Spatial variation in the evolutionary potential and constraints of basal metabolic rate and body mass in a wild bird

An organism's energy budget is strongly related to resource consumption, performance, and fitness. Hence, understanding the evolution of key energetic traits, such as basal metabolic rate (BMR), in natural populations is central for understanding life-history evolution and ecological processes. Here we used quantitative genetic analyses to study evolutionary potential of BMR in two insular populations of the house sparrow (Passer domesticus). We obtained measurements of BMR and body mass (M_b) from 911 house sparrows on the islands of Leka and Vega along the coast of Norway. These two populations were the source populations for translocations to create an additional third, admixed ‘common garden’ population in 2012. With the use of a novel genetic group animal model concomitant with a genetically determined pedigree, we differentiate genetic and environmental sources of variation, thereby providing insight into the effects of spatial population structure on evolutionary potential. We found that the evolutionary potential of BMR was similar in the two source populations, whereas the Vega population had a somewhat higher evolutionary potential of M_b than the Leka population. BMR was genetically correlated with M_b in both populations, and the conditional evolutionary potential of BMR (independent of body mass) was 41% (Leka) and 53% (Vega) lower than unconditional estimates. Overall, our results show that there is potential for BMR to evolve independently of M_b, but that selection on BMR and/or M_b may have different evolutionary consequences in different populations of the same species.     

Dynamic sensitivity and nonlinear interactions influence the system-level evolutionary patterns of phototransduction proteins

Determining the influence of complex, molecular-system dynamics on the evolution of proteins is hindered by the significant challenge of quantifying the control exerted by the proteins on system output. We have employed a combination of systems biology and molecular evolution analyses in a first attempt to unravel this relationship. We employed a comprehensive mathematical model of mammalian phototransduction to predict the degree of influence that each protein in the system exerts on the high-level dynamic behaviour. We found that the genes encoding the most dynamically sensitive proteins exhibit relatively relaxed evolutionary constraint. We also investigated the evolutionary and epistatic influences of the many nonlinear interactions between proteins in the system and found several pairs to have coevolved, including those whose interactions are purely dynamical with respect to system output. This evidence points to a key role played by nonlinear system dynamics in influencing patterns of molecular evolution.     

Selection for a dominant oncogene and large male size as a risk factor for melanoma in the Xiphophorus animal model

Adult height is a risk factor in numerous human cancers that involve aberrant receptor tyrosine kinase (RTK) signalling. However, its importance is debated due to conflicting epidemiological studies and the lack of useful in vivo models. In Xiphophorus fishes (Platyfishes/Swordtails), a functional RTK, Xiphophorus melanoma receptor kinase (Xmrk), serves as the dominant oncogene and has been maintained for several million years despite being deleterious and in an extremely unstable genomic region. Here we show that the Xmrk genotype is positively correlated with standard length in male and female wild caught Xiphophorus cortezi sampled throughout their phylogeographic distribution. Histopathology confirms the occurrence of malignant melanomas in both sexes; however, melanoma incidence was extremely male biased. Furthermore, males collected with malignant melanomas in the field were significantly larger than both Xmrk males collected without melanomas and wildtype (Xmrk deficient) males. These results not only provide a novel selective mechanism for the persistence of the germline Xmrk oncogene but also create an innovative avenue of melanoma research within the Xiphophorus fishes. Wildlife cancer in natural systems is a growing concern, therefore, future research investigating life history characteristics associated with certain phenotypes and genotypes that predispose an individual to cancer will be fundamental to increasing our understanding of the evolutionary biology of cancer in nature as well as in humans.     

Evolutionary rate variation in anthocyanin pathway genes

Over a broad taxonomic range that spans monocots and dicots, upstream enzymes of the anthocyanin pigment pathway have evolved less rapidly than downstream enzymes. In this article we show that this pattern is also evident within the genus Ipomoea. Specifically, the most upstream enzyme, chalcone synthase (CHS-D), evolves more slowly than the two most downstream enzymes, ancyocyanidin synthase (ANS) and UDP glucose flavonoid 3-oxy-glucosyltransferase (UFGT). This pattern appears not to be due to variation in mutation rates, because the CHS-D gene exhibits higher synonymous substitution rates than the genes for the other two enzymes. Codon-based tests for positive selection suggest that it has been negligible or absent in all three genes. In addition, the mean number of indel-creating events is four times as high in the downstream genes as in CHS-D. Unlike the downstream genes, CHS-D also exhibits evidence of codon bias. Together, the evidence suggests that the difference in nonsynonymous substitution rates between upstream and downstream genes is due to relaxed constraint on the downstream genes rather than a greater frequency of positively selected substitutions.     

