title: The mating brain: early maturing sneaker males maintain investment into the brain also under fast body growth in Atlantic salmon (Salmo salar).
abstract: It has been suggested that mating behaviours require high levels of cognitive ability. However, since investment into mating and the brain both are costly features, their relationship is likely characterized by energetic trade-offs. Empirical data on the subject remains equivocal. We investigated if early sexual maturation was associated with brain development in Atlantic salmon (Salmo salar), in which males can either stay in the river and sexually mature at a small size (sneaker males) or migrate to the sea and delay sexual maturation until they have grown much larger (anadromous males). Specifically, we tested how sexual maturation may induce plastic changes in brain development by rearing juveniles on either natural or ad libitum feeding levels. After their first season we compared brain size and brain region volumes across both types of male mating tactics and females. Body growth increased greatly across both male mating tactics and females during ad libitum feeding as compared to natural feeding levels. However, despite similar relative increases in body size, early maturing sneaker males maintained larger relative brain size during ad libitum feeding levels as compared to anadromous males and females. We also detected several differences in the relative size of separate brain regions across feeding treatments, sexes and mating strategies. For instance, the relative size of the cognitive centre of the brain, the telencephalon, was largest in sneaker males. Our data support that a large relative brain size is maintained in individuals that start reproduction early also during fast body growth. We propose that the cognitive demands during complex mating behaviours maintain a high level of investment into brain development in reproducing individuals.
authors.affiliation: Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden ; Department for Integrative Biology and Evolution (KLIVV), Veterinary University Vienna, Savoyenstrasse 1A, 1160 Vienna, Austria.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kotrschal
authors.affiliation: Department of Organismal Biology, Comparative Physiology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, 75236 Uppsala, Sweden.
authors.forename: Susanne
authors.initials: S
authors.lastname: Trombley
authors.affiliation: Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden ; School of Biological Sciences, Monash University, Clayton, VIC 3800 Australia.
authors.forename: Björn
authors.initials: B
authors.lastname: Rogell
authors.affiliation: Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden ; Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden.
authors.forename: Ioana
authors.initials: I
authors.lastname: Brannström
authors.affiliation: Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden.
authors.forename: Eric
authors.initials: E
authors.lastname: Foconi
authors.affiliation: Department of Organismal Biology, Comparative Physiology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, 75236 Uppsala, Sweden.
authors.forename: Monika
authors.initials: M
authors.lastname: Schmitz
authors.affiliation: Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden ; Department of Zoology/Ethology, Stockholm University, 10691 Stockholm, Sweden.
authors.forename: Niclas
authors.initials: N
authors.lastname: Kolm
keywords: Atlantic salmon; Brain; Brain development; Mating strategy; Salmo salar; Sneaker; Trade-off