Enzyme Heterozygosity Research Articles

The Effect of Enzyme Heterozygosity on Growth in a Strictly Outcrossing Species, the Self-Incompatible Arabis Petraea (Brassicaceae)

The mating system and the relation between electrophoretic variation and morphological characters were investigated using seed families from two populations of Arabis petruea (Brassicaceae) from Iceland. The mating system analysis revealed that despite the presence of a strong sporophytic self-incompatibility system, gene-flow is restricted and biparental inbreeding common. The amount of isozyme heterozygosity (the number of heterozygous loci in an individual) positively affected the sizes of progeny grown in the greenhouse. Though intrinsic overdominance is commonly used as an explanation for a positive effect of isozyme heterozygosity on fitness in strictly outbreeding species, it is argued that the results in this study can be explained by associative overdominance through gametic disequilibrium created by restricted dispersal. The effect of heterozygosity is due partly to an effect of the mother plant, since more heterozygous mothers produced larger progeny even when the effect of offspring heterozygosity was controlled for. The presence of a maternal effect tends to inflate the effect of heterozygosity, a bias that is rarely controlled for in studies of heterozygosity effects on fitness.

Enzyme heterozygosity and developmental stability

Regular development of morphology is challenged by any environmental influence that draines energy from developing individuals. For half a century biologist have recognized that developmental stability, measured as the capability to regulate development of normal morphological structures, is influenced by genetic variation. This review considers the influence of enzyme polymorphism upon developmental stability. Empirical studies in a wide variety of animals have reported morphological variability and bilateral assymmetry to decrase with the heterozygosity of enzyme polymorphism. A controversy focuses on the question of whether the enzymes are neutral markers that either reveal variation in levels of inbreeding or are in linkage disequilibrium with genes directly influencing development. Another controversy focuses on whether the relationships between enzyme heterozygosity and development stability, most commonly reported in poikilotherms, will also be found homeotherms. These controversies are addressed by considering recent empirical studies of enzyme polymorphism and developmental stability.

Lack of an association between heterozygosity and growth rate in the wood frog,Rana sylvatica

The effect of both multilocus and single-locus heterozygosity on growth rate was examined in a cohort of larvae of the wood frog, Rana sylvatica, collected from a pond during the later stages of premetamorphic development. Seven electrophoretically detected enzyme loci were used to determine individual heterozygosity, whereas the growth rate was measured as wet mass. In all cases, no significant correlation was found between multilocus heterozygosity and mass among larvae collected at intervals during the developmental period. In addition, multiple regression analyses indicated that no single locus had a demonstrable effect on growth rate. The results of this study, therefore, provide no evidence for a link between enzyme heterozygosity and growth rate during the later stages of premetamorphic development in wood frog larvae.

Genetic and environmental correlates of variation in body weight of brook trout (Salvelinus fontinalis)

Families of brook trout (Salvelinus fontinalis) were produced from adults collected from Mykiss Lake, Algonquin Provincial Park, Ontario, and reared in the laboratory for 1 year. Egg size and hatching time explained a significant amount of variation among families in mean weight of hatched embryos. Heavier embryos were produced from larger eggs, and embryos with earlier hatching times were also larger. First-feeding alevins reared at higher densities were smaller than those at lower densities. Multilocus enzyme heterozygosity was neither a significant predictor of mean family body weight at any age nor significantly associated with body weight of juveniles within families. Analyzing each enzyme locus separately revealed significant effects for G3PDH-1 in two families but in different directions. Fish from two mitochondrial DNA phylogenetic assemblages, A and B, differed significantly in weight as hatched embryos and first-feeding alevins. Similarly, the progeny of different males and females differed significantly in body weight at all ages sampled. Thus, parental effects were the most persistent correlates of body size of all those examined. The statistical analyses and the nested designs suggest that variation in body weight among the progeny of specific parents can partially be attributed to genetic effects.

Allozyme and RFLP heterozygosities as correlates of growth rate in the scallop Placopecten magellanicus: a test of the associative overdominance hypothesis.

