Nancy L. Staub

Hormones, Sex Accessory Structures, and Secondary Sexual Characteristics in Amphibians

SUMMARY Gonadal steroid hormones, particularly testosterone (T) and related androgens, are important in the development and seasonal variation of sexually dimorphic organs. Other hormones, such as prolactin, have been found to be necessary in conjunction with gonadalsteroids forthefull structuraldevelopmentandfunction of some sex accessory structures (e.g., oviductal and cloacal gland secretions) and secondary sexual characteristics (e.g., genial glands and skin glands of newts). Thyroid hormones work synergistically with prolactin and T in hypertrophy of the tail fin and nuptial pads of American newts (e.g.,Notophthalmus viridescens), whereas oxytocin antagonizes the influence of prolactin. In the Japanese newt (Cynops pyrrhogaster), however, estrogens block the action of prolactin on increasing tail height, explaining the sexual differences in tail morphology. Arginine vasotocin (AVT) has been shown to stimulate labor in the viviparous salamandrid Salamandra salamandra, corticosterone influences the development of salamander cloacal glands, and prostaglandin PGF2a causes the release of sperm from the salamander spermatheca by triggering contraction of the myoepithelium. The sex accessory structures of amphibians are the genital ducts and derivatives of these structures. The secondary sexual characteristics are all of the differences between the sexes due to sexual maturation other than those connected with the gonads and their ducts. In this chapter, we review the effects of hormones on development, anatomy, function, and seasonal variation of the sex accessory structures and secondary sexual characteristics of amphibians. We introduce the more general term, secondary characteristics, to refer to non-sexually dimorphic traits that arise at sexual maturity. A list of the structures considered is presented in Table 5.1 and we will report on representative studies related to these organs.

Scaling Up: Adapting a Phage-Hunting Course to Increase Participation of First-Year Students in Research

To offer a research experience to all students taking introductory biology, the authors modified the traditional two-semester Science Education Alliance Phage Hunters Advancing Genomics and Evolutionary Science (SEA-PHAGES) course by streamlining the first semester Phage Discovery lab and integrating research from the second SEA-PHAGES semester into other courses in the biology curriculum.

The Age of Plethodontid Salamanders: A Short Review on Longevity

It is difficult to determine how long salamanders live in the wild. The maximum age estimates using skeletochronology tend to be lower than estimates based on recaptures and size-frequency studies. This discrepancy between techniques suggests it may well be difficult to discern the lines of arrested growth in bones when salamanders are old and their growth rate very low. I review techniques used to estimate longevity, compare age estimates from field (recapture and size frequency comparisons) studies with those from skeletochronology, review growth models, and suggest future work that specifically addresses salamander longevity. Based on observations from captive animals, plethodontids can live a long time (e.g., 36 years). A better understanding of natural longevity is important for understanding the actual age structure of populations and for conservation efforts.

Age, Sexual Dimorphism, and Growth Rates in the Black Salamander, Aneides flavipunctatus (Plethodontidae)

To understand how rates of growth interact to result in sexual dimorphism in the Black salamander, Aneides flavipunctatus, I conducted a mark–recapture study in Mendocino County, California. Five hundred captures (420 unique animals plus 80 recaptures over four occasions) were measured (body length, head width, head length) and released. Adult males and females are not sexually dimorphic in body length, but are dimorphic in head width; males have wider heads compared to females. From 80 recaptures, growth rates were determined for body length and head size. As expected, juveniles grow faster relative to adults; growth rates decrease as body size increases. Adult males and females have similar growth rates of body length. Males and juveniles have greater head-width growth rates compared to adult females. Head size dimorphism in A. flavipunctatus is a result of a higher head growth rate in males at sexual maturity relative to females. Because body growth rates are not significantly different between adult males and females, adult salamanders of similar size are of similar age. The Von Bertalanffy growth model fit to the mark–recapture growth data conservatively predicts that salamanders of 79 mm snout–vent length are 18 years old. Because of certain assumptions of the model, the oldest salamanders in the population are more likely to be up to 25–30 years old.

A dorsal tail tubercle containing hypertrophied granular and mucous glands is present in female Salamandra luschani (salamandridae)

The salamander Salamandra luschani is characterized by a tubercle, well documented in males, projecting from the dorsal surface of the tail base. To determine whether females have a tubercle containing modified secretory glands, we surveyed museum specimens and conducted a histological investigation of the dorsal tail base region. Our results show that most mature females do have a tubercle in the dorsal tail base region and even nontubercle females have hypertrophied glands in this area. Both granular and mucous glands within the tubercle are hypertrophied. The tubercle is smaller in females than in males. Underlying the hypertrophied granular glands in the tubercle region of some females are very large, previously undocumented, exocrine glands.

