Polygyny and fertility in Morocco: the effect of marital instability

This paper analyses the relationship between polygyny and female fertility in the province of Marrakech (Morocco) taking into account the effect of the previous marital instability (number of marriages) and the possible association between female sterility and type of marriage. In the analysed population, polygyny increases in the small towns. Polygynously married women have a higher level of education and show a higher percentage of use of contraceptive methods than the monogamously married ones. Although polygynously married women initially show lower fertility, multivariate analysis carried out on the group of women between 35 and 49 years old show that there are no significant differences in fertility between monogamously and polygynously married women when the effect of the previous marital instability is considerer. Female sterility does not determine marital instability, although it does determine a significant increase in polygynous marriages among the women without children.     

A Survey of Non-Classical Polyandry

We have identified a sample of 53 societies outside of the classical Himalayan and Marquesean area that permit polyandrous unions. Our goal is to broadly describe the demographic, social, marital, and economic characteristics of these societies and to evaluate some hypotheses of the causes of polyandry. We demonstrate that although polyandry is rare it is not as rare as commonly believed, is found worldwide, and is most common in egalitarian societies. We also argue that polyandry likely existed during early human history and should be examined from an evolutionary perspective. Our analysis reveals that it may be a predictable response to a high operational sex ratio favoring males and may also be a response to high rates of male mortality and, possibly, male absenteeism. Other factors may contribute, but our within-polyandry sample limits analysis.     

Correcting contraceptive failure rates for sample composition and sample selection bias

Abstract

There is reason to believe that in the short run marriages are becoming more stable in some Western African countries such as Cameroon. One of the crucial questions facing these countries is whether fertility rates can be expected to increase or decrease due in part to the increased stability of marriages. Analyzing 1978 Cameroon World Fertility Survey data and using a multivariate regression model which compares the fertility rate of women who have had at least one marital disruption with that of continuously married women, we studied the relationship between marital instability and fertility. The results show that fertility rates for women married more than once are significantly lower than those for continuously married women even before the end of their first marriage. Furthermore, marital disruption significantly reduces fertility rates after the dissolution of the first marriage. Finally, even after the length of reproductive time lost is controlled, there is an inverse relationship between the number of marriages and fertility. The results are discussed in the context of economic development, modernization, and urbanization.     

The influence of social niche on cultural niche construction: modelling changes in belief about marriage form in Taiwan

With introduction of social niche effects into a model of cultural change, the frequency of a practice cannot predict the frequency of its underlying belief. The combination of a general model with empirical data from a specific case illustrates the importance of collaboration between modellers and field researchers, and identifies the type of quantitative data necessary for analysing case studies. Demographic data from colonial-period household registers in Taiwan document a shift in marriage form within 40 years, from a mixture of uxorilocal marriages and virilocal marriages to the latter's dominance. Ethnographic data indicate marriage-related beliefs, costs, ethnic effects and colonial policies as well as the importance of horizontal cultural transmission. We present a formal model for the effects of moral beliefs about marriage and a population economic index on the decline of uxorilocal marriage. We integrate empirical marriage rates and an estimated economic index to produce five projections of the historical frequencies of one belief. These projections demonstrate how economic development may affect a cultural niche. They also indicate the need for future research on the relationship between wealth and cultural variability, the motivational force of cultural versus social factors, and the process of cultural niche construction.     

Determinants of marital behaviour in five Apennine communities of Central Italy inferred by surname analysis,repeated pairs and kinship estimates

The work makes use of surname analysis, repeated pairs and kinship estimates in 11,009 marriage records celebrated in five communities of the Italian Central Apennine (Celano, Lecce dei Marsi, Ortucchio, Roio, Villavallelonga) from 1802 to 1965 with the objective to deepen knowledge of the relative influence of several determinants on their marital behaviour. These towns are part of the same geographic and economic environment: the slopes of the ancient Fucino Lake. This work further elaborates the results from previous studies on the bio-demographic model of the region. The data were analyzed according to three periods of approximately 50 years. Results show the highest inbreeding coefficients in the pastoral towns of Roio and Villavallelonga. Repeated pair analysis highlights a certain degree of population subdivision which declined in time in Celano, Lecce dei Marsi and Ortucchio. The highest and increasing values of RP-RPr in time in Roio suggest a general reduction in genetic heterogeneity. This is possibly due to the celebration of marriages among families selected on the economic basis of pastoralism, as this town historically has had a leading tradition of sheep-farming. Villavallelonga, excluding isonymous marriages, shows an increase in repeated pair unions in time, thus revealing a substructure with marriages among preferred lineages. This is in line with previous results on consanguineous marriages which indicated the tendency of avoiding unions between close relatives in this small geographic isolate. This study demonstrates the influence of geographical (altitude) and social factors (pastoralism) on the marital structures of the investigated populations.     

