INHERITANCE OF MERISTIC VARIATION AND THE EVOLUTION OF DEVELOPMENTAL STABILITY IN RAINBOW TROUT

Evolution and disappearance of sympatric Coregonus albula in a changing environment-A case study of the only remaining population pair in Sweden

During the past 50 years, Fennoscandian populations of spring-spawning Baltic cisco (Coregonus albula), sympatric to common autumn-spawners, have declined or disappeared; for example, three out of four known spring-spawning populations in Sweden are regarded as extinct. Over the same period, the climate has changed and populations have been subject to other anthropogenic stressors. We compared historic (1960s) and recent (1990-2000s) morphological data from the still-existent sympatric cisco populations in Lake Fegen, Sweden. Phenotypic changes were found for spring-spawners making them more similar to the sympatric autumn-spawners that had remained virtually unchanged. Based on results for other salmoniform fishes, a phenotypically plastic response to increased temperature during early development appears unlikely. The recent material was also analyzed with microsatellite markers; long-term effective population size in spring-spawners was estimated to be about 20 times lower than autumn-spawners, with signs of long-term gene flow in both directions and a recent genetic bottleneck in spring-spawners. We suggest the change toward a less distinct phenotype in spring-spawners to reflect a recent increase in gene flow from autumn-spawners. Time since divergence was estimated to only c. 1,900 years (95% CI: 400-5,900), but still the Fegen populations represent the most morphologically and genetically distinct sympatric populations studied. Consequently, we hypothesize that less distinct population pairs can be even younger and that spring-spawning may have repeatedly evolved and disappeared in several lakes since the end of the last glaciation, concurrent with changed environmental conditions.

Vertebral column regionalisation in Chinook salmon, Oncorhynchus tshawytscha

Teleost vertebral centra are often similar in size and shape, but vertebral-associated elements, i.e. neural arches, haemal arches and ribs, show regional differences. Here we examine how the presence, absence and specific anatomical and histological characters of vertebral centra-associated elements can be used to define vertebral column regions in juvenile Chinook salmon (Oncorhynchus tshawytscha). To investigate if the presence of regions within the vertebral column is independent of temperature, animals raised at 8 and 12 °C were studied at 1400 and 1530 degreedays, in the freshwater phase of the life cycle. Anatomy and composition of the skeletal tissues of the vertebral column were analysed using Alizarin red S whole-mount staining and histological sections. Six regions, termed I-VI, are recognised in the vertebral column of specimens of both temperature groups. Postcranial vertebrae (region I) carry neural arches and parapophyses but lack ribs. Abdominal vertebrae (region II) carry neural arches and ribs that articulate with parapophyses. Elastic- and fibrohyaline cartilage and Sharpey's fibres connect the bone of the parapophyses to the bone of the ribs. In the transitional region (III) vertebrae carry neural arches and parapophyses change stepwise into haemal arches. Ribs decrease in size, anterior to posterior. Vestigial ribs remain attached to the haemal arches with Sharpey's fibres. Caudal vertebrae (region IV) carry neural and haemal arches and spines. Basidorsals and basiventrals are small and surrounded by cancellous bone. Preural vertebrae (region V) carry neural and haemal arches with modified neural and haemal spines to support the caudal fin. Ural vertebrae (region VI) carry hypurals and epurals that represent modified haemal and neural arches and spines, respectively. The postcranial and transitional vertebrae and their respective characters are usually recognised, but should be considered as regions within the vertebral column of teleosts because of their distinctive morphological characters. While the number of vertebrae within each region can vary, each of the six regions is recognised in specimens of both temperature groups. This refined identification of regionalisation in the vertebral column of Chinook salmon can help to address evolutionary developmental and functional questions, and to support applied research into this farmed species.

