Life history, ecology and parasite community structure in Soviet birds

The paper describes an investigation of parasite richness in relation to host life history and ecology using data from an extensive survey of helminth parasites (cestodes, trematodes and nematodes) in Soviet birds. Correlates of parasite richness (number of parasite species per host species) were sought among 13 life-history variables, 13 ecological variables and one non-biological variable (number of host individuals examined) across a sample of 158 species of host. A statistical method to control for the effects of phylogenetic association was adopted throughout. Parasite richness correlates positively with the number of hosts examined (sample size) in all three parasite groups. Positive correlations (after controlling for the effects of sample size) were also found between host body weight and parasite richness for trematodes and nematodes, but not for cestodes.
A number of ecological variables were associated with parasite richness. However, when the effects of sample size and body weight were controlled for, only a single significant correlation (an association between trematode richness and aquatic habitat) remained. Similarly, a number of significant correlates of parasite richness were found among the life-history variables examined. Though several of these were robust to the confounding effects of sample size, all could be explained by the co-variation between life-history traits and body weight among the host species under investigation.     

Parasitic worms: strategies of host finding, recognition and invasion

Many parasitic worms enter their hosts by active invasion. Their transmission success is often based on a mass production of invasive stages. However, most stages show a highly specific host-finding behaviour. Information on host-finding mechanisms is available mainly for trematode miracidia and cercariae and for nematode hookworms. The larvae find and recognise their hosts, in some cases even with species specificity, via complex sequences of behavioural patterns with which they successively respond to various environmental and host cues. There is often a surprisingly high diversity of host-recognition strategies. Each parasite species finds and enters its host using a different series of cues. For example, different species of schistosomes enter the human skin using different recognition sequences. The various recognition strategies may reflect adaptations to distinct ecological conditions of transmission. Another question is how, after invasion, parasitic worms find their complex paths through their host's tissues to their often very specific microhabitats. Recent data show that the migrating parasite stages can follow local chemical gradients of skin and blood compounds, but their long-distance navigation within the host body still remains puzzling.

The high complexity, specificity and diversity of host-recognition strategies suggest that host finding and host recognition are important determinants in the evolution of parasite life cycles.     

Ecdysteroids in adult males and females of Drosophila melanogaster

Ecdysteroid titres in whole flies and different tissues of adult male and female Drosophila were determined at various times after eclosion using a radioimmunoassay. The ecdysteroid titre decreased as the flies matured after eclosion. The differences in titre between males and females can be accounted for by their difference in body weight. The ecdysteroids were found to be distributed throughout several tissues. At eclosion not all of the ecdysteroid complement present could be accounted for by that found localised in tissues. After maturation of the flies the ecdysteroids in various tissues can account for the majority of that detected in whole-fly extracts. Ecdysteroids were produced during in vitro culture of various tissues, but the quantities detected were low by comparison with ring glands of wandering 3rd-instar larvae. Neither the ovaries nor the abdominal body walls (fat body) seem to be a major source of hormone, and they are only able to convert minute quantities of ecdysone to the biologically active form, 20-hydroxyecdysone, in vitro. The amounts of 20-hydroxyecdysone present were measured using high performance liquid chromatography and radioimmunoassay. We tentatively suggest that the differential experession of the yolk-protein-genes in the fat bodies of males and females does not result from differences in hormone titres between them.     

The position of the Haplotaxidae in the evolution of oligochaete annelids

The Haplotaxidae have all the characteristics to support the hypothesis that they are the living descendents of the stem forms from which all of the Oligochaeta Clitellata (Orders Lumbriculida, Haplotaxida, Lumbricida, Tubificida) can be derived. The Aphanoneura are distinct from the Clitellata and are raised to a separate Class. There is no evidence to support the view that the elaborate setae of many Tubificida are derived from a polychaete ancestry; both are held to be independent modifications to aquatic life derived from a simple burrowing protoannelid with lumbricine setae.     

Transfer of Schistosoma mansoni into the mesenteric veins of hamsters

A simple and rapid procedure for the transfer of schistosomes into the mesenteric veins of hamsters is described. Recovery of worms was equally high (67%) for schistosomes grown in the hamster and for those grown in the mouse, while it was only slightly lower for rat worms (63%). Survival of recipient hamsters was 80%. The transfer procedure did not seem to affect the normal development of worms and led to a rapid recovery of rat worms with resumption of their egg-laying capacity. The potential usefulness of the method is outlined, with special emphasis on its recommended use for schistosome genetics.     

Mysterious `crystals': found attached to the epidermal peritoneum of marine tubificid (Annelida,Clitellata) species

Marine tubificids are abundant and diverse in the carbonate sediments of Bermuda, as well as in many other tropical and subtropical locations. Recently, during microscopic observations of living specimens, crystal-like structures were observed attached to the coelomic peritoneum and in the coelomic cavity of some Bermuda species, including phallodrilines of the genera Aktedrilus and Pectinodrilus,and a rhyacodriline of the genus Heterodrilus. Similar structures were not seen in tubificid species of Thallasodrilides and other limnodriloidines, a second species of Heterodrilus, a tubificine of the genusTubificoides, a phallodriline of the genus Bathydrilus,nor in a number of marine enchytraeid genera and species found in Bermuda. The crystal-like structures have two needle arms, each about 5–10 m long and about 0.5 m in diameter, meeting at an obtuse angle. At the junction of the arms, there is a small membrane-bound `knob', about 1 m in diameter, which may be continuous with the coelomic peritoneum. The numbers of `crystals' per individual worm are estimated at 100–400 per body segment, or well over 2 × 10³ in an adult worm. `Crystals' are found: throughout the length of the worms, in all individuals of species in which `crystals' occur, and over the range of environmental conditions where these species are found in Bermuda. Simple digestions with hypochlorite, weak and dilute acids, and staining with nuclear and cytoplasmic stains indicate that the composition of the knob is organic and the arms inorganic. The fluorescent tracer Calcein (Sigma) was not incorporated into any structures during a 24-h bath incubation of living worms, and the `crystals' do not show birefringence when viewed between crossed polarizing filters. These last two results do not support an hypothesis that these are calcium carbonate `crystals'. Geographically, the crystal-like structures are widespread, and have also been observed in a species of immature (unidentified) marine tubificid from Rottnest Island, Western Australia.