Status,reproductive success,and marrying polygynously

A study of female reproductive histories from nineteenth-century Utah shows that although women who married polygynously had fewer children, their number of grandchildren was equal to that of women who married monogamously. Women who chose to marry high-status men polygynously traded decreased fertility for enhanced reproductive performance of offspring. High status can be associated with low fertility and yet still be consistent with fitness optimization. These results suggest how female reproductive decisions influence social structure and challenge previous assumptions concerning proximate measures of fitness.     

Handedness and reproductive success in two large cohorts of French adults

Left- and right-handers in humans coexist at least since the Paleolithic, and this variation in hand preference has a heritable basis. Because there is extensive evidence of an association between left-handedness and several fitness costs, the persistence of the polymorphism requires an explanation. It is not known whether the frequency of left-handedness in Western societies is stable or not. If the polymorphism is at equilibrium and maintained by frequency dependence, it implies that the fitness of left-handers equals that of right-handers. On the contrary, if left- and right-handers have a different fitness, the polymorphism will evolve. Using two large cohorts of French adults (men and women), we investigated the relations between handedness and several estimators of the reproductive value: marital status, number of sexual partners (of the opposite sex), number of children, and number of grandchildren. Left-handers seem to have disadvantages for some life-history traits, such as marital status (for women) and number of children. For other traits, we observed sex-dependent interactions with socioeconomic status: for high-income categories, left-handed women report less sex partners and left-handed men have more grandchildren. These kinds of interactions are to be expected under the hypothesis that the polymorphism of handedness is stable.     

Reproductive measures, fitness, and migrating Mennonites: an evolutionary analysis

Given the same reproductive span, more children with shorter interbirth intervals and less parental attention per child should not do as well. There should be intermediate optima in family sizes, but only two studies have demonstrated optima. The goal here is to determine whether the relationship between fitness and fertility is linear and whether this relationship masks underlying variation in reproductive behaviors in a Mennonite congregation that lived in two disease settings, Prussia/Russia vs. Kansas. The relationships between children born and fitness were determined by calculating linear and quadratic regressions for total, Prussia/Russia vs. Kansas, and families with deaths vs. families with no deaths for total, Prussia/Russia, and Kansas. Variation was examined in terms of measures of reproductive success and reproductive span. Comparisons were made by t tests with Bonferroni correction. Regressions demonstrate equally well that the more children women bear, the higher the reproductive success, whether in the harsher disease ecology of rural Prussia/Russia or in less challenging rural Kansas and whether the women experience deaths or not. Prussian/Russian mothers bore significantly more children (6.5+/-0.3) than Kansan mothers (5.6+/-0.2) over longer reproductive spans but did not significantly increase the number of surviving children (4.9+/-0.2 vs. 4.7+/-0.2, respectively). Families experiencing deaths vs. no deaths exhibit significantly longer reproductive spans, reflecting a significantly earlier start at childbearing and a later finish, and produce significantly more children (5.4+/-0.2 vs. 4.2+/-0.2). Cox regressions were run, and the most significant covariates to negatively affect survivorship to 15 years were death in the family and length of the previous interbirth intervals. There was variation in families, but perhaps most had adequate nutrition, which may explain the lack of optima in fitness.     

Personality and long-term reproductive success measured by the number of grandchildren

Personality, that is, individual behavioral tendencies that are relatively stable across situations and time, has been associated with number of offspring in many animals, including humans, suggesting that some personality traits may be under natural selection. However, there are no data on whether these associations between personality and reproductive success extend over more than one generation to numbers of grandchildren. Using a large representative sample of contemporary Americans from the Health and Retirement Study (n = 10,688; mean age 67.7 years), we studied whether personality traits of the Five Factor Model were similarly associated with number of children and grandchildren, or whether antagonistic effects of personality on offspring number and quality lead to specific personality traits differently maximizing short and long-term fitness measures. Higher extraversion, lower conscientiousness, and lower openness to experience were similarly associated with both higher number of children and grandchildren in both sexes. In addition, higher agreeableness was associated with higher number of grand-offspring only. Our results did not indicate any quality–quantity trade-offs in the associations between personality and reproductive success. These findings represent the first robust evidence for any species that personality may affect reproductive success over several generations.     

