Whether to have a second child or not? An integrative approach to women's reproductive decision-making in current China

The transition to low fertility worldwide has led to introduction of diverse frameworks across disciplines to understand its causes and consequences. Previous attempts to compare the relative importance of the key factors influencing women's fertility decision-making largely focused on a single rather than multiple steps of decision-making—an important problem if different factors are associated with different steps. Furthermore, insufficient attention has been paid explicitly to husband's and already-born children's influences, two potentially important factors. Here we introduce a framework covering three steps of reproductive decision-making—ideal family size, fertility desire and fertility intention—and test it using multi-level survey data collected from Chinese one-child mothers. Mother's attitudes towards having two children were paramount factors underlying her ideal family size, and husband's and the firstborn child's attitudes were critical to her desire to have a second child, which in turn played a decisive role in her intention to have a second child. Although husband's attitude was related to all steps, most factors were only relevant to one step; e.g., perceived child mortality and value for old-age security predicted ideal family size, admiration—a prerequisite for social learning—for two-child families predicted fertility desire, and physical/economic constraints primarily predicted fertility intention. Our study emphasizes multiple decision-makers in family reproduction; indicates the relative importance of fertility-influencing factors could vary with steps of decision-making; and has important implications for population policy in low-fertility societies.     

Maternal and sibling factors induce dormancy in dimorphic seed pairs of Aegilops triuncialis

Germination and emergence are stimulated by environmental cues, but strongly influenced by maternal controls. However, traits related to seed dispersal may have important influences on germination as well. For example, the sibling rivalry hypothesis suggests that germination may be inhibited when sibling seeds remain within a single dispersal unit. These two influences on germination suggest different, and possibly conflicting, evolutionary strategies for optimizing individual fitness. Using an invasive annual grass that produces dispersal units with dimorphic seeds, I found significant reductions in seedling emergence that suggested the presence of both strong maternal and sibling influences on the germination of the smaller seed of dimorphic pairs. Both influences were capable of nearly complete germination suppression of the small seed, but there was no strong evidence for a hierarchy among the two factors. The maternal effect is consistent with a bet-hedging strategy for survival in variable environments where resource availability can be unpredictable, but the sibling effect likely represents a mechanism for reducing competition between closely related individuals, particularly under conditions of resource limitation.     

Simple sequence repeat marker diversity in cassava landraces: genetic diversity and differentiation in an asexually propagated crop

Cassava (Manihot esculenta) is an allogamous, vegetatively propagated, Neotropical crop that is also widely grown in tropical Africa and Southeast Asia. To elucidate genetic diversity and differentiation in the crop's primary and secondary centers of diversity, and the forces shaping them, SSR marker variation was assessed at 67 loci in 283 accessions of cassava landraces from Africa (Tanzania and Nigeria) and the Neotropics (Brazil, Colombia, Peru, Venezuela, Guatemala, Mexico and Argentina). Average gene diversity (i.e., genetic diversity) was high in all countries, with an average heterozygosity of 0.5358 ± 0.1184. Although the highest was found in Brazilian and Colombian accessions, genetic diversity in Neotropical and African materials is comparable. Despite the low level of differentiation [F_st(theta) = 0.091 ± 0.005] found among country samples, sufficient genetic distance (1-proportion of shared alleles) existed between individual genotypes to separate African from Neotropical accessions and to reveal a more pronounced substructure in the African landraces. Forces shaping differences in allele frequency at SSR loci and possibly counterbalancing successive founder effects involve probably spontaneous recombination, as assessed by parent-offspring relationships, and farmer-selection for adaptation.Communicated by H.C. Becker     

GENETIC ANALYSIS OF MORNINGNESS AND EVENINGNESS

We studied the influence of genetic factors on individual differences in morningness-eveningness in a sample of Dutch twin families. Data were collected from adolescent twins (mean age 17.8 yr) and their parents (mean age of fathers 48.0 yr and of mothers 46.0 yr) and a sample of older twins (mean age 46.5 yr). Scores on morningness-eveningness were rated on a 5-point scale. Parents were more morning oriented than their children, and women were more morning oriented than men. With a twin-family study, separation of genetic and environmental influences on variation in morningness-eveningness is possible. Including parents and older twins in the study makes it possible to explore generation differences in these effects. The correlation between monozygotic twins was more than twice the correlation between dizygotic twins. This indicates that genetic effects may not operate in an additive manner. Therefore, a model that included genetic dominance was explored. Biometrical model fitting showed no sex differences for the magnitude of genetic and environmental factors. The total heritability—the sum of additive and nonadditive genetic influences—for morningness-eveningness was 44% for the younger generation and 47% for the older generation. However, the genetic correlation between the generations turned out to be lower than 0.5, suggesting that different genes for morningness-eveningness are expressed in both generations. (Chronobiology International, 18(5), 809-822, 2001)     

