Range position and climate sensitivity: The structure of among-population demographic responses to climatic variation.

Species' distributions will respond to climate change based on the relationship between local demographic processes and climate and how this relationship varies based on range position. A rarely tested demographic prediction is that populations at the extremes of a species' climate envelope (e.g., populations in areas with the highest mean annual temperature) will be most sensitive to local shifts in climate (i.e., warming). We tested this prediction using a dynamic species distribution model linking demographic rates to variation in temperature and precipitation for wood frogs (Lithobates sylvaticus) in North America. Using long-term monitoring data from 746 populations in 27 study areas, we determined how climatic variation affected population growth rates and how these relationships varied with respect to long-term climate. Some models supported the predicted pattern, with negative effects of extreme summer temperatures in hotter areas and positive effects on recruitment for summer water availability in drier areas. We also found evidence of interacting temperature and precipitation influencing population size, such as extreme heat having less of a negative effect in wetter areas. Other results were contrary to predictions, such as positive effects of summer water availability in wetter parts of the range and positive responses to winter warming especially in milder areas. In general, we found wood frogs were more sensitive to changes in temperature or temperature interacting with precipitation than to changes in precipitation alone. Our results suggest that sensitivity to changes in climate cannot be predicted simply by knowing locations within the species' climate envelope. Many climate processes did not affect population growth rates in the predicted direction based on range position. Processes such as species-interactions, local adaptation, and interactions with the physical landscape likely affect the responses we observed. Our work highlights the need to measure demographic responses to changing climate.

In vitro and in vivo characterization of p-amino-phenethyl-m-trifluoromethylphenyl piperazine (PAPP), a novel serotonergic agonist with anthelmintic activity against Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis.

The neurotransmitter serotonin (5-hydroxy tryptamine or 5HT) regulates key physiological processes in nematodes such as locomotion and feeding. PAPP (p-amino-phenethyl-m-trifluoromethylphenyl piperazine) is a known agonist of the 5-HT(1Hc) receptor of the barber pole worm, Haemonchus contortus. In this study, PAPP was highly active against L3-stage larvae of H. contortus and Trichostrongylus colubriformis in an in vitro larval migration assay, with EC50 values of 9.36 and 11.8 microM, respectively, that were comparable to levamisole (10.2 microM) and superior to pyrantel (55.39 microM). When administered orally or subcutaneously to nematode infected gerbils, PAPP provided >99% efficacy against H. contortus and >98% efficacy against Teladorsagia circumcincta at 100 mg/kg, comparable to levamisole at 10 mg/kg. Drug titration revealed significant activity down to 50 mg/kg against these two species. Spectrum was limited, however, with somewhat lower efficacy (83%) in T. colubriformis infected gerbils at 100 mg/kg. Oral delivery of hydrochloride, acetate and phosphate salts of PAPP to nematode infected gerbils did not result in an increase in either potency or spectrum. The finding that PAPP exhibits significant anthelmintic activity suggests that the nematode-specific serotonergic system is a viable target for future anthelmintic discovery.

An in vivo rodent model for identifying and characterizing acaricides.

Evaluation of candidate acaricides in livestock or companion animals is expensive, time-consuming, and usually requires large quantities of test material. To identify promising substances at the earliest possible stage of the development process, robust and predictive surrogate animal models, capable of rapidly characterizing potency with minimal compound requirements, are necessary. The objective of this study was to generate an in vivo surrogate animal bioassay capable of rapidly and accurately predicting the topical activity of acaricides emerging from in vitro acaricide bioassays. The rat acaricide test (RAT) requires adult rats, Rattus norvegicus (Berkenhout, 1769), a flexible tick containment device fastened to their dorso-thoracic region, and the nymphal stage of the lone star tick, Amblyomma americanum (L.). The feeding kinetics of A. americanum nymphs on rats was assessed, and compound efficacies were determined by measuring tick survivorship and engorgement weight on acaricide-treated animals. Results from this bioassay demonstrated efficacy with fipronil, ivermectin, permethrin, and chlorpyrifos, and dose-response relationships for each acaricide were determined. The rank order of potencies was fipronil > ivermectin > chlorpyrifos = permethrin for nymphal mortality and fipronil > ivermectin > chlorpyrifos > permethrin for inhibition of nymphal engorgement. The activity of permethrin against nymphs in the RAT was positively correlated with potency values for technical and commercial permethrin formulations against adult A. americanum infestations on cattle. The RAT proved to be an economical, rapid surrogate animal bioassay that together with the in vitro acaricide bioassay can be used for the rapid identification, characterization, and prioritization of candidate acaricides.

Comparison of in vitro and in vivo ectoparasiticide activity of experimental benzimidazole-carbamate with permethrin and amitraz.