Social and biological determinants of reproductive success in Swedish males and females born 1915–1929

Studying biological and social determinants of mortality and fertility provides insight into selective pressures in a population and the possibility of trade-offs between short- and long-term reproductive success. Limited data is available from post-demographic transition populations. We studied determinants of reproductive success using multi-generational data from a large, population-based cohort of 13,666 individuals born in Sweden between 1915 and 1929. We studied the effects of birthweight for gestational age, preterm birth, birth multiplicity, birth order, mother's age, mother's marital status and family socioeconomic position (SEP) upon reproductive success, measured as total number of children and grandchildren. We further tested the hypothesis that number of grandchildren would peak at intermediate family size, as predicted by some life history explanations for fertility limitation. Reproductive success was associated with both social and biological characteristics at birth. In both sexes, a higher birthweight for gestational age, a term birth and a younger mother were independently associated with a greater number of descendants. A married mother and higher family SEP were also associated with a greater number of descendants in males (but not in females), while higher birth order was associated with a greater number of descendents in females (but not males). These effects were mediated by sex-specific effects upon the probability of marriage. Marriage was also affected by other early life characteristics including birthweight, indicating how ‘biological’ characteristics may operate via social pathways. Number of grandchildren increased with increasing number of children in both sexes, providing no evidence for a trade-off between quantity of offspring and their subsequent reproductive ‘quality’.     

Invasion fitness,inclusive fitness,and reproductive numbers in heterogeneous populations

How should fitness be measured to determine which phenotype or “strategy” is uninvadable when evolution occurs in a group‐structured population subject to local demographic and environmental heterogeneity? Several fitness measures, such as basic reproductive number, lifetime dispersal success of a local lineage, or inclusive fitness have been proposed to address this question, but the relationships between them and their generality remains unclear. Here, we ascertain uninvadability (all mutant strategies always go extinct) in terms of the asymptotic per capita number of mutant copies produced by a mutant lineage arising as a single copy in a resident population (“invasion fitness”). We show that from invasion fitness uninvadability is equivalently characterized by at least three conceptually distinct fitness measures: (i) lineage fitness, giving the average individual fitness of a randomly sampled mutant lineage member; (ii) inclusive fitness, giving a reproductive value weighted average of the direct fitness costs and relatedness weighted indirect fitness benefits accruing to a randomly sampled mutant lineage member; and (iii) basic reproductive number (and variations thereof) giving lifetime success of a lineage in a single group, and which is an invasion fitness proxy. Our analysis connects approaches that have been deemed different, generalizes the exact version of inclusive fitness to class‐structured populations, and provides a biological interpretation of natural selection on a mutant allele under arbitrary strength of selection.     

Month of birth predicted reproductive success and fitness in pre-modern Canadian women

Conditions experienced during early development affect human health and survival in adulthood, but whether such effects have consequences for fitness is not known. One surrogate for early conditions is month of birth, which is known to influence health and survival in many human populations. We show that in nineteenth century Canada, month of birth predicted a woman's fitness measured by the number of grandchildren produced, with the genetic contribution to the following generations by women born in different months differing by over seven grandchildren. This difference was mainly caused by differences in the reproductive rates of both mothers and their offspring, rather than differences in their survival. Women born in the best months of the year had longer reproductive lifespans, larger numbers of live births and raised more offspring to adulthood than those who were born in the worst months. Furthermore, the offspring of those women born in the best months also had greater reproductive rates, suggesting that month of birth also influenced a mother's ability to invest in her offspring. Our results suggest that early conditions may have important consequences for human lifetime reproductive performance within and between generations, and that timing of birth had large effects on fitness in this rural community.     

