiosperms, have been proposed to have the potential to increase offspring quantity in apocarpous species through the intercarpellary growth of pollen tubes. To date, the impact of an extragynoecial compitum on fruit or seed set has not been studied in any species. This study investigated the pollen tube pathway between adjacent carpels and its contribution to fruit set in Schisandra sphenanthera. We investigated the fruit set ratio in the field and collected hundreds of gynoecia at their full flowering stage. Pollinated carpel ratio and pollen tube pathway observations were performed using fluorescence optics. Pollen grains germinated and tubes extended along the pseudostyle surface. Some of them turned and entered the ovules at the end of the stigmatic crest, whereas others subsequently grew into neighboring carpels through promontory connections located at the base of the unfused carpels. No tubes were found growing on the surface of the receptacle. More than 24 carpels could be fertilized by pollen tubes from one carpel through hand pollination. The pollinated carpel ratio was significantly lower than the fruit set ratio under natural conditions. Pollen tubes from one carpel can easily cross in the extragynoecial compitum between the adjacent carpels of S. sphenanthera, and this intercarpellary growth of pollen tubes can significantly increase the fruit set of apocarpous species, at least in S. sphenanthera.

Enhancing offspring quality or quantity? Different ways for using nectar amino acids in female butterflies

Butterfly-pollinated flowers offer nectar with higher amino acid concentrations than most flowers pollinated by other animals, and female butterflies of some species prefer to consume amino acid-rich nectar. However, for over 30 years, there has been an ongoing discussion about whether nectar amino acids benefit butterfly fitness. A clear positive effect was only shown for the nectar-feeding Araschnia levana, and females of the fruit-feeding Bicyclus anynana also increased offspring quality when they were fed amino acids as adults. Thus, severe doubts remain about the general significance of these single positive results. We therefore tested a further species from a phylogenetically different butterfly subfamily, the small heath (Coenonympha pamphilus L., Satyrinae), taking into account feeding conditions over the whole life cycle of this species. C. pamphilus females receiving nectar amino acids as adults, irrespective of larval food quality, produced heavier larvae and also increased the hatching success of their eggs over the oviposition period. Furthermore, females raised under nitrogen-poor larval conditions tended to use nectar amino acids to increase the number of eggs laid. Thus, C. pamphilus females used nectar amino acids primarily to increase their offspring quality, and secondly tended to increase offspring quantity, if larval resources were scarce, showing a resource allocation pattern differing from both B. anynana and A. levana. Our study supports the old postulate that nectar amino acids generally enhance butterfly fitness.

Maladaptive Habitat Selection of a Migratory Passerine Bird in a Human-Modified Landscape

In human-altered environments, organisms may preferentially settle in poor-quality habitats where fitness returns are lower relative to available higher-quality habitats. Such ecological trapping is due to a mismatch between the cues used during habitat selection and the habitat quality. Maladaptive settlement decisions may occur when organisms are time-constrained and have to rapidly evaluate habitat quality based on incomplete knowledge of the resources and conditions that will be available later in the season. During a three-year study, we examined settlement decision-making in the long-distance migratory, open-habitat bird, the Red-backed shrike (Lanius collurio), as a response to recent land-use changes. In Northwest Europe, the shrikes typically breed in open areas under a management regime of extensive farming. In recent decades, Spruce forests have been increasingly managed with large-size cutblocks in even-aged plantations, thereby producing early-successional vegetation areas that are also colonised by the species. Farmland and open areas in forests create mosaics of two different types of habitats that are now occupied by the shrikes. We examined redundant measures of habitat preference (order of settlement after migration and distribution of dominant individuals) and several reproductive performance parameters in both habitat types to investigate whether habitat preference is in line with habitat quality. Territorial males exhibited a clear preference for the recently created open areas in forests with higher-quality males settling in this habitat type earlier. Reproductive performance was, however, higher in farmland, with higher nest success, offspring quantity, and quality compared to open areas in forests. The results showed strong among-year consistency and we can therefore exclude a transient situation. This study demonstrates a case of maladaptive habitat selection in a farmland bird expanding its breeding range to human-created open habitats in plantations. We discuss the reasons that could explain this decision-making and the possible consequences for the population dynamics and persistence.

