npr-1 Regulates foraging and dispersal strategies in Caenorhabditis elegans

Wild isolates of Caenorhabditis elegans differ in their tendency to aggregate on food [1, 2]. Most quantitative variation in this behavior is explained by a polymorphism at a single amino acid in the G protein-coupled receptor NPR-1: gregarious strains carry the 215F allele, and solitary strains carry the 215V allele [2]. Although npr-1 regulates a behavioral syndrome with potential adaptive implications, the evolutionary causes and consequences of this natural polymorphism remain unclear. Here we show that npr-1 regulates two behaviors that can promote coexistence of the two alleles. First, gregarious and solitary worms differ in their responses to food such that they can partition a single, continuous patch of food. Second, gregarious worms disperse more readily from patch to patch than do solitary worms, which can cause partitioning of a fragmented resource. The dispersal propensity of both gregarious and solitary worms increases with density. npr-1-dependent dispersal is independent of aggregation and could be part of a food-searching strategy. The gregarious allele is favored in a fragmented relative to a continuous food environment in competition experiments. We conclude that the npr-1 polymorphism could be maintained by a trade-off between dispersal and competitive ability.     

Depicting the phenotypic space of the annual plant Diplotaxis acris in hyperarid deserts

The phenotypic space encompasses the assemblage of trait combinations yielding well‐suited integrated phenotypes. At the population level, understanding the phenotypic space structure requires the quantification of among‐ and within‐population variations in traits and the correlation pattern among them. Here, we studied the phenotypic space of the annual plant Diplotaxis acris occurring in hyperarid deserts. Given the advance of warming and aridity in vast regions occupied by drylands, D. acris can indicate the successful evolutionary trajectory that many other annual plant species may follow in expanding drylands. To this end, we conducted a greenhouse experiment with 176 D. acris individuals from five Saudi populations to quantify the genetic component of variation in architectural and life history traits. We found low among‐population divergence but high among‐individual variation in all traits. In addition, all traits showed a high degree of genetic determination in our study experimental conditions. We did not find significant effects of recruitment and fecundity on fitness. Finally, all architectural traits exhibited a strong correlation pattern among them, whereas for life history traits, only higher seed germination implied earlier flowering. Seed weight appeared to be an important trait in D. acris as individuals with heavier seeds tended to advance flowering and have a more vigorous branching pattern, which led to higher fecundity. Population divergence in D. acris might be constrained by the severity of the hyperarid environment, but populations maintain high among‐individual genetic variation in all traits. Furthermore, D. acris showed phenotypic integration for architectural traits and, to a lesser extent, for life history traits. Overall, we hypothesize that D. acris may be fine‐tuned to its demanding extreme environments. Evolutionary speaking, annual plants facing increasing warming, aridity, and environmental seasonality might modify their phenotypic spaces toward new phenotypic configurations strongly dominated by correlated architectural traits enhancing fecundity and seed‐related traits advancing flowering time.     

Dietary Regimens Modify Early Onset of Obesity in Mice Haploinsufficient for Rai1

Smith-Magenis syndrome is a complex genomic disorder in which a majority of individuals are obese by adolescence. While an interstitial deletion of chromosome 17p11.2 is the leading cause, mutation or deletion of the RAI1 gene alone results in most features of the disorder. Previous studies have shown that heterozygous knockout of Rai1 results in an obese phenotype in mice and that Smith-Magenis syndrome mouse models have a significantly reduced fecundity and an altered transmission pattern of the mutant Rai1 allele, complicating large, extended studies in these models. In this study, we show that breeding C57Bl/6J Rai1^+/− mice with FVB/NJ to create F1 Rai1^+/− offspring in a mixed genetic background ameliorates both fecundity and Rai1 allele transmission phenotypes. These findings suggest that the mixed background provides a more robust platform for breeding and larger phenotypic studies. We also characterized the effect of dietary intake on Rai1^+/− mouse growth during adolescent and early adulthood developmental stages. Animals fed a high carbohydrate or a high fat diet gained weight at a significantly faster rate than their wild type littermates. Both high fat and high carbohydrate fed Rai1^+/− mice also had an increase in body fat and altered fat distribution patterns. Interestingly, Rai1^+/− mice fed different diets did not display altered fasting blood glucose levels. These results suggest that dietary regimens are extremely important for individuals with Smith- Magenis syndrome and that food high in fat and carbohydrates may exacerbate obesity outcomes.     