Associations of muscular fitness with psychological positive health, health complaints, and health risk behaviors in Spanish children and adolescents

We examined the association of muscular fitness with psychological positive health, health complaints, and health risk behaviors in 690 (n = 322 girls) Spanish children and adolescents (6-17.9 years old). Lower body muscular strength was assessed with the standing long jump test, and upper-body muscular strength was assessed with the throw basketball test. A muscular fitness index was computed by means of standardized measures of both tests. Psychosocial positive health, health complaints, and health risk behaviors were self-reported using the items of the Health Behavior in School-aged Children questionnaire. Psychological positive health indicators included the following: perceived health status, life satisfaction, quality of family relationships, quality of peer relationships, and academic performance. We computed a health complaints index from 8 registered symptoms: headache, stomach ache, backache, feeling low, irritability or bad temper, feeling nervous, difficulties getting to sleep, and feeling dizzy. The health risk behavior indicators studied included tobacco use, alcohol use, and getting drunk. Children and adolescents with low muscular fitness (below the mean) had a higher odds ratio (OR) of reporting fair (vs. excellent) perceived health status, low life satisfaction (vs. very happy), low quality of family relationships (vs. very good), and low academic performance (vs. very good). Likewise, children and adolescents having low muscular fitness had a significantly higher OR of reporting smoking tobacco sometimes (vs. never), drinking alcohol sometimes (vs. never), and getting drunk sometimes (vs. never). The results of this study suggest a link between muscular fitness and psychological positive health and health risk behavior indicators in children and adolescents.     

Physiological dynamics,reproduction‐maintenance allocations,and life history evolution

Allocation of resources to competing processes of growth, maintenance, or reproduction is arguably a key process driving the physiology of life history trade‐offs and has been shown to affect immune defenses, the evolution of aging, and the evolutionary ecology of offspring quality. Here, we develop a framework to investigate the evolutionary consequences of physiological dynamics by developing theory linking reproductive cell dynamics and components of fitness associated with costly resource allocation decisions to broader life history consequences. We scale these reproductive cell allocation decisions to population‐level survival and fecundity using a life history approach and explore the effects of investment in reproduction or tissue‐specific repair (somatic or reproductive) on the force of selection, reproductive effort, and resource allocation decisions. At the cellular level, we show that investment in protecting reproductive cells increases fitness when reproductive cell maturation rate is high or reproductive cell death is high. At the population level, life history fitness measures show that cellular protection increases reproductive value by differential investment in somatic or reproductive cells and the optimal allocation of resources to reproduction is moulded by this level of investment. Our model provides a framework to understand the evolutionary consequences of physiological processes underlying trade‐offs and highlights the insights to be gained from considering fitness at multiple levels, from cell dynamics through to population growth.     

Ecological reproductive isolation of coast and inland races of Mimulus guttatus

Adaptive divergence due to habitat differences is thought to play a major role in formation of new species. However it is rarely clear the extent to which individual reproductive isolating barriers related to habitat differentiation contribute to total isolation. Furthermore, it is often difficult to determine the specific environmental variables that drive the evolution of those ecological barriers, and the geographic scale at which habitat-mediated speciation occurs. Here, we address these questions through an analysis of the population structure and reproductive isolation between coastal perennial and inland annual forms of the yellow monkeyflower, Mimulus guttatus. We found substantial morphological and molecular genetic divergence among populations derived from coast and inland habitats. Reciprocal transplant experiments revealed nearly complete reproductive isolation between coast and inland populations mediated by selection against immigrants and flowering time differences, but not postzygotic isolation. Our results suggest that selection against immigrants is a function of adaptations to seasonal drought in inland habitat and to year round soil moisture and salt spray in coastal habitat. We conclude that the coast and inland populations collectively comprise distinct ecological races. Overall, this study suggests that adaptations to widespread habitats can lead to the formation of reproductively isolated species.     

