Biology subjects

Alward, B. A.

Publications and source records attributed to Alward, B. A..

10 recordsLinked to original sources

bioRxiv2026

Cell-type-specific architecture of the hypothalamus in a socially plastic vertebrate

The hypothalamus orchestrates social behaviors by integrating physiological state with environmental information, but the cellular substrates of this plasticity remain unresolved. We combined single-cell and spatial transcriptomics to generate a cell-type map of the hypothalamus in Astatotilapia burtoni, a cichlid fish that forms dynamic social hierarchies. We identified 28 neuronal, glial, neurogenic, and immune cell populations and mapped their organization across hypothalamic nuclei. Social status, sex, and reproductive state engaged coordinated, cell-type-specific transcriptional programs, revealing modular deployment of steroid hormone signaling and plasticity-associated genes. The atlas identified elevated sst1.1 expression in the hypothalamus of dominant males that we localized to the teleost VMH. CRISPR-Cas9 disruption of sst1.1 increased body size, suggesting a role for optimal metabolic and energy allocation. These results define a cellular framework for understanding how hypothalamic plasticity enables flexible social behavior.

neuroscience↗

bioRxiv2024

Sexually dimorphic control of aggression by androgen signaling in a cichlid

Innate social behaviors like aggression are modulated by sex steroid hormones such as androgens and estrogens. However, we know little about how the same hormone regulates similar behaviors in both sexes. We investigated the role of androgenic signaling in the regulation of aggression in Astatotilapia burtoni, a social fish in which males and females perform similar aggressive behaviors. We used AR knockout (KO) animals for this study, which was recently shown to be required for male-typical aggression and mating. Surprisingly, AR KO females did not show deficits in aggression. We also determined that females lacking the other AR, AR{beta} showed normal levels of aggression. Blocking both ARs pharmacologically confirmed that neither AR is necessary for aggression in females. However, AR KO males showed clear deficits in attacks. Thus, in A. burtoni there appears to be a sexual dimorphism in the role of AR in the control of aggression.

neuroscience↗

bioRxiv2024

Expression of novel androgen receptors in three GnRH neuron subtypes in the cichlid brain

Within a social hierarchy, an individuals social status determines its physiology and behavior. In A. burtoni, subordinate males can rise in rank to become dominant, which is accompanied by the upregulation of the entire HPG axis, including activation of GnRH1 neurons, a rise in circulating androgen levels and the display of specific aggressive and reproductive behaviors. Cichlids possess two other GnRH subtypes, GnRH2 and GnRH3, the latter being implicated in the display of male specific behaviors. Interestingly, some studies showed that these GnRH neurons are responsive to fluctuations in circulating androgen levels, suggesting a link between GnRH neurons and androgen receptors (ARs). Due to a teleost-specific whole genome duplication, A. burtoni possess two AR paralogs (AR and AR{beta}) that are encoded by two different genes, ar1 and ar2, respectively. Even though social status has been strongly linked to androgens, whether AR and/or AR{beta} are present in GnRH neurons remains unclear. Here, we used immunohistochemistry and in situ hybridization chain reaction (HCR) to investigate ar1 and ar2 expression specifically in GnRH neurons. We find that all GnRH1 neurons intensely express ar1 but only a few of them express ar2, suggesting the presence of genetically-distinct GnRH1 subtypes. Very few ar1 and ar2 transcripts were found in GnRH2 neurons. GnRH3 neurons were found to express both ar genes. The presence of distinct ar genes within GnRH neuron subtypes, most clearly observed for GnRH1 neurons, suggests differential control of these neurons by androgenic signaling. These findings provide valuable insight for future studies aimed at disentangling the androgenic control of GnRH neuron plasticity and reproductive plasticity across teleosts.

neuroscience↗

bioRxiv2023

Female cichlids attack and avoid-but will still mate with-androgen receptor mutant males that lack male-typical body coloration

