Continuing dispersal of freshwater triclads (Platyhelminthes; Turbellaria) in Britain with particular reference to lakes

1. A survey of lakes in Anglesey and Snowdonia, Wales, in the summer of 1997 recorded changes in the triclad fauna which had occurred since earlier studies in the 1950s and in 1973. Two native species, Polycelis tenuis and Dugesia polychroa, and two immigrants, Planaria torva and especially Dugesia tigrina, have increased their range. The triclad fauna has remained unchanged with time in eleven out of sixteen lakes in Snowdonia, in contrast to only one out of fourteen lakes on Anglesey. This supports the hypothesis produced in the 1950s, that the triclad fauna of the ion-poor, unproductive lakes in Snowdonia would change little with time, being maintained by ecological interactions, whereas the ion-rich, productive lakes on Anglesey, from which native Dugesia spp. and Dendrocoelum lacteum are historically absent, would increase in triclad diversity. 2. An examination of national records for the distribution of D. tigrina and Pl. torva indicated their continuing dispersal in both still and running waters in mainland Britain, with the former species having the greater frequency of occurrence. 3. The reasons for this may be that D. tigrina is (a) more easily dispersed, (b) a more opportunistic, catholic feeder, (c) a more vigorous competitor, (d) able to reproduce asexually and (e) able to prey to some extent on other triclad species, as shown in the laboratory but not yet confirmed in the field. The absence of D. tigrina and Pl. torva from unproductive lakes may be explained in terms of low temperature and feeding mode, and a low standing crop of gastropods, respectively. 4. Seven surveys (1961–1997) of the triclad fauna (six species) of Colemere, England, revealed that D. tigrina was confined to one small area of the littoral zone until the mid-1980s, after which it spread fairly rapidly to occupy the entire shore by 1997. Its expansion has been to the detriment of all the native species, particularly P. tenuis, except Dd. lacteum. The possible extinction of Pl. torva may be linked to a numerical reduction in snails, particularly Potamopyrgus jenkinsi. 5. Dugesia tigrina has an adverse effect on the native triclad fauna in lakes, particularly when only a few species are present. This has been explained in terms of the availability of a wider variety of food. The presence of a larger number of triclad species denies the immigrant food items, particularly crustaceans and snails, the food refuges of Dd. lacteum and Dugesia spp., respectively. However, the long-term study of Colemere has shown that more diverse triclad faunas may also be vulnerable to this immigrant. The effect of Pl. torva on native triclads remains uncertain.     

A re-examination of the subspecies of Red deer (Cervus elaphus) with particular reference to the stocks in Britain

In 1906, Lönnberg identified a native subspecies of Red deer Cervus elaphus scoticus L., in Britain after examining a sample of stags' skulls from Glenquoich (Inverness-shire, Scotland). In north-west England, it is commonly believed that "Red deer of indigenous stock have persisted in this area (Furness Fells, Lancashire, England) from time immemorial…" (Chard, 1966). Arrangements were made to introduce animals into a park within this area in 1970, which, in view of this local opinion, would have been the only Red deer within the district not of native origin. Therefore, it was thought desirable to examine all the stocks of wild or feral Red deer in Britain and to determine which, if any, of them could be considered native and thus deserving of special measures to ensure their survival.
After examining samples of skulls, using multivariate analysis, it appeared that, within the limits of the material representing the various subspecies of the world, there was little support for the concept of subspeciation in Red deer. In Great Britain, however, there appeared to be two distinct forms of Red deer leading a free existence, one presumed to be native and the other to be of park derivation. Visually, the differences were indetectable and could be demonstrated only by discriminant analyses.     

Biogeography of limno-terrestrial Tardigrada, with particular reference to the Antarctic fauna

The Tardigrada is a cosmopolitan phylum of pre-Pangaean origin, yet tardigrade families and genera show distinct biogeographic components isolated by two major geological events. Separate Laurasian and Gondwanan familial clusters correlate with the Triassic disintegration of Pangaea, while discrete Antarctic, Australian and New Zealand familial/generic clusters relate to the subsequent Jurassic/Cretaceous disintegration of Gondwana.     

Status of the Nightingale Luscinia megarhynchos in Britain at the end of the 20th Century with particular reference to climate change

Capsule The population level may be unchanged but the range has contracted.

Aims To establish the current status of the Nightingale in Britain and explore causes for any changes.

Methods Over 3000 sites where Nightingales were known to have occurred since 1980 were surveyed by volunteers between mid-April and early June 1999. A selection of 135 random tetrads were also surveyed to gauge the efficiency of the volunteer survey in locating Nightingales.

