HOMOGENEITY OF THE GENETIC VARIANCE-COVARIANCE MATRIX FOR ANTIPREDATOR TRAITS IN TWO NATURAL POPULATIONS OF THE GARTER SNAKE THAMNOPHIS ORDINOIDES

Quantitative genetic models of evolution rely on the genetic variance-covariance matrix to predict the phenotypic response to selection. Both prospective and retrospective studies of phenotypic evolution across generations rely on assumptions about the constancy of patterns of genetic covariance through time. In the absence of robust theoretical predictions about the stability of genetic covariances, this assumption must be tested with empirical comparisons of genetic parameters among populations and species. Genetic variance-covariance matrices were estimated for a suite of antipredator traits in two populations of the northwestern garter snake, Thamnophis ordinoides. The characters studied include color pattern and antipredator behaviors that interact to facilitate escape from predators. Significant heritabilities for all traits were detected in both populations. Genetic correlations and covariances were found among behaviors in both populations and between color pattern and behavior in one of the populations. Phenotypic means differed among populations, but pairwise comparisons revealed no heterogeneity of genetic parameters between the populations. The structure of the genetic variance-covariance matrix has apparently not changed significantly during the divergence of these two populations.     

VARIATION IN GENETIC ARCHITECTURE OF CALLING SONG AMONG POPULATIONS OF ALLONEMOBIUS SOCIUS,A. FASCIATUS,AND A HYBRID POPULATION: DRIFT OR SELECTION?

Predictions using quantitative genetic models generally assume that the variance-covariance matrices remain constant over time. This assumption is based on the supposition that selection is generally weak and hence variation lost through selection can be replaced by new mutations. Whether this is generally true can only be ascertained from empirical studies. Ideally for such a study we should be able to make a prediction concerning the relative strength of selection versus genetic drift. If the latter force is prevalent then the variance-covariances matrices should be proportional to each other. Previous studies have indicated that females in the two sibling cricket species Allonemobius socius and A. fasciatus do not discriminate between males of the two species by their calling song. Therefore, differences between the calling song of the two males most likely result from drift rather than sexual selection. We test this hypothesis by comparing the genetic architecture of calling song of three populations of A. fasciatus with two populations of A. socius. We found no differences among populations within species, but significant differences in the G (genetic) and P (phenotypic) matrices between species, with the matrices being proportional as predicted under the hypothesis of genetic drift. Because of the proportional change in the (co)variances no differences between species are evident in the heritabilities or genetic correlations. Comparison of the two species with a hybrid population from a zone of overlap showed highly significant nonproportional variation in genetic architecture. This variation is consistent with a general mixture of two separate genomes or selection. Qualitative conclusions reached using the phenotypic matrices are the same as those reached using the genetic matrices supporting the hypothesis that the former may be used as surrogate measures of the latter.     

EVOLUTION OF TRADE-OFFS BETWEEN SEXUAL AND ASEXUAL PHASES AND THE ROLE OF REPRODUCTIVE PLASTICITY IN THE GENETIC ARCHITECTURE OF APHID LIFE HISTORIES

Life‐history theory postulates that evolution is constrained by trade‐offs (i.e., negative genetic correlations) among traits that contribute to fitness. However, in organisms with complex life cycles, trade‐offs may drastically differ between phases, putatively leading to different evolutionary trajectories. Here, we tested this possibility by examining changes in life‐history traits in an aphid species that alternates asexual and sexual reproduction in its life cycle. The quantitative genetics of reproductive and dispersal traits was studied in 23 lineages (genotypes) of the bird cherry‐oat aphid Rhopalosiphum padi, during both the sexual and asexual phases, which were induced experimentally under specific environmental conditions. We found large and significant heritabilities (broad‐sense) for all traits and several negative genetic correlations between traits (trade‐offs), which are related to reproduction (i.e., numbers of the various sexual or asexual morphs) or dispersal (i.e., numbers of winged or wingless morphs). These results suggest that R. padi exhibits lineage specialization both in reproductive and dispersal strategies. In addition, we found important differences in the structure of genetic variance–covariance matrices ( G ) between phases. These differences were due to two large, negative genetic correlations detected during the asexual phase only: (1) between fecundity and age at maturity and (2) between the production of wingless and winged parthenogenetic females. We propose that this differential expression in genetic architecture results from a reallocation scheme during the asexual phase, when sexual morphs are not produced. We also found significant G × E interaction and nonsignificant genetic correlations across phases, indicating that genotypes could respond independently to selection in each phase. Our results reveal a rather unique situation in which the same population and even the same genotypes express different genetic (co)variation under different environmental conditions, driven by optimal resource allocation criteria.     

