Developmental plasticity of the stress response in female but not in male guppies

To survive, animals must respond appropriately to stress. Stress responses are costly, so early-life experiences with potential stressors could adaptively tailor adult stress responses to local conditions. However, how multiple stressors influence the development of the stress response remains unclear, as is the role of sex. Trinidadian guppies (Poecilia reticulata) are small fish with extensive life-history differences between the sexes and population variation in predation pressure and social density. We investigated how sex and early-life experience influence hormonal stress responses by manipulating conspecific density and perceived predation risk during development. In adults, we sampled cortisol twice to measure initial release and change over time in response to a recurring stressor. The sexes differed considerably in their physiological stress response. Males released more cortisol for their body mass than females and did not reduce cortisol release over time. By contrast, all females, except those reared at high density together with predation cues, reduced cortisol release over time. Cortisol responses of males were thus less dynamic in response to current circumstances and early-life experiences than females, consistent with life-history differences between the sexes. Our study underscores the importance of early-life experiences, interacting ecological factors and sex differences in the organization of the stress response

Indigenous modernism: dehabituating reading practices

This paper experiments with formal style as a way of working through the literary discipline’s lacunae regarding aesthetic value, race, and coloniality. Using a “counter taxonomy” as an example of academic dissent, this paper considers the limits of this form of dissenting speech within “public discourse” (Fraser; Habermas) by demonstrating a persistent occlusion in the literary discipline related to this mode of speech, which concerns the “primitive” subject. I define a term to unsettle a series of categorical terms long-held as guiding frameworks in our discipline: modernism, Native and Harlem renaissances, etc. This term is “Indigenous modernism,” a category that is a contradiction in terms because it announces its inclusion of the original term’s constitutive exclusion, ie. the primitive within the modern, through the language producing its erasure. Through this experiment, I argue for the necessity of a different kind of dissent, specifically a more capacious form of literary critique that interrogates the problems of holding a discourse in common and the specific needs of anti-colonial work. As a pedagogical exercise that models the benefits of failure, I suggest that this intervention requires us to think about how we represent truth through critiqueDecolonial methodologiesIndigenous studiesCultural studiesGlobal avantgardesEste artículo experimenta con el estilo formal, como forma de trabajar a través de la disciplina literaria de la laguna, en cuanto a su valor estético, raza y colonialidad. Este artículo usa una ‘contra-taxonomía’ como ejemplo de disconformidad académica, para considerar así los límites de esta misma disconformidad en el diálogo en el ‘diálogo público’ (Fraser; Habermas); demostrando una oclusión persistente en la disciplina literaria, asociada con este modo de diálogo, cuya preocupación es el tema “primitivo”. En este artículo, defino un término para perturbar a una serie de términos categóricos antiguos como marco de orientación en nuestra disciplina: modernismo, renacimientos del Harlem y de los Nativos Americanos, etc. Este término es “modernismo indígena”, una categoría que se ve en contradicción, ya que anuncia su inclusión de la exclusión constitutiva del término original, es decir, lo primitivo dentro de lo moderno, a través del lenguaje que produce su corrección. Mediante este experimento, peleó por la necesidad de un diferente tipo de disconformidad, especialmente una forma de crítica literaria más amplia, que interrogue los problemas de tener un diálogo común, y las necesidades específicas del trabajo anticolonial. Como un ejercicio pedagógico que exponga los beneficios del fracaso, sugiero que esta intervención nos obligue a pensar sobre cómo representamos la verdad a través de la crítica. Palabras claves: Métodos decoloniales; estudios Nativos Americanos; estudios culturales; ventajas globales

Social decision-making in a group living cichlid fish

For my doctoral research I examined social decision-making in a cooperatively breeding cichlid fish, Neolamprologus pulcher with a focus on affiliation and aggression. I investigated the role that the nonapeptide hormone, isotocin, plays in modulating social decisions in these contexts. I show that N. pulcher males prefer to join larger groups regardless of the rank at which they will join, whereas females prefer larger groups only when they can join a group in a high rank (Chapter 2). I examined decision-making during resource contests in (Chapter 3) and found that N. pulcher are sensitive to the size of their opponents, making fighting decisions depending on their opponents’ body size. I also found that smaller N. pulcher are more motivated to persist within contests, showing a shorter latency to resume fighting following interruption (Chapter 4). In Chapters 5 and 6, I explored the role of isotocin (the teleost fish homologue of oxytocin) in regulating social behaviour. I discovered that an increase in isotocin increased responsiveness to social information. Fish treated with isotocin were more sensitive to their opponent’s size in contests and were more submissive to dominant individuals within their social group (Chapter 5). Unexpectedly, I found that exogenous isotocin reduced sociality in N. pulcher, and that an isotocin receptor antagonist increased it (Chapter 6). These results suggest that the relationship between isotocin and social behaviour is both complex and context specific. In my final data chapter, I used social network analysis to explore the role of dominance interactions in determining the structure of N. pulcher social groups. I found that N. pulcher dominance hierarchies are highly linear, but that dominance interactions are not predicted by sex or body size asymmetry (Chapter 7). I found that conflict within N. pulcher social groups is greatest at the top of the dominance hierarchy. Taken together the results of my thesis helps to elucidate the behavioural and hormonal basis of social decision-making in a cooperatively breeding vertebrate and help to illuminate the evolution of social behaviour.Doctor of Philosophy (PhD

Demasculinization of male guppies increases resistance to a common and harmful ectoparasite

