An experimental study on strain combinations in heterosis in salinity tolerance of the guppy Poecilia reticulata

Abstract

SUMMARY: As an experimental model of heterosis in fish, the present study examined the amount of heterosis in salinity tolerance in four crosses between guppy strains having various kinships. Salinity tolerance was measured as survival time after transfer from fresh water to 35 ppt seawater. The amount of heterosis, expressed by the difference between the means of the parents and their F1 hybrids in every pair, was larger in the strain combinations having distant kinship than in those having close kinship. The result indicates that the average amount of heterosis is dependent on the magnitude of kinship between the strains. The average survival times of the F1 hybrids did not correlate with those of female parents, male parents, or mid‐parent values but correlated closely with the average amount of heterosis in the four strain combinations, indicating that the average phenotypic value of the F1 hybrids is not influenced by that of their parents but is dependent on the average amount of heterosis brought by the strain combination. Within each strain combination, variance in the amount of heterosis among pairs was larger in the strain combinations having close kinship than in those having distant kinship. These results indicate that the amount of heterosis was larger and more uniform in the strain combinations having distant kinship than in those having close kinship. The present study experimentally demonstrates that the strain combination having distant kinship is more useful for genetic improvement utilizing heterosis in fish.

Adaptation as a potential response to sea‐level rise: a genetic basis for salinity tolerance in populations of a coastal marsh fish

“…A third possible explanation is that individuals collected from populations with a history of salinity exposure have adaptations that promote survival in highsalinity environments. Genetic adaptation to salinity tolerance has been documented in laboratory strains of P. reticulata (Shikano and Fujio 1998c;Shikano et al 1998Shikano et al , 2000Shikano et al , 2001. Here, we use the term 'adaptation' to refer to a tolerance advantage with a genetic basis resulting from a population being exposed to elevated environmental salinities for several generations.…”

Surviving ability in albino newly hatched larvae of Japanese flounder determined by high salinity tolerance

“…This would mean that the surviving ability of albino was inferior to wild type pigmentation. However, in the guppy, salinity tolerance ability was increased by hybridization among strains according to the heterosis 9 . Examined parental fish of normal type in this study was used from inbred population for at least three generations.…”

“…However, in the guppy, salinity tolerance ability was increased by hybridization among strains according to the heterosis. 9 Examined parental fish of normal type in this study was used from inbred population for at least three generations. Therefore, normal family (NNF4) might show lower salinity tolerance than hetero families (ANF3 and NAF4) according to the inbreeding effect.…”

Asymmetric paternal effect on offspring size linked to parent‐of‐origin expression of an insulin‐like growth factor

“…The size of offspring from matings between populations can depart from additive expectations for several reasons. In positive heterosis (hybrid vigor, or simply “heterosis”; Shull, ), offspring from both reciprocal crosses would be expected to be similarly larger (or healthier, or fitter) than offspring form the parental populations (e.g., Shikano, Nakadate, & Fujio, ), whereas outbreeding depression would cause smaller or less fit offspring in both interpopulation crosses. These effects are expected to be symmetrical, due to either the amelioration of mutational load (Keller & Waller, ) or the breakdown of co‐adapted genomes (Templeton et al., ) and are thus unlikely explanations for the phenotypic effects seen here (but we note that M‐Z hybrids were somewhat, but nonsignificantly, larger than M‐M offspring).…”