Constraints on evolution and postcopulatory sexual selection: trade-offs among ejaculate characteristics.

Previous work (Reynolds and Gross 1992) has demonstrated that mate choice enables female guppies, Poecilia reticulata , to obtain heritable benefits (‘good genes’) for their offspring. It is not yet known whether males also signal their functional fertility, that is, their viability as fathers, to female guppies. Our study tested the hypothesis that a male9s behaviour reveals characteristics of his ejaculate. We uncovered a strong correlation between display rate and sperm number in male guppies derived from two wild Trinidadian populations. This result indicates that information on the functional fertility of potential mates is available to females. However, our investigation also found a significant relationship between the frequency of sneaky mating and sperm number. Female guppies in wild populations, particularly those experiencing a high predation regime, are constantly subjected to sneaky mating attempts. As the males responsible for these sneaky matings have highest reserves of sperm they may have the capacity to undermine female choice. The implications of these findings for sperm competition are discussed.

Exposure to extreme temperatures is increasingly likely to impose strong selection on many organisms in their natural environments. The ability of organisms to adapt to such selective pressures will be determined by patterns of genetic variation and covariation. Despite increasing interest in thermal adaptation, few studies have examined the extent to which the genetic covariance between traits might constrain thermal responses. Furthermore, it remains unknown whether sex-specific genetic architectures will constrain responses to climatic selection. We used a paternal half-sibling breeding design to examine whether sex-specific genetic architectures and genetic covariances between traits might constrain evolutionary responses to warming climates in a population of Drosophila melanogaster. Our results suggest that the sexes share a common genetic underpinning for heat tolerance as indicated by a strong positive inter-sexual genetic correlation. Further, we found no evidence in either of the sexes that genetic trade-offs between heat tolerance and fitness will constrain responses to thermal selection. Our results suggest that neither trade-offs, nor sex-specific genetics, will significantly constrain an evolutionary response to climatic warming, at least in this population of D.melanogaster.

Three main hypotheses, have been invoked to explain divergent genital evolution, the lock and key, pleiotropy, and sexual selection hypotheses, each of which make different predictions about how genital traits are inherited. Here we used a half-sib breeding design to examine the patterns of genetic variation and covariation between male genital sclerites, and their covariance with general body morphology in the dung beetle Onthophagus taurus. We found CV(A)'s and CV(P)'s were similar for both genital and general morphological traits and that CV(R)'s were large for both trait types. We found that male genital sclerites were negatively genetically correlated with general morphological traits. Variation in male genital morphology has direct implications for a male's fertilization success and the resulting sexual selection acting on male genitalia is predicted to maintain high levels of additive genetic variance. Contrary to this prediction, we found that individual genital sclerites all had low levels of additive genetic variance and large maternal and environmental sources of variation. Our data suggest that the genital sclerites in O. taurus are not inherited independently but as a genetically integrated unit. More importantly, the way the different sclerites function to influence male fertilization success reflects this genetic integration. Even though levels of V(A) in individual genital sclerites may be low, there may still be sufficient V(A) in multivariate trait space for selection to generate evolutionary change in the overall morphology of male genitalia.

We combine the methods of geometric morphometrics and multivariate quantitative genetics to study the patterns of phenotypic and genetic variation of mandible shape in random-bred mice. The data are the positions of 11 landmarks on the mandibles of 1241 mice from a parent-offspring breeding design. We use Procrustes superimposition to extract shape variation and restricted maximum likelihood to estimate the additive genetic and environmental components of variance and covariance. Matrix permutation tests showed that the genetic and phenotypic as well as the genetic and environmental covariance matrices were similar, but not identical. Likewise, principal component analyses revealed correspondence in the patterns of phenotypic and genetic variation. Patterns revealed in these analyses also showed similarities to features previously found in the effects of quantitative trait loci and in the phenotypes generated in gene knockout experiments. We used the multivariate version of the breeders' equation to explore the potential for short-term response to selection on shape. In general, the correlated response is substantial and regularly exceeds the direct response: Selection applied locally to one landmark usually produces a response in other parts of the mandible as well. Moreover, even selection for shifts of the same landmark in different directions can yield dramatically different responses. These results demonstrate the role of the geometry and anatomical structure of the mandible, which are key determinants of the patterns of the genetic and phenotypic covariance matrices, in molding the potential for adaptive evolution. Corresponding Editor: J. Merilä

