Delayed Breeding Affects Lifetime Reproductive Success Differently in Male and Female Green Woodhoopoes

Life history theory suggests that reproduction at one point in time involves costs in terms of energy, reduced survival, or probability of reproduction at a future point in time. ln long-lived iteroparous organisms, initiating reproduction at a relatively young age may exact a cost in terms of reduced survivorship, but an early age of first reproduction could be beneficial if it lengthens the breeding lifespan. Data collected over 30 years from one population of rhesus macaques, Macaca mulatta, were analyzed to determine the fertility and survivorship costs of initiating reproduction at a relatively young age. Low population density and high social status increased the chances of accelerating age at first parturition, but high dominance rank was not associated with greater lifetime reproductive success. Rapid reproductive maturation neither reduced short-term survivorship nor decreased lifespan. Fertility costs arose if young females reared a male, but not female, offspring. The fitness consequences of rapid reproductive maturation depend upon longevity, with age at death having a significantly greater impact on lifetime reproductive success than age at first parturition.

Evolutionary biologists often argue that menopause evolved in the human female as the result of selection for a postreproductive phase of life, during which increased maternal investment in existing progeny could lead to enhanced survivorship of descendents. Adaptive theories relating menopause to enhanced maternal investment are known as the mother (first-generation) and grandmother (second-generation-offspring) hypotheses. Although menopause—universal midlife termination of reproduction—has not been documented in primates other than humans, some researchers have argued that postreproductive alloprimates also have a positive impact on the survivorship of first and second generation progeny. We tested the maternal investment hypotheses in Japanese macaques by comparing the survivorship of offspring, final infants, and great-offspring of females that terminated reproduction before death with females that continued to reproduce until death. SURVIVAL analyses revealed no significant difference in the survivorship of descendents of postreproductive and reproductive females, though final infants of postreproductive females were 13% more likely to survive than final infants of females that reproduced until death were. We also explored possible differences between these two groups of females, other than survivorship of progeny. We found no difference in dominance rank, matrilineal affiliation, body weight, infant sex ratio, age at first birth, fecundity rate or lifetime reproductive success. However, postreproductive females are significantly longer-lived than reproductive females and as a result experienced more years of reproduction and produced more infants in total. Apart from final infants, offspring survival is marginally lower in postreproductive females. Since offspring survival is not significantly enhanced in postreproductive females, the greater number of infants produced did not translate into greater lifetime reproductive success. Our findings fail to support the maternal investment hypotheses and instead suggest that reproductive termination in this population of Japanese macaques is most closely associated with enhanced longevity and its repercussions.

We investigated fitness, military rank and survival of facial phenotypes in large-scale warfare using 795 Finnish soldiers who fought in the Winter War (1939–1940). We measured facial width-to-height ratio—a trait known to predict aggressive behaviour in males—and assessed whether facial morphology could predict survival, lifetime reproductive success (LRS) and social status. We found no difference in survival along the phenotypic gradient, however, wider-faced individuals had greater LRS, but achieved a lower military rank.

Explaining variation in individual fitness is a key goal in evolutionary biology. Recently, telomeres, repeating DNA sequences capping chromosome ends, have gained attention as a biomarker for body state, physiological costs, and senescence. Existing research has provided mixed evidence for whether telomere length correlates with fitness, including survival and reproductive output. Moreover, few studies have examined how the rate of change in telomere length correlates with fitness in wild populations. Here, we intensively monitored an insular population of house sparrows, and collected longitudinal telomere and life history data (16 years, 1225 individuals). We tested whether telomere length and its rate of change predict fitness measures, namely survival, lifespan and annual and lifetime reproductive effort and success. Telomere length positively predicted short-term survival, independent of age, but did not predict lifespan, suggesting either a diminishing telomere length-survival correlation with age or other extrinsic factors of mortality. The positive association of telomere length with survival translated into reproductive benefits, as birds with longer telomeres produced more genetic recruits, hatchlings and reared more fledglings over their lifetime. In contrast, there was no association between telomere dynamics and annual reproductive output, suggesting telomere dynamics might not reflect the costs of reproduction in this population, potentially masked by variation in individual quality. The rate of change of telomere length did not correlate with neither lifespan nor lifetime reproductive success. Our results provide further evidence that telomere length correlates with fitness, and contribute to our understanding of the selection on, and evolution of, telomere dynamics.

