SUMMARYMicrosporidia are intracellular parasites, frequently infecting the planktonic crustaceanDaphnia.Questioning the ability to detect and identify microsporidia with conventional microscopic techniques, we applied molecular methods in order to investigate the distribution and co-infection patterns of this parasite among 8 communities of theDaphnia longispinahybrid complex. Eight microsporidian taxa were detected, including 3 that previously had not been characterized genetically. Microsporidian communities from nearby lakes were found to be more similar to each other, apparently due to short distance dispersal via secondary hosts. Moreover, we detected seasonal (but not interannual) changes in microsporidian community structure. With some microsporidia being host-specific, these changes might have resulted from seasonal changes in host taxon and clonal composition. The 2 dominant and closely related parasite species were found mainly in single infections, whereas another pair of related microsporidians was found predominantly in co-infections; suggesting species-level differences in the ability to colonize infected hosts. By applying molecular methods, we were not only able to unambiguously identify parasite taxa but also to reveal multiple infections that otherwise would have remained undetected. Given the increased level of accuracy and sensitivity, we highly recommend molecular approaches in future parasite surveys ofDaphniainfections.
Specimens of the fish louse Anilocra physodes L. from the Mediterranean Sea exhibited a striking colour asymmetry in their dorsal pigmentation: one longitudinal half of their back was dark, the opposite half was lightcoloured. The dark side corresponded with the physiological upper side when the fish louse was attached to the flank of a host fish.The colour pattern derives from the different shape (stellate/punctate) of chromatophores, which lie immediately beneath the epidermis. The appearance and distribution of the chromatophore stages indicate the possibility of physiological colour change in Anilocra. In this way the fish louse probably achieves adaptive countershading and thus additional protection from predators, advantageous for both parasite and host.
The egg of the leafhopper Euscelis plebejus contains 2 types of symbiontic bacteria classified by MüLLER (1949) as t- and a-symbionts. They are lodged near the posterior egg pole as a nearly spherical mass surrounded by periplasm. During anatrepsis of the germ band the volume of the symbiont mass increases considerably. At the same time the a-symbionts are taken up by primary a-mycetocytes which then form a spherical layer around the as yet extracellular mass of t-symbionts. When the mesoderm of the abdominal segments starts to differentiate into organ primordia, a cluster of presumably polyploid mesoderm cells leaves the 2nd abdominal segment and migrates towards the 5th and 6th abdominal segments where the symbionts are lodged. There these cells are filled with the t-symbionts which they harbour through all further stages of embryonic and postembryonic life. The a-symbionts before katatrepsis of the germ band appear to be taken over by a second type of a-mycetocyte which stems from the genital ridge of the 4th-6th abdominal segments and as a rule is binucleate. During and after katatrepsis the t-mycetocytes and secondary a-mycetocytes migrate from their medial position to the lateral walls of the abdomen where they form one compound mycetome on each side.
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