Do all portable cases constructed by caddisfly larvae function in defense?

The portable cases constructed by caddisfly larvae have been assumed to act as a mechanical defense against predatory attacks. However, previous studies have compared the survival of caddisflies with different cases, thereby precluding an analysis of the survival benefits of "weaker" case materials. The level of protection offered by caddisfly cases constructed with rock, stick, or leaf material, as well as a no-case control, was investigated against predatory dragonfly nymphs (Anax junius Drury (Anisoptera: Aeshnidae)). A valid supposition is that the cases made of stronger material are more effective at deterring predators. Yet, observations revealed that there was no difference in survival between the case types. All caddisflies with a case experienced high survival in comparison to caddisflies removed from their case. In addition, larvae with stick-cases experienced fewer attacks and captures by dragonflies. These results showed that the presence of a case, regardless of the material used in its construction, offers survival benefits when faced with predatory dragonfly nymphs.

Land Ho! Polarized light serves as a visual signal for landward orientation in displaced spiders.

An organism's ability to identify goals within their environment, orient towards those goals, and successfully navigate to them are critical to all aspects of survival. Long-jawed orb weavers (Tetragnatha elongata) occupy riparian zones and perform orientation behaviors when displaced from this habitat onto the water. Spiders prefer to move toward the closest shoreline, regardless of release location, likely to avoid predation from fish. In this study, we conducted a series of investigations to determine the mechanism by which these spiders rapidly achieve zonal recovery. Occlusion experiments indicate that spiders use visual information to identify characteristics of the riparian habitat and navigate to shelter. While environmental characteristics such as color, contrast, and the sun's position do not appear to factor into this orientation behavior, the polarization of light appears critical. We propose that the polarization of light reflecting off the water's surface acts as a water detector and the absence of such at the edges of the pond (or via experimental induction) serves as a visual reference for the closest suitable habitat.

Predatory caddisfly larvae sequester tetrodotoxin from their prey, eggs of the rough-skinned newt (Taricha granulosa).

Caddisfly larvae (Limnophilus spp.) are important predators of eggs of the rough-skinned newt (Taricha granulosa). Newts may possess extremely large quantities of the neurotoxin tetrodotoxin (TTX) in their skin, and females may provision this toxin in their eggs. Using a competitive inhibition enzymatic immunoassay, we examined TTX-resistant caddisflies, sympatric with the known most toxic population of newts, for the presence of TTX. We found that caddisflies sequester TTX after consuming eggs in the laboratory. Caddisfly larvae that were frozen immediately after collecting in the wild possessed TTX. Finally, wild-caught larvae reared on a TTX-free diet in the laboratory retained TTX for up to 134 days, through metamorphosis and into the adult stage.

Tetrodotoxin levels in lab-reared Rough-Skinned Newts (Taricha granulosa) after 3 years and comparison to wild-caught juveniles.

The origin and biogenesis of tetrodotoxin (TTX) is one of the most interesting and perplexing questions remaining for TTX researchers. Newts can possess extreme quantities of TTX and are one of the most well-studied of all TTX-bearing organisms, yet seemingly conflicting results between studies on closely related species continues to generate debate. In this study, eggs from 12 female newts (Taricha granulosa) were reared in captivity and the metamorphosed juveniles were fed a TTX-free diet for 3 years. Using a non-lethal sampling technique, we collected skin samples from each individual each year. Wild-caught juveniles from the same population were also sampled for TTX. In lab-reared juveniles, mass increased rapidly, and after only 2 years individuals approached adult body mass. TTX levels increased slowly during the first two years and then jumped considerably in year three when fed a diet free of TTX. However, wild-caught juvenile newts of unknown age were more toxic than their lab-reared counterparts. These results, coupled with additional data on the long-term production and synthesis of TTX in adult newts suggest that TTX is unlikely to come through dietary acquisition, but rather newts may be able to synthesize their own toxin or acquire it from symbiotic bacteria.

