Roger W. Doyle

DNA fingerprint based analysis of paternal and maternal effects on offspring growth and survival in communally reared rainbow trout

Abstract This study was initiated to assess the feasibility of establishing pedigrees in mixed aquaculture populations and of selection programs for commercial aquaculture operations based on genetic profiling data from microsatellite markers. Complete factorial crosses between ten sires and ten dams were performed in a small rainbow trout farm. The largest and smallest progenies were sampled after 1 year of communal rearing, and their parentage was established with four or five microsatellite markers. About 91% of the fish could be traced to one or two parental couples out of the 100 possible couples. There were significant differences among sires and dams for the growth and survival of their progeny. There were also indications that progeny of inbred crosses have depressed performances. Based on these results, a breed improvement program has been implemented in this small hatchery.

Stability in the historical pattern of genetic structure of Newfoundland cod (Gadus morhua) despite the catastrophic decline in population size from 1964 to 1994

We report on evidence of long term stability inthe geographic pattern of geneticdifferentiation among cod (Gadus morhua)collected from 5 spawning banks offNewfoundland and Labrador over a periodspanning three decades (1964–1994) and 2orders of magnitude of population sizevariation. Six microsatellite DNA lociamplified from archived otoliths (1964 and1978) and contemporary (1990s) tissue samplesrevealed fidelity to natal spawning banks overthis period. A two level (spawning bank anddecade) hierarchical and multilocus AMOVAindicated that 1.55% of the total variation inallele frequencies could be attributed(P = 0.036) to spatial structure while novariance component could be attributed totemporal changes. A finer scale analysis amongcod from just 3 of these spawning banksreveals, however, evidence consistent with somepost-collapse mixing between cod from twobanks. In the context of fisheries managementand conservation, the survival of the spatialpattern of genetic differentiation during thepopulation collapse suggests that if recoveryeventually occurs it will likely be throughpopulation re-growth in situ rather thanby migratory influx.

Early growth performance of Atlantic salmon full-sib families reared in single family tanks versus in mixed family tanks

The present experiment was designed to assess the impact of the confounding of environmental tank effect with genetic family effect during early rearing periods. In November 1989, two sets of mixed family tanks were created in the Salmon Genetic Research Program (SGRP) hatchery by pooling equal numbers of eggs from four and eight families, respectively. In July 1990, tissue samples and length and weight measurements were collected on fish from both individual family tanks and mixed family tanks. Four polymorphic microsatellites were used to determine unambiguously the family of origin of 790 mixed group fish. There was a strong correlation of family survival rates measured in the mixed tanks and in the single family tanks. Differences among families for length and growth were observed in both the mixed tanks and the single family tanks. However, family growth performance in the single tank environment was poorly correlated with family growth performance in the mixed tank environment and appeared to reflect environmental differences among tanks rather than genetic differences among families. Neither family growth performance in the mixed tanks nor in the single family tanks appeared strongly correlated with subsequent family growth performance up to smolt stage.

An approach to the quantitative analysis of domestication selection in aquaculture

Abstract Domestication selection is defined as natural selection on traits which affect survival and reproduction in a human-controlled (domestic) environment. By altering various aspects of the environment, domestication selection can be made to augment or oppose artificial selection on traits of commercial importance. A quantitative, analytical framework based on multiple regression is presented. The analytical techniques are illustrated with five examples of controllable selection in aquaculture environments: 1. (1) Selection on growth associated with fertility variation in Salmo trutta fed at different ration levels. 2. (2) Selection on growth in Macrobrachium rosenbergii associated with variable development rate and age-at-harvest. 3. (3) Selection on growth as it is influenced by the interaction between fertility and development rate in a continuously re-stocked population (Gammarus lawrencianus). 4. (4) Selection on growth caused by size-selective mortality in juvenile lobsters (Homarus spp.). 5. (5) Selection on growth confounded by phenotypic effects associated with stocking density (stunting) in Pleuronectes platessa. In each of the examples the selection differential is, or can easily be made to be, comparable to the intensity of artificial selection. Although genetic changes classifiable as domestication are known in aquaculture, the selection which causes it has not previously been analysed quantitatively. It is concluded that management procedures can have strong selective effects and that genetic changes (for good or for ill) may be expected to occur rapidly if the obvious genetic conditions are met.

