Plethodon stormi

Number of Pages: 2Integrative BiologyGeological Science

Plethodon elongatus

Number of Pages: 2Integrative BiologyGeological Science

Taricha torosa

Number of Pages: 4Integrative BiologyGeological Science

Phenotypic Mismatches Reveal Escape from Arms-Race Coevolution

Because coevolution takes place across a broad scale of time and space, it is virtually impossible to understand its dynamics and trajectories by studying a single pair of interacting populations at one time. Comparing populations across a range of an interaction, especially for long-lived species, can provide insight into these features of coevolution by sampling across a diverse set of conditions and histories. We used measures of prey traits (tetrodotoxin toxicity in newts) and predator traits (tetrodotoxin resistance of snakes) to assess the degree of phenotypic mismatch across the range of their coevolutionary interaction. Geographic patterns of phenotypic exaggeration were similar in prey and predators, with most phenotypically elevated localities occurring along the central Oregon coast and central California. Contrary to expectations, however, these areas of elevated traits did not coincide with the most intense coevolutionary selection. Measures of functional trait mismatch revealed that over one-third of sampled localities were so mismatched that reciprocal selection could not occur given current trait distributions. Estimates of current locality-specific interaction selection gradients confirmed this interpretation. In every case of mismatch, predators were “ahead” of prey in the arms race; the converse escape of prey was never observed. The emergent pattern suggests a dynamic in which interacting species experience reciprocal selection that drives arms-race escalation of both prey and predator phenotypes at a subset of localities across the interaction. This coadaptation proceeds until the evolution of extreme phenotypes by predators, through genes of large effect, allows snakes to, at least temporarily, escape the arms race

To stress or not to stress: Physiological responses to tetrodotoxin in resistant gartersnakes vary by sex

The activation of the hypothalamic pituitary adrenal (HPA) axis is one of the most important physiological processes in coping with any deviation in an organism’s homeostasis. This activation and the secretion of glucocorticoids, such as corticosterone, allow organisms to cope with perturbations and return to optimal physiological functioning as quickly as possible. In this study, we examined the HPA axis activation in common gartersnakes (Thamnophis sirtalis) as a response to a natural toxin, tetrodotoxin (TTX). This neurotoxin is found in high levels in the Rough-skinned Newt (Taricha granulosa), which is a prey item for these snakes. To consume this toxic prey, these snakes have evolved variable resistance. We hypothesized that the more resistant individuals would show a lower HPA axis response than less resistant individuals, as measured by corticosterone (CORT) and bactericidal ability, which is a functional downstream measurement of CORT’s activity. We determined “resistance level” for tetrodotoxin from each individual snake by determining the dose which reduced race speed by 50%. Individuals were injected them with an increasing amount of tetrodotoxin (10, 25, and 50 MAMUs) to determine this value. Thirty minutes after every injection, we gathered blood samples from each snake. Our results show that, while there were no significant differences among individual CORT levels in a dose-dependent manner, female snakes did have a larger stress response when compared to both males and juveniles. Different life-histories could explain why females were able to mount a higher HPA axis response. However, TTX had no downstream effects on bactericidal ability, although juveniles had consistently lower values than adults. Our research shows a possible dichotomy between how each sex manages tetrodotoxin and gives way for a more comprehensive analysis of tetrodotoxin in an ecological context

Taricha

Number of Pages: 2Integrative BiologyGeological Science

Investigations on the toxin of Taricha granulosa

There are essentially no publications dealing with the skin toxin of Taricha granulosa. This study has undertaken investigations with this toxin in an attempt to determine its potency and its effect on the newt's potential predators. Test solutions were made by macerating a known volume of newt skin in a known volume of saline solution. A known volume of this mixture was injected into a test animal to check the animal's susceptibility to the toxin. The skin solution was found to be toxic when used in oral, subcutaneous, and intraperitoneal injections. Tests were also made by feeding, both voluntary and by force, portions or entire newts to potential predators. It was found that one mouse unit (dose, injected intraperitoneally needed to kill a 21 gr. white mouse in ten minutes) equaled 0.0002 cc. of back skin from an adult terrestrial Taricha granulosa. Forty-two vertebrate taxa (3 fish, 6 amphibians, 14 reptiles, 5 birds, and 14 mammals) were tested either with injections or by feeding; all except Thamnophis sp. were conclusively proven to be susceptible to the newt skin toxin. Thamnophis sp. were killed by very large injections but survived after eating adult newts. A toxin was also found to be present in ovarian eggs, oviducal eggs, and the blood of adult males (females were not tested). Very little or no toxin is present in larvae. Terrestrial newts appear to be more toxic than aquatic newts and back skin appears to be more toxic than ventral skin

Geographic variation and systematics of the western Plethodon

The western Plethodon include vandykei vandykei, v. idahoensis, larselli, dunni,vehiculum, stormi, elongatus, and an undescribed form referred to as the "unstriped" Plethodon. These salamanders have been placed into three species groups: the Vandykei group, the Vehiculum group, and the Elongatus group. Range maps are provided and geographic variation is discussed for each species. Emphasis is placed on costal groove and tooth number but other characters, such as head width and length, stripe width, and limb length are also considered. The pigmentation of each species was described in detail. A key is provided. P. vandykei idahoensis is thought to be the most primitive western Plethodon and a dendrogram is presented

An Investigation into Tetrodotoxin (TTX) Levels Associated with the Red Dorsal Spots in Eastern Newt (Notophthalmus viridescens) Efts and Adults

We investigated the concentration of tetrodotoxin (TTX) in sections of skin containing and lacking red dorsal spots in both Eastern newt (Notophthalmus viridescens) efts and adults. Several other species, such as Pleurodeles waltl and Echinotriton andersoni, have granular glands concentrated in brightly pigmented regions on the dorsum, and thus we hypothesized that the red dorsal spots of Eastern newts may also possess higher levels of TTX than the surrounding skin. We found no difference between the concentrations of TTX in the red spots as compared to neighboring skin lacking these spots in either efts or adults. However, efts with more red dorsal spots had elevated TTX levels relative to efts with fewer spots

An analysis of single clutch paternity in the burrower bug Sehirus cinctus using microsatellites

Recent studies of the burrower bug, Sehirus cinctus, have examined the genetic basis of parental care. An understanding of the burrower bug mating system, and the subsequent pattern of offspring relatedness that this system generates, is critical to further interpret genetic data. To this end, we developed three consistently amplifiable highly polymorphic microsatellite loci and used them to determine genotypic patterns at the level of both the population and the single clutch. We found that all clutches were sired by single males. Further, we find no evidence for inbreeding. We hypothesize that single paternity within a clutch may play an important role in reducing the potential for sibling rivalry, by increasing the relatedness among clutchmates