HOW SIMILAR ARE GENETIC CORRELATION STRUCTURES? DATA FROM MICE AND RATS

An integral assumption of many models of morphometric evolution is the equality of the genetic variance-covariance structure across evolutionary time. To examine this assumption, the quantitative-genetic aspects of morphometric form are examined for eight pelvic traits in laboratory rats (Rattus norvegicus) and random-bred ICR mice (Mus musculus). In both species, all traits are significantly heritable, and there are significant phenotypic and genetic correlations among traits, although environmental correlations among the eight traits are low. The size relations among the pelvic variables are isometric. Three matrix-permutation tests are used to examine similarity of phenotypic, genetic, and environmental covariance and correlation matrices within and between species. Independent patterns of morphometric covariation and correlation arise from genetic and environmental effects within each species and from environmental effects between species. The patterns of phenotypic and genetic covariation and correlation are similar within each species, and the phenotypic and genetic correlations are also similar between these species. However, genetic covariance matrices show no significant statistical association between species. It is suggested that the assumption of equality of genetic variance-covariance structures across divergent taxa should be approached with caution.     

QUANTITATIVE GENETICS OF SURVIVAL AND GROWTH IN IMPATIENS CAPENSIS

When variation in life-history characters is caused by many genes of small effect, then quantitative-genetic parameters may quantify constraints on rate and direction of microevolutionary change. I estimated heritabilities and genetic correlations for 16 life-history and morphological characters in two populations of Impatiens capensis, a partially self-pollinating herbaceous annual. The Madison population had little or no additive genetic variance for any of these characters, while the Milwaukee population had significant narrowsense heritabilities and genetic correlations for several traits, including adult size, which is highly correlated with fitness. All genetic correlations among fitness components were positive, hence there is no evidence for antagonistic pleiotropy among these traits. Dissimilarity of heritabilities in the two populations supports theoretical predictions that long-term changes in genetic variance-covariance patterns may occur when population sizes are small and selection is strong, as may occur in many plant species.     

DEVELOPMENT,FUNCTION, AND THE QUANTITATIVE GENETICS OF WING MELANIN PATTERN IN PIERIS BUTTERFLIES

Do genetic correlations among phenotypic characters reflect developmental organization or functional coadaptation of the characters? We test these hypotheses for the wing melanin pattern of Pieris occidentalis butterflies, by comparing estimated genetic correlations among wing melanin characters with a priori predictions of the developmental organization and the functional (thermoregulatory) organization of melanin pattern. There were significant broad-sense heritabilities and significant genetic correlations for most melanin characters. Matrix correlation tests revealed significant agreement between the observed genetic correlations and both developmental and functional predictions in most cases; this occurred even when the overlap between developmental and functional predictions was eliminated. These results suggest that both developmental organization and functional coadaptation among melanin characters influence the genetic correlation structure of melanin pattern in this species. These results have two important implications for the evolution of melanin pattern in P. occidentalis and other butterflies: 1) most phenotypic variation in pattern may reflect variation among, rather than within, sets of developmentally homologous wing melanin characters; and 2) in a changing selective environment, genetic correlations may retard the disruption of functionally coupled melanin characters, thus affecting the evolutionary response to selection.     

THE HERITABLE BASIS OF VARIATION IN LARVAL DEVELOPMENTAL PATTERNS WITHIN POPULATIONS OF THE WOOD FROG (RANA SYLVATICA)

This study compares the heritable basis of variation in larval developmental patterns of mountain and lowland populations of the wood frog, Rana sylvatica. Additive genetic variances, heritabilities, and genetic correlations for larval developmental time and size at metamorphosis are estimated from half-sib and full-sib crosses. Considerable additive-genetic variances and high heritabilities are revealed for developmental time in both the mountain and the lowland population. There was a high level of additive-genetic variance and high heritability for body size at metamorphosis in the mountain population, but these were very low in the lowland population. The genetic correlations between developmental rate and larval body size are negative for the mountain population and near zero for the lowland population. It is argued that the differences in genetic structure between these two populations reflect differences in the selective regimes of their respective environments.     