Extra‐gynoecial pollen‐tube growth in apocarpous angiosperms is phylogenetically widespread and probably adaptive

• Fusion of floral carpels (syncarpy) in angiosperms is thought to have allowed for significant improvements in offspring quantity and quality in syncarpous species over gymnosperms and apocarpous (free-carpelled) angiosperms. Given the disadvantages of apocarpy, it remains an evolutionary puzzle why many angiosperm lineages with free carpels (apocarpy) have been so successful and why some lineages show reversals to apocarpy. • To investigate whether some advantages of syncarpy may accrue in other ways to apocarpous species, we reviewed previous studies of pollen-tube growth in apocarpous species and also documented pollen-tube growth in nine additional apocarpous species in six families. • Anatomical studies of a scattering of apocarpous paleodicots, monocots, and eudicots show that, after transiting the style, 'extra' pollen tubes exit fully fertilized carpels and grow to other carpels with unfertilized ovules. In many species this occurs via openings in the simple carpels, as we report here for Sagittaria potamogetifolia, Sagittaria pygmaea, Sedum lineare, and Schisandra sphenanthera. • The finding that extra-gynoecial pollen-tube growth is widespread in apocarpous species eliminates the possibility of a major fitness cost of apocarpy relative to syncarpy and may help to explain the persistence of, and multiple reversals to, apocarpy in the evolutionary history of angiosperms.

Hatching asynchrony and brood reduction influence immune response in Common Kestrel Falco tinnunculus nestlings

The onset of incubation before the end of laying imposes asynchrony at hatching and, therefore, a size hierarchy in the brood. It has been argued that hatching asynchrony might be a strategy to improve reproductive output in terms of quality or quantity of offspring. However, little is known about the mediating effect of hatching asynchrony on offspring quality when brood reduction occurs. Here, we investigate the relationship between phenotypic quality and hatching asynchrony in Common Kestrel Falco tinnunculus nestlings in Spain. Hatching asynchrony did not increase breeding success or nestling quality. Furthermore, hatching asynchrony and brood reduction had different effects on nestlings’ phytohaematogglutinin (PHA)-mediated immune response and nestling growth. In asynchronous and reduced broods (in which at least one nestling died), nestlings showed a stronger PHA-mediated immune response and tended to have a smaller body size compared with nestlings raised in synchronous and reduced broods. When brood reduction occurred in broods hatched synchronously, there was no effect on nestling size, but nestlings had a relatively poor PHA-mediated immune response compared with nestlings raised in asynchronous and reduced broods. We suggest that resources for growth can be directed to immune function only in asynchronously hatched broods, resulting in improved nestling quality, as suggested by their immune response. We also found that males produced a greater PHA-mediated immune response than females only in brood-reduced nests without any effect on nestling size or condition, suggesting that females may trade off immune activities and body condition, size or weight. Overall, our results suggest that hatching pattern and brood reduction may mediate resource allocation to different fitness traits. They also highlight that the resolution of immune-related trade-offs when brood reduction occurs may differ between male and female nestlings.

Comparison of Mating Behavior and Offspring Production Success of the Guppy, Poecilia reticulata, Stocked Under Different Operational Sex Ratios

Experiments were conducted to record mating behavior (Experiment 1) and offspring production (Experiment 2) in the guppy, Poecilia reticulata, stocked under different operational sex ratios. Male and female guppies were stocked in aquaria (Experiment 1) and in concrete tanks (Experiment 2) at sex ratios (male:female) of 2:1 (Treatment 1), 1:1 (Treatment 2), and 1:2 (Treatment 3). Courtship displays were significantly less in Treatment 3 (P < 0.05). Sneak copulation was highest in Treatment 1 (P < 0.05). Time spent by the focal female on feeding was highest in Treatment 3 and lowest in Treatment 1 (P < 0.05). Offspring production per female, initial weight of offspring, and growth values recorded for the adult female fish were highest in Treatment 3 (P < 0.05). Weight and survival rate of offspring produced from each experiment was highest in Treatment 3 (P < 0.05). Treatment 3 appeared to be the most viable in terms of both quality and quantity of offspring produced. The results indicate a female biased sex ratio (adult male:female, 1:2) to be more effective than a male biased or an evenly matched sex ratio for enhanced offspring production in the guppy.

