In watersheds of equatorial West Africa, monophyletic groups of killifish species (genus Aphyosemion) occur in discrete
altitudinal ranges, low altitude species (LA, sea level to ,350 m) or high altitude species (HA, 350 to 900 m). We
investigated the hypothesis that local adaptation to altitude by the LA and HA species would be revealed as divergent
effects of temperature on their physiological energetics. Two species from each group (mass ,350 mg) were acclimated to
19, 25 and 28uC, with 19 and 28uC estimated to be outside the thermal envelope for LA or HA, respectively, in the wild. Wildcaught
animals (F0 generation) were compared with animals raised in captivity at 25uC (F1 generation) to investigate the
contribution of adaptation versus plasticity. Temperature significantly increased routine metabolic rate in all groups and
generations. However, LA and HA species differed in the effects of temperature on their ability to process a meal. At 25uC,
the specific dynamic action (SDA) response was completed within 8 h in all groups, but acclimation to temperatures beyond
the thermal envelope caused profound declines in SDA performance. At 19uC, the LA required ,14 h to complete the SDA,
whereas the HA required only ,7 h. The opposite effect was observed at 28uC. This effect was evident in both F0 and F1.
Reaction norms for effects of temperature on SDA therefore revealed a trade-off, with superior performance at warmer
temperatures by LA being associated with inferior performance at cooler temperatures, and vice-versa in HA. The data
indicate that divergent physiological responses to temperature in the LA and HA species reflect local adaptation to the
thermal regime in their habitat, and that local adaptation to one thermal environment trades off against performance in
another
