This striking mismatch can be explained by pleiotropy

However, fitness converges between populations: replicate populations evolved in the two temperature regimes exhibit a similar fitness increase relative to the ancestral populations.

Divergence at the genomic level: Consistent with a temperature-specific selection response, we find that 93% of the SNPs with significant allele frequency changes are restricted to one of the two temperature regimes.

Experimental Design: We evolved replicated Drosophila simulans populations in laboratory conditions that differed only in their temperature regime. One group of populations evolved under a constant temperature of 23 °C, while the other experienced temperature fluctuations around the same mean.