Orientation behavior of riparian long-jawed orb weavers (Tetragnatha elongata) after displacement over water.

Many organisms possess remarkable abilities to orient and navigate within their environment to achieve goals. We examined the orientation behavior of a riparian spider, the Long-Jawed Orb Weaver (Tetragnatha elongata), when displaced onto the surface of the water. When displaced, spiders move with alternating movements of the first three leg pairs while dragging the most posterior pair of legs behind them. In addition, spiders often perform a series of orientation behaviors consisting of concentric circles before ultimately choosing a path of travel directly toward the nearest point to land. While the number of orientation behaviors increased with increasing distance from shore, distance from shore had no effect on the direction of travel, which was significantly oriented toward the closest shoreline. These results indicate a complex ability to orient toward land when displaced onto water, possibly to decrease the amount of time on the surface of the water and thus decrease predation risk.

The indestructible insect: Velvet ants from across the United States avoid predation by representatives from all major tetrapod clades.

Velvet ants are a group of parasitic wasps that are well known for a suite of defensive adaptations including bright coloration and a formidable sting. While these adaptations are presumed to function in antipredator defense, observations between potential predators and this group are lacking. We conducted a series of experiments to determine the risk of velvet ants to a host of potential predators including amphibians, reptiles, birds, and small mammals. Velvet ants from across the United States were tested with predator's representative of the velvet ants native range. All interactions between lizards, free-ranging birds, and a mole resulted in the velvet ants survival, and ultimate avoidance by the predator. Two shrews did injure a velvet ant, but this occurred only after multiple failed attacks. The only predator to successfully consume a velvet ant was a single American toad (Anaxyrus americanus). These results indicate that the suite of defenses possessed by velvet ants, including aposematic coloration, stridulations, a chemical alarm signal, a hard exoskeleton, and powerful sting are effective defenses against potential predators. Female velvet ants appear to be nearly impervious to predation by many species whose diet is heavily derived of invertebrate prey.

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.

When can embryos learn? A test of the timing of learning in embryonic amphibians.

Learning is crucial to the survival of organisms across their life span, including during embryonic development. We set out to determine when learning becomes possible in amphibian development by exposing spotted salamander (Ambystoma maculatum) embryos to chemical stimuli from a predator (Ambystoma opacum), nonpredator (Lithobates clamitans), or control at developmental stages 16-21 or 36-38 (Harrison 1969). Once exposures were completed and embryos hatched, we recorded the number of movements and time spent moving of individuals in both groups and all treatments. There was no significant difference in number of movements or time spent moving among any of the treatments. The groups that were exposed to predator stimuli and a blank control at stages 36-38 were also tested to determine whether there was a difference in refuge preference or difference in survivorship when exposed to a predator (marbled salamander). There was no difference in survival or refuge preference between individuals; however, all individuals preferred vegetated over open areas regardless of treatment type. We discuss hypotheses for the absence of embryonic learning in this species and suggest it may be the result of the intensity of the predator-prey interaction between the predator, large marbled salamander larvae, and the prey, spotted salamander larvae.

Tetrodotoxin concentrations within a clutch and across embryonic development in eggs of the rough-skinned newts (Taricha granulosa).

Tetrodotoxin is an enigmatic neurotoxin that is found in a wide-variety of organisms. Unfortunately, tetrodotoxin (TTX) toxicity across life-history stages is poorly understood in most organisms. Rough-skinned newts (Taricha granulosa) possess the greatest known quantities of TTX of any organism and numerous studies have begun to elucidate these patterns in this species. We conducted a series of studies to answer the following questions: (1) do eggs from a single female's clutch vary in toxicity? (2) does TTX concentration change during embryonic development? and (3) does the jelly coat from newt eggs possess TTX? We found that the amount of TTX in newt eggs depended on the relative "position" of the egg within a clutch; eggs deposited at the beginning of the clutch had substantially more TTX than those at the end. During development egg toxicity remained consistent until hatching. The jelly coat contained small quantities of TTX, but these were not correlated with the toxicity of the embryo. These results clarify several long-held interpretations about embryo toxicity and continue to elucidate the life-history patterns of tetrodotoxin toxicity in this amphibian.