Patterns of genetic variation reflect interactions among microevolutionary forces that vary in strength with changing demography. Here, patterns of variation within and among samples of the mouthbrooding gafftopsail catfish (Bagre marinus, Family Ariidae) captured in the U.S. Atlantic and throughout the Gulf of Mexico were analyzed using genomics to generate neutral and non-neutral SNP data sets. Because genomic resources are lacking for ariids, linkage disequilibrium network analysis was used to examine patterns of putatively adaptive variation. Finally, historical demographic parameters were estimated from site frequency spectra. The results show four differentiated groups, corresponding to the (1) U.S. Atlantic, and the (2) northeastern, (3) northwestern, and (4) southern Gulf of Mexico. The non-neutral data presented two contrasting signals of structure, one due to increases in diversity moving west to east and north to south, and another to increased heterozygosity in the Atlantic. Demographic analysis suggested that recently reduced long-term effective population size in the Atlantic is likely an important driver of patterns of genetic variation and is consistent with a known reduction in population size potentially due to an epizootic. Overall, patterns of genetic variation resemble that of other fishes that use the same estuarine habitats as nurseries, regardless of the presence/absence of a larval phase, supporting the idea that adult/juvenile behavior and habitat are important predictors of contemporary patterns of genetic structure.

Complex phenotypes are constructed during development by interactions among an intricate array of factors including genes, gene products, developmental units, and environmental influences. Although patterns of genetic variation and covariation play a clear role in determining patterns of phenotypic evolution (Lande 1979), it can be difficult to understand how various patterns of developmental interactions affect the evolutionary process, due to the complexity of developmental systems. However, recent advances in theory (e.g., Cowley and Atchley 1992; Atchley et al. 1994; Rice 1998, 2002; Gilchrist and Nijhout 2001; Wolf et al. 2001), and an explosion of interest in evolution and development, make it clear that a consideration of developmental interactions provides major insights into character evolution, including the evolution of phenomena such as canalization (Rice 1998), phenotypic integration (Cheverud 1996; Rice 2000), and genetic variance-covariance structure (Atchley 1984; Atchley and Hall 1991; Atchley et al. 1994; Atchley and Zhu 1997). These insights might allow one to predict (Rice 2002) or reconstruct (Lande 1979; Schluter 1996) evolutionary trajectories, and to identify the proximate basis of differentiation within or among species (e.g., Stem 1998; Kopp et al. 2000; Sucena and Stern 2000).

SummaryThe present study utilized pedigree data from three ethnically different populations of Kirghizstan, Turkmenia and Chuvasha. Principal component analysis was performed on a matrix of genetic correlations between 22 measures of adiposity, including skinfolds, circumferences and indices. Findings are summarized as follows: (1) All three genetic matrices were not positive definite and the first four factors retained even after exclusion RG ⩾ 1.0, explained from 88% to 97% of the total additive genetic variation in the 22 traits studied. This clearly emphasizes the massive involvement of pleiotropic gene effects in the variability of adiposity traits. (2) Despite the quite natural differences in pairwise correlations between the adiposity traits in the three ethnically different samples under study, factor analysis revealed a common basic pattern of covariability for the adiposity traits. In each of the three samples, four genetic factors were retained, namely, the amount of subcutaneous fat, the total body obesity, the pattern of distribution of subcutaneous fat and the central adiposity distribution. (3) Genetic correlations between the retained four factors were virtually non-existent, suggesting that several independent genetic sources may be governing the variation of adiposity traits. (4) Variance decomposition analysis on the obtained genetic factors leaves no doubt regarding the substantial familial and (most probably genetic) effects on variation of each factor in each studied population. The similarity of results in the three different samples indicates that the findings may be deemed valid and reliable descriptions of the genetic variation and covariation pattern of adiposity traits in the human species.

