Factors affecting the larval growth and development of laboratory-reared Ambystoma gracile (Baird) from natural populations of different temperature regimes.

Temperature-transfer of Ambystoma gracile larvae from 11 degrees C to 21 degrees C does not significantly alter growth rates at the higher temperature when compared to larvae continuously grown at 21 degrees C. Temperature-transfer does not alter the incidence of neoteny within populations, even though interpopulation neotenic tendencies differ. Salamander larvae from the high altitude population exhibit larvae from the high altitude population exhibit faster growth rates than the larvae reared from eggs from the low altitude-population. These high altitude larvae exhibit faster growth rates both at the lower and higher temperatures suggesting a greater sensitivity to growth-promoting factors and/or higher rates of synthesis or secretion of such factors. Experiments utilizing ovine prolactin indicated that prolactin-injected experimentals were significantly longer (P less than 0.025) after 60 days of treatment than were placebo-injected controls. A prolactin-like hormone is suggested as thepossible growth-promoting factor in larval Ambystoma gracile.