Quantitative genetic models of sexual selection

Summary Quantitative genetic models of sexual selection have disporven some of the central tenets of both the handicap mechanism and the sexy son hypothesis. These results suggest that the good genes approach to sexual selection may generally lead to erroneous results.Runaway sexual selection seems possible under a wide variety of circumstances. Quantittive genetic models have revealed runaway processes for sexually selected attributes expressed in both sexes and for attributes of parental care. Furthermore, the runaway could occur simultaneously in a series of populations that straddle an environmental gradient. While the models support the feasibility of runaway processes, empirical studies are needed to evaluate whether runaways actually happen. Estimates of critical genetic parameters are particularly needed, as well as measures of natural and sexual selection acting on the same population.The models also show that sexual selection has tremendous potential to produce population differentiation, particularly in epigamic traits. Differentiation is promoted by indeterminancy of evolutionary outcome, transient differences among populations during the final slow approach to equilibrium, sampling drift among equilibrium populations, and the tendency of sexual selection to amplify geographic variation arising from spatial differences in natural selection. Recent work with two- and three-locus models of sexual selection has produced results that parallel the results of the polygenic models^36–38,58. Thus the feature of indeterminate equilibria (outcome dependent on initial conditions) is common to both types of model.     

Heritability of locomotor performance and its correlates in a natural population

Summary Locomotor capacities and their physiological bases are thought to be of considerable selective importance in natural populations. Within this functional complex, organismal performance traits (e.g., speed, stamina) are expected to be of more direct selective importance than their suborganismal determinants (e.g., heart size). Quantitative genetics theory predicts that traits of greater selective importance should generally have lower heritabilities at equilibrium. Contrary to these expectations, we report that organismal performance traits had the highest heritabilities in a natural population of garter snakes.     

Testing hypothesized causes of within-island geographic variation in the colour of lizards

Summary Within the island of Tenerife the lizardGallotia galloti shows geographic variation in a range of features, most notably the colour pattern of breeding males. Numerous (7) specific causal hypotheses, both phylogenetic and ecogenetic, are proposed or plausible for this geographic variation and these are simultaneously tested against the observed multivariate pattern. The hypotheses based on the divergence in allopatry (e.g. the secondary contact of populations from the precursor islands of Anaga and Teno and the separation of high- and low-altitude populations by encircling cloud) are rejected. The hypothesis that the pattern is caused by topographically determined climatic differences within the island is not rejected. The climate may influence the balance between selection for signalling colouration for sexual/territorial purposes and natural selection for crypsis.     

Fluctuating rates of evolution

Summary Constant evolutionary rates are possible only in verylarge populations, where natural selection does not exhaust varition because mutation supplies fresh variability. In a small population where a small number of genes influence an integrated system like brain and body size which have an allometric relationship, variation is removed rapidly under natural selection, This occurs even when the final fitness of the population is not optimal.     

Habitat marking: males attracted to residual odors of twoDrosophila species

Summary We have found that males of the sibling speciesD. melanogaster andD. simulans are preferentially attracted to sites marked by the residual odors of conspecific females, especially if non-virgin. In natural populations, this could enhance sexual selection among males, and cause some isolation at the microhabitat level.     

Genetic susceptibility to hypertensive renal disease

Hypertensive renal disease occurs at increased frequency among the relatives of patients with this disease compared to individuals who lack a family history of disease. This suggests a heritable risk in which genetic variation may play a role. These observations have motivated a search for genetic variation contributing to this risk in both experimental animal models and in human populations. Studies of animal models indicate the capacity of natural genetic variants to contribute to disease risk and have produced a few insights into the disease mechanism. In its current phase, human population genetic studies have sought to associate genetic variation with disease in large populations by testing genotypes at a large number of common genetic variations in the genome, expecting that common genetic variants contributing to renal disease risk will be identified. These genome-wide association studies (GWAS) have been productive and are a clear technical success; they have also identified narrowly defined loci and genes containing variation contributing to disease risk. Further extension and refinement of these GWAS are likely to extend this success. However, it is also clear that few additional variants with substantial effects accounting for the greatest part of heritability will be uncovered by GWAS. This raises an interesting biological question regarding where the remaining unaccounted heritable risk may be located. At present, much consideration is being given to this question and to the challenge of testing hypotheses that lead from the various alternative mechanisms under consideration. One result of the progress of GWAS is likely to be a renewed interest in mechanisms by which related individuals can share and transmit traits independently of Mendelian inheritance. This paper reviews the current progress in this area and considers other mechanisms by which familial aggregation of risk for renal disease may arise.     

