A sex-specific test of selection in utero

We find support for the hypothesis that changes in the monthly odds of a twin among live-born males predict subsequent and opposite changes in the odds of a twin among live-born females. The hypothesis arises from the long standing argument that natural selection has conserved mechanisms by which pregnant women in stressed populations spontaneously abort fetuses least likely to yield grandchildren. Previous attempts to empirically test this argument focus almost entirely on males. We contribute to the literature by showing that, consistent with the logic of natural selection, maternal adaptations to environmental changes likely have effects on the survival of both male and female conceptuses and fetuses.     

Aspects of the distribution of HbS in the United States

Frequencies of HbS obtained by several screening clinics are analyzed for age, sex, and location effects. All seem to be present in some form, though age and sex effects may be conditional on location. An attempt is made to elaborate the common observation of increasing frequency with age. This is shown to be the result of differences in fertility favoring the normal. A simulation which íncludes 25% admixture was done. The results indicate a genetically relevant New World experience for the population to be about 9–12 generations with the heterozygote having fitness of 0.96–0.99.     

Measurement and Selection of Parasitoid Quality for Mass-Reared Trichogramma minutum Riley Used in Inundative Release

Parasitoid quality, subject to both genetic and environmental influences, is critical to the success of any biological control program, however, its measurement and improvement is poorly understood. In this study, a classic genetic approach is taken to develop two indices, namely a character index and a fitness index, for the measurement and selection of high quality parasitoids used in inundative release. Six life-history traits and corresponding fitness components in 33 inbred strains of Trichogramma minutum were used to generate both genotypic and phenotypic variance-covariance matrices that then allowed for the construction of the indices. Most traits and their fitness components were positively correlated, both phenotypically and genotypically, with lifetime fecundity and the number of female offspring appearing to have an important influence. Selection of the top three strains showed that parasitoid quality could be improved by 36% using the character index and possibly up to 150% using the fitness index. The two indices were linearly correlated suggesting that either could be used to measure quality. The character index is recommended because it requires information on only three life-history traits (fecundity, number of female offspring, and number of male offspring) and has highly correlated responses of fitness components. Our work demonstrates that the best quality T. minutum will be obtained by using the character index to select for inbred strains which have high fecundity and number of female offspring.     

Behavioural fitness component effects of the alba polymorphism of Colias (Lepidoptera, Pieridae): resource and time budget analysis

1. Alba, a white wing colour morph of butterflies of the genus Colias , makes fitness-related changes at several levels of phenotypic organization: physiology, development and behaviour. Two sympatric species of Colias are studied, which differ greatly in their frequency of alba vs its sister yellow/orange morph. How resource and time constraints on Colias interact with the morphs' different patterns of pupal resource allocation to alter the balance of the morphs' fitness components in the two species is discussed.
2. These species, C. alexandra and C. scudderi , differ in melanin-based solar energy absorption, in larval dietary richness and in local adult nectar resources. The two female morphs determine alternate thermal balance, internal resource allocation and behavioural effects in each species, thus changing the morphs' time budgets and fitness-component impacts between the species. In particular, female egg output differences between the morphs appears to reverse between species: alba fecundity is greater than yellow fecundity in C. scudderi , but alba is less than yellow in C. alexandra .
3. These differences are consistent with the large observed differences in alba frequency between the species. Some important questions about the selective regime maintaining a polymorphism here, rather than an alternation of monomorphisms, remain.     

The estimation of a bivariate fitness function from two samples taken from a population

Summary The fitness of animals subjected to natural selection can be defined as the probability of surviving selection for a given interval of time, or some convenient multiple of this. If the fitness is related to some measurable variablesX, Y, Z,… then the relationship is expressed mathematically in the fitness functionw(x, y, z,…) and this function can be estimated by comparing the joint distribution ofX, Y, Z,… in samples taken before and after selection. In an earlier paper (Manly, 1975) the problems involved in estimating a fitness function of one variable were discussed. In the present paper various methods for estimating a bivariate fitness function are proposed and compared on some semiartificial sample data. It is concluded that either a generalized version ofO’Donald’s (1968) method of moments or a weighted multiple regression method will be most satisfactory. Alternative methods involving assumptions of normality will need to be used with great care.     

