Histological,Biochemical, and Ultrastructural Studies on Hyperpigmented Human Skin Xenografts

The mechanisms for hyperpigmentation observed in human cutaneous xenografts placed on athymic nude mice was investigated. Histologic, biochemical, histochemical, and ultrastructural examinations were performed on human skin prior to grafting and at various times ranging from 2 weeks to 30 weeks post-grafting (PG). Hyperpigmentation was macroscopically visible on the graft as early as 4–6 weeks. The number of Dopa-positive melanocytes per unit area was increased at 2 weeks PG and remained elevated until 20 weeks PG. The surface area of the melanocytes, a measure of the activity of the cells, also increased significantly and remained above the pre-grafting size throughout the study. Western blot analysis using tyrosinase specific antibody (αTy-SP) revealed the presence of tyrosinase exclusively in the grafted skin from 2 weeks to 12 weeks PG tested. Histological and ultrastructural observations revealed the presence of numerous dendritic melanocytes, indeterminant clear cells suggestive of Langerhans cells, and dermal melanophages. The results of this study suggest that the observed hyperpigmentation in grafted tissue is caused by an increase in the number of Dopa-positive melanocytes and probably from enhanced melanin production. Extracts of proteins from the xenografts exhibited prominent differences in low and high molecular proteins between pre- and post-grafted skin. Among them, the exclusive appearance of a protein doublet with apparent mw ～14 kDa was found in grafted skin, and subsequent studies indicate it has potent effects on melanocyte function.     

Population structure in Mediterranean islands and risk of genetic invasion in Culexpipiens L. (Diptera: Culicidae)

The mosquito Culex pipiens is subjected to organophosphate treatments in both Corsica and southern Sardinia, but the resistance gene A2-B2, which is currently in a worldwide expansion, has only reached Sardinia. In order to understand this situation, the genetic structure of populations sampled in Sardinia and Corsica was assessed using 15 isozymes. Two loci (HK1 and HK2) were not taken into account because of the possibility of selection. For trie other loci, statistical independence was not rejected for all possible pairs, and no deviation from Hardy-Weinberg expectations was apparent. Low but significant genie differentiation was present between Corsica and Sardinia, as well as between northern and southern Sardinia, despite a large number of effective migrants per generation. These results are discussed in the context of the high probability of extinction/recolonization of breeding sites, the flight migration ability of this mosquito, and the pleiotropic cost of insecticide resistances genes. It is concluded that A2-B2 resistance is unlikely to reach Corsica from southern Sardinia, unless accidental human transportation occurs.     

Cleavage Furrow Establishment--A Preliminary to Cylindrical Shape Change

The predictable pattern of cell shape changes characterizinganimal development must be a consequence of control mechanismsthat are at least analogous to those operating in dividing cells.When cells change shape by an internal mechanism, it is impliedthat they also contain systems that will activate and deactivatethe mechanism, localize it within the cell, insure proper timing,and impart the proper vectoral qualities. Experimental investigationsdesigned to elucidate similar processes in dividing cells revealthat the physical mechanism that accomplishes cytokinesis isestablished at or near the equatorial cell surface by the mitoticapparatus. The process is completed by late metaphase or earlyanaphase. In cleaving eggs a pair of asters can substitute forthe intact mitotic apparatus. The nature of the stimulus whichapparently passes from the mitotic apparatus to the surfaceis presently unknown. It moves toward the surface at about 6microns per minute and requires about 1 minute to establishthe mechanism. The resulting equatorial contractile activityis initially isotropic but becomes anisolropic at the beginningof visible constriction.     

Microsatellite markers developed from Theobroma cacao L. expressed sequence tags

Theobroma cacao L. expressed sequence tags (ESTs) were converted into useful genetic markers for fingerprinting individuals and genetic linkage mapping. Primers were designed to microsatellite‐containing ESTs. Twenty‐two T. cacao accessions, parents of various mapping populations segregating for disease resistance and crop yield characteristics, were tested. Twenty‐seven informative loci were discovered with 26 primer pairs. The number of detected alleles ranged from two to 11 and averaged 4.4 per locus. All 27 markers could be mapped into at least one of the existing F₁ or F₂ populations segregating for agronomically important traits.     

Testing the Adaptive Significance of Acclimation: A Strong Inference Approach

Acclimation is a common phenotypic response to environmentalchange. Acclimation is often thought to enhance performanceand thus to be adaptive. This view has recently been formalizedas the "Beneficial Acclimation Hypothesis" and predicts thatindividuals acclimated to one environment perform better inthat environment than do individuals acclimated to a differentenvironment. Although Beneficial Acclimation is appealing andwidely supported, recent studies with E. coli and Drosophilahave challenged its general validity. Although these challengescould be dismissed as mere exceptions, they encourage a re-evaluationof the adaptive significance of acclimation. Our philosophicalapproach differs from that of most previous studies of acclimation,in which the prediction derived from a Beneficial Acclimationperspective (e.g., heat tolerance is positively correlated withacclimation temperature) is tested against the null hypothesis("single hypothesis approach"). Instead, we follow Huey andBerrigan (1996) in advocating a strong inference approach (sensuPlatt, 1964), which recognizes that Beneficial Acclimation isactually one of a set of competing hypotheses that make differentpredictions as to how developmental temperature influences thethermal sensitivity of adults ("developmental acclimation").Using this perspective, Huey and Berrigan proposed a factorialexperimental design (3 developmental by 3 adult temperatures)designed to discriminate among all competing hypotheses. Wenow derive a formal statistical model (ANOVA with orthogonalpolynomial contrasts) for this experimental design and use itto evaluate simultaneously the relative impact of each competinghypothesis. We then apply this model to several case studies(Drosophila, Volvox, Trichogramma), and we review also a recentstudy with E. coli. The influence of Beneficial Acclimationis supported (albeit often weakly) in most cases. Nevertheless,other hypotheses (especially the Optimal Developmental TemperatureHypothesis) often have a greater impact. Even so, however, BeneficialAcclimation usually predicts relative performance at extremetest temperatures. We conclude that, although rumors of itsdeath are premature, Beneficial Acclimation cannot be viewedas the dominant expectation, at least with regard to developmentaltemperature acclimation. Moreover, our findings reinforce theview that a strong inference approach provides a more comprehensiveportrait of complex biological responses than do single-hypothesisapproaches.     