DO WOLBACHIA‐ASSOCIATED INCOMPATIBILITIES PROMOTE POLYANDRY?

The genetic incompatibility avoidance hypothesis as an explanation for the polyandrous mating strategies (mating with more than one male) of females of many species has received significant attention in recent years. It has received support from both empirical studies and a meta-analysis, which concludes that polyandrous females enjoy increased reproductive success through improved offspring viability relative to monandrous females. In this study we investigate whether polyandrous female Drosophila simulans improve their fitness relative to monandrous females in the face of severe Wolbachia-associated reproductive incompatibilities. We use the results of this study to develop models that test the predictions that Wolbachia should promote polyandry, and that polyandry itself may constrain the spread of Wolbachia. Uniquely, our models allow biologically relevant rates of incompatibility to coevolve with a polyandry modifier allele, which allows us to evaluate the fate of the modifier and that of Wolbachia. Our empirical results reveal that polyandrous females significantly reduce the reproductive costs of Wolbachia, owing to infected males being poor sperm competitors. The models show that this disadvantage in sperm competition can inhibit or prevent the invasion of Wolbachia. However, despite the increased reproductive success obtained by polyandrous females, the spread of a polyandry modifier allele is constrained by any costs that might be associated with polyandry and the low frequency of incompatible matings when Wolbachia has reached a stable equilibrium. Therefore, although incompatibility avoidance may be a benefit of polyandry, our findings do not support the hypothesis that genetic incompatibilities caused by Wolbachia promote the evolution of polyandry.     

Is polygyny a risk factor for poor growth performance among Tanzanian agropastoralists?

Anthropologists and demographers have devoted considerable attention to testing the fertility-polygyny hypothesis, which posits that polygynously married women have lower fertility than their monogamously married counterparts. Much less attention has been paid to the potential impact of polygynous marriages on the health and well-being of children. The objective of this paper was to assess whether polygynous marital status is a risk factor for poor nutritional status and growth performance among a cohort of young Tanzanian children. Using data collected from both wet and dry season periods, we tested for an association from both cross-sectional and longitudinal perspectives. Despite relatively high nutritional status compared to other agropastoralists and horticultural populations, as well as the presence of various socioecological factors that were expected to mitigate any "costs" to polygynous marriage, we found that among our target population, polygynous marital status is a risk factor for poor growth performance. This association is most pronounced in the wet season, and maintains even after allowing for the potential influences of child age and sex, and household characteristics. These results counter our original expectation, and suggest that polygyny is costly to children in this population; this does not appear to be the result of difference in early child environment or household wealth.     

Does Marriage Really Matter to Health? Intra- and Inter-Country Evidence from China,Japan, Taiwan,and the Republic of Korea

Background

The health benefits of marriage have been demonstrated mainly by studies on Western populations. This study aims to test whether the benefits are also valid in East Asian populations.

Methodology/Principal Findings

Individuals (n = 8,538) from China, Japan, Taiwan, and the Republic of Korea were sampled from the 2006 East Asian Social Survey. The association between self-rated health status and two marriage-related independent variables was analyzed using multivariate logistic regression models. In a two-level analysis for individuals from all countries, married individuals were more likely to report very good or good health compared to their never-married counterparts [odds ratio (OR) 1.56; 95% confidence interval (95% CI) 1.16−2.10]. However, the addition of marital satisfaction disintegrated the significant association of marriage with self-rated health. Married individuals in satisfying marriages were more likely to report very good or good health compared with never-married individuals (OR 1.85; 95% CI 1.37−2.50). In contrast, married individuals in dissatisfying marriages were as likely to report very good or good health as never-married individuals (OR 0.78; 95% CI 0.50−1.24). In a one-level analysis for each country, the importance of marital satisfaction varied greatly across countries. Unlike in other countries, in Japan, married individuals in dissatisfying marriages were about half as likely to report very good or good health as never-married individuals (OR 0.51, 95% CI 0.31−0.83), thereby showing no significant benefits from marriage with regard to self-rated health.

