ORIGIN OF VARIATION IN ISOGENIC, GYNOGENETIC, AND ANDROGENETIC STRAINS OF COMMON CARP, CYPRINUS-CARPIO

After androgenetic or gynogenetic reproduction, a large expansion of p henotypic variance is generally observed. Within one homozygous family , this expansion is the result of increased environmental variance, si nce genetic variance does not increase. We consider three types of env ironmental variance (V-E) within homozygous offspring: (1) ''true'' V- E (inter-individual variance), (2) V-E, due to developmental instabili ty (DI, intra-individual variance) and (3) V-E originating from embryo nic damage (ED) caused by the chromosome manipulation treatment. We ex amined the importance of these three types of V-E It is thought that h omozygous individuals show high levels of true V-E and DI. Therefore, in the first experiment we compared three F1-isogenic and one partly o utbred strain of common carp, Cyprinus carpio, in true V-E of length, body weight, and number of dorsal fin rays. The isogenic strains varie d in degree of homozygosity (coefficient of inbreeding F: 0 to 0.99). DI was determined by measuring fluctuating asymmetry (FA) of five bila teral symmetric characteristics. We found the strain with the highest F to display the lowest true V-E FA was equal in all isogenic strains but highest in the partly outbred strain. In a second experiment, simi lar observations were performed on gynogenetic and androgenetic offspr ing from parents with identical genotypes. Homozygous (endomitosis, EM : F = 1) and partly heterozygous (2pb-gynogenesis: F = 0.74) gynogenet ic groups were produced. Normal fertilizations (F = 0.75) served as co ntrols. The androgenetic groups showed highest FA and variations cause d by ED, followed by 2pb- and EM-gynogenetic groups, respectively. We conclude that increased variation within gynogenetic or androgenetic o ffspring is the result of ED, caused by the chromosome manipulation tr eatment. (C) 1997 Wiley-Liss, Inc.