The temporal window of ecological adaptation in postglacial lakes: a comparison of head morphology, trophic position and habitat use in Norwegian threespine stickleback populations

Background: Studying how trophic traits and niche use are related in natural populations is important in order to understand adaptation and specialization. Here, we describe trophic trait diversity in twenty-five Norwegian freshwater threespine stickleback populations and their putative marine ancestor, and relate trait differences to postglacial lake age. By studying lakes of different ages, depths and distance to the sea we examine key environmental variables that may predict adaptation in trophic position and habitat use. We measured trophic traits including geometric landmarks that integrated variation in head shape as well as gillraker length and number. Trophic position (Tpos) and niche use (α) were estimated from stable isotopes (δ13C, δ15N). A comparison of head shape was also made with two North American benthic-limnetic species pairs. Results: We found that head shape differed between marine and freshwater sticklebacks, with marine sticklebacks having more upturned mouths, sma..., Read me file with location codes0 Sample codes to locality names.xls1 Dataset-FreshwaterData comparing the freshwater stickleback only; with principal component scores (see details in the manuscript).2 Dataset-Freshwater and marineData comparing the marine and freshwater stickleback; with principal component scores (see details in the manuscript).3 Dataset- Freshwater, marine and North AmericanData comparing the marine and freshwater stickleback from Norway and the two North American species pairs; with principal component scores (see details in the manuscript).,