A key challenge in animal behavior is disentangling the social stimuli that drive conspecific behaviors. For behaviors like birdsong, insights can be made through the experimental isolation of relevant cues that affect behavior. However, for some species like teleost fish, putative sexual signaling cues are inextricably linked to others, making it difficult to parse the precise roles distinct signals play in driving conspecific behaviors. In the African cichlid Astatotilapia burtoni, males are dominant or subordinate, wherein bright coloration and territorial and courtship behavior inextricably correlate positively with rank. Here, we leveraged androgen receptor (AR) mutant male A. burtoni that lack dominance-typical coloration but not behavior to isolate the role of male coloration in driving female mating behaviors in this species. We found in independent behavioral assays that females behave aggressively towards AR mutant but not WT males but still mated with both types of males. Females showed enhanced activation of esr2b+ cells in the hypothalamus when housed with either mutant or WT males and this activation scaled with spawning activities. Therefore, there is not a simple relationship between male coloration and female mating behaviors in A. burtoni, suggesting independent sensory mechanisms converge on hypothalamic esr2b+ cells to coordinate behavioral output.

animal behavior and cognition↗

bioRxiv2023

Sex differences in aggression and its neural substrate in a cichlid fish

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.

neuroscience↗

bioRxiv2022

A phylogenetics-based nomenclature system for steroid receptors in teleost fishes

Teleost fishes have emerged as tractable models for studying the neuroendocrine regulation of social behavior via molecular genetic techniques, such as CRISPR/Cas9 gene editing. Moreover, teleosts provide an opportunity to investigate the evolution of steroid receptors and their functions, as species within this lineage possess novel steroid receptor paralogs that resulted from a teleost-specific whole genome duplication. Although teleost fishes have grown in popularity as models for behavioral neuroendocrinology, there is not a consistent nomenclature system for steroid receptors and their genes, which may impede a clear understanding of steroid receptor paralogs and their functions. Here, we used a phylogenetic approach to assess the relatedness of protein sequences encoding steroid receptor paralogs in 18 species from 12 different orders of the Infraclass Teleostei. While most similarly named sequences grouped based on the established phylogeny of the teleost fish lineage, our analysis revealed several inconsistencies in the nomenclature of steroid receptor paralogs, particularly for sequences encoding estrogen receptor beta (ER{beta}). Based on our results, we propose a nomenclature system for teleosts in which Greek symbols refer to proteins and numbers refer to genes encoding different subtypes of steroid receptors within the five major groups of this nuclear receptor subfamily. Collectively, our results bridge a critical gap by providing a cohesive naming system for steroid receptors in teleost fishes, which will serve to improve communication, promote collaboration, and enhance our understanding of the evolution and function of steroid receptors across vertebrates.

evolutionary biology↗

bioRxiv2021

Control of testes mass by androgen receptor paralogs in a cichlid

Steroid hormones play numerous important and diverse roles in the differentiation and development of vertebrate primary and secondary reproductive characteristics. However, the exact role of androgen receptors (ARs)--which bind circulating androgens--in this regulatory pathway is unclear. Teleost fishes further complicate this question by having two paralogs of AR (AR and AR{beta}) resulting from a duplication of their ancestral genome. We investigated the functional role of these two ARs on testes growth and development by experimentally eliminating receptor function of one or both paralogs using CRISPR/Cas9 genome edited Astatotilapia burtoni, an African cichlid fish. Fish with two or more functional receptor alleles were more likely to be male compared to fish with one or fewer, suggesting that the two paralogs of the receptor may be redundant in regulating early sex determination. In contrast, we found that adult testes size was significantly affected by distinct combinations of mutant and wild-type AR alleles. We present a working model whereby AR{beta} facilitates testes growth and AR causes testes regression. This mechanism may contribute to the robust social and physiological plasticity displayed by A. burtoni and other social teleost fish.

physiology↗

bioRxiv2020

A behavioral logic underlying aggression in an African cichlid fish

Social rank in a hierarchy determines which individuals have access to important resources such as food, shelter, and mates. In the African cichlid fish Astatotilapia burtoni, rank is under social control, such that larger males are more likely than smaller males to be dominant in rank. Although it is well known that the relative size of A. burtoni males is critical in controlling social rank, the specific behavioral strategies underlying responses to males of different sizes are not well understood. In this research, our goal was to characterize these responses by performing resident-intruder assays, in which aggressive behaviors were measured in territorial males in response to the introduction of unfamiliar males that differed in relative standard length (SL). We found that the relative SL of intruders played an important role in determining behavioral performance. Resident males exposed to larger (>5% larger in SL) or matched (between 0 and 5% larger or smaller in SL) intruder males performed more lateral displays, a type of non-physical aggression, compared to resident males exposed to smaller (>5% smaller in SL) intruder males. However, physical aggression, such as chases and bites, did not differ as a function of relative SL. Our results suggest that A. burtoni males amplify non-physical aggression to settle territorial disputes in response to differences in relative SL that were not previously considered to be behaviorally relevant. HighlightsO_LIRelative size determines social rank in the African cichlid Astatotilapia burtoni C_LIO_LIResident male A. burtoni respond differently to small size differences in intruder males C_LIO_LIResidents perform more non-physical aggression against larger intruders C_LIO_LIResidents do not alter physical aggression as a function of differently sized intruders C_LIO_LIDistinct behavioral strategies are used against different intruders C_LI