EVIDENCE FOR SYMPATRIC GENETIC DIVERGENCE OF ANADROMOUS AND NONANADROMOUS MORPHS OF SOCKEYE SALMON (ONCORHYNCHUS NERKA)

Anadromous and nonanadromous morphs of the Pacific salmon Oncorhynchus nerka spawn in close physical proximity in tributaries to Takla Lake, British Columbia, yet differ in morphology, gill raker number, allozyme allele frequencies, and reproductive traits. Both morphs are semelparous typically maturing at age four, the anadromous morph (sockeye) at fork lengths of 38-65 cm and the nonanadromous morph (kokanee) at 17-22 cm. When reared together, pure and hybrid morphs also exhibited different growth rates and maturity schedules. Collectively, these large differences between the morphs confirm that sockeye and kokanee exist as reproductively isolated populations. Average gene flow (m) was estimated to be 0.1-0.8% between morphs, 1.7-3.7% among tributaries for kokanee, and 0.3-5.6% among tributaries for sockeye. We conclude that divergence has occurred in sympatry and examine potential isolating mechanisms.

FLUCTUATING ODONTOMETRIC ASYMMETRY, MORPHOLOGICAL VARIABILITY, AND GENETIC MONOMORPHISM IN THE CHEETAH ACINONYX JUBATUS

The magnitudes of dimensional variability and fluctuating asymmetry in dental dimensions are reported for a sample of South African cheetah Acinonyx jubatus. To test the hypothesis that elevated levels of variability and asymmetry are associated with the increased developmental instability reported for this species, our results were contrasted to those for two other felids: Felis lybica and F. caracal. These findings suggest that dental dimensions in cheetahs are not significantly more variable or asymmetric. Hence, it is concluded that the cheetah may not be as developmentally unstable as was previously supposed.

THE ASSOCIATION BETWEEN FLUCTUATING ASYMMETRY, TRAIT VARIABILITY, TRAIT HERITABILITY, AND STRESS: A MULTIPLY REPLICATED EXPERIMENT ON COMBINED STRESSES IN DROSOPHILA MELANOGASTER

A number of hypotheses have been proposed about the association between developmental stability phenotypic variability, heritability, and environmental stress. Stress is often considered to increase both the asymmetry and phenotypic variability of bilateral traits, although this may depend on trait heritability. Empirical studies of such associations often yield inconsistent results. This may reflect the diversity of traits and conditions used or a low repeatability of any associations. To test for repeatable associations between these variables, multiply replicated experiments were undertaken on Drosophila melanogaster using a combination stress at the egg, larval and adult stages of reduced protein, ethanol in the medium, and a cold shock. Both metric and meristic traits were measured and levels of heritable variation for each trait estimated by maximum likelihood and parent-offspring regression over three generations. Trait means were reduced by stress, whereas among-individual variation increased Fluctuating asymmetry (FA) was increased by stress in some cases, but few comparisons were significant. Only one trait orbital bristle, showed consistent increases in FA. Changes in trait means, trait phenotypic variability, and developmental stability as a result of stress were not correlated. Extreme phenotypes tended to have higher levels of FA but only the results for orbital bristles were significant. All traits had low to intermediate heritabilities except orbital bristle, which showed no heritable variation. Only traits with low heritability and high levels of phenotypic variability may show consistent increases in FA under stress. Overall, the independence of phenotypic variability, plasticity, and the developmental stability of traits extend to changes in these measures under stressful conditions.

SEXUAL SELECTION IN THE BARN SWALLOW (HIRUNDO RUSTICA). IV. PATTERNS OF FLUCTUATING ASYMMETRY AND SELECTION AGAINST ASYMMETRY

The patterns of variation in fluctuating asymmetry were studied in four morphological characters of the barn swallow Hirundo rustica. The level of absolute and relative asymmetry was larger in the secondary sexual character "outer tail length" than in three nonsexual morphological traits (wing, central tail, and tarsus length). The extent of individual asymmetry in outer tail length was negatively correlated with tail-ornament size, whereas the relationship between asymmetry of all other morphological characters and their size was flat or U-shaped. Asymmetry in outer tail length was unrelated to asymmetry in other morphological characters, whereas asymmetries in the length of wing, central tail, and tarsus were positively correlated. Male bam swallows exhibited larger asymmetry in outer tail length than females. Asymmetry of most morphological traits exhibited intermediate repeatabilities between years, with the exception of male and female outer tail length, which were highly repeatable. Tail asymmetry of offspring weakly, though significantly, resembled that of their parents. Asymmetry in wing and outer tail length was also significantly related to several fitness components. Male barn swallows that acquired a mate were less asymmetric in wing and outer tail length than unmated males. Females with more asymmetrical tails laid eggs significantly later. Annual reproductive success was unrelated to fluctuating asymmetry. Male barn swallows that survived were less asymmetric in wing and outer tail length than nonsurvivors, whereas female survivors were less asymmetric in outer tail length than nonsurvivors. These results suggest that levels of fluctuating asymmetry in barn swallows are associated with differences in fitness.

