Universiẗat, Diss., 2004--Bremen.

Terrestrial salamanders of the genus Plethodon are among many vertebrates possessing both main olfactory and vomeronasal systems, which the Volatility Theory posits are for detection of volatile and soluble olfactory cues, respectively. Further recent work showing a high amount of convergence between the two olfactory subsystems at the level of the central nervous system suggests complementary or overlapping roles for them. This study examined the use of the olfactory subsystems in prey detection from the perspectives of behaviour and neurobiology. Red-backed salamanders, Plethodon cinereus, were observed in standardized behavioural assays with both volatile and soluble prey olfactory cues. Naïve salamanders showed an increase in nosetapping as well as a side preference in the presence of soluble and volatile prey cues when tested in a 22°C day/20°C night room. In a 15°C day /12°C night room, salamanders increased nosetapping in the presence of soluble prey cues. Salamanders showed a pattern of responses that differed based on their previous experience with the assay, as well as the temperature of the testing room. Attempts to study the neurobiology of olfactory function in Plethodon shermani were inconclusive up to this point, but future directions are discussed. This study shows the importance of olfaction in prey detection by salamanders and that prey searching behaviour is exhibited in the exclusive presence of olfactory cues.

Sexual selection can influence the mating system of an organism through multiple mechanisms. These mechanisms result in variation in reproductive success among individuals, and include scramble competition, endurance rivalries, contests, mate choice and cryptic choice, and sperm competition. Understanding the mating system of a species requires the identification of which processes are occurring, and to what degree. In this thesis, I explored the influence of mate choice mechanisms on the mating system of the terrestrial red-legged salamander, Plethodon shermani. I also documented the potential for post-copulatory processes (such as sperm competition and cryptic choice) to influence mating system dynamics. The evolution of mate choice requires (among other factors) variation in the reproductive value of potential mates. This variation is made apparent to choosy individuals through cues. Most animals use multiples cues incorporating many modalities to assess the reproductive quality of potential mates. In Chapter 2, I tested the contribution of two cues (chemical and visual) to mate choice by female P. shermani. I found that a male visual cue ("foot-dancing") increased courtship success. In contrast, delivery of non-volatile pheromones during courtship did not influence courtship success in the laboratory setting, but did affect the duration of one of the courtship stages. In Chapter 4, I identified a tactile cue that was significantly correlated with male reproductive success. Thus, P. shermani females could use at least three modalities to assess the reproductive quality of potential mates. Mate choice can also evolve in males. In Chapter 3, I tested this possibility in P. shermani. I found that males vary the reproductive effort they invest in a particular courtship based on the reproductive value of their partner, indicating male mate choice is occurring. A male invested most when paired with a female with large, well developed ova, and invested less with females that were non-gravid or had small ova. In addition to documenting male mate choice, I showed that the male visual display ("foot-dancing") that affected female mate choice was correlated with male condition, implying foot-dancing may be an honest indicator of male quality. Finally, in Chapter 5, I explored the potential for post-copulatory processes to influence the P. shermani mating system. The opportunity for sperm from multiple males to overlap in the female reproductive tract (i.e., the opportunity for females to mate multiply) is necessary for post-copulatory processes such as cryptic choice and sperm competition. The capacity for long-term sperm storage by females can increase the likelihood that this overlap in sperm from multiple males will occur. I found that females can store viable sperm for at least 9 months and in some cases beyond oviposition. In addition, I documented one female with sperm in her sperm storage organ from a mating that occurred 17 months earlier. Such lengthy sperm storage allows the possibility of sperm from one breeding season to interact with sperm from a subsequent season. Thus, the potential for post-copulatory sexual selection within this salamander system is high. / Graduation date: 2012