Social Environment Influences the Temporal Dynamics of Sneak-Spawning in a Fish with Alternative Reproductive Tactics.

AbstractSeveral predictions of sperm competition theory are not well supported empirically. One potential reason is that most current theory and empirical research ignore how the social environment influence the temporal dynamics of mating. We propose that understanding these dynamics is key to understanding sexual selection and improving the predictive power of theory. To demonstrate the importance of these dynamics, we quantify how males' social role, interactions among males, and current social environment influence the timing of mating in Symphodus ocellatus, a species with three alternative male reproductive tactics. Nesting males spawn synchronously with females; sneakers and satellites sneak-spawn with some time delay. Satellites also cooperate with nesting males. We found that satellites have shorter sneak-spawning delays than sneakers, a benefit of their cooperation with nesting males. Sneak-spawning delays decreased with increasing nest activity for sneakers but not for satellites, suggesting that sneakers may benefit from increased sperm competition intensity. Current sperm competition models ignore this potential benefit, which may be why the prediction that males should decrease investment when sperm competition involves more than two males is not well supported. Our study provides insight into mechanisms that drive variation in the timing of spawning, which could explain mismatches between theoretical and empirical results.

Ejaculate Allocation and Sperm Characteristics Differ among Alternative Male Types in a Species of Fish with Cooperation and Competition among Unrelated Males.

Sexual selection arising from sperm competition has driven the evolution of immense variation in ejaculate allocation and sperm characteristics not only among species, but also among males within a species. One question that has received little attention is how cooperation among males affects these patterns. Here we ask how male alternative reproductive types differ in testes size, ejaculate production, and sperm morphology in the ocellated wrasse, a marine fish in which unrelated males cooperate and compete during reproduction. Nesting males build nests, court females and provide care. Sneaker males only "sneak" spawn, while satellite males sneak, but also help by chasing away sneakers. We found that satellite males have larger absolute testes than either sneakers or nesting males, despite their cooperative role. Nesting males invested relatively less in testes than either sneakers or satellites. Though sneakers produced smaller ejaculates than either satellite or nesting males, we found no difference among male types in either sperm cell concentration or sperm number, implying sneakers may produce less seminal fluid. Sperm tail length did not differ significantly among male types, but sneaker sperm cells had significantly larger heads than either satellite or nesting male sperm, consistent with past research showing sneakers produce slower sperm. Our results highlight that social interactions among males can influence sperm and ejaculate production.

How Live Music Moves Us: Head Movement Differences in Audiences to Live Versus Recorded Music.

A live music concert is a pleasurable social event that is among the most visceral and memorable forms of musical engagement. But what inspires listeners to attend concerts, sometimes at great expense, when they could listen to recordings at home? An iconic aspect of popular concerts is engaging with other audience members through moving to the music. Head movements, in particular, reflect emotion and have social consequences when experienced with others. Previous studies have explored the affiliative social engagement experienced among people moving together to music. But live concerts have other features that might also be important, such as that during a live performance the music unfolds in a unique and not predetermined way, potentially increasing anticipation and feelings of involvement for the audience. Being in the same space as the musicians might also be exciting. Here we controlled for simply being in an audience to examine whether factors inherent to live performance contribute to the concert experience. We used motion capture to compare head movement responses at a live album release concert featuring Canadian rock star Ian Fletcher Thornley, and at a concert without the performers where the same songs were played from the recorded album. We also examined effects of a prior connection with the performers by comparing fans and neutral-listeners, while controlling for familiarity with the songs, as the album had not yet been released. Head movements were faster during the live concert than the album-playback concert. Self-reported fans moved faster and exhibited greater levels of rhythmic entrainment than neutral-listeners. These results indicate that live music engages listeners to a greater extent than pre-recorded music and that a pre-existing admiration for the performers also leads to higher engagement.

Isotocin neuronal phenotypes differ among social systems in cichlid fishes.