Familial hemophagocytic lymphohistiocytosis: a model for understanding the human machinery of cellular cytotoxicity

Cytotoxic T lymphocytes, natural killer cells, and NKT cells are effector cells able to kill infected cells. In some inherited human disorders, a defect in selected proteins involved in the cellular cytotoxicity mechanism results in specific clinical syndromes, grouped under the name of familial hemophagocytic lymphohistiocytosis. Recent advances in genetic studies of these patients has allowed the identification of different genetic subsets. Additional genetic immune deficiencies may also induce a similar clinical picture. International cooperation and prospective trials resulted in refining the diagnostic and therapeutic approach to these rare diseases with improved outcome but also with improved knowledge of the mechanisms underlying granule-mediated cellular cytotoxicity in humans.     

The variability of patterns of sexual dimorphism in the hominoid skull

Univariate and multivariate statistical analyses are applied to a number of cranial dimensions and angles from living hominoids in order to investigate the patterns of sexual dimorphism in these groups. Clear differences in patterns of cranial sexual dimorphisms are demonstrated not only between genera but also within a single species (Homo). These differences overlay the common finding of a sexual size difference in all groups. The results imply that caution is required in using the sexual dimorphisms of living hominoids as models for those anticipated in fossils.     

The variability of patterns of sexual dimorphism in the hominoid skull

Summary Univariate and multivariate statistical analyses are applied to a number of cranial dimensions and angles from living hominoids in order to investigate the patterns of sexual dimorphism in these groups. Clear differences in patterns of cranial sexual dimorphisms are demonstrated not only between genera but also within a single species (Homo). These differences overlay the common finding of a sexual size difference in all groups. The results imply that caution is required in using the sexual dimorphisms of living hominoids as models for those anticipated in fossils.     

Sexual reproduction in the Candida clade: cryptic cycles, diverse mechanisms, and alternative functions

To have sex, or not to have sex, is a question posed by many microorganisms. In favor of a sexual lifestyle is the associated rearrangement of genetic material that confers potential fitness advantages, including resistance to antimicrobial agents. The asexual lifestyle also has benefits, as it preserves complex combinations of genes that may be optimal for pathogenesis. For this reason, it was thought that several pathogenic fungi favored strictly asexual modes of reproduction. Recent approaches using genome sequencing, population analysis, and experimental techniques have now revised this simplistic picture. It is now apparent that many pathogenic fungi have retained the ability to undergo sexual reproduction, although reproduction is primarily clonal in origin. In this review, we highlight the current understanding of sexual programs in the Candida clade of species. We also examine evidence that sexual-related processes can be used for functions in addition to mating and recombination in these organisms.     

Impact of corrections for dynamic selection bias on forecasts of retention behavior

We investigate the impact of corrections for dynamic selection bias on forecasting accuracy in a multi‐period stay/leave model. While corrections for selection bias are needed for consistent coefficient estimates, they do not necessarily produce more accurate forecasts than uncorrected techniques. Theorem 1 shows that, apart from estimation errors, a shrinkage principle applies: the heterogeneity restriction imposed by uncorrected and combination techniques improves accuracy for forecasting individuals that leave, and hurts accuracy for forecasting individuals that stay. This has important implications for decision making because of the potential for asymmetric losses. We also present an illustrative empirical application and results from Monte Carlo experiments. We find that differences in relative accuracy vary directly with the degree of selection bias and inversely with the percentage of the initial population that stays. Copyright © 2007 John Wiley & Sons, Ltd.     

Quantitative genetics of zooplankton life histories

Quantitative genetic techniques are powerful tools for use in understanding the microevolutionary process. Because of their size, lifespan, and ease of culture, many zooplankton species are ideal for quantitative genetic approaches. As model systems, studies of zooplankton life histories are becoming increasingly used for examination of the central paradigms of evolutionary theory. Two of the fundamental empirical questions that zooplankton quantitative genetics studies can answer are: 1) How much genetic variance exists in natural populations for life history traits? 2) What is the empirical evidence for trade-offs that permeate life history theory based on optimality approaches? A review of existing data onDaphnia indicates substantial genetic variance for body size, clutch size, and age at first reproduction. Average broad-sense heritabilities for these three characters across 19 populations of 6 species are 0.31, 0.31, and 0.34, respectively. Although there is some discrepancy between the two pertinent studies that were designed to decompose the total genetic variance into its additive and non-additive components, a crude average seems to suggest that approximately 60% of the total genetic variance has an additive basis. The existing data are somewhat inconsistent with respect to presence/absence of trade-offs (negative genetic correlations) among life history traits. A composite of the existing data seems to argue against the existence of strong trade-offs between offspring size and offspring number, between present and future reproduction, and between developmental rate and fecundity. However, there is some evidence for a shift toward more negative (less positive) covariances in more stressful environments (e.g., low food). Zooplankton will prove to be very useful in future study in several important areas of research, including the genetics and physiology of aging, the importance of genotype-environment interaction for life history traits, and the evolution of phenotypic plasticity.     

