ST increases in warmer environments

    In population cage experiments with two lines of D. pseudobscura initially homokaryotic* for the ST or CH chromosome arrangements, the proportion of ST increases relative to CH over time when raised at a constant 25^oC, whereas relative proportions remain unchanged at a constant 16^oC. This supports the hypothesis that CH is better adapted to relatively cooler environments on the Mexican plateau rather than warmer ones closer to sea level .

*(By analogy with alleles at a locus, homokaryotes have two identical chromosome arrangements: cf heterokaryotes with two different chromosomes).