Both nitric oxide (NO) and serotonin (5HT) mediate swim acceleration in the marine mollusk, Clione limacina. In this study, we examine the role that the second messenger, cyclic guanosine monophosphate (cGMP), plays in mediating NO and 5HT-induced swim acceleration. We observed that the application of an analog of cGMP or an activator of soluble guanylyl cyclase (sGC) increased fictive locomotor speed recorded from Pd-7 interneurons of the animal’s locomotor central pattern generator. Moreover, inhibition of sGC decreased fictive locomotor speed. These results suggest that basal levels of cGMP are important for slow swimming and that increased production of cGMP mediates swim acceleration in Clione. Because NO has its effect through cGMP signaling and because we show herein that cGMP produces cellular changes in Clione swim interneurons that are consistent with cellular changes produced by 5HT application, we hypothesize that both NO and 5HT function via a common signal transduction pathway that involves cGMP. Rhapontigenin Our results show that cGMP mediates NO-induced but not 5HT-induced swim acceleration in Clione.While sexual dimorphism has long received special attention from biologists, derived monomorphism, the condition in which both males and females express similar derived features has been less well studied. Historically, the appearance of “male-like” features in females has been explained by the genetic correlation between the sexes. Recent work emphasizes the importance of studying the independent selective forces on both females and males to understand sexual dimorphism. Sexual dimorphism and derived monomorphism in the genus Aneides are examined in light of predictions of social selection. Aneides hardii shows the greatest degree of sexual dimorphism in snout-vent length and head width, with the other species of Aneides less sexually dimorphic. This reduced dimorphism, however, is not a return to an ancestral monomorphic state, but rather exemplifies derived monomorphism because females express traits that were limited in expression to males of ancestral species. Instead of calling these “male-typical” traits in females, I suggest the term “derived monomorphic” traits as these traits are typical in these females, and “derived monomorphic” can apply to both sexes. Increased attention to studying the patterns and ecological significance of derived monomorphism will shed light on the underlying selective forces, including sexual selection, on both females and males.Epidermal lipids serve as the primary barrier to cutaneous water loss (CWL) and play a significant role in water conservation and homeostasis. Previous studies have shown the correlation between increased aridity of habitats and the amount of epidermal lipids among species. Generally, increased amounts of epidermal lipids lower skin permeability. Species-specific differences in CWL and prey preferences between two sympatric snake species, the Northern Cottonmouth (Agkistrodon piscivorus) and the Eastern Copperhead (Agkistrodon contortrix), motivated us to question if prey-base can result in these observed species-specific differences in CWL. We experimentally controlled the diets for a captive colony of Northern Cottonmouths (A. piscivorus) by feeding either fish (Notemigonus crysoleucas) or mice (Mus musculus) to investigate if diet can affect the quantity and quality of epidermal lipids and the rates of CWL. Snakes fed mice gained consistently more mass, but diet treatments did not affect growth rate. We found no significant differences in quantitative lipid content or rates of CWL between diet treatments. An analysis for qualitative lipid content using infrared spectrophotometry also showed no diet effect, thus suggesting that lipid content and CWL are strong species-specific physiological performance traits not influenced by recent dietary history. While there is some evidence that epidermal permeability may be variable under certain environmental conditions (e.g., humidity), our findings show that diet has no effect and that a shift in prey preference may not influence or enhance physiological performance for decreasing CWL.The ultrastructure of the nictitating membrane in the little penguin Eudyptula minor was studied using both scanning and transmission electron microscopy to improve our understanding of the function of ocular adnexa in diving birds. Following euthanasia, eyes were enucleated and immersion fixed in Karnovsky’s fixative. The nictitating membrane and conjunctiva were embedded in araldite and semi- or ultra-thin sections were stained and photographed using compound and transmission electron microscopes, respectively. Ultrastructural dimensions were measured directly from digital photographs. Surface ultrastructure was examined using scanning electron microscopy. The transparent nictitating membrane consists of a dense stroma surrounded by epithelia on both the external (conjunctival) and internal (bulbar) surfaces. The conjunctival surface of the membrane near the leading edge is covered by microvilli, which transition to microplicae and finally to microridges in the periphery. Beneath the epithelial cells, there is a well-developed basement membrane. Scattered throughout this epithelium are a few goblet cells. The surface of the bulbar epithelium is covered by microvilli near the leading edge, which become denser peripherally. The stroma consists of densely-packed collagen fibrils, which are randomly oriented in bundles near the leading edge but are aligned in the same direction parallel with the epithelial and corneal surfaces and with the leading edge, when the membrane is extended. The ultrastructure of the nictitating membrane in the little penguin differs from other birds and its function is predominantly protective, while preserving clear vision in both water and air.Sound production in tiger moths (Erebidae Arctiinae) plays a role in natural selection. Some species use tymbal sounds as jamming signals avoiding bat predation. High duty cycle signals have the greatest efficacy in this regard. Tiger moth sounds can also be used for intraspecific communication. Little is known about the role of sound in the mating behavior of jamming species or the signal preferences underlying mate choice. We recorded sound production during the courtship of two high duty cycle arctiines, Bertholdia trigona and Carales arizonensis. We characterized variation in their acoustic signals, measured female preference for male signals that vary in duty cycle, and performed female choice experiments to determine the effect of male duty cycle on the acceptance of male mates. Although both species produced sound during courtship, the role of acoustic communication appears different between the species. Bertholdia trigona was acoustically active in all intraspecific interactions. Females preferred and ultimately mated with males that produced higher duty cycles.