Evolution In Natural Populations Research Articles

MORPHOLOGICAL EVOLUTION IN RESPONSE TO FLUCTUATING SELECTION.

A central issue in the study of evolution in natural populations is how morphology evolves in response to environmental complexity, especially when environmental variation results in contrasting selective pressures (Levins 1968; Boyce 1979; Gomulkiewicz and Kirkpatrick 1992). In birds, contrasting selective pressures associated with seasonal fluctuations are common (e.g., Fretwell 1972; Newton 1972; Baker and Baker 1973; Price and Grant 1984; Schluter and Smith 1986). Here, we explore the consequences of seasonal fluctuations on the evolution of morphological traits related to foraging in the red crossbill (Loxia curvirostra). Crossbills are highly specialized for foraging on seeds in conifer cones (Benkman 1988, 1993; Benkman and Lindholm 1991) and rely on conifer seeds year-round (Newton 1972; Benkman 1987a, 1990, 1992). In seed-eating birds, bill size is the likely target of selection and so provides a logical focal trait for a study of the evolution of morphology related to foraging (e.g., Grant 1986). Here, we consider the evolution of bill size of one sibling species of red crossbill (L. curvirostra complex) that Groth (1993) designates as type 5. (Call types are recognized by their vocalizations, but also differ in bill and body size; Groth 1993.) Morphological traits associated with avian foraging ecology are, with few exceptions (e.g., Smith 1993), polygenically inherited (Boag and van Noordwijk 1987; Grant and Grant 1989). To make predictions concerning the evolution of quantitative traits, estimates of both the amount of genetic variation for the trait and the pattern of selection acting on the trait are needed. In this study, we assume that evolution of bill size is not genetically constrained and is determined mostly by selection. Based on the results of other studies of seed-eating birds (Boag and van Noordwijk 1987; Grant and Grant 1989) this simplifying assumption is unlikely to interfere with our predictions. The form of selection depends on the relationship between the trait and fitness. Field estimates of fitness are difficult to obtain for nomadic species such as red crossbills. Therefore, we make use of the partitioning suggested by Arnold (1983) where first the relationship between the trait and some measure of performance is estimated and then performance is related to fitness. We use the time to extract seeds from cones as a measure of performance, which can be measured in aviaries (Benkman 1993). Furthermore, we adjust foraging ef-

Evolution in Natural Populations: Personal Perspectives

EcologyVolume 76, Issue 1 p. 318-318 Book Review Evolution in Natural Populations: Personal Perspectives Kimberly A. Hughes, Kimberly A. HughesSearch for more papers by this author Kimberly A. Hughes, Kimberly A. HughesSearch for more papers by this author First published: 01 January 1995 https://doi.org/10.2307/1940658Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume76, Issue1January 1995Pages 318-318 RelatedInformation

Evolution of morphological differences with moderate genetic correlations among traits as exemplified by two flycatcher species ( Ficedula; Muscicapidae)

Theoretical work on multivariate evolution predicts that genetic correlations can act to constrain the rate at which new adaptive peaks are reached, but there is very limited empirical information available on this issue so far. To evaluate the importance of genetic correlations for evolutionary change, we studied the morphological differences between two flycatcher species ( Ficedula albicollis and F. hypoleuca) using both univariate and multivariate quantitative genetic models. Comparison of the results obtained using these different models revealed that even relatively low genetic correlations between traits will considerably increase the net selection forces needed for evolutionary changes in morphology. In particular, the divergence in wing and tail length, which are positively genetically correlated, would require a considerable amount of antagonistic selection. Because of the genetic correlations, strong selection will be needed to retain certain traits unchanged while others are changing. Based on these results, we argue that it is unlikely that small morphological differences such as between these two species could have evolved during a short (200 years) time period, i.e. the period of sympatry of these species in Sweden. These findings support the hypothesis that even relatively low genetic correlations may constrain short-term adaptive evolution in natural populations.