Several studies have reported positive correlations between the degree of enzyme heterozygosity and fitness-related traits. Notable among these are the correlations between heterozygosity and growth rate in marine bivalves. Whether the correlation is the result of intrinsic functional differences between enzyme variants at the electrophoretic loci scored or arises from non-random genotypic associations between these loci and others segregating for deleterious recessive genes (the associative overdominance hypothesis) is a matter of continuing debate. A prediction of the associative overdominance hypothesis, not shared by explanations that treat the enzyme loci as causative agents of the correlation, is that the correlation is not specific to the type of genetic marker used. We have tested this prediction by scoring heterozygosity at single locus nuclear restriction fragment length polymorphisms (RFLPs) in a cohort of juvenile scallops (Placopecten magellanicus) in which growth rate was known to be positively correlated with an individual's degree of allozyme heterozygosity. A total of 222 individuals were scored for their genotypes at seven allozyme loci, two nonspecific protein loci of unknown function and eight nuclear RFLPs detected by anonymous cDNA probes. In contrast to the enzyme loci, no correlation was observed between growth rate and the degree of heterozygosity at the DNA markers. Furthermore, there was no relationship between the magnitude of heterozygote deficiency at a locus and its effect on the correlation. The differences observed between the effects of allozyme and RFLP heterozygosity on growth rate provide evidence against the associative overdominance hypothesis, but a strong case against this explanation must await corroboration from similar studies in different species.

Mitochondrial DNA and allozyme variation in Ontario cultured rainbow trout spawning in different seasons

Rainbow trout ( Oncorhynchus mykiss) from 7 Ontario trout farms as well as fish collected from the Ganaraska River and a descendant stock maintained at Normandale Fish Culture Station, Ontario Ministry of Natural Resources, were analyzed for restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) and variation at protein coding loci. Our objective was to determine (1) the genetic similarity of fish from different farms and (2) if the progeny of fish spawning in different seasons are genetically different. The 340 rainbow trout sampled for mtDNA variation could be categorized into 27 haplotypes. The aquaculture stocks had approximately one-half the mtDNA haplotype variation of that of wild and descendant Ganaraska rainbow trout. Polymorphism was detected at 15 protein coding loci in the sample of 670 trout analyzed. The aquaculture stocks did not have reduced enzyme heterozygosity relative to the naturalized population. Fish from different farms showed varying degrees of genetic similarity based on both mtDNA and allozyme variation. Highly significant genetic differences were detected among fish from the same farm but spawning at different times of the year. The mtDNA analysis grouped fish more according to spawning season than to farm of origin whereas the allozyme analysis did not. This suggests that females spawning in a particular season are derived from a limited number of matriarchal lineages which differ from those in other seasons. The lack of a similar pattern in allozyme variation can be attributed to gene flow, primarily male-mediated, among fish spawning in different seasons.

Enzyme heterozygosity, metabolism, and developmental stability

Enzyme heterozygosity, metabolism, and developmental stability

Morphological Variability and Enzyme Heterozygosity: Individual and Population Level Correlations

Morphological Variability and Enzyme Heterozygosity: Individual and Population Level Correlations

The independence of enzyme heterozygosity and life-history traits in natural populations of Salvelinus fontinalis (brook trout)

The independence of enzyme heterozygosity and life-history traits in natural populations of Salvelinus fontinalis (brook trout)

APPARENT SELECTIVE NEUTRALITY OF MITOCHONDRIAL DNA SIZE VARIATION: A TEST IN THE DEEP-SEA SCALLOP PLACOPECTEN MAGELLANICUS.

Animal mitochondrial DNA (mtDNA) is believed to have evolved under intense selection for economy of the size of the molecule. Among scallop species mtDNA size may vary by a factor of two and among conspecific individuals by as much as 25%. We have examined the possibility that large mtDNA size differences may be associated with fitness in the deep sea scallop Placopecten magellanicus by comparing shell lengths of individuals with different copy numbers of a large mtDNA repeated sequence. Among juvenile cohorts of same age, shell length is known to be a good index of overall fitness in marine bivalves and it is shown here to be affected by differences in nuclear genotype, expressed as the degree of enzyme heterozygosity. We have observed no correlation between shell length and mtDNA length and interpreted this to mean that variation in the size of animal mtDNA is effectively neutral to the forces of natural selection acting on the individual. This type of mtDNA variation must, therefore, be explained in terms of biases in the molecular mechanisms causing expansion or contraction of the molecule, differential replication rates of mtDNA molecules of different size, and the stochastic assortment of mtDNA size classes among individuals.

