Stacey L. Weiss

Pterin‐based ornamental coloration predicts yolk antioxidant levels in female striped plateau lizards (Sceloporus virgatus)

1. Maternal investment in egg quality can have important consequences for offspring fitness. For example, yolk antioxidants can affect embryonic development as well as juvenile and adult phenotype. Thus, females may be selected to advertise their yolk antioxidant deposition to discriminatory males via ornamental signals, perhaps depending on the reproductive costs associated with signal production. 2. Female striped plateau lizards (Sceloporus virgatus) develop pterin-based orange colour patches during the reproductive season that influence male behaviour and that are positively associated with the phenotypic quality of the female and her offspring. Here, we assessed one potential developmental mechanism underlying the relationship between offspring quality and female ornamentation in S. virgatus, by examining the relationship between ornament expression and yolk antioxidant levels. 3. As expected, concentrations of the yolk antioxidants vitamin A, vitamin E and carotenoids (lutein and zeaxanthin) were strongly positively intercorrelated. Eggs from larger clutches had fewer antioxidants than eggs from smaller clutches, suggesting that females may be limited in antioxidant availability or use. Fertilized and unfertilized eggs did not differ in yolk antioxidant levels. 4. The size of a females ornament was positively related to both the concentration and total amount of yolk antioxidants, and ornament colour was positively related to yolk antioxidant concentration. Thus, in S. virgatus, female ornaments may advertise egg quality. In addition, these data suggest that more ornamented females may produce higher-quality offspring, in part because their eggs contain more antioxidants. As the colour ornament of interest is derived from pterins, not carotenoids, direct resource trade-offs between ornaments and eggs may be eliminated, reducing reproductive costs associated with signalling. 5. This is the first example of a positive relationship between female ornamentation and yolk antioxidants in reptiles and may indicate the general importance of these patterns in oviparous vertebrates.

Steroid hormone mediation of limbic brain plasticity and aggression in free-living tree lizards, Urosaurus ornatus

The neural mechanisms by which steroid hormones regulate aggression are unclear. Although testosterone and its metabolites are involved in both the regulation of aggression and the maintenance of neural morphology, it is unknown whether these changes are functionally related. We addressed the hypothesis that parallel changes in steroid levels and brain volumes are involved in the regulation of adult aggression. We examined the relationships between seasonal hormone changes, aggressive behavior, and the volumes of limbic brain regions in free-living male and female tree lizards (Urosaurus ornatus). The brain nuclei that we examined included the lateral septum (LS), preoptic area (POA), amygdala (AMY), and ventromedial hypothalamus (VMH). We showed that the volumes of the POA and AMY in males and the POA in females vary with season. However, reproductive state (and thus hormonal state) was incompletely predictive of these seasonal changes in males and completely unrelated to changes in females. We also detected male-biased dimorphisms in volume of the POA, AMY, and a dorsolateral subnucleus of the VMH but did not detect a dimorphism between alternate male morphological phenotypes. Finally, we showed that circulating testosterone levels were higher in males exhibiting higher frequency and intensity of aggressive display to a conspecific, though brain nucleus volumes were unrelated to behavior. Our findings fail to support our hypothesis and suggest instead that plasma testosterone level covaries with aggression level and in a limited capacity with brain nucleus volumes but that these are largely unrelated relationships.

Steroid hormones alter neuroanatomy and aggression independently in the tree lizard

Steroid hormones effect changes in both neuroanatomy and aggressive behavior in animals of various taxa. However, whether changes in neuroanatomy directly underlie changes in aggression is unknown. We investigate this relationship among steroid hormones, neuroanatomy, and aggression in a free-living vertebrate with a relatively simple nervous system, the tree lizard (Urosaurus ornatus). Weiss and Moore [1] manipulated testosterone and progesterone levels in adult male tree lizards and found that both hormones facilitated aggressive behavior toward a conspecific. In this study, we examined the brains of a subset of these animals to determine whether changes in limbic morphology were associated with hormone-induced changes in aggressive behavior. Specifically, we tested the hypothesis that testosterone and/or progesterone cause changes in neural morphology that are necessary for the expression of testosterones effects on aggressive behavior. We found that both hormones increased aggression; however, only testosterone induced changes in neuroanatomy. Testosterone increased the size of both the amygdala and nucleus sphericus. However, we could detect no individual correlations between neuroanatomy and aggression levels suggesting that the observed large-scale changes in neuroanatomy are not precisely reflective of changes in mechanisms underlying aggression.

