Sex-specific effects of testosterone on vocal output in a tropical suboscine bird

Systems biology as a framework to understand the physiological and endocrine bases of behavior and its evolution-From concepts to a case study in birds

Organismal behavior, with its tremendous complexity and diversity, is generated by numerous physiological systems acting in coordination. Understanding how these systems evolve to support differences in behavior within and among species is a longstanding goal in biology that has captured the imagination of researchers who work on a multitude of taxa, including humans. Of particular importance are the physiological determinants of behavioral evolution, which are sometimes overlooked because we lack a robust conceptual framework to study mechanisms underlying adaptation and diversification of behavior. Here, we discuss a framework for such an analysis that applies a "systems view" to our understanding of behavioral control. This approach involves linking separate models that consider behavior and physiology as their own networks into a singular vertically integrated behavioral control system. In doing so, hormones commonly stand out as the links, or edges, among nodes within this system. To ground our discussion, we focus on studies of manakins (Pipridae), a family of Neotropical birds. These species have numerous physiological and endocrine specializations that support their elaborate reproductive displays. As a result, manakins provide a useful example to help imagine and visualize the way systems concepts can inform our appreciation of behavioral evolution. In particular, manakins help clarify how connectedness among physiological systems-which is maintained through endocrine signaling-potentiate and/or constrain the evolution of complex behavior to yield behavioral differences across taxa. Ultimately, we hope this review will continue to stimulate thought, discussion, and the emergence of research focused on integrated phenotypes in behavioral ecology and endocrinology.

An investigation of syrinx morphometry and sound frequency association during the chirping period in lovebirds ( Agapornis fischeri)

Background: In the issue of biodiversity, the domestication of birds as pets and trade animals requires special attention as a conservation effort. Lovebirds ( Agapornis fischeri) are popular birds worldwide, due to their varied ornamentation and melodic chirping sound. Syrinx structure is suspected to be the main source of sound production during the chirping period. This study aimed to investigate syrinx morphometry and its correlation with sound frequency produced in lovebirds. Methods: A total of 24 lovebirds of different ages and gender were investigated. Polymerase chain reaction method was performed to determine lovebird gender, meanwhile bird age was identified based on post-hatch recordings at the breeding farm. Thus, we enrolled male (n=12) and female (n=12) lovebirds aged 2 (n=4), 3 (n=4), and 4 (n=4) months in the investigation group, respectively. Fast Fourier Transform (FFT) was performed to evaluate sound frequency during chirping period. Then, syrinx morphometry was identified using a topographic approach and methylene blue staining. Each variable was evaluated with Image J software and vernier caliper. Results: Based on a topographical approach, we reported the general cartilage structure of the tracheosyringeal, bronchosyringeal, paired protrusions, tracheolateral muscles, sternotracheal muscles, and syringeal muscles in lovebird syrinx. In particular, the tympaniform membranes lateral lead a crucial role in modulating the frequency of male lovebirds more significantly (p=0,009) compared to female. On the other hand, the tympaniform membranes lateral dexter (p=0,02) and sinister (p=0,05) in females showed wider compared to male. We also reported a negative correlation between sound frequency compared to tympaniform membranes lateral dexter (y = -913,56x + 6770,8) and sinister (y = -706,16x + 5736). Conclusions: It can be concluded that the tympaniform membranes lateral produced the lovebirds' primary sound. The sound frequency of male lovebirds was higher compared to female, however negatively correlated with the area of tympaniform membranes lateral.

Activational vs. organizational effects of sex steroids and their role in the evolution of reproductive behavior: Looking to foot-flagging frogs and beyond

Sex steroids play an important role in regulation of the vertebrate reproductive phenotype. This is because sex steroids not only activate sexual behaviors that mediate copulation, courtship, and aggression, but they also help guide the development of neural and muscular systems that underlie these traits. Many biologists have therefore described the effects of sex steroid action on reproductive behavior as both "activational" and "organizational," respectively. Here, we focus on these phenomena from an evolutionary standpoint, highlighting that we know relatively little about the way that organizational effects evolve in the natural world to support the adaptation and diversification of reproductive behavior. We first review the evidence that such effects do in fact evolve to mediate the evolution of sexual behavior. We then introduce an emerging animal model - the foot-flagging frog, Staurois parvus - that will be useful to study how sex hormones shape neuromotor development necessary for sexual displays. The foot flag is nothing more than a waving display that males use to compete for access to female mates, and thus the neural circuits that control its production are likely laid down when limb control systems arise during the developmental transition from tadpole to frog. We provide data that highlights how sex steroids might organize foot-flagging behavior through its putative underlying mechanisms. Overall, we anticipate that future studies of foot-flagging frogs will open a powerful window from which to see how sex steroids influence the neuromotor systems to help germinate circuits that drive signaling behavior. In this way, our aim is to bring attention to the important frontier of endocrinological regulation of evolutionary developmental biology (endo-evo-devo) and its relationship to behavior.

Behavioral Sex Differences and Hormonal Control in a Bird with an Elaborate Courtship Display

Gonadal hormones can activate performance of reproductive behavior in adult animals, but also organize sex-specific neural circuits developmentally. Few studies have examined the hormonal basis of sex differences in the performance of elaborate, physically complex and energetic male courtship displays. Here we describe our studies over more than 20 years examining sex difference and hormonal control of courtship in Golden-collared manakins (Manacus vitellinus) of Panamaian rainforests. Our recent studies of birds studied in an artificial "lek" in a rainforest aviary provide many new insights. Wild and captive males and females differ markedly in their performance of male-typical behaviors. Testosterone (T) treatment augments performance of virtually all of these behaviors in juvenile males with low levels of circulating T. By contrast, T-treatment of females (with low circulating T) either failed to activate some behaviors or activated male behaviors weakly or strongly. These results are discussed within a framework of our appreciation for hormonal vs genetic basis for sex differences in behavior with speculation about the neural mechanisms producing these patterns of hormonal activation.

Neuroendocrinology of Sex-Role Reversal

Females of some species are considered sex-role reversed, meaning that they face stronger competition for mates compared to males. While much attention has been paid to behavioral and morphological patterns associated with sex-role reversal, less is known about its physiological regulation. Here, we evaluate hypotheses relating to the neuroendocrine basis of sex-role reversal. We refute the most widely tested activational hypothesis for sex differences in androgen secretion; sex-role reversed females do not have higher levels of androgens in circulation than males. However, we find some evidence that the effects of androgens may be sex-specific; circulating androgen levels correlate with some competitive phenotypes in sex-role reversed females. We also review evidence that sex-role reversed females have higher tissue-specific sensitivity to androgens than males, at least in some species and tissues. Organizational effects may explain these relationships, considering that early exposure to sex steroids can shape later sensitivity to hormones, often in sex-specific ways. Moving forward, experimental and correlative studies on the ontogeny and expression of sex-role reversal will further clarify the mechanisms that generate sex-specific behaviors and sex roles.