A series of in vitro and in vivo bioassays were conducted to assess the ectoparasiticide activity of isopropyl-4-nitro-2,6-bis(trifluoromethyl)-1-benzimidazole-carbamate, an experimental benzimidazole-carbamate class compound. This compound was less potent than permethrin against ectoparasiticide-susceptible larvae of the lone star tick, Amblyomma americanum (L.) (Acari: Ixodidae); larvae of the southern cattle tick, Boophilus microplus (Canestrini); and adult stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae) in vitro, but it was significantly more potent than permethrin against the Santa Luiza strain of B. microplus known to possess high-level resistance to amitraz and pyrethroids. In contrast, the benzimidazole-carbamate was substantially more efficacious than permethrin when applied topically onto rats that were infested with A. americanum nymphs. These results suggest that this experimental compound may be a viable candidate ectoparasiticide that retains significant activity against resistant B. microplus and also suggests that the benzimidazole-carbamate chemistry may be useful for addressing the growing problem of resistance in ectoparasites.

An in vitro larval immersion microassay for identifying and characterizing candidate acaricides.

We have optimized a larval immersion microassay (LIM) that offers superior sensitivity, flexibility to accommodate multiple formulations, and a robust capability for rapidly screening many compounds with a minimal requirement of test article for evaluation. Dose-response studies were conducted for representative members from the organophosphate, pyrethroid, pyrazole, carbamate, macrocyclic lactone, and formamidine chemistries against Amblyomma americanum (L.). Time-response experiments revealed that permethrin was the most rapid acting, whereas fipronil had the slowest speed-of-kill against A. americanum. Comparison of drug susceptibility profiles between multiple ixodid ticks suggests that A. americanum is an effective model for predicting compound potency against Boophilus spp. in this bioassay. The LIM is suitable for the identification and characterization of active molecules from small- and medium-sized compound or natural product libraries, and it can be a useful tool to prioritize molecules for further in vivo testing in animal models.

Novel thiophenes and analogues with anthelmintic activity against Haemonchus contortus.

A new series of analogues of 4-(4-fluorophenyl)-2-methylthio-thiophene-3-carbonitrile (1) were synthesized and evaluated for their in vitro and in vivo anthelmintic activity against Haemonchus contortus.

Synthesis and evaluation of a series of 1,4-diarylbutadienes for anticoccidial activity.

During the course of a collaborative screening program, a set of 1-phenyl-4-pyridyl-butadienes was found to exhibit in vitro activity against Eimeria tenella in a cell-based assay. Activity was dependent on the chain length and degree of unsaturation of the linker between the two aryl groups as well as substitution of the pyridine moiety. Structure-activity relationship studies were subsequently conducted over a larger range of 1,4-diarylbutadienes in order to determine the scope of active compounds, to identify structural patterns governing activity and to enhance in vitro potency against E. tenella. In addition, the efficacy of many compounds for treating coccidiosis in chickens was measured by testing the ability of the compound to prevent or reduce intestinal and cecal lesions when administered by oral gavage. A few compounds in the series were identified that exhibited a moderate degree of in vitro and in vivo activity.

Molecular cloning and characterization of an SRCAP chromatin remodeling homologue in Toxoplasma gondii.

We have identified and mapped a gene in Toxoplasma gondii that encodes a homologue of SRCAP (Snf2-related CBP activator protein), a member of the SNF/SWI family of chromatin remodeling factors. The genomic locus (TgSRCAP) is present as a single copy and contains 16 introns. The predicted cDNA contains an open reading frame of 8,775 bp and encodes a protein of 2,924 amino acids. We have identified additional SRCAP-like sequences in Apicomplexa for comparison by screening genomic databases. An analysis of SRCAP homologues between species reveals signature features that may be indicative of SRCAP members. Expression of mRNA encoding TgSRCAP is upregulated when tachyzoite (invasive form) parasites are induced to differentiate into bradyzoites (encysted form) in vitro. Recombinant TgSRCAP protein is functionally equivalent to the human homologue, being capable of increasing transcription mediated by CREB.

THE DYNAMICS OF TWO HYBRID ZONES IN APPALACHIAN SALAMANDERS OF THE GENUS PLETHODON.

Two zones of intergradation between populations of Plethodon have been studied for 18 and 20 years, respectively. The data consist of systematic scores of colors, made at least twice annually. Near Heintooga Overlook in the Balsam Mountains (Great Smoky Mountains National Park), the salamanders' cheeks are gray. Proceeding north toward the Smokies, there is increasing frequency and intensity of red color at two, four, and six miles. There has been no change in the scores at any location. The width of the zone and our failure to detect any change can be explained by assuming neutrality of the character and random diffusion during the probable time since contact between the two intergrading forms, which most likely took place after the Hypsithermal Interval, 8,000-5,000 BP. At Coweeta Hydrologic Laboratory in the Nantahala Mountains, Plethodon jordani and P. glutinosus hybridize at intermediate elevations. The lateral white spots of glutinosus decrease and the red on the legs of jordani increases with elevation from 685 m to 1,052 m. At the higher elevation, the proportion of animals scored as "pure" jordani declined significantly from 1974 to 1990, an indication that the hybrid zone is spreading upward. The rate of spread is too great to be explained by random diffusion, so selection for glutinosus characters is the best explanation. The rate of spread of the hybrid zone indicates that hybridization began 60-65 years ago, at the end of the time of intense timbering. Such human disturbances have caused hybridization in other organisms.