Galanin and prolactin expression in relation to parental care in two sympatric cichlid species from Lake Tanganyika.

Our understanding of the hormonal mechanisms underlying parental care mainly stems from research on species with uniparental care. Far less is known about the physiological changes underlying motherhood and fatherhood in biparental caring species. Here, using two biparental caring cichlid species (Neolamprologus caudopunctatus and Neolamprologus pulcher), we explored the relative gene-expression levels of two genes implicated in the control of parental care, galanin (gal) and prolactin (prl). We investigated whole brain gene expression levels in both, male and female caring parents, as well as in non-caring individuals of both species. Caring males had higher prl and gal mRNA levels compared to caring females in both fish species. Expression of gal was highest when young were mobile and the need for parental defense was greatest and gal was lowest during the more stationary egg tending phase in N. caudopunctatus. The onset of parenthood was associated with lower expression of prl and higher expression of gal in N. pulcher, but this pattern was not observed in N. caudopunctatus. Our study demonstrates that gal gene expression is correlated with changes in parental care in two biparental cichlid species and extends both knowledge and taxonomic coverage of the possible neurogenetic mechanisms underlying parental care.

Mate choice and genetic monogamy in a biparental, colonial fish.

In socially monogamous species, in which both sexes provide essential parental care, males as well as females are expected to be choosy. Whereas hundreds of studies have examined monogamy in biparental birds, only several such studies exist in fish. We examined mate choice in the biparental, colonial cichlid fish Neolamprologus caudopunctatus in Lake Tanganyika, Zambia. We genotyped more than 350 individuals at 11 microsatellite loci to investigate their mating system. We found no extrapair paternity, identifying this biparental fish as genetically monogamous. Breeders paired randomly according to their genetic similarity, suggesting a lack of selection against inbreeding avoidance. We further found that breeders paired assortatively by body size, a criterion of quality in fish, suggesting mutual mate choice. In a subsequent mate preference test in an aquarium setup, females showed a strong preference for male size by laying eggs near the larger of 2 males in 13 of 14 trials.

Sex biases in kin shoaling and dispersal in a cichlid fish.

Animal dispersal is associated with diverse costs and benefits that vary among individuals based on phenotype and ecological conditions. For example, females may disperse when males benefit more from defending territories in familiar environments. Similarly, size differences in dispersal propensity may occur when dispersal costs are size-dependent. When individuals do disperse, they may adopt behavioral strategies that minimize dispersal costs. Dispersing fish, for example, may travel within shoals to reduce predation risks. Further, kin shoaling may augment inclusive fitness by reducing predation of relatives. However, studies are lacking on the role of kin shoaling in dispersal. We explored how sex and size influence dispersal and kin shoaling in the cichlid Neolamprologus caudopunctatus. We microsatellite genotyped over 900 individuals from two populations separated by a potential dispersal barrier, and documented patterns of population structure, migration and within-shoal relatedness. Genetic differentiation across the barrier was greater for smaller than larger fish, suggesting larger fish had dispersed longer distances. Females exhibited weaker genetic differentiation and 11 times higher migration rates than males, indicating longer-distance female-biased dispersal. Small females frequently shoaled with siblings, possibly offsetting dispersal costs associated with higher predation risks. In contrast, small males appeared to avoid kin shoaling, possibly to avoid local resource competition. In summary, long-distance dispersal in N. caudopunctatus appears to be female-biased, and kin-based shoaling by small females may represent a behavioral adaptation that reduces dispersal costs. Our study appears to be the first to provide evidence that sex differences in dispersal influence sex differences in kin shoaling.

Non-random brood mixing suggests adoption in a colonial cichlid.

Parental care of unrelated offspring is widespread but not well understood. We used 11 polymorphic microsatellite loci to investigate the relatedness of fry and parentally caring adults in a 118-nest colony of the socially and genetically monogamous cichlid fish Neolamprologus caudopunctatus in Lake Tanganyika. There was a high proportion of brood mixing, with 59% of 32 broods containing fry unrelated to both parents, and 18% of all 291 sampled fry being unrelated to the breeding pair. There was no evidence of kin selection for adoption because the genetic and foster parents were not more related than expected by chance. Parentage was assigned to 12 adopted fry from 10 broods. Distances traversed by fry varied markedly, from less than one to over 40 meters. The larger distances suggest that at least some brood mixing was instigated by parents transporting portions of their broods in their mouths, as occurs in some cichlids. Further evidence of non-random brood mixing was that foreign fry did not differ in size from their foster siblings within broods, even though they were significantly larger than fry produced by the tending pairs within the colony. These findings suggest that at least some foreign fry had dispersed non-randomly and were adopted by their foster parents. Enlarged broods are known to provide reduced per capita predation, making it potentially adaptive for breeders to adopt unrelated offspring.

Exploring novelty: a component trait of behavioural syndromes in a colonial fish.

Individual differences in exploratory behaviour have been shown to be consistent across contexts and suggested to be part of behavioural syndromes in a diversity of species, including fish. Exploration has also been shown to be a key factor in understanding complex ecological processes such as sexual selection and cooperation. Another important question in ecology is why animals breed in colonies. Exploration syndromes, by affecting prospecting behaviour, dispersal and public information use may also contribute to our understanding of coloniality. This study aims at investigating whether an exploration syndrome exists in a colonial fish species, Neolamprologus caudopunctatus. Individuals of this species were subjected to two consecutive tests, a novel environment and a novel object test. Results show that more explorative individuals in a novel environment are also less neophobic in the presence of a novel object, suggesting that the tendency to engage with novelty per se is a consistent trait and part of an exploration syndrome. These results are discussed in light of the contribution of an exploration syndrome to explain colony formation in animals.

Extended phenotypes as signals.

Animal signals may result from construction behaviour and can provide receivers with essential information in various contexts. Here we explore the potential benefits of extended phenotypes with a signalling function as compared to bodily ornaments and behavioural displays. Their independence of the body, their physical persistence and the morphological and cognitive conditions required for their construction allow unique communication possibilities. We classify various levels of information transfer by extended phenotype signals and explore the differences between secreted signals and signals resulting from collection and construction, which usually involve higher behavioural complexity. We examine evolutionary pathways of extended phenotypes with a signalling function with help of a comparative evaluation and conclude that often constructions first provide a direct fitness benefit, with a signalling function becoming more and more prominent during evolutionary progression. The abundance and variability of extended phenotypes as signals is impressive and provides unique possibilities for animal communication research.