PAIRWISE VERSUS DIFFUSE NATURAL SELECTION AND THE MULTIPLE HERBIVORES OF SCARLET GILIA,IPOMOPSIS AGGREGATA

Recent theoretical studies have argued that plant-herbivore coevolution proceeds in a diffuse rather than a pairwise manner in multispecies interactions when at least one of two conditions are met: (1) genetic correlations exist between plant resistances to different herbivore species; and (2) ecological interactions between herbivores sharing a host plant cause nonadditive impacts of herbivory on plant fitness. We present results from manipulative field experiments investigating the single and interactive fitness effects of three types of herbivory on scarlet gilia (Ipomopsis aggregata) over two years of study. We utilize these data to test whether selection imposed by herbivore attack on date of first flowering is pairwise (independent) or diffuse (dependent) in nature. Our results reveal complex patterns of the fitness effect of herbivores. Simulated early season browsing had a strong negative fitness effect on plants and also reduced subsequent insect attack. Surprisingly, this ecological interaction did not translate into significant interactions between clipping and insect manipulations on plant fitness. However, we detected a significant interaction between seed fly and caterpillar herbivory on plant fitness, with the negative effect of either insect being greatest when occurring alone. These results suggest that herbivore-imposed selection may have pairwise and diffuse components. In our selection analysis of flowering phenology, we discovered significant pairwise linear selection imposed by clipping, diffuse linear selection imposed by insects, and diffuse nonlinear selection imposed by clipping and insect attack acting simultaneously. Our results reveal that the evolution of flowering phenology in scarlet gilia may be in response to diffuse and pairwise natural selection imposed by multiple herbivores. We discuss the evolution of resistance characters in light of diffuse versus pairwise forms of linear and nonlinear selection and stress the complexity of selection imposed by suites of interacting species.     

QUANTITATIVE GENETICS OF SEXUAL SIZE DIMORPHISM IN THE COLLARED FLYCATCHER,FICEDULA ALBICOLLIS

Quantitative genetic theory predicts that evolution of sexual size dimorphism (SSD) will be a slow process if the genetic correlation in size between the sexes is close to unity, and the heritability of size is similar in both sexes. However, there are very few reliable estimates of genetic correlations and sex-specific heritabilities from natural populations, the reasons for this being that (1) offspring have often been sexed retrospectively, and hence, selection acting differently with respect to body size in the two sexes between measuring and sex identification can bias estimates of SSD; and (2) in many taxa, parents may be incorrectly assigned to offspring either because of assignment errors or because of extrapair paternity. We used molecular sex and paternity identification to overcome these problems and estimated sex-specific heritabilities and the genetic correlation in body size between the two sexes in the collared flycatcher, Ficedula albicollis. After exclusion of the illegitimate offspring, the genetic correlation in body size between the sexes was 1.00 (SE = 0.22), implying a severe constraint on the evolution of SSD in this species. Furthermore, sex-specific heritability estimates were very similar, indicating that neither sex will be able to evolve faster than the other. By using estimated genetic parameters, together with empirically derived estimates of sex-specific selection gradients, we further demonstrated that the predicted selection response in female tarsus length is displaced about 200% in the opposite direction from that to be expected if there were no genetic correlation between the sexes. The correspondence between the biochemically estimated rate of extrapair paternity (about 15 % of the young) and that estimated from the “heritability method” (11%) was good. However, the estimated rate of extrapair paternity with the heritability method after exclusion of the illegitimate young was 22%, adding to increasing evidence that factors other than extrapair paternity (e.g., maternal effects) may be resposible for the commonly observed higher mother-offspring than father-offspring resemblance.     

