Non-random brood mixing suggests adoption in a colonial cichlid

Sensory Mechanisms of Parent-Offspring Recognition in Fishes, Amphibians, and Reptiles

Parental care is important for offspring survival and success. Recognition of offspring by parents is critical to ensure parents direct care behaviors at related offspring and minimize energy lost by caring for unrelated young. Offspring recognition of parents prevents possible aggressive interactions between young and unrelated adults and allows offspring to direct begging behaviors toward the correct adult. Despite its importance and widespread nature, much of the current research has focused on a small range of species, particularly mammals and birds. We review the existing literature on the sensory mechanisms of parent-offspring recognition in fishes, amphibians, and reptiles. Within these groups, there is diversity in the presence and strategies for parent-offspring recognition. Future studies should continue to identify these mechanisms, as well as the neural and endocrine underpinnings in non-model organisms to expand our knowledge of this behavior and inform our understanding of the evolution of parent-offspring recognition.

Territorial behaviour and conflict management in a semi-social cichlid fish, Neolamprologus caudopunctatus

Conflict solving strategies can prevent fights from escalating and reduce the costs of aggressive encounters. Having the capacity to efficiently assess an opponent’s fighting abilities before fully committing to a fight is a useful social skill. Here, we conducted two experiments to investigate how a colony living, cichlid species, Neolamprologus caudopunctatus, changes its aggressive behaviour when faced with familiar vs unfamiliar opponents. First, we staged size matched, same-sex, dyadic resource contests and found that fights were always of low-intensity with neither familiarity nor sex influencing how quickly the conflict ended. Second, we explored the dual defence of mated territorial pairs together defending their territory boundaries against other pairs, either familiar or unfamiliar ones, and discovered that fights between two pairs were more vigorous, and that unfamiliar neighbouring pairs were attacked significantly more often than familiar pairs. We also observed that dark bars sometimes appeared on the sides of contestant’s bodies, and that these bars were far more common in winners than in losers, suggesting that these might be visual signals of dominance. However, conflicts where contestants displayed bars were of longer duration than those without. Taken together, our results further advance our understanding of territoriality and conflict resolution strategies and set the stage for future studies focusing on how animals manage to co-exist in closely aggregated breeding territories and to form colonies.

The functional role of sibling aggression and “best of a bad job” strategies in cichlid juveniles

Siblings often compete for limited resources, such as food provided by their parents. However, although several functions of nonlethal sibling (nonsiblicidal) aggression have been proposed, there is currently little empirical evidence for these, apart from food monopolization. Here, we investigated the functions of nonlethal sibling aggression in the biparental-caring territorial herbivorous cichlid Varibilichromis moorii. We found that the juveniles of this species are highly aggressive and that larger juveniles are more aggressive toward their smaller siblings. Larger juveniles feed on algae more frequently than smaller siblings, thereby indicating a dominance hierarchy. Sibling aggression decreased when algae in the nest was experimentally removed. Furthermore, the removal of smaller juveniles decreased sibling aggression among the remaining larger juveniles, whereas the removal of larger juveniles increased aggression among smaller juveniles. The algal feeding rate of juveniles only increased when larger individuals were removed from the nest. Moreover, larger juveniles attained higher growth rates and remained in natal nests longer than smaller individuals. Our results indicate that sibling aggression may facilitate the monopolization of resources by larger juveniles and extend the parental care period. Interestingly, a small subset of juveniles was observed to migrate to other nests. These juveniles were larger than those of the host brood, and their growth rate increased within the new nests. We suggest that subordinate juveniles may disperse from natal nests and sneak into new nests to enhance their rank, which may represent a novel example of a “best of a bad job” strategy associated with sibling competition.

Genetic evidence for prevalence of alloparental care in a socially monogamous biparental cichlid fish, Perissodus microlepis, from Lake Tanganyika supports the "selfish shepherd effect" hypothesis

Alloparental care – care for unrelated young – is rare in animals, and its ecological or evolutionary advantages or, alternative maladaptive nature, remain unclear. We investigate alloparental care in the socially monogamous cichlid fish Perissodus microlepis from Lake Tanganyika that exhibits bi‐parental care. In a genetic parentage analysis, we discovered a surprisingly high percentage of alloparental care represented by brood mixing, extra‐pair paternity and extra‐pair maternity in all broods that we investigated. The percentage of nondescendant juveniles of other parents, i.e., brood mixing, ranged from 5% to 57% (mean = 28%). The distribution of genetic parentage also suggests that this socially monogamous species has, in fact, polygamous mating system. The prevalence of genetically mixed broods can be best explained by two, not mutually exclusive hypotheses on farming‐out and fostering behaviors. In the majority of broods, the sizes of the parents’ own (descendant) offspring were significantly larger than those of the adopted (nondescendant) juveniles, supporting the ‘selfish shepherd effect’ hypothesis, i.e., that foster parents preferentially accept unrelated “smaller or not larger” young since this would tend to lower the predation risks for their own larger offspring. There was also a tendency for larger parents particularly mothers, more so than smaller parents, to care predominantly for their own offspring. Larger parents might be better at defending against cuckoldry and having foreign young dumped into their broods through farming‐out behavior. This result might argue for maladaptive effects of allopatric care for the foster parents that only larger and possibly more experienced pairs can guard against. It needs to be determined why, apparently, the ability to recognize one's own young has not evolved in this species.

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.

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.