Increased Androgenic Sensitivity in the Hind Limb Muscular System Marks the Evolution of a Derived Gestural Display

Physical gestures are prominent features of many species’ multi- modal displays, yet how evolution incorporates body and leg movements into animal signaling repertoires is unclear. Andro- genic hormones modulate the production of reproductive signals and sexual motor skills in many vertebrates; therefore, one possi- bility is that selection for physical signals drives the evolution of androgenic sensitivity in select neuromotor pathways. We exam- ined this issue in the Bornean rock frog (Staurois parvus, family: Ranidae). Males court females and compete with rivals by per- forming both vocalizations and hind limb gestural signals, called “foot flags.” Foot flagging is a derived display that emerged in the ranids after vocal signaling. Here, we show that administration of testosterone (T) increases foot flagging behavior under seminatural conditions. Moreover, using quantitative PCR, we also find that adult male S. parvus maintain a unique androgenic phenotype, in which androgen receptor (AR) in the hind limb musculature is expressed at levels ∼10× greater than in two other anuran species, which do not produce foot flags (Rana pipiens and Xenopus laevis). Finally, because males of all three of these species solicit mates with calls, we accordingly detect no differences in AR expression in the vocal apparatus (larynx) among taxa. The results show that foot flagging is an androgen-dependent gestural signal, and its emergence is associated with increased androgenic sensitivity within the hind limb musculature. Selection for this novel gestural signal may therefore drive the evolution of increased AR expres- sion in key muscles that control signal production to support adap- tive motor performance

A Common Endocrine Signature Marks the Convergent Evolution of an Elaborate Dance Display in Frogs

Unrelated species often evolve similar phenotypic solutions to the same environmental problem, a phenomenon known as convergent evolution. But how do these common traits arise? We address this question from a physiological perspective by assessing how convergence of an elaborate gestural display in frogs (foot-flagging) is linked to changes in the androgenic hormone systems that underlie it. We show that the emergence of this rare display in unrelated anuran taxa is marked by a robust increase in the expression of androgen receptor (AR) messenger RNA in the musculature that actuates leg and foot movements, but we find no evidence of changes in the abundance of AR expression in these frogs’ central nervous systems. Meanwhile, the magnitude of the evolutionary change in muscular AR and its association with the origin of foot-flagging differ among clades, suggesting that these variables evolve together in a mosaic fashion. Finally, while gestural displays do differ between species, variation in the complexity of a foot-flagging routine does not predict differences in muscular AR. Altogether, these findings suggest that androgen-muscle interactions provide a conduit for convergence in sexual display behavior, potentially providing a path of least resistance for the evolution of motor performance

Supplementary Data File from Macroevolutionary patterning of woodpecker drums reveals how sexual selection elaborates signals under constraint

Drum and morphological dat

Appendix A from Macroevolutionary patterning of woodpecker drums reveals how sexual selection elaborates signals under constraint

Supplementary methods and information regarding the use of quantile regression in behavioral analyses

Supplementary Recording List from Macroevolutionary patterning of woodpecker drums reveals how sexual selection elaborates signals under constraint

Sexual selection drives elaboration in animal displays used for competition and courtship, but this process is opposed by morphological constraints on signal design. How do interactions between selection and constraint shape display evolution? One possibility is that sexual selection continues exaggeration under constraint by operating differentially on each signal component in complex, modular displays. This is seldom studied on a phylogenetic scale, but we address the issue herein by studying macroevolutionary patterning of woodpecker drum displays. These territorial displays are produced when an individual rapidly hits its bill on a hard surface, and drums vary across species in the number of beats included (length) and the rate of drumbeat production (speed). We report that species body size limits drum speed, but not drum length. As a result of this biomechanical constraint, there is less standing variation in speed than length. We also uncover a positive relationship between sexual size dimorphism and the unconstrained trait (length), but with no effect on speed. This suggests that when morphology limits the exaggeration of one component, sexual selection instead exaggerates the unconstrained trait. Modular displays therefore provide the basis for selection to find novel routes to phenotypic elaboration after previous ones are closed

Sex differences in neuromuscular androgen receptor expression and sociosexual behavior in a sex changing fish

<div><p>Androgen signaling, via receptor binding, is critical for regulating the physiological and morphological foundations of male-typical reproductive behavior in vertebrates. Muscles essential for male courtship behavior and copulation are highly sensitive to androgens. Differences in the distribution and density of the androgen receptor (AR) are important for maintaining dimorphic musculature and thus may provide for anatomical identification of sexually selected traits. In <i>Lythrypnus dalli</i>, a bi-directional hermaphroditic teleost fish, both sexes produce agonistic approach displays, but reproductive behavior is sexually dimorphic. The male-specific courtship behavior is characterized by rapid jerky movements (involving dorsal fin erection) towards a female or around their nest. Activation of the supracarinalis muscle is involved in dorsal fin contributions to both agonistic and sociosexual behavior in other fishes, suggesting that differences in goby sexual behavior may be reflected in sexual dimorphism in AR signaling in this muscle. We examined sex differences in the local distribution of AR in supracarinalis muscle and spinal cord. Our results demonstrate that males do express more AR in the supracarinalis muscle relative to females, but there was no sex difference in the number of spinal motoneurons expressing AR. Interestingly, AR expression in the supracarinalis muscle was also related to rates of sociosexual behavior in males, providing evidence that sexual selection may influence muscle androgenic sensitivity to enhance display vigor. Sex differences in the distribution and number of cells expressing AR in the supracarinalis muscle may underlie the expression of dimorphic behaviors in <i>L</i>. <i>dalli</i>.</p></div

Immunolocalization of spinal cord androgen receptor (AR) expression between the sexes and differences in expression between the sexes in the ventral and dorsal horn of the spinal cord.

<p>Representative AR staining in the dorsal and ventral horn of male (n = 12) (<b>A</b>) and female (n = 8) (<b>B</b>) <i>L</i>. <i>dalli</i>. Mean (±SEM) AR staining intensity within the dorsal and ventral horns of the spinal cord in males and females (<b>C</b>). DH = dorsal horn, VH = ventral horns.</p

Immunolocalization of androgen receptor (AR) expression between sexes in different muscle types.

<p>Representative AR staining within the supracarinalis muscle of males (<b>A</b>) and females (<b>B</b>), and the epaxial and hypaxial muscles of males (n = 12) (<b>C/E</b>) and females (n = 8) (<b>D/F</b>) respectively. The mean (±SEM) number of AR positive cells within the supracarinalis, epaxial, and hypaxial muscles in males and females (<b>G</b>). All images were captured under a 40x objective. Scale bar = 50 μm *** denotes a significant difference at p < 0.001.</p

Location and size of the supracarinalis muscle in <i>L</i>. <i>dalli</i>.

<p>Illustration of where the supracarinalis muscle is located (shown in red) and relative area sectioned in this study to assess receptor expression (<b>A</b>). Hemotoxylin and eosin stained cross section showing the exact location of the supracarinalis muscle relative to other muscles and peripheral tissues (<b>B</b>). Mean (±SEM) relative supracarinalis muscles size (muscle area (μm²) / standard length (mm) in male (n = 10) and female (n = 7) <i>L</i>. <i>dalli</i> (<b>C</b>).</p