FREQUENCY-DEPENDENT SEED PRODUCTION AND HYBRIDIZATION RATES: IMPLICATIONS FOR GENE FLOW BETWEEN LOCALLY ADAPTED PLANT POPULATIONS

Gene flow between genetically distinct plant populations can have significant evolutionary consequences. It can increase genetic diversity, create novel gene combinations, and transfer adaptations from one population to another. This study addresses the roles of frequency-dependent selection and mating system in gene exchange between two subspecies of Gilia capitata (Polemoniaceae). Long-distance migrants are likely to be rare in new habitats, and the importance of immigrant frequency to fitness, gene exchange, and ultimately introgression, has not been explored. To test for the importance of frequency in migration, a field experiment was conducted in which artificial populations (arrays) composed of different mixtures of the two subspecies were placed in the home habitats of both. Female function (seed production) and a portion of male function (hybridization rate) were compared for the two subspecies to assess the potential for gene exchange and introgression between them. Individual fitness (through both hybridization and seed production) for the inland subspecies varied with its frequency as an immigrant at the coastal site. Rare immigrants produced fewer seeds and fathered fewer hybrid offspring. In contrast, both forms of reproductive function were frequency independent for the coastal subspecies when it was an immigrant at the inland site. Seed production was high and insensitive to frequency, and immigrants from the coast never successfully fertilized the inland subspecies' seeds. To control for the effects of frequency-dependent pollinator behavior in the field, hand crosses were performed in the greenhouse using a range of pollen mixtures. The greenhouse experiment demonstrated that cross-fertilization is possible in only one direction, that cross-pollination in the other direction is only partially successful, and that pollen from the coastal subspecies has a strong negative effect on seed production by the inland subspecies. Experimental pollen supplementation in the field verified both the unilateral incompatibility and the negative effect of coastal pollen on inland plant seed production observed in the greenhouse. Contrasts between field array and greenhouse results suggest that pollinator behavior and other ecological factors act to exaggerate reproductive barriers between the two subspecies. In this system, immigrant frequency interacts with reproductive biology and pollinator ecology to enhance gene flow between the populations in one direction, while restricting gene establishment and introgression in the other direction.     

LOCAL ADAPTATION IN TWO SUBSPECIES OF AN ANNUAL PLANT: IMPLICATIONS FOR MIGRATION AND GENE FLOW

Plant populations often adapt to local environmental conditions. Here we demonstrate local adaptation in two subspecies of the California native annual Gilia capitata using standard reciprocal transplant techniques in two sites (coastal and inland) over three consecutive years. Subspecies performance in each site was measured in four ways: probability of seedling emergence, early vegetative size (length of longest leaf), probability of flowering, and total number of inflorescences produced per plant. Analysis of three of the four variables demonstrated local adaptation through site-by-subspecies interactions in which natives outperformed immigrants. The disparity between natives and immigrants in their probability of emergence and probability of flowering was greater at the coastal site than at the inland site. Treated in isolation, these two fitness components suggest that migration from the coast to the inland site may be less restricted by selection than migration in the opposite direction. Two measurements of individual size (leaf length and number of inflorescences), suggest (though not strongly) that immigrants may be subject to weaker selection at the coastal site than at the inland site. A standard cohort life table is used to compare replacement rates (R₀) for each subspecies at each site. Comparisons of R₀s suggest that immigrants are under a severe demographic disadvantage at the coastal site, but only a small disadvantage at the inland site. The results point out the importance of integrating over several fitness components when documenting the magnitude of local adaptation.     

Conditional Grandmother Effects on Age at Marriage, Age at First Birth, and Completed Fertility of Daughters and Daughters-in-law in Historical Krummh?rn

Based on historical data pertaining to the Krummh?rn population (eighteenth and nineteenth centuries, Germany), we compared reproductive histories of mothers according to whether the maternal grandmother (MGM) or the paternal grandmother (PGM) or neither of them was resident in the parents' parish at the time of the mother's first birth. In contrast to effects of PGMs, we discovered conditional differences in the MGM's effects between landless people and wealthier, commercial farmers. Our data indicate that the presence of the MGM only lowers the woman's age at marriage (AAM) and her age at the birth of her first child (AFB) in the case of landless families. However, among commercial farmers, who can generally be characterized by a lower AAM and AFB, we found opposite tendencies for the MGM's effect leading to a relatively small delay in AAM and AFB. Moreover, we also analyzed differences in the completed fertility (i.e., children ever born: CEB). Results indicate that landless families in general do have fewer CEB compared with commercial farmers except for those families in which the MGM has been present. Emphasizing that the adaptiveness of investment decisions should depend on the interaction of genetic, lineage-specific (intrinsic) and ecologically imposed (extrinsic) constraints, we conclude that kin strategies consequently address different fitness components under different conditions.     