animal behavior and cognition↗

bioRxiv2020

Modular genetic control of social status in a cichlid fish

Social hierarchies are ubiquitous in social species and profoundly influence physiology and behavior. Androgens like testosterone have been strongly linked to social status, yet the molecular mechanisms regulating social status are not known. The African cichlid fish Astatotilapia burtoni is a powerful model species for elucidating the role of androgens in social status given their rich social hierarchy and genetic tractability. Dominant A. burtoni males possess large testes, bright coloration, and perform aggressive and reproductive behaviors while non-dominant males do not. Social status in A. burtoni is in flux, however, as males alter their status depending on the social environment. Due to a teleost-specific whole-genome duplication, A. burtoni possess two androgen receptor (AR) paralogs, ARα and ARβ, providing a unique opportunity to disentangle the role of gene duplication in the evolution of social systems. Here, we used CRISPR/Cas9 gene editing to generate AR mutant A. burtoni and performed a suite of experiments to interrogate the mechanistic basis of social dominance. We find that ARβ, but not ARα, is required for testes growth and bright coloration, while ARα, but not ARβ, is required for the performance of reproductive behavior and aggressive displays. Both receptors are required to reduce flees from females and either AR is sufficient for attacking males. Thus, social status in A. burtoni is inordinately dissociable and under the modular control of two AR paralogs. This type of non-redundancy may be important in facilitating social plasticity in A. burtoni and other species whose social status relies on social experience.Significance Statement Social rank along a hierarchy determines physiological state and behavioral performance. A ubiquitous feature of social hierarchies is the communication of rank through non-physical signaling systems (e.g., coloration) and aggression, traits that correlate with the reproductive status of an individual. Despite the links identified between social status, physiology, and behavior, the molecular basis of social status is not known. Here, we genetically dissect social status in the African cichlid fish Astatotilapia burtoni using CRISPR/Cas9 gene editing. We show that two distinct androgen receptor (AR) genes control social status in a highly modular manner. This type of coordination of social status may be fundamental across species that rely on social information to optimally guide physiology and behavior.Competing Interest StatementThe authors have declared no competing interest.View Full Text

animal behavior and cognition↗

bioRxiv2018

Hormonal regulation of social ascent and temporal patterns of behavior in an African cichlid

For many species, social rank determines which individuals perform certain social behaviors and when. Higher ranking or dominant (DOM) individuals maintain status through aggressive interactions and perform courtship behaviors while non-dominant (ND) individuals do not. In some species ND individuals ascend (ASC) in social rank when the opportunity arises. Many important questions related to the mechanistic basis of social ascent remain to be answered. We probed whether androgen signaling regulates social ascent in male Astatotilapia burtoni, an African cichlid whose social hierarchy can be readily controlled in the laboratory. As expected, androgen receptor (AR) antagonism abolished reproductive behavior during social ascent. However, we discovered multiple AR-dependent--and AR-independent--temporal behavioral patterns that typify social ascent and dominance. AR antagonism in ASC males reduced the speed of behavioral performance compared to DOM males. Socially ascending males, independent of AR activation, were more likely than DOM males to follow aggressive displays with another aggressive display. Further analyses revealed differences in the sequencing of aggressive and courtship behaviors, wherein DOM males were more likely than ASC males to follow male-directed aggression with courtship displays. Strikingly, this difference was driven mostly by ASC males taking longer to transition from aggression to courtship, suggesting ASC males can perform certain DOM-typical temporal behavioral patterns. Our results indicate androgen signaling drives social ascent, but hormonal signaling and social experience shape the full suite of DOM-typical behavioral patterns.

animal behavior and cognition↗