Kathy L. Knudsen

Superior Developmental Stability of Heterozygotes at Enzyme Loci in Salmonid Fishes

We examined the association between heterozygosity at 42 enzyme loci and fluctuating asymmetry at five bilateral meristic characters in 14 population samples of rainbow trout, cutthroat trout, and brook trout. There is a significant negative correlation between heterozygosity and the proportion of asymmetric characters per individual in two populations of rainbow trout and two populations of cutthroat trout. This correlation is negative in 13 of the 14 population samples (sign test, P < .001). Thus, individuals that are more heterozygous at isozyme loci have reduced fluctuating asymmetry; this appears to be general among salmonid fishes. We also found that individuals with obvious morphological deformities in three populations have increased fluctuating asymmetry. Thus, fluctuating asymmetry appears to be a reliable indicator of overall developmental stability and is therefore negatively correlated with fitness. The association between heterozygosity and asymmetry and between asymmetry and morphological deformities suggest that heterozygosity is positively correlated with fitness in these fishes.

DEVELOPMENTAL INSTABILITY AND HIGH MERISTIC COUNTS IN INTERSPECIFIC HYBRIDS OF SALMONID FISHES

Interspecific hybrids have been proposed to have reduced developmental stability in comparison to their parental species because the parental genomes have not undergone selection for the maintenance of developmental stability when they occur together. We present data from four interspecific hybrids of salmonid fishes that support this view. Natural hybrids of bull trout (Salvelinus confluentus) with brook trout (Salvelinus fontinalis) and laboratory hybrids of rainbow trout (Salmo gairdneri) with Yellowstone (Salmo clarki bouvieri), westslope (S. c. lewisi), and coastal (S. c. clarki) cutthroat trout all have higher levels of fluctuating asymmetry than either of their parental species raised in the same environment. Thus, the hybrids have reduced developmental stability.

Heterozygosity and developmental stability in gynogenetic diploid and triploid rainbow trout

We have previously reported that rainbow trout (Salmo gairdneri) more heterozygous at enzyme loci generally show increased developmental stability, as measured by reduced fluctuating asymmetry. We experimentally produced gynogenetic diploid and triploid individuals to test the effect of extreme heterozygosities on developmental stability. Gynogenetic diploids are identical by descent at an estimated 34 per cent of all loci and show a 50 per cent increase in the mean proportion of traits asymmetric per individual compared to normal rainbow trout. Triploids from two different strains have an estimated 30 per cent increase in genomic heterozygosity and a 14 per cent decrease in the mean proportion of traits asymmetric per individual compared to normal diploids. These changes in asymmetry induced by gynogenesis and triploidy are not as great as we expected based on the association between heterozygosity and fluctuating asymmetry in random mating populations. The narrow range of mean asymmetry in rainbow trout may result from an upper limit restricted by directional selection for developmental stability and a lower limit determined by inherent randomness in the developmental process.

Androgenetic rainbow trout produced from inbred and outbred sperm sources show similar survival

Abstract Androgenesis is a technique that could facilitate the rapid production of completely homozygous isogenic lines of fish. We induced diploid androgenesis in rainbow trout (Salmo gairdneri) by fertilizing 60Co gamma-irradiated eggs with untreated sperm and then blocking the first cleavage division with hydrostatic pressure. Electrophoresis of enzymes encoded by seven loci confirmed the complete homozygosity and all-paternal inheritance of the androgenetic progeny. We used sperm from both inbred and outbred strains to determine if the survival of androgens was greater with sperm from inbred males because of a reduction in the number of deleterious recessive alleles in inbred strains. Survival of androgenetic diploids from inbred and outbred sperm sources was similar and significantly below that of outbred controls. The similar survival of androgens from inbred and outbred sperm sources may be the result of high treatment mortality associated with androgenesis.