Evolution of morphological differences with moderate genetic correlations among traits as exemplified by two flycatcher species (Ficedula; Muscicapidae)

Abstract Theoretical work on multivariate evolution predicts that genetic correlations can act to constrain the rate at which new adaptive peaks are reached, but there is very limited empirical information available on this issue so far. To evaluate the importance of genetic correlations for evolutionary change, we studied the morphological differences between two flycatcher species ( Ficedula albicollis and F. hypoleuca ) using both univariate and multivariate quantitative genetic models. Comparison of the results obtained using these different models revealed that even relatively low genetic correlations between traits will considerably increase the net selection forces needed for evolutionary changes in morphology. In particular, the divergence in wing and tail length, which are positively genetically correlated, would require a considerable amount of antagonistic selection. Because of the genetic correlations, strong selection will be needed to retain certain traits unchanged while others are changing. Based on these results, we argue that it is unlikely that small morphological differences such as between these two species could have evolved during a short (200 years) time period, i.e. the period of sympatry of these species in Sweden. These findings support the hypothesis that even relatively low genetic correlations may constrain short-term adaptive evolution in natural populations.

Effects of Chromosomal Addition on Reaction Norms of Triticum aestivum

A better knowledge of the genetics and degree of variability of phenotypic plasticity is particularly important for the understanding of evolution in natural populations. Also, for agronomically significant plants, plasticity has implications for the yield in different conditions. Phenotypic response to three levels of nitrogen availability was investigated in Triticum aestivum var. Chinese Spring (CS). A CS pure line and seven chromosomal addition lines from a wild relative (Elytrigia elongata) were grown in a greenhouse. Two-way ANOVAs of 19 morphological traits were used to detect the presence of main line effects, main treatment effects, and line x treatment interactions. We found genetic variation for character means in 10 traits, and evidence for plasticity in six traits, but no significant genetic variation for plasticity. A multivariate approach allowed us to summarize the phenotypic variation using three principal factors: the first one relating to reproductive output, the second one to plant size, and the third one to shape of flag leaf and first spike. The first and third factors turned out to be significantly plastic according to the analysis of variance, while the first and second components presented genetic variation. Addition lines of T. aestivum lack genetic variation for plasticity. The mean phenotypic response, however, shows complex genetic effects, with more than one addition chromosome interfering in the control of the average across-treatments phenotype.

Environmental and Demographic Correlates of Spatial and Seasonal Genetic Structure in the Eastern Cottontail (Sylvilagus floridanus)

Elucidation of the complex interactions of forces that affect genetic structure within and among populations is important in the assessment of short-term viability and evolution of natural populations. We examined spatial and temporal changes in genetic, demographic, and ecologic characteristics of the eastern cottontail (Sylvilagusfloridanus; n = 543) within two isolated populations inhabiting playa lake basins in the Texas Panhandle. Spatial autocorrelation and contiguous clustering analyses documented nonrandom dispersion of genotypes within both populations, during each of four consecutive seasons. Considerable seasonal variation in genotypic autocorrelative patterns and size, position, and genotypic composition of significant contiguous clusters also was observed. Genotypic structuring within playa basins was particularly evident during spring, summer, and autumn; greater randomization of genetic distributions occurred in the winter, prereproductive season. Presence of spatial associations of genotypes and changes in their position and composition over seasons were influenced by episodic exchange of individuals from genetically different populations, subsequent random mating and restoration of Hardy-Weinberg genotypic proportions in resulting offspring, and patchy distribution of habitat types within playa basins. Mantel matrix regressions, which were used to test relationships among demographic, habitat, and genotypic variables show that the relative importance of each factor changes seasonally. Differences in habitat use among individuals were significantly correlated with genotypic cluster affiliation during the prereproductive period, whereas age structure became increasingly important in explaining spatial arrangement of genotypes during later periods. Although populations from different playa basins differ in gene frequency, seasonal changes in genetic structure within each population were correlated.