ABsTRAc-r.-Recent studies have reported lifetime reproductive success (LRS) as empirical counts of fledglings, yearlings, or breeders produced by individuals during their lifetimes. In this paper, I show how the mean LRS of the breeding individuals of a population can be calculated from age-specific probabilities of survival and fecundity. An analysis of a simulated population shows that the LRS of males and females from the same population can be different, even though the rates of change in numbers of males and females are identical. Thus, although LRS may be a measure of individual fitness, differences in LRS, even among individuals with different phenotypes and genotypes, cannot be construed to have evolutionary significance. The proper measure of fitness is the Malthusian parameter (mrj). Received 5 March 1991, accepted 30 July 1991. THE ANALYSIS of data from long-term studies of marked birds has resulted in the measurement of lifetime reproductive success (LRS), which refers to the actual production of offspring of specific individuals (Brown 1988, Partridge 1989). Lifetime reproductive success is the product of an individual's reproductive life span (L), fecundity per reproductive year (F), and offspring survival (S; e.g. Brown 1988, Grafen 1988). Usually, investigators calculate the means and variances of LRS and its components (see studies in Clutton-Brock 1988a and Newton 1989a). There is general agreement that LRS is not a measure of Darwinian fitness (e.g. Grafen 1988, Newton 1989b, Partridge 1989). Nevertheless, Newton (1989b:441) suggested that it provides a better basis for estimating biological fitness than any other measure yet available, and Partridge (1989:435) indicated that it is probably a good approximation to [fitness] for many bird populations. In this paper I will show how the mean LRS of a group of breeders can be calculated from life-table probabilities and, having done that, I will discuss the evolutionary significance of lifetime reproductive success.

In iteroparous mammals, conditions experienced early in life may have long-lasting effects on lifetime reproductive success. Human-induced mortality is also an important demographic factor in many populations of large mammals and may influence lifetime reproductive success. Here, we explore the effects of early development, population density, and human hunting on survival and lifetime reproductive success in brown bear (Ursus arctos) females, using a 25-year database of individually marked bears in two populations in Sweden. Survival of yearlings to 2 years was not affected by population density or body mass. Yearlings that remained with their mother had higher survival than independent yearlings, partly because regulations prohibit the harvest of bears in family groups. Although mass as a yearling did not affect juvenile survival, it was positively associated with measures of lifetime reproductive success and individual fitness. The majority of adult female brown bear mortality (72%) in our study was due to human causes, mainly hunting, and many females were killed before they reproduced. Therefore, factors allowing females to survive several hunting seasons had a strong positive effect on lifetime reproductive success. We suggest that, in many hunted populations of large mammals, sport harvest is an important influence on both population dynamics and life histories.

Individual variation in lifetime reproductive success (number of weaned offspring in a lifetime) of female red squimels was studied in two populations in North Belgium for 8 yr. Fitness, the number of reproducing offspring, was calculated combining expected survival to reproductive age of dispersing young and reproductive performance of local recruits. Of 66 resident females, 20 (30%) never produced young. 89% of territorial females had offspring, while all non-territorial females failed to reproduce. Lifetime reproductive success of mothers (females that produced at least one weaned young) averaged 5.04 young (range 1-11), fitness averaged 2.07 (range 0.26-4.44). Both measures of reproductive success were strongly correlated (R 2 =0.73). Variation in fitness and lifetime reproductive success was mainly the consequence of variation in the number of litters produced. Variation in body condition, foot length (size) and territory quality explained 50% of variation in the number of litters. Variation in the number of young/litter, age at first breeding and year of birth were not significantly correlated with variation in lifetime reproductive success. We conclude that large, heavy females that established home ranges in food-rich areas live longer and produce more young than lighter, shorter-lived females living in poorer territories. and discuss the occurrence of chance-events affecting reproductive output in young and old squirrels

The mechanisms that contribute to variation in lifetime reproductive success are not well understood. One possibility is that telomeres, conserved DNA sequences at chromosome ends that often shorten with age and stress exposures, may reflect differences in vital processes or influence fitness. Telomere length often predicts longevity, but longevity is only one component of fitness and little is known about how lifetime reproductive success is related to telomere dynamics in wild populations. We examined the relationships between telomere length beginning in early life, telomere loss into adulthood and lifetime reproductive success in free-living house sparrows (Passer domesticus). We found that females, but not males, with longer telomeres during early life had higher lifetime reproductive success, owing to associations with longevity and not reproduction per year or attempt. Telomeres decreased with age in both sexes, but telomere loss was not associated with lifetime reproductive success. In this species, telomeres may reflect differences in quality or condition rather than the pace of life, but only in females. Sexually discordant selection on telomeres is expected to influence the stability and maintenance of within population variation in telomere dynamics and suggests that any role telomeres play in mediating life-history trade-offs may be sex specific.

