Use of an alarm pheromone against ants for gaining access to aphid/scale prey by the red velvet mite Balaustium sp. (Erythraeidae) in a honeydew-rich environment.

This study shows that honeydew prompts arrestment and reduced activity, but not attraction, by the mite Balaustium sp. nr. putmani. When presented with short-range, two-choice bioassays, mites ceased their characteristic rapid crawling activity when they encountered honeydew-treated surfaces, resulting in them clustering around the honeydew. Approximately 80% of mites were retained by honeydew, with responses being independent of both mite life-history stage and source of honeydew (coccid scale insect or aphid). No obvious crawling movements or redirection of running path were made to the honeydew by the mites, implying the lack of any kind of attractant. Response of mites to single-sugar presentations of the main honeydew components--glucose, sucrose, fructose and trehalose--(0.001-0.1 mmol l(-1)) were inconsistent and failed to reproduce the arrestment/clustering associated with raw honeydew, suggesting that none of these sugars is an active arrestant ingredient. Formation of feeding clusters on honeydew does not contribute to enhancing water conservation by suppressing net transpiration (water loss) rates of individual mites as group size increases, indicating that the clustering is an artifact of arrestment. We hypothesize that release of neryl formate by the mites reduces negative interactions with the local ant species commonly associated with honeydew. We hypothesize that honeydew serves as: (1) a cue that facilitates discovery of scale/aphid prey; (2) a retainer on plants where these prey are present, signaling abundance and quality; and (3) an alternative and supplemental food source like that noted for other plant-inhabiting predatory mites. Neryl formate serves as an alarm pheromone and foul-tasting allomonal defense secretion that prevents predation of mites by ants that co-exist with aphid/scale insects in these honeydew-rich habitats.

Histological analysis of spermatogenesis and the germ cell development strategy within the testis of the male Western Cottonmouth Snake, Agkistrodon piscivorus leucostoma.

Cottonmouth (Agkistrodon piscivorus leucostoma) testes were examined histologically to determine the germ cell development strategy employed during spermatogenesis. Testicular tissues from Cottonmouths were collected monthly from swamps around Hammond, Louisiana. Pieces of testis were fixed in Trump's fixative, dehydrated in ethanol, embedded in Spurr's plastic, sectioned with an ultramicrotome, and stained with toluidine blue and basic fuchsin. Spermatogenesis within Cottonmouths occurs in two independent events within a single calendar year. The testes are active during the months of March-June and August-October with spermiation most heavily observed during April-May and October. To our knowledge, this is the first study that describes bimodal spermatogenesis occurring in the same year within the subfamily Crotalinae. During spermatogenesis, no consistent spatial relationships are observed between germ cell generations. Typically, either certain cell types were missing (spermatocytes) or the layering of 3-5 spermatids and/or spermatocytes within the same cross-section of seminiferous tubule prevented consistent spatial stages from occurring. This temporal pattern of sperm development is different from the spatial development found within birds and mammals, being more reminiscent of that seen in amphibians, and has now been documented within every major clade of reptile (Chelonia, Serpentes, Sauria, Crocodylia). This primitive-like sperm development, within a testis structurally similar to mammals and birds, may represent an intermediate testicular model within the basally positioned (phylogenetically) reptiles that may be evolutionarily significant.

Pollution and genetic structure of North American populations of the common dandelion (Taraxacum officinale).

Assessing the genetic structure of natural populations differentially impacted by anthropogenic contaminants can be a useful tool for evaluating the population genetic consequences of exposure to pollution. In this study, measures of genetic diversity at variable-number-tandem-repeat loci in six dandelion populations (3 urban and 3 rural) showed patterns that may have been influenced by exposure to environmental contaminants. Mean genetic similarity among individuals within a population was significantly and positively correlated with increasing levels of airborne particulate matter (< or = 10 microm, PM10) and soil concentrations of four metals (Cd, Fe, Ni and Pb). In addition, mean genetic similarity was always significantly higher at the urban sites compared to rural sites. There was a significant negative correlation between the number of genotypes at a site and increasing amounts of PM10, concentrations of five soil metals (Cd, Cu, Fe, Ni and Pb), leaf tissue levels of Fe and a significant positive correlation between the extent of clonality at a site and levels of PM10 and soil concentrations of five metals (Cd, Cu, Fe, Ni and Pb). Although, this study does not directly establish a causal link between the specific contaminants detected at the study sites and differences in genetic diversity, our data are consistent with the hypothesis that pollution-induced selection has contributed in some fashion to the lower genetic diversity found at the urban sites.

Clonal variation in floral stage timing in the common dandelion Taraxacum officinale (Asteraceae).

We investigated the hypothesis that dandelion clones (Taraxacum officinale Weber, sensu lato; Asteraceae) differ in their floral stage timing characteristics under a constant set of environmental conditions. To test this hypothesis, plants representing nine different dandelion clones (identified by DNA fingerprinting) were grown in groups of five (N = 45) in a growth chamber for a period of 8 mo, with chamber settings similar to environmental conditions at peak dandelion flowering time for their population sites. Five flowering phenology parameters were monitored daily for a total of 301 buds developing during this time: (1) time to bud; (2) time to full opening and inflorescence maturation (i.e., first anthesis); (3) time to re-closure of an inflorescence; (4) time to fruit (full re-opening of the inflorescence); and (5) total flowering time. Scape length at the appearance of a fully expanded infructescence was also measured for each individual. Significant differences in mean time to inflorescence, mean time to re-closure, mean time to fruit, and mean total flowering time were revealed among some dandelion clones (Kruskal-Wallis, P ≤ 0.0005). No differences in mean number of inflorescence buds per plant (P = 0.2217), mean time to bud (P = 0.2396), or mean scape length (P = 0.3688) were detected among the nine clones. These results suggest that differences in floral stage timing may in part involve varying genotypic environmental response characteristics and that these differences may have potential fitness effects. Further research is needed to determine if such clonal differences are observed under a broader range of uniform environmental conditions.

Minisatellite DNA mutation rate in dandelions increases with leaf-tissue concentrations of Cr, Fe, Mn, and Ni.

We have examined whether mutation rates at minisatellite DNA loci in dandelions (Taraxacum officinale Weber, sensu lato: Asteraceae) increase with increasing exposure to metal pollution. From 16 sites (Colorado to Pennsylvania, USA) covering a range of airborne particulate-matter exposures, soil metal concentrations, and leaf-tissue metal concentrations, we grew an average of 7.9 offspring from each of 10 parent plants, and we analyzed the parent-offspring transmission of 82,715 minisatellite DNA markers to 1,258 offspring for rates of mutation. The mean number of markers examined per individual (using six minisatellite probes) was 65.8. Detection of mutations is facilitated by agamospermous reproduction (clonal seed production) in dandelions. Across sites, the average single-event, parent-offspring marker transmission mutation rate was 0.0067, ranging from 0.002 to 0.015 (a 7.5-fold difference). No significant correlation was detected between site single-event mutation rates and either airborne particulate-matter or soil concentrations for any of the metals. However, across sites, mutation rates were significantly (p < 0.05) and positively correlated to increasing leaf-tissue concentrations of Cr, Fe, Mn, and Ni (Cd, Cu, Pb, and Zn exhibited no correlation). Multiple-regression analyses suggest that a model including three metals--in order of importance: Cr (p = 0.002), Fe (p = 0.02), and Ni (p = 0.005); overall, p = 0.001--may improve the ability to predict mutation rate relative to leaf metal concentrations in dandelions. Mutations at minisatellite DNA loci in sexually apomictic organisms may thus provide convenient biomarkers by which to assess the mutagen stressor risk in environments.