Results The survey located 4565 singing male Nightingales while the random tetrad surveys suggest that c. 32% of birds occur away from known sites, increasing the estimate for the British Nightingale population to 6700 males (95% confidence limits 5600–9350) in 1999. A higher proportion of Nightingales was found in scrub (46.7%) than in 1976 (28.4%), suggesting a recent shift in habitat use.

Conclusion There is little evidence of a change in the size of the British Nightingale population, probably because earlier surveys underestimated numbers. The range has contracted markedly over the last few decades and numbers outside the core areas in southeast England are now low. Changes in habitat quality and increasing deer populations have caused decreases on a local scale. Changes in climate on the breeding grounds and general changes in climate or habitat suitability on the African winter quarters are likely to be important in influencing the distribution within England. Models of the effects of future climate change on Nightingale distribution in Britain predict that numbers and range should increase over the next few decades.     

Evolutionary ecology of colonial reef-organisms, with particular reference to corals

Sedentary reef-organisms such as sponges, colonial coelenterates, bryozoans and compound ascidians produce repeated modules (aquiferous systems, polyps, zooids) as they grow. Modular construction alleviates constraints on biomass imposed by mechanical and energetic factors that are functions of the surface area to volume ratio. Colonies thus may grow large whilst preserving optimal modular dimensions. Among corals, optimal polyp size is smaller in the more autotrophic than in the more heterotrophic species. Modular construction allows flexibility of growth form, which can adapt to factors such as water currents, silting, light intensity and proximity of competitors. Modular colonies have great regenerative capacities, even separated fragments may survive and grow into new colonies. All fragments from a parental colony are genetically identical and large branching corals frequently undergo clonal propagation through fragmentation during storms. Soft corals can also fragment endogenously. By spreading the risk of mortality among independent units, the generation and dispersal of fragments lessens the likelihood of clonal extinction. In spite of their ability to propagate asexually, most benthic colonial animals also reproduce asexually. The selective advantages of the genetic diversity among sexually produced offspring seem not to be linked with dispersal, but probably lie in the biological interactions with competitors, predators and pathogens in the parental habitat. Age at first sexual maturity and the proportional investment of resources in sexual reproduction are related to colonial survivorship. Small branching corals on reef flats grow quickly, attain sexual maturity within 1–4 years, planulate extensively, but reach only small sizes before dying. Massive corals are longer lived and have the opposite characteristics of growth and reproduction. Most sessile reef organisms compete for space, food or light. Faster growers can potentially outcompete slower growers, but are often prevented from doing so by several forms of aggression from competitors and by the damage inflicted by storms. Competitive interactions among sedentary organisms on coral reefs are unlikely to be linear or deterministic, and so the co-existence of diverse species is possible.     

Oviduct function in pigs, with particular reference to the pathological condition of polyspermy

Because the exceptionally high incidence of polyspermic fertilisation has been emphasised as a major defect in systems of in vitro fertilisation in pigs, the aetiology of the condition has been analysed in a series of experiments in vivo in the search for a common underlying cause and possible means of mitigation. Whereas the defense mechanism against polyspermy in pig oocytes is classically viewed as zona reaction, more recent evidence suggests a secondary block at the vitelline surface. Both blocks may be compromised in situations leading to polyspermy, although deleterious influences seem to be expressed principally in an inadequate zona block, as judged by the presence of perivitelline spermatozoa. Postovulatory aging of mammalian oocytes prior to sperm penetration leads to polyspermy, as can be demonstrated in pig eggs. The primary lesion may concern the cortical reaction, owing to a delayed and incomplete exocytosis of the vesicular contents. Eggs ovulated after gonadotrophin treatment during the luteal phase of the cycle show a high incidence of polyspermic penetration (60.6%), as do those shed at estrus in animals treated with progesterone systemically (40%) or by local microinjections in the oviduct wall (32.3%). Whereas progesterone may be modifying interactions of the gametes and responses of the egg organelles in all four above experimental situations, enhanced numbers of spermatozoa ascending a more patent isthmus appear to be the principal cause of polyspermy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular cytogenetics and taxonomy of insects,with particular reference to the coleoptera

We assess and review the impact of the new cytogenetic techniques in insects for their roles in taxonomy and for a better knowledge of their chromosomal structure. Particular emphasis is given to molecular cytogenetics by fluorescent in situ hybridization, localization of AT- or GC-rich regions with fluorochromes, and restriction endonuclease banding in beetle chromosomes. The main features of the cytogenetics of Coleoptera are treated in detail, taking into account the range of variation in chromosome number and genome size, and our in-depth findings on the constitutive heterochromatin and satellite DNAs of tenebrionid beetles. Some other topics of interest for insect cytogenetics, such as the meiotic association of sex chromosomes, the nucleolar organizing regions (NORs), and the molecular constitution of telomeres, are also discussed from the taxonomic and structural viewpoints.