Seasonal plasticity in the copulatory neuromuscular system of green anole lizards: a role for testosterone in muscle but not motoneuron morphology.
The copulatory system of green anoles is highly sexually dimorphic. Males possess bilateral copulatory organs called hemipenes, each independently controlled by two muscles: the transversus penis (TPN) and retractor penis magnus (RPM). The TPN everts the hemipene through the cloaca and the RPM retracts it. Adult females do not possess hemipenes or either of these two muscles. The spinal nucleus projecting to the TPN and RPM contains more and larger motoneurons in males than females. Because anoles breed seasonally, two experiments were designed to test whether adult copulatory morphology varies with environmental condition, and if so, whether the effect is mediated by testicular androgens. Three groups of adult males were used in each experiment: males from breeding environmental conditions with reproductive testes (BS); males in breeding conditions with regressed testes (BS-X); and males in nonbreeding conditions with regressed testes (NBS). Experiment 1 compared gonadally intact males and Experiment 2 compared castrated males treated with either testosterone (T) or an empty implant. In both experiments, copulatory and control motoneurons appeared smaller in NBS males, but T did not affect their size. In contrast, while hemipene and RPM muscle fiber size were not plastic across season in gonadally intact males, T in castrated males significantly increased both measures under BS and BS-X, but not NBS, conditions. These results demonstrate that neuron soma size might change on a general level and environmental cues can mediate T-induced changes in peripheral structures, suggesting that plasticity across copulatory system components is regulated by different mechanisms.
Holmes
Melissa M
MM
Michigan State University, East Lansing, 48824 USA. holmes22@msu.edu
Wade
Juli
J
D000818:Animals; D002369:Castration; D003307:Copulation / Q000502:physiology*; D005837:Genitalia, Male / Q000033:anatomy & histology / Q000187:drug effects; D008116:Lizards / Q000502:physiology*; D008297:Male; D009046:Motor Neurons / Q000166:cytology* / Q000187:drug effects; D009132:Muscles / Q000033:anatomy & histology / Q000187:drug effects / Q000294:innervation; D009473:Neuronal Plasticity / Q000502:physiology*; D012621:Seasons; D013045:Species Specificity; D013739:Testosterone / Q000378:metabolism* / Q000494:pharmacology
D013739:Testosterone