Seasonal Pattern of Batrachochytrium dendrobatidis Infection and Mortality in Lithobates areolatus: Affirmation of Vredenburg's “10,000 Zoospore Rule”

To fully comprehend chytridiomycosis, the amphibian disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), it is essential to understand how Bd affects amphibians throughout their remarkable range of life histories. Crawfish Frogs (Lithobates areolatus) are a typical North American pond-breeding species that forms explosive spring breeding aggregations in seasonal and semipermanent wetlands. But unlike most species, when not breeding Crawfish Frogs usually live singly—in nearly total isolation from conspecifics—and obligately in burrows dug by crayfish. Crayfish burrows penetrate the water table, and therefore offer Crawfish Frogs a second, permanent aquatic habitat when not breeding. Over the course of two years we sampled for the presence of Bd in Crawfish Frog adults. Sampling was conducted seasonally, as animals moved from post-winter emergence through breeding migrations, then back into upland burrow habitats. During our study, 53% of Crawfish Frog breeding adults tested positive for Bd in at least one sample; 27% entered breeding wetlands Bd positive; 46% exited wetlands Bd positive. Five emigrating Crawfish Frogs (12%) developed chytridiomycosis and died. In contrast, all 25 adult frogs sampled while occupying upland crayfish burrows during the summer tested Bd negative. One percent of postmetamorphic juveniles sampled were Bd positive. Zoospore equivalents/swab ranged from 0.8 to 24,436; five out of eight frogs with zoospore equivalents near or >10,000 are known to have died. In summary, Bd infection rates in Crawfish Frog populations ratchet up from near zero during the summer to over 25% following overwintering; rates then nearly double again during and just after breeding—when mortality occurs—before the infection wanes during the summer. Bd-negative postmetamorphic juveniles may not be exposed again to this pathogen until they take up residence in crayfish burrows, or until their first breeding, some years later

Revisiting the Medieval Black Death of 1347-1351: Spatiotemporal Dynamics Suggestive of an Alternate Causation

Recent research points to multiple inconsistencies regarding modern Yersinia pestis (in Bubonic, Pneumonic, or Septicemic Plague variants) as a causative agent for the Medieval Black Death (MBD). Published arguments at odds with a Y. pestis-caused epidemic include differences in recorded periodicity, seasonal mortality peaks, relevant biogeographical details, genetic findings, and spatiotemporal dynamics, among other inconsistencies. Here, we describe and expand on some of the recent literature noting these items. In addition, we discuss preliminary research related to our recently published theory, in which we agree with research suggesting that the MBD was caused by a virus, not a bacterium, and elucidate our contention that seasonal changes and medieval human trade patterns controlled the timing of peak mortality during the MBD and subsequent ‘plagues’. Epidemic evidence from the first epidemic wave and later outbreaks is presented in support of our hypothesis

Time fluctuations of the phase modulation in a liquid crystal on silicon display: characterization and effects in diffractive optics

In this paper we provide evidence of the temporal fluctuations of the phase modulation property of a liquid crystal on silicon (LCoS) display, and we analyze its effect when the device is used for displaying a diffractive optical element. We use a commercial twisted nematic LCoS display configured to produce a phase-only modulation, and we provide time resolved measurements of the diffraction efficiency that show rapid fluctuations of the phase modulation, in the millisecond order. We analyze how these fluctuations have to be considered in two typical methods for the characterization of the phase modulation: two beam interference and diffraction from a binary grating. We finally provide experimental results on the use of this device for displaying a computer generated hologram. A reduction of the modulation diffraction efficiency results from the phase modulation fluctuation.We acknowledge financial support from the Spanish Ministerio de Educación y Ciencia (grants FIS2006-13037-C02-01 and FIS2006-13037-C02-02) and from Generalitat de Catalunya (grant ACI2003-42). C. Iemmi gratefully acknowledges the support of the Universidad de Buenos Aires and CONICET (Argentina)