A trans-acting regulatory product necessary for expression of the Drosophila melanogaster 68C glue gene cluster

The mutation I(1)npr-1 is located at cytological location 2B5 on the X chromosome in Drosophila melanogaster. We have found that this mutation causes absence of the normal product of the 2B5 locus and that it has the following phenotypes: the 68C glue puff on the third chromosome does not regress when mutant salivary glands are cultured in the presence of ecdysterone; the three 68C glue protein mRNAs are not synthesized; and a transformed Drosophila strain carrying both a normal resident 68C Sgs-3 gene and an introduced functional Sgs-3 gene with only a few kb of flanking sequences expresses neither Sgs-3 RNA if the I(1)npr-1 mutation is crossed into the stock. Thus the normal product of the I(1)npr11 gene is required for regression of the 68C puff, and the I(1)npr-1 gene product allows expression of the Sgs-3 gene by interacting, either directly or indirectly, with DNA sequences near this glue protein gene.     

Beyond mean allelic effects: A locus at the major color gene MC1R associates also with differing levels of phenotypic and genetic (co)variance for coloration in barn owls

The mean phenotypic effects of a discovered variant help to predict major aspects of the evolution and inheritance of a phenotype. However, differences in the phenotypic variance associated to distinct genotypes are often overlooked despite being suggestive of processes that largely influence phenotypic evolution, such as interactions between the genotypes with the environment or the genetic background. We present empirical evidence for a mutation at the melanocortin‐1‐receptor gene, a major vertebrate coloration gene, affecting phenotypic variance in the barn owl, Tyto alba. The white MC1R allele, which associates with whiter plumage coloration, also associates with a pronounced phenotypic and additive genetic variance for distinct color traits. Contrarily, the rufous allele, associated with a rufous coloration, relates to a lower phenotypic and additive genetic variance, suggesting that this allele may be epistatic over other color loci. Variance differences between genotypes entailed differences in the strength of phenotypic and genetic associations between color traits, suggesting that differences in variance also alter the level of integration between traits. This study highlights that addressing variance differences of genotypes in wild populations provides interesting new insights into the evolutionary mechanisms and the genetic architecture underlying the phenotype.     

Variations in life history traits and flight capacity among populations of the light brown apple moth Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae)

Abstract The empirical study of interpopulation variation in life history and other fitness traits has been an important approach to understanding the ecology and evolution of organisms and gaining insight into possible sources of variation. We report a quantitative analysis for variations of five life history traits (larval developmental time, adult body weight, adult lifespan, age at first reproduction, total fecundity) and flight capacity among populations of Epiphyas postvittana originating from four localities in Australia and one in New Zealand. These populations were compared at two temperatures (15° and 25°C) after being maintained under uniform laboratory conditions for 1.5 generations, so that the relative role of genetic divergence and phenotypic plasticity in determining interpopulation variation could be disentangled. Genetic differentiation between populations was shown in all measured traits, with the greatest divergence occurring in developmental time, fecundity and adult body size. However, these traits were highly sensitive to changes in environmental temperatures; and furthermore, significant interactions between population and temperature occurred in all traits except for flight capacity of female moths. Thus, phenotypic plasticity may be another cause of interpopulation variation. The interpopulation variation for some measured traits was apparently related to climatic differences found where the populations originated. Individuals of the populations from the warmer climates tended to develop more slowly at immature stages, producing smaller and less fecund moths but with stronger flight capacity, in comparison to those from the cooler regions. It seems, therefore, that natural populations of E. postvittana have evolved different strategies to cope with local environmental conditions.     

