Critical thermal maxima of juvenile alligator gar (Atractosteus spatula, Lacépède, 1803) from three Mississippi-drainage populations acclimated to three temperatures

Abstract

Local adaptation may cause thermal tolerance to vary between nearby but distinct populations of a species. During the summer of 2013, alligator gar Atractosteus spatula spawned from broodstock collected from three populations within the Mississippi River drainage separated by a 5° latitudinal gradient were acclimated to three temperatures (25, 30, and 35°C). Ten fish from each population were acclimated at each temperature. CTMax was determined at each temperature for each population, using five fish for each population-acclimation temperature pairing. CTMax for each population-acclimation temperature pairing was compared using two-factor anova. CTMax increased significantly with acclimation temperature (F2,40 = 600.5, P < 0.001) but population had no significant effect (F2,40 = 1.882, P = 0.166). Temperature tolerance appears to be consistent across populations of alligator gar, with no evidence of local adaptation.