Conclusion/Significance

The present study of East Asian countries suggests that marital satisfaction is of greater importance in determining self-rated health than marriage itself, and that the importance of marital satisfaction varies across countries. Further research is required to better understand the relationship between marital satisfaction and self-rated health in different socio-cultural settings, and to establish effective social policies aiming at improving public health.     

THE CHARACTERISTICS AND OCCURRENCE OF COOPERATIVE POLYANDRY

This paper discusses the relative position of cooperative polyandry among models for the evolution of both polyandry and cooperative breeding. Cooperative polyandry is described as the situation where more than one male and one female breed as a group with males sharing equally in copulations and the care of one set of young. Sequential and simultaneous polyandry are defined to show how they differ from cooperative polyandry. These systems generally are characterized by the care of only one parent for each set of young, a trait which is in sharp contrast to cooperative polyandry. An argument is made that the present models for the evolution of polyandry cannot be expanded to include the cooperatively polyandrous species. Instead, the cooperative traits of cooperative polyandry fit within the array of characteristics of cooperative (communal) breeding. General characteristics of all cooperative species (monogamous, promiscuous and polyandrous) are reviewed and possible reasons for the evolution of equal-status males are discussed. A plea is made for the unification of evolutionary models dealing with mating systems and cooperative systems.     

Demographic factor affecting the fitness of polyandry for human males: A mathematical model and computer simulation

Polyandry has occurred rarely among humans; and has almost always consisted of brothers sharing a wife. The reduced opportunity for fertilization of females that occurs in polyandry would appear to make it a maladaptive mating system for human males. Previous evolutionary studies of human polyandry have suggested that kin selection may play a role in maintaining polyandry in some populations. A mathematical model for determining the fitness of polyandry for males is presented, and a simple deterministic analytic solution is derived. The model indicates that for polyandry to be an adaptive alternative to monogamy, the number of surviving offspring must be greater than the number of surviving offspring under monogamy times the number of males sharing a wife. This model exists in the literature. The unrealistic assumptions made in deriving this simple equation are revealed. An alternative stochastic computer simulation model is presented. The reproductive life history of a set of brothers is simulated under different demographic conditions, using data from polyandrous societies to estimate probabilities of fitness-related events. Under the assumption of equality of values of demographic variables for polyandry and monogamy, polyandry achieved or exceeded fitness parity with monogamy one third of the time. This contrasts with the prediction of the deterministic model stating that polyandry will never be an adaptive alternative to monogamy when fitness-related parameters are equal. The conditions improving fitness expectations for polyandry are conditions where genetic replication is decreased, i.e., with fewer brothers, high female sterility, decreased offspring survival, and decreased female fertility. Also, increased age difference between brothers enhances the fitness of polyandry. Genetic relatedness between brothers did not significantly affect the fitness of polyandry; therefore the kin selection hypothesis does not receive support. To a certain degree, these conditions exist for polyandrous populations in the Himalayas. Multivariate statistical analyses of simulation results revealed that most of the effects of these demographic factors could be accounted for by their association with increased probability of household extinction under monogamy and increased number of years of reproductive monogamy within polyandry. Although conditions favoring polyandry could be specified, analysis of the correlation between adaptiveness of polyandry and amount of genetic replication revealed that the demographic conditions favoring polyandry also lead to family extinction. Deficiencies in the model are discussed. It is suggested that future studies identify the advantages polyandry may have over monogamy in the values of demographic variables (e.g., increased offspring survival, increased extramarital reproduction), and take a multigenerational approach.     

Do polyandrous shorebirds trade off egg size with egg number?

Classical polyandry in birds is rare and is most frequent in the shorebirds (Charadriiformes). Polyandrous shorebirds lay smaller eggs for their body masses than non-polyandrous shorebirds, indicating that polyandrous female shorebirds may trade egg size off against number of eggs in order to maximize reproductive success. However, this trade-off may be confounded by phylogeny because most polyandrous species belong to a single family, the Jacanidae. I re-analysed this adaptive hypothesis using phylogenetically-independent contrast analyses. These analyses showed that there was no statistically significant difference in egg size between polyandrous and monogamous shorebirds once the effects of phylogeny had been incorporated. This is one of the first studies to show that the results of independent contrasts analyses differ from those where phylogenetic effects have not been taken into account.     