Ecology and genetics of insecticide resistance inHelicoverpa armigera: Interactions between selection and gene flow

Pyrethroid resistance inHelicoverpa armigera provides a model system in which to study evolution in natural populations. Resistance is seen to evolve as a consequence of selection pressure that varies within and between life-stages and gene flow. Although three different mechanisms are involved, present day fluctuations in phenotype frequency can be explained by variation in only one of these, metabolic resistance, that is inherited as a single, incompletely dominant gene,mfo. Selective mortality of phenotypes occurs in both larvae and adults in the presence of the pyrethroid insecticides. Although most individuals of all three genotypes are killed in young larvae, selection in this age-class contributes significantly to evolution of resistance. While there is some evidence of reduced fitness of resistant pupae during winter diapause, most of the decline in resistance frequencies each spring occurs as a result of immigration of susceptible individuals into insecticide-treated populations.

Evolution of the Drosophila melanogaster-sigma virus system in natural populations from Languedoc (southern France).

An analysis of natural populations of Drosophila melanogaster in a southern French region (Languedoc) was started in 1983, concerning two non Mendelian systems: the P-M system of transposable elements and the sigma virus. This virus is not contagious, but only transmitted through gametes; it is usually present in a minority of individuals in natural populations. The first data collected revealed unexpectedly clear and fast-evolving phenomena; they also gave evidence of some interesting correlations between the two systems. This paper presents all the results gathered from 1983 to 1991 in the Drosophila-sigma system. Striking correlations were observed for three interconnected parameters: frequency of infected flies, frequency of an allele of the fly giving resistance to the virus, and adaptation of the virus to this allele. This adaptation consisted of a qualitative step (change of viral type) followed by quantitative variation (better adaptation to the allele). This analysis also showed, firstly, that the evolution of natural populations differs completely in Languedoc from the rest of France; secondly, that three geographical zones where selective forces worked differently persisted over time in Languedoc.

Clinal Variation in Cold Adaptation in Mus domesticus: Verification of Predictions from Laboratory Populations

The aim of this study was to test whether heritabilities of traits contributing to cold adaptation and genetic correlations among those traits, all obtained from laboratory populations, could predict adaptive evolution in natural populations. Body weight and nesting scores had substantial heritabilities and were expected to respond to selection, whereas body temperature and weight of brown adipose tissue had negligible heritabilities and should not be easily modified. In laboratory-reared mice originating from five geographical populations forming a cline along the east coast of the United States, body weight and nesting did exhibit adaptive variation: more northern mice were heavier and built larger nests. These traits may have been shaped by selection acting through ambient temperature differences. Body temperature and brown adipose tissue did not vary clinally, although there were some differences among the populations. Reaction norms for nesting at warm and cold temperatures were similar for laborator...

Selection response in traits with maternal inheritance

Maternal inheritance is the non-Mendelian transmission of traits from mothers to their offspring. Despite its presence in virtually all organisms, acting through a variety of mechanisms, the evolutionary consequences of maternal inheritance are not well understood. Here we review and extend a model of the inheritance and evolution of multiple quantitative characters with complex pathways of maternal effects. Extensions of the earlier model include common family environmental effects not associated with maternal phenotype, sexual dimorphism, and paternal effects (non-Mendelian influence of the father on offspring traits). We find that, in contrast to simple Mendelian inheritance, maternal inheritance produces qualitatively different evolutionary dynamics for two reasons: (1) the response to selection on a set of characters depends not only on their additive genetic variances and covariances, but also on maternal characters that influence them, and (2) time lags in the response to selection create a form of evolutionary momentum. These results have important implications for evolution in natural populations and practical applications in the economic improvement of domesticated species. We derive selection indices that maximize either the economic improvement in a single generation of artificial selection or the asymptotic rate of improvement in long-term selection programmes, based on individual merit or a combination of individual and family merit. Numerical examples show that accounting for maternal inheritance can lead to considerable increases in the efficiency of artificial selection.

