Heterozygosity and developmental stability in gynogenetic diploid and triploid rainbow trout

Abstract

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.

Developmental stability, heterozygosity, and fitness in two introduced fire ants (Solenopsis invicta and S. richteri) and their hybrid

“…Fluctuating asymmetry is defined as minor random deviations from perfect bilateral symmetry, as evidenced by measurable differences between the right and left sides of single characters on single individuals (Van Valen, 1962). Because both sides of a character are the products of expression of a single genome, such departures from bilateral symmetry presumably reflect the inability of the genome to coordinate development precisely; that is, fluctuating asymmetry reflects non-heritable developmental "noise" (Mather, 1953;Lerner, 1954;Van Valen, 1962;Soulé, 1979, 1982; Leamy, 1984;Leary et a!., 1985a;Palmer, 1986). Several studies have suggested that high levels of fluctuating asymmetry are likely to be associated with a decrease in individual fitness (Soulé, 1982;Leary et a!., 1984Leary et a!., , 1985bClarke and McKenzie, 1987; see also Bruckner, 1976), a result that is expected if developmental stability is an important component of fitness.…”

Developmental Instability and High Meristic Counts in Interspecific Hybrids of Salmonid Fishes

“…This type of asymmetry results from the inability of individuals to develop precisely along genetically determined pathways since both sides ofindividuals reflect the same genome. Fluctuating asymmetry, therefore, can be used as a measure of developmental stability (Mather, 1953;reviewed by Soule and Cuzin-Roudy, 1982;Leary et al, 1985b). Higherlevels offluctuating asymmetry indicate reduced developmental stability.…”

Diploid and triploid Chinook salmon, Oncorhynchus tshawytscha (walbaum): An exploration of induction efficacy, performance and genomic architecture.

“…The existence of such radical differences in primary biological structure (Benfey 1999) suggests that integrated physiological functioning might be impaired but that these negative effects might be offset by positive fitness related effects of increased genetic diversity (Leary et al 1985;Allendorf and Leary 1984), reallocation of energy to somatic growth, gene dosage effects (genetic expression directly proportional to ploidy) and/or protection from mutagenic events (Thorgaard et ai. 1999).…”

“…In relation to diploids, these include: 1) nuclear enlargement with triploids containing 50% more DNA, 2) larger cell size with approximate maintenance of the nuclear:cytoplasmic ratio along with a reduction in the surface areaivolume ratio, 3) fewer cells, but maintenance of diploid tissue, organ and body size and 4) increased allelic diversity with potentially three different alleles at each locus (Swarup 1959a;Leary et al 1985;Benfey 1999). These conditions suggest that triploids may experience potentially positive fitness or production related effects due to increased allelic diversity, higher genetic expression of growth related loci and somatic reallocation of energy normally invested in the maturational process.…”

“…However, it is known that in addition to the increase in DNA quantity, shock-induced triploidy increases allelic diversity and number (i.e. three versus two alleles at each locus and potentially an additional different allele per locus (depending on recombination rate) (Thorgaard et al 1983;Allendorf and Leary 1984;Leary et al 1985). This increased genetic diversity might be expected to have positive fitness-related effects (e.g., deleterious alleles may have a higher probability of being masked or a synergistically favorable combination of alleles may occur (Garnier-Gere et al 2002;Wang et al 2002).…”