Electrophysiological responses of the antennal campaniform sensilla to rapid changes of temperature in the ground beetles Pterostichus oblongopunctatus and Poecilus cupreus (Tribe Pterostichini) with different ecological preferences

Abstract.  Cold cells innervating antennal campaniform sensilla of the ground beetles Pterostichus oblongopunctatus (Fabricius, 1787) and Poecilus cupreus (Linnaeus, 1758) belonging to the tribe Pterostichini fire at a stationary rate of 22–23 imp s⁻¹ at 23 °C. In P. oblongopunctatus , there is a strong negative correlation between the stationary firing rate of the cold cell and temperature. By contrast, no relationship between the firing rate and temperature is observed in P. cupreus. Mean peak frequencies, reaching up to nearly 500 Hz, and first-second firing rates, reaching up to 140 imp s⁻¹, are observed at the beginning of the phasic-tonic response to rapid cooling of the cold cells of P. cupreus, which are significantly higher than those for P. oblongopunctatus . However, firing rates of the cold cells of the two ground beetles studied do not differ 3 s later, during the tonic stabilization period of the response. The length of the long interspike period, lasting up to several seconds, at the beginning of rapid warming, is a positive function of the extent of change in temperature, and is longer in P. oblongopunctatus than in P. cupreus . These differences in the responses of the cold cells are related to the ecological preferences of the two ground beetles.     

Multiple determinants influence root colonization and induction of induced systemic resistance by Pseudomonas chlororaphis O6

Colonization of the roots of tobacco by Pseudomonas chlororaphis O6 induces systemic resistance to the soft-rot pathogen, Erwinia carotovora ssp. carotovara SCC1. A screen of the transposon mutants of P. chlororaphis O6 showed mutants with about a fivefold reduction in ability to induce systemic resistance to the soft-rot disease. These mutations disrupted genes involved in diverse functions: a methyl-accepting chemotaxis protein, biosynthesis of purines, phospholipase C, transport of branched-chain amino acids and an ABC transporter. Additional mutations were detected in the intergenic spacer regions between genes encoding a GGDEF protein and fumarate dehydratase, and in genes of unknown function. The mutants in the ABC transporters did not display reduced root colonization. However, the other mutants had up to 100-fold reduced colonization levels. Generally the production of metabolites important for interactions in the rhizosphere, phenazines and siderophores, was not altered by the mutations. A reduced induction of systemic resistance by a purine biosynthesis mutant with a disrupted purM gene correlated with poor growth rate, lesser production of phenazines and siderophore and low levels of root colonization. These studies showed that multiple determinants are involved in the induction of systemic resistance, with there being a requirement for strong root colonization.     

Effects of winter conditions on Daphnia dynamics and genetic diversity in a dimictic temperate reservoir

1. Winter conditions shape plankton dynamics and community composition in temperate regions, but their effect on dynamics and genetic composition of cyclical parthenogens like Daphnia is largely unclear. 2. For 5 years, we studied the dynamics, hatching from resting eggs and genetic structure of a D. galeata × longispina hybrid complex in a dimictic, temperate reservoir. Our main hypothesis was that higher spring densities and an earlier population peak will be observed after warmer winters, with a lower genetic diversity because of a lower contribution of resting eggs to population growth. 3. The study period could clearly be categorised into cold‐winter years (n = 3) and warm‐winter years (n = 2). Daphnia densities at the end of spring overturn were ～10‐fold lower after cold winters than after warm ones, but no pattern emerged concerning the timing and the height of the population peak in early summer. 4. Hatching intensity from resting eggs was higher and contributed up to 8.5% to Daphnia abundance in a cold‐winter year compared to a negligible contribution in a warm‐winter year. Consistent with this finding, new multilocus genotypes (MLGs) adding to the overwintering stock after the end of spring overturn and presumably originating from resting eggs increased genetic diversity and attained high frequencies within the population only after a cold winter. New MLGs were recorded also after warm winters, but they never gained dominance and no shift in genetic diversity was observed. However, genetic diversity was not generally reduced after warm winters. 5. Our results confirm earlier findings that winter conditions have only a limited effect on the main growth phase and the peak of Daphnia during late spring and early summer. However, winter conditions determine the contribution of resting eggs to the population development, which may profoundly alter the genetic composition of the population compared to the previous season.     