Parallel evolution in sympatric, hybridizing species: performance of Colias butterflies on their introduced host plants

Shared ancestry and introgression can contribute to genetic similarity between hybridizing species, and it is generally difficult to disentangle these causes. However, shared ancestry plays a more limited role in traits that have recently undergone parallel directional selection in the two species, permitting the role of introgression to be better understood. The butterflies Colias eurytheme (Boisduval) and Colias philodice (Godart) (Lepidoptera, Pieridae) are native to North America and have shifted their host ranges in parallel onto several introduced weedy and agricultural legumes. These butterflies hybridize at moderate rates throughout their range, and there is a strong possibility that they could be sharing host‐associated adaptations. We split families of each species among nine introduced, prospective hosts and measured survivorship, larval duration, pupal weight, and a new variable, effective daily growth rate (DGR), analogous to a compound daily interest rate in economics. We found strong effects of host, sex, and family (species), but negligible effects of the host*species interaction that would indicate species‐specific differences in performance on different hosts. We found species‐specific life‐history differences: C. eurytheme matured significantly later and reached a significantly larger body size than C. philodice while growing at the same DGR. Protandry was strong, and males, in addition to pupating sooner than females, grew significantly faster than females as measured by DGR. We measured broad‐sense heritabilities and genetic correlations for host‐associated performance variables. Most pairwise comparisons of performance among hosts and most pairwise comparisons between performance variables showed positive genetic correlations, except survivorship where little heritability was found. Nevertheless, a factorial multivariate analysis of variance of G‐matrices showed highly significant species, host, and host*species interactions, suggesting differentially evolving genetic architectures underlying host adaptation in these two species, despite the small differences in overall performance. At least some of the genes affecting host performance in Colias are likely to be in the small, species‐diagnostic regions and not shared via introgression between these hybridizing species. For biologists interested in the evolutionary ecology of their host associations, including applied biologists managing their agricultural pest potential, C. eurytheme and C. philodice are most usefully studied as if they were a single polymorphic species wherever they co‐exist. In studying species that hybridize readily with a sympatric congener, it may often be necessary to include the second species in the experimental design.     

THE GENETIC BASIS OF ZEBRA FINCH VOCALIZATIONS

Animal vocalizations play an important role in individual recognition, kin recognition, species recognition, and sexual selection. Despite much work in these fields done on birds virtually nothing is known about the heritability of vocal traits in birds. Here, we study a captive population of more than 800 zebra finches ( Taeniopygia guttata ) with regard to the quantitative genetics of call and song characteristics. We find very high heritabilities in nonlearned female call traits and considerably lower heritabilities in male call and song traits, which are learned from a tutor and hence show much greater environmental variance than innate vocalizations. In both sexes, we found significant heritabilities in several traits such as mean frequency and measures of timbre, which reflect morphological characteristics of the vocal tract. These traits also showed significant genetic correlations with body size, as well as positive genetic correlations between the sexes, supporting a scenario of honest signaling of body size through genetic pleiotropy ("index signal"). In contrast to such morphology-related voice characteristics, classical song features such as repertoire size or song length showed very low heritabilities. Hence, these traits that are often suspected to be sexually selected would hardly respond to current directional selection.     

QUANTITATIVE GENETICS OF MORPHOLOGICAL DIFFERENTIATION IN PEROMYSCUS. I. TESTS OF THE HOMOGENEITY OF GENETIC COVARIANCE STRUCTURE AMONG SPECIES AND SUBSPECIES

Phenotypic and additive genetic covariance matrices were estimated for 15 morphometric characters in three species and subspecies of Peromyscus. Univariate and multivariate ANOVAs indicate these groups are highly diverged in all characters, P. leucopus having the largest body size, P. maniculatus bairdii the smallest, and P. maniculatus nebrascensis being intermediate. Comparing the structure of P and G within each taxon revealed significant similarities in all three cases. This proportionality was strong enough to justify using P in the place of G to analyze evolutionary processes using quantitative genetic models when G can not be estimated, as in fossil material. However, the similarity between genetic and phenotypic covariance structures is sufficiently low that estimates of the genetic parameters should be used when possible. The additive genetic covariance matrices were compared to examine the assumption that they remain constant during evolution, an assumption which underlies many applications of quantitative-genetic models. While matrix permutation tests indicated statistically significant proportionality between the genetic covariance structures of the two P. maniculatus subspecies, there is no evidence of significant genetic structural similarity between species. This result suggests that the assumption of constant genetic covariance structure may be valid only within species. (It does not, however, necessarily imply a causal relationship between speciation and heterogeneity of genetic covariance structures.) The low matrix correlation for the two P. maniculatus subspecies' genetic covariance matrices indicates G may not be functionally constant, even within species. The lack of similarity observed here may be due partly to sampling variation.     

