Toe Tip Morphology in Six Species of Salamanders, genus Ambystoma (Caudata: Ambystomatidae) from Arkansas Using Scanning Electron Microscopy

The toe tip friction surface in six species of Ambystoma (A. annulatum, A.maculatum, A.opacum, A. talpoideum, A. texanum, and A. tigrinum) from Arkansas was examined using scanning electron microscopy. We found no sexual dimorphism in cell surface ultrastructure. Variation within and between species was considerable. The most active burrower, A. tigrinum, possessed the most disorganized cell surface, whereas the least active burrowers (A.annulatum, A.maculatum, and A. opacum) had morphologically similar and relatively smooth toe tips. In A. talpoideum and A. texanum, cell surfaces exhibited microprojections. Only these two species possessed mucous pores in close proximity to the friction surface. The microstructure of cell surfaces transcended species groups in Ambystoma and would not represent a reliable taxonomic tool

An Assembly Contamination Model

Mathematical model of spacecraft contamination for treating contamination amount and its surface distribution on structures as random variable

Comparing modern and Pleistocene ENSO-like influences in NW Argentina using nonlinear time series analysis methods

Higher variability in rainfall and river discharge could be of major importance in landslide generation in the north-western Argentine Andes. Annual layered (varved) deposits of a landslide dammed lake in the Santa Maria Basin (26 deg S, 66 deg W) with an age of 30,000 14C years provide an archive of precipitation variability during this time. The comparison of these data with present-day rainfall observations tests the hypothesis that increased rainfall variability played a major role in landslide generation. A potential cause of such variability is the El Nino/Southern Oscillation (ENSO). The causal link between ENSO and local rainfall is quantified by using a new method of nonlinear data analysis, the quantitative analysis of cross recurrence plots (CRP). This method seeks similarities in the dynamics of two different processes, such as an ocean-atmosphere oscillation and local rainfall. Our analysis reveals significant similarities in the statistics of both modern and palaeo-precipitation data. The similarities in the data suggest that an ENSO-like influence on local rainfall was present at around 30,000 14C years ago. Increased rainfall, which was inferred from a lake balance modeling in a previous study, together with ENSO-like cyclicities could help to explain the clustering of landslides at around 30,000 14C years ago.Comment: 11 pages, 9 figure

Seasonal Activity, Population Characteristics, and Age Estimation in the Aquatic Salamander, Siren intermedia nettingi (Goin)

We conducted a study of the Western Lesser Siren (Siren intermedia nettinigi), at a locality termed the Airport Road site in Jonesboro (Craighead County, AR) from November 2004 until March 2007. This site consisted of a network of roadside ditches in cultivated lawns in an industrial park. Even though sirens are known to occur frequently in ditches, most studies of the genus Siren have taken place in natural wetlands. We compiled mark-recapture data at the Airport Road site for each season to determine if the seasonal activity pattern for sirens in northeast Arkansas varied from activity data previously published from other localities in the range of this species. Capture rates were higher in the fall and spring. The predicted overall population size was 110 sirens at a density of 0.81 sirens per linear m. This density was less than the densities (in sirens/m2 ) reported by previous studies. We found two prominent peaks in sirens per size class: the first at 161-170 mm, and the second at 201-210 mm. Other researchers have assumed that the two most abundant size classes in siren populations represent one-year-old and two-year-old cohorts. The sirens captured at the Airport Road site are smaller, on average, than those reported in previous population studies. We found no significant difference between the growth rates of sirens larger than 200 mm SVL and those smaller than 200 mm snout-vent length (= SVL; P = 0.957, confidence interval -1.945, 2.045, n = 16). Our mean growth rates did not significantly differ from growth rates reported for sirens elsewhere. We sectioned siren humeri to identify and quantify lines of arrested growth (LAGs) as part of a skeletochronological analysis. The use of SVL was a poor indicator of number of LAGs. The difference in the weather pattern history in each of the voucher sirens used likely resulted in broad ranges of LAGs for each SVL size class

Status of Three Plethodontid Salamanders (Genus Plethodon) From the Ouachita National Forest of Southwest Arkansas

