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H Esch

Publications and source records attributed to H Esch.

7 recordsLinked to original sources
PubMed2003

A comparison of the dance language in Apis mellifera carnica and Apis florea reveals striking similarities.

Honeybees have a dance language by which successful foragers inform nestmates about attractive food patches. The classical concept of dialects in the dance language of honeybees points to two differences in the dances by different species and races, firstly in the flight distance at which the dancers start performing waggle dances instead of round dances, and secondly in the circuit duration of the waggle dance performed for a given flight distance. However, recent findings have indicated that the dance language is influenced and affected by a number of parameters, both genetic and environmental. The current study was carried out to see whether the distance at which dancers change from round dances to waggle dances is statistically different in two different species, Apis mellifera carnica and A. florea and to develop a set of definitions for such comparative studies. Results show that the two species do not differ in the relative proportion of waggle dances and round dances performed at a given distance. Thus, this study points to the need of addressing the dialect question again.

Animal Communication↗
PubMed1999

Phytochrome-controlled phototropism of protonemata of the moss ceratodon purpureus: physiology of the wild type and class 2 ptr-mutants

Phototropism and polarotropism in protonemata of the moss Ceratodon purpureus are controlled by the photoreceptor phytochrome. One class of phototropism mutants is characterised by growing randomly when kept for a prolonged time (5 d or longer) in unilateral red light. It was found that a subclass of these mutants grows faster than the wild type, the rate of cell division and the length of the cells being increased. This difference is found for light-grown and dark-grown filaments. It is therefore suggested that the mutant phenotype neither results from a defect in phytochrome photoconversion nor from a defect in phytochrome-gradient formation. Instead, it is possible that a factor which is involved in both signal transduction of phototropism and regulation of cell size and cell division is deregulated. If dark-grown mutant filaments are phototropically stimulated for 24 h, they show a weak phototropic response. Phototropism and polarotropism fluence-rate effect curves for mutants were flattened and shifted to higher fluence rates compared with those for the wild type. With wild-type filaments, a previously unreported response was observed. At a low fluence rate, half of the filaments grew positively phototropically, while the other half grew negatively phototropically. It seems that under these conditions, a phytochrome gradient with two maxima for the far-red-absorbing form of phytochrome (Pfr) within the cross-section of the cell is displayed by the response of the filaments. At higher fluence rates, all filaments of the wild type grew towards the light. These data and results from microbeam irradiation experiments and from phototropism studies with filaments growing within agar, indicate that light refraction plays an important role in the formation of the Pfr gradient in phototropism of Ceratodon.

Journal Article↗
PubMed1998

Light regulation of phytochrome content in wild-type and aphototropic mutants of the moss Ceratodon purpureus.

In filaments of the moss Ceratodon purpureus, phototropism is controlled by the photoreceptor phytochrome. Thirty-three aphototropic mutants with a proposed defect in phytochrome-chromophore biosynthesis were isolated and analyzed. The phototropic response of those mutants was rescued with the precursor of the phytochrome chromophore, biliverdin. Phytochrome spectral activity was measured in 19 arbitrarily chosen mutants. All contained low but still measurable quantities of photoactive phytochrome; the highest level was around 15% of the wild-type. The level of total phytochrome (apophytochrome and holophytochrome) as assayed by immunoblotting was indistinguishable from wild-type. The content of photoactive phytochrome in Ceratodon is light-regulated. Phytochrome of wild-type kept for 24 h in red light was reduced to 50% as compared to dark controls but was unaffected by blue. The red-light-induced decrease was partially reversible by far-red light, indicating that phytochrome itself is the photoreceptor for this response. This regulation was further analyzed with the mutant ptr114, which contains 15% photoactive phytochrome as compared to the wild-type. In this mutant, continuous red light given for 6 days decreased the level of spectrally active phytochrome down to 25% of dark controls, whereas the amount of phytochrome found on immunoblots was hardly reduced. This indicates that the loss of phytochrome affects only the holoprotein and implies that Ceratodon phytochrome is specifically degraded as a far-red-absorbing phytochrome.