Testosterone and social context affect singing behavior but not song control region volumes in adult male songbirds in the fall.

Testosterone (T) induces singing behavior and mediates changes in the sizes and neuroanatomical characteristics of brain regions controlling singing behavior (song control regions, SCRs) in songbirds. These effects may require the enzymatic conversion of T into androgenic and estrogenic metabolites by brain tissues and can be modulated by factors such as season and social context. Testosterone administration to adult male House Finches, Carpodacus mexicanus, in the spring increases the size of their SCRs. Here, we used males of this species to investigate effects of T and T metabolism on brain morphology and singing behavior in the fall. Birds received Silastic capsules containing androgens, estrogens, and/or inhibitors of androgenic action or estrogen synthesis to determine effects of these hormones on song rates and SCR volumes. We also manipulated the social environment by changing the number of birds in visual contact with each other. Testosterone treatment stimulated singing behavior in finches held in small, visually isolated groups and exposed to song playbacks. However, administration of T or T metabolites did not increase SCR sizes. The data suggest that photoperiodic condition and social context may modulate the effects of steroids on SCRs and singing behavior.

Sex-specific asymmetry within the cloacal microbiota of the striped plateau lizard, Sceloporus virgatus

The structure and diversity of microbial communities in wild vertebrate populations remain poorly understood, but are expected to have important consequences for individual survival and reproductive success. For instance, recent work has demonstrated that cloacal microbe assemblages of wild birds are related to the phenotypic quality of the host. To contribute to this field of study, we examined the composition and diversity of the cloacal microbiota of free-ranging striped plateau lizards, Sceloporus virgatus, using 16s rRNA-based culture independent techniques. Our dataset, generated from cloacal swabs of six males and six females, and based on twenty five 16s rRNA clones from each sample, revealed (i) low overall microbial diversity, (ii) a striking sex asymmetry in microbial community composition with males displaying cloacal microbiota more typical of gastrointestinal residents found in other organisms, while females display only gammaproteobacterial phylotypes, (iii) a significant sex difference in microbial community structure, with females having significantly lower microbial diversity and richness than do males, and (iv) that the diversity of the female microbial community is negatively correlated to her ectoparasitic mite load. It is not yet clear if the female-specific paucity of cloacal microbial diversity is due to host function or microbe-microbe interactions, or whether the relationship to female mite load is causal, however these findings are expected to have relevance to the species’ life history and ecology. Although the diversity of microbiota from humans, mice, birds, zebrafish, and invertebrates is widely investigated, this is one of only a few reports in the literature describing the cloacal microbiota of a wild vertebrate, and is perhaps the first report for wild reptiles that utilizes culture-independent techniques.

Effect of stress on female-specific ornamentation

SUMMARY Signal honesty is theorized to be maintained by condition-dependent trait expression. However, the mechanisms mediating the condition dependence of sexually selected traits are often unknown. New work suggests that elevated glucocorticoid levels during physiological stress may play a role in maintaining signal honesty. Here, we experimentally examine the effect of both chronic and acute stress on the expression of the condition-dependent ornamentation of female striped plateau lizards, Sceloporus virgatus. Females were stressed either chronically via corticosterone implants or relatively acutely via autotomy, were sham manipulated or were left unmanipulated. Both stressors resulted in elevations in corticosterone within physiologically relevant levels, though the implants resulted in significantly higher levels than did autotomy. Corticosterone-implanted females were less likely to produce a clutch of eggs, but those individuals that did reproduce had reproductive output similar to that of females from other treatment groups. Compared with females in other groups, the corticosterone-implanted females tended to develop smaller ornaments that had less UV and orange-to-red wavelength reflectance relative to medium wavelength reflectance. The sex steroid hormones testosterone and estradiol were correlated to corticosterone levels, but did not appear to underlie the effect on ornament expression; of the steroids measured, only corticosterone levels were negatively related to ornament size and coloration. Thus, the condition-dependent ornamentation of female lizards is sensitive to chronic elevations in stress hormones, supporting their importance in the maintenance of signal honesty.

