Survival Costs Of Reproduction Research Articles

Survival costs and benefits of reproduction: A register-based study in 20th century Estonia.

Patterns of individual variation in lifespan and senescence depend on the associations between parental survival and reproductive rates. We studied the associations between parity and survival among 579,271 Estonians born between 1905 and 1945 and in a cohort with a completed lifespan born in 1905-1927. For this cohort, selection for increased lifespan operated on both sexes, but it was stronger in men than in women. However, the median lifespan increased between the subsequent cohorts in women but stagnated in men. Selection for longer lifespan was caused by the below-average lifespan of individuals with no or single offspring. Despite a general positive selection for lifespan, survival costs of reproduction were also detected among a relatively small proportion of individuals with high parities, as mothers of two and fathers of two and three children had the highest median lifespans. Fathers of more than six children had better survival than fathers of few children in their reproductive age, but this association reversed after age 70. The reversal of this association between survival and parity at old age indicates that relative mortality risks between those with lower versus higher parities change across ages, as predicted by the antagonistic pleiotropy theory of aging.

Climate and non‐native herbivores influence reproductive investment by Greater Sage‐grouse

AbstractHighly seasonal environments can increase competition among herbivores for nutrients, affecting rates of reproduction and survival. There is concern about the impacts of non‐native ungulates on Greater Sage‐grouse in the Great Basin of North America. We estimated nesting propensity, the annual proportion of females attempting a nest, for Greater Sage‐grouse in relation to the abundance of ungulates using 7 years of data from the northwestern Great Basin, USA. We focused on nesting because it is the necessary first major investment required for the production of new recruits. We used a Bayesian multistratum model to investigate the effects of weather and sympatric non‐native herbivores, free‐roaming horses and domestic cattle, on reproductive rates and female survival of adult and yearling sage‐grouse. Adults nested at a higher rate (0.931, 95% CI, 0.904–0.953) than yearlings (0.867, 95% CI, 0.802–0.922) under average conditions of covariates other than age. If the first nest failed, renesting rates were similar between adults (0.349, 95% CI, 0.292–0.410) and yearlings (0.353, 95% CI, 0.217–0.507). Females in better body condition at the start of the season nested at higher rates, and moderately snowy winters led to the highest nesting propensity during the following spring. Drier conditions led to low rates of nesting, particularly in areas with dense cattle grazing. Female survival was lower for nesting females, indicating a survival cost of reproduction. Areas with abundant free‐roaming horses had slightly higher nesting propensity, though other research suggests negative impacts later in the breeding cycle. Sage‐grouse face life history trade‐offs that may be shifting due to changing climatic conditions. Our work suggests that the effects of competition with non‐native ungulates on sage‐grouse life histories may be exacerbated by adverse weather.

Female reproduction bears no survival cost in captivity for gray mouse lemurs.

The survival cost of reproduction has been revealed in many free‐ranging vertebrates. However, recent studies on captive populations failed to detect this cost. Theoretically, this lack of survival/reproduction trade‐off is expected when resources are not limiting, but these studies may have failed to detect the cost, as they may not have fully accounted for potential confounding effects, in particular interindividual heterogeneity. Here, we investigated the effects of current and past reproductive effort on later survival in captive females of a small primate, the gray mouse lemur. Survival analyses showed no cost of reproduction in females; and the pattern was even in the opposite direction: the higher the reproductive effort, the higher the chances of survival until the next reproductive event. These conclusions hold even while accounting for interindividual heterogeneity. In agreement with aforementioned studies on captive vertebrates, these results remind us that reproduction is expected to be traded against body maintenance and the survival prospect only when resources are so limiting that they induce an allocation trade‐off. Thus, the cost of reproduction has a major extrinsic component driven by environmental conditions.

Is parental competitive ability in winter negatively affected by previous springs' family size?

Reproductive behavior cannot be understood without taking the local level of competition into account. Experimental work in great tits (Parus major) showed that (1) a survival cost of reproduction was paid in environments with high levels of competition during the winter period and (2) experimentally manipulated family size negatively affected the ability of parents to compete for preferred breeding boxes in the next spring. The fact that survival was affected in winter suggests that the competitive ability of parents in winter may also be affected by previous reproductive effort. In this study, we aim to investigate whether (1) such carryover effects of family size on the ability of parents to compete for resources in the winter period occurred and (2) this could explain the occurrence of a survival cost of reproduction under increased competition. During two study years, we manipulated the size of in total 168 great tit broods. Next, in winter, we induced competition among the parents by drastically reducing the availability of roosting boxes in their local environment for one week. Contrary to our expectation, we found no negative effect of family size manipulation on the probability of parents to obtain a roosting box. In line with previous work, we did find that a survival cost of reproduction was paid only in plots in which competition for roosting boxes was shortly increased. Our findings thus add to the scarce experimental evidence that survival cost of reproduction are paid under higher levels of local competition but this could not be linked to a reduced competitive ability of parents in winter.

