Asexual propagation and reproductive strategies in aquatic Oligochaeta

A great variety of asexual reproductive modes are known among aquatic oligochaetes. The main types of these modes are shortly described. Based upon observations on natural populations, the possible genetical and ecological implications of asexual reproduction are discussed. The following points are emphasized: (1) The often expressed expectations of a strong predominance of one particularly adaptive genotype is not born out. (2) In most cases, a number of genetically distinct clones are present in each population, and they show a strong differential distribution in heterogeneous environments, indicating an effective exploitation of the available resources. (3) Most cases of asexual propagation are reproductive strategies of their own and not escape mechanisms. (4) The mechanisms underlying asexual propagation are complex and involve many aspects of the life history. The great variety of types among aquatic oligochaetes offer particularly useful models for the study of these problems.     

Progress in cohort cultures of aquatic Oligochaeta

Our laboratory work on the life cycle of aquatic Oligochaeta has been extended to the tubificids Potamothrix hammoniensis and P. heuscheri, as well as to the lumbriculid Bichaeta sanguinea.Basically we measured the duration of the time required for the embryonic development inside the cocoons, at different temperatures. In addition, cohorts of these species were cultured and the time required to attain the sexual maturation and the cocoon laying stages were estimated.The results concerning these three species are consistent with the field observations, as far as their value as indicator species is concerned, and contribute to a further understanding of the role of biotic factors in determining the distribution and succession of some aquatic Oligochaeta.     

The effect of water movement on the distribution of Oligochaeta in lakes

The Oligochaeta are more exposed to disturbance under conditions of intense water movement than other invertebrates, particularly when the substrate is unstable. Furthermore, low mobility of bottom water, which can lead to excessive accumulation of organic matter in sediments, and to the formation of sapropel, can also be limiting to the distribution of oligochaetes. Organic contamination in conditions of low water dynamics can result in the absence of Oligochaeta through oxygen depletion. Dynamic water movement can stimulate the mass development of Oligochaeta in organically polluted areas.     

Distribution and ecology of Middle Atlantic Bight Oligochaeta

Distribution and ecology of continental shelf oligochaetes are poorly understood. From 1975 through 1977 baseline ecological studies were conducted in the Middle Atlantic Bight prior to oil exploration activities. A total of 38 species in three oligochaete families were collected. Of this total one family and 29 of the species were undescribed at the time of collection. The most abundant and widely distributed species were Limnodriloides monothecus, L. medioporus, Bathydrilus longus, Phallodrilus biprostatus, and Tubificoides diazi. No single species dominated the oligochaete fauna. All the oligochaete species responded to changes in physical parameters over the shelf similarly to the total macrofauna. Seasonal trends within the oligochaetes were not found. Species that preferred coarser sand sediments were all small interstitial forms. The finer sand and eurytopic species were all burrowers. Zoogeographically the Middle Atlantic Bight oligochaetes were predominantly temperate (16 species) with some southern species (8). Seven species were broadly distributed from the Caribbean to Massachusetts or around the world. Seven species were only known from the area studied.Contribution No. 1397 of the Virginia Institute of Marine Science.     

Life-cycle and karyology of Branchiura sowerbyi Beddard (Oligochaeta,Tubificidae)

Data on the life-cycle of a population of Branchiura sowerbyi Beddard in a water-lily tank at the Botanical Garden in Padua are reported. The breeding period is from April to July, after which the reproductive system is partially resorbed (August–September) and reformed later in the autumn. The karyology of the species was also studied, and revealed 38 mitotic chromosomes in the gonia, and 19 bivalents in the primary spermatocytes and in the primary oocytes.     

New records of aquatic Oligochaeta from Texas,with observations on their ecological characteristics

Twenty-six species of aquatic oligochaetes are reported from Texas, including 18 Naididae, seven Tubificidae, and one Glossoscolecidae. Illustrations are provided for ten species recorded for the first time from the state: Chaetogaster cristallinus, Nais elinguis, Nais pardalis, Pristina acuminata, Pristina sima, Stylaria lacustris, Aulodrilus limnobius, Ilyodrilus templetoni, Limnodrilus claparedianus, and Sparganophilus tamesis. Species accounts include presently known distributions in Texas and ecological and morphological characteristics.     

Oxygen demand and long term changes of profundal zoobenthos

The paper attempts to combine the low oxygen content of the hypolimnion during stratification and the oxygen uptake of zoobenthos. Data of declining oxygen content in the hypolimnion and critical limits of respiration are combined for Chironomus anthracinus, Potamothrix hammoniensis and three species of Pisidium, P. casertanum, P. subtruncatum and P. henslowanum. The respiratory adaptation to low oxygen content influences both growth and population dynamics of the different species. The results have important bearing on eutrophication of the Lake Esrom ecosystem and temperate eutrophic lakes in general as well as the composition of profundal zoobenthos and its population dynamics.Publication No. 389 from Freshwater-Biological Laboratory, University of Copenhagen.     