Can revisionism,in evolutionary biology,help in formulating hypotheses about hominid evolution?

While evolutionary theory has been undergoing considerable revision for more than a decade scarcely any biological scientists are willing to resurrect the notion of acquired inheritance since it totally jndermines the concept of ancestor-descendant stability. Acquired inheritance is divisible into two components, soma to germ transfer to replicable information and directed or anticipatory mutation. Pure soma to germ transfer still allows for random events or natural selection as is evident from E. Steel’s proposal of the “somatic selection hypothesis”. Directed mutation is non-stochastic and self-referent. Recent bacterial research has claimed strong support for directed mutation but this phenomenon still would not be important for the small proportion of living taxa (including primates) who sequester their germlines early in ontogeny. There is a basic incompatibility between purposeful responses to final growth stages in complex metazoans and the need to permanently fix future growth into heritable programs. Symposium on Foundations for different approaches to the study of human evolution September 1–3, 1989, Liblice, Czechoslovakia, Czechoslovak Academy of Science     

Selection for character displacement is constrained by the genetic architecture of floral traits in the ivyleaf morning glory

Evolutionary theory predicts that interactions between species such as resource competition or reproductive interference will generate selection for character displacement where similar species co-occur. However, the rate and direction of character displacement will depend not only on the strength of selection for trait divergence, but also on the amount of genetic variation for selected traits and the nature of genetic correlations between them. To assess the importance of genetic constraints for the evolution of character displacement, we examined the genetic architecture of a suite of floral traits previously shown to be under selection in the annual plant Ipomoea hederacea when this species co-occurs with Ipomoea purpurea. We found that the six floral traits we measured are all positively genetically correlated. We also demonstrate, using new statistical approaches, that the predicted response to selection for four of these six traits is substantially constrained by their genetic correlation structure. Most notably, the response to selection for reduced separation of the tallest and shortest anthers, which reduces the degree of detrimental heterospecific pollen flow, is substantially constrained. Our results suggest that the rate of evolution of reproductive character displacement in I. hederacea is limited by the genetic architecture of floral traits.     

Observed and expected variation in hominid evolution

All of the major groups of fossil hominids (australopithecines, pithecanthropines, Neandertals, and early sapiens) were discovered by 1925, and therefore prior to the formulation of the synthetic theory of evolution that revolutionized the concept of the species in systematics. While these fossil finds were being made the framework for their interpretation included several assumptions: (1) that the number of living hominoid species was great, and that intraspecific variation was slight (authoritative sources recognized as many as 14 separate species of chimpanzees and 15 species of gorillas); (2) that the timescale of human evolution was brief (measured in tens or hundreds of thousands of years). As a result of these premises the consensus that hominid evolution was characterized by a large number of sympatric and synchronic species was virtually inevitable.In contrast, recent molecular studies demonstrate that genetic diversity among recent hominoids is so slight that even humans and chimpanzees differ at only about 1% of the loci that have been sampled so far; evidently, very small genetic differences can produce rather great contrasts in morphology. At the same time, geological break-throughs have increased the timescale for human evolution to several million years.It is concluded that morphological differences among fossil hominids, even if very appreciable and complex, do not necessarily reflect a great degree of either genetic or taxonomic diversity. Potential effects of evolutionary change through time should be incorporated into models of hominid evolution as a means of assessing the minimum number of lineages required to account for observed variations among hominid specimens.     