Age at first reproduction and probability of reproductive failure in women

Life history theory predicts a trade-off between fitness benefits and costs of delaying age at first reproduction (AFR). In many human populations, maternal AFR has been increasingly delayed beyond sexual maturity over the past decades, raising a question of whether any fitness benefits accrued outweigh costs incurred. To investigate the cost–benefit trade-off concerning AFR in women, we construct a theoretical model and test its predictions using pedigree data from historical Finnish mothers. The model predicts that the probability of reproductive failure (no offspring produced reaching breeding) will increase with AFR if the benefit with delaying in terms of improvement to offspring quality (i.e., breeding probability) cannot offset the cost from decline in offspring quantity. The data show that offspring quantity declined significantly with delayed reproduction, while offspring quality remained initially constant before declining when AFR was delayed beyond 30. Consistent with the theoretical model's predictions, reproductive failure probability increased markedly with delaying AFR after 30, independently of maternal socioeconomic status. Our study is the first to investigate the associations between delay in AFR after sexual maturity and changes in not only offspring quantity but also offspring quality and suggest a significant evolutionary disadvantage of delayed AFR beyond 30 for lineage persistence in a predemographic transition society.

Cost of Female Intrasexual Aggression in Terms of Offspring Quality: A Cross-Fostering Study

Growing evidence that female ornaments and armaments may be important for female reproductive success suggests that a reevaluation of the costs of these potentially sexually selected traits is also necessary. Here, I examine whether intrasexual aggression, a trait favored during direct female‐female competition for nesting sites in tree swallows (Tachycineta bicolor), is costly in terms of the quantity or quality of offspring. I compared measures of female aggressiveness to clutch size, and I also cross-fostered offspring just after hatching to explore a possible causal link between female aggression and nestling mass, an established proxy for offspring quality. High levels of aggression in females were not associated with the quantity of offspring, but instead more aggressive females had offspring of lower quality. While several causal factors appear to influence offspring quality, the mechanism most consistent with this cost of aggression is a trade-off between female aggression and aspects of maternal care. Site differences may create variation in how selection shapes female aggression, but the finding that more aggressive females had lower-quality control offspring indicates that this cost may work counter to selection favoring aggressive behavior in the context of competition over nestboxes.

Seasonally contrasting life-history strategies in the land snail Cornu aspersum: physiological and ecological implications

When a life history is characterized by both seasonality in reproduction and seasonality in offspring fitness, trade-offs in reproductive traits might be adjustments to seasonal time constraints to optimize reproductive success. Therefore, we compared in the laboratory the trade-offs in reproductive traits between early (after maturity) and delayed (after dormancy) reproduction in young land snails Cornu aspersum (Müller, 1774) (syn. Helix aspersa ), depending on food energy content. We also investigated the maternal investment in reproductive output in both breeding periods. After attaining maturity, snails produced single clutches with many small eggs, which resulted, in contrast to previous studies, in large offspring with a low hatching rate owing to high within-clutch cannibalism. The young cannibals may have a higher survival probability in the following hibernation. Snails starting to reproduce after hibernation had smaller clutches of larger eggs, resulting in high quantity of lighter offspring. The clutch mass was positively correlated with maternal mass in snails reproducing after having attained maturity and negatively correlated in snails reproducing after hibernation. Multiple oviposition occurred only after hibernation, thereby enhancing reproductive success. An energy-rich diet did not affect reproductive strategies. Further studies should focus on seasonal plasticity of reproductive strategies in natural populations of C. aspersum and investigate survival probabilities of breeders and juveniles in an evolutionary context.