Enzyme heterozygosity and growth in rainbow trout: genetic and physiological explanations.

The possibility of whether the association between enzyme heterozygosity and body size (fork length) is consistent among rainbow trout (Oncorhynchus mykiss) with different degrees of relationship and is affected by fish age was determined. Six-month-old full-sibs and progeny groups from five and 13 parents of each sex do not show the positive associations between multilocus heterozygosity and fork length which are detectable in larger pooled gamete matings (25 females x 25 males). Moreover, the relationship between heterozygosity at single loci and fork length is inconsistent among families. These data suggest that chromosomal segments, marked by the enzyme loci, are responsible for the phenotypic effects (associative overdominance). Fish age affects both the strength and direction of the association between multilocus heterozygosity and fork length; the association is positive in 6-month-old rainbow trout but is weaker, negative, or differs between the sexes in fish at 1 year. Moreover, the strength of the relationship changes over time in repeated measurements on the same fish. A decline in growth of larger and more heterozygous fish, because of precocial sexual maturation, may partially explain the changing relationship between multilocus heterozygosity and fork length. Sexually mature males are significantly more heterozygous than immature males and show significantly reduced recent growth rates as measured by white muscle RNA concentration. However, females, who rarely mature at 1 year, show significantly higher recent growth rates. Thus, heterozygosity is differentially associated with the allocation of energy resources into somatic and reproductive tissue in male and female rainbow trout.

Are Cultured Stocks of Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss) Genetically Similar to Their Source Populations?

The Ontario Ministry of Natural Resources (OMNR) implemented a controlled breeding program in the early 1980's with the objective of culturing fish that are genetically representative of the source populations. We describe the OMNR brookstock management plan for brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) and test its effectiveness by comparing the allozyme variation of the source fish collected from the Ganaraska River, Ontario to several descendant hatchery lines. Ancestral and descendant rainbow trout do not show significantly different allele frequencies. However, significant differences were detected in brown trout. The absence of several rare alleles in hatchery fish can be explained by sampling error rather than inappropriate propagation methods. Hatchery stocks of either species do not show reduced enzyme heterozygosity compared to wild fish suggesting that the OMNR hatchery system has been successful in retaining allelic variation during broodstock founding and propagation.

Genetic Variation and Fitness: A Test in a Naturalized Population of Brook Trout (Salvelinus fontinalis)

The relationship between enzyme heterozygosity and several components of fitness (size and survival) was examined in a naturalized population of brook trout (Salvelinus fontinalis) from Algonquin Provincial Park, Ontario. Significant differences in allele frequency and the number of heterozygous loci per individual were found among five age classes spanning most of the life history stages of brook trout in this population. A young of the year (YOY) cohort sampled after a period of high natural mortality had significantly greater numbers of heterozygous loci per individual than YOY sampled shortly after emergence from redd sites. A positive association between heterozygosity and size was only found in YOY sampled in June and not in the other age classes in which sexual maturity was not a complicating factor. The association between heterozygosity and size was affected by the onset of sexual maturity. Significant negative regressions between multilocus or single locus heterozygosity and size were found in mature males whereas heterozygosity was positively associated with size in females. These dissimilarities may be the result of differences in growth rates prior to sexual maturation and differential allocation of energy towards gametic and somatic tissue.

Enzyme heterozygosity and growth of rainbow trout reared at two rations

The relationship between heterozygosity at nine enzyme loci and both size and growth in rainbow trout (Salmo gairdneri) reared at either low (LRT) or high (HRT) ration for 84 days is reported. The experimental fish were progeny produced from a pooled mating of 25 female and 25 male rainbow trout captured in spawning condition at the Ganaraska River, Ontario. There is a significant negative regression between the number of heterozygous loci per fish and size (fork length and weight) among fish at the beginning of the experiment. Heterozygotes at two loci, Sod and Mdh3,4, were significantly smaller than homozygotes. A significant negative regression between multilocus heterozygosity and size was detectable among the fish reared at HRT for 84 days but not at LRT. Ration appeared to affect the strength of the association between heterozygosity and growth because at HRT homozygotes at the majority of loci grew faster than heterozygotes, but the reverse was true at LRT.