甘肃汉族头面部特征亲子相关研究

本文对甘肃永登农村地区69个汉族家庭的父母和成年子女头面部特征进行了亲子相关研究。结果表明:头颅部指数似乎儿子受父亲母亲的影响较强,测量项目似乎女儿受父亲的影响较强;脸面部测量项目的亲子相关表现出一定程度的方向性,儿子或女儿垂直方向的尺寸(高度)似乎受父亲的影响较强,横向(宽度)似乎受母亲的影响较强,从指数上来看,母亲对子女脸面部的影响似乎比父亲强一些。     

Response to vocal music in Angelman syndrome contrasts with Prader-Willi syndrome

Parent-offspring conflict—conflict over resource distribution within families due to differences in genetic relatedness—is the biological foundation for many psychological phenomena. In genomic imprinting disorders, parent-specific genetic expression is altered, causing imbalances in behaviors influenced by parental investment. We use this natural experiment to test the theory that parent-offspring conflict contributed to the evolution of vocal music by moderating infant demands for parental attention. Individuals with Prader-Willi syndrome, a genomic imprinting disorder resulting from increased relative maternal genetic contribution, show enhanced relaxation responses to song, consistent with reduced demand for parental investment (Mehr, Kotler, Howard, Haig, & Krasnow, 2017, Psychological Science). We report the necessary complementary pattern here: individuals with Angelman syndrome, a genomic imprinting disorder resulting from increased relative paternal genetic contribution, demonstrate a relatively reduced relaxation response to song, suggesting increased demand for parental attention. These results support the extension of genetic conflict theories to psychological resources like parental attention.     

亲子典型相关在家蚕育种中的应用

运用典型相关理论分析了家蚕亲代和子代两组数量性状,并对其遗传育种学意义作了探讨。由于亲子典型相关系数在数值上就等于亲子间典型性状的回归系数,所以亲子典型相关系数也代表了亲代典型性状将其遗传特征传递给子代典型性状的能力。典型性状作为多个数量性状的公共因子,在亲子代间具有最大的传递能力,对亲代典型性状进行选择,将具有最大的选择效果和最小的估计误差。     

Condition-dependent effects of corticosterone on a carotenoid-based begging signal in house sparrows

Begging is a complex display involving a variety of different visual and auditory signals. Parents are thought to use these signals to adjust their investment in food provisioning. The mechanisms that ensure the honesty of begging displays as indicators of need have been recently investigated. It has been shown that levels of corticosterone (Cort), the hormone released during the stress response, increase during food shortage and are associated with an increased begging rate. In a recent study in house sparrows, although exogenous Cort increased begging rate, parents did not accordingly adjust their provisioning rate. Here, we tested the hypothesis that Cort might affect the expression of other components of begging displays, such as flange color (a carotenoid-based trait). We experimentally increased levels of circulating Cort and investigated the effects of the treatment on (1) the flange coloration of the nestlings, (2) the behavioral response and (3) the parental allocation of food and (4) nestling condition and cell-mediated immune response. We found that Cort affected flange coloration in a condition-dependent way. Cort-injected nestlings had less yellow flanges than controls only when in poor body condition. Parental feeding rate was also affected by the Cort treatment in interaction with flange color. Feeding rate of Cort-injected nestlings was negatively and significantly correlated with flange color (nestlings with yellower flanges receiving more food), whereas feeding rate and flange color were not correlated in control chicks. We also found that nestlings injected with Cort showed a weaker immune response than controls. These results suggest that, indeed, Cort has the potential to affect multiple components of the begging display. As Cort levels naturally raise during fasting, parents have to take into account these multiple components to take a decision as to optimally share their investment among competing nestlings.     

Parent-offspring conflict over clutch size

Summary We present a model for sexually-reproducing diploids in which a female can produce a variable (generally large) clutch size, where the sibs then compete over some fixed resource, and where certain offspring use siblicide to reduce the primary clutch/brood size created by the mother. Where siblicide involves neither direct energy loss (e.g. fighting cost) nor gain (e.g. cannibalism) to an offspring, the optimal clutch size for an offspring can differ from the optimum for the mother, i.e. there can be parent-offspring conflict over clutch size. The magnitude of this evolutionary conflict (measured in terms of difference between clutch size optima) increases with multipaternity of the brood and with the steepness of the initial decline in offspring survivorship (through sib-competition as further offspring are added to the brood). However, the disparity in clutch size optima may not be great. Where the integer clutch size optima are the same, there will clearly be no conflict. Where this differs, resolution of the evolutionary conflict could involve much apparent behavioral conflict, commonly manifest as siblicidal aggression.The ESS (evolutionarily stable strategy) for such a game will depend upon the direct costs and benefits of siblicide, as well as on the indirect costs to sibs via relatedness. If the only costs of siblicide arise through relatedness, then offspring will win in the sense that the eventual clutch size will match the offspring optimum. Whether or not the mother will produce this clutch size depends on the mechanism controlling siblicide. A siblicidal ESS will occur when offspring are programmed to kill a fixed number/proportion of a brood (victim-based siblicide), but not if programmed to reduce the sibship to the offspring optimum (survivor-based siblicide). With survivor-based siblicide, the mother can do no better than to lay the offsprings' optimal clutch size.