Effective population size and rate of inbreeding in aquaculture of Indian major carps

Abstract Induced spawning of Indian major carps by hypophysation has been practiced extensively since the mid-nineteen-fifties. At present, all hatcheries function as isolated genetically closed units raising their own stock of breeders and producing fish seed for distribution to grow-out areas. The individuals for replenishment of broodstock are those which were retained after the hatchery has reached its seed production target for a given year. There is a growing concern that hatchery stocks may be severely inbred because their overall performance has been rapidly deteriorating. Exact estimates of the rate of inbreeding accumulation, however, is difficult because the effective population size is not known and systematic records of various broodstock management operations are not available. In this paper, effective population size ( N e ) and the rate of inbreeding ( ΔF ) have been estimated in terms of the numbers of new individuals entering the broodstock population each year and the variance of their reproductive success. This study is based on data collected during the 1987–1988 breeding season from 18 fish hatcheries in Karnataka State, southern India. N e ranges from as low as 3 to a maximum of 30, and ΔF from 2% to 17% per year. Rapid inbreeding of stocks is evident. Possible ways of reducing further accumulation of inbreeding in broodstock populations are discussed.

Control of epiphytes in seaweed cultures using grazers

Abstract Two crustaceans, Gammarus lawrencianus and Idotea baltica , grazed selectively on Enteromorpha spp. and Ectocarpus spp. which often grow epiphytically on Chondrus crispus in culture. Idotea baltica readily consumed C. crispus when no other food was available while G. lawrencianus did not. Results indicate that these animals could also be used to control epiphytes on Gracilaria tikvahiae and Gymnogongrus sp. but not on Palmaria palmata as the latter was consumed together with the epiphytes.

Genetic changes in “fitness” and yield of a crustacean population in a controlled environment

Abstract The amphipod, Gammarus lawrencianus Bousfield, was maintained for ≈ 26 generations in a laboratory environment that permitted constantly increasing population size. The intrinsic rate of population growth, rm, increased 1.7-fold as a result of heritable changes in survivorship and fertility. Yield of biomass of large animals (“harvestable” biomass) increased 2.6-fold for each 45-day harvest cycle. Yield is correlated with fitness in this environment and therefore increased, although not selected for directly. Changes in life history traits are interpreted in terms of selection for Darwinian fitness in a controlled environment. The potential for genetic domestication of Crustacea is proportional to the variance of the major components of fitness, which can be estimated experimentally.

An ecological genetic analysis of the settling behaviour of a marine polychaete

SummaryThe settling behaviour of larvae of Spirorbis borealis from several ecologically contrasting environments was analysed in terms of means and genetic variances (the latter expressed as heritability) of two components—the probability of settling when presented with a particular substrate, and the gregarious behaviour of the larvae. Larval behaviour differed markedly according to the population from which they came: animals from a sheltered tidepool prefer Ascophyllum, and are distinctly gregarious, while those from a semi-exposed embayment settle much more readily on Fucus and are not as gregarious. Animals collected from an environmental cline ranging in conditions from tidepool-like to embayment-like exhibit a corresponding range in behaviour. This interpopulation variation in character means is interpretable in terms of adaptation to differential selection pressures known to be acting on the populations; consideration of intra-population genetic variances gives an indication of the mechanism of the adaptation.

Genetic variation in Ophiomusium lymani (Echinodermata) populations in the deep sea

Abstract Gene and genotype frequencies in a polymorphic esterase isoenzyme system were measured in collections of the brittle-star Ophiomusium lymani taken at approximately 2000 meters off the coast of North Carolina. Frequencies varied with the depth of the collections but not with their geographical location along the contours. An excess of a homozygote above Hardy-Weinberg expectation was observed in the deeper samples.

Effective population size and selection in variable aquaculture stocks

Abstract Effective population size and inbreeding rates are derived in terms of the variability of broodstock replacement; the parameters are more useful for extensive aquaculture than the usual formulation. It is shown that response to mass selection may improve if variability in birth date and age is reduced by weight-specific rather than age-specific selection for growth rate. Current studies on domestication selection in Asia suggest that traditional broodstock management may be causing stocks to deteriorate.