Autotomy occurs when an animal intentionally sacrifices an appendage to escape predation or free a limb. While immediately beneficial, loss of an appendage can lead to a variety of future costs. In many spiders, leg autotomy is common; previous work has sometimes demonstrated autotomy costs in some behaviors, while other times, no costs of autotomy occur. We examined frequency of autotomy in two riparian zone populations of the wolf spider Pardosa valens Barnes, 1959 and then used both mark–recapture work at these sites and laboratory predation trials to determine whether autotomy affected survival. Autotomy occurred in 31% of spiders; males were more likely than females to have a missing leg, but female reproductive status (carrying an egg sac or not) was unrelated to leg loss status. At both sites, survival over 1 week in the field was significantly higher for intact spiders than for spiders missing a leg, for both sexes and both female reproductive states. Additionally, when we paired intact and autotomized spiders with a predator (the larger wolf spider Rabidosa santrita (Chamberlin & Ivie, 1942)), autotomized spiders were more likely to be attacked and eaten. Our results suggest that leg autotomy in P. valens leads to a significant future survival cost, and we discuss how this cost may affect males and females differently.

Many species use autotomy, the self-amputation of an appendage, as a last-gasp method to escape a predator. Although this behavior can have immediate survival benefits, it can also negatively affect future survival or reproduction. The wolf spider Pardosa valens Barnes 1959 occurs along small mountain streams in southeastern Arizona, where it moves both on cobble along the stream and on top of the water's surface. Autotomy of legs is common in this species, and we hypothesized that such leg loss could lead to decreased sprint speed in both terrestrial and aquatic locomotion. We examined burst speed in the laboratory on artificial terrestrial and aquatic racetracks during 2005 (both males and females) and 2006 (females only). In 2005 terrestrial trials, intact spiders were faster than autotomized spiders, but there was no effect of sex on speed. In contrast, 2005 aquatic trials revealed that females ran faster than males, but that autotomy had a negative impact on the speed of females only. Additionally, female spiders generally ran faster on the terrestrial track later in the day than earlier in the day, suggesting that environmental variables such as temperature may have some influence on spider locomotion. Males were less likely to run on water than were females, and ran shorter distances when they did run. Results for females during 2006 also showed a decline in speed with autotomy, and an increase during later trials, although the results were weaker than during 2005, with only the aquatic trials showing a significant difference. These results suggest that leg autotomy in this spider does have a cost, but that the magnitude of this cost depends on aspects of the spider (e.g., sex) and habitat (e.g., substrate and environmental conditions).

Three species of Five-lined Skinks (Plestiodon fasciatus, P. laticeps, and P. inexpectatus) are found in the forest of the southeastern United States. They are similar in morphology and habit and are sympatric over the southern portion of their ranges. Field observations suggest that temperatures of preferred natural habitat differ among these species. To determine whole-animal physiological differences associated with thermal aspects of their habitats, we quantified and compared maximum sprint speed at four ecologically significant temperatures. This study is unique among lizard studies due to the high degree of morphological similarity exhibited by these species, thereby allowing direct comparisons of locomotor performance responses to temperature that are not confounded by differences in morphology. As expected with diurnal lizards, the sprint speed of all three species increased significantly at the temperature interval that approximate the elevation of temperature from dawn to mid-day (20 degrees C to 25 degrees C). Additionally, P. inexpectatus was significantly faster than P. fasciatus and P. laticeps at the temperatures where these species generally would be active. Plestiodon laticeps exhibited a significantly lower sprint speed at 15 degrees C than the other two species. All species exhibited their fastest sprint speed at the highest experimental temperature. The temperature coefficient (Q(10)) for maximum locomotor performance across each 5 degrees C interval follow the same general pattern, with P. laticeps exhibiting a significantly higher Q(10) over the interval of 15 degrees C to 20 degrees C. These findings generally correspond to the observed association of P. inexpectatus with warmer, open canopy microhabitats and P. fasciatus and P. laticeps with cooler, closed-canopy microhabitats.

BACKGROUND:The primary objective of this study is to reconstruct the phylogeny of the hentzi species group and sister species in the North American tarantula genus, Aphonopelma, using a set of mitochondrial DNA markers that include the animal "barcoding gene". An mtDNA genealogy is used to consider questions regarding species boundary delimitation and to evaluate timing of divergence to infer historical biogeographic events that played a role in shaping the present-day diversity and distribution. We aimed to identify potential refugial locations, directionality of range expansion, and test whether A. hentzi post-glacial expansion fit a predicted time frame.METHODS AND FINDINGS:A Bayesian phylogenetic approach was used to analyze a 2051 base pair (bp) mtDNA data matrix comprising aligned fragments of the gene regions CO1 (1165 bp) and ND1-16S (886 bp). Multiple species delimitation techniques (DNA tree-based methods, a "barcode gap" using percent of pairwise sequence divergence (uncorrected p-distances), and the GMYC method) consistently recognized a number of divergent and genealogically exclusive groups.CONCLUSIONS:The use of numerous species delimitation methods, in concert, provide an effective approach to dissecting species boundaries in this spider group; as well they seem to provide strong evidence for a number of nominal, previously undiscovered, and cryptic species. Our data also indicate that Pleistocene habitat fragmentation and subsequent range expansion events may have shaped contemporary phylogeographic patterns of Aphonopelma diversity in the southwestern United States, particularly for the A. hentzi species group. These findings indicate that future species delimitation approaches need to be analyzed in context of a number of factors, such as the sampling distribution, loci used, biogeographic history, breadth of morphological variation, ecological factors, and behavioral data, to make truly integrative decisions about what constitutes an evolutionary lineage recognized as a "species".

