Mitochondrial and nuclear DNA sequence variability among populations of rainbow trout (Oncorhynchus mykiss).

Mitochondrial and nuclear DNA variability was examined to assess population genetic structure and phylogeographic relationships in rainbow trout. Single-strand conformation polymorphisms and restriction site differences within 1055 bp of the mitochondrial D-loop region and 1566 bp of nuclear DNA in six single-copy nuclear DNA regions identified 31 mitochondrial genotypes and 50 nuclear alleles. Gene trees were constructed by sequencing each variant allele or mitochondrial genotype identified. Examination of 30 populations in 10 native rainbow trout groups using analysis of molecular variance (AMOVA) indicated that 65% of mitochondrial variability and 35% of nuclear variability was explained by differences among the 10 groups. Phylogenetic patterns evident in mitochondrial and nuclear DNA were not always concordant. Differences in the evolutionary patterns detected by mitochondrial and nuclear DNA may reflect the differential impact of past introgression events on variability in the two genomes.

Polymorphic molecular markers from anonymous nuclear DNA for genetic analysis of populations.

A simple method is presented for developing polymorphic, anonymous DNA markers suitable for population genetic studies. Anonymous DNA fragments are screened for sequence variability using a common mutation detection technique (single strand conformation polymorphism analysis; SSCP) and locus-specific PCR primers are designed for polymorphic DNA fragments. Detection of the markers by SSCP analysis coupled with sequence analysis of SSCP variants allows rapid screening while retaining information about the genealogical relationship among alleles. Variability detected for six markers was assessed in rainbow trout Oncorhynchus mykiss and was compared with variability detected by similar analysis of intron loci. Between three and 12 distinct alleles were observed at each marker locus, and average within-population heterozygosity ranged from 0.12 to 0.44. Advantages and limitations of the methodology for population genetic analysis are discussed.

Genetics and reproduction in fish culture.

Fish genetics has made major strides during the past 20 yr due both to improvements in the ability of fish culturists to manage reproduction and to deliberate experimentation and application. The general finding has been that the quantitative genetics of fish differ little from those of other animals and that the applications of animal improvement techniques are similar for fish and other animals. In addition, a number of novel techniques, such as ploidy manipulation and sex reversal, are relatively easy to achieve with a number of fish species. As a result, some very specialized approaches to research have been possible, and applications to fish production seem to be limited only to the imagination of the breeder. However, only limited application has occurred over a major portion of the industry, and genetic improvement of stocks has been achieved in very few instances. The reason for this apparent dichotomy between opportunity and reality seems to be related to the industry's lack of emphasis on genetic improvement.

Para-albumin polymorphism: an unlinked two-locus system in rainbow trout.

Para-albumin (PALB), a new polymorphic protein system in rainbow trout, is described. Data from 20 ful-sib families established that the observed electrophoretic variability was controlled by two loci. Differential staining of two bands expressed by heterozygotes indicated that the PALB protein was a monomer and that the variability was the result of the expression of two alleles at each locus. The alleles at the two loci were further shown to be identical with regard to electrophoretic mobilities of the proteins. There was no evidence of linkage between the two loci. Consequently, it is concluded that the loci, PALB-1,2, reside on duplicate chromosomes that have retained their integrity since a tetraploidation event.

Genotype-environment interaction effects on reproductive performance in Tribolium castaneum.

Three lines of Tribolium castaneum were raised totally on a yeast-free or yeast-supplemented diet, or raised to pupation on a yeast-free diet and then on a yeast-supplemented diet, and vice versa, to study the effects of genotype x environment interaction and diet changes after pupation on reproduction.Feeding the yeast-supplemented diet generally resulted in earlier sexual maturation, heavier adult weights and higher egg production. The diets had no effects on larval viability. Changes in diet after pupation had no effects on age at sexual maturity or adult weight. Egg production was determined largely by the environment just prior to and during egg laying. However, egg production on the yeast-free diet was influenced by the pre-pupation diet.There was significant line x environment interaction effects on age at sexual maturity, mature egg production and adult weight (P<0.01). There was also a sire x environment effect on egg production (P<0.05).

Artificial selection for 18-day pupa weight and opposing simulated naturel selection in Tribolium castaneum.

