Data from: Immune-challenged fish up-regulate their metabolic scope to support locomotion

Energy-based trade-offs occur when investment in one fitness-related trait
diverts energy away from other traits. The extent to which such trade-offs
are shaped by limits on the rate of conversion of energy ingested in food
(e.g. carbohydrates) into chemical energy (ATP) by oxidative metabolism
rather than by the amount of food ingested in the first place is, however,
unclear. Here we tested whether the ATP required for mounting an immune
response will lead to a trade-off with ATP available for physical activity
in mosquitofish (Gambusia holbrooki). To this end, we challenged fish
either with lipopolysaccharide (LPS) from E. coli or with Sheep Red Blood
Cells (SRBC), and measured oxygen consumption at rest and during swimming
at maximum speed 24h, 48h and 7 days post-challenge in order to estimate
metabolic rates. Relative to saline-injected controls, only LPS-injected
fish showed a significantly greater resting metabolic rate two days
post-challenge and significantly higher maximal metabolic rates two and
seven days post-challenge. This resulted in a significantly greater
metabolic scope two days post-challenge, with LPS-fish transiently
overcompensating by increasing maximal ATP production more than would be
required for swimming in the absence of an immune challenge.
LPS-challenged fish therefore increased their production of ATP to
compensate physiologically for the energetic requirements of immune
functioning. This response would avoid ATP shortages and allow fish to
engage in an aerobically-challenging activity (swimming) even when
simultaneously mounting an immune response. Nevertheless, relative to
controls, both LPS- and SRBC-fish displayed reduced body mass gain one
week post-injection, and LPS-fish actually lost mass. The concomitant
increase in metabolic scope and reduced body mass gain of LPS-challenged
fish indicates that immune-associated trade-offs are not likely to be
shaped by limited oxidative metabolic capacities, but may instead result
from limitations in the acquisition, assimilation or efficient use of
resources.