Micro-localisation of lamina-located visual cell activities in the compound eye of the blowfly Calliphora

Summary Intracellular light-evoked potentials were recorded from the lamina site of a photoreceptor. Exact localisation of the tip of recording electrode was done by combining the techniques of dye-marking and of histological tip-identification.To Professor H. Autrum I am much indebted for the facilities to work in his Institute and for his generous help.This work was supported by a grant of the Deutsche Forschungsgemeinschaft.     

Microbial community structure across the tree of life in the extreme Río Tinto

Understanding biotic versus abiotic forces that shape community structure is a fundamental aim of microbial ecology. The acidic and heavy metal extreme Río Tinto (RT) in southwestern Spain provides a rare opportunity to conduct an ecosystem-wide biodiversity inventory at the level of all three domains of life, because diversity there is low and almost exclusively microbial. Despite improvements in high-throughput DNA sequencing, environmental biodiversity studies that use molecular metrics and consider entire ecosystems are rare. These studies can be prohibitively expensive if domains are considered separately, and differences in copy number of eukaryotic ribosomal RNA genes can bias estimates of relative abundances of phylotypes recovered. In this study we have overcome these barriers (1) by targeting all three domains in a single polymerase chain reaction amplification and (2) by using a replicated sampling design that allows for incidence-based methods to extract measures of richness and carry out downstream analyses that address community structuring effects. Our work showed that combined bacterial and archaeal richness is an order of magnitude higher than eukaryotic richness. We also found that eukaryotic richness was highest at the most extreme sites, whereas combined bacterial and archaeal richness was highest at less extreme sites. Quantitative community phylogenetics showed abiotic forces to be primarily responsible for shaping the RT community structure. Canonical correspondence analysis revealed co-occurrence of obligate symbionts and their putative hosts that may contribute to biotic forces shaping community structure and may further provide a possible mechanism for persistence of certain low-abundance bacteria encountered in the RT.     

Comparative water balance profiles of Orchidaceae seeds for epiphytic and terrestrial taxa endemic to North America

The Orchidaceae have dust-like seeds that use wind currents for long-distance dispersal. Lacking endosperm, orchid embryos consume free-living, mycorrhizal fungi as a carbon source (mycotrophy) after settling on a substrate. Few studies have investigated orchid seed morphology as it relates to ecology, but conceivably variations in seed size and testa characteristics could be linked to water loss rates aimed at maximizing germination in a particular habitat. Seeds of 2 epiphytic, 1 aquatic, and 7 terrestrial orchids native to North America were compared with respect to water balance profiles: Cleistes bifaria, Encyclia tampensis, Epidendrum nocturnum, Habenaria repens, Isotria medeoloides, Liparis elata, L. hawaiensis, Platanthera holochila, P. integrilabia, and P. leucophaea. Water content, water loss rate, activation energy, and equilibrium humidity were assessed for each species. Seeds of epiphytic orchids were smaller, lighter, more porous, and had higher water loss rates compared to terrestrials. No active mechanism for water absorption exists in seeds of either group. Water loss appears to be a species-specific phenomenon that may be linked to the ecological niches these species occupy.