A taxonomic and faunistic survey of the marine Tubificidae and Enchytraeidae (Oligochaeta) of Italy. Introduction and preliminary results

On the basis of material collected along the Ligurian, Tyrrhenian, Ionic and Adriatic coasts of Italy, a tentative list of 26 species (18 tubificids, 8 enchytraeids) of marine Oligochaeta is presented. Most of the species are new to science, and it can therefore be concluded that there is a very high diversity of oligochaetes in the Mediterranean Sea.     

Oligochaeta of the middle Po River (Italy): principal component analysis of the benthic data

The application of principal component analysis to two types of habitat (the benthos of macrophytes and of central river bed) enabled us to single out some of the factors that affect the dynamics and the structure of the oligochaete population and its various reactions to environmental conditions. As regards macrophytes, the distribution of the variables on the basis of the first component is correlated, to a certain extent, with a seasonal factor without any significant differences among sites. The largest population is most closely correlated with the summer months. In fact, we found that the Naididae and Tubificidae species generally develop in larger numbers at higher temperatures. For the Tubificidae, we could detect a precise seasonal cycle. In the central river bed habitat, the first component was correlated with the river discharge, which determines the granulometric characteristics of the sediment; we noticed a correlation among the sites that have the same characteristics, regardless of sampling site or date. The species which correlate most closely among themselves are the Tubificidae Limnodrilus hoffmeisteri, Tubifex tubifex, L. udekemianus and L. profundicola, which are very characteristic of environments that contain abundant organic matter. The second component is correlated with temperature, and hence with the availability of oxygen, which determines the presence and the abundance of more sensitive species.     

The occurrence of species of semi-aquatic Enchytraeidae (Oligochaeta) in Ireland

The Enchytraeidae are essentially terrestrial oligochaetes but many species have marked aquatic tendencies. Over two thirds of recorded Irish species were found in soils which were submerged or frequently flooded and 35% showed a distinct preference for these conditions. Relatively few species were living in soils subject to drought. Red blood was present in 28 species, all but one from soils with more than 55% water. Cognettia sphagnetorum and C. glandulosa developed red blood in very wet conditions. In a survey of Irish wetlands, samples were taken from bog, heath, marsh, fen, margins of lakes and rivers, and saltmarsh. The influence of various environmental parameters was determined using ordination techniques. Magnesium and pH were found to be the most important factors. A high level of magnesium distinguished coastal sites and pH 5.2 separated two clusters representing acid peat and marsh-fen-aquatic sites. Groups of indicator species characterized each of the three clusters. The ecological distribution of the indicator species is described, and their usefulness in classifying enchytraeid communities is discussed.     

Preliminary study of the aquatic Oligochaeta of the Changjiang (Yangtze) River

The aquatic oligochaetes in mainstream of the Changjiang River have not been studied previously. Since 1983, benthic samples have been collected mainly from mid-upper reach of the river. Altogether 19 species belonging to 4 families of the Oligochaeta were found. Among them, Nais inflata is the commonest species throughout the river, whereas Nais sp., Arcteonais lomondi, Limnodrilus silvani, Rhyacodrilus riabuschinskii and Telmatodrilus sp. ae recorded from China for the first time.Quantitatively, the aquatic oligochaetes constitute the majority of zoobenthos in the mainstream. In 1984, the standing crop of the Tubificidae was 231–343 ind·m^-2 in density and 0.73–0.97 g·m^-2 (wet weight) in biomass, and that of the Naididae was 21–4982 ind·m^-2 and 0.003–1.75 g·m^-2 (wet weight) respectively.     

Preliminary report on the Enchytraeidae (Oligochaeta) of West Florida

A wide range of habitats, both terrestrial and marine littoral, were sampled in an area between Pensacola and Tallahassee. Enchytraeids were present in all moist or wet soils and in marine habitats enriched by organic matter but were absent or rare in very dry soils, saturated or flooded substrates and clean intertidal sand. Between 70 and 75 species were distinguished of which 50–55 are new to North America and about 25 are probably new to science. The genera represented are the same as those occurring in Western Europe but their relative importance differs and there are some tropical elements. The number of species occurring in terrestrial sites was greater than recorded in similar surveys in southwestern France and Ireland (approximately the same-sized area, number of sites and size of sample), but the number of species per sample was lower than in either of the other countries. It is concluded that species distribution in western Florida is very patchy. Possible reasons for this patchiness are discussed.     

A comparison of phenetic and phylogenetic methods applied to the systematics of Oligochaeta

A comparative study of naidid subfamilies shows that a combination of ordination, Jaccard/Average Linkage cluster analysis and Wagner parsimony provides a useful basis for a rational phylogeny but that this does not differ markedly from the original proposed by Sperber nearly four decades ago. Hennig rules, modified by Wiley, permit a preliminary phylogeny and classification of the Annelida to be made by hand. An error in earlier versions suggested that the Dorydrilidae lacked prostate glands, and this is corrected.     