Evolution of natural populations in the Drosophila melanogaster sigma system II. Northern and Central France

A survey of French natural populations of Drosophila melanogaster has been systematically performed, concerning their status of infection by the sigma virus and the characteristics of viral clones. These investigations, which were not as extensive as those performed in the Languedoc region (Fleuriet et al., 1990) nevertheless give a good representation of the evolution of this system because of the long period involved (almost 20 years). Some trends were observed in all French populations such as (1) a decrease in the high efficiency of transmission by males (which is an important parameter for the viral invading ability); (2) high frequency of a best adapted viral Type. These high frequencies might be due to a recent invasion which is expected to spread to other European populations. However, the frequency of infected flies remained low in northern and central France, unlike in Languedoc. The complexity of this, apparently simple, system of two well-known coevolving organisms should once again be stressed. It is impossible with the known parameters to arrive at a general interpretation of observations made in Languedoc and the rest of France. These data may also throw some light on the structure of French wild populations of D. melanogaster which appear to be subdivided into local populations between which gene flow might be low.

Diazinon resistance, fluctuating asymmetry and fitness in the Australian sheep blowfly, lucilia cuprina.

Genetic evidence suggests that the evolution of resistance to the insecticide diazinon in Lucilia cuprina initially produced an increase in asymmetry. At that time resistant flies were presumed to be at a selective disadvantage in the absence of diazinon. Subsequent evolution in natural populations selected modifiers to ameliorate these effects. The fitness and fluctuating asymmetry levels of resistant flies are currently similar to those of susceptibles. Previous genetic analyses have shown the fitness modifier to co-segregate with the region of chromosome III marked by the white eyes, w, locus, unlinked to the diazinon resistance locus, Rop-1, on chromosome IV. This study maps the asymmetry modifier to the same region, shows, as in the case of the fitness modifier, its effect to be dominant and presents data consistent with the fitness/asymmetry modifier being the same gene (gene complex). These results suggest changes in fluctuating asymmetry reflect changes in fitness.

MAXIMUM-LIKELIHOOD APPROACHES APPLIED TO QUANTITATIVE GENETICS OF NATURAL POPULATIONS.

Growing interest in adaptive evolution in natural populations has spurred efforts to infer genetic components of variance and covariance of quantitative characters. Here, I review difficulties inherent in the usual least-squares methods of estimation. A useful alternative approach is that of maximum likelihood (ML). Its particular advantage over least squares is that estimation and testing procedures are well defined, regardless of the design of the data. A modified version of ML, REML, eliminates the bias of ML estimates of variance components. Expressions for the expected bias and variance of estimates obtained from balanced, fully hierarchical designs are presented for ML and REML. Analyses of data simulated from balanced, hierarchical designs reveal differences in the properties of ML, REML, and F-ratio tests of significance. A second simulation study compares properties of REML estimates obtained from a balanced, fully hierarchical design (within-generation analysis) with those from a sampling design including phenotypic data on parents and multiple progeny. It also illustrates the effects of imposing nonnegativity constraints on the estimates. Finally, it reveals that predictions of the behavior of significance tests based on asymptotic theory are not accurate when sample size is small and that constraining the estimates seriously affects properties of the tests. Because of their great flexibility, likelihood methods can serve as a useful tool for estimation of quantitative-genetic parameters in natural populations. Difficulties involved in hypothesis testing remain to be solved.

DYNAMICS OF MORPHOLOGICAL DIFFERENTIATION: TEMPORAL IMPACT OF GENE FLOW IN POCKET GOPHER POPULATIONS.