Disease resistance and enzyme heterozygosity in rainbow trout

The relationship between heterozygosity at nine polymorphic enzyme loci and disease resistance was examined in 373 individually identified rainbow trout (Oncorhynchus mykiss) from 12 full-sib families and a pooled gamete cross. These fish were challenged with bacterial gill disease, a potentially lethal epizootic in freshwater fishes. The 213 surviving fish had significantly greater numbers of heterozygous loci per fish and were significantly larger than the 160 individuals that died. Survivors, on average, had higher heterozygosity at six out of nine loci than non-survivors. The differences were significant at three of these loci. These findings suggest that more heterozygous rainbow trout have superior disease resistance than less heterozygous fish.

Enzyme Heterozygosity, Growth Rate, and Viability in Mytilus edulis: Another Look

Enzyme Heterozygosity, Growth Rate, and Viability in Mytilus edulis: Another Look

Genetic variability and components of fitness in hatchery strains of rainbow trout

Two fitness components, development rate and egg size, were examined in six hatchery strains of rainbow trout, Oncorhynchus mykiss (syn. Salmo gairdneri Richardson), with different amounts of enzyme heterozygosity. The average expected heterozygosities per strain ranged from 4 to 8%, based upon an electrophoretic analysis of the protein products of 42 loci. Strains with higher heterozygosities had faster development rates, as measured by hatching time, than strains with lower heterozygosity. Concordance between hatching time and another measure of development rate, degree of yolk‐sac resorption, suggests that hatching time is a valid measure of embryonic development rate in salmonid fishes. Earlier‐hatching embryos were longer and heavier at the time of yolk‐sac resorption than later‐hatching fish. Females from more‐heterozygous strains also had a tendency to have larger eggs. These data suggest that genetic variation is an important biological resource to be conserved in hatchery stocks.

Morphological variance and enzyme heterozygosity in Eleutheronema tetradactylum and Strongylura strongylura collected from Khor Al-Zubair area, Basrah, Iraq

Abstract Eleutheronema tetradactylum and Strongylura strongylura were studied in testing the association of enzyme heterozygosity with decreased morphological variance. Six polymorphic loci and three meristic characters were used in this test. The results show that such a relationship, although observed by several other workers may not be universal and hence such a hypothesis was not confirmed.

Morphological variance and enzyme heterozygosity in Eleutheronema tetradactylum and Strongylura strongylura collected from Khor al-Zubair area, Basrah, Iraq

Abstract Eleutheronema tetradactylum and Strongylura strongylura were studied in testing the association of enzyme heterozygosity with decreased morphological variance. Six polymorphic loci and three meristic characters were used in this test. The results show that such a relationship, although observed by several other workers may not be universal and hence such a hypothesis was not confirmed.

The Relation of Enzyme Heterozygosity to Standard and Active Oxygen Consumption and Body Size of Tiger Salamanders, Ambystoma tigrinum

We addressed the questions concerning what relation exists between enzyme heterozygosity and standard or active oxygen consumption (V̇o2) and whether the genotype at a particular locus could predict differences in body size. Of the 25 enzyme loci evaluated in liver tissue, eight were polymorphic; no individual was heterozygous at more than five loci. Standard V̇o2 was most strongly associated with heterozygosity at the glucose phosphate isomerase and alcohol dehydrogenase (ADH) loci, whereas active V̇o2 was most tightly associated with heterozygosity at the ADH locus. Overall, standard V̇o2 was inversely correlated with multiple-locus heterozygosity at the eight loci, whereas active V̇o2 was positively correlated with heterozygosity. The significant correlation between polymorphism at the ADH locus and both standard and active V̇o2 led us to examine the relation between heterozygosity at the ADH locus and body size in a natural population. Body size in a single age class of larvae was greatest in heterozygotes and smallest in the least common homozygote, suggesting an important role for ADH in whole-body physiology. Analysis of the relation between genotypes and physiological characteristics may reveal some of the causes of variation in physiological performance among individuals. Furthermore, these analyses may generate testable hypotheses concerning the selective advantage of biochemical mechanisms and properties.