Past climate change is known to have strongly impacted current patterns of genetic variation of animals and plants in Europe. However, ecological factors also have the potential to influence demographic history and thus patterns of genetic variation. In this study, we investigated the impact of past climate, and also the potential impact of host plant species abundance, on intraspecific genetic variation in three codistributed and related specialized solitary bees of the genus Melitta with very similar life history traits and dispersal capacities. We sequenced five independent loci in samples collected from the three species. Our analyses revealed that the species associated with the most abundant host plant species (Melitta leporina) displays unusually high genetic variation, to an extent that is seldom reported in phylogeographic studies of animals and plants. This suggests a potential role of food resource abundance in determining current patterns of genetic variation in specialized herbivorous insects. Patterns of genetic variation in the two other species indicated lower overall levels of diversity, and that M.nigricans could have experienced a recent range expansion. Ecological niche modelling of the three Melitta species and their main host plant species suggested a strong reduction in range size during the last glacial maximum. Comparing observed sequence data with data simulated using spatially explicit models of coalescence suggests that M.leporina recovered a range and population size close to their current levels at the end of the last glaciation, and confirms recent range expansion as the most likely scenario for M.nigricans. Overall, this study illustrates that both demographic history and ecological factors may have contributed to shape current phylogeographic patterns.

Genetics of serum carotenoid concentrations and their correlation with obesity-related traits in Mexican American children

BackgroundPleistocene climatic oscillations and historical geological events may both influence current patterns of genetic variation, and the species in southern China that faced unique climatic and topographical events have complex evolutionary histories. However, the relative contributions of climatic oscillations and geographical events to the genetic variation of these species remain undetermined. To investigate patterns of genetic variation and to test the hypotheses about the factors that shaped the distribution of this genetic variation in species of southern China, mitochondrial genes (cytochrome b and NADH dehydrogenase subunit 2) and nine microsatellite loci of the Omei tree frog (Rhacophorus omeimontis) were amplified in this study.ResultsThe genetic diversity in the populations of R. omeimontis was high. The phylogenetic trees reconstructed from the mitochondrial DNA (mtDNA) haplotypes and the Bayesian genetic clustering analysis based on microsatellite data both revealed that all populations were divided into three lineages (SC, HG and YN). The two most recent splitting events among the lineages coincided with recent geological events (including the intense uplift of the Qinghai-Tibet Plateau, QTP and the subsequent movements of the Yun-Gui Plateau, YGP) and the Pleistocene glaciations. Significant expansion signals were not detected in mismatch analyses or neutrality tests. And the effective population size of each lineage was stable during the Pleistocene.ConclusionsBased on the results of this study, complex geological events (the recent dramatic uplift of the QTP and the subsequent movements of the YGP) and the Pleistocene glaciations were apparent drivers of the rapid divergence of the R. omeimontis lineages. Each diverged lineages survived in situ with limited gene exchanges, and the stable demographics of lineages indicate that the Pleistocene climatic oscillations were inconsequential for this species. The analysis of genetic variation in populations of R. omeimontis contributes to the understanding of the effects of changes in climate and of geographical events on the dynamic development of contemporary patterns of genetic variation in the species of southern China.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0572-1) contains supplementary material, which is available to authorized users.