Fitness consequences of egg-size variation in the lesser snow goose

We investigated the relationship between eggsize variation and (a) egg hatching success, (b) chick survival to fledging and recruitment, and (c) adult female survival, over 12 years in the lesser snow goose (Anser caerulescens caerulescens). By comparing the means and variances of egg size for successful and unsuccessful eggs, our aim was to assess the relative fitness of eggs of different sizes and to determine the type of selection operating on egg size in this species. As both egg size and reproductive success vary with age in the lesser snow goose we controlled for the effects of female age. Egg-size variation is very marked in this population, varying by up to 52% for eggs hatching successfully. However, there was no relationship between egg size and post-hatching survival of goslings to fledging or recruitment, either within or between broods, pooling across years. Egg size varied significantly between successful and unsuccessful clutches in only 2 of 33 individual year comparisons. First-laid eggs surviving to onset of incubation, and eggs hatching successfully, were on average larger than unsuccessful eggs, but this was probably due to the confounding effects of female age-specific and sequence-specific egg survival. Variance of egg size differed significantly between successful and unsuccessful eggs in only 3 of 24, and 0 of 21, individual year comparisons for pre- and post-hatching survival respectively. We therefore found little evidence for a relationship between egg-size variation and offspring fitness, or for strong directional, normalising or diversifying selection operating on egg size, in the lesser snow goose. In addition, there was only weak support for the hypothesis that egg-size variation is maintained by temporal variation in selection pressure (sensu Ankney and Bisset 1973). It is likely that egg-size variation represents the pleiotropic expression of alleles affecting more general physiological or metabolic processes. While this does not rule out the existence of alleles with more direct effects on egg size we suggest that their contribution to heritable egg size is small.     

Phenological mismatch drives selection on elevation,but not on slope,of breeding time plasticity in a wild songbird

Phenotypic plasticity is an important mechanism for populations to respond to fluctuating environments, yet may be insufficient to adapt to a directionally changing environment. To study whether plasticity can evolve under current climate change, we quantified selection and genetic variation in both the elevation (RN_E) and slope (RN_S) of the breeding time reaction norm in a long‐term (1973–2016) study population of great tits (Parus major). The optimal RN_E (the caterpillar biomass peak date regressed against the temperature used as cue by great tits) changed over time, whereas the optimal RN_S did not. Concordantly, we found strong directional selection on RN_E, but not RN_S, of egg‐laying date in the second third of the study period; this selection subsequently waned, potentially due to increased between‐year variability in optimal laying dates. We found individual and additive genetic variation in RN_E but, contrary to previous studies on our population, not in RN_S. The predicted and observed evolutionary change in RN_E was, however, marginal, due to low heritability and the sex limitation of laying date. We conclude that adaptation to climate change can only occur via micro‐evolution of RN_E, but this will necessarily be slow and potentially hampered by increased variability in phenotypic optima.     

Fitness costs in spatially structured environments

The clustering of individuals that results from limited dispersal is a double‐edged sword: although it allows for local interactions to be mostly among related individuals, it also results in increased local competition. Here I show that, because they mitigate local competition, fitness costs such as reduced fecundity or reduced survival are less costly in spatially structured environments than in nonspatial settings. I first present a simple demographic example to illustrate how spatial structure weakens selection against fitness costs. Then, I illustrate the importance of disentangling the evolution of a trait from the evolution of potential associated costs, using an example taken from a recent study investigating the effect of spatial structure on the evolution of host defense. In this example indeed, the differences between spatial and nonspatial selection gradients are due to differences in the fitness costs, thereby undermining interpretations of the results made in terms of the trait only. This illustrates the need to consider fitness costs as proper traits in both theoretical and empirical studies.     

食物供应量对转红色荧光蛋白基因唐鱼 生存和生长的影响

选取雄性杂合子转红色荧光蛋白基因唐鱼(Tanichthys albonubes)(简称:转基因唐鱼)与雌性非转基因唐鱼交配产卵,出膜7d后,在水温(25.0 ±2.0)℃条件下,选择健康仔鱼进行饱食(食物供应量高)、半饥饿(食物供应量中)和饥俄(食物供应量低)3种处理,结果显示:(1)出膜后7～72 d的唐鱼饱食组与半...     

Wealth, status, and fitness: a historical study of Norwegians in variable environments

Wealth and status covary with lifetime reproductive success in preindustrial human populations. Local ecology is likely to modify this association, but details of this presumed relationship are not yet known. We sought to determine whether local ecology modifies the relationship between status and fitness (number of grandchildren). Our approach to the problem was to measure variation in fitness relative to status (landless or with land) and to local ecology (inland versus coastal communities). We also analyzed life history traits that might explain observed variations in fitness. Our results confirm previous findings that both status (landless=9.9 vs. with land=16.5) and ecology (inland=12.3 vs. coast=14.1) affect the number of grandchildren produced by a female in pre-industrial society. We also found that the differences in number of children between the status groups were less pronounced on the coast (landless=12.0 vs. with land=16.1) than inland (landless=7.8 vs. with land=16.8). Our findings are novel because they suggest that the fitness consequences of human status may depend on details of local ecology. We discuss four different mechanisms that could account for these fitness differences: (1) differential reproductive rate of mothers, (2) differential marriage rate of children (3) differential survival rate of children, and (4) different social practices (breastfeeding, inheritance of property and diet).