Social status mediates behavioral, endocrine, and neural responses to an intruder challenge in a social cichlid, Astatotilapia burtoni.

Most animals encounter social challenges throughout their lives as they compete for resources. Individual responses to such challenges can depend on social status, sex, and community-level attributes, yet most of our knowledge of the behavioral and physiological mechanisms by which individuals respond to challenges has come from dyadic interactions between a resource holder and a challenger (usually both males). To incorporate differences in individual behavior that are influenced by surrounding group members, we use naturalistic communities of the cichlid fish, Astatotilapia burtoni, and examine resident dominant male responses to a territorial intrusion within the social group. We measured behavior and steroid hormones (testosterone and cortisol), and neural activity in key brain regions implicated in regulating territorial and social dominance behavior. In response to a male intruder, resident dominant males shifted from border defense to overt attack behavior, accompanied by decreased basolateral amygdala activity. These differences were context dependent - resident dominant males only exhibited increased border defense when the intruder secured dominance. Neither subordinate males nor females changed their behavior in response to a territorial intrusion in their community. However, neural activity in both hippocampus and lateral septum of subordinates increased when the intruder failed to establish dominance. Our results demonstrate how a social challenge results in multi-faceted behavioral, hormonal, and neural changes, depending on social status, sex, and the outcome of an intruder challenge. Taken together, our work provides novel insights into the mechanisms through which individual group members display context- and status-appropriate challenge responses in dynamic social groups.

Early social deprivation shapes neuronal programming of the social decision-making network in a cooperatively breeding fish.

The early social environment an animal experiences may have pervasive effects on its behaviour. The social decision-making network (SDMN), consisting of interconnected brain nuclei from the forebrain and midbrain, is involved in the regulation of behaviours during social interactions. In species with advanced sociality such as cooperative breeders, offspring are exposed to a large number and a great diversity of social interactions every day of their early life. This diverse social environment may have life-long consequences on the development of several neurophysiological systems within the SDMN, although these effects are largely unknown. We studied these life-long effects in a cooperatively breeding fish, Neolamprologus pulcher, focusing on the expression of genes involved in the monoaminergic and stress response systems in the SDMN. N. pulcher fry were raised until an age of 2 months either with their parents, subordinate helpers and same-clutch siblings (+F), or with same-clutch siblings only (-F). Analysis of the expression of glucocorticoid receptor, mineralocorticoid receptor, corticotropin releasing factor, dopamine receptors 1 and 2, serotonin transporter and DNA methyltransferase 1 genes showed that early social experiences altered the neurogenomic profile of the preoptic area. Moreover, the dopamine receptor 1 gene was up-regulated in the preoptic area of -F fish compared to +F fish. -F fish also showed up-regulation of GR1 expression in the dorsal medial telencephalon (functional equivalent to the basolateral amygdala), and in the dorsolateral telencephalon (functional equivalent to the hippocampus). Our results suggest that early social environment has life-long effects on the development of several neurophysiological systems within the SDMN.

Examining the disconnect between prolactin and parental care in avian brood parasites.

Prolactin is often referred to as the "parental hormone" but there are examples in which prolactin and parental behavior are disconnected. One intriguing example is in avian obligate brood parasites; species exhibiting high circulating prolactin but no parental care. To understand this disconnect, we examined transcriptional and behavioral responses to prolactin in brown-headed (Molothrus ater) and bronzed (M aeneus) brood parasitic cowbirds. We first examine prolactin-dependent regulation of transcriptome wide gene expression in the preoptic area (POA), a brain region associated with parental care across vertebrates. We next examined prolactin-dependent abundance of seven parental care-related candidate genes in hypothalamic regions that are prolactin-responsive in other avian species. We found no evidence of prolactin sensitivity in cowbirds in either case. To understand this prolactin insensitivity, we compared prolactin receptor transcript abundance between parasitic and nonparasitic species and between prolactin treated and untreated cowbirds. We observed significantly lower prolactin receptor transcript abundance in brown-headed but not bronzed cowbird POA compared with a nonparasite and no prolactin-dependent changes in either parasitic species. Finally, estrogen-primed female brown-headed cowbirds with or without prolactin treatment exhibited significantly greater avoidance of nestling begging stimuli compared with untreated birds. Taken together, our results suggest that modified prolactin receptor distributions in the POA and surrounding hypothalamic regions disconnect prolactin from parental care in brood parasitic cowbirds.

Differential sensitivity to estrogen-induced opsin expression in two poeciliid freshwater fish species.