Fine-scale selection by ovipositing females increases egg survival.

One of the most important defenses for the eggs of ovipositing female organisms is to avoid being laid in the same habitat as their predators. However, for most organisms, completely avoiding an offspring's predators is not possible. One mechanism that has been largely overlooked is for females to partition an oviposition site into microhabitats that differ in quality for offspring survival. We conducted a series of experiments to examine whether female newts avoid microhabitats utilized by their offspring's primary predator, caddisfly larvae. Female newts avoided laying eggs near predatory caddisflies and shifted egg laying upward in the water column when provided with a vertical dimension. Caddisflies were attracted to chemical stimuli from female newts and their eggs, yet primarily used benthic areas in experimental chambers. Finally, results from a field experiment indicate that the behavioral strategy employed by female newts increases offspring survival. This subset of non-genetic maternal effects, micro-oviposition avoidance, is likely an important yet underexplored mechanism by which females increase offspring survival.

Interfamily variation in amphibian early life-history traits: raw material for natural selection?

The embryonic development and time to hatching of eggs can be highly adaptive in some species, and thus under selective pressure. In this study, we examined the underlying interfamily variation in hatching timing and embryonic development in a population of an oviparous amphibian, the rough-skinned newt (Taricha granulosa). We found significant, high variability in degree of embryonic development and hatching timing among eggs from different females. Patterns of variation were present regardless of temperature. We also could not explain the differences among families by morphological traits of the females or their eggs. This study suggests that the variation necessary for natural selection to act upon is present in the early life history of this amphibian.

Female newts (Taricha granulosa) produce tetrodotoxin laden eggs after long term captivity.

We investigated the presence of tetrodotoxin (TTX) in the eggs of wild-caught newts (Taricha granulosa) at capture and again after one, two, and three years in captivity. Females initially produced eggs that contained quantities of TTX similar to previous descriptions of eggs from wild-caught adults. After the first year in captivity, the egg toxicity from each female declined, ultimately remaining constant during each of the successive years in captivity. Despite declining, all females continued to produce eggs containing substantial quantities of TTX during captivity. The decline in toxicity can not be attributed to declining egg mass but may be the result of the abbreviated reproductive cycle to which the captive newts were subjected in the lab. Finally, an estimate of the amount of TTX provisioned in the entire clutch from each female is similar to the quantity of TTX regenerated in the skin after electrical stimulation. These results, coupled with other long-term studies on the maintenance and regeneration of TTX in the skin, suggests an endogenous origin of TTX in newts.

Tetrodotoxin levels in larval and metamorphosed newts (Taricha granulosa) and palatability to predatory dragonflies.

Some populations of the newt Taricha granulosa possess extremely high concentrations of the neurotoxin tetrodotoxin (TTX). Tetrodotoxin is present in adult newts and their eggs, but has been assumed to be absent from the larval stage. We tested larval and metamorphosed juveniles for the presence of TTX and evaluated the palatability of these developmental stages to predatory dragonfly nymphs. All developmental stages retained substantial quantities of TTX and almost all individuals were unpalatable to dragonfly nymphs. Tetrodotoxin quantity varied greatly among individuals. When adjusted for mass, TTX concentrations declined steadily through metamorphosis. Several juveniles were palatable to dragonflies and these individuals had significantly lower TTX levels than unpalatable juveniles. These results suggest that despite previous assumptions, substantial quantities of TTX, originally deposited in the embryo, are retained by the developing larvae and metamorphosed juveniles and this quantity is enough to make them unpalatable to some potential predators.