Natural selection on a leaf-shape polymorphism in the ivyleaf morning glory (Ipomoea hederacea)

Leaf shape is one of the most variable plant traits. Previous work has provided much indirect evidence that leaf-shape variation is adaptive and that leaf shape influences thermoregulation, water balance, and resistance to natural enemies. Nevertheless, there is little direct evidence that leaf shape actually affects plant fitness. In this study, we first demonstrate that populations of the ivyleaf morning glory, Ipomoea hederacea, in North and South Carolina are frequently polymorphic at a locus that influences leaf shape. We then employ several field experiments to show that this polymorphism is subject to selection. In two of the experiments, at different sites, heterozygotes enjoyed a fitness advantage over both homozygotes. At a third site, in one year directional selection favored lobed leaves, whereas in a second year the pattern of fitnesses was consistent with similar directional selection or heterozygote superiority. Computer simulations of heterozygote advantage under the high selfing rates of I. hederacea indicate that balancing selection of the magnitude observed can by itself stabilize the polymorphism, although spatially and temporally variable selection may also contribute to its long-term maintenance.     

Testing the molecular and evolutionary causes of a 'leapfrog' pattern of geographical variation in coloration

Understanding the mechanisms accounting for the evolution of phenotypic diversity is central to evolutionary biology. We use molecular and phenotypic data to test hypotheses for 'leapfrog' patterns of geographical variation, in which phenotypically similar, disjunct populations are separated by distinct populations of the same species. Phylogenetic reconstructions revealed independent evolution of melanic plumage characters in different populations in the Neotropical avian genus Arremon. Thus, phenotypic similarities between distant populations cannot be explained by close phylogenetic affinity. Nor can they be attributed to recurring mutations in the MC1R gene, a locus involved in melanic pigmentation. A coalescent analysis indicates that plumage traits have become fixed at a faster rate than expected under genetic drift, suggesting that selection underlies their repeated evolution. In contrast to views that genetic drift drives phenotypic differentiation in Neotropical montane birds, our results imply that geographical variation preceding speciation may reflect the action of deterministic selective processes.     

Mitochondrial variation in small brown planthoppers linked to multiple traits and probably reflecting a complex evolutionary trajectory

While it has been proposed in several taxa that the mitochondrial genome is associated with adaptive evolution to different climatic conditions, making links between mitochondrial haplotypes and organismal phenotypes remains a challenge. Mitonuclear discordance occurs in the small brown planthopper (SBPH), Laodelphax striatellus, with one mitochondrial haplogroup (HGI) more common in the cold climate region of China relative to another form (HGII) despite strong nuclear gene flow, providing a promising model to investigate climatic adaptation of mitochondrial genomes. We hypothesized that cold adaptation through HGI may be involved, and considered mitogenome evolution, population genetic analyses, and bioassays to test this hypothesis. In contrast to our hypothesis, chill‐coma recovery tests and population genetic tests of selection both pointed to HGII being involved in cold adaptation. Phylogenetic analyses revealed that HGII is nested within HGI, and has three nonsynonymous changes in ND2, ND5 and CYTB in comparison to HGI. These molecular changes likely increased mtDNA copy number, cold tolerance and fecundity of SBPH, particularly through a function‐altering amino acid change involving M114T in ND2. Nuclear background also influenced fecundity and chill recovery (i.e., mitonuclear epistasis) and protein modelling indicates possible nuclear interactions for the two nonsynonymous changes in ND2 and CYTB. The high occurrence frequency of HGI in the cold climate region of China remains unexplained, but several possible reasons are discussed. Overall, our study points to a link between mtDNA variation and organismal‐level evolution and suggests a possible role of mitonuclear interactions in maintaining mtDNA diversity.     

A developmental approach to the problem of variation in evolutionary rates

Certain general features are widely recognized in evolution, one of which is the variability in the rate at which morphological characters evolve and taxa are replaced by others. Although some rate-variability in evolution no doubt arises because of different rates of ecological change, it is proposed that some of the variability also arises from developmental, rather than ecological, sources. A theory is outlined whereby early-acting genes influencing the course of development evolve more slowly, but have individually larger effects, than genes affecting development at a later stage in the life-cycle. The erratic course of morphological evolution that results is illustrated by computer simulation. It is suggested that the applicability of the theory is restricted to long-term evolution and that variability in the rate of evolution over shorter periods may be of an entirely different nature.     

