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Unlike eusocial systems, which are characterized by reproductive division of labour, cooperative breeders were predicted not to exhibit any reproductive specialization early in life. nevertheless, also cooperative breeders face a major life-history decision between dispersal and independent breeding vs staying as helper on the natal territory, which might affect their reproductive strategies. In the cooperatively-breeding cichlid Neolamprologus pulcher early-life social and predator experiences induce two behavioural types differing in later-life social and dispersal behaviour. We performed a long-term breeding experiment to test whether the two early-life behavioural types differ in their reproductive investment. We found that the early-dispersing type laid fewer and smaller eggs, and thus invested overall less in reproduction, compared to the philopatric type. thus N. pulcher had specialised already shortly after birth for a dispersal and reproductive strategy, which is in sharp contrast to the proposition that reproductively totipotent cooperative breeders should avoid reproductive specialization before adulthood. Cooperative animal societies range from eusocial species with a clear division in fecund queens and sterile workers 1 to systems where subordinate group members help raising dominants' offspring but remain fully fertile. Eusociality occurs predominantly in insect species, in which large breeding females are capable to produce far more offspring than the much smaller subordinates could do 2-4. Insect queens have evolved morphological specializations allowing them to maximize reproductive investment as they do not incur the physiological constraints of internal gestation 4. Contrary to eusocial insects, in cooperative breeding systems as occurring in many vertebrates, a dominant breeder pair producing all or most of the offspring is assisted by fully fecund subordinates, which delay natal dispersal and forgo own reproduction to help raising the dominants' offspring ('helpers') 5,6. In cooperative breeders an early specialization of reproductive strategies should nevertheless not be expected, because all subordinates can potentially become breeders themselves at some stage of their life 4. Maintaining full flexibility of the reproductive strategy would enable subordinates to respond quickly to any opening opportunities for independent breeding 4. Accordingly, there is no evidence for reproductive specialization from early life onwards in any cooperative breeder to date. Many cooperative breeders face a major life history decision early in life, namely whether to delay dispersal into later adulthood and stay as subordinate brood care helper or to disperse soon after attaining sexual maturity and to breed independently 7-9. This major life-history decision should influence an individual's reproductive opportunities, and therefore it might affect major life history traits already well ahead of this major decision, such as age and size of sexual maturation, and the development of reproductive organs. Delayi...

The early social environment an animal experiences may have pervasive effects on its behaviour. The social decision‐making network (SDMN), consisting of interconnected brain nuclei from the forebrain and midbrain, is involved in the regulation of behaviours during social interactions. In species with advanced sociality such as cooperative breeders, offspring are exposed to a large number and a great diversity of social interactions every day of their early life. This diverse social environment may have life‐long consequences on the development of several neurophysiological systems within the SDMN, although these effects are largely unknown. We studied these life‐long effects in a cooperatively breeding fish, Neolamprologus pulcher, focusing on the expression of genes involved in the monoaminergic and stress response systems in the SDMN. N. pulcher fry were raised until an age of 2 months either with their parents, subordinate helpers and same‐clutch siblings (+F), or with same‐clutch siblings only (−F). Analysis of the expression of glucocorticoid receptor, mineralocorticoid receptor, corticotropin releasing factor, dopamine receptors 1 and 2, serotonin transporter and DNA methyltransferase 1 genes showed that early social experiences altered the neurogenomic profile of the preoptic area. Moreover, the dopamine receptor 1 gene was up‐regulated in the preoptic area of −F fish compared to +F fish. −F fish also showed up‐regulation of GR1 expression in the dorsal medial telencephalon (functional equivalent to the basolateral amygdala), and in the dorsolateral telencephalon (functional equivalent to the hippocampus). Our results suggest that early social environment has life‐long effects on the development of several neurophysiological systems within the SDMN.

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