Genetic basis of some morphological differences between temperate and equatorial populations ofDrosophila melanogaster

The genetic basis of three morphological traits (ovariole number, sternopleural bristle number and wing length) ofDrosophila melanogaster has been investigated in natural populations that show great differences in these traits, i. e. Bordeaux (France) and Loua (Congo). F1 and F2 crosses, and chromosome substitutions between these two populations, were analysed. Maternal and/or X chromosome effects were found for sternopleural bristle number and wing length. For all traits, significant effects from each of the three chromosomes were found, but in general only one or two chromosomes had a major effect. Moreover, in all cases significant interactions between chromosomes were observed, suggesting the existence of epistatic effects. Our results are discussed and compared to those obtained from the analysis of selected laboratory strains.     

Developmental genes as a potential tool in population ecology of complex animal life cycles?

Many aquatic invertebrates possess complex life cycles, which include a switch from a vegetative to a sexual mode of reproduction. While sexual reproduction is usually linked to slow rates of propagation, vegetative reproduction leads to high rates of clonal propagation and a fast increase in population size. I have attempted to identify developmental genes which are differentially expressed between sexually and vegetatively reproducing individuals. Quantitative assays of the expression of those diagnostic genes could be applied to field samples to gain information on the reproductive status of the sample. Here I outline a general strategy for identifying and testing the usefulness of homeobox genes as candidates for regulatory genes whose expression patterns are indicative of a sexual or vegetative developmental phase.     

Genetic variation in natural populations: Morphological traits inDrosophila melanogaster

Summary In a wild population ofDrosophila melanogaster located near Madrid (Spain), it has been found that the frequency of morphological mutant phenotypes is 0.36 per captured female. The study of these females shows that they carry 3.6 recessive mutants in heterozygous condition per female. The genetic variability found is higher than the frequencies observed by other authors in other natural populations.I thank Dr F.J. Ayala for useful discussions and help in preparing the English text.     

Epigenetic mechanisms of tumor resistance to immunotherapy

The recent impact of cancer immunotherapies has firmly established the ability and importance of the immune system to fight malignancies. However, the intimate interaction between the highly dynamic tumor and immune cells leads to a selection process driven by genetic and epigenetic processes. As the molecular pathways of cancer resistance mechanisms to immunotherapy become increasingly known, novel therapeutic targets are being tested in combination with immune-stimulating approaches. We here review recent insights into the molecular mechanisms of tumor resistance with particular emphasis on epigenetic processes and place these in the context of previous models.     

Genetic changes of pupa weight inTribolium castaneum under domestication

Summary The evolution of the genetic and phenotypic parameters of pupa weight in 6 wild populations ofTribolium castaneum under domestication was studied. A gradual increase of the phenotypic and additive genetic variances of the populations was detected accompanied by small or non-significant changes of the mean. These results are interpreted as short-term consequences of the relaxation of centripetal (stabilizing) selection forces under laboratory conditions.We wish to thank Prof. F.J. Ayala for useful discussions in the preparation of this paper.     

Population genetic structure and mating system evolution in freshwater pulmonates

Freshwater gastropods (Basommatophora and Prosobranchia) harbor a variety of mating systems. In particular, apomictic parthenogenesis in prosobranchs and self-fertilization in the hermaphrodite pulmonates may be viable alternatives to outcrossing sexuality in a number of species. The coexistence of different mating systems in extant populations provides opportunities to examine the forces directing their evolution. We review the models analyzing and predicting genetic variability in subdivided populations, with an emphasis on the effects of inbreeding. Population genetic data on freshwater pulmonates are examined in the context of selfing rates and the loss of variability under selfing. Furthermore, the genetic and demographic factors thought to influence mating system evolution are considered, and we highlight the different approaches available to estimate mating system parameters, in particular the selfing rate. Recent population biological studies on polyploid species (Bulinus truncatus, Ancylus fluviatilis) indicate that selfing is the predominant mating system. These studies have contributed to a deeper understanding of conceptual issues in the evolution of selfing rates. Throughout, we emphasize the need for further carefully designed studies.     

Sexual isolation betweenDrosophila melanogaster females andD. simulans males. Male mating propensities versus success in hybridization

Genetic variation has been found in males of aD. simulans population for their eagerness to hybridize withD. melanogaster females. In a search for traits involved in this hybridization, males ofD. simulans were tested for mating speed and sexual vigour. Between-male differences were detected in both sexual traits, but no relationship was noticed between them, nor with the frequency of hybridization. Thus male mating propensities appear to be unrelated to the breakdown of sexual isolation between these sibling species.