Early fitness consequences and hormonal correlates of parental behaviour in the social rodent, Octodon degus

Males are expected to assist their mates whenever this behaviour raises survival of offspring with little expense in terms of mating opportunities. At a more proximate level, cortisol and testosterone hormones seem involved in the expression of parental care in mammals. We examined the consequences to postnatal offspring development and survival of the males' presence in the social rodent, Octodon degus. Offspring quality and quantity, and maternal condition of females were contrasted among females rearing their litters in the presence of the sire, females breeding in the presence of a non-breeding female, and females breeding solitarily. We related these differences to variation in parental behaviour and plasma levels of testosterone and cortisol. Twenty two females and their litters were studied under constant conditions of adult density, nest availability, food availability, and breeding experience. Males huddled over and groomed offspring. However, neither the number nor the mass of pups from dams that nested with the sire differed from those recorded to breeding females that nested with a non-breeding female and females that nested solitarily. Body weight loss and associated levels of plasma cortisol in dams nesting with the sire were similar to those of solitary females, but higher than mothers nesting with a non-breeding female. Thus, male care had no consequences to offspring, and seemed detrimental to breeding females. Circulating levels of cortisol and total testosterone were either poor (mothers) or no (fathers, non-breeding females) predictors of parental care.

Context-dependent effects of parental effort on malaria infection in a wild bird population, and their role in reproductive trade-offs

Although trade-offs between reproductive effort and other fitness components are frequently documented in wild populations, the underlying physiological mechanisms remain poorly understood. Parasitism has been suggested to mediate reproductive trade-offs, yet only a limited number of parasite taxa have been studied, and reproductive effort-induced changes in parasitism are rarely linked to trade-offs observed in the same population. We conducted a brood size manipulation experiment in blue tits (Cyanistes caeruleus) infected with malaria (Plasmodium) parasites, and used quantitative PCR to measure changes in parasitaemia. In one of two years investigated, parasitaemia increased as a result of brood enlargement, and was also positively associated with two other indicators of reproductive effort: clutch size and single parenthood. These associations between both experimental and naturally varying reproductive effort and parasitaemia suggest that immune control of chronic malaria infections can be compromised when parents are working hard. Brood size manipulation significantly affected the number of independent offspring produced, which was maximised when brood size was unchanged. Moreover, when parents were infected with one of two common Plasmodium species, the shape of this trade-off curve was more pronounced, suggesting that parasitic infection may exacerbate the trade-off between quantity and quality of offspring. Although the involvement of parasites in survival costs of reproduction has received much attention, these results suggest their role in other commonly documented reproductive trade-offs, such as that between number and quality of offspring, warrants further study.

Personality and reproductive success in a high-fertility human population

The existence of interindividual differences in personality traits poses a challenge to evolutionary thinking. Although research on the ultimate consequences of personality differences in nonhuman animals has recently undergone a surge of interest, our understanding of whether and how personality influences reproductive decisions in humans has remained limited and informed primarily by modern societies with low mortality-fertility schedules. Taking an evolutionary approach, we use data from a contemporary polygynous high-fertility human population living in rural Senegal to investigate whether personality dimensions are associated with key life-history traits in humans, i.e., quantity and quality of offspring. We show that personality dimensions predict reproductive success differently in men and women in such societies and, in women, are associated with a trade-off between offspring quantity and quality. In women, neuroticism positively predicts the number of children, both between and within polygynous families. Furthermore, within the low social class, offspring quality (i.e., child nutritional status) decreases with a woman's neuroticism, indicating a reproductive trade-off between offspring quantity and quality. Consistent with this, maximal fitness is achieved by women at an intermediate neuroticism level. In men, extraversion was found to be a strong predictor of high social class and polygyny, with extraverted men producing more offspring than their introverted counterparts. These results have implications for the consideration of alternative adaptive hypotheses in the current debate on the maintenance of personality differences and the role of individual factors in fertility patterns in contemporary humans.