A new African species of parasitic Dero (Annelida, Clitellata, Naididae) in the urinary tract of reed frogs

A new species of naidid oligochaete, Dero rwandae, detected in the bladder and the Wolffian ducts of reed frogs Hyperolius kivuensis from Rwanda, is described. Until now, D. bauchiensis was the only endoparasitic Dero known to infect African frogs infesting the eyes and Harderian glands. To the best of our knowledge, the finding of D. rwandae is the first record of an African Dero species infecting the urinary tract of anurans. In general morphology, the two African Dero parasites resemble each other, but differences in the features of ventral setae morphology exist. Parts of the mitochondrial 16S rRNA locus and the nuclear 18S and 28S rRNA loci were sequenced to assess the phylogenetic relationships to other Dero spp. Among those few species, that are barcoded so far, the closest relative of the new taxon is D. superterrenus, a free-living South American species. The species groups formerly termed subgenera Allodero, Aulophorus and Dero within the genus Dero do not represent distinct evolutionary lineages and the genus is paraphyletic including Branchiodrilus.

Seasonal changes in the tolerance of osmotic stress in natterjack toads (Bufo calamita)

1. Bufo calamita were exposed to tap water to solutions of urea (up to 1000 mM) and NaCl (up to 250 mM). 2. The effects of season and nutrition on the adaptation to osmotic stress were studied by monitoring body mass, moulting rate, hematocrit, plasma osmolality and the plasma concentrations of urea, chloride and glucose. 3. There were marked seasonal changes in the time of survival in tap water as well as in the ability to acclimate to high concentrations of urea and NaCl. 4. The maximal concentration of urea in the plasma of starving toads was greater in winter (650 mM) than in summer (410 mM), but fed toads also reached winter levels (653 mM) during summer. 5. Salt acclimation was accompanied by urea accumulation in plasma up to 175 mM. 6. Salinities exceeding 454 mOsmol/l of NaCl were lethal.

Reabsorption of water and electrolytes in the urinary bladder of intact frogs (genus Rana)

1. Water and electrolyte reabsorption of the urinary bladder epithelia has been studied in intact, fully hydrated frogs (Rana temporaria, R. lessonae, R. ridibunda). 2. The rates of water reabsorption were lower in frogs on wet soil than in those on dry soil and related to the degree of terrestrialism: R. temporaria greater than R. lessonae greater than R. ridibunda. 3. Samples of urine stored up to 24 hr within the urinary bladder were analysed for osmolality and the concentration of urea, ammonia, sodium, potassium, magnesium and calcium. 4. Selective reabsorption of sodium was detected in all species, that of calcium only in R. ridibunda. The efficiency of electrolyte reabsorption was also related to the degree of terrestrialism. 5. In conclusion, in fully hydrated frogs reabsorption by the bladder epithelia contributes significantly to the water and electrolyte conservation.

Orientation behaviour of toads (Bufo bufo) displaced from the breeding site

The sensory basis and spatial range of orientation to the breeding site were studied in the toad Bufo bufo, during two breeding seasons. Toads were displaced passively from their breeding pond and fitted with a tracking device to record the path of migration in individuals. The directional choice and the straightness of trails after release were used to quantify the effect of experimental treatments. In both years, control (untreated) toads headed to the breeding site with the same precision at all release sites. The initial orientation of toads blinded by opaque tape over their eyes did not differ from controls, but the return paths were not as direct. The directional choice of anosmic toads was apparently random, however, individuals followed a straight path in a chosen direction. Anosmic toads also blinded were completely disoriented, moving in cycloid trails. Bar magnets glued to the head caused an increase in dispersion of toads. However, in some individual releases a directional bias without increased dispersion was observed. Sky conditions (clear or overcast) did not influence the initial orientation or the dispersion of toads. Nevertheless, the breeding site component was significantly correlated with wind direction in relation to the breeding site. Wind blowing from the breeding site improved the initial orientation, whereas wind from the opposite direction reduced the breeding site component. The spatial range for the ability to relocate the breeding pond after displacement exceeded 3 km, but the time taken to select the correct direction increased with the displacement distance. The results indicate that after displacement the initial orientation of B. bufo is based mainly on olfactory and magnetic cues, with visual control of straightness.