Developmental Instability as an Indicator of Reduced Genetic Variation in Hatchery Trout

Abstract We present evidence for reduced developmental stability in a hatchery stock of westslope cutthroat trout Salmo clarki lewisi. These fish have a high frequency of two obvious morphological deformities and an unusually high amount of asymmetry at five bilateral meristic traits. We have previously reported that this stock has a reduced amount of genetic variation at 35 isozyme loci compared to the wild population from which it was derived. The loss of genetic variation in this stock apparently has reduced the ability of these fish to develop precisely along genetically determined developmental pathways. We also present the biological rationale and the methods for using fluctuating asymmetry as a diagnostic tool for detecting the effects of the loss of genetic variation in cultured stocks of fish. Received April 7, 1984 Accepted November 8, 1984

Genetic Divergence and Identification of Seven Cutthroat Trout Subspecies and Rainbow Trout

Abstract We estimated the amount of genetic divergence among seven cutthroat trout Salmo clarki subspecies and rainbow trout Salmo gairdneri using electrophoretic data from 46 protein loci. There was little genetic divergence among the Colorado River, finespotted, greenback, and Yellowstone subspecies of cutthroat trout, but a large amount existed among the coastal, Lahontan, and westslope subspecies. These latter three subspecies were electrophoretically as similar to rainbow trout—or more so—as they were to the other four subspecies of cutthroat trout examined. Morphologically, in contrast, the cutthroat trout subspecies were all more similar to each other than to rainbow trout. The data, therefore, suggest that morphological and protein evolution have proceeded at different rates among some of these fishes. The presence of fixed or nearly fixed allele-frequency differences between the subspecies of cutthroat trout and rainbow trout and between many pairs of cutthroat trout subspecies provides a powerfu...

HETEROZYGOSITY AND DEVELOPMENTAL RATE IN A STRAIN OF RAINBOW TROUT (SALMO GAIRDNERI )

Rainbow trout (Salmo gairdneri) with greater heterozygosity at enzyme loci also have greater developmental stability, as measured by bilateral symmetry of five meristic traits. Fish with increased amounts of liver phosphoglucomutase activity have greater developmental stability and develop faster than fish with normal activity. These observations suggest that the differences in developmental stability between homozygotes and heterozygotes may be the result of differences in developmental rate. Faster developmental rates are expected to decrease the probability of accidents during critical periods of development, resulting in a more stable or uniform phenotype.

Systematic Implications of Geographic Patterns of Genetic Variation in the Genus Dicamptodon

WHITT, G. S. 1970. Developmental genetics of the lactate dehydrogenase isozymes of fish. J. Exp. Zool. 175:1-35. , W. F. CHILDERS AND P. L. CHO. 1973. Allelic expression at enzyme loci in an intertribal hybrid sunfish. J. Hered. 64:55-61. 9 AND T. E. WHEAT. 1971. The inheritance of tissue-specific lactate dehydrogenase isozymes in interspecific bass (Micropterus) hybrids. Biochem. Genet. 5:257-273.

Effects of rearing density on meristics and developmental stability of rainbow trout

We investigated the effects of a four-fold difference in incubation and rearing density on developmental rate, counts of eight meristic characters, and fluctuating asymmetry of rainbow trout, Oncorhynchus mykiss. Fish from the high density group had significantly more vertebrae and rays in the pelvic fins. The overall magnitude of morphological divergence between treatment groups, however, was small compared to that associated with genetic and temperature-induced alterations of developmental rate. Fish from the high density treatment had greater mean fluctuating asymmetry than those in the low density group, but this difference is not statistically significant. Hatching time did not differ significantly between treatment groups. The effects of density on meristic counts, therefore, appear to be independent of developmental rate.

Genetic Differences among Rainbow Trout Spawned on Different Days within a Single Season

Abstract We found statistically significant differences in gene frequencies at protein loci among progeny produced throughout the spawning season by two hatchery strains of rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri). In addition, progeny produced in the middle of the spawning season generally had more genetic variation than progeny produced either early or late in the spawning season. These results suggest that spawning time is likely to be influenced by many genes spread throughout the genome of rainbow trout. The genetic variation in a hatchery brood stock, therefore, can best be maintained by retaining progeny produced throughout most of the spawning season as future brood fish.