No experimental evidence for sneaking in a west african cichlid fish with extremely long sperm

Sex-specific effects of inbreeding on body colouration and physiological colour change in the cichlid fish Pelvicachromis taeniatus

Background

Colour expression is highly variable in animals. In fishes, rapid colour change, i.e. physiological colour change, can be observed in multiple contexts, e.g. in camouflage or communication, and is affected by various factors, such as stress. Pelvicachromis taeniatus is a cichlid fish from West Africa with sexual dichromatism and both sexes being brightly coloured and flexible in ornament expression. In the present study, inbred and outbred P. taeniatus were photographed before and after a stress situation to investigate the stress response regarding colour expression in both sexes.

Results

The chromaticity and the colour patch size (relative coloured area at the abdomen) were determined at both timepoints and the changes were analysed. Additionally, the coefficients of variation within family groups for the chromaticity (CV_chromaticity) and colour patch size (CV_area) were calculated. Chromaticity as well as the extent of colouration increased significantly following handling stress. The change in chromaticity was not significantly different between in- and outbred individuals in females and males. Inbred males showed more intense yellow colouration than outbred males. Independent from inbreeding, the CV_chromaticity decreased following the handling stress. The change in CV_area of females and males differed between in- and outbred individuals. In females, the decrease was significantly stronger in inbred individuals and in males the decrease was stronger in the outbred group.

Conclusion

The results show that short-term stress can increase colouration, potentially advertising individual’s stress tolerance. Furthermore, this study shows positive inbreeding effects on a sexually selected trait.

Intrasexual selection: Kin competition increases male-male territorial aggression in a monogamous cichlid fish

During intrasexual competition, individuals of the same sex compete for access to breeding sites and mating partners, often accompanied by aggressive behavior. Kin selection theory predicts different kin-directed social interactions ranging from cooperation to aggression depending on the context and the resource in question. Kin competition reducing indirect fitness might be avoided by actively expelling relatives from territories and by showing higher aggression against kin. The West-African cichlid Pelvicachromis taeniatus is a monogamous cave breeder with males occupying and defending breeding sites against rivals. This species is capable of kin recognition and shows kin-preference during juvenile shoaling and mate choice. However, subadults of P. taeniatus seem to avoid the proximity of same-sex kin. In the present study, we examined territorial aggression of territory holders against intruding related and unrelated males as well as intruder's behavior. We observed higher aggression among related competitors suggesting that related males are less tolerated as neighbors. Avoidance of intrasexual competition with relatives might increase indirect fitness of males in monogamous species.

Presence of same-sex kin promotes explorative behavior in subadult cichlid fish

While the importance of kin discrimination, that is, kin recognition and subsequent differential treatment of kin and nonkin, is well established for kin-directed cooperation or altruism, the role of kin discrimination in the context of kin competition and kin avoidance is largely unexplored. Theory predicts that individuals avoiding competition with kin should be favored by natural selection due to indirect fitness benefits. Using an experimental approach, we investigated whether the presence of same-sex kin affects avoidance and explorative behavior in subadult Pelvicachromis taeniatus, a West African cichlid fish with strong intrasexual competition in both sexes. Pelvicachromis taeniatus is capable of recognizing kin using phenotype matching and shows kin discrimination in diverse contexts. When exposed to a same-sex conspecific, both males and females tended to interact less with the related opponent. Moreover, individuals explored a novel environment faster after exposure to kin than to nonkin. This effect was more pronounced in females. Individuals avoiding the proximity of same-sex relatives may reduce kin competition over resources such as mating partners or food.

Nest defense in the face of cuckoldry: evolutionary rather than facultative adaptation to chronic paternity loss

Background

Raising unrelated offspring is typically wasteful of parental resources and so individuals are expected to reduce or maintain low levels of parental effort when their parentage is low. This can involve facultative, flexible adjustments of parental care to cues of lost parentage in the current brood, stabilizing selection for a low level of paternal investment, or an evolutionary reduction in parental investment in response to chronically low parentage.

