Proportion regulation in the planarian,Dugesia tigrina following regeneration of structures

Planarian regenerates with abnormal body proportioning were followed after structure formation in order to determine if body proportion will ‘normalize’ over time. Results show proportioning will occur following structure formation since the pharynx in regenerates with proportionally larger heads and prepharyngeal area moved anteriorly over time. This occurred regardless of whether regenerates were provided with a normal feeding regime which allowed for an increase in body area or if they were on a maintenance diet which did not permit growth. An examination of mitotic indices did not demonstrate significant differences in the level of mitotic activity between pre- and postpharyngeal regions. It is concluded that the ‘normalizing’ of proportion in these abnormal regenerates does occur, but the process by which it occurs is not solely explained through normal growth. This revised version was published online in July 2006 with corrections to the Cover Date.     

Notes on the biology of the freshwater planarian Dugesia bengalensis (Platyhelminthes Turbellaria Tricladida)

Dugesia bengalensis was described by Kawakatsu (Kawakatsu et al., 1983) from specimens collected in West Bengal. We have been studying populations from many different localities in Santiniketan and adjoining areas of West Bengal and can provide additional biological information.The species is hermaphroditic, and its breeding season was found to occur usually between October and March when the winter temperature falls below 25 °C. Outside of the breeding season, D. bengalensis is capable of asexual reproduction by binary fission (Mahapatra et al., 1987).Development of the reproductive organs appeared to be from neoblasts and other mesenchymal cells and, therefore, to be like that typical of other triclads with the exception that some of the neoblasts used for the reproductive tissue appeared to be derived from the intestinal region (Ghosh, 1988; cf. Teshirogi, 1986).During copulation, the partners were oriented in the same direction and not in a head-to-tail position as has been reported (Hyman, 1945) for some planarians.The oval, stalked cocoons were laid in marshy places, and during the period of summer (usually from April to June) they lay dormant in the sandy soil until the onset of the monsoon rains. Then, typically three or four months after they were laid, the cocoons hatched to yield three or four young, a remarkably low number for freshwater triclads (cf Ball & Reynoldson, 1981).     

Colonization of rivers and canals in Great Britain by Dugesia tigrina(Girard) (Platyhelminthes: Tricladida)

SUMMARY. 1. Prior to 1975 Dugesia tigrina , an Americati immigrant triclad, was known from only a few flowing water sites in Great Britain. Since then it has been found in a large number of lowland rivers and canals in England and Wales, and in 1985 it was reported from the lower reaches of the River Tweed in Scotland.
2. This note gives the recorded distribution of D. tigrina up to the end of 1985 (115 10 km squares now occupied) and summarizes the environmental conditions at a subset of twenty-five sites where D. tigrina occurs.
3. Information on the native triclads at sites recently colonized by D. tigrina is used as a basis for speculating on the rivers most vulnerable to the future spread of this species.
4. Possible methods of dispersal of D. tigrina and the features which make it a successful colonist are discussed.     

The population biology ofTapinoma minutum (Hymenoptera: Formicidae) in Australia

Summary Nests ofTapinoma minutum were collected and mapped from a wet sclerophyll forest in New South Wales during the spring, summer, and fall seasons. Queen number was variable, indicating the population is both facultatively polygynous and polydomous. Electrophoretic data from three polymorphic enzymes revealed that relatedness among workers conformed to the Hamiltonian expectation of 0.75. Colony boundaries were inferred from electrophoretic data synthesized with nest spatial locations. For this species colonies were composed of at most three nests; this simple pattern of polydomy suggests it has a recent origin in this population. The pattern of facultative polygyny may be linked to an apparent high rate of colony orphaning.     

Population Growth in Planaria Dugesia tigrina (Gerard) : Regulation by the absolute number in the population

Planaria reproduce by transverse fission. Isolated worms increase in number exponentially, while social animals at the same density are inhibited in terms of numerical increase, but over a 25 day period undergo a larger increase in mass. Isolated posterior fission products reproduce faster than isolated anterior fission products. Regulation of population growth is independent of density over a 16-fold range and regulatory factors cannot be demonstrated in the medium. Regulation of population growth depends on direct contact between animals. Fission period varies from individual to individual and from period to period for a given individual. Doubling time is related to the absolute number of individuals comprising the population as follows: P_N = (P_M · N)/(K + N), where P_N is the doubling period of a population of N individuals, P_M is the doubling time of an infinitely large population, N is the number of individuals in the population, and K is the number of individuals in a population the period of which is one-half P_M. At 22°–24°C P_M is estimated to be 43.3 days and K is 1.87 individuals. A model system assumes that inhibitor flows through the population from animal to animal from the slowest to the fastest animal in the population thus acting to synchronize population increase as well as to determine the rate of population growth. A possible source of the inhibitor is discussed.     

