Data from: 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,
smaller eyes, larger opercula and deeper heads. Size-adjusted gillraker
lengths were larger in marine than in freshwater stickleback. Norwegian
sticklebacks were compared on the same head shape axis as the one
differentiating the benthic-limnetic North American threespine stickleback
species pairs. Here, Norwegian freshwater sticklebacks with a more
"limnetic head shape" had more and longer gillrakers than
sticklebacks with "benthic head shape". The "limnetic
morph" was positively associated with deeper lakes. Populations
differed in α (mean ± sd: 0.76 ± 0.29) and Tpos (3.47 ± 0.27), where α
increased with gillraker length. Larger fish had a higher Tpos than
smaller fish. Compared to the ecologically divergent stickleback species
pairs and solitary lake populations in North America, Norwegian freshwater
sticklebacks had similar range in Tpos and α values, but much less trait
divergences. Conclusions: Our results showed trait divergences between
threespine stickleback in marine and freshwater environments. Freshwater
populations diverged in trophic ecology and trophic traits, but trophic
ecology was not related to the elapsed time in freshwater. Norwegian
sticklebacks used the same niches as the ecologically divergent North
American stickleback species pairs. However, as trophic trait divergences
were smaller, and not strongly associated with the ecological niche,
ecological adaptations along the benthic-limnetic axis were less developed
in Norwegian sticklebacks.