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.

Spatial asymmetry of the paternity success in nests of a fish with alternative reproductive tactics

Guard-sneaker tactics are widespread among fish, where territorial males defend a nest and provide parental care while sneakers try to steal fertilizations. Territorials and sneakers adopt diverse pre- and post-mating strategies, adjusting their ejaculate investment and/or behavioural responses to the presence of competitors. The relative distance of competitors from the spawning female plays a major role in influencing male mating strategies and the resulting paternity share. However, territorial male quality and sneaking intensity do not fully account for the variability in the relative siring success occurring among species. An often neglected factor potentially affecting sneakers proximity to females is the nest structure. We conducted a field experiment using the black goby, whose nests show two openings of different size. We found that territorial males defend more and sneaking pressure is higher at the front, larger access of the nest than at the back, smaller one. Moreover, microsatellite paternity analysis shows that territorials sire more offspring at the back of their nest. Such a predictable spatial distribution of the paternity share suggests that nest structure might work as an indirect cue of male relative siring success, potentially influencing the territorial male investment in parental care and/or the female egg deposition strategy.

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.

Sex-specific offspring discrimination reflects respective risks and costs of misdirected care in a poison frog

The ability to differentiate between one's own and foreign offspring ensures the exclusive allocation of costly parental care to only related progeny. The selective pressure to evolve offspring discrimination strategies is largely shaped by the likelihood and costs of offspring confusion. We hypothesize that males and females with different reproductive and spatial behaviours face different risks of confusing their own with others' offspring, and this should favour differential offspring discrimination strategies in the two sexes. In the brilliant-thighed poison frog, Allobates femoralis, males and females are highly polygamous, terrestrial clutches are laid in male territories and females abandon the clutch after oviposition. We investigated whether males and females differentiate between their own offspring and unrelated young, whether they use direct or indirect cues and whether the concurrent presence of their own clutch is essential to elicit parental behaviours. Males transported tadpoles regardless of location or parentage, but to a lesser extent in the absence of their own clutch. Females discriminated between clutches based on exact location and transported tadpoles only in the presence of their own clutch. This sex-specific selectivity of males and females during parental care reflects the differences in their respective costs of offspring confusion, resulting from differences in their spatial and reproductive behaviours.

Do dogs (Canis lupus familiaris) prefer family?

Kin recognition requires the ability to discriminate between one's own genetic relatives and non-relatives. There are two mechanisms that aid in kin discrimination: phenotype matching and familiarity. Dogs may be a good model for assessing these mechanisms as dogs are a promiscuous social species with a keen sense of smell. Domestic dogs of both sexes were presented with two scents (close kin, distant-kin) and preference was assessed through three measures (latency to approach, number of visits, time spent). Experiment 1 explored the possibility of phenotype matching as subjects had no contact with sires, whose scent was presented alongside a control male's scent. Experiment 2 explored recognition of siblings raised with the subjects and then separated at seven weeks of age. Whereas female dogs in this experiment did not show a statistically significant preference, male dogs showed a preference for distant-kin when presented with sire and female sibling samples.

Sensory cues employed for the acquisition of familiarity-dependent recognition of a shoal of conspecifics by climbing perch (Anabas testudineus Bloch)

In this study we showed that a freshwater fish, the climbing perch (Anabas testudineus) is incapable of using chemical communication but employs visual cues to acquire familiarity and distinguish a familiar group of conspecifics from an unfamiliar one. Moreover, the isolation of olfactory signals from visual cues did not affect the recognition and preference for a familiar shoal in this species.

Detective mice assess relatedness in baboons using olfactory cues

The assessment of relatedness may be crucial in the evolution of socio-sexual behaviour, because it can be associated with fitness benefits mediated by both nepotism and inbreeding avoidance. In this context, one proposed mechanism for kin recognition is 'phenotype matching'; animals might compare phenotypic similarities between themselves and others in order to assess the probability that they are related. Among cues potentially used for kin discrimination, body odours constitute interesting candidates that have been poorly investigated in anthropoid primates so far, because of a mixture of theoretical considerations and methodological/experimental constraints. In this study, we used an indirect approach to examine the similarity in odour signals emitted by related individuals from a natural population of chacma baboons (Papio ursinus). For that purpose, we designed an innovative behavioural tool using mice olfactory abilities in a habituation-discrimination paradigm. We show that: (i) mice can detect odour differences between individuals of same sex and age class in another mammal species, and (ii) mice perceive a higher odour similarity between related baboons than between unrelated baboons. These results suggest that odours may play a role in both the signalling of individual characteristics and of relatedness among individuals in an anthropoid primate. The 'biological olfactometer' developed in this study offers new perspectives to the exploration of olfactory signals from a range of species.