Phylogenetic analysis of the aquatic Oligochaeta under the principle of parsimony

Phylogenetic relationships between five subfamilies of Tubificidae and ten other families of microdrile oligochaetes were estimated by a Wanger parsimony analysis using PAUP (Phylogenetic Analysis Using Parsimony, by D. L. Swofford). As the apomorph character state is ambiguous for some characters, different assumptions of directionality as well as deletions of some characters are tested in a number of analyses. A general pattern is evident from the study; (1) the majority of the aquatic families are members of a large monophyletic group (the order Tubificida in a somewhat restricted sense) defined by the shared possession of atria (generally with well developed external prostate glands), but the family Tubificidae is paraphyletic within this group; (2) the Enchytraeidae appear to form a second group (the Enchytraeida) together with the exclusively marine Capilloventridae and Randiellidae, all three families characterized by the anterior location of the spermathecae; (3) the Haplotaxidae are a plesiomorph family, which stands out as a branch of its own and constitutes the ancestral part of a group comprising also all the megadriles (the Haplotaxida). However, monophyly of the Haplotaxida is likely only if the haplotaxid octogonadial condition is assumed to be derived from the tetragonadial condition characterizing most microdriles, a situation not envisaged by previous authors. The implications of the parsimony method are briefly discussed.     

A phenetic and cladistic study of spermatozoal ultrastructure in the Oligochaeta (Annelids)

Spermatozoal ultrastructure of nine oligochaete families has been examined for congruence with phylogenetic and taxonomic systems for the Oligochaeta based on general morphology, particularly the holomorphological hennigian analysis of Jamieson (1978a, 1980, 1983). Estimation of congruence has been made following phenetic and cladistic (phylogenetic) analysis. Correspondence, in phenograms and phylograms, of sperm types with taxonomic and phylogenetic groupings previously recognized is generally good. Departure from this rule in the similarity of the phreodrilid sperm to that of the Lumbricina suggests a corresponding alteration of fertilization biology in the phreodrilids. The results indicate that the Haplotaxidae lie at the base of the opisthopores though they do not unequivocally contraindicate acceptance of a Haplotaxis like form as a stem form of the Haplotaxida (opisthopores and Haplotaxidae) and Tubificida. An even more basal position for prosopores, now represented by the Lumbriculida, cannot yet be dismissed.     

Phylogenetic and taxonomic problems in freshwater Oligochaeta with special emphasis on chitinous structures in Tubificinae

Setae and chitinous penis sheaths are the main characters used to distinguish genera and species of the subfamily Tubificinae. Genital setae and penis sheaths are of functional importance to facilitate copulation. Similar structures in different genera may be homologous or products of parallel evolution (homoiologous). Form and dimensions of the penis sheaths of many tubificine species are very variable. Transspecific overlap of quantitative species characters can make the determination of specimens in the genus Limnodrilus difficult. The configuration of the distal ends of the penis sheaths is an important character to distinguish Limnodrilus species. The definition of the intraspecific variability of this morphological character is problematic.     

Sublittoral and profundal Oligochaeta fauna of the Lake Constance (Bodensee-Obersee)

Fourteen tubificid species and one lumbriculid make up the oligochaete population of the northern half of Lake Constance, a meso- to mesoeutrophic lake. Tubifex tubifex makes up 72% of the total abundance, the clean water species Stylodrilus heringianus only 0.1%. No correlation exists between total worm abundance and organic carbon content of the sediment, only 4% of the organic carbon being used by the worms. A highly significant correlation between particulate organic matter loading and its organic carbon content from 10 tributaries and total oligochaete abundance is demonstrated. The ecological index I_PA is defined and used to assess the biologically relevant trophic status of the lake bed. This integrates information on the percent representation of three groups of worm species classified on atrophic basis and total abundance of the worms. Despite control of the increase in phosphorus loadings progressive eutrophication of sediments was observed after an 8 year interval.     

The depth distribution of Oligochaeta in an Irish quaking marsh

The depth distribution of oligochaetes was studied in a quaking marsh at Tinure, Co. Louth, Ireland. The dominant plants were grasses which formed a fibrous mat floating on semi-liquid peat. The water level remained near the surface except for a few weeks in winter and early spring when up to 50% surface cover of water was seen. Depth profiles of pH and redox potential showed seasonal variations with the anaerobic layer approaching the surface in summer. Oligochaetes were the most important group of invertebrates and were represented by 7 species of Naididae, 7 Tubificidae, 2 Lumbriculidae, 13 Enchytraeidae and 1 Lumbricidae. Lumbricids and most species of Enchytraeidae were concentrated at the surface but the enchytraeids Marionina riparia, Cernosvitoviella spp. and Cognettia glandulosa were frequent in the anaerobic layer. Aquatic oligochaetes were most numerous below the surface. Tubificids penetrated further than other groups and reached a peak at 4–6 cm. The effects of lowering the water level were studied in pot cultures where water was maintained at 4 different levels. Enchytraeids always remained near the surface, while aquatic oligochaetes concentrated nearer the water level. It is concluded that enchytraeids are prevented from colonizing most freshwater habitats by their inability to tolerate extended periods of anoxia.     

The geographