Seawater Adaptability, Osmoregulatory Function, and Branchial Chloride Cells in the Strain Selected for High Salinity Tolerance of the Guppy <i>Poecilia reticulata</i>

Abstract

Seawater adaptability, osmoregulatory function, and branchial chloride cells were compared be tween the original strain (S3) and the selected strain for high salinity tolerance (S3-SR3) of the guppy. Survival time in 35 ppt seawater was significantly longer in the S3-SR3 strain than in the S3 strain, in dicating the higher salinity tolerance of the S3-SR3 strain. When fish were acclimated to 15 ppt dilute seawater, LD50 (ppt) of the S3 and S3-SR3 strains gradually and significantly increased with increase in the acclimation periods in parallel, and the S3-SR3 strain acquired seawater adaptability earlier than the S3 strain. Blood osmotic pressure after direct transfer to 15 ppt dilute seawater of the S3 strain sig nificantly increased 1 day and 2 days after the transfer while that of the S3-SR3 strain did not significant ly increase throughout the experiment. Branchial chloride cells of the S3-SR3 strain increased about 50% in number and about 15% in size in comparison with those of the S3 strain in fresh water. These results suggest that genetic increase in the number and size of branchial chloride cells in the S3-SR3 strain caused the improvements of salinity tolerance, seawater adaptability, and osmoregulatory func tion.

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 high‐salinity environments. Genetic adaptation to salinity tolerance has been documented in laboratory strains of P. reticulata (Shikano and Fujio 1998c; Shikano et al. 1998, 2000, 2001).…”

“…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.…”

Selection Experiments and Experimental Evolution of Performance and Physiology

“…So far as we are aware, only three vertebrate studies, two selecting on body size in mice (Bunger et al 2001;Renne et al 2003;andWirth-Dzie˛ciolowska et al 2000, 2005; see also Rosochacki et al 2005) and the other selecting for litter size in mice (Holt et al 2004(Holt et al , 2005, have gone as many as one hundred generations, hence crossing into the category of "long-term" selection experiments (Laurie et al 2004;Travisano this volume). Surprisingly, with one short-term exception (Shikano et al 1998), small fishes (e.g., guppies, zebra fish, mosquito fish) have yet to be the subject of a selection experiment designed to alter whole-animal performance (see also Garland 2003).…”