Bryopsida↗
PubMed1997

Phytochrome control of phototropism and chlorophyll accumulation in the apical cells of protonemal filaments of wildtype and an aphototropic mutant of the moss Ceratodon purpureus.

The aphototropic mutant line ptr116 of the moss Ceratodon purpureus shows characteristics of a deficiency in the phytochrome chromophore. Photoreversibility measurements indicate an approximately 20 time lower concentration of spectrally active phytochrome compared to wild-type, whereas normal phytochrome apoprotein levels are found on immunoblots. Feeding with the tetrapyrroles biliverdin, the proposed precursor of the phytochrome chromophore, or phycocyanobilin, which may replace the phytochrome chromophore, resulted in the rescue of ptr116 phototropism. The ptr116 mutant and the phenotypically-related mutant ptr1 contain lower chlorophyll levels than the wild-type. Chlorophyll content of wildtype and mutant tissue grown under different light conditions was estimated using conventional spectrophotometry of extracts and fluorimetrically, on single apical cells. Dark-grown tissue contained about 100 times less chlorophyll than tissue grown under standard white light conditions. Red light given for 24 h to dark adapted filaments induced an increase in the chlorophyll content in the wildtype, but not in ptr116. Blue light induced an increase in chlorophyll both in wildtype and in ptr116. The red light effect on the wildtype was partially reversible with far-red. If ptr116 was grown on phycocyanobilin, an increase in chlorophyll was also found when cells were irradiated with red light. The results indicate that phytochrome as well as a blue light photoreceptor regulate chlorophyll accumulation in C. purpureus protonemata. It can be assumed that in ptr116, the synthesis of the phytochrome chromophore is blocked specifically beyond the synthesis common to chlorophyll and the phytochrome chromophore and affects an enzymatic step between protoporphyrin and biliverdin.

Bryopsida↗
PubMed1996

Distance estimation by foraging honeybees

Honeybees are widely believed to assess feeder distances by the energy spent on foraging flights. However, a critical review of this 'energy hypothesis' reveals many inconsistencies in the experiments from which it was derived. In fact, new evidence shows that the energy hypothesis cannot be correct. Foragers loaded with weights do not overestimate distance, as indicated by their waggle dances performed upon return to the hive. Bees that climb to a feeder on top of a high building (50 m) signal the same distance as hive mates that visit an equidistant feeder at ground level. Foragers visiting a feeder suspended from a balloon at 70 m from their hive underestimate the distance flown dramatically when the balloon lifts the feeder from ground level to 90 m, even though the energy required to reach the feeder increases considerably. Foragers from a hive situated on a high building (50 m) that fly to a feeder on the roof of another high building (34 m) signal a much shorter distance than the actual distance flown. We propose instead an 'optical flow hypothesis': bees use the speed of retinal image motion perceived from the ground to estimate the distance flown. Flight altitude is important for distance estimation by retinal image flow, because objects move faster and farther across the retina when the bee flies closer to the ground. When the forager's flight behavior is considered, the optical flow hypothesis does not conflict with previous findings.

Journal Article↗
PubMed1988

Neuromuscular electrophysiology of the filarial helminth Dipetalonema viteae.

1. A body wall preparation is described which permits intracellular recording from the somatic muscle cells of the small filarial nematode, Dipetalonema viteae. Using this preparation, resting membrane potentials were measured and spontaneous muscle depolarizations described. 2. Stimulatory effects noted upon the addition of acetylcholine, or the cholinergic agonists suggest the hypothesis that acetylcholine is the excitatory neurotransmitter. However, in contrast with vertebrate tissues, the cholinergic antagonists, d-tubocurarine, hexamethonium and pentolinium do not inhibit somatic muscle activity of the worm. 3. GABA inhibited somatic muscle depolarizations, suggesting the possibility that it may serve as an inhibitory neurotransmitter. 4. The anthelmintic drug, levamisole, produced a depolarizing block. Effects of other pharmacological agents are described, discussed and compared with effects on vertebrate muscles.

Animals↗