Tibetan Fraternal Polyandry: A Test of Sociobiological Theory

This paper tests sociobiological hypotheses regarding the way practitioners of fraternal polyandry in a Tibetan population in Nepal may enhance their inclusive fitness. Demographic data demonstrate higher mortality and lower survivorship of offspring in fraternal polyandry than monogamy. Moreover, the probability of allele transmission for an ego is lower in fraternal polyandrous unions than in monogamous unions. On the basis of the measured parameters, Tibetan fraternal polyandry does not appear to enhance the fitness of individuals who practice it and, in fact, seems to entail substantial reproductive sacrifice . [sociobiology, fraternal polyandry, inclusive fitness, demography, Tibet]     

Seasonality of marriages in sardinian pastoral and agricultural communities in the nineteenth century

The study of marriage seasonality of populations with different socioeconomic backgrounds may contribute to the better understanding their reproductive behaviours. This study analyses the monthly distribution of marriages in the 19th century in four agricultural villages and four pastoral villages on the island of Sardinia (Italy). The data were derived from 7340 marriage acts (3571 for the four agricultural villages and 3769 for the four pastoral villages). The aim is to ascertain whether the Sardinian agricultural and pastoral communities followed the matrimonial models reported for contemporary Italy and Europe and whether there was a change in the monthly distribution of marriages between the two halves of the 19th century. The results suggest that the marriage seasonality of the Sardinian farmers and shepherds was very similar to the patterns shown in the 19th century by Italian and European agricultural and pastoral communities. The Sardinian farmers preferred to marry in autumn-winter, while the Sardinian shepherds had a very high concentration of marriages in summer-autumn. Both communities avoided marriages in the Advent and Easter periods and in the month of May (dedicated to the Virgin Mary), and the farmers also in August (also dedicated to the Virgin Mary). Despite a certain seasonal stability, there was a significant change in the monthly distribution of marriages between the two halves of the 19th century in both the agricultural and pastoral communities, probably due to a series of laws that transformed the centuries-old socioeconomic system of Sardinia in the second half of the century.     

Socioeconomic, demographic and legal influences on consanguinity and kinship in northern coastal Sweden 1780-1899

Most studies on consanguinity have been conducted on contemporary populations and have focused on the prevalence and types of preferred intra-familial marriage. With its comprehensive birth, marriage and deaths records dating back to the late 17th century, and the legal bar on first cousin marriage removed in the mid-19th century, Sweden offers unique opportunities to examine the factors that determine by whom, where and why consanguineous marriages were contracted. The present study covers the period 1780-1899 and presents a detailed portrait of cousin and sibling exchange marriages in the Skellefte? region of northern coastal Sweden. The combined prevalence of first, second and third cousin marriage increased from 2.3% in 1790-1810 to 8.8% in 1880-1899, and multi-generation consanguinity also increased significantly over the study period. The distribution and prevalence of first cousin marriages was strikingly non-random, with a significantly greater propensity for consanguinity among land-owning families, especially involving first-born sons, within specific pedigrees, and in a number of more remote inland communities. Additional factors associated with a greater likelihood of consanguineous marriage included physical or mental disability among males, and among females the prior birth of an illegitimate child. Besides the inherent interest in the social and demographic structure of this region of northern Sweden during the course of the 19th century, in future studies it will be important to determine the degree to which the observed patterns of consanguineous and sibling exchange marriages in these past generations could have influenced present-day genetic structure.     

Bet hedging via multiple mating: A meta‐analysis

Polyandry has been hypothesized to allow females to “bet hedge” against mating only with unsuitable mates, reducing variance in offspring fitness between members of a polyandrous lineage relative to a single‐mating one. Theoretically, this reduction in fitness variance could select for polyandrous genotypes even when polyandry carries a direct cost, especially in small populations. However, this hypothesis is controversial and difficult to test empirically. Here, I apply a novel simulation model to 49 published empirical datasets, and quantify the potential selective advantage of multiple mating via reduced offspring fitness variance. For a wide range of assumptions, including those that most favor the evolution of bet hedging, I show that any fitness gains are meager. The variance in offspring quality caused by mate identity does not appear to be high enough for bet hedging to drive the evolution of polyandry.     

Benefits of polyandry in Parthenium beetle,Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae)

The influence of polyandry on the reproductive performance of females and on offspring fitness in Zygogramma bicolorata Pallister was investigated using four experimental treatments, viz. (A) monandrous, limited mating, (B) monandrous, unlimited mating, (C) polyandrous, no-choice limited mating, and (D) polyandrous, mate choice unlimited mating. Polyandrous females had higher reproductive performance than monandrous ones. Monandrous females subjected to unlimited matings had higher egg viability than those subjected to limited matings, but fecundity did not differ significantly. In polyandrous females, the freedom to choose mates did not affect reproductive performance. However, offspring of polyandrous females allowed mate choice developed fastest and had the highest survival at 25, 27, and 30 °C. Thus, polyandry in Z. bicolorata appears to provide both direct (material) and indirect (genetic) benefits resulting in better reproductive performance and increased adaptability of the offspring to counter environmental stresses. The present study not only adds to the knowledge of reproductive biology of Z. bicolorata but it could also be of economic value as it may help in the mass rearing of Z. bicolorata and in the management of Parthenium hysterophorus.     