Effects of reproduction on growth and survival in Atlantic cod, Gadus morhua, assessed by comparison to triploids

Despite increasing interest in optimal life history theory and the associated physiological, ecological and evolutionary processes, little information exists on gonad–soma tradeoffs and longevity of individuals over long time periods. We examined somatic and survival costs of reproduction in captive iteroparous, batch-spawning Atlantic cod (Gadus morhua), utilizing diploids and triploids, knowing that triploid females invest little to no energy into gametogenesis. Based on annual specific growth rate, there was no evidence for a somatic cost of reproduction at ages 2 (virgin year) and 4years, but there was at age 3years. At age 2years, low investment in reproduction likely accounted for the lack of a somatic cost of reproduction, whereas at age 4 the absence was associated with heightened growth post-spawning enabling mature fish to catch up to immature fish. At age 3, compensatory growth during post-spawning was below that of immature fish. Survival represented a significant component of the cost of reproduction. Laboratory experiments examining the cost of reproduction have traditionally focused on shorter time periods, commonly spanning several months, whereas ours spanned nearly four years. Although previously done for bivalves, to our knowledge, this is the first time the cost of reproduction has been evaluated using triploid fish as a comparator.

Survival costs of reproduction in Drosophila

Reproduction shortens lifespan in practically all organisms examined so far, but the underlying mechanisms remain largely unknown to date. Here I review what evolutionary and molecular biologists have learned about such "costs of reproduction" in the fruit fly (Drosophila melanogaster) since Maynard Smith's (1958) seminal discovery that sterile mutants in D. subobscura live substantially longer than fertile wildtype flies. Together with observations from the nematode worm (Caenorhabditis elegans) and other organisms, the data from Drosophila suggest that there are at least four general principles that underlie trade-offs between reproduction and lifespan: (1) trade-offs between survival and reproduction are widespread; (2) the relationship between increased lifespan and decreased fecundity can be uncoupled under certain conditions; (3) while survival costs of reproduction might not necessarily be due to competitive resource allocation, we lack robust alternative explanations for their occurrence; and (4) physiological trade-offs between reproduction and longevity do not always translate into evolutionary genetic trade-offs. I conclude that – despite much recent progress – our current understanding of the proximate basis of survival costs of reproduction remains very limited; much future work on the genetics and physiology of such trade-offs will be required to uncover their mechanistic basis.

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.

Fitness costs of reproduction depend on life speed: empirical evidence from mammalian populations

Fitness costs of reproduction play a key role in understanding the evolution of reproductive tactics. Nevertheless, the detection and the intensity of costs of reproduction vary according to which life-history traits and species are studied. We propose an evolutionary model demonstrating that the chance of detecting a cost of reproduction should be lower when the fitness component studied has a low rather than high variance. Consequently, the fitness component that is affected the most by costs of reproduction should vary with life speed. Since long-lived species have developed a strategy that avoids jeopardizing their survival and short-lived species favour current reproduction, variance in survival is smaller and variance in reproduction higher in long-lived vs. short-lived species. We review empirical studies of costs of reproduction in free-ranging mammals, comparing evidence of costs reported among species and focal traits. In support of our model, more studies reported evidence of reproductive costs of reproduction in ungulates than in rodents, whereas survival costs of reproduction were more frequent in rodents than in ungulates. The life-history model we propose is expected to apply to any species, and hence provides a better understanding of life-history variation, which should be relevant to all evolutionary ecologists.

Marker‐assisted determination of the relationship between body size and reproductive success and consequences for evaluation of adaptive life histories

We tested for differences in the predicted optimal ages at first maturity in brook charr (Salvelinus fontinalis) in Freshwater River, Newfoundland, when life-history data were collated based on the marker-assisted estimation of the relationship between body size and reproductive success rather than using fecundity as a surrogate for reproductive success. Jointly with capture-recapture data to estimate the growth and survival costs of reproduction, we found that weak relationships between body size and reproductive success generate selection against delayed maturation. This finding would not have held for females if the relationship between body size and fecundity had been used as a surrogate for the relationship between body size and reproductive success. This shows that predictions of optimal life histories can be qualitatively changed when using molecular markers to directly evaluate age- and/or size-specific effects of body size on reproductive success.