The sensory system shapes an individual's perception of the world, including social interactions with conspecifics, habitat selection, predator detection, and foraging behavior. Sensory signaling can be modulated by steroid hormones, making these processes particularly vulnerable to environmental perturbations. Here we examine the influence of exogenous estrogen manipulation on the visual physiology of female western mosquitofish (Gambusia affinis) and sailfin mollies (Poecilia latipinna), two poeciliid species that inhabit freshwater environments across the southern United States. We conducted two experiments to address this aim. First, we exposed females from both species to a one-week dose response experiment with three treatments of waterborne ß-estradiol. Next, we conducted a one-week estrogen manipulation experiment with a waterborne estrogen (ß-Estradiol), a selective estrogen receptor modulator (tamoxifen), or combination estrogen and tamoxifen treatment. We used quantitative PCR (qPCR) to examine the expression of cone opsins (SWS1, SWS2b, SWS2a, Rh2, LWS), rhodopsin (Rh1), and steroid receptor genes (ARα, ARß, ERα, ERß2, GPER) in the eyes of individual females from each species. Results from the dose response experiment revealed estradiol-sensitivity in opsin (SWS2a, Rh2, Rh1) and androgen receptor (ARα, ARß) gene expression in mosquitofish females, but not sailfins. Meanwhile, our estrogen receptor modulation experiments revealed estrogen sensitivity in LWS opsin expression in both species, along with sensitivity in SWS1, SWS2b, and Rh2 opsins in mosquitofish. Comparisons of control females across experiments reveal species-level differences in opsin expression, with mosquitofish retinas dominated by short-wavelength sensitive opsins (SWS2b) and sailfins retinas dominated by medium- and long-wavelength sensitive opsins (Rh2 and LWS). Our research suggests that variation in exogenous levels of sex hormones within freshwater environments can modify the visual physiology of fishes in a species-specific manner.

Holding water steroid hormones in the African cichlid fish Pseudocrenilabrus multicolor victoriae.

Measuring hormone levels multiple times on the same individual across different life stages or treatments can facilitate our understanding of hormonal regulation of physiological and behavioral events. The conventional method of hormone measurement requires blood sampling, which is potentially lethal to small individuals. In fishes, there is an alternative non-invasive method of hormone measurement using the release of hormones across gill membranes from blood into holding water. Validation of this method is required to evaluate its application value to different species. In the present study we used the maternal mouth-brooding African cichlid fish, Pseudocrenilabrus multicolor victoriae to (i) investigate whether handling involved in using the holding water technique is a stressor by measuring excreted cortisol in male and female P. multicolor handled one or multiple times, (ii) validate use of this technique by quantifying the relationship between plasma and holding water measures of sex hormones in male P. multicolor, and (iii) demonstrate the biological relevance of this technique using excreted levels of sex hormones in female P. multicolor across different reproductive stages. Excreted cortisol and estradiol levels did not differ between fish handled one or more times, suggesting that the repeated sampling approach over the breeding cycle that we propose to use does not affect the excreted level of the hormone of interest. Measurements from plasma and holding water samples were positively related for both testosterone and estradiol, indicating that the holding water technique is a reliable index of plasma hormone levels. Excreted sex hormone levels varied with reproductive state, suggesting that the technique is a useful, non-invasive measure of sex hormone levels in P. multicolor.

The effect of hypoxia on sex hormones in an African cichlid Pseudocrenilabrus multicolor victoriae.

Human activities increase the occurrence of aquatic hypoxia (low dissolved oxygen) globally. In fishes, short term hypoxia impairs multiple stages of reproduction (e.g., behavior, hormones, development), but no studies have investigated a species that lives and reproduces under hypoxia. This study examines the effects of hypoxia on sex hormones in the mouth brooding African cichlid Pseudocrenilabrus multicolor victoriae. Non-invasive measures of testosterone and estradiol levels in females were collected across the reproductive cycle in the laboratory, and at the time of capture in the field. In the laboratory, hormone levels were higher during pre-brooding (T=1.06, E2=1.62pg/mL/h) than brooding (T=0.61, E2=0.34pg/mL/h) or post-brooding (T=0.53, E2=0.51pg/mL/h) phases, but did not differ between hypoxic (1.2±0.0mg/L) and normoxic (7.3±0.1mg/L) populations. In the field, females were sampled from one low and one high oxygen population in two regions in Uganda (Mpanga River, Nabugabo Region). In both regions, hypoxic populations exhibited higher levels of testosterone than well-oxygenated populations, although there was no population level difference in estradiol levels. Hypoxic sites were also characterized by a higher testosterone/estradiol ratio and a lower proportion of brooding females. These results provide field evidence of hypoxia-mediated endocrine disruption in a fish species that experiences lifelong hypoxia.