Parasites are detrimental to host fitness and therefore should strongly select for host defence mechanisms. Yet, hosts vary considerably in their observed parasite loads. One notable source of inter-individual variation in parasitism is host sex. Such variation could be caused by the immunomodulatory effects of gonadal steroids. Here we assess the influence of gonadal steroids on the ability of guppies (Poecilia reticulata) to defend themselves against a common and deleterious parasite (Gyrodactylus turnbulli). Adult male guppies underwent 31 days of artificial demasculinization with the androgen receptor-antagonist flutamide, or feminization with a combination of flutamide and the synthetic oestrogen 17 β-estradiol, and their parasite loads were compared over time to untreated males and females. Both demasculinized and feminized male guppies had lower G. turnbulli loads than the untreated males and females, but this effect appeared to be mainly the result of demasculinization, with feminization having no additional measurable effect. Furthermore, demasculinized males, feminized males and untreated females all suffered lower Gyrodactylus-induced mortality than untreated males. Together, these results suggest that androgens reduce the ability of guppies to control parasite loads, and modulate resistance to and survival from infection. We discuss the relevance of these findings for understanding constraints on the evolution of resistance in guppies and other vertebrates

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

Gene-environment interactions in obesity: results from the multi-ethnic cohort EpiDREAM

Background: Obesity is now considered to be a global epidemic and gene-environment interaction studies are crucial to understanding the genetic architecture of this disease. The objectives of this research were to (1) review the current evidence of gene-environment interactions in the field of obesity, (2) examine the interactions between obesity predisposing gene variants and physical activity using precise physical activity data and (3) analyze a novel gene-environment interaction between obesity predisposing gene variants and multiple pregnancies. Methods: The data for the gene-environment interaction analyses were collected from the EpiDREAM study: a prospective cohort including participants of six ethnic backgrounds from 21 countries worldwide. A subset of 17 423 participants with complete genotype and phenotype information was included in the analysis. Obesity predisposing single nucleotide polymorphisms were analyzed independently and as a genetic risk score. General linear models were used to analyze all main effects and interactions. Results: Physical activity interacted with FTO rs9939609 to modulate BMI (Pinteraction=0.032) and BAI (Pinteraction=3.26 x 10-4). Increased physical activity attenuated the impact of FTO on obesity. Four SNPs displayed significant associations with physical activity: NTRK2 rs1211166 (P=0.015), BDNF rs6265 (P=0.007), BDNF rs1401635 P=0.003) and NPC1 rs1805081 (P=3.52 x 10-4). Multiple pregnancies was significantly associated with BMI (Pinteraction=1.17 x 10-5) BAI (Pinteraction=3.47 x 10-7) and also interacted with FTO rs9939609 to modulate BMI (Pinteraction=0.014). The impact of FTO on BMI was accentuated by multiple pregnancies in the EpiDREAM cohort. Discussion: Both physical activity and parity have a significant impact on obesity measures and these effects appear to be relevant on a global scale. Our results confirm the physical activity x FTO interaction in a multi-ethnic context and indicate that parity may also interact with FTO polymorphisms.ThesisMaster of Science (MSc

Gene-environment interactions in obesity: current evidence and future directions

Background: Obesity is a multifactorial disease caused by the interplay of environmental and genetic risk factors. With the prevalence of obesity more than doubling since 1980, this disease has become a global epidemic. The objectives of this research were to (1) review the current evidence of gene-environment interactions (GEI) in the field of obesity, (2) investigate novel GEI involving sedentary behaviour, sleep duration and alcohol consumption, (3) assess GEI using a cumulative environmental risk score, and (4) provide an overview of methodological weaknesses in GEI studies and provide suggestions for future directions. Methods: The data for the gene-environment interaction analyses were collected from the EpiDREAM study: a cohort study including participants of six ethnic backgrounds from 17 countries worldwide. A subset of 17 423 participants with complete genotype and phenotype information was included in the analysis. Twenty-three obesity predisposing single nucleotide polymorphisms (SNPs) were analyzed independently and as a genetic risk score (GRS). Linear regression models were used to analyze these interactions. Results: Heritability, monogenic and polygenic obesity studies provide converging evidence that obesity-predisposing genes interact with a variety of environmental exposures including physical activity and diet patterns. In the EpiDREAM cohort, we found that increased sedentary time did not interact with obesity predisposing SNPs or the GRS to modulate BMI. The interaction between sedentary time and physical activity was also not significant. We observed a U-shaped association between sleep duration and BMI and sleep duration did not appear to moderate the impact of the obesity predisposing SNPs or the GRS. However, we did observe an alcohol x FTO rs1421085 interaction, whereby increased alcohol consumption attenuated the impact of FTO rs1421085 variation on BMI. We also found that the combined effect of several environmental risk factors significantly modified the effect of FTO rs3751812 on BMI. Specifically, we found that the effect of the FTO rs3751812 SNP on BMI was over two times greater among those in the highest quartile of environmental risk compared to those in the lowest quartile. The GRS did not interact with any of the exposures tested. Discussion: Our results indicate that sedentary behaviour did not moderate the impact of obesity predisposing genes, while alcohol consumption decreased the impact of variation in FTO rs3751812 on BMI. We also observed that variation in FTO rs3751812 interacted with a cumulative environmental risk score to moderate BMI. The growing body of GEI evidence has provided a deeper understanding of obesity aetiology and may have tremendous applications in the emerging field of personalized medicine and individualized lifestyle recommendations. Although the number of gene-environment interaction analyses has increased rapidly across multiple disciplines, addressing methodological concerns such as statistical modeling, confounding, biological assumptions and measurement precision will be necessary to fully exploit the potential of the GEI field. With the development of new methodological and measurement techniques such as hypothesis-free genome wide interaction studies and deep phenotyping, it may be possible to translate the information from GEI studies into public health policy and personalized medicine for obesity and other complex human diseases.ThesisDoctor of Philosophy (PhD