Monoclonal antibodies as markers of specific cell types and regional antigens in the freshwater planarian Dugesia (G.) tigrina

We have produced monoclonal antibodies (mAb's) against antigens of the fresh-water planarian Dugesia (G.) tigrina (Girard) using standard protocols. Labeling these mAb's with PAP (peroxidase-antiperoxidase) and indirect-immunofluorescence methods, we then determined the distribution of their antigens in the planarian. Out of 112 mAb's that showed some specificity for restricted parts of the planarian, 71 were found to be cell- or tissue-specific — among them 36 for parenchymal cells, 7 for muscle cells, 11 for epidermal cells, 8 for gastrodermis, and 7 to basement membrane. Another 41 showed different, but overlapping, regional specificities, namely to pharynx and parenchyma. So far, we have been unable to isolate specific mAb's against undifferentiated cells (neoblasts). These mAb's should be important tools in study of tissue and cell morphology, regeneration, and growth and degrowth.     

Positional information and gonadal differentiation in the planarian Dugesia lugubris (Turbellaria)

The planarian Dugesia lugubris is a balanced hermaphrodite, meaning that male genetic factors are in equilibrium with female factors. Differentiation of the gonads is controlled by the region in which they develop. According to the classical theory of germ cell formation, these cells stem from neoblasts that are induced to differentiate by factors specific to the gonadal regions, factors presumably due to gradients formed by neurosecretory activity of the cephalic ganglia and longitudinal nerve cords. A more recently proposed theory holds that germ cells in regenerates originate not from neoblasts but from dedifferentiated cells and that characteristics of the gonadal regions are determined by direct interactions of cells here. Results of our experiments with homo- and autoplastic grafst support the classical theory. Prepharyngeal portions grafted onto posterior body portions retained their ability to maintain or induce development of ovaries. Postpharyngeal portions grafted onto anterior portions produced only testes even though the brain developed normally in these regenerates. Under these experimental conditions, gonad regeneration took longer than it does in normal regeneration (i.e., that in which body regions are not displaced).Translated, from the French, by Marianne Klauser and Seth Tyler.     

On reconstructing the (once) living population from osteological age data

It is shown how the sex and age distribution of the (once) living population can be calculated from estimated mortalities. Fertility calculations and estimations of the number of children per woman are provided as well. The method is applied to two materials from the Middle Ages: Westerhus and Helgeandsholmen.     

The population biology of Camallanus lacustris (Zoega) in eels, Anguilla anguilla (Linnaeus), and their status as its host

The population biology of Camallanus lacustris (Zoega) and the status of the eel, Anguilla anguilla (Linnaeus), as its definitive host have been studied in a small Devon lake. No clear seasonal pattern in prevalence and abundance was observed, and recruitment of the new generation may occur in all seasons. However, reproduction exhibits some seasonality as adult nematodes were the commonest stage in the parasite population from early summer onwards and production of first-stage larvae appeared to occur primarily during this period. These larvae were viable, and shown experimentally to be infective to copepods. The occurrence of the nematode and its development to full maturity in eels, the absence of its typical definitive host ( Perca fluviatilis Linnaeus) from the lake and the absence of the nematode from other species of fish in the lake indicate that eels serve as the only, true definitive host of the nematode in this locality. It is suggested that account must be taken of this alternative host when the population of C. lacustris is investigated in the future.     

TCAV-1, a monoclonal antibody specific to epithelial pharyngeal cells in the planarian Dugesia (Girardia) tigrina. Application to pattern formation of the pharynx during regeneration

During regeneration in planarians, anterior (head and prepharyngeal) and posterior (postpharyngeal and tail) fragments rebuild one of the most peculiar structures of planarians: the pharynx and the pharynx cavity. Previous studies (see Brønsted, 1969, for a general review, and Asai, 1990, 1991, for anterior regeneration) have shown that within postpharyngeal pieces both structures appear in the old stump from clusters of undifferentiated cells. However, the lineage and differentiation of their elements (inner and outer epithelial cells, muscle layers, gland cells, nerve rings) and the overall pattern of growth and differentiation is not clear.     