Parasite-mediated sexual selection and species divergence in Lake Victoria cichlid fish

We investigate the role of parasite-mediated sexual selection in the divergence of two species of Lake Victoria cichlids. Pundamilia pundamilia and Pundamilia nyererei represent a common pattern of male nuptial colour divergence between haplochromine sister species: metallic grey–blue in P. pundamilia and bright yellow and red in P. nyererei . Female mating preferences for different male colours maintain the genetic and phenotypic differentiation of the two species in clear water. Previous work indicated that the red coloration of P. nyererei males, which is subject to directional sexual selection, may be a carotenoid-dependent signal of parasite infestation rate. In the present study, we find a parallel result for P. pundamilia : bright blue males are infected with fewer species of parasites. We also find that parasite infestation rates differ quantitatively between the two species in a way that is consistent with species differences in diet and microhabitat. We conclude that parasite-mediated sexual selection may have contributed to the divergence of female mating preferences between P. pundamilia and P. nyererei , and may currently strengthen reproductive isolation between these species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 53–60.     

Distribution of the neurotoxic nonprotein amino acid BMAA in Cycas micronesica

BMAA (β-methylamino-L-alanine), a nonprotein amino acid with neurotoxic properties occurs in the cycad Cycas micronesica Hill in Guam. BMAA may have originally played a role as an antiherbivory compound in the plant, but is now of great interest because of its possible link to ALS-PDC, a neurological disease among the Chamorro people of Guam. Biomagnified cycad neurotoxins may play a role because they accumulate in flying foxes of the genus Pteropus that are eaten during traditional feasts. Since flying foxes feed on the seed sarcotesta it is important to understand the distribution of BMAA in the various tissues of the cycad. Using HPLC techniques, we quantified both BMAA and glutamic acid (GLU) in all cycad tissues. Although GLU is distributed randomly throughout the plant, BMAA is concentrated in cycad reproductive organs, with the highest concentrations being found in the immature staminate sporangium and the outmost layer of the sarcotesta. This finding is consistent with the putative evolutionary role of BMAA as an antiherbivory compound, as well as the biomagnification of the compound in flying foxes that ingest the seed sarcotesta.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 165–168.     

Long-term response and recovery to nutrient addition of a partitioned arctic lake

1. To study the bottom‐up linkages in arctic lakes, we treated one side of a partitioned lake with inorganic nitrogen and phosphorus for a 6‐week period each summer for 6 years starting in the summer of 1985. We took a variety of weekly measurements to determine the impact of the nutrient loading on the lake and continued weekly measurements for 2–6 years after the cessation of nutrient loading to observe the recovery of the treated side. The loading rates (2.91 mmol N m^?2 day^?1 and 0.23 mmol P m^?2 day^?1) were five times the calculated loading rates for Toolik Lake, located nearby. 2. In all 6 years of nutrient addition, phytoplankton biomass and productivity were greater in the treated sector than the reference sector. In the first 4 years of nutrient addition there was no flux of phosphorus from the mineral‐rich sediments. This changed in the last 2 years of nutrient addition as phosphorus was released to the lake. 3. The response of the animal community to increased plant production was mixed. One of the four macro‐zooplankton species (Daphnia longiremis) increased in number by about twofold in the first 5 years. However, the copepod Cyclops scutifer showed no response during the treatment phase of the study. The benthic invertebrate response was also mixed. After a 2‐year lag time the snail Lymnaea elodes increased in the treated lake sector but chironomids did not. 4. Ecosystem response to fertilisation was not controlled solely by nutrient addition because phosphorus was not recycled from the sediments until the last 2 years of nutrient addition. Phytoplankton still showed the effects of nutrient addition in the recovery period and the hypolimnion of the treated sector was still anaerobic starting at 6 m in 1996.