SELECTIVE PREDATION FOR VERTEBRAL PHENOTYPE IN GASTEROSTEUS ACULEATUS: REVERSAL IN THE DIRECTION OF SELECTION AT DIFFERENT LARVAL SIZES

Variation in the number of vertebrae is widespread in fishes, and is partly genetic in origin. The adaptive significance of this variation was tested by exposing larvae of the threespine stickleback (Gasterosteus aculeatus) to predation by sunfish (Lepomis gibbosus). Two vertebral characters were considered: the total number (VN) and the ratio of abdominal to caudal vertebrae (VR). Predation was selective for both characters, but selection was more directly related to VR than to VN. The direction of selection depended on larval length: as length increased, optimal VR decreased. Total selection for VR was a combination of direct selection and an indirect effect of selection acting on a correlated trait, the ratio of precaudal to caudal length. Direct and indirect selection were in opposing directions at a given larval length. Variation in vertebral number may be maintained in populations partly because the strength of selection is reduced by opposing directions between direct and indirect selection, and between total selection at different larval lengths.

META-ANALYSES OF THE ASSOCIATION BETWEEN MULTILOCUS HETEROZYGOSITY AND FITNESS

Meta-analyses of published correlation coefficients between multilocus heterozygosity (MLH) and two fitness surrogates, growth rate and fluctuating asymmetry, suggested that the strength of these correlations are generally weak. A variety of plants and animals was included in the meta-analyses. A statistically homogeneous group of MLH-growth rate correlation coefficients that included both plants and animals yielded a common correlation of r_z = 0.133. A common correlation of r_z = -0.170 was estimated for correlations between MLH and fluctuating asymmetry in three species of salmonid fishes. These results suggest that selection, including overdominance, has at most a weak effect at allozyme loci and cast some doubt on the widely held notion that heterozygosity and individual fitness are strongly correlated.

Causes and consequences of intra-specific variation in vertebral number

Intraspecific variation in vertebral number is taxonomically widespread. Much scientific attention has been directed towards understanding patterns of variation in vertebral number among individuals and between populations, particularly across large spatial scales and in structured environments. However, the relative role of genes, plasticity, selection, and drift as drivers of individual variation and population differentiation remains unknown for most systems. Here, we report on patterns, causes and consequences of variation in vertebral number among and within sympatric subpopulations of pike (Esox lucius). Vertebral number differed among subpopulations, and common garden experiments indicated that this reflected genetic differences. A Q_ST-F_ST comparison suggested that population differences represented local adaptations driven by divergent selection. Associations with fitness traits further indicated that vertebral counts were influenced both by stabilizing and directional selection within populations. Overall, our study enhances the understanding of adaptive variation, which is critical for the maintenance of intraspecific diversity and species conservation.