What role does gene flow play in the evolution of natural populations? This has been an often debated question during the past two decades for at issue is a fundamental understanding of the relative roles of different evolutionary forces which may shape population and species differentiation (see Mayr, 1982). Gene flow has been viewed as a retarding element of speciation (Mayr, 1963) and the glue that holds populations together (Hartl, 1981). Gene flow may also provide a source of new genetic variation when migration occurs between populations with large differences in gene frequencies, such as well differentiated races. From single locus theory one can predict that . .. if the difference between the donor populations and the population that receives immigrants is .15 or greater, gene migration is at least equally potent in evolution, and usually more so, than selection pressures of equal magnitude (Wilson and Bossert, 1971 p. 63-64). On the other hand, Ehrlich and Raven (1969) and others have argued that gene flow may be only of minor significance in evolution because of the low dispersal propensity of many organisms (but see also Jackson and Pounds, 1979). The problem in assessing the evolutionary role of gene flow lies in the difficulty of documenting unequivocally its effects in natural populations. Indeed, few such studies are known. In the case of the water snake, Natrix sipedon, on islands in Lake Erie, selection against banded individuals is apparently balanced by migration of banded snakes from the mainland (Camin and Ehrlich, 1958). Most studies in the literature, however, involve measurement of individual movements, or dispersal, which is taken as an indirect measure of gene flow potential. Even so, these measures may vary geographically (e.g., Euphydryas editha on Jaspar Ridge [Brussard et al., 1974] as opposed to other localities [Gilbert and Singer, 1973]) so the significance of gene flow in any particular situation is difficult to ascertain from this perspective alone. Our study explores the potential impact of gene flow on morphological change in several natural populations of the pocket gopher, Thomomys bottae. Samples available from museum collections permit examination of both temporal and spatial variation over a period of less than one hundred years. Such temporal series, when examined in the context of spatial variation, are useful in distinguishing between patterns resulting from gene flow and those due to selection along environmental gradients. Pocket Gophers of the Colorado River. -Two geographic units within the Thomomys bottae complex meet along the lower Colorado River in California and Arizona (Smith and Patton, 1980). These are strongly differentiated electromorphically (mean genetic similarity is only .67), but population groupings based on either phenetic or phyletic analyses of genic data are discordant with morphological relationships suggested by previous authors. Three different systematic views of these populations are summarized in Figure 1. Thomomys b. albatus is a large, pale form inhabiting the Colorado River delta region in the Yuma Valley as well as irrigated land in the Imperial Valley of California. Thomomys b. riparius is also a large, pale form, found in the Palo Verde Valley to the north on the California side of the river. Thomomys b. chrysonotus is a small, pale gopher

PARTIAL REPRODUCTIVE ISOLATION IN THE GENUS PARTULA (GASTROPODA) ON MOOREA.

The polymorphic land snails of the genus Partula provide unusual opportunities for the study of evolution in natural populations. At the species level, the diversity of forms permits the investigation of the control of gene frequencies in populations. Above the species level, the occurrence of a number of similar species invites the study of speciation and reproductive isolation in the group. In his classic monograph on the members of the genus Partula inhabiting the island of Moorea, Crampton (1932) recognized 10 separate species. These taxonomic entities represent very different degrees of relatedness to one another. On the one hand, P. suturalis and P. taeniata are broadly sympatric and quite distinct. On the other, P. suturalis and P. dendroica are allopatric populations which should certainly be included within a single superspecies (Mayr, 1931), if not within the same species. Two groups of populations, inhabiting a few valleys in northeastern Moorea, present special problems which we wish to discuss. Each group consists of a closely related pair of entities which were accorded specific status by Crampton. While reserving judgment on the taxonomic relationships, we have found it convenient to use Crampton's names to refer to these groups as the Partula suturalis/aurantia and Partula taeniata/exigua complexes. In each case our field collections show a range of variation in the degree of distinctiveness of the members of the pairs. After failing in our attempt to separate the entities into meaningful conventional specific categories, we have turned to the method of rank correlation for our analysis. This paper explores some of the relationships revealed by this technique.