The Presence of Caudal Courtship-Like Glands in Male and Female Ouachita Dusky Salamanders (Desmognathus brimleyorum)

Abstract Plethodontid salamander courtship is an elaborate yet conserved set of behaviors that involve many different sensory signals. Exocrine glands in the skin produce pheromones that facilitate courtship. These glands, known as courtship glands, are described as being sexually dimorphic, only present in males. Thus, we were surprised to discover glands in female Desmognathus brimleyorum that are histochemically and morphologically similar to male courtship glands. These glands are on the dorsal tail base and are sexually dimorphic in size; male glands are larger than those in females. Granular and mucous glands are not sexually dimorphic. The function of these glands in females is unknown, but could be involved in pheromone delivery to the male during courtship. Glands that are histochemically similar to courtship glands are present on the ventral tail surface in males and females as well. This is the first description of dorsal courtship-like glands in females and of ventral courtship-like glands in male and female D. brimleyorum.

A Description of the Skin Glands and Cloacal Morphology of the Plethodontid Salamander Karsenia koreana

The skin glands and cloacal morphology of the Korean crevice salamander, Karsenia koreana, were similar to those of other plethodontids. The skin contained mucous, granular, and modified granular glands in varying frequencies and sizes. Males had sexually dimorphic glands in the skin of the chin (mental glands) and the dorsal tail base (caudal courtship glands). On the ventral surface of the tail base, modified granular glands were sexually dimorphic in size, with male glands larger than those in females. The cloacal glands in males, as in other plethodontids, consisted of four eosinophilic gland clusters (dorsal pelvic glands, lateral pelvic glands, caudal pelvic glands, and vent glands) and three basophilic glands (anterior ventral glands, posterior ventral glands, and Kingsburys glands). In females, the only cloacal gland was the spermatheca, which, as in other plethodontids, was a compound tubulo-alveolar gland in the roof of the cloaca.

Multi-Institutional, Multidisciplinary Study of the Impact of Course-Based Research Experiences

Numerous national reports have called for reforming laboratory courses so that all students experience the research process. In response, many course-based research experiences (CREs) have been developed and implemented. Research on the impact of these CREs suggests that student benefits can be similar to those of traditional apprentice-model research experiences. However, most assessments of CREs have been in individual courses at individual institutions or across institutions using the same CRE model. Furthermore, which structures and components of CREs result in the greatest student gains is unknown. We explored the impact of different CRE models in different contexts on student self-reported gains in understanding, skills, and professional development using the Classroom Undergraduate Research Experience (CURE) survey. Our analysis included 49 courses developed and taught at seven diverse institutions. Overall, students reported greater gains for all benefits when compared with the reported national means for the Survey of Undergraduate Research Experiences (SURE). Two aspects of these CREs were associated with greater student gains: 1) CREs that were the focus of the entire course or that more fully integrated modules within a traditional laboratory and 2) CREs that had a higher degree of student input and results that were unknown to both students and faculty.

David Burton Wake

D AVID BURTON WAKE lives the life of the mind. Well, the mind and the field. His work is intellectually sharp and has deep roots in the natural history of the salamanders he studies. In spite of living in large cities and working at large universities most of his life, Dave is basically a small town kind of guy. He fostered within his lab group that small town atmosphere—where everyone knows one another and will help each other out as needed. Through his decades-long research focus on a single taxon, he and his ‘‘small town’’ uncovered fundamental principles of how organisms develop and function, and how populations of organisms evolve.

Science in Action! Outreach Program Promotes Confidence in Teaching Science

Abstract Leading scientists recognize the need to be proactive about educational reform. To address some of the challenges of teaching K-6 science, our outreach program, Science in Action! (SIA!), pairs undergraduates with K-6 classrooms to do hands-on, inquiry-based science. Our goal is to increase science literacy in our community through developing the science understanding and teaching skills of pre-service teachers, recruit more STEM majors into teaching careers, and promote enthusiasm and curiosity in the science K-6 classroom. We describe Science in Action! and describe the effect participation in the program has on undergraduates. In particular, we asked how participation effects pre-service elementary school teachers, who generally have a limited science background, and science majors, who are in the process of deciding a future career path. Pre-service teachers reported that their participation in SIA! deepened both their understanding of the scientific method and science content, as well as increased their confidence in being able to teach science. The number of science majors seriously considering a teaching career increased significantly after participating in Science in Action!