Population genetic variation in gene expression is associated with phenotypic variation in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Background

The relationship between genetic variation in gene expression and phenotypic variation observable in nature is not well understood. Identifying how many phenotypes are associated with differences in gene expression and how many gene-expression differences are associated with a phenotype is important to understanding the molecular basis and evolution of complex traits.

Results

We compared levels of gene expression among nine natural isolates of Saccharomyces cerevisiae grown either in the presence or absence of copper sulfate. Of the nine strains, two show a reduced growth rate and two others are rust colored in the presence of copper sulfate. We identified 633 genes that show significant differences in expression among strains. Of these genes, 20 were correlated with resistance to copper sulfate and 24 were correlated with rust coloration. The function of these genes in combination with their expression pattern suggests the presence of both correlative and causative expression differences. But the majority of differentially expressed genes were not correlated with either phenotype and showed the same expression pattern both in the presence and absence of copper sulfate. To determine whether these expression differences may contribute to phenotypic variation under other environmental conditions, we examined one phenotype, freeze tolerance, predicted by the differential expression of the aquaporin gene AQY2. We found freeze tolerance is associated with the expression of AQY2.

Conclusions

Gene expression differences provide substantial insight into the molecular basis of naturally occurring traits and can be used to predict environment dependent phenotypic variation.

     

Oxytocin and Vasopressin Receptor Gene Variation as a Proximate Base for Inter- and Intraspecific Behavioral Differences in Bonobos and Chimpanzees

Recent literature has revealed the importance of variation in neuropeptide receptor gene sequences in the regulation of behavioral phenotypic variation. Here we focus on polymorphisms in the oxytocin receptor gene (OXTR) and vasopressin receptor gene 1a (Avpr1a) in chimpanzees and bonobos. In humans, a single nucleotide polymorphism (SNP) in the third intron of OXTR (rs53576 SNP (A/G)) is linked with social behavior, with the risk allele (A) carriers showing reduced levels of empathy and prosociality. Bonobos and chimpanzees differ in these same traits, therefore we hypothesized that these differences might be reflected in variation at the rs53576 position. We sequenced a 320 bp region surrounding rs53576 but found no indications of this SNP in the genus Pan. However, we identified previously unreported SNP variation in the chimpanzee OXTR sequence that differs from both humans and bonobos. Humans and bonobos have previously been shown to have a more similar 5′ promoter region of Avpr1a when compared to chimpanzees, who are polymorphic for the deletion of ∼360 bp in this region (+/− DupB) which includes a microsatellite (RS3). RS3 has been linked with variation in levels of social bonding, potentially explaining part of the interspecies behavioral differences found in bonobos, chimpanzees and humans. To date, results for bonobos have been based on small sample sizes. Our results confirmed that there is no DupB deletion in bonobos with a sample size comprising approximately 90% of the captive founder population, whereas in chimpanzees the deletion of DupB had the highest frequency. Because of the higher frequency of DupB alleles in our bonobo population, we suggest that the presence of this microsatellite may partly reflect documented differences in levels of sociability found in bonobos and chimpanzees.     

The Apolipoprotein E (APOE) Gene Appears Functionally Monomorphic in Chimpanzees (Pan troglodytes)

Background

The human apolipoprotein E (APOE) gene is polymorphic, with three primary alleles (E2, E3, E4) that differ at two key non-synonymous sites. These alleles are functionally different in how they bind to lipoproteins, and this genetic variation is associated with phenotypic variation for several medical traits, including cholesterol levels, cardiovascular health, Alzheimer’s disease risk, and longevity. The relative frequencies of these alleles vary across human populations, and the evolution and maintenance of this diversity is much debated. Previous studies comparing human and chimpanzee APOE sequences found that the chimpanzee sequence is most similar to the human E4 allele, although the resulting chimpanzee protein might function like the protein coded for by the human E3 allele. However, these studies have used sequence data from a single chimpanzee and do not consider whether chimpanzees, like humans, show intra-specific and subspecific variation at this locus.