Wild birds prefer the familiar of striped and unstriped artificial prey

Previous work has shown that wild birds can become trained to search for a prey type on the basis of its colour. The experiments presented in this paper extended this work to two types of green artificial prey that were identical except for the presence or absence of a red stripe. Wild birds at six widely separated sites were trained on populations of one type and then were offered a choice between equal numbers of the familiar type and a second type. All the populations were presented on lawn backgrounds. The experiments were then repeated at each site with the birds being trained on the second prey type. The results showed that there was a consistent tendency for the familiar prey type to be overpredated and this was statistically significant. The behaviour described in this paper, if it occurs in nature, could lead to frequency-dependent (apostatic) selection and the maintenance of polymorphism in prey species in which the morphs are distinguished by colour patterns.     

Traffic Volume Alters Elk Distribution and Highway Crossings in Arizona

ABSTRACT We used 38,709 fixes collected from December 2003 through June 2006 from 44 elk (Cervus elaphus) fitted with Global Positioning System collars and hourly traffic data recorded along 27 km of highway in central Arizona, USA, to determine how traffic volume affected elk distribution and highway crossings. The probability of elk occurring near the highway decreased with increasing traffic volume, indicating that elk used habitat near the highway primarily when traffic volumes were low (<100 vehicles/hr). We used multiple logistic regression followed by model selection using Akaike's Information Criterion to identify factors influencing probability of elk crossings. We found that increasing traffic rates reduced the overall probability of highway crossing, but this effect depended on both season and the proximity of riparian meadow habitat. Elk crossed highways at higher traffic volumes when accessing high quality foraging areas. Our results indicate that 1) managers assessing habitat quality for elk in areas with high traffic-volume highways should consider that habitat near highways may be utilized at low traffic volumes, 2) in areas where highways potentially act as barriers to elk movement, increasing traffic volume decreases the probability of highway crossings, but the magnitude of this effect depends on both season and proximity of important resources, and 3) because some highway crossings still occurred at the high traffic volumes we recorded, increasing traffic alone will not prevent elk-vehicle collisions. Managers concerned with elk-vehicle collisions could increase the effectiveness of wildlife crossing structures by placing them near important resources, such as riparian meadow habitat.     

Diagnostic Genetic Marker That Differentiates Eastern Fox Squirrels From Eastern Gray Squirrels

Abstract The Delmarva fox squirrel (Sciurus niger cinereus) has been listed as endangered by the United States Department of Interior since 1967. A high-priority task for the recovery of this taxon is to determine its current geographic distribution. Toward this end, we have identified a microsatellite locus that unambiguously differentiates Delmarva fox squirrels from eastern gray squirrels (S. carolinensis), which frequently co-occur with Delmarva fox squirrels. Analysis of this marker in noninvasively collected hair samples will allow unequivocal identification of localities occupied by Delmarva fox squirrels with a minimum investment of funds, time, and effort because handling individuals will be unnecessary. This protocol will expedite site review in connection with the Endangered Species Act consultation process.     

Productivity and significance of headwater streams: population structure and biomass of the black-bellied salamander (Desmognathus quadramaculatus)

1. Headwater streams are a significant feature of the southern Appalachian landscape, comprising more than 70% of the total stream length in the region. Salamanders are the dominant vertebrate within headwater‐riparian forest ecosystems, but their ecological role is not clearly understood. 2. We studied a population of black‐bellied salamanders (Desmognathus quadramaculatus) at a headwater stream in the southern Appalachian Mountains using radio‐telemetry and mark‐recapture methods. The length and area of headwater streams in the region were estimated using GIS. 3. Home ranges of radio‐tracked salamanders were relatively small (mean = 1.06 m²). Adult salamanders in our telemetry study inhabited edge microhabitats significantly more often than either stream or riparian microhabitats, and the same trend was observed in the mark‐recapture study. 4. We estimated the population density at this site to be 11 294 salamanders ha^?1, amounting to 99.30 kg ha^?1 of biomass, an estimate that is six times greater than reported in previous studies. The majority of this biomass was found within the stream, but 22% was found in the surrounding riparian habitat more than 1 m from the stream. Using headwater stream length and area estimates, we extrapolated biomass estimates for black‐bellied salamanders inhabiting stream and riparian microhabitats across the study region. 5. We report one of the largest estimates of secondary consumer biomass for a headwater ecosystem, attesting to the overall productivity of headwater streams. Headwaters are known to be important for ecological and ecosystem processes and our biomass estimates suggest that salamanders are a critical component to these systems.