RESUMEN
Reproductive investment decision is an integral part of life-history theory. Differential allocation hypothesis predicts that females should increase investment when mated to high-quality males, conversely, reproductive compensation hypothesis predicts that females should increase investment when mated to low-quality males. Empirical research dominantly focuses on polygamous species and rarely on serially monogamous species. So, the question remains: which hypothesis does serially monogamous species fit? And if it fits reproductive compensation hypothesis, do females only compensate once or continuously for multiple times when mating to low-quality males? Here, we used a serially monogamous fish, the lined seahorse (Hippocampus erectus), to investigate the reproductive investment pattern of females in relation to male quality (measured by sexual attractiveness). We found that females allocated more resources into eggs when they mated to less-sexually-attractive males, indicating the investment pattern of lined seahorse falls in with the prediction of reproductive compensation hypothesis. This finding may imply that the sex role of seahorses is reversed, and female is the side imposed on a greater sexual selection pressure. On this basis, we compared the investment difference of females in two consecutive breeding events when mated to less-sexually-attractive males. We found that females allocated less resources into eggs in the second breeding than in the first one. Females reduced their reproductive compensation in the second breeding, which may be attributed to the improvement in the quality (e.g., paternal care ability) of their mates after the first breeding, thus eliminating the need for them to invest more in the second breeding.
Asunto(s)
Reproducción , Conducta Sexual Animal , Smegmamorpha , Animales , Masculino , Femenino , Reproducción/fisiología , Conducta Sexual Animal/fisiología , Smegmamorpha/fisiología , Preferencia en el Apareamiento Animal/fisiología , Peces/fisiologíaRESUMEN
Bateman's principles heavily influence the understanding of human reproductive behaviour. Yet, few rigorous studies on Bateman's principles in contemporary industrialized populations exist. Most studies use small samples, exclude non-marital unions, and disregard recent insights on within-population heterogeneity in mating strategies. We assess mating success and reproductive success using population-wide Finnish register data on marital and non-marital cohabitations and fertility. We examine variability across social strata in the Bateman principles and analyse the mate count, the cumulated duration with a mate, and the association with reproductive success. Results support Bateman's first and second principles. Regarding Bateman's third principle, the number of mates is more positively associated with reproductive success for men than women, but this association is driven by ever having a mate. Having more than one mate is on average associated with lower reproductive success. However, for men in the lowest income quartile, having more than one mate positively predicts reproductive success. Longer union duration is associated with higher reproductive success, and more so for men. We note that sex differences in the relationship between mating success and reproductive success differ by social strata, and argue that mate duration may be an important component of mating success alongside mate count.
Asunto(s)
Fertilidad , Reproducción , Femenino , Humanos , Masculino , Finlandia , Comunicación CelularRESUMEN
Subsocial Cryptocercus cockroaches are the sister group to termites and considered to be socially monogamous. Because genetic monogamy is a suggested requirement for evolution of cooperative breeding/eusociality, particularly in hymenopterans, clarification of the mating biology of Cryptocercus would help illuminate evolutionary trends in eusocial insects. To investigate possible extra-pair paternity in C. punctulatus, microsatellite markers were used to analyse offspring parentage, the stored sperm in females and results of experimental manipulation of sperm competition. Extra-pair paternity was common in field-collected families, but a lack of maternal alleles in several nymphs suggests sampling error or adoption. Isolating prereproductive pairs and assaying subsequently produced nymphs confirmed that nymphs lacked alleles from the pair male in 40% of families, with extra-pair male(s) siring 27%-77% of nymphs. Sperm of extra-pair males was detected in the spermatheca of 51% of paired prereproductive females. Mate switching and surgical manipulation of male mating ability indicated a tendency towards last male sperm precedence. Overall, the results demonstrate that about half of young females are serially monogamous during their maturational year, but bond, overwinter and produce their only set of offspring in company of the last mated male (=pair male). Repeated mating by the pair male increases the number of nymphs sired, but because many females use stored sperm of previous copulatory partners to fertilize eggs, pair males extend parental care to unrelated nymphs. The results suggest that genetic monogamy either developed in the termite ancestor after splitting from the Cryptocercus lineage, or that genetic monogamy may not be a strict prerequisite for the evolution of termite eusociality.