Toward an integration of evolutionary biology and ecosystem science

At present, the disciplines of evolutionary biology and ecosystem science are weakly integrated. As a result, we have a poor understanding of how the ecological and evolutionary processes that create, maintain, and change biological diversity affect the flux of energy and materials in global biogeochemical cycles. The goal of this article was to review several research fields at the interfaces between ecosystem science, community ecology and evolutionary biology, and suggest new ways to integrate evolutionary biology and ecosystem science. In particular, we focus on how phenotypic evolution by natural selection can influence ecosystem functions by affecting processes at the environmental, population and community scale of ecosystem organization. We develop an eco-evolutionary model to illustrate linkages between evolutionary change (e.g. phenotypic evolution of producer), ecological interactions (e.g. consumer grazing) and ecosystem processes (e.g. nutrient cycling). We conclude by proposing experiments to test the ecosystem consequences of evolutionary changes.     

Fundamental links between genes and elements: evolutionary implications of ecological stoichiometry

Organisms require elements to live and reproduce. We already know that availability of certain elements [e.g. phosphorus (P)] is highly variable spatiotemporally. In addition, there is variability in demand for various elements ontogenetically, as well as phylogenetically. Nonetheless, we know little about the underlying causes for such variation. In this study, we surveyed the literature to identify genes involved in the homeostasis of one biogenic element, P. Evidence from the literature suggests that variation in the environmental supply of P affects expression of highly conserved genes (e.g. the phosphate transporter system). In addition, we found evidence for genetic variation in the acquisition, assimilation, and allocation of P. Such effects of P supply should impinge on fitness, and drive evolutionary change. Further understanding of the inter- and intraspecific fitness consequences to imbalances in the availability of P in relation to other biogenic elements may be useful to disentangle primary mechanisms driving diversifications. We argue that studying the interactions between stoichiometric constraints and underlying genes is relevant to the majority of organisms, and conclude by furnishing information on designing and interpreting experiments using this approach.     

Statistical and molecular analyses of evolutionary significance of red-green color vision and color blindness in vertebrates

Red-green color vision is strongly suspected to enhance the survival of its possessors. Despite being red-green color blind, however, many species have successfully competed in nature, which brings into question the evolutionary advantage of achieving red-green color vision. Here, we propose a new method of identifying positive selection at individual amino acid sites with the premise that if positive Darwinian selection has driven the evolution of the protein under consideration, then it should be found mostly at the branches in the phylogenetic tree where its function had changed. The statistical and molecular methods have been applied to 29 visual pigments with the wavelengths of maximal absorption at approximately 510-540 nm (green- or middle wavelength-sensitive [MWS] pigments) and at approximately 560 nm (red- or long wavelength-sensitive [LWS] pigments), which are sampled from a diverse range of vertebrate species. The results show that the MWS pigments are positively selected through amino acid replacements S180A, Y277F, and T285A and that the LWS pigments have been subjected to strong evolutionary conservation. The fact that these positively selected M/LWS pigments are found not only in animals with red-green color vision but also in those with red-green color blindness strongly suggests that both red-green color vision and color blindness have undergone adaptive evolution independently in different species.     

植物种群分子进化中对生境的适应——对荒漠植物遗传多样性研究结果的初步分析

长期以来,自然选择理论与中性理论对生物分子进化中的环境适应机理存在着激烈争论。目前,在植物种群分子进化中对生境适应的研究中正面临着一些难题：中性突变是分子水平进化的唯一原因,自然选择发挥主要作用的适应性进化是否存在于分子水平,选择与中性两种学说两种机制完全不同,如何才能将两者联系和统一起来,部分学者利用建立各种模型来描述自然选择对分子标记位点以及连锁序列的直接作用,如生态位宽度变异假设等。本研究小组以新疆阜康荒漠植物为研究对象,通过对两种重要荒漠植物遗传多样性的研究,分析两种植物各亚种群不同生境的生态因子与其遗传变异的关系,讨论生态位宽度变异假设,揭示遗传变异的产生与维持。中性论者与选择论者都试图解释生物环境适应与分子变异之间的关系。中性论和选择论是反映进化的两个侧面,它们不是绝对的,可以相互转化。