Comparative biochemistry of oxygen toxicity in lactic acid-forming aquatic fungi

Taxonomically diverse aquatic fungi ranging in oxidative capabilities from obligate aerobes to aerotolerant anaerobes were examined for growth under hyperbaric (0.9 atm) O₂, and for the ability to degrade H₂O₂ and O ₂ ^- . The results support the presumption that several Oomycetes and Chytridiomycetes are biochemically adapted to environments low in O₂. Results further indicate significant differences between Oomycetes and Chytridiomycetes in the enzymatic means of dealing with O ₂ ^- and H₂O₂, supporting the recent concept of a great evolutionary divergence between the groups. In general, facultative anaerobes and aerotolerant anaerobes were more severely inhibited by hyperbaric O₂, and they exhibited lower superoxide dismutase (SOD), catalase and peroxidase activities than did strongly-oxidative species. SOD activity, which was detected in all isolates, was insensitive to cyanide in Oomycetes but cyanide sensitive in the Blastocladiales (Chytridiomycetes). All strongly-oxidative Oomycetes exhibited readily-detectable catalase and peroxidase activities, while activities were very low or absent in strongly-fermentative species. As with the Oomycetes, peroxidase activities among the Blastocladiales were high in aerobes and low in strong fermenters. Surprisingly, however, none of the Blastocladiales, including strongly-oxidative species, exhibited substantial catalase activity. Catalase and SOD activities in faculatively anaerobic Oomycetes increased with increasing O₂ concentration; but even in hyperbaric (0.5 atm) O₂, activities for both enzymes in the aerotolerant anaerobe Aqualinderella fermentans were very low compared with activities in aerobes.Abbreviation SOD Superoxide dismutase     

Integrated control of apple pests in New Zealand

A technique is described whereby 5th‐instar larvae of the codling moth (Laspeyresia pomonella) which have finished feeding can be tagged externally with cobalt‐58 and released on apple trees, where they seek cocooning sites. Two μCi ⁵⁸Co per insect did not significantly affect larval survival in the field, or subsequent pupation, emergence, mating, and oviposition in the laboratory. Tagging was more efficient than whole‐tree scraping for the location of cocoons, and was non‐destructive of both the insects and their cocooning sites.

Relocation and observation of the tagged larvae in their cocoons permitted accurate estimation of mortality from when they left the fruit (= release) until adult emergence in the following spring. Natural mortality of larvae seeking cocooning sites was attributed mainly to insect predators, and varied significantly between trees and blocks, averaging 57% over 6 years. Avian predation by the silvereye (Zosterops lateralis) was the greatest hazard to cocooned larvae; this, too, varied significantly between blocks, and averaged 53% over the same period. Both mortalities appeared to be density‐related.     

Chytrid infections of Daphnia pulicaria: development, ecology, pathology and phylogeny of Polycaryum laeve

1. We combined ecological surveys, life table studies, microscopy and molecular sequencing to determine the development, ecology, pathology and phylogeny of Polycaryum laeve, an endoparasite of cladocerans. We report the first records of P. laeve from North America, where we have used a polymerase chain reaction primer and microscopic examination to confirm infections in 14 lakes. Infections are highly pathogenic and caused increased mortality, reduced growth, and reproductive castration in Daphnia pulicaria during life table studies. 2. Biweekly data from Allequash Lake (Wisconsin, U.S.A.) throughout 2003 indicated that fecundity and infection prevalence were inversely correlated. Infection prevalence was highest in late winter and early spring (up to 80%) and lowest during late summer. Epidemics were generally followed by sharp declines in host population density (up to 99%). 3. Within the haemocoel of its host, P. laeve forms thick‐walled sporangia, which occur systemically in later stages of infection. Fungal thalli associate closely with muscle fibres and connective tissue, leading to degeneration as the infection becomes advanced. Following death of the host, flagellated zoospores are released through an exit papilla on the sporangium. Based on the infection‐induced castration of the host and increases in infection prevalence with Daphnia size, we postulate that transmission is horizontal, but may be indirect through an additional host or free‐living stage. 4. Molecular and morphological data clearly indicate that P. laeve belongs in the fungal phylum Chytriodiomycota, order Blastocladiales. Based on ribosomal RNA gene sequences and morphological features, we transfer the genus Polycaryum from the Haplosporidia to the Chytridiomycota, and designate a lectotype and epitype for P. laeve. Considering the high prevalence of P. laeve infection within Daphnia populations, the frequency with which we detected infections among lakes, and the keystone importance of large‐bodied Daphnia in aquatic food webs, we suggest that P. laeve may exert a regulatory influence on Daphnia populations in lake ecosystems.