Parasite-induced fruit mimicry in a tropical canopy ant.

Some parasites modify characteristics of intermediate hosts to facilitate their consumption by subsequent hosts, but examples of parasite-mediated mimicry are rare. Here we report dramatic changes in the appearance and behavior of nematode-parasitized ants such that they resemble ripe fruits in the tropical rain forest canopy. Unlike healthy ants, which are completely black, infected ants have bright red, berry-like gasters full of parasite eggs. The infected gasters are held in a conspicuous elevated position as the ants are walking, and they are easily detached from living ants, which also exhibit reduced defensive responses. This combination of changes presumably makes the infected ants attractive to frugivorous birds, which ingest the red gasters and pass the parasite eggs in their feces. The feces are collected by ants and fed to the developing brood, thus completing the cycle. This is the first documentation of parasites causing apparent fruit mimicry in an animal host to complete their life cycle.

Specificity of tyrosinase and HMB45 PCR in the detection of melanoma metastases in sentinel lymph node biopsies.

AIMS: Sentinel lymph node biopsy is an increasingly established procedure in the primary staging of high-risk melanoma patients. However, the laboratory evaluation of sentinel lymph node biopsies is a matter of controversy. The aim of this study was to determine the specificity of polymerase chain reaction (PCR) techniques for the evaluation of lymph nodes with regard to melanoma metastases in comparison with histology and immunohistology. METHODS AND RESULTS: Sentinel lymph nodes (n = 41) from 29 melanoma patients and 29 lymph nodes from 27 patients without melanoma were analysed by histology (H&E) and immunohistology (Melan A, HMB45). cDNA of these lymph nodes was subjected to LightCycler PCR amplification using primers specific for tyrosinase and HMB45. Two melanoma sentinel lymph nodes contained naevus cells by histology and immunohistology and were therefore excluded from further evaluation. Eight (20.5%) of the remaining 39 melanoma sentinel lymph nodes were positive by histology and immunohistology and tyrosinase PCR, 15.4% (6/39) were positive only by tyrosinase PCR, 2.6% (1/39) were positive only by histology and immunohistology. HMB45 PCR revealed positive results in 7.7% (3/39) sentinel lymph nodes, which were also positive by tyrosinase PCR and histology and immunohistology. Of non-melanoma lymph nodes 13.8% (4/29) and 14.8% (4/27) of non-melanoma patients were positive by tyrosinase PCR but negative by histology and immunohistology and HMB45 PCR. Thus, tyrosinase PCR had a specificity of only 85.2%. CONCLUSIONS: The specificity of tyrosinase PCR and the sensitivity of HMB45 PCR are too low to recommend these PCR examinations for the guidance of therapy, in particular complete regional lymph node dissection.

Application of imiquimod by suppositories (anal tampons) efficiently prevents recurrences after ablation of anal canal condyloma.

BACKGROUND: After surgical removal, anal canal condyloma (ACC) has a higher risk of recurrence compared with extragenital warts. OBJECTIVES: To reduce local recurrences of ACC using follow-up treatment with imiquimod-containing suppositories (anal tampons). METHODS: After ablation of ACC, 10 male patients received treatment with imiquimod suppositories three times weekly for 3-4 months. RESULTS: Treatment with imiquimod anal tampons was well tolerated. Early initial recurrences in some patients cleared after treatment with the imiquimod suppositories. Within a mean follow-up of 9 months no patient demonstrated recurrence of ACC. CONCLUSIONS: These data suggest that imiquimod anal tampons may represent a new therapeutic option to prevent recurrences of ACC following ablative surgery.

Successful treatment of anogenital Bowen's disease with the immunomodulator imiquimod, and monitoring of therapy by DNA image cytometry.

Imiquimod (Aldara, 3M) is an immune response modifier used for the treatment of anogenital warts. We report a 55-year-old non-immunocompromised woman with extensive, human papillomavirus (HPV) 16-positive anogenital Bowen's disease. After 5 months of local treatment with imiquimod, the lesions completely regressed clinically and histologically, and HPV 16 DNA was no longer detectable. Moreover, DNA image cytometry revealed DNA aneuploidy (an indicator of prospective malignancy) in pretreatment samples but not in post-treatment samples. Therefore, imiquimod might be a treatment option for Bowen's disease, particularly in patients where other treatment modalities such as surgery are contraindicated.

Three energy variables predict ant abundance at a geographical scale.

Energy theory posits three processes that link local abundance of ectotherms to geographical gradients in temperature. A survey of 49 New World habitats found a two order of magnitude span in the abundance (nests m(-2)) of ground nesting ants (Formicidae). Abundance increased with net primary productivity (r2=0.55), a measure of the baseline supply of harvestable energy. Abundance further increased with mean temperature (r2=0.056), a constraint on foraging activity for this thermophilic taxon. Finally for a given mean temperature, ants were more abundant in seasonal sites with longer, colder winters (r2 = 0.082) that help ectotherm taxa sequester harvested energy in non-productive months. All three variables are currently changing on a global scale. All should be useful in predicting biotic responses to climate change.

Energy, Density, and Constraints to Species Richness: Ant Assemblages along a Productivity Gradient.

Species richness describes the number of species of a given taxon in a given time and space. The energy limitation hypothesis links the species richness of consumer taxa to net primary productivity (NPP) through two relationships: NPP limits a taxon's density, and taxon density limits species richness. We study both relationships with a survey of 15 ground ant assemblages, along a productivity gradient from deserts to rain forests. Ant density (colonies m-2) was a positive, decelerating function of net aboveground productivity (NAP). A stepwise regression suggests that the efficiency with which NAP is converted to ant colonies increases with maximum summer temperature and decreases with precipitation. Ant species richness was a positive decelerating function of density at three spatial scales. This supports the energy limitation hypothesis' assumption that average population densities are higher in environments that are more productive. These two nonlinear functions (NAP-density and density-species richness) combine to create, at a variety of scales, positive, decelerating, productivity-diversity curves for a common, ecologically dominant taxon across the terrestrial productivity gradient. However, variance in the density and diversity explained by NAP decreases with scale, suggesting that energy limitation of diversity predominates at small spatial scales (<1 ha).

Worker size and seed size selection by harvester ants in a neotropical forest.

The rules ants follow when selecting seeds are important both to theories of colony organization and to the shaping of their impact as harvesters. Two Costa Rican forests yielded the most diverse harvester ant assemblages yet studied (41 and 44±4 species). I assayed seed size preferences within and between species using milled barley. Seed size selection varied at a number of levels. First, species differed in seed size use: small species mainly carried off small seeds; large species retrieved a broad range of seed sizes. Within species, one-third of those tested yielded inter-colony differences in preferred seed sizes. Finally, workers of polymorphic species tested showed significant worker/seed size correlations. Species, colony, and worker level differences are common among harvester ants. Their significance to community organization and colony ergonomics however is hotly debated and requires a better understanding of the dynamics of food limitation. From the plant's perspective, small seeds will be harvested by a wider variety of ants than large seeds.