Ontogenetic shifts in morphology and resource use of cisco Coregonus artedi

Two previously described lacustrine cisco Coregonus spp. morphs [i.e. a small (<300 mm fork length, L(F)), low-gillraker (≤44) morph and a large (≥300 mm L(F) ), high-gillraker (≥45) morph] from Great Slave Lake, NT, Canada, were found to be synonymous with cisco Coregonus artedi. Geometric body shape did not differ between the two size classes nor could they be differentiated by 24 size-corrected linear measurements, indicating that the two groups had similar phenotypes. Strong, positive correlations between all linear characters and geometric centroid size (a composite variable of fish body length, mass and age) suggested that body morphology changed with age as fish grew. Total gillraker number (N(GR)) increased with L(F) according to: N(GR) = 36.3 + 0.034L(F). Differences in gillraker number and phenotype with age and size were explained by shifts in habitat and trophic resource use. Relative abundance within 0-30, 30-60, 60-90 and >90 m depth strata differed between size classes suggesting that morphology changed when fish shifted their habitat as they grew older. Large C. artedi had lower δ(13)C and slightly higher δ(15)N, indicating greater reliance on pelagic prey resources (i.e. more or larger zooplankton, such as Mysis spp.), compared to small C. artedi, which relied slightly more on benthic prey. Gillraker shape and number have always been used as key diagnostic characters in coregonine taxonomy; based on the findings presented here, ontogenetic shifts should be accounted for in resulting classifications.

Genetics of microenvironmental sensitivity of body weight in rainbow trout (Oncorhynchus mykiss) selected for improved growth

Microenvironmental sensitivity of a genotype refers to the ability to buffer against non-specific environmental factors, and it can be quantified by the amount of residual variation in a trait expressed by the genotype's offspring within a (macro)environment. Due to the high degree of polymorphism in behavioral, growth and life-history traits, both farmed and wild salmonids are highly susceptible to microenvironmental variation, yet the heritable basis of this characteristic remains unknown. We estimated the genetic (co)variance of body weight and its residual variation in 2-year-old rainbow trout (Oncorhynchus mykiss) using a multigenerational data of 45,900 individuals from the Finnish national breeding programme. We also tested whether or not microenvironmental sensitivity has been changed as a correlated genetic response when genetic improvement for growth has been practiced over five generations. The animal model analysis revealed the presence of genetic heterogeneity both in body weight and its residual variation. Heritability of residual variation was remarkably lower (0.02) than that for body weight (0.35). However, genetic coefficient of variation was notable in both body weight (14%) and its residual variation (37%), suggesting a substantial potential for selection responses in both traits. Furthermore, a significant negative genetic correlation (-0.16) was found between body weight and its residual variation, i.e., rapidly growing genotypes are also more tolerant to perturbations in microenvironment. The genetic trends showed that fish growth was successfully increased by selective breeding (an average of 6% per generation), whereas no genetic change occurred in residual variation during the same period. The results imply that genetic improvement for body weight does not cause a concomitant increase in microenvironmental sensitivity. For commercial production, however, there may be high potential to simultaneously improve weight gain and increase its uniformity if both criteria are included in a selection index.

The population growth consequences of variation in individual heterozygosity

Heterozygosity has been associated with components of fitness in numerous studies across a wide range of taxa. Because heterozygosity is associated with individual performance it is also expected to be associated with population dynamics. However, investigations into the association between heterozygosity and population dynamics have been rare because of difficulties in linking evolutionary and ecological processes. The choice of heterozygosity measure is a further issue confounding such studies as it can be biased by individual differences in the frequencies of the alleles studied, the number of alleles at each locus as well as the total number of loci typed. In this study, we first examine the differences between the principal metrics used to calculate heterozygosity using long-term data from a marked population of Soay sheep (Ovis aries). Next, by means of statistical transformation of the homozygosity weighted by loci index, we determine how heterozygosity contributes to population growth in Soay sheep by modelling individual contributions to population growth (p_t(i)) as a function of several covariates, including sex, weight and faecal egg count – a surrogate of parasitic nematode burden in the gut. We demonstrate that although heterozygosity is associated with some components of fitness, most notably adult male reproductive success, in general it is only weakly associated with population growth.