The effect of simulated opposing natural selection on the response to mass selection for 18-day pupa weight of Tribolium castaneum was studied for 10 generations of selection. Natural selection was simulated in replicated treatment lines by imposing a negative relationship between mid-parent genetic value for pupa weight and fertility. Responses to selection and realized heritabilities were smaller (P < 0.05 and P < 0.10, respectively) for the treatment lines than for control lines under selection for pupa weight only. One treatment, line E3G1, reached an intermediate selection plateau by generation 10, and responded linearly to 4 generations of artificial selection after natural selection had been discontinued. Possible explanations for the different behaviors of the replicate lines E3G1 and E3G2 were also discussed.

Adult triploids in a rainbow trout family.

Six triploid individuals were found in a full-sib family of 11 adult rainbow trout (Salmo gairdneri) from a domesticated hatchery stock. The triploid individuals were normal in size and external appearance, had underdeveloped gonads, and showed no evidence of 3n/2n chimerism or mosaicism. XXY triploids were males, suggesting that the Y chromosome is male determining in trout. Because they may avoid production losses associated with sexual maturation in normal fish, triploid trout and salmon could potentially be useful in fish culture.

Electrophoretic variation and differentiation in four strains of domesticated rainbow trout (Salmo gairdneri).

A total of 1462 rainbow trout (Salmo gairdneri Richardson) representing four California domestic strains, were examined electrophoretically at 24 gene loci to investigate the amount of genetic variability within strains and genetic differentiation between strains, relative to wild populations. Estimated heterozygosities of 0.071 to 0.134 were similar to those reported for wild populations and thus indicated that the domestic strains were at least as variable as wild populations. Genetic distances between strains ranged from 0.011 to 0.067, values typical of the level of differentiation observed between local conspecific populations in a variety of organisms. It was suggested that this high level of heterozygosity is due to mixing of populations in the strains' histories and perhaps also to balancing selection.

Biochemical genetic variation in populations of golden trout, Salmo aguabonita: evidence of the threatened Little Kern River golden trout, S.a. whitei.

Eight wild populations of the High Sierra golden trout, Salmo aguabonita, and one domestic stock of rainbow trout, Salmo gairdneri, were examined for biochemical-genetic variation in eight protein systems. Variation within the eight systems was determined by at least 10 loci in both golden and rainbow trout and all the alleles identified in rainbow trout were observed as electro-phoretically identical phenotypes in golden trout. Variation was observed at an average of 51 percent of the loci in the golden trout samples and for five of the 10 loci in the rainbow trout. Average heterozygosity ranged from 12.6 to 13.9 percent for seven of the golden trout populations with one showing a low value of 5.4 percent. A comparable estimate of 12.1 percent was found for the rainbow stock. On the basis of genetic variation and allele frequencies at three loci, the eight golden trout populations were divided into two distinct groups. Three populations sampled from the Little Kern River basin tended to be genetically distinct from two additional Little Kern River basin populations and from three geographically distinct populations sampled from the eastern Kern River area. The former three populations were hypothesized to be of a recent rainbow-golden hybrid origin. Trout in the other two Little Kern River basin populations, sampled in head-waters of a stream tributary to the Little Kern River, were considered to be the threatened Little Kern golden trout, S. a. whitei Evermann, due to their high degree of genetic similarity to the geographically distinct subspecies S. a. aguabonita sampled from the eastern Kern River area. The finding of substantial genetic variation in the wild golden trout populations indicates that this threatened species is not at present genetically impoverished and thus does not appear to be in immediate danger of extinction through lack of adaptive capability.

Growth Rate, Body Composition, Cellular Growth and Enzyme Activities in Lines of TRIBOLIUM CASTANEUM Selected for 21-Day Pupa Weight.

Growth rate, body composition, cell number, cell size, and the activity of four dehydrogenase enzymes were studied from 10 to 25 days of age in one control (1C) and three lines (3, 9, 10) of Tribolium castaneum that had been subjected to long term selection for large 21-day pupae weight.-Selected lines were two- to three-fold larger in size than the control line throughout development. No major differences in percent of protein were detected among the lines but at any particular age, the selected lines were found to have a higher fat content than the control line. The differences in fat content were closely correlated with development such that all the lines reached very similar levels of percent of fat just prior to pupation. Water content showed an inverse relation to percent of fat.-Selection was observed to have caused major changes in the cellular response to growth. The selected lines had an average of from 17% to 48% larger cells (measured as protein/DNA) and were found to have from 37 to 62% more cells (measured as total DNA) than the control line at all ages from 10 to 19 days of age. In addition, the selected lines had a higher RNA content at all ages studied and higher RNA:DNA ratios at the young ages. In contrast the enzyme activities of ICDH and LDH were 60% lower. The results are interpreted as indicating that a more efficient metabolic machinery had evolved in the rapidly growing selected lines.

