Figure 1.

Locations of the populations sampled in (a) the central United States, (b) the North Cascades Range and (c) the Southern Alps of New Zealand. In the North Cascades, the transects sampled (from west to east) were Cypress Mt, Mt Seymour and Mt Baker. In New Zealand, the transects sampled (from northernmost to southernmost) were from Christchurch to Arthur's Pass, from Timaru to Mt Cook and from Oamaru to Lindis Pass. The blue to red gradient indicates minimum winter temperature as determined from the BIOCLIM data set (Hijmans et al., 2005). Inserts indicate locations of regions on a global map.