Variance in reproductive success (sk2, with k = number of offspring) plays a large role in determining the rate of genetic drift and the scope within which selection acts. Various frameworks have been proposed to parse factors that contribute to sk2, but none has focused on age‐specific values of ϕ=sk2/k¯, which indicate the degree to which reproductive skew is overdispersed (compared to the random Poisson expectation) among individuals of the same age and sex. Instead, within‐age effects are generally lumped with residual variance and treated as “noise.” Here, an ANOVA sums‐of‐squares framework is used to partition variance in annual and lifetime reproductive success into between‐group and within‐group components. For annual reproduction, the between‐age effect depends on age‐specific fecundity (bx), but relatively few empirical data are available on the within‐age effect, which depends on ϕx. By defining groups by age‐at‐death rather than age, the same ANOVA framework can be used to partition variance in lifetime reproductive success (LRS) into between‐group and within‐group components. Analytical methods are used to develop null‐model expectations for random contributions to within‐group and between‐group components. For analysis of LRS, random variation in longevity appears as part of the between‐group variance, and effects (if any) of skip breeding and persistent individual differences contribute to the within‐group variance. Simulations are used to show that the methods for variance partitioning are asymptotically unbiased. Practical application is illustrated with empirical data for annual reproduction in American black bears and lifetime reproduction in Dutch great tits. Results show that overdispersed within‐age variance (1) dominates annual sk2 in both male and female black bears, (2) is the primary factor that reduces annual effective size to a fraction of the number of adults, and (3) represents most of the opportunity for selection. In contrast, about a quarter of the variance in LRS in great tits can be attributed to random variation in longevity, and most of the rest is due to modest differences in fecundity with age estimated for a single cohort of females. R code is provided that reads generic input files for annual and lifetime reproductive success and allows users to conduct variance partitioning with their own data.

Natural temperature variation across an optimal reproductive range for wild flies (Drosophila melanogaster) modulates the impact of sexual conflict on female fitness via asymmetric effects on pre- and post-copulatory male harm mechanisms.

Natural temperature variation across an optimal reproductive range for wild flies (Drosophila melanogaster) modulates the impact of sexual conflict on female fitness via asymmetric effects on pre- and post-copulatory male harm mechanisms.

Life-history theory states that reproductive events confer costs upon mothers. Many studies have shown that reproduction causes a decline in maternal condition, survival or success in subsequent reproductive events. However, little attention has been given to the prospect of reproductive costs being passed onto subsequent offspring, despite the fact that parental fitness is a function of the reproductive success of progeny. Here we use pedigree data from a pre-industrial human population to compare offspring life-history traits and lifetime reproductive success (LRS) according to the cost incurred by each individual's mother in the previous reproductive event. Because producing a son versus a daughter has been associated with greater maternal reproductive cost, we hypothesize that individuals born to mothers who previously produced sons will display compromised survival and/or LRS, when compared with those produced following daughters. Controlling for confounding factors such as socio-economic status and ecological conditions, we show that those offspring born after elder brothers have similar survival but lower LRS compared with those born after elder sisters. Our results demonstrate a maternal cost of reproduction manifested in reduced LRS of subsequent offspring. To our knowledge, this is the first time such a long-term intergenerational cost has been shown in a mammal species.

Polyandry and fitness in female horned flour beetles, Gnatocerus cornutus

Generation time determines the pace of key demographic and evolutionary processes. Quantified as the weighted mean age at reproduction, it can be studied as a life-history trait that varies within and among populations and may evolve in response to ecological conditions. We combined quantitative genetic analyses with age- and density-dependent models to study generation time variation in a bird metapopulation. Generation time was heritable, and males had longer generation times than females. Individuals with longer generation times had greater lifetime reproductive success but not a higher expected population growth rate. Density regulation acted on recruit production, suggesting that longer generation times should be favoured when populations are closer to carrying capacity. Furthermore, generation times were shorter when populations were growing and longer when populations were closer to equilibrium or declining. These results support classic theory predicting that density regulation is an important driver of the pace of life-history strategies.

A detailed analysis of singing performance of male Blue Tits is given, in relation to reproductive success and survival. Singing performance varied considerably between males and differences between males were probably retained from one year to the next. The lengths of 2 different song types were correlated but the size of the song repertoire was not correlated with song length. Two kinds of song features other than repertoire size, a measure of length and the rate at which the song slows down, seemed to reflect singing capacity. Males with longer songs survived better but there was no evidence that they had a greater lifetime reproductive success. Survival and reproductive success were not correlated with various measures of body size.