Inheritance of vertebral number in the three-spined stickleback (Gasterosteus aculeatus)

Intraspecific variation in the number of vertebrae is taxonomically widespread, and both genetic and environmental factors are known to contribute to this variation. However, the relative importance of genetic versus environmental influences on variation in vertebral number has seldom been investigated with study designs that minimize bias due to non-additive genetic and maternal influences. We used a paternal half-sib design and animal model analysis to estimate heritability and causal components of variance in vertebral number in three-spined sticklebacks (Gasterosteus aculeatus). We found that both the number of vertebrae (h(2) = 0.36) and body size (h(2) = 0.42) were moderately heritable, whereas the influence of maternal effects was estimated to be negligible. While the number of vertebrae had a positive effect on body size, no evidence for a genetic correlation between body size and vertebral number was detected. However, there was a significant positive environmental correlation between these two traits. Our results support the generalization--in accordance with results from a review of heritability estimates for vertebral number in fish, reptiles and mammals--that the number of vertebrae appears to be moderately to highly heritable in a wide array of species. In the case of the three-spined stickleback, independent evolution of body size and number of vertebrae should be possible given the low genetic correlation between the two traits.

Conservation prioritization in widespread species: the use of genetic and morphological data to assess population distinctiveness in rainbow trout (Oncorhynchus mykiss) from British Columbia, Canada

Prioritization of efforts to maintain biodiversity is an important component of conservation, but is more often applied to ecosystems or species than within species. We assessed distinctiveness among 27 populations of rainbow trout (Salmonidae: Oncorhynchus mykiss) from British Columbia, Canada, using microsatellite DNA variation (representing historical or contemporary demography) and morphology (representing adaptive variation). Standardized genetic scores, that is, the average deviation across individuals within populations from the overall genetic score generated by factorial correspondence analysis, ranged from 1.05 to 4.90 among populations. Similar standardized morphological scores, generated by principal components analysis, ranged from 1.19 to 5.35. There was little correlation between genetic and morphological distinctiveness across populations, although one population was genetically and morphologically the most distinctive. There was, however, a significant correlation (r = 0.26, P = 0.008) between microsatellite (F_ST) and morphological (P_ST) divergence. We combined measures of allelic richness, genetic variation within, and divergence among, populations and morphological variation to provide a conservation ranking of populations. Our approach can be combined with other measures of biodiversity value (habitat, rarity, human uses, threat status) to rationalize the prioritization of populations, especially for widespread species where geographic isolation across distinct environments promotes intraspecific variability.

Estimation of heritability for fluctuating asymmetry in chickens by restricted maximum likelihood. Effects of age and sex

The purposes of the present study were to estimate the heritability of the fluctuating asymmetry in chickens, using the restricted maximum likelihood procedure, and to evaluate the effects of age and sex on the fluctuating asymmetry. Leg, wing, and feather lengths and ear-lobe and wattle areas were measured. In experiment 1, 1,073 birds were used from 2 generations with complete pedigree of the Quail Castellana breed to estimate the heritability for the fluctuating asymmetry at 36 wk of age. The estimated heritability of absolute fluctuating asymmetry was not significantly different from zero for all 5 traits, and similar estimates were obtained for relative fluctuating asymmetry, directional asymmetry, transformed absolute and relative fluctuating asymmetry, and 3 alternative indexes of fluctuating asymmetry. The heritability of the combined absolute or relative fluctuating asymmetry was still very low, indicating that fluctuating asymmetry was determined solely by environmental sources of variation and that fluctuating asymmetry estimates should not be confounded by appreciable additive genetic contributions. The genetic correlation between sides was not significantly different from one, indicating that differences between sides were purely environmental in origin. Different traits rarely showed much correlation in their level of fluctuating asymmetry, indicating that the level of fluctuating asymmetry in all traits did not reflect equally the quality of animals. In experiment 2, fluctuating asymmetry differences among ages and sexes were investigated at 8, 12, 16, 20, 24, 28, 32, 36, and 40 wk in 360 birds from the same breed. Significant variation with age was observed in leg length, wing length, feather length (females), and wattle area (females), which was mainly related to onset of sexual maturity and adult stage. Females showed significantly greater fluctuating asymmetry for ear-lobe area than males. There were significant differences in fluctuating asymmetry for wing length, feather length, and wattle area near the onset of sexual maturity, with males having significantly greater fluctuating asymmetry than females for wing length and the opposite being true for feather length and wattle area.