Food Consumption, Feed Efficiency, Metabolic Rate and Utilization of Glucose in Lines of TRIBOLIUM CASTANEUM Selected for 21-Day Pupa Weight.

Food consumption, feed efficiency, metabolic rate and glucose utilization were studied throughout development in one control (1C) and three selected lines (3, 9, 10) of Tribolium castaneum that had been subjected to long term selection for 21-day pupae weight. Growth rate, body composition, cellular growth and the activity of four dehydrogenase enzymes in the same lines have been reported (Medrano and Gall 1976).-Larva of selected lines consumed 1.2 times as much food as the control and gained an average of 2.9 times as much weight. The rapid growth of the selected lines was associated with a gross feed efficiency 20 to 30% above that for the control line. There was also a small but consistent improvement in the conversion of digested food. Average digestibility was higher for selected lines.-There was little apparent differentiation between the control and selected lines in metabolic rate/individual, but the rate measured on a per-unit weight basis was two- to three-fold greater for the control during the active growth stages. Respiratory quotients (R.Q.) of 1.0, indicative of carbohydrate oxidation, were observed through larval growth in all lines. Pupae at 21 days showed R.Q. values greater than 1.0, which were interpreted as resulting from a phenomenon in insects in which CO(2) is released by pupae, in large bursts at irregular intervals. The rate constant of glucose oxidation, measured as the rate of C(14) labelled CO(2) respired during 2- to 6-hour incubation periods, was two- to three-fold higher in the control. In addition, the control line larvae expired 5% to 17% more of the ingested C(14) as CO(2). It was apparent that control line individuals maintained a much more active turnover of metabolites but without an effective retention of carbon as body substances. The results are discussed in support of the hypothesis that selection for large body size resulted in improved control mechanisms that influence the biological efficiency of growth in Tribolium.

Chromosome cytology and polymorphism in the California High Sierra golden trout (Salmo aguabonita).

The population variability in chromosome karyotype was examined in six samples of California High Sierra golden trout, Salmo aguabonita. From the analysis of 1,318 cells from anterior kidney tissue of 92 specimens, the modal diploid chromosome number was 2n equals 58 with 104 chromosome arms. Of cells with 2n equals 58 chromosomes, the typical karyotype was one containing 44 chromosomes with median centromeres, 2 chromosomes with submedian centromeres, 2 with subterminal centromeres and 10 with terminal centromeres. In addition, many cells contained a chromosome with a prominent satellite. Variability in chromosome number within the six populations followed a Robertsonian pattern and permitted the identification of two distinct population distributions. One population, made up of two samples, was more variable than the other and supported the hypothesis that this population was of golden trout times rainbow trout hybrid origin. Texamination of metaphase 1 cells from testes showed numerous ring and rod multivalents consistent with the random nature of Robertsonian variability.

Replicated selection for 21-day pupa weight of Tribolium castaneum.

Response to upward selection in 10 replicate lines was linear through 15 generations, had slowed considerably in many lines by generation 23 and continued in other lines through 30 generations. The lines tended to group into those which responsed slowly during early generations and continued to respond through later generations and those which gave rapid early response and very low response later coupled with marked reduction in fitness. Response to downward selection was similar for 3 replicate lines but only 50% as great as that for the high lines. Response declined more rapidly in the low lines due to reduced fitness, declining selection differentials and a marked drop in phenotypic variance.

Growth of the laboratory mouse.

Body weights and tail lengths were observed every 3 days from birth to 60 days of age and every 6 days from 60 to 96 days in four lines of mice: C57BL/6J, an inbred; J, a synthetic outbred; GR, Goodale large body size line; and FR, Falconer large body size line. Mean 96-day body weights for lines C57BL, J, GR and FR were 25.4, 29.7, 48.8 and 49.1 gm for males, and 19.9, 23.8, 38.5 and 38.2 gm for females, respectively. Lines GR and FR gave identical body weights at all ages studied. Both of these lines had previously plateaued in response to selection for large body size. The variability in body weight was smallest for lines C57BL and J, intermediate for FR and highest for GR. The pattern of variance over time was very similar in all lines and both sexes, showing a minimum at birth and a maximum at age of inflection. Growth in tail length of the four lines showed similar between line differences except that length in GR was greater than in FR. Age at vaginal opening in females coincided closely with age of inflection in body weight growth. Age at point of inflection did not differ between lines but appeared to occur somewhat earlier in females than in males.