The effect of school performance upon marriage and long-term reproductive success in 10,000 Swedish males and females born 1915–1929

Humans are an exceptionally intelligent species, and the selective pressures which may have shaped these advanced cognitive powers are therefore of interest. This study investigates the fitness consequences of pre-reproductive school performance in a Swedish population-based cohort of 5244 males and 4863 females born 1915-1929. School performance was measured at around age 10 using three variables: mean school marks, being promoted/held back in school, and recognised learning difficulties. Our primary outcomes were probability of ever marrying, total number of children and total number of grandchildren. In males (but not females), poorer school performance predicted fewer children and grandchildren. This was primarily mediated via probability of marriage; mortality and fertility within marriage were not important mediating pathways. The effect of school performance upon marriage in males was independent of early-life social and biological characteristics, including birth weight for gestational age, preterm birth, family composition, and family socioeconomic position. The effect of school performance upon the probability of marriage in males was, however, largely mediated by adult socioeconomic position. This suggests that in general sexual selection for cognitive abilities per se did not play a major role in either males or females in this cohort. Adult socioeconomic position did not, however, fully explain the marriage disadvantage in males or (at marginal significance) females with particularly poor school performance. We conclude that school performance can affect long-term reproductive success. In this population, however, the effect is confined to males and is largely mediated by the increased probability of marriage which comes with their greater socioeconomic success.     

Adaptive walks through fitness landscapes for early vascular land plants

Hypothetical adaptive walks (i. e., morphological transformation series gaining increasing relative fitness) were simulated through a computer-generated domain for early vascular land plant morphologies to examine the relationship between the dynamics of adaptive walks and the topologies of fitness landscapes. A total of 15 hypothetical adaptive walks were simulated, assuming that relative fitness was based on performing one or more of four biological tasks: maximizing light interception, mechanical stability, and reproductive success, and minimizing total surface area. Morphologies occupying fitness peaks typically were similar to some early vascular land plant remains. The most stringent task (the minimization of total surface area) resulted in a few, comparatively small Y-shaped morphologies. Based on the 15 walks, the number of fitness peaks increased and their heights decreased as the number of tasks simultaneously performed increased. These results (which are consistent with prior computer-simulated walks treating light interception, mechanical stability, and reproductive success) suggest that the biological requirement to conserve water reduced the number of phenotypic options available to the earliest land plants, and that, once this adaptive hurtle was overcome, the simultaneous performance of two or more tasks, increased the number of phenotypic options with equivalent relative fitnesses that could be rapidly reached due to the comparatively small fitness differential between derived and ancestral morphologies.     

Resource competition and reproduction

A family reconstitution study of the Krummhörn population (Ostfriesland, Germany, 1720–1874) reveals that infant mortality and children’s probabilities of marrying or emigrating unmarried are affected by the number of living same-sexed sibs in farmers’ families but not in the families of landless laborers. We interpret these results in terms of a “local resource competition” model in which resource-holding families are obliged to manipulate the reproductive future of their offspring. In contrast, families that lack resources have no need to manipulate their offspring and are more likely to benefit from allowing their offspring to capitalize on whatever opportunities to reproduce present themselves.     

Do baseline glucocorticoids simultaneously represent fitness and environmental quality in a declining aerial insectivore?