Why are rare traits unilaterally expressed?: Trait frequency and unilateral expression for cranial nonmetric traits in humans

Based on an analysis of nonmetric trait databases from several large skeletal series in Northern Europe and South America, representing 27 bilateral traits, we report a predictable relationship between the frequency of nonmetric traits and the probability that they are expressed bilaterally. In a wider sampling of traits and populations, this study thus confirms the findings of an earlier study by Ossenberg ([1981] Am. J. Phys. Anthropol. 54:471-479), which reported the same relationship for two mandibular traits. This trend was previously explained by extending the multifactorial threshold model for discontinuous traits to incorporate either separate thresholds for unilateral or bilateral expression, or by a fuzzy threshold in which the probability of bilateral expression increases away from the median threshold value. We show that the trend is produced under the standard multifactorial threshold model for discontinuous traits simply if the within-individual or developmental instability variance remains relatively constant across the range of liability. Under this assumption, the number of individuals in which one side but not the other is pushed over the threshold for trait formation will be a larger proportion of the number of individuals expressing the trait when the trait frequency is low. As trait frequency increases, the significance of within-individual variance as a determinant of trait formation decreases relative to the genetic and among-individual environmental variance. These results have implications for interpreting nonmetric trait data as well as for understanding the prevalence of unilateral vs. bilateral expression of a wide variety of discontinuous traits, including dysmorphologies in humans.

Genetic basis of variation in morphological and life-history traits of a wild population of pink salmon

Understanding the genetic basis of phenotypic variation is essential for predicting the direction and rate of phenotypic evolution. We estimated heritabilities and genetic correlations of morphological (fork length, pectoral and pelvic fin ray counts, and gill arch raker counts) and life-history (egg number and individual egg weight) traits of pink salmon (Oncorhynchus gorbuscha) from Likes Creek, Alaska, in order to characterize the genetic basis of phenotypic variation in this species. Families were created from wild-caught adults, raised to the fry stage in the lab, released into the wild, and caught as returning adults and assigned to families using microsatellite loci and a growth hormone locus. Morphological traits were all moderately to highly heritable, but egg number and egg weight were not heritable, suggesting that past selection has eliminated additive genetic variation in egg number and egg weight or that there is high environmental variance in these traits. Genetic correlations were similar for nonadjacent morphological traits and adjacent traits. Genetic correlations predicted phenotypic correlations fairly accurately, but some pairs of traits with low genetic correlations had high phenotypic correlations, and vice versa, emphasizing the need to use caution when using phenotypic correlations as indices of genetic correlations. This is one of only a handful of studies to estimate heritabilities and genetic correlations for a wild population.

Heritability and "evolvability" of meristic characters in a natural population ofGasterosteus aculeatus

Phenotypic and genetic variabilities of nine meristic traits (in threespine stickleback, Gasterosteus aculeatus) were calculated for 33 full-sib families raised under controlled laboratory conditions and for 33 pairs caught in nature. Heritabilities were measured using three methods: regression (across environments, laboratory–nature), full sib (laboratory), and minimum estimate (nature). Evolvabilities, as an alternative measure of genetic variability, were computed from the genetic coefficient of variation across environments, in the laboratory, and in nature. In general terms, phenotypic variability was smaller in laboratory-reared fish than in wild fish. Results applying both parameters (heritability and evolvability) suggest that in the natural environment, there is a relevant presence of additive genetic variability for lateral-plate number and, to a lesser extent, for lower gill rakers, as well as maternal effects on caudal and abdominal vertebrae and paternal effects on dorsal fin rays. Some of the meristic traits examined are bilateral. Heritabilities across environments and in the laboratory for fluctuating asymmetry values were calculated according to conventional methods and also employing method 2 of Falconer. Qualitatively, the results were almost the same using the two methods: most heritability values were around zero, even taking into account overall measures of fluctuating asymmetry.