Results

We studied parental care in Variabilichromis moorii, a socially monogamous, biparental cichlid fish, whose mating system is characterized by frequent cuckoldry and whose primary form of parental care is offspring defense. We combine field observations with genetic parentage analyses to show that while both parents defend their nest against intruding con- and hetero-specifics, males and females may do so for different reasons. Males in the study group (30 breeding pairs) sired 0–100% (median 83%) of the fry in their nests. Males defended less against immediate threats to the offspring, and more against threats to their territories, which are essential for the males’ future reproductive success. Males also showed no clear relationship between their share of defense and their paternity of the brood. Females, on the other hand, were related to nearly all the offspring under their care, and defended almost equally against all types of threats.

Conclusion

Overall, males contributed less to defense than females and we suggest that this asymmetry is the result of an evolutionary response by males to chronically high paternity loss in this species. Although most males in the current study group achieved high parentage in their nests, the average paternity in V. moorii, sampled across multiple seasons, is only about 55%. We highlight the importance and complexity of studying nest defense as a form of parental care in systems where defense may serve not only to protect current offspring, but also to ensure future reproductive success by maintaining a territory.

Brood-tending males in a biparental fish suffer high paternity losses but rarely cuckold

Extra‐pair paternity within socially monogamous mating systems is well studied in birds and mammals but rather neglected in other animal taxa. In fishes, social monogamy has evolved several times but few studies have investigated the extent to which pair‐bonded male fish lose fertilizations to cuckolders and gain extra‐pair fertilizations themselves. We address this gap and present genetic paternity data collected from a wild population of Variabilichromis moorii, a socially monogamous African cichlid with biparental care of offspring. We show that brood‐tending, pair‐bonded males suffer exceptionally high paternity losses, siring only 63% of the offspring produced by their female partners on average. The number of cuckolders per brood ranged up to nine and yet, surprisingly, brood‐tending males in the population were rarely the culprits. Brood‐tending males sired very few extra‐pair offspring, despite breeding in close proximity to one another. While unpaired males were largely responsible for the cuckoldry, pair‐bonded males still enjoyed higher fertilization success than individual unpaired males. We discuss these results in the context of ecological and phenotypic constraints on cuckoldry and the fitness payoffs of alternative male tactics. Our study provides new insights into how pair‐bonded males handle the trade‐off between securing within‐pair and extra‐pair reproduction.

Mate choice and genetic monogamy in a biparental, colonial fish

We report a rare case of genetic monogamy in a biparental fish species. Males and females paired assortatively by size, which is compatible with mutual mate choice. Mate choice in monogamous species is interesting because both sexes provide essential parental care, making males, as well as females, choosy. Social monogamy in the form of biparental care is well known from a variety of species, but uncommon in 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.

Genetic evidence for mixed broods and extra-pair matings in a socially monogamous biparental cichlid fish

Mobile young under parental care have a high potential for intermixing with other broods, which potentially increases the costs to the foster parents. Here, we examined for the first time the genetic composition of wild-caught broods of the convict cichlid (Amatitlania siquia), a socially monogamous biparental fish, for evidence of brood mixing and adoption. Our microsatellite genotyping data revealed that 79% of broods contained adopted young. Moreover, 25% of broods contained adopted sibsets likely arising from extra-pair matings, a phenomenon hitherto not documented for this species. Overall, adopted foreign fry and host fry in mixed broods were generally different in body length, as would be expected if they have different parents. However, fry from possible extra-pair matings were similar in body length to host fry, suggesting that they are of similar age. Our results are important because they reveal a very high prevalence and degree of brood mixing, and indicate that social monogamy does not necessarily lead to genetic monogamy in the convict cichlid in nature. These findings raise questions about potential brood-mixing mechanisms and the reproductive ecology (especially opportunities for polygamy in nature) of this important model species in the study of animal behaviour.