Dopamine mediates life-history responses to food abundance in Daphnia

Abstract

Expression of adaptive reaction norms of life-history traits to spatio-temporal variation in food availability is crucial for individual fitness. Yet little is known about the neural signalling mechanisms underlying these reaction norms. Previous studies suggest a role for the dopamine system in regulating behavioural and morphological responses to food across a wide range of taxa. We tested whether this neural signalling system also regulates life-history reaction norms by exposing the zooplankton Daphnia magna to both dopamine and the dopamine reuptake inhibitor bupropion, an antidepressant that enters aquatic environments via various pathways. We recorded a range of life-history traits across two food levels. Both treatments induced changes to the life-history reaction norm slopes. These were due to the effects of the treatments being more pronounced at restricted food ration, where controls had lower somatic growth rates, higher age and larger size at maturation. This translated into a higher population growth rate ( r ) of dopamine and bupropion treatments when food was restricted. Our findings show that the dopamine system is an important regulatory mechanism underlying life-history trait responses to food abundance and that bupropion can strongly influence the life history of aquatic species such as D. magna . We discuss why D. magna do not evolve towards higher endogenous dopamine levels despite the apparent fitness benefits.

Effect of dopamine on early larvae of sea urchins, Mesocentrotus nudus and Strongylocentrotus intermedius

“…In Daphnia species, dopamine affects life-history response of the animals to the availability of food (Issa et al, 2020) and it is involved in the development of predator-induced morphological defenses (Weiss, Leese, Laforsch, & Tollrian, 2015). More specifically, studies of marine invertebrates other than sea urchins have shown that dopamine has an effect on the embryonic and early larval development in the crab Metacarcinus magister (Van Alstyne, Harvey, & Cataldo, 2014), the mussel Mytilus edulis (Beiras & Widdows, 1995), and the Pacific oyster Crassostrea gigas (Rivera Vázquez et al, 2017).…”

“…Studies on the role of dopamine across a variety of invertebrates showed that it affects animal's behavioral response to food stimuli in cnidarians (Hanai & Kitajima, 1984), nematodes (Sawin, Ranganathan, & Horvitz, 2000), insects (Honjo & Furukubo‐Tokunaga, 2009; Wright et al, 2010), crustaceans (Van Alstyne, Nelson, Vyvyan, & Cancilla, 2006), molluscs (Kemenes, Hiripi, & Benjamin, 1990; Van Alstyne et al, 2006), and adult sea urchins (Van Alstyne et al, 2006). In Daphnia species, dopamine affects life‐history response of the animals to the availability of food (Issa et al, 2020) and it is involved in the development of predator‐induced morphological defenses (Weiss, Leese, Laforsch, & Tollrian, 2015). More specifically, studies of marine invertebrates other than sea urchins have shown that dopamine has an effect on the embryonic and early larval development in the crab Metacarcinus magister (Van Alstyne, Harvey, & Cataldo, 2014), the mussel Mytilus edulis (Beiras & Widdows, 1995), and the Pacific oyster Crassostrea gigas (Rivera Vázquez et al, 2017).…”

Maternal dopamine exposure provides offspring starvation resistance in Daphnia

“…These observations raise the question of why endogenous dopamine levels do not evolve towards higher values. Issa et al (2020) suggested this may be due to costs of high dopamine levels being paid by the offspring generation, which was not quantified in their study. Negative maternal effects on offspring size from dopamine treatments were detected.…”

“…At the physiological level, the neurotransmitter dopamine plays an important role as mediator of trait responses to food (see Barron et al, 2010 for a review on dopamine-mediated behavioural and morphological responses to food across taxa). Issa et al (2020) showed that in addition to influencing morphological and behavioural traits, dopamine can regulate life-history responses to food abundance. Specifically, in the zooplankton species Daphnia magna, exposure to dopamine caused life-history reaction norms (age at maturation, fecundity) to change in a way that resulted in higher population growth rates (calculated from maternal life history traits) when food was limited (Issa et al, 2020).…”

“…Issa et al (2020) showed that in addition to influencing morphological and behavioural traits, dopamine can regulate life-history responses to food abundance. Specifically, in the zooplankton species Daphnia magna, exposure to dopamine caused life-history reaction norms (age at maturation, fecundity) to change in a way that resulted in higher population growth rates (calculated from maternal life history traits) when food was limited (Issa et al, 2020). This happened without any apparent fitness costs at high food abundance.…”