Origin of variation in isogenic, gynogenetic, and androgenetic strains of common carp,Cyprinus carpio

Abstract

After androgenetic or gynogenetic reproduction, a large expansion of phenotypic variance is generally observed. Within one homozygous family, this expansion is the result of increased environmental variance, since genetic variance does not increase. We consider three types of environmental variance (VE) within homozygous offspring: (1) “true” VE (inter-individual variance), (2) VE, due to developmental instability (DI, intra-individual variance) and (3) VE originating from embryonic damage (ED) caused by the chromosome manipulation treatment. We examined the importance of these three types of VE. It is thought that homozygous individuals show high levels of true VE and DI. Therefore, in the first experiment we compared three F1-isogenic and one partly outbred strain of common carp, Cyprinus carpio, in true VE of length, body weight, and number of dorsal fin rays. The isogenic strains varied in degree of homozygosity (coefficient of inbreeding F: 0 to 0.99). DI was determined by measuring fluctuating asymmetry (FA) of five bilateral symmetric characteristics. We found the strain with the highest F to display the lowest true VE. FA was equal in all isogenic strains but highest in the partly outbred strain. In a second experiment, similar observations were performed on gynogenetic and androgenetic offspring from parents with identical genotypes. Homozygous (endomitosis, EM: F = 1) and partly heterozygous (2pb-gynogenesis: F = 0.74) gynogenetic groups were produced. Normal fertilizations (F = 0.75) served as controls. The androgenetic groups showed highest FA and variations caused by ED, followed by 2pb- and EM-gynogenetic groups, respectively. We conclude that increased variation within gynogenetic or androgenetic of offspring is the result of ED, caused by the chromosome manipulation treatment. J. Exp. Zool. 277:72–79, 1997. © 1997 Wiley-Liss, Inc.