Sex differences in survival costs of reproduction in a promiscuous primate.

In sexually promiscuous mammals, female reproductive effort is mainly expressed through gestation, lactation, and maternal care, whereas male reproductive effort is mainly manifested as mating effort. In this study, we investigated whether reproduction has significant survival costs for a seasonally breeding, sexually promiscuous species, the rhesus macaque, and whether these costs occur at different times of the year for females and males, namely in the birth and the mating season, respectively. The study was conducted with the rhesus macaque population on Cayo Santiago, Puerto Rico. Data on 7,402 births and 922 deaths over a 45-year period were analyzed. Births were concentrated between November and April, while conceptions occurred between May and October. As predicted, female mortality probability peaked in the birth season whereas male mortality probability peaked in the mating season. Furthermore, as the onset of the birth season gradually shifted over the years in relation to climatic changes, there was a concomitant shift in the seasonal peaks of male and female mortality. Taken together, our findings provide the first evidence of sex differences in the survival costs of reproduction in nonhuman primates and suggest that reproduction has significant fitness costs even in environments with abundant food and absence of predation.

Influence of growth and survival costs of reproduction on Atlantic cod, Gadus morhua, population growth rate

A stochastic, age-structured life history model was used to examine how age at maturity (theta), pre- (Zimm) and postreproductive (Zmat) mortality, and postreproductive growth rate can affect maximum reproductive rates of fish at low population size. Simulations suggest that annual (r) and per-generation (R0) metrics of population growth for Newfoundland's northern Grand Bank Atlantic cod, Gadus morhua, are primarily influenced by changes to mortality prior to and following reproduction. At observed weights at age and Zmat = 0.2, r ranged between 0.135 and 0.164 for cod maturing at between 4 and 7 years. Incremental increases in either Zimm or Zmat of 0.1 were associated with 0.03-0.05 reductions in r. To effect similar reductions, individual growth rate would have to decline by approximately one half. At observed weights at age, increases in Zmat from 0.20 to 0.45 increased the probability of negative per-generation growth from 3 to 26% for cod maturing at 4 years and from 6 to 46% for cod maturing at 7 years. Thus, even in the absence of fishing mortality, little or no population growth by Atlantic cod may not be unexpected in the presence of environmental stochasticity, particularly when accompanied by increases in mortality and declining individual growth.

Influence of growth and survival costs of reproduction on Atlantic cod, <i>Gadus morhua</i>, population growth rate

A stochastic, age-structured life history model was used to examine how age at maturity (theta), pre- (Zimm) and postreproductive (Zmat) mortality, and postreproductive growth rate can affect maxim...

ENERGY, RISK, AND REPTILIAN REPRODUCTIVE EFFORT: A REPLY TO NIEWIAROWSKI AND DUNHAM.

[Extract] Based on simple mathematical models, Shine and Schwarzkopf (1992; SS) suggested that survival costs of reproduction were likely to be more important evolutionary determinants of reproductive effort (RE) than were growth costs in many reptiles, and hence that energy-based measures were unlikely to be of general use in testing predictions derived from RE theory. These conclusions were strongly challenged by Niewiarowski and Dunham (1994; ND), who argued that our models lacked generality. In this paper, we reexamine ND's analyses and show that their models actually support, rather than refute, our original conclusions.

THE EVOLUTION OF REPRODUCTIVE EFFORT IN LIZARDS AND SNAKES.

Life history theory suggests that the optimal evolved level of reproductive effort (RE) for an organism depends upon the degree to which additional current reproductive investment reduces future reproductive output. Future reproduction can be decreased in two ways, through (i) decreases in the organism's survival rate, and/or (ii) decreases in the organism's growth (and hence subsequent fecundity). The latter tradeoff-that is, the "potential fecundity cost"-should affect the evolution of RE only in species with relatively high survival rate, a relatively high rate of fecundity increase with body size, or a relatively high reproductive frequency per annum. Unless these conditions are met, the probable benefit in future fecundity obtained from decreasing present reproductive output is too low for natural selection to favor any reduction in RE below the maximum physiologically possible. Published data on survival rate, reproductive frequency and relative clutch mass (RCM) suggest that many lizard species fall well below the level at which natural selection can be expected to influence RE through such "potential fecundity" tradeoffs. Hence, the relative allocation of resources between growth and reproduction is unlikely to be directly optimized by natural selection in these animals. Instead, energy allocation should influence the evolution of RE only indirectly, via effects on an organism's probability of survival during reproduction. Survival costs of reproduction may be the most important evolutionary determinants of RE in many reptiles, and information on the nature and extent of such costs is needed before valid measures of reptilian RE can be constructed.