GENETIC CONSTRAINTS ON THE INDEPENDENT EVOLUTION OF MALE AND FEMALE REPRODUCTIVE CHARACTERS IN THE TRISTYLOUS PLANT LYTHRUM SALICARIA

Here we test whether the potential exists for the independent evolution of allocation to male, female, and attractive functions within a flower. We employed half-sib and parent-offspring regression methods in the tristylous plant Lythrum salicaria to determine whether there is additive genetic variation for characters important to male and female reproductive success and whether genetic correlations could constrain the independent evolution of male and female function. Although significance levels were not consistent among morph types or between populations, there were significant narrow-sense heritabilities for several traits including stamen mass, pistil mass, perianth mass, petal length, and calyx length. Traits that might be under strong stabilizing selection to promote specific pollen transfer, such as stamen and style lengths, had little heritable variation. In the majority of cases in which heritable variation was present, there were positive genetic correlations among floral traits. A strong positive genetic correlation appeared between stamen and pistil mass in the short-styled morph from one of the populations studied. This suggests that selection might not be able to act independently on biomass allocation to male and female flower parts. No evidence of negative genetic correlations appeared that would suggest trade-offs and that could augment a selection response towards sexual specialization. The observed positive correlations could be explained if we consider the “functional architecture” that underlies the covariance structure. If there is more covariance generated by pleiotropic loci controlling overall flower size than at loci controlling male versus female allocation, it could result in the observed positive covariance. At the phenotypic level, we did find significant negative partial correlations between male and female traits when flower size was controlled, but these trade-offs were among rather than within morphs.     

PHENOTYPIC AND GENETIC EFFECTS OF HYBRIDIZATION IN DARWIN'S FINCHES

Morphological consequences of hybridization were studied in a group of three interbreeding species of Darwin's finches on the small Galápagos island of Daphne Major in the inclusive years 1976 to 1992. Geospiza fortis bred with G. scandens and G. fuliginosa. Although interbreeding was always rare (< 5%), sufficient samples of measurements of hybrids and backcrosses were accumulated for analysis. Five beak and body dimensions and mass were measured, and from these two synthetic (principal-component) traits were constructed. All traits were heritable in two of the interbreeding species (G. fuliginosa were too rare to be analyzed) and in the combined samples of F, hybrids and backcrosses to G. fortis. In agreement with expectations from a model of polygenic inheritance, hybrid and backcross classes were generally phenotypically intermediate between the breeding groups that had produced them. Hybridization increased additive genetic and environmental variances, increased heritabilities to a moderate extent, and generally strengthened phenotypic and genetic correlations. New additive genetic variance introduced by hybridization is estimated to be two to three orders of magnitude greater than that introduced by mutation. Enhanced variation facilitates directional evolutionary change, subject to constraints arising from genetic correlations between characters. The Darwin's finch data suggest that these constraints become stronger when species with similar proportions hybridize, but some become weaker when the interbreeding species have different allometries. This latter effect of hybridization, together with an enhancement of genetic variation, facilitates evolutionary change in a new direction.     

EVALUATING A HYPOTHESIS ABOUT HETEROCHRONY: LARVAL LIFE-HISTORY TRAITS AND JUVENILE HIND-LIMB MORPHOLOGY IN HYLA CRUCIFER

This paper reports the results of an investigation into whether selection on genetically based differences in the timing or rate of development (heterochrony) can give rise to nonadaptive morphological differences among individual frogs. We used a quantitative-genetics approach to examine the relationships among the life-history characters time to metamorphosis and larval-growth rate and a functionally significant morphological features, relative hind-limb length, in the spring peeper, Hyla crucifer. Time to metamorphosis and growth rate had low heritabilities in our population. Morphological traits had moderate heritabilities. There were positive genetic correlations between the life-history traits and the components of relative hind-limb length but no significant correlations with the shape variable itself. We used field observations of pond-drying time and experimental results of selection on growth rate to simulate the correlated responses of hind-limb shape to four reasonable selection regimes on the life-history traits. We found little evidence to suggest that relative hind-limb length would display much of a correlated response to such selection. The differences in relative hind-limb length seen among closely related species or among populations of a single species that appear to be unrelated to performance differences are not obviously explicable as neutral correlated responses to selection on larval traits.     

