Population differences in early development in grayling (Thymallus thymallus) : a common garden experiment

Abstract

Following colonization of new habitats and subsequent strong selection, adaptation to environmental conditions might be expected to be rapid. In a mountainous lake in Norway, Lesjaskogsvatnet, more than 20 distinct spawning demes of grayling have been established since the lake was colonized, less than 25 generations ago. The demes spawn in tributaries consistently exhibiting either cold or warm temperature conditions. I conducted a common garden experiment to investigate if differences in early developmental characters had been established between four demes in response to the different nursery environments the grayling embryos and larvae experience. Different subsets of individuals from the four demes were subjected to three different treatment temperatures to test for temperature effects. Traits related to timing of development (i.e. eye pigmentation and hatching) as well as growth and energy consumption (i.e. length and yolk sack size) were measured for individuals from daily samples from all demes in all temperatures. I found no differences in the timing of early developmental traits. However, traits related to larval growth and energy consumption showed significant variation. Such variation most likely reflects genetic differences; however the observed variation did not unambiguously correspond with predictions of countergradient variation or local adaptation. I conclude that the observed differences in growth related traits between demes are most probably a result of both directional and random processes influencing evolutionary change.