Study sites, fish collection and maintenance conditions
Fish used for this experiment were also part of a candidate gene study,
and more methodological details can be found in Taugbøl et al. (2014).
Adult sticklebacks were captured at two locations near Oslo, Norway
(Figure 1 ), during May and June 2010. The marine site,
Sandspollen, has a salinity varying between 22-29 ‰, while the
freshwater pond, Glitredammen, is stable at 0 ‰. Coastal stickleback
populations in Norway are considered to be purely marine, potentially
with some gene flow from nearby freshwater populations (Klepaker 1996).
Fish from Sandspollen breed locally (are not anadromous). The two
locations are geographically isolated by approximately 35 km (shortest
distance through water) (Figure 1b ), where about 8.5 km is
through the river Sandvikselva that contains several steep waterfalls
and dams. This makes downstream movement of fish from Glitredammen
towards the marine sampling site possible, but upstream movement from
the fjord impossible. The stickleback in Glitredammen has probably been
separated from marine ancestors for at least 7000 years, as the age of
the lake has been estimated to 7800 years before present using the
program Sealevel32 (Møller 2003). The lake Glitredammen is located at
82.2 m above sea level.
After capture, the fish were acclimated to holding conditions in their
native salinity (30 or 0 ‰) for minimum three weeks prior to the
experiment. To reduce potential male nesting behaviour, the tanks were
not equipped with any environmental enrichment, leaving the tanks free
of sand and vegetation. The temperature in the tanks was maintained at
room temperature (about 20°C), and the light regime was set at a 12:12
light: dark-cycle. The fish were fed two times a day with frozen red
bloodworms throughout the acclimation period. More details on fish
maintenance can be found in Taugbøl et al. (2014a).