Ornamentation, age, and survival of female striped plateau lizards, Sceloporus virgatus

Individuals with greater expression of secondary sexual traits are often older and have higher survivorship than individuals with lower expression; if so, assessment of such indicator traits may provide genetic and/or direct benefits to potential mates. I examined the relationship between ornament expression, age, and survival in the striped plateau lizard, Sceloporus virgatus, a species with female-specific ornamentation that honestly signals reproductive quality. I followed a group of females from 2008 to 2013, examined ornament color and size as females aged, and compared ornamentation of survivors versus non-survivors. In addition, I explored whether other (non-ornamental) phenotypic characters predicted survival. I found that peak ornament expression (both color and size) of individual females changed year to year but appeared to be a weak signal of age due to high among-female variation in ornament expression that occurred independent of age and a non-linear pattern of change for ornament color. However, both absolute and relative ornament size did increase significantly as an individual aged and therefore may provide some age-related information such as reproductive investment, which is expected to increase as residual reproductive value declines with age. Individual survival was unrelated to peak ornament expression and to other phenotypic variables measured, providing no support for the ornament as a viability indicator and suggesting that individual survival prospects are affected by stochastic and environmental factors.

Male mate choice as differential investment in contest competition is affected by female ornament expression

Abstract High male mating effort and high variation in female quality select for male mate choice, which may be expressed as differential investment of reproductive effort based on female value. Male reproductive effort includes investment in direct contest competition with rival males for access to females, yet variation in male–male contest behavior is rarely examined in the context of male mate choice. We examine such male response to variation in female body size, reproductive state, and female-specific ornamentation in the striped plateau lizard, Sceloporus virgatus. We housed lizards in trios of 2 size-matched males and one female for 5 days, such that all 3 lizards were physically isolated and the males could see the female but not each other. We then placed males simultaneously into the female’s cage and scored the interaction. Male–male aggression was not significantly affected by female body size, reproductive state, nor ornament color, but was influenced by ornament size which reliably signals the phenotypic quality of the female and her offspring. In the presence of larger-ornamented females, males engaged in more male–male aggressive display behavior more quickly, and performed fewer high-intensity contact behaviors but were equally likely to escalate to this riskier level of fighting. Our data suggest that males adjust their energetic investment during intrasexual competitive interactions in response to variation in the contested female which, assuming males gain direct or indirect benefits from their strategic allocation of reproductive effort, fits the modern understanding of male mate choice.

Skin lipids of the striped plateau lizard (Sceloporus virgatus) correlate with female receptivity and reproductive quality alongside visual ornaments

Sex pheromones can perform a variety of functions ranging from revealing the location of suitable mates to being honest signals of mate quality, and they are used in the mate selection process by many species of reptile. In this study, we determined whether the skin lipids of female striped plateau lizards (Sceloporus virgatus) can predict the reproductive quality of females, thereby having the potential to serve as pheromones. Using gas chromatography/mass spectrometry, we identified 17 compounds present in skin lipids of female lizards. Using principal component analysis to compare the skin lipid profile of receptive and non-receptive females, we determined that an uncharacterized compound may allow for chemical identification of receptive mates. We also compared extracted principal components to measures of female fitness and reproductive qualities and found that the level of two 18 carbon fatty acids present in a female’s skin lipids may indicate her clutch size. Finally, we compared the information content of the skin lipids to that of female-specific color ornaments to assess whether chemical and visual cues transmit different information or not. We found that the chroma of a female’s orange throat patch is also related to her clutch size, suggesting that chemical signals may reinforce the information communicated by visual ornamentation in this species which would support the “backup signals” hypothesis for multiple signals.

Do Small Classes in Higher Education Reduce Performance Gaps in STEM

Performance gaps in science are well documented, and an examination of underlying mechanisms that lead to underperformance and attrition of women and underrepresented minorities (URM) may offer highly targeted means to promote such students. Determining factors that influence academic performance may provide a basis for improved pedagogy and policy development at the university level. We examined the impact of class size on students in 17 biology courses at four universities. Although the female students underperformed on high-stakes exams compared with the men as class size increased, the women received higher scores than the men on nonexam assessments. The URM students underperformed across grade measures compared with the majority students regardless of class size, suggesting that other characteristics of the education environment affect learning. Student enrollment is expected to increase precipitously in the next decade, underscoring the need to prioritize individual student potential rather than yield to budget constraints when considering equitable pedagogy and caps on classroom sizes.