Repeated DNA elements in planarians of the Dugesia gonocephala group (Platyhelminthes,Tricladida)

The results of the isolation of repetitive DNA elements in the genome of Dugesia etrusca, a species of the Dugesia gonocephala group, are reported. These sequences, about 1.4 kb long, represent only a part of longer interspersed genomic units (De1 family) and appear to be limited to the genome of some planarians of this group, as indicated by a Southern blot analysis performed in different species and populations. The genomic relationships among different species and populations of the D. gonocephala group are discussed in relation to the results obtained in the present work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ultrastructural observations on gastrodermal regeneration in the planarian Dugesia japonica (Turbellaria)

The earliest detectable change during regeneration of the gastrodermis in Dugesia japonica was an aggregation of regenerative cells underneath the gastrodermis remaining at the wound margin. The gastrodermal cells in experimental regenerates retained some of their original characters and presented no indication of cell dedifferentiation. The regenerative cells came into contact with the basal surface of gastrodermal cells, forming stratified cell layers. Differentiation of these cells into gastrodermal cells was initiated by the development of synthetic organelles within their cytoplasm. These differentiating cells gave rise to two different types of gastrodermal cells, namely phagocytic cells and sphere cells. In later stages, there was an apparent movement of differentiated gastrodermal cells towards the parenchyma.     

Population responses of perch (Perca fluviatilis) and roach (Rutilus rutilus) to recovery from acidification in small Finnish lakes

Decreasing trends in atmospheric emissions and acidic deposition during the 1990s have resulted in chemical recovery from acidification in the sensitive surface water systems of southern Finland. Responses of perch and roach populations to the improved water quality were studied in 30 small lakes with the aid of water chemistry monitoring data gathered in 1987–2002 and the data collected from two consecutive periods of gillnet test fishing, 1985–1988 and 2001–2002. In the most acidified lakes, alkalinity and ANC have increased and sulphate and labile aluminium concentrations decreasæed markedly. The response of perch populations to the improved water quality is seen in improved reproduction success, indicated by a higher CPUE in numbers and a lower mean weight. The growth rate of perch has declined as the population density has increased. Roach populations have not recovered in the same way as perch, there being no major changes in NPUE or mean weight. Lower growth rates were, however, observed in the roach populations of all study lakes. The increased perch population density as an obstacle to the recovery of roach populations is discussed. Despite the chemical and biological recovery of the study lakes, the buffer capacity of many headwater lakes is low and the lakes will be sensitive to any increases in acidic deposition in the future.     

Effects of fluctuating temperatures on the population dynamics of Hexarthra bulgarica (Wiszniewski) from high mountain lakes in Sierra Nevada (Spain)

We examine the development of Hexarthra bulgarica (Wisniewski) populations in relation to thermal stability in natural environments. A high frequency sampling program was developed simultaneously in two high mountain lakes: a shallow one, with daily large temperature changes but little surface-bottom temperature difference and a deeper one with more stable temperature but vertical heterogeneity in the water profile. Since the capacity of H. bulgarica to perform vertical migrations in these lakes of Sierra Nevada is already known, we have studied the relationship between egg ratios and chlorophyll-a concentration, mean temperatures and temperature instability (measured as the daily rate of temperature change — TCR — as well as the surface-bottom temperature difference — SBT -) in both lakes. Results show that the intensity of temperature fluctuations has a positive effect on the egg-ratios, as TCR is only correlated with that variable in the shallow lake and SBT is only correlated with egg-ratios in the deeper one.     

Nitrogen in the Pyrenean lakes (Spain)

Lakes in the Pyrenees show a broad variability in nitrogen content and in the distribution of its different oxidation forms, which has no direct relation with any single physiographical, chemical or trophic feature of the lakes. Concentration of bound nitrogen in rain is low compared with other European mountains, but the annual load lies in the middle range. Seasonal and local variation in the composition of rainwater mainly depends on the geographical origin of the storms. Catchment and in-lake processes introduce further variability: NH₄ ⁺, which is at similar concentration to NO₃ ^- in the rain, is quickly oxidized or adsorbed in the catchment; aquatic macrophytes can either reduce mean NO₃ ^- concentration in lake water (Ranunculo-Potametum) or greatly increase it in sediment pore water (Isoetes); NO₂ ^- depends on pH; decomposition of particulate nitrogen in sediments changes with depth; lakes act as traps for dissolved inorganic nitrogen; changes in dissolved organic nitrogen suggest high microbial activities even in cold waters; melting period introduces most of the seasonal variability. Institute of High-Mountain Research, University of Barcelona     

