Patterns of variation in the acoustic calling signals of Chloriona planthoppers (Homoptera: Delphacidae) coexisting on the common reed Phragmites australis

Populations of the Tour species of Chloriona commonly found in the Netherlands C dorsata, C. glaucescens, C. smaragdula and C. vasconica –were cultured in the laboratory on Phragmites australis, their exclusive host plant in the field. The low frequency substrate-transmitted signals produced during the calling phase of mating behaviour were digitally analysed for the males and females of each species. Variables selected to cover most aspects of the call were measured, and variation was quantified within species and statistically tested among species using univariate and multivariate techniques. The calls of the males were more complex in structure than those of the females, with two different phase patterns recognized, and were species-specific. C. glaucescens and C vasconica were also separated on variables of the female call, but C dorsata and C. smaragdula completely overlapped. No significant differences were found between the calls of the long-winged and.short-winged female morphs of C. smaragdula. A possible role for variation in calling signals, and responses to them, in the evolution and maintenance of reproductive isolation in Chlonona is discussed.     

Isoprene synthesis protects transgenic tobacco plants from oxidative stress

Isoprene emission represents a significant loss of carbon to those plant species that synthesize this highly volatile and reactive compound. As a tool for studying the role of isoprene in plant physiology and biochemistry, we developed transgenic tobacco plants capable of emitting isoprene in a similar manner to and at rates comparable to a naturally emitting species. Thermotolerance of photosynthesis against transient high-temperature episodes could only be observed in lines emitting high levels of isoprene; the effect was very mild and could only be identified over repetitive stress events. However, isoprene-emitting plants were highly resistant to ozone-induced oxidative damage compared with their non-emitting azygous controls. In ozone-treated plants, accumulation of toxic reactive oxygen species (ROS) was inhibited, and antioxidant levels were higher. Isoprene-emitting plants showed remarkably decreased foliar damage and higher rates of photosynthesis compared to non-emitting plants immediately following oxidative stress events. An inhibition of hydrogen peroxide accumulation in isoprene-emitting plants may stall the programmed cell death response which would otherwise lead to foliar necrosis. These results demonstrate that endogenously produced isoprene provides protection from oxidative damage.     

Acclimation to temperature and temperature sensitivity of metabolism by ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi contribute significantly to ecosystem respiration, but little research has addressed the effect of temperature on ECM fungal respiration. Some plants have the ability to acclimate to temperature such that long‐term exposure to warmer conditions slows respiration at a given measurement temperature and long‐term exposure to cooler conditions increases respiration at a given measurement temperature. We examined acclimation to temperature and temperature sensitivity (Q₁₀) of respiration by ECM fungi by incubating them for a week at one of three temperatures and measuring respiration over a range of temperatures. Among the 12 ECM fungal isolates that were tested, Suillus intermedius, Cenococcum geophilum, and Lactarius cf. pubescens exhibited significant acclimation to temperature, exhibiting an average reduction in respiration of 20–45% when incubated at 23 °C compared with when incubated at 11 or 17 °C. The isolates differed significantly in their Q₁₀ values, which ranged from 1.67 to 2.56. We also found that half of the isolates significantly increased Q₁₀ with an increase in incubator temperature by an average of 15%. We conclude that substantial variation exists among ECM fungal isolates in their ability to acclimate to temperature and in their sensitivity to temperature. As soil temperatures increase, ECM fungi that acclimate may require less carbon from their host plants than fungi that do not acclimate. The ability of some ECM fungi to acclimate may partially ameliorate the anticipated positive feedback between soil respiration and temperature.     

The Geoelectric Effect in Plant Shoots: I. THE CHARACTERISTICS OF THE EFFECT

A comparative study has been made of the geoelectric effectin Helianthus hypocotyls and Zea coleoptiles using two electrodesystems. With the static-drop electrode system a potential differencedeveloped between the upper and lower surfaces of the shootsimmediately after they were turned into the horizontal position.The lower surface of the shoot became positively charged withrespect to the upper surface. In non-decapitated shoots thispotential difference continued to increase for at least 20 min,whereas in decapitated shoots no further increase occurred afterabout 10 min from the moment of reorientation. In contrast,with a flowing-solution electrode system no potential differencedeveloped in non-decapitated shoots until about 12 min afterthey were placed in the horizontal position. Thereafter thelower surface became increasingly positively charged with respectto the upper surface for at least a further 12 min. In decapitatedshoots there was no tendency whatsoever for the lower surfaceof the horizontal shoot to become positively charged with respectto the upper surface, even after 25 min in the horizontal position.The static-drop electrode system has an inherent sensitivityto reorientation in a gravitational field; a potential differencedevelops immediately after reorientation, and increases to amaximum value within the first 10 min of reorientation, regardlessof whether or not the electrodes are in contact with plant tissue.The continued increase in the potential difference measuredacross the shoots with the static-drop electrode system, andthe entire development of the potential difference measuredwith the flowing-solution electrode system, are both dependentupon the shoot apex being intact. These facts have enabled usto show that the electro-potential difference measured acrosshorizontally placed non-decapitated tissues with the static-dropelectrode system is the resultant of two distinct processes:(a) an immediate, purely physical electrical effect generatedin the electrodes themselves, and (b) a delayed geoelectriceffect which arises solely in the living tissues of the shootand which is dependent upon the apex of the shoot being intact.     

Paternal Care in Canids

Paternal care has never been reported as absent in any canidspecies, and some form of care has been seen in 18 of the 36species in the family. Food provisioning, active defense ofthe young, and protecting young by remaining at the den as thefemale forages appear to be the commonest forms of male care.In addition males may groom, retrieve, play and rest with young.Male canids are rarely involved in den selection or construction.The effect on the fitness of the young of indirect forms ofmale care such as provisioning the female and territory defenseare hard to assess. Quantitative studies of male provisioningin seven species offer few generalizations. In two species (Canisaureus, C mesomelas) females provided more food to the youngthan males; in one species (Alopex lagopus) the pair contributedequally to feeding young, and in four species (Canis lupus,Vulpes vulpes, Chrysocyon brachyurus, and Lycaon pictus), malesprovided more food than females. Much more data are required,particularly from field studies, before patterns of variationcan be interpreted.     

DORID, DENDRONOTID AND ARMINID NUDIBRANCHIATE MOLLUSCA FROM BARBADOS

15 species of nudibranchiate mollusc are described from Barbadoscomprising 11 dorids, three dendronotaceans and one arminacean.A list of 35 species of nudibranch recorded from Barbados isgiven. (Received 4 November 1983;