Asunto(s)
Cucarachas , Paternidad , Animales , Cucarachas/genética , Copulación , Humanos , Conducta Sexual Animal , MaderaRESUMEN
Human marriage systems, characterized by long-term partnerships and extended windows of parental care, differ from the mating systems of pulsed or seasonally breeding non-human animals in which Bateman's principles were originally tested. These features, paradigmatic of but not unique to humans, complicate the accurate measurement of mating success in evaluating Bateman's three principles. Here, we unpack the concept of mating success into distinct components: number of partners, number of years partnered, the timing of partnerships, and the quality of partners. Drawing on longitudinal records of marriage and reproduction collected in a natural-fertility East African population over a 20-year period, we test and compare various models of the relationship between mating success and reproductive success (RS), and show that an accurate assessment of male and female reproductive behaviour requires consideration of all major components of mating success. Furthermore, we demonstrate that while Bateman's third principle holds when mating success is defined in terms of years married, women's fitness increases whereas men's fitness decreases from an increase in the number of marriage partners, holding constant the total effective duration of marriages. We discuss these findings in terms of the distinct, sex-specific pathways through which RS can be optimized, and comment on the contribution of this approach to the broader study of sexual selection.
Asunto(s)
Matrimonio/estadística & datos numéricos , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Femenino , Humanos , Masculino , Persona de Mediana Edad , Factores Sexuales , Tanzanía , Adulto JovenRESUMEN
Under life-history theories of ageing, increased senescence should follow relatively high reproductive effort. This expectation has rarely been tested against senescence varying between and within the two sexes, although such an approach may clarify the origins of sex-specific ageing in the context of a given mating system. Nazca boobies (Sula granti; a seabird) practise serial monogamy and biparental care. A male-biased population sex ratio results in earlier and more frequent breeding by females. Based on sex-specific reproductive schedules, females were expected to show faster age-related decline for survival and reproduction. Within each sex, high reproductive effort in early life was expected to reduce late-life performance and accelerate senescence. Longitudinal data were used to (a) evaluate the sex specificity of reproductive and actuarial senescence and then (b) test for early-/late-life fitness trade-offs within each sex. Within-sex analyses inform an interpretation of sex differences in senescence based on costs of reproduction. Analyses incorporated individual heterogeneity in breeding performance and cohort-level differences in early-adult environments. Females showed marginally more intense actuarial senescence and stronger age-related declines for fledging success. The opposite pattern (earlier and faster male senescence) was found for breeding probability. Individual reproductive effort in early life positively predicted late-life reproductive performance in both sexes and thus did not support a causal link between early-reproduction/late-life fitness trade-offs and sex differences in ageing. A high-quality diet in early adulthood reduced late-life survival (females) and accelerated senescence for fledging success (males). This study documents clear variation in ageing patterns-by sex, early-adult environment and early-adult reproductive effort-with implications for the role mating systems and early-life environments play in determining ageing patterns. Absent evidence for a disposable soma mechanism, patterns of sex differences in senescence may result from age- and condition-dependent mate choice interacting with this population's male-biased sex ratio and mate rotation.
Asunto(s)
Aves , Reproducción , Envejecimiento , Animales , Cruzamiento , Femenino , Masculino , Caracteres Sexuales , Razón de MasculinidadRESUMEN
Serial monogamy is likely an adaptive mating strategy for women when the expected future fitness gains with a different partner are greater than expected future fitness with one's current partner. Using interview data from more than 400 women in San Borja, Bolivia, discrete-time event history analyses and random effects regression analyses were conducted to examine predictors of marital dissolution, separated by remarriage status, and child educational outcomes. Male income was found to be inversely associated with women's risk of "divorce and remarriage," whereas female income is positively associated with women's risk of "divorce, but not remarriage." Children of women who divorce and remarry tend to have significantly lower educational outcomes than children of married parents, but women with higher incomes are able to buffer their children from the negative educational outcomes of divorce and remarriage. Counter to predictions, there is no evidence that women with kin in the community have a significant difference in likelihood of divorce or a buffering effect of child outcomes. In conclusion, predictors of divorce differ depending on whether the woman goes on to remarry, suggesting that male income may be a better predictor of a serial monogamy strategy whereas female income predicts marital dissolution only. Thus, women who are relatively autonomous because of greater income may not benefit from remarriage.