Social living has evolved numerous times across a diverse array of animal taxa. An open question is how the transition to a social lifestyle has shaped, and been shaped by, the underlying neurohormonal machinery of social behaviour. The nonapeptide neurohormones, implicated in the regulation of social behaviours, are prime candidates for the neuroendocrine substrates of social evolution. Here, we examined the brains of eight cichlid fish species with divergent social systems, comparing the number and size of preoptic neurons that express the nonapeptides isotocin and vasotocin. While controlling for the influence of phylogeny and body size, we found that the highly social cooperatively breeding species (n = 4) had fewer parvocellular isotocin neurons than the less social independently breeding species (n = 4), suggesting that the evolutionary transition to group living and cooperative breeding was associated with a reduction in the number of these neurons. In a complementary analysis, we found that the size and number of isotocin neurons significantly differentiated the cooperatively breeding from the independently breeding species. Our results suggest that isotocin is related to sociality in cichlids and may provide a mechanistic substrate for the evolution of sociality.

Sperm competition shapes gene expression and sequence evolution in the ocellated wrasse.

Gene expression differences between males and females often underlie sexually dimorphic phenotypes, and the expression levels of genes that are differentially expressed between the sexes are thought to respond to sexual selection. Most studies on the transcriptomic response to sexual selection treat sexual selection as a single force, but postmating sexual selection in particular is expected to specifically target gonadal tissue. The three male morphs of the ocellated wrasse (Symphodus ocellatus) make it possible to test the role of postmating sexual selection in shaping the gonadal transcriptome. Nesting males hold territories and have the highest reproductive success, yet we detected feminization of their gonadal gene expression compared to satellite males. Satellite males are less brightly coloured and experience more intense sperm competition than nesting males. In line with postmating sexual selection affecting gonadal gene expression, we detected a more masculinized expression profile in satellites. Sneakers are the lowest quality males and showed both de-masculinization and de-feminization of gene expression. We also detected higher rates of gene sequence evolution of male-biased genes compared to unbiased genes, which could at least in part be explained by positive selection. Together, these results reveal the potential for postmating sexual selection to drive higher rates of gene sequence evolution and shape the gonadal transcriptome profile.

Ovarian fluid allows directional cryptic female choice despite external fertilization.

In species with internal fertilization, females can favour certain males over others, not only before mating but also within the female's reproductive tract after mating. Here, we ask whether such directional post-mating (that is, cryptic) female mate choice can also occur in species with external fertilization. Using an in vitro sperm competition experiment, we demonstrate that female ovarian fluid (ovarian fluid) changes the outcome of sperm competition by decreasing the importance of sperm number thereby increasing the relative importance of sperm velocity. We further show that ovarian fluid does not differentially affect sperm from alternative male phenotypes, but generally enhances sperm velocity, motility, straightness and chemoattraction. Under natural conditions, female ovarian fluid likely increases the paternity of the preferred parental male phenotype, as these males release fewer but faster sperm. These results imply females have greater control over fertilization and potential to exert selection on males in species with external fertilization than previously thought possible.

Within-group relatedness is correlated with colony-level social structure and reproductive sharing in a social fish.

In group-living species, the degree of relatedness among group members often governs the extent of reproductive sharing, cooperation and conflict within a group. Kinship among group members can be shaped by the presence and location of neighbouring groups, as these provide dispersal or mating opportunities that can dilute kinship among current group members. Here, we assessed how within-group relatedness varies with the density and position of neighbouring social groups in Neolamprologus pulcher, a colonial and group-living cichlid fish. We used restriction site-associated DNA sequencing (RADseq) methods to generate thousands of polymorphic SNPs. Relative to microsatellite data, RADseq data provided much tighter confidence intervals around our relatedness estimates. These data allowed us to document novel patterns of relatedness in relation to colony-level social structure. First, the density of neighbouring groups was negatively correlated with relatedness between subordinates and dominant females within a group, but no such patterns were observed between subordinates and dominant males. Second, subordinates at the colony edge were less related to dominant males in their group than subordinates in the colony centre, suggesting a shorter breeding tenure for dominant males at the colony edge. Finally, subordinates who were closely related to their same-sex dominant were more likely to reproduce, supporting some restraint models of reproductive skew. Collectively, these results demonstrate that within-group relatedness is influenced by the broader social context, and variation between groups in the degree of relatedness between dominants and subordinates can be explained by both patterns of reproductive sharing and the nature of the social landscape.