Context-dependent genetic benefits of polyandry in a marine hermaphrodite

Numerous studies emphasize the potential indirect (genetic) benefits of polyandry in animals with resource-free mating systems. In this paper, we examine the potential for these benefits to fuel sexual selection and polyandry in the hermaphroditic ascidian Pyura stolonifera. Individuals were designated either sire (sperm producers) or dam (egg producers) at random and crossed in a North Carolina II breeding design to produce both paternal and maternal half siblings for our quantitative genetic analysis. We then partitioned the phenotypic variance in fertilization and hatching rates into additive and non-additive variance components. We found significant additive variance attributable to sire and dam effects at fertilization and hatching, suggesting the potential for selection to favour individuals carrying intrinsically 'good genes' for these traits. In separate analyses involving monandrous and polyandrous clutches, we found that both traits were elevated under polyandry, but the difference in hatching rates was due entirely to the difference in fertilization rates between treatments. When the hatching rates were standardized to account for variance at fertilization, there was no overall net benefit of polyandry for this trait. Despite this, we found that hatching success declined with increasing embryo densities, and that the slope of this decline was significantly greater in monandrous than polyandrous clutches. Hence, selection on embryo viability may still favour polyandry under restricted environmental conditions. Nevertheless, our results caution against interpreting elevated hatching success as an indirect genetic benefit of polyandry when variance in fertilization is not controlled.     

Experimental Removal of Sexual Selection Reveals Adaptations to Polyandry in Both Sexes

Polyandrous mating is extremely common, yet for many species the evolutionary significance is not fully resolved. In order to understand the evolution of mating systems, it is crucial that we investigate the adaptive consequences across many facets of reproduction. We performed experimental evolution with the naturally polygamous flour beetle Tribolium castaneum subjected to either polyandry or enforced monogamy, creating contrasting selection regimes associated with the presence or absence of sexual selection. After 36 generations, we investigated male and female adaptations by mating beetles with an unselected tester strain to exclude potential effects of male–female coevolution. Reproductive success of focal monogamous and polyandrous beetles from each sex was assessed in separate single male and multiple male experiments emulating the different selection backgrounds. Males and females from the polyandrous regime had more offspring in the experiments with multiple males present than monogamous counterparts. However, in single male experiments, neither females nor males differed between selection regimes. Subsequent mating trials with multiple males suggested that adaptations to polyandry in both sexes provide benefits when choice and competition were allowed to take place. Polyandrous females delayed the first copulation when given a choice of males and polyandrous males were quicker to achieve copulation when facing competition. In conclusion, we show that the expected benefits of evolutionary adaptation to polyandry in T. castaneum depended on the availability of multiple mates. This context-dependent effect, which concerned both sexes, highlights the importance of realistic competition and choice experiments.     

Polyandrous females provide sons with more competitive sperm: Support for the sexy‐sperm hypothesis in the rattlebox moth (Utetheisa ornatrix)

Given the costs of multiple mating, why has female polyandry evolved? Utetheisa ornatrix moths are well suited for studying multiple mating in females because females are highly polyandrous over their life span, with each male mate transferring a substantial spermatophore with both genetic and nongenetic material. The accumulation of resources might explain the prevalence of polyandry in this species, but another, not mutually exclusive, possibility is that females mate multiply to increase the probability that their sons will inherit more‐competitive sperm. This latter “sexy‐sperm” hypothesis posits that female multiple mating and male sperm competitiveness coevolve via a Fisherian runaway process. We tested the sexy‐sperm hypothesis by using competitive double matings to compare the sperm competition success of sons of polyandrous versus monandrous females. In accordance with sexy‐sperm theory, we found that in 511 offspring across 17 families, the male whose polyandrous mother mated once with each of three different males sired significantly more of all total offspring (81%) than did the male whose monandrous mother was mated thrice to a single male. Interestingly, sons of polyandrous mothers had a significantly biased sex ratio of their brood toward sons, also in support of the hypothesis.