Methodology and Principal Findings

To examine potential intraspecific variation, we sequenced the APOE gene of 32 chimpanzees. This sample included 20 captive individuals representing the western subspecies (P. troglodytes verus) and 12 wild individuals representing the eastern subspecies (P. t. schweinfurthii). Variation in our resulting sequences was limited to one non-coding, intronic SNP, which showed fixed differences between the two subspecies. We also compared APOE sequences for all available ape genera and fossil hominins. The bonobo APOE protein is identical to that of the chimpanzee, and the Denisovan APOE exhibits all four human-specific, non-synonymous changes and appears functionally similar to the human E4 allele.

Conclusions

We found no coding variation within and between chimpanzee populations, suggesting that the maintenance of functionally diverse APOE polymorphisms is a unique feature of human evolution.     

A naturally occurring variant of Hsp90 that is associated with decanalization

The heat shock protein Hsp90 has been the focus of many studies since it was suggested that it acts to mediate the buffering of phenotypic variation. Hsp90-mediated buffering may result in the accumulation of cryptic genetic variation that, when released either as a consequence of environmental or genetic stress, increases the evolvability of a population. Recent studies using laboratory-induced mutations of Hsp90 and/or chemical inhibition to disrupt Hsp90 function confirm that Hsp90 can buffer cryptic genetic variation. We have previously identified a naturally occurring variant in the charged linker region of the Hsp90 gene, and now examine whether this variant is associated with altered levels of trait variability. The variant is associated with the release of cryptic genetic variation for canalized morphological (bristle) traits, but not for uncanalized morphological (wing and bristle) traits, and the effect on canalized traits depends on culture temperature. This suggests that natural genetic variation in Hsp90 may mediate the evolution of canalized morphological traits even if it does not influence the expression of variation for uncanalized traits.     

Phenotypic divergence and inter-specific trait correlation in a plant-pollinator/seed predator mutualism

Plant-pollinator interactions have been suggested as key drivers of morphological divergence and speciation of the involved taxa. These interactions can also promote sexual dimorphism in both the plant and pollinator, particularly if the pollinator is also a seed-eater and/or exerts different selection pressures on male and female plants. Here we tested the hypotheses that plant-pollinator interactions can be reflected in trait variation and sexual dimorphism in both organisms within and across populations. Across nine European populations, we examined intraspecific variation and sexual dimorphism in phenotypic traits potentially involved in the plant–insect interaction of the dioecious white campion Silene latifolia (Caryophyllaceae) and its specialist pollinator Hadena bicruris (Noctuidae). This interaction is expected to entail sex-specific selective pressures, as female moths lay eggs on female plants and the larvae predate on the seeds during their development. We compared divergence in phenotypic traits among populations and between sexes within populations, examined correlations between plant and pollinator traits, and between phenotypic distances and genetic distances among co-occurring populations for both plants and insects. We found key differences in phenotypic traits across populations of both the plant and moth, though only in the moth were these differences correlated with geographic distances. We also found evidence for sexual dimorphism in the plant but not in the pollinator. Evolution of floral sexual dimorphism in S. latifolia most likely results from the joint contribution of different selective forces, including biotic interactions with H. bicruris moths.     