Species-specific patterns of nonapeptide brain gene expression relative to pair-bonding behavior in grouping and non-grouping cichlids.

Comparative studies have revealed that vasopressin-oxytocin pathways are associated with both pair bonding and grouping behavior. However, the relationship between pair bonding and grouping behavior remains unclear. In this study, our aim was to identify whether two species that differ in grouping behavior display a corresponding difference in their pair bonds, and in the underlying vasopressin-oxytocin hormonal pathways. Using two species of cichlid fishes, the highly social Neolamprologus pulcher and the non-social Telmatochromis temporalis, we measured proximity of pairs during pair bond formation, and then measured social behaviors (proximity, aggression, submission, affiliation) and brain gene expression of isotocin and arginine vasotocin (the teleost homologues of oxytocin and vasopressin, respectively), as well as their receptors, after a temporary separation and subsequent reunion of the bonded pairs. Pairs of the social species spent more time in close proximity relative to the non-social species. Rates of aggression increased in both species following the separation and reunion treatment, relative to controls that were not separated. Overall, whole brain expression of isotocin was higher in the social species relative to the non-social species, and correlated with proximity, submission, and affiliation, but only in the social species. Our results suggest that both a social and a non-social cichlid species have similar behavioral responses to a temporary separation from a mate, and we found no difference in the brain gene expression of measured hormones and receptors based on our separation-reunion treatment. However, our results highlight the importance of isotocin in mediating submissive and affiliative behaviors in cichlid fishes, and demonstrate that isotocin has species-specific correlations with socially relevant behaviors.

Is there convergence in the molecular pathways underlying the repeated evolution of sociality in African cichlids?

Despite wide variation in the complexity of social interactions across taxa, the basic behavioral components of sociality appear to be modulated by conserved hormone pathways. Specifically, the nonapeptide hormones oxytocin and vasopressin and their receptors have been implicated in regulating diverse social behaviors across vertebrates. Here, we took advantage of the repeated evolution of cooperative breeding in African cichlids to investigate whether there are consistent brain gene expression patterns of isotocin and arginine vasotocin (teleost homologues of oxytocin and vasopressin), as well as their receptors, between four closely related pairs of social (cooperative) and non-social (non-cooperative) species. We first found that the coding sequences for the five genes studied were highly conserved across the eight species. This is the first study to examine the expression of both isotocin receptors, and so we performed a phylogenetic analysis that suggests that these two isotocin receptors are paralogues that arose during the teleost genome duplication. When we then examined brain gene expression patterns relative to social system, we found that there were whole-brain gene expression differences between the social and non-social species in many of the species pairs. However, these relationships varied in both the direction and magnitude among the four species pairs. In conclusion, our results suggest high sequence conservation and species-specific gene expression patterns relative to social behavior for these candidate hormone pathways in the cichlid fishes.

Reproductive sharing in relation to group and colony-level attributes in a cooperative breeding fish.

The degree to which group members share reproduction is dictated by both within-group (e.g. group size and composition) and between-group(e.g. density and position of neighbours) characteristics. While many studies have investigated reproductive patterns within social groups, few have simultaneously explored how within-group and between-group social structure influence these patterns. Here, we investigated how group size and composition, along with territory density and location within the colony, influenced parentage in 36 wild groups of a colonial, cooperatively breeding fish Neolamprologus pulcher. Dominant males sired 76% of offspring in their group, whereas dominant females mothered 82% of offspring in their group. Subordinate reproduction was frequent, occurring in 47% of sampled groups. Subordinate males gained more paternity in groups located in high-density areas and in groups with many subordinate males. Dominant males and females in large groups and in groups with many reproductively mature subordinates had higher rates of parentage loss, but only at the colony edge. Our study provides, to our knowledge,the first comprehensive quantification of reproductive sharing among groups of wild N. pulcher, a model species for the study of cooperation and social behaviour. Further, we demonstrate that the frequency of extra-pair parentage differs across small social and spatial scales.