Paternity, parental behavior and circulating steroid hormone concentrations in nest-tending male bluegill

Like many teleost fishes, bluegill (Lepomis macrochirus) are characterized by sole male parental care of offspring. In addition, bluegill parental males experience cuckoldry by specialized parasitic male morphs. This cuckoldry has previously been shown to influence the expression of parental care behavior. To better understand some of the proximate mechanisms mediating parental behavior, we examined the relationships between circulating steroid hormones, paternity, and parental behavior during the egg and fry stages of care in parentals that spawned during the first third of the breeding season. During the egg stage of care, we found that males with higher paternity had lower levels of testosterone, but there was no relationship between paternity and either 11-ketotestosterone or cortisol. There also was no relationship between the hormones and care behavior comprising fanning of the eggs, nest rim circles, chases of brood predators, or pecking at the eggs (indicative of egg cannibalism), except for a negative relationship between cortisol and pecking behavior. During the fry stage of care, we conversely found that males with higher paternity had higher levels of testosterone and 11-ketotestosterone. There also was a negative relationship between the concentrations of these two androgens and the defensive behavior of males when exposed to a potential brood predator (a pumpkinseed, Lepomis gibbosus). We discuss these results in relation to previous work in fishes and other vertebrate taxa. Overall, our data suggest a complex relationship between circulating steroid hormone levels, paternity and parental behavior.

Kin recognition in zebrafish: a 24-hour window for olfactory imprinting

Distinguishing kin from non-kin profoundly impacts the evolution of social behaviour. Individuals able to assess the genetic relatedness of conspecifics can preferentially allocate resources towards related individuals and avoid inbreeding. We have addressed the question of how animals acquire the ability to recognize kin by studying the development of olfactory kin preference in zebrafish (Danio rerio). Previously, we showed that zebrafish use an olfactory template to recognize even unfamiliar kin through phenotype matching. Here, we show for the first time that this phenotype matching is based on a learned olfactory imprinting process in which exposure to kin individuals on day 6 post fertilization (pf) is necessary and sufficient for imprinting. Larvae that were exposed to kin before or after but not on day 6 pf did not recognize kin. Larvae isolated from all contact with conspecifics did not imprint on their own chemical cues; therefore, we see no evidence for kin recognition through self-matching in this species. Surprisingly, exposure to non-kin odour during the sensitive phase of development did not result in imprinting on the odour cues of unrelated individuals, suggesting a genetic predisposition to kin odour. Urine-born peptides expressed by genes of the immune system (MHC) are important messengers carrying information about 'self' and 'other'. We suggest that phenotype matching is acquired through a time-sensitive learning process that, in zebrafish, includes a genetic predisposition potentially involving MHC genes expressed in the olfactory receptor neurons.

Behavioural ecology: promiscuous fathers sire young that recognize true family

Most theories of kin selection assume that animals are able to distinguish relatives from non-relatives. This is especially difficult in situations where mixed parentage precludes that relatedness is recognised by familiarity. Recent work shows that, within the same brood, young bluegill sunfish that are fathered by cuckolders--but not those sired by parental males--pick out their relatives using self-referent phenotype matching and not familiarity.

Promiscuity drives self-referent kin recognition

Kin selection theory has been one of the most significant advances in our understanding of social behavior . However, the discovery of widespread promiscuity has challenged the evolutionary importance of kin selection because it reduces the benefit associated with helping nestmates . This challenge would be resolved if promiscuous species evolved a self-referent kin-recognition mechanism that enables individuals to differentiate kin and nonkin . Here, we take advantage of an asymmetry in the level of promiscuity among males of alternative life histories in the bluegill sunfish (Lepomis macrochirus). We show that, as a consequence of this asymmetry, offspring of "parental" males have a high level of relatedness to nestmates, whereas offspring of "cuckolder" males have a low level of relatedness to nestmates. We find that offspring of parentals do not use a direct recognition mechanism to discriminate among nestmates, whereas offspring of cuckolders use kin recognition by self-referent phenotype matching to differentiate between kin and nonkin. Furthermore, we estimate that the cost of utilizing such self-referent kin recognition is equivalent to a relatedness (R) of at least 0.06. These results provide compelling evidence for adaptive use of kin recognition by self-referent phenotype matching and confirm the importance of kinship in social behavior.