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Predictability is attractive: Female preference for behaviourally consistent males but no preference for the level of male aggression in a bi-parental cichlid.

ABSTRACT: Although personality traits can largely affect individual fitness we know little about the evolutionary forces generating and maintaining personality variation. Here, we investigated the hypothesis that personality variation in aggression is sexually selected in the monogamous, bi-parental cichlid Pelvicachromis pulcher. In this species, breeding pairs form territories and they aggressively defend their territory and offspring against con- and heterospecific intruders. In our mate choice study, we followed up two alternative hypotheses. We either expected females to show a directional preference for a high level and high consistency of aggression (potentially indicating mate choice for male parental quality). Alternatively, we expected females to choose males for (dis-)similarity in the level/consistency of aggression (potentially indicating mate choice for compatibility). Individual level and consistency of aggression were assessed for males and females using mirror tests. After eavesdropping on aggressive behaviour of two males (differing in level and consistency of aggression) females were then allowed to choose between the two males. Males, but not females, showed personality variation in aggression. Further, females generally preferred consistent over inconsistent males independent of their level of aggression. We did not detect a general preference for the level of male aggression. However, we found an above average preference for consistent high-aggression males; whereas female preference for inconsistent high-aggression did not deviate from random choice. Our results suggest behavioural consistency of aggression in male rainbow kribs is selected for via female mate choice. Further, our study underlines the importance of considering both the level and the consistency of a behavioural trait in studies of animal behaviour.

SUBMITTER: Scherer U

PROVIDER: S-EPMC5892930 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Aggression is ubiquitous among social species and functions to maintains social dominance hierarchies. The African cichlid fish Astatotilapia burtoni is an ideal study species for studying aggression due to their unique and flexible dominance hierarchy. However, female aggression in this species and the neural mechanisms of aggression in both sexes is not well understood. To further understand the potential sex differences in aggression in this species, we characterized aggression in male and female A. burtoni in a mirror assay. We then quantified neural activation patterns in brain regions of the social behavior network (SBN) to investigate if differences in behavior are reflected in the brain with immunohistochemistry by detecting the phosphorylated ribosome marker phospho-S6 ribosomal protein (pS6), a marker for neural activation. We found that A. burtoni perform both identical and sex-specific aggressive behaviors in response to a mirror assay. We observed sex differences in pS6 immunoreactivity in the Vv, a homolog of the lateral septum in mammals. Males but not females had higher ps6 immunoreactivity in the ATn after the aggression assay. The ATn is a homolog of the ventromedial hypothalamus in mammals, which is strongly implicated in the regulation of aggression in males. Several regions also have higher pS6 immunoreactivity in negative controls than fish exposed to a mirror, implicating a role for inhibitory neurons in suppressing aggression until a relevant stimulus is present. Male and female A. burtoni display both similar and sexually dimorphic behavioral patterns in aggression in response to a mirror assay. There are also sex differences in the corresponding neural activation patterns in the SBN. In mirror males but not females, the ATn clusters with the POA, revealing a functional connectivity of these regions that is triggered in an aggressive context in males. These findings suggest that distinct neural circuitry underlie aggressive behavior in male and female A. burtoni, serving as a foundation for future work investigating the molecular and neural underpinnings of sexually dimorphic behaviors in this species to reveal fundamental insights into understanding aggression.

Project description:Purpose: The goal of this study is to identify genes that showed a pattern of differential expression between species within activated neurons during mirror-elicited aggression between two species of Lake Malawi cichlid fish which differ in aggressive behaviors, Mchenga conophoros (MC, sand-dwelling) and Petrotilapia chitimba (PC, rock-dwelling). To do this, we use antibodies to phosphorylated ribosomal protein S6 (pS6) to enrich for transcripts bound to phosphorylated ribosomes followed by RNA-seq (PhosphoTRAP). In neurons, this phosphorylation occurs downstream of the binding of neurotransmitters and, thus, pS6 antibodies are increasingly being used as markers of neural activity, similar to immediate early genes (IEGs) like c-fos or egr-1. Methods: Whole brain mRNA samples were collected from 8 adult male cichlids (4 MC, 4 PC) 90min following either 15min exposure to mirror in home tank (Mirror Test) or a Control condition. RNA-immunoprecipitation using antibodies to pS6 were performed and RNA was extracted from immunoprecipitated (IP) RNA samples. We also collected total RNA (input), prior to immunoprecipitation. For details see extraction protocol below. RNA from both input and IP samples was reverse transcribed using the SMART-Seq v4 Ultra Low Input RNA kit. Libraries were prepped using the NEBNext Ultra II FS DNA library Prep Kit for Illumina and sequenced. Sequence reads that passed quality filters were aligned to the Metriaclima zebra (Malawi cichlid) reference genome UMD2A using HiSat2. Transcripts were quantified using StringTie and differential expressional analyses were performed using DESeq2. Results: We identified a large number of genes showing differential expression in mirror-elicited aggression, as well as many genes that differ between ecotypes. These genes, which may underly species differences in behavior, include several neuropeptides, genes involved in the synthesis of steroid hormones, and neurotransmitter activity. Conclusions: This work lays the foundation for future experiments using this emerging genetic model system to investigate the genomic basis of evolved species differences in both brain and behavior.

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Predictability is attractive: Female preference for behaviourally consistent males but no preference for the level of male aggression in a bi-parental cichlid.

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