Glucocorticoids (GCs) are often interpreted as indicators of disturbance, habitat quality, and fitness in wild populations. However, since most investigations have been unable to examine habitat variability, GC levels, and fitness simultaneously, such interpretations remain largely unvalidated. We combined a quantification of two habitat types, a manipulation of foraging ability (feather‐clipping just prior to nestling rearing), multiple baseline plasma GC measures, and multi‐year reproductive monitoring to experimentally examine the linkages between habitat quality, GCs, and fitness in female tree swallows Tachycineta bicolor. Control females experiencing the higher early‐season food resources of inland–pasture habitat laid larger clutches, but fledged an equal number but lower mass offspring compared to those in riparian–cropland habitat. Despite these differences in reproductive success, females nesting in the two habitat types did not differ in baseline GC levels at the early‐ or late‐breeding stage. Feather‐clipping reduced provisioning rate in both habitat types. However, baseline GC levels were affected in a habitat‐specific way; only individuals in inland–pasture habitats showed an increase in GCs. Despite this difference in GC levels, the manipulation did not influence offspring mass, reproductive output, adult return rate (a proxy for survival) to the following year, or reproductive success in the subsequent year. Nonetheless, regardless of treatment, individuals with higher GC levels during the late breeding stage returned in the following year with higher GC levels at incubation, indicating a long‐term effect on future GC levels. Our results indicate that environmental changes (e.g. foraging conditions) can have consequences for body condition, behaviour, and current and future baseline GC levels without concomitant influences on fitness, and that differences in fitness components between habitats may not be reflected in baseline GC levels. These results illustrate that baseline GCs may not simultaneously reflect environmental quality and fitness, potentially limiting their application in ecological and conservation settings.     

When fecundity does not equal fitness: evidence of an offspring quantity versus quality trade-off in pre-industrial humans

Maternal fitness should be maximized by the optimal division of reproductive investment between offspring number and offspring quality. While evidence for this is abundant in many taxa, there have been fewer tests in mammals, and in particular, humans. We used a dataset of humans spanning three generations from pre-industrial Finland to test how increases in maternal fecundity affect offspring quality and maternal fitness in contrasting socio-economic conditions. For 'resource-poor' landless families, but not 'resource-rich' landowning families, maternal fitness returns diminished with increased maternal fecundity. This was because the average offspring contribution to maternal fitness declined with increased maternal fecundity for landless but not landowning families. This decline was due to reduced offspring recruitment with increased maternal fecundity. However, in landowning families, recruited offspring fecundity increased with increased maternal fecundity. This suggests that despite decreased offspring recruitment, maternal fitness is not reduced in favourable socio-economic conditions due to an increase in subsequent offspring fecundity. These results provide evidence consistent with an offspring quantity-quality trade-off in the lifetime reproduction of humans from poor socio-economic conditions. The results also highlight the importance of measuring offspring quality across their whole lifespan to estimate reliably the fitness consequences of increased maternal fecundity.     

Inbred women in a small and isolated Swiss village have fewer children

Despite overwhelming evidence for a negative effect of inbreeding on fitness in plants and nonhuman animals, the exact nature of its effect in humans remains subject to debate. To obtain a better understanding of the effects of inbreeding on reproductive success in humans, we reconstructed the genealogies of the current inhabitants of a small and isolated Swiss village and used these to estimate the level of inbreeding of both members of all married couples, as well as their relatedness (i.e. the level of inbreeding of their offspring). Although there was no effect of parental relatedness on the number of children a couple had, we found that inbred mothers, but not inbred fathers, had significantly fewer children. Thus, although related couples did not have fewer children themselves, their inbred daughters did leave them with fewer grandchildren. Thereby, we provide evidence for the existence of inbreeding depression in human fertility, also in relatively outbred and egalitarian communities.     

Shared patterns of species turnover between seaweeds and seed plants break down at increasing distances from the sea

We tested for correlations in the degree of spatial similarity between algal and terrestrial plants communities along 5500 km of temperate Australian coastline and whether the strength of correlation weakens with increasing distance from the coast. We identified strong correlations between macroalgal and terrestrial plant communities within the first 100 km from shore, where the strength of these marine–terrestrial correlations indeed weakens with increasing distance inland. As such, our results suggest that marine‐driven community homogenization processes decompose with increasing distance from the shore toward inland. We speculate that the proximity to the marine environment produces lower levels of community turnover on land, and this effect decreases progressively farther inland. Our analysis suggests underlying ecological and evolutionary processes that give rise to continental‐scale biogeographic influence from sea to land.