CHANGES IN THE VARIATION PATTERN OF A HYBRID POPULATION OFHELIANTHUSOVER AN EIGHT-YEAR PERIOD

Recent studies of natural populations of higher plants have pointed consistently to the hypothesis that hybridization between populations having markedly different adaptive properties, particularly if it occurs in a disturbed, changing environment where new ecological niches are likely to be available, is one of the strongest factors bringing about evolutionary change (Stebbins, 1959). Consequently studies of such populations, even if carried out over the relatively short periods of time available to the average investigator, should yield valuable information about the evolution of natural populations. The annual species of Helianthus, or sunflowers, are particularly favorable for this purpose. They are variable, widespread, and weedy, entering often into disturbed habitats. They are cross-fertilizing, due to self-incompatibility. Hybridization between species occurs frequently, and the interspecific hybrids, although highly sterile, nevertheless can produce some offspring, particularly through backcrossing, or introgression. There is some evidence that the variation of some species has been increased by this process. Since all of the annual species have the same chromosome number, n= 17, evolution within the group has not involved polyploidy. Finally, the group has been subjected to a series of careful cytotaxonomic studies by Heiser (1947, 1949, 1951a,b, 1954) from whose work the above information was obtained. The two annual sunflowers of California, Helianthus annuus and H. Bolanderi, occupy different ecological niches. The former is a weed of roadsides, very common in the Central Valley and in Southern California. The commonest subspecies is subsp. lenticularis (Dougl.) Ckll., which was already in the state when the first botanical collections were made, and was used by the Indians for various purposes (Heiser, 1949). Since it does not now occur in natural sites in California, it was very likely introduced originally by the Indians from farther east. Since the advent of the white man, repeated introductions from the eastern states have almost certainly been made. The cultivated sunflower, H. annuus subsp. macrocarpus, frequently escapes to roadsides, and hybrids between the two subspecies are not uncommon (Heiser, 1949, 1954). Helianthus Bolanderi, on the other hand, is a native, endemic species, its natural range extending from southern Oregon to south central California. It consists of two races, one of which is found in the inner coast ranges and Sierra foothills, chiefly on serpentine soil; the other is a ruderal plant which replaces or occurs with H. annuus subsp. lenticularis, in the western part of the Sacramento Valley, particularly in Solano, Yolo, and Colusa counties. Heiser (1949) made artificial hybrids between H. annuus and H. Bolanderi, and compared them directly with the natural hybrid swarms. He found that the F1 hybrids had variable pollen and seed fertility, ranging mostly between 2 and 10 per cent. Meiosis in them is somewhat irregular, with chains of 6 chromosomes being usually found and chains of 8 occasionally. The two species differ, therefore, by several reciprocal translocations. Plants of backcross progenies have fertility values ranging from as low as the F1 hybrids to as high as the parental species. 1 Part of this study was carried out at Brookhaven National Laboratory under the auspices of the U. S. Atomic Energy Commission. 2 Present address: Department of Biological Sciences, San Fernando Valley State College, Northridge, California.

DARWINISM AND THE STUDY OF EVOLUTION IN NATURAL POPULATIONS

Journal Article DARWINISM AND THE STUDY OF EVOLUTION IN NATURAL POPULATIONS Get access E. B. Ford, F.R.S. E. B. Ford, F.R.S. 1Genetic Laboratories, Department of Zoology, University Museum, Oxford Search for other works by this author on: Oxford Academic Google Scholar Zoological Journal of the Linnean Society, Volume 44, Issue 295, July 1958, Pages 41–48, https://doi.org/10.1111/j.1096-3642.1958.tb01707.x Published: 28 June 2008

DARWINISM AND THE STUDY OF EVOLUTION IN NATURAL POPULATIONS

Journal Article DARWINISM AND THE STUDY OF EVOLUTION IN NATURAL POPULATIONS Get access E. B. Ford, F.R.S. E. B. Ford, F.R.S. 1Genetic Laboratories, Department of Zoology, University Museum, Oxford Search for other works by this author on: Oxford Academic Google Scholar Botanical Journal of the Linnean Society, Volume 56, Issue 365, July 1958, Pages 41–48, https://doi.org/10.1111/j.1095-8339.1958.tb01707.x Published: 01 April 2011