Population biology of Proteocephalus macrocephalus (Creplin) in the European eel, Anguilla anguilla (Linnaeus), in two small rivers

Seasonal changes in populations of Proteocephalus macrocephalus (Creplin) were investigated for 17 months in the European eel, Anguilla anguilla (Linnaeus), in two rivers in Devon, SW England, but no clear seasonal patterns in prevalence and abundance were apparent. Population levels of the cestode are low in both localities, and it is suggested that natural population levels of P. macrocephalus may generally be low. However, growth and maturation of the cestode show marked seasonality with both occurring mainly in early summer.     

TCEN-49, a monoclonal antibody that identifies a central body antigen in the planarian Dugesia (Girardia) tigrina. Implications for pattern formation and positional signalling mechanisms

We have produced monoclonal antibodies (mAbs) against antigens of the freshwater planarian Dugesia (G.) tigrina (Girard) using standard protocols. One of these mAbs, TCEN-49, detects an antigen (TCEN-49Ag) present in most cells of the central area of the body, including the pharynx. Labelled cells seem more related by position than by lineage, suggesting that TCEN-49Ag is involved somehow in the expression of central body positional identity. The spatial and temporal changes in TCEN-49Ag expression during growth/degrowth and regeneration have been monitored and the implications of these results are discussed.     

Morphological stages of regeneration in the planarian Dugesia tigrina: A light and electron microscopic study

A precise sequence of four morphological stages of head regeneration in the planarian Dugesia tigrina has been determined by light and electron microscopy. Each stage is identified by a particular morphogenetic process: I, wound healing; II, blastema development; III, growth; IV, differentiation. A wound epidermis consisting of a thin, sheet-like layer of cells, rapidly forms from undamaged epidermal cells at the wound margin. The early blastema is comprised of neoblasts which mature into regeneration cells. The maturational changes include the appearance of a nucleolus, nuclear pores, and perinuclear dense aggregates of granulofibrillar material in these cells. These elements are not evident in the neoblasts of the younger blastema. No mitotic cells are encountered in the blastema or wound epidermis. Cytoplasmic expansion of the regeneration cells is correlated with the formation of numerous microtubules radiating from a juxtanuclear centrosphere. During differentiation of muscle cells, distended, granule-studded cisternae, having moderately fibrillar contents, are regularly disposed adjacent to small patches of myofilaments. Presumptive epidermal cells are recognized by prominent “islands” of finely fibrillar cytoplasm. These cytoplasmic zones persist for a time during definitive differentiation when Golgi bodies, vacuoles, mucous droplets, and rhabdites become evident. The newly formed epidermal cells become inserted among the cells of the wound epidermis. Thus, cells of both the blastema and of the wound epidermis contribute to the reconstituted epidermis.     

Inhibition of regeneration in the planarian Dugesia polychroa (Schmidt) by treatment with magnesium chloride: a morphological study of wound closure

At a concentration of 0.2% (21 m M) in culture water, magnesium chloride impaired muscle contraction and completely inhibited head regeneration in specimens of Dugesia polychroa cut prepharyngeally. The wound stayed open for nine days, with neoblasts accumulating beneath the wound without any signs of differentiation. Extremely delayed wound closure occurred by spreading epithelial cells, and was completed after 30 days in the magnesium chloride solution. Histological examination confirmed the absence of any regenerated head structures. Interestingly, the inhibitory effect was removed when such headless fragments were cut once more and kept in normal culture water: complete head regeneration then occurred at a normal rate. Among several possible explanations for the failure to regenerate, the following hypothesis is an attractive alternative: direct contact between parenchyma and epithelial cells during the period following injury seems to be an essential stimulus for the start of cell differentiation within the blastema, and the lack of such contact as a result of the drug action prevents normal regeneration. When the wound has eventually closed, a continuous basement membrane separates epithelium from parenchyma. Thus a direct contact between these tissues is never established. This revised version was published online in July 2006 with corrections to the Cover Date.