Brain nonapeptide levels are related to social status and affiliative behaviour in a cooperatively breeding cichlid fish.

The mammalian nonapeptide hormones, vasopressin and oxytocin, are known to be potent regulators of social behaviour. Teleost fishes possess vasopressin and oxytocin homologues known as arginine vasotocin (AVT) and isotocin (IT), respectively. The role of these homologous nonapeptides in mediating social behaviour in fishes has received far less attention. The extraordinarily large number of teleost fish species and the impressive diversity of their social systems provide us with a rich test bed for investigating the role of nonapeptides in regulating social behaviour. Existing studies, mostly focused on AVT, have revealed relationships between the nonapeptides, and both social behaviour and dominance status in fishes. To date, much of the work on endogenous nonapeptides in fish brains has measured genomic or neuroanatomical proxies of nonapeptide production rather than the levels of these molecules in the brain. In this study, we measure biologically available AVT and IT levels in the brains of Neolamprologus pulcher, a cooperatively breeding cichlid fish, using high performance liquid chromatography with fluorescence detection. We found that brain AVT levels were higher in the subordinate than in dominant animals, and levels of IT correlated negatively with the expression of affiliative behaviour. We contrast these results with previous studies, and we discuss the role the nonapeptide hormones may play in the regulation of social behaviour in this highly social animal.

A comparative study of an innate immune response in Lamprologine cichlid fishes.

Social interactions facilitate pathogen transmission and increase virulence. Therefore, species that live in social groups are predicted to suffer a higher pathogen burden, to invest more heavily in immune defence against pathogens, or both. However, there are few empirical tests of whether social species indeed invest more heavily in immune defence than non-social species. In the current study, we conducted a phylogenetically controlled comparison of innate immune response in Lamprologine cichlid fishes. We focused on three species of highly social cichlids that live in permanent groups and exhibit cooperative breeding (Julidochromis ornatus, Neolamprologus pulcher and Neolamprologus savoryi) and three species of non-social cichlids that exhibit neither grouping nor cooperative behaviour (Telmatochromis temporalis, Neolamprologus tetracanthus and Neolamprologus modestus). We quantified the innate immune response by injecting wild fishes with phytohaemagglutinin (PHA), a lectin that causes a cell-mediated immune response. We predicted that the three highly social species would show a greater immune reaction to the PHA treatment, indicating higher investment in immune defence against parasites relative to the three non-social species. We found significant species-level variation in immune response, but contrary to our prediction, this variation did not correspond to social system. However, we found that immune response was correlated with territory size across the six species. Our results indicate that the common assumption of a positive relationship between social system and investment in immune function may be overly simplistic. We suggest that factors such as rates of both in-group and out-group social interactions are likely to be important mediators of the relationship between sociality and immune function.

The stress response of the highly social African cichlid Neolamprologus pulcher.

In group-living species, dominant individuals are frequently aggressive toward subordinates, and such dominant aggression can lead to chronic stress, higher glucocorticoid levels, and decreased fitness for subordinates. However, in many cooperatively breeding species, it is surprisingly the dominants rather than the subordinates that exhibit higher levels of glucocorticoids, a possible consequence of the demands of maintaining high social rank and socially suppressing the reproduction of other group members. This study investigates the relationship between social status and circulating plasma cortisol in groups of the cooperatively breeding African cichlid Neolamprologus pulcher. Baseline (resting) levels of cortisol were quantified, as was the cortisol response following an acute stressor. Dominants had the higher cortisol concentrations, and these were not related to their social behavior. Cortisol concentrations correlated (positively) with social behaviors and general activity levels only in subordinate males, arguably the individuals with the least stability in the social group. No status-dependent differential responses to acute stress were detected, suggesting that the status-induced chronic stress has little effect on the capacity to mount a full stress response to large-scale, life-threatening risk.