Family association between immune parameters and resistance to Aeromonas hydrophila infection in the Indian major carp, Labeo rohita

Seven innate immune parameters were investigated in 64 full-sib families (the offspring of 64 sires and 45 dams) from two year-classes of farmed rohu carp (Labeo rohita). Survival rates were also available from Aeromonas hydrophila infection (aeromoniasis) recorded in controlled challenge tests on a different sample of individuals from the same families. Due to strong confounding between the animal additive genetic effect and the family effects (common environmental + non-additive genetic), reliable additive (co)variance components and hence heritabilities and genetic correlations could not be obtained for the investigated parameters. Therefore, estimates of the association of challenge test survival with the studied immune parameters were obtained as product moment correlations between family least square means. These correlations revealed statistically significant (p < 0.05) negative correlations of survival with bacterial agglutination titre (−0.48), serum haemolysin titre (−0.29) and haemagglutination titre (−0.34); and significant positive correlation with ceruloplasmin level (0.51). The correlations of survival to aeromoniasis with myeloperoxidase activity, superoxide production and lysozyme activity were found to be not significantly different from zero (p > 0.05). Assuming that the negatively correlated candidate traits are not favourable as indirect selection criteria, the results suggest that ceruloplasmin level could potentially be a marker for resistance to aeromoniasis in rohu. The use of this immune parameter as an indirect selection criterion for increased resistance to aeromoniasis in rohu will, however, require that the parameter shows significant additive genetic variation and a significant genetic correlation with survival. Further studies are therefore needed to obtain a reliable heritability estimate for ceruloplasmin and its genetic correlation with survival from aeromoniasis.     

QUANTITATIVE GENETICS OF BRYOZOAN PHENOTYPIC EVOLUTION. II. ANALYSIS OF SELECTION AND RANDOM CHANGE IN FOSSIL SPECIES USING RECONSTRUCTED GENETIC PARAMETERS

The roles of natural selection and random genetic change in the punctuated phenotypic evolution of eight Miocene-Pliocene tropical American species of the cheilostome bryozoan Metrarabdotos are analyzed by quantitative genetic methods. Trait heritabilities and genetic covariances reconstructed by partitioning within- and among-colony phenotypic variance are similar to those previously obtained for living species of the cheilostome Stylopoma using breeding data. The hypothesis that differences in skeletal morphology between species of Metrarabdotos are entirely due to mutation and genetic drift cannot be rejected for reasonable rates of mutation maintained for periods brief enough to account for the geologically abrupt appearances of these species in the fossil record. Except for one pair of species, separated by the largest morphologic distance, directional selection acting alone would require unrealistically high rates of selective mortality to be maintained for these periods. Thus, directional selection is not strongly implicated in the divergence of Metrarabdotos species. Within species, rates of net phenotypic change are slow enough to require stabilizing selection, but mask large, relatively rapid fluctuations, all of which, however, can be attributed to chance departures from the mean phenotype by mutation and genetic drift, rather than to tracking environmental fluctuation by directional selection. The results are consistent with genetic models involving shifts between multiple adaptive peaks on which phenotypes remain more or less static through long-term stabilizing selection. Regardless of the degree to which directional selection may be involved in peak shifts, phenotypic differentiation is thus related to processes different than the pervasive stabilizing selection acting within species.     