Nearly 25 years ago, Allan Wilson and colleagues isolated DNA sequences from museum specimens of kangaroo rats (Dipodomys panamintinus) and compared these sequences with those from freshly collected animals (Thomas et al. 1990). The museum specimens had been collected up to 78 years earlier, so the two samples provided a direct temporal comparison of patterns of genetic variation. This was not the first time DNA sequences had been isolated from preserved material, but it was the first time it had been carried out with a population sample. Population geneticists often try to make inferences about the influence of historical processes such as selection, drift, mutation and migration on patterns of genetic variation in the present. The work of Wilson and colleagues was important in part because it suggested a way in which population geneticists could actually study genetic change in natural populations through time, much the same way that experimentalists can do with artificial populations in the laboratory. Indeed, the work of Thomas et al. (1990) spawned dozens of studies in which museum specimens were used to compare historical and present-day genetic diversity (reviewed in Wandeler et al. 2007). All of these studies, however, were limited by the same fundamental problem: old DNA is degraded into short fragments. As a consequence, these studies mostly involved PCR amplification of short templates, usually short stretches of mitochondrial DNA or microsatellites. In this issue, Bi et al. (2013) report a breakthrough that should open the door to studies of genomic variation in museum specimens. They used target enrichment (exon capture) and next-generation (Illumina) sequencing to compare patterns of genetic variation in historic and present-day population samples of alpine chipmunks (Tamias alpinus) (Fig. 1). The historic samples came from specimens collected in 1915, so the temporal span of this comparison is nearly 100 years.

Synopsis Body weights, egg weights and egg numbers were measured at different ages in two distinct, fully pedigreed, random bred strains of White Leghorns over a period of 3 years. The heritabilities of the separate measurements and the genetic correlations between them were obtained by an analysis of variance and covariance. The principal findings were: (i) The heritability of weight gain declined sharply with age over consecutive periods after 12 weeks. The genetic correlation of body weight at 12 weeks with gain in subsequent periods was low. There appeared to be sufficient genetic variance in growth rate in these later periods to alter the growth curve substantially by selection. For example, it should be possible to breed strains with a rapid early growth and low mature body size. (ii) There was evidence of genetic variation in the change of egg weight with time. The genetic variation was, however, so low that in any selection programme to improve 28‐week egg weight without changing 44‐week egg weight the progress would be very slow. (iii) Body weight at 12 weeks was genetically negatively correlated with sexual maturity. Its correlation with production in the first 44 weeks was positive in both strains, but not significantly different from zero. (iv) Body weights after 28 weeks were apparently uncorrelated with egg production or sexual maturity. (v) Egg weight and production traits show considerable heterogeneity of variance between years, probably partly due to their distribution not being normal. (vi) The pattern of genetic variation appeared to differ significantly between the two strains so that correlated responses would not necessarily be the same. (vii) There was a suggestion of maternal effects acting upon body weight but the evidence was somewhat contradictory and inconclusive due to the high standard error of the estimates. (viii) None of the 15 traits measured regressed over the 3 year period of relaxation of selection.

Genetic diversity, as the fundamental resource of Glacier National Park (GNP), is central to the characterization of biodiversity present in GNP. Preserving the genetic variation in species maintains their intrinsic flexibility to deal with variable abiotic and biotic environments. Although often not readily apparent as visible morphologic (phenotypic) differences, genetic variation may occur 1) between individuals within a population and 2) between populations of a species. Managers need to consider these two components of genetic variation when mediating the effects of human disturbance in GNP. However, very little is currently known about these levels of genetic organization in GNP species. Our three year project examines the presence and patterns of genetic variation in two GNP species: strawberry (Fragaria virginiana Duchesne) and mountain brome (Bromus carinatus Hook. and Arn.). We are quantifying the amount and distribution of genetic and phenotypic variation using quantitative genetic and electrophoretic methods and are identifying phenotypic characters subject to natural selection, i.e., those characters important for survival and reproduction differences in populations.