We investigated the behavioral response of male Paruroctonus boreus to male and female pheromones of conspecifics. Adult male scorpions actively search for females during the mating season, but lack visual cues to direct their movement. Chemical cues (pheromones) are thought to be responsible for directing movement. In a series of laboratory experiments, in Y-mazes, males were exposed to areas that had contained males and females from the same population and areas that had contained conspecifics from different populations. Males spent significantly more time in areas that had contained females from the same population but did not show a preference for areas exposed to females from different populations. Males also significantly avoided areas exposed to males from the same population. Our results suggest that P. boreus has a sex-specific response to pheromones and that this response may be population-specific.

The relationship between running speed and flight distance is an important one in terms of escape from predators, especially in species that may have multiple defensive strategies. In the wolf spider Hogna carolinensis, one important antipredator mechanism is flight. We examined the relationship between sprint speed and flight distance in wolf spiders by measuring sprint speed on a running track and, in a separate set of experiments with the same individual spiders, measured the distance at which they fled from an advancing model predator. Sprint speed was not significantly correlated with mass, size, or sex of the spiders. Sprint speed was positively correlated with flight distance. This correlation may be the result of a trade-off between two competing modes of antipredator mechanisms: escape and crypsis. In individuals with higher sprint speeds, escape may be the more advantageous option. Slower individuals may have a greater chance of surviving an encounter with a predator simply by remaining still and relying on crypsis.

We examined the sexually dimorphic head morphology of Schistometopum thomense, a West African species of caecilian. Morphometric data were correlated with experimentally determined burrowing speeds for each sex to determine the relationship between morphology and. burrowing proficiency. Males had larger heads and slower burrowing speeds. Field-collected individuals of this species bear marks indicative of biting. We examined the frequency, location, and nature of bite marks on a series of field-collected, preserved specimens of S. thomense. Bite marks occurred on the head region more frequently than expected. We discuss hypotheses regarding the potential functions of biting.

Although information concerning variation among and within populations is essential to understanding an organism's life history, little is known of such variation in any species of scorpion. We show that reproductive investment by the scorpion Centruroides vittatus varied among three Texas populations during one reproductive season. Females from the Kickapoo population produced smaller offspring and larger litters than females from the Independence Creek or Decatur populations; this pattern remained when adjusting for among population variation in either female mass or total litter mass. Relative clutch mass (RCM) and within-litter variability in offspring mass (V*) did not differ among populations. Among-population variation may result from genetic differences or from phenotypically plastic responses to differing environments. Within populations, the interrelationships among reproductive variables were similar for Decatur and Independence Creek: females investing more in reproduction (measured by total litter mass, TLM) produced larger litters and larger offspring, and V* decreased with increased mean offspring mass (and with decreased litter size at Decatur). At Kickapoo, larger females produced larger litters and had larger TLM; females investing more in reproduction produced larger litters but not larger offspring. Within litter variability in offspring mass was not correlated with any reproductive variables in this latter population. These patterns may be explained by the fractional clutch hypothesis, the inability of females precisely to control investment among offspring or morphological constraints on reproduction.

The effects of hunger and experience on the avoidance of unpalatable prey were examined. Larvae of the predaceous diving beetle, Dytiscus verticalis, after feeding on one of two feeding regimes, were offered palatable and unpalatable prey during a series of trials. Consumption of palatable prey (calf heart) was not affected by hunger or experience. Avoidance of unpalatable prey (tails of the red-spotted newt Notophthalmus viridescens) decreased with increased hunger, with hungrier predators sampling unpalatable prey more often. Although the overall level of avoidance varied across trials, the degree of difference in avoidance between predators at different hunger levels remained relatively constant across trials. Beetle larvae responded to an increase in their feeding regime within 36 h (after two trials), by becoming more selective. In a separate experiment, hunger level affected the number of beetle larvae that seized unpalatable newt tails, but experience did not.

Among invertebrates, scorpions possess a relatively unique set of reproductive traits. The interrelationships of these traits may have important implications for life history theory, yet there have been few studies of these traits in scorpions. Our data indicate that larger female Centruroides vittatus produce more offspring and have a higher total litter mass than smaller females. There was, however, no significant relationship between offspring size and female or litter size. Mean offspring mass increased with increases in total litter mass and within litter variation in offspring size (coefficients of variation) decreased with increasing total litter mass. These results suggest that large female scorpions with a larger investment in reproduction produced more offspring that were more uniform in size, but not significantly larger, than small females with less investment. The fractional clutch principle and physiological and functional constraints on size and number of offspring are suggested as possible explanations for the relationships we found among offspring size, variation in offspring size and total investment in offspring in C. vittatus.