Asunto(s)
Crianza del Niño/etnología , Divorcio/etnología , Escolaridad , Renta , Matrimonio/etnología , Adulto , Bolivia/etnología , Niño , Femenino , Humanos , Persona de Mediana EdadRESUMEN
Fertility decline is a great challenge to evolutionary approaches to human behavior. In this study, we apply the perspective of sexual conflict between mother and father to the fertility decline. We predict that, under serial monogamy allowing for mate changes, the ideal number of children for women should be smaller than that for men, because the cost of reproduction for women should be higher than that for men. Our reasoning is that if the cost of child-bearing and child-rearing is higher for women than men, and if women, who therefore would want a smaller number of children than their husbands, have gained more power in reproductive decision-making within a couple owing to the modernization of society, fertility should decline. Until now, few evolutionary studies have analyzed empirical data in modern developed societies with such a perspective. Our questionnaire survey in an urban area in Japan revealed that mothers did experience greater cost during childcare than fathers. However, in contrast to our prediction, we found no sex differences in the ideal number of children between mothers and their husbands in many cases. About 60% of parents remembered wanting two children when they were childless. Moreover, mothers and their husbands had equal power in their decision-making regarding having children. After presenting these results, we discuss some perspectives to advance our understanding of fertility decline in terms of sexual conflict.
Asunto(s)
Composición Familiar/etnología , Padre , Madres , Población Urbana , Adulto , Femenino , Fertilidad , Humanos , Japón , Masculino , Encuestas y CuestionariosRESUMEN
This study examined the association of sexual debut and sexual partnering among men in the United States aged 21 to 44 years who participated in the 2006-2010 National Survey of Family Growth. Age at debut was categorized as <15 years, 15 to 17 years, and ≥18 years to permit comparison with previous research. Sexual partnering was defined as being concurrent, serial monogamist, or monogamist in prior year. Eleven percent reported concurrent partnerships and 6% serial monogamy. Sexual debut <15 and 15 to 17 years was associated with concurrency (adjusted odds ratio [aOR] < 15 = 2.22; 95% confidence interval [CI] = 1.37-3.61; aOR 15-17 = 1.69; 95% CI = 1.05-2.74). Irrespective of age at sexual debut, interventions to reduce risky lifetime number of partners may prevent risky sexual behavior in early adulthood and later in life.
Asunto(s)
Coito , Parejas Sexuales , Adolescente , Adulto , Factores de Edad , Encuestas Epidemiológicas , Humanos , Masculino , Estados Unidos , Adulto JovenRESUMEN
Having multiple sexual partners concurrently increases the risk of transmission of a sexually transmitted infection. Even if partnerships do not overlap, transmission potential exists when the gap between partnerships is shorter than the remaining infectious period. In the present article, we quantify the gap between partners to assess transmission potential using data collected by a cross-sectional survey of 2,203 genitourinary medicine clinic patients in England in 2009. Questionnaires asked about patients' 3 most recent partnerships. Gaps were calculated as time (days) between the last sexual encounter with a former partner and the first sexual encounter with the next partner. Among 1,875 patients who reported 1 or more partners in the previous 3 months, 47.6% of men and 27.7% of women reported 2 or more partners. Forty-two percent of the gaps were negative (i.e., partnerships that were concurrent); the median gaps were -7 and -17 days for men and women, respectively (i.e., overlaps were 7 and 17 days for men and women, respectively). Although half of the gaps were positive (serially monogamous partnerships), many were of short duration; the median gaps were 14 and 24 days for men and women, respectively. In over half of the gaps, condoms were used inconsistently with one or both partners, and in one-quarter, condoms were never used with either partner. There is thus a high potential for sexually transmitted infections, as even if partnerships are not behaviorally concurrent, they may be biologically concurrent. These data have important implications for designing and targeting effective health promotion messages.