Both lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) activity, a biomarker of inflammation, and concentration of its primary associated lipoprotein, LDL, are correlated with adverse coronary outcomes. We previously reported a quantitative trait locus (QTL) corresponding to HSA2p24.3-p23.2 with pleiotropic effects on Lp-PLA(2) activity and LDL-cholesterol (LDL-C) concentration in baboons fed a basal diet. Here, our goal was to locate pleiotropic QTLs influencing both traits in the same baboons fed a high-cholesterol, high-fat (HCHF) diet, and to assess whether shared genetic effects on these traits differ between diets. We assayed Lp-PLA(2) activity and LDL-C concentration in 683 baboons fed the HCHF diet. We used a bivariate maximum likelihood-based variance components approach in whole-genome linkage screens to locate a QTL [logarithm of odds (LOD) = 3.13, genome-wide P = 0.019] corresponding to HSA19q12-q13.2 with pleiotropic effects on Lp-PLA(2) activity and LDL-C levels in the HCHF diet. We additionally found significant evidence of genetic variance in response to diet for Lp-PLA(2) activity (P = 0.0017) and for LDL-C concentration (P = 0.00001), revealing a contribution of genotype-by-diet interaction to covariation in these two traits. We conclude that the pleiotropic QTLs detected at 2p24.3-p23.2 and 19q12-q13.2 on the basal and HCHF diets, respectively, exert diet-specific effects on covariation in Lp-PLA(2) activity and LDL-C concentration.

Improvements of longevity in sows are of overriding importance from an animal welfare as well as from an economic perspective, also in the local Swabian-Hall Landrace (SHL) breed. Consequently, the aim of the present study was a detailed assessment of linear conformation traits in the context of early predictions of sow stayability and to infer genetic (co)variance components between conformation traits with reproduction and performance traits. In this regard, we implemented a linear 9-point scoring system for conformation traits reflecting the body morphology and feet and leg characteristics in gilts. Linear conformation trait scoring included body length (BLEN), body height (BHEI), hind leg angularity (HLANG), hind leg pastern (HLPAS), hind cannon bone strength (HCBS), hind leg position (HLPOS), front leg position (FLPOS), claw length (CLEN) and muscling (MUSC) from 6042 SHL gilts before first insemination at the age of 180-200 days. For the same gilts, performance traits included average daily gain (ADG) and back fat thickness (BF) measured via ultrasound, reproduction traits included the number of piglets born alive (NBA) and the number of piglets weaned (NWEAN), and stayability was a binary trait reflecting sow survival after parity 2 (STAY_12), 3 (STAY_13) and 4 (STAY_14). For the estimation of variance components and heritabilities, single-trait linear animal models were defined for conformation, performance and reproduction traits, and single-trait generalized linear mixed models with a logit link function for binary stayability traits. Genetic covariances and correlations were inferred in series of bivariate runs for all combinations of conformation and remaining traits. The distribution of the assigned conformation scores reflected a Gaussian distribution, but a large fraction of records was assigned to the intermediate score classes 4, 5 and 6. Accordingly, the restricted utilization of the 9-point scale might explain the small genetic variances and small heritabilities for feet and leg traits in the range from 0.06 to 0.17. Heritabilities were larger for the linear traits reflecting body morphology, i.e., for BLEN (0.21) and BHEI (0.20). For conformation traits, the common litter environment explained up to 17% of the phenotypic trait variation. Genetic and especially phenotypic correlations between linear conformation traits with the reproduction traits NBA and NWEAN were close to zero. Heritabilities for STAY_12, STAY_13 and STAY_14 were 0.08, 0.07 and 0.05, respectively. Moderate genetic relationships were estimated between STAY_14 with some conformation traits. Especially high scores for BHEI and BLEN (i.e., long and large gilts) implied a decline in STAY_14 genetically (rg =-0.24 and -0.53, respectively). Moderate genetic correlations were estimated between HLANG with STAY_14 (0.28), and between HCBS with STAY_12 (0.23). For most of the conformation traits with intermediate optimum, genetic correlations with STAY were close to zero, indicating improved longevity for gilts representing the population average with scores 4, 5 or 6, and suggesting the development of appropriate selection indices in this regard.