Abstract
The neurotransmitter dopamine has been shown to play an important role
in modulating behavioural, morphological and life-history responses to
food abundance. However, costs of expressing high dopamine levels remain
poorly studied and are essential for understanding the evolution of the
dopamine system. Negative maternal effects on offspring size from
enhanced maternal dopamine levels have previously been documented inDaphnia . Here, we tested whether this translates into fitness
costs in terms of lower starvation resistance in offspring. We exposedDaphnia magna mothers to aqueous dopamine (2.3 mg/L or 0 mg/L for
the control) at two food levels (ad libitum versus 30% ad
libitum ) and recorded a range of maternal life history traits. The
longevity of their offspring was then quantified in the absence of food.
In both control and dopamine treatments, mothers that experienced
restricted food ration had lower somatic growth rates and higher age at
maturation. Maternal food restriction also resulted in production of
larger offspring that had a superior starvation resistance, compared toad libitum groups. However, although dopamine exposed mothers
produced smaller offspring than controls at restricted food ration,
these smaller offspring survived longer under starvation. Hence,
maternal dopamine exposure provided an improved offspring starvation
resistance. We discuss the relative importance of proximate and ultimate
causes for why D. magna may not evolve towards higher endogenous
dopamine levels despite the fitness benefits this appears to have.