Directional and fluctuating asymmetry in the black-winged damselfly Calopteryx maculata (Beauvois) (Odonata: Calopterygidae)

Directional asymmetry (DA) has received considerably less attention than fluctuating asymmetry (FA) in the literature. Evidence for DA, however, is building among insect taxa. We examined asymmetries in two wing traits within both sexes of the damselfly Calopteryx maculata (Beauvois) (Odonata: Calopterygidae) sampled from three sites in southeastern Ontario. After accounting for measurement error, we show that proximal segments within right fore and hind wings are consistently longer than those in the left in all but one sample group. Full wing lengths, however, exhibited FA rather than DA. Mean asymmetry values for both traits (segment and length) occurred in the direction of right-wingedness significantly more often than expected by chance. Patterns of asymmetry were generally consistent among the sexes and sites, although males tended to exhibit more pronounced DA. We suggest that the wings of C. maculata may undergo compensatory development, so that full lengths are more bilaterally symmetrical than their component parts.

A meta-analysis of fluctuating asymmetry in relation to heterozygosity

Fluctuating asymmetry, the random departure from perfect bilateral symmetry, is a common measure of developmental instability that has been hypothesized to be inversely correlated with heterozygosity. Although this claim has been widely repeated, several studies have reported no such association. Therefore, we test the generality of this association, using meta-analysis, by converting test statistics for the relationship between heterozygosity (H) and fluctuating asymmetry (FA) into a common effect size, the Pearson's product-moment correlation coefficient. We have analysed a database containing 41 studies with a total of 118 individual samples. Overall we found an unweighted mean negative effect size; r=-0.09 (i. e. a negative correlation between H and FA). Significant heterogeneity in effect size was mainly caused by a difference between ectothermic and endothermic animals, and to a lesser extent by the use of different study designs (i.e. within-population vs. among-populations). Mean effect size for endothermic animals was positive and significantly different from the mean effect size for ectothermic animals. Only for within-population studies of ectothermic animals did we find a significantly negative effect size (r=-0.23 +/- 0.09). The distribution of effect sizes in relation to sample size provided little evidence for patterns typical of those produced by publication bias. Our analysis suggests, at best, only a weak association between H and FA, and heterozygosity seems to explain only a very small amount of the variation in developmental instability among individuals and populations (r2=0.01 for the total material).

Fluctuating asymmetry and disorders of developmental origin

Environmental and/or genetic stresses may cause a breakdown in developmental homeostasis, resulting in increased bilateral asymmetry of morphological traits. The degree of these deviations (termed "fluctuating asymmetry") is thought to correlate with the severity of the stress. If these stresses also play a role in the appearance of developmental disorders, then increased morphological asymmetry may serve as a risk marker for disorders of developmental origin. This would be possible if 1) the environmental stress that caused a breakdown in developmental stability also contributed to the appearance of the disorder, and/or 2) the genetic predisposition (liability) to the disorder and increased susceptibility to fluctuating asymmetry have a common cause. Although a number of authors have reported associations between increased fluctuating asymmetry and disorders of presumed developmental origin, the usefulness of fluctuating asymmetry as a risk marker has not been established. One obstacle to this assessment is the lack of odds ratios reported by previous authors.

Asymmetry--where evolutionary and developmental genetics meet

The mechanisms responsible for the fine tuning of development, where the wildtype phenotype is reproduced with high fidelity, are not well understood. The difficulty in approaching this problem is the identification of mutant phenotypes indicative of a defect in these fine-tuning control mechanisms. Evolutionary biologists have used asymmetry as a measure of developmental homeostasis. The rationale for this was that, since the same genome controls the development of the left and right sides of a bilaterally symmetrical organism, departures from symmetry can be used to measure genetic or environmental perturbations. This paper examines the relationship between asymmetry and resistance to organophosphorous insecticides in the Australian sheep blowfly, Lucilia cuprina. A resistance gene, Rop-1, which encodes a carboxylesterase enzyme, also confers a significant increase in asymmetry. Continued exposure of resistant populations to insecticide has selected a dominant suppressor of the asymmetry phenotype. Genetic evidence indicates that the modifier is the L. cuprina Notch homologue.