Environmental determinants of population divergence in life‐history traits for an invasive species: climate,seasonality and natural enemies

Invasive species cope with novel environments through both phenotypic plasticity and evolutionary change. However, the environmental factors that cause evolutionary divergence in invasive species are poorly understood. We developed predictions for how different life‐history traits, and plasticity in those traits, may respond to environmental gradients in seasonal temperatures, season length and natural enemies. We then tested these predictions in four geographic populations of the invasive cabbage white butterfly (Pieris rapae) from North America. We examined the influence of two rearing temperatures (20 and 26.7 °C) on pupal mass, pupal development time, immune function and fecundity. As predicted, development time was shorter and immune function was greater in populations adapted to longer season length. Also, phenotypic plasticity in development time was greater in regions with shorter growing seasons. Populations differed significantly in mean and plasticity of body mass and fecundity, but these differences were not associated with seasonal temperatures or season length. Our study shows that some life‐history traits, such as development time and immune function, can evolve rapidly in response to latitudinal variation in season length and natural enemies, whereas others traits did not. Our results also indicate that phenotypic plasticity in development time can also diverge rapidly in response to environmental conditions for some traits.     

Morphological Variation in Wild Marmosets (Callithrix penicillata and C. geoffroyi) and Their Hybrids

Evolutionary theory and observation predict wider phenotypic variation in hybrids than parental species. Emergent phenotypic novelty in hybrids may in turn drive new adaptations or speciation by breaking parental phenotypic constraints. Primate hybridization is often documented through genetic evidence, but knowledge about the primate hybrid phenotype remains limited due to a small number of available studies on hybrid primate morphology. Here, we examine pelage and morphometric variation in two Brazilian marmoset species (Callithrix penicillata and C. geoffroyi) and their hybrids. Hybrids were sampled in an anthropogenic hybrid zone in the municipality of Viçosa, Minas Gerais state, Brazil. We analyzed hybrid facial and body pelage color variation, and compared 13 morphometric measures between hybrids and parental species. Five different hybrid facial morphotypes were observed, varying from intermediate to parental-like. Hybrid facial morphotypes were biased towards C. penicillata, suggesting that the pelage of this species may be dominant to that of C. geoffroyi in this context, and indicating that mate preference, and therefore gene flow/introgression, may be biased towards C. penicillata within the hybrid zone. Hybrid morphometric features were on average intermediate to parental species traits, but transgressive hybrids were also observed, suggesting that morphometric variation for the studied traits is consistent with Rieseberg’s complementary allele model. Finally, we observed a decoupling of facial patterning and size/shape in hybrids, relative to parent phenotypes, suggesting that an important factor driving phenotypic novelty within the Viçosa marmoset hybrid zone might be the loosening of evolutionary constraints on phenotypic trait integration.     

Geographic variation in body size, sexual size dimorphism and fitness components of a seed beetle: local adaptation versus phenotypic plasticity

Variation in body size, growth and life history traits of ectotherms along latitudinal and altitudinal clines is generally assumed to represent adaptation to local environmental conditions, especially adaptation to temperature. However, the degree to which variation along these clines is due to adaptation vs plasticity remains poorly understood. In addition, geographic patterns often differ between females and males – e.g. sexual dimorphism varies along latitudinal clines, but the extent to which these sex differences are due to genetic differences between sexes vs sex differences in plasticity is poorly understood. We use common garden experiments (beetles reared at 24, 30 and 36°C) to quantify the relative contribution of genetically‐based differentiation among populations vs phenotypic plasticity to variation in body size and other traits among six populations of the seed‐feeding beetle Stator limbatus collected from various altitudes in Arizona, USA. We found that temperature induces substantial plasticity in survivorship, body size and female lifetime fecundity, indicating that developmental temperature significantly affects growth and life history traits of S. limbatus. We also detected genetic differences among populations for body size and fecundity, and genetic differences among populations in thermal reaction norms, but the altitude of origin (and hence mean temperature) does not appear to explain these genetic differences. This and other recent studies suggest that temperature is not the major environmental factor that generates geographic variation in traits of this species. In addition, though there was no overall difference in plasticity of body size between males and females (when averaged across populations), we did find that the degree to which dimorphism changed with temperature varied among populations. Consequently, future studies should be extremely cautious when using only a few study populations to examine environmental effects on sexual dimorphism.