A three-year field investigation was initiated in 1996 to update previous information on the local abundance and distribution of three salamanders of the genus Plethodon (P. caddoensis, P.fourchensis, and P. ouachitae); these salamanders are found within a five-county area of the Ouachita National Forest in southwestern Arkansas. Plethodon fourchensis was most numerous at three sites in Polk County; a total of 18 specimens was found. Searching for Plethodon fourchensis was successful following moderate-to-heavy precipitation but only in selected habitats on Fourche and Irons Forks mountains. The preferred habitats of P. caddoensis were talus-covered slopes and wet ravines consisting of mostly small loose rocks within the Caddo Mountains. This species was found at 17 of 25 collection sites (n =108); the largest single collection (n =52) occurred on 19 April 1998. Rocky habitats with an abundance of leaf litter on Rich Mountain yielded Plethodon ouachitae in modest numbers (n =45); three new locality sites were found during this study. Although new localities were discovered for each species during this study, none occurred outside its currently recognized range. Current forest management/landscape practices should strive to prevent any precipitous declines in populations of these salamanders

Skeletochronological Study of Adult Spiny Softshell Turtles (Apalone spinifera) from Northeastern Arkansas

Skeletochronological techniques were used to examine age and growth in adult spiny softshell turtles {Apalone spiniferd) from northeastern Arkansas. The diaphyseal region offemurs of 24 specimens (8 mars mars; 16 venus venus) was excised, decalcified in weak hydrochloric acid, and histologically prepared for light microscopy. Skeletal growth was determined from histosectioned bones by measuring femur diameters as well as by counting lines of arrested growth (LAGs) that appear between distinct periosteal layers (marks of skeletal growth =MSGs) laid down during a single growing season. Although significant positive correlations were found between carapace length (CL) and femur diameter in both males and females (r= 0.75; 0.92, respectively), correlation coefficients generated between CL and LAGs (r= 0.30; 0.45, respectively) were not significant. Sources of variation in counts of LAGs include endosteal resorption and remodeling, the lack of visible growth layers, the presence of accessory LAGs, and the compaction of MSGs; this variability introduces sampling error and diminishes the value of this technique as a method of aging adult softshell turtles

Status of the Ozark Hellbender, Cryptobranchus Bishopi (Urodela: Cryptobranchidae), in the Spring River, Fulton County, Arkansas

We conducted a tag and release study of the Ozark hellbender along a 26 km stretch of the Spring River from mid-July through mid-November, 1991, to determine current population levels. Salamanders were collected by hand with the aid of scuba diving equipment. Thirteen visits(36 dive hrs.) to10 selected access sites yielded 20 animals. Compared to previously published data of the early 1980\u27s which indicated large, striving populations of C. bishopi(in some cases, \u3e 300 individuals) in the Spring River, our study found perilously low numbers of salamanders. This drastic decline may be attributed to over collection of specimens for scientific or other purposes and habitat alteration related to recreational activities. Other contributing factors for this decline could be the inadventent killing of animals during human activity (seining, swimming, canoeing, and fishing), the elimination of riparian habitats leading to an increase in the silt burden, and water pollution associated with human occupation and development along the river

Exploring Individual User Attitudes Towards Performance with Web Search Engines: An Extension Study

As the Internet fulfills an increasingly important role in society, study into human behavior and interaction with the technology becomes key to the development of improved systems. As a result, the research agenda of the authors seeks to identify the role of individual differences with users of technology and its subsequent impact on performance. In this initial study, we examine an instance of individual differences with users of the World Wide Web by evaluating user attitudes and performance with Web search engines. Search engine importance is connected to their role as the primary vehicle for locating content on the Internet. Prior research into user attitude has shown a connection with use of technology. In our study we replicate, extend, and critique an investigation conducted by Liaw and Huang (2003) into user attitudes toward search engines as information retrieval tools. Liaw and Huang found that factors such as individual computer experience, quality of search systems, motivation, and perceptions of technology acceptance impact users desire to use search engines as a tool for information retrieval. However, the connection is not drawn to actual individual user performance with a searching task. Based upon the analysis of our data, we were unable to replicate the results achieved in the Liaw and Huang study or draw a connection between these factors and performance. This finding, that our analysis yielded different results, supports the need for further investigation into individual differences and suggests areas for future research