Fluctuating asymmetry does not increase with moderate inbreeding in Drosophila melanogaster

Fluctuating asymmetry, the unsigned difference between character values on the left and right sides of an individual, is often thought to be highly correlated with the heterozygosity of individuals or populations. A large sample of Drosophila melanogaster individuals with an inbreeding coefficient of F = 0.25 was derived from a laboratory population and compared to a sample of outbred individuals for the fluctuating asymmetry of sternopleural bristle number. Inbred flies were not more asymmetric than outbred flies. There was no evidence for heritability of fluctuating asymmetry, as measured by variance among full-sib lines. Fluctuating asymmetry may not be a reliable measure of the degree of inbreeding at the relatively low levels found in most animal populations and should be used with caution in the management of endangered species.

Are paw preference differences in HI and LO mice the result of specific genes or of heterosis and fluctuating asymmetry?

Collins (1985) has described two separate mouse strains, obtained by selective breeding, which differ in having high (HI) or low (LO) degrees of paw preference on a standard test. In this paper I argue that the differences between these strains may not be due to a specific gene (or genes) but, instead, probably reflect differences in the total heterozygosity of the strains, such that the HI strain is more heterotic than the LO strain. Greater degrees of heterozygosity are argued to buffer against fluctuating asymmetry and hence result in a greater degree of paw preference.

MITOCHONDRIAL GENOTYPES HAVE NO DETECTABLE EFFECTS ON MERISTIC TRAITS IN CUTTHROAT TROUT HYBRID SWARMS

Efforts to detect effects of cytoplasmic genes are confounded by the problem of partitioning nuclear and cytoplasmic effects. In this study we test for effects of mtDNA haplotype on development in hybrid populations of cutthroat trout (Oncorhynchus clarki) with randomly associated nuclear and mtDNA genotypes. We have previously described several intraspecific hybrid swarms formed by interbreeding of westslope cutthroat trout (O. c. lewisi) and Yellowstone cutthroat trout (O. c. bouvieri). Genetic distance between these subspecies is high (Nei's D = 0.30; mtDNA P = 0.02), and diagnostic alleles at multiple nuclear loci and two distinct mtDNA haplotypes are present in the hybrids. Historical associations between alleles at nuclear loci and between cytotypes and nuclear alleles have largely decayed. We test for differences in meristic characters between fish with alternate mtDNA haplotypes. Counts and fluctuating bilateral asymmetry for these characters have been previously shown to be sensitive indicators of genetic differences that affect development. No differences were found between mtDNA types in meristic counts or fluctuating asymmetry. Therefore, the alternate mtDNA haplotypes had no detectable effect on development as measured by meristic counts in these hybrid populations. However, diagnostic alleles at one nuclear allozyme locus (CK-CI) were associated with several fin ray counts.

Effects of inbreeding on economic traits of channel catfish

Inbred channel catfish (Ictalurus punctatus) were produced from two generations of full-sib matings to study the effect of inbreeding on reproduction, growth and survival. A randomly mated control line was propagated from the same base population to be used for the evaluation of the inbred fish. First generation inbred (I1) and control (C1) lines comprised five full-sib families each. Second generation inbred (I2) and control (C2) lines were produced by mating each male catfish from the I1 or C1 line to two females in sequence, one from the I1 and one from the C1 line. The design also produced two reciprocal outcross lines to be compared to their contemporary inbred and control lines. The coefficient of inbreeding for the inbred line increased from 0.25 in generation 1 to 0.375 in generation 2. The inbreeding coefficient was zero for all other lines. The resulting fish were performance tested in two locations, Tifton, Georgia and Auburn, Alabama and no genotype-environment interactions occurred. Results indicated that one generation of inbreeding increased number of days required for eggs to hatch by 21%, but did not significantly influence spawn weight or hatchability score. However, inbred females produced more eggs/kg body weight than control females. Two generations of full-sib mating in Georgia did not depress weight when expressed as a deviation to random controls but was depressed 13-16% when expressed as a deviation to half-sib out-crosses. Second generation inbreds produced in Alabama exhibited a 19% depression for growth rate when compared to either random or half-sib outcross controls. Survival rates at various age intervals was not decreased by inbreeding. The amount of inbreeding depression varied among families and between sexes.