EVOLUTION OF FLORAL TRAITS IN A HERMAPHRODITIC PLANT: FIELD MEASUREMENTS OF HERITABILITIES AND GENETIC CORRELATIONS

Genetic variances, heritabilities, and genetic correlations of floral traits were measured in the monocarpic perennial Ipomopsis aggregata (Polemoniaceae). A paternal half-sib design was employed to generate seeds in each of four years, and seeds were planted back in the field near the parental site. The progeny were followed for up to eight years to estimate quantitative genetic parameters subject to natural levels of environmental variation over the entire life cycle. Narrow-sense heritabilities of 0.2–0.8 were detected for the morphometric traits of corolla length, corolla width, stigma position, and anther position. The proportion of time spent by the protandrous flowers in the pistillate phase (“proportion pistillate”) also exhibited detectable heritability of near 0.3. In contrast, heritability estimates for nectar reward traits were low and not significantly different from zero, due to high environmental variance between and within flowering years. The estimates of genetic parameters were combined with phenotypic selection gradients to predict evolutionary responses to selection mediated by the hummingbird pollinators. One trait, corolla width, showed the potential for a rapid response to ongoing selection through male function, as it experienced both direct selection, by influencing pollen export, and relatively high heritability. Predicted responses were lower for proportion pistillate and corolla length, even though these traits also experienced direct selection. Stigma position was expected to respond positively to indirect selection of proportion pistillate but negatively to selection of corolla length, with the net effect sensitive to variation in the selection estimates. Anther position also was not directly selected but could respond to indirect selection of genetically correlated traits.     

A COMPARATIVE ANALYSIS OF MORPHOLOGICAL VARIATION PATTERNS IN THE PAPIONINS

Comparative studies of intraspecific variation patterns are important in attempts to reconstruct the differential selection pressures experienced by related species and in assessing the resultant observed interspecific variation. Reconstruction of past selection depends on an assumption of relatively stable patterns of genetic variance and covariance through time and across related species. Models by Lande (1979) and Turelli (1988a, 1988b) lead to contrasting expectations of stability versus lability of variation patterns, respectively, at least for closely related species. I report on a comparative study of phenotypic variance and correlation patterns in seven species of papionins, including macaques, baboons, and mangabeys, in order to determine the stability of variation patterns in this group. The three-dimensional coordinates of 12 bony landmarks on the face were used in a finite-element scaling analysis in order to measure local size variation at each landmark. Variances and correlations for these local size metrics were calculated using pooled sex-specific values. Variation patterns were compared across species using vector and matrix correlations in combination with various randomization-based significance tests. Patterns of variation and correlation were generally quite similar across the seven species, although some differences were also apparent. The overall magnitude of correlation is also similar among species, as only a few interspecific comparisons showed significant differences. Thus, it is concluded that patterns of variation and correlation in facial morphology have tended to remain stable in this group of primates. This result should allow for reconstruction of past differential selection pressures in the clade. The pattern of similarity among correlation structures for these species showed no association with their phylogenetic relationships.     

LIFE-CYCLE COMPONENTS OF SELECTION IN ERIGERON ANNUUS: II. GENETIC VARIATION

Genetic variation for seedling and adult fitness components was measured under natural conditions to determine the relative importance of the seedling stage for lifetime fitness in Erigeron annuus. Variation in lifetime reproductive success can result from both the persistent effects of genetic variation expressed among seedlings and from variation in adult fitness components. Analysis of covariance was used to separate the stage specific from the cumulative effects of genetic variance expressed earlier in the life cycle. E. annuus produces seeds through apomixis, which allowed measurement of the fitness of replicate genotypes from germination through the entire life cycle. There were significant differences among genotypes for date of emergence, seedling size, survivorship and fecundity, but heritabilities were low, indicating slow response to selection. For all characters, environmental components of variance were one to two orders of magnitude larger than genetic variance components, resulting in broad sense heritabilities less than 0.1. For seedling size and fecundity, all of the genetic variance was in the form of genotype-environment interactions, often with large negative genetic correlations across environments. In contrast, genotypes differed in mean survivorship through one year, but there were no genotype-environment interactions for viability. Genetic differences in viability were primarily expressed as differences in overwinter survivorship. Genotype × environment interactions among sites and blocks were generated early in the life cycle while the genotype × environment interactions in response to competitive environment (open, annual cover, perennial cover) first appeared in adult fecundity. Genetic variation in lifetime fitness was not significant, despite a fourfold difference in mean fitness among genotypes.