Does the Aquatic Isopod Idotea baltica Minimize the Survival Costs of Reproduction?

In field data, the survival of Idotea baltica females has earlier been observed to decline soon after the delivery of juveniles from brood pouches. To test if this could be a direct consequence of the costs of reproduction, the survivorship of females was followed in the laboratory during and after the incubation period by rearing them at 13°C (1984) and 15°C (1985). Mortality was minimal during the incubation period, but increased gradually after the delivery of juveniles. However, we found no direct trade-off between reproduction and female survival. First, gravid females survived equally well (1984) or even better (1985) after the release of broods than did non-ovigerous females. Second, there was no clear trade-off between offspring production and survival among gravid females. In the first year, longevity was uncorrelated with brood size, whereas a statistically significant positive correlation was found in the second year. Since the results indicated no direct survival costs at the temperatures tested, our original working hypothesis presumably must be rejected. Instead, the present results seem to be consistent with a hypothesis that I. baltica females may adjust their egg production to avoid the survival costs of reproduction. This is a reasonable assumption, as any reduction in female survival during the incubation period would also increase the risk of failure in reproduction. A tactic for minimizing these risks could be an adjustment of egg production in relation to the resource reserves accumulated by females during maturation before the onset of breeding.

Components of Reproductive Effort in the Aquatic Isopod Idotea baltica

Condition index (CI), relating body weight to length, was used to indicate changes in body mass of the aquatic isopod Idotea baltica during maturation and breeding. The condition index of females increased during maturation and declined as eggs were deposited into brood pouches, whereas in males CI did not show such fluctuations. The condition index of gravid females differed significantly from that of non-ovigerous mature females but not from that of adult immature females. Thus reproduction of I. baltica is supported more by biomass accumulated during maturation than by resources drained from somatic growth. Therefore, we divided the total reproductive effort (RET) into accumulated resources (REA) and somatic costs (REs), and estimated these indices in terms of body weight changes in females. Since REA slightly exceeded RET, REs was negative and thus total effort is presumably restrained to a level at which somatic costs are not enough to cause significant survival costs of reproduction.

The Role of Reproduction and Life Histories in Models of Small Rodent Population Dynamics

Mammalian reproduction consists of internal fertilization, a period of intrauterine development, parturition, a period of postnatal dependence (lactation), and weaning. Quantitative aspects of this process include the time for development (both intrauterine and postnatal), the number of offspring raised, the age at maturation and the frequency of breeding. These characteristics are governed, within the constraints of morphology, physiology and genetics, by natural selection. Life historians have attempted to understand how organisms are adapted to their environments by considering age specific breeding patterns and the probability of reproductive success in relation to the survival costs of reproduction. Their studies have emphasized the constraints on reproductive patterns, the coevolved nature of reproductive characteristics, and the relationships between these patterns and nutritive resources or social systems (see Clutton-Brock and Harvey 1979, Zeveloff and Boyce 1980, Stearns 1983, Gittleman 1986, Harvey 1986 for examples). Population processes represent the cumulative effects of life history patterns. Many of the consequences of life histories (e.g. population growth) are too far removed from the immediate environment of organisms to be of great interest to life historians. Similarly, some aspects of life histories (e.g. neonatal weights and development) have no direct effects on population growth or density and are of little interest to population ecologists. Nevertheless, there are areas of mutual interest where improved communication may be beneficial. These comments will be restricted to life history principles that may be useful to population ecologists, particularly those who incorporate individual responses into their hypotheses. Reproductive processes are fueled by energy, with specific requirements dictated by the rate of metabolism and number of offspring raised. Among small mammals, reproduction is energetically expensive because basal metabolic rates are generally high (McNab 1986) and several young are produced per litter. Small mam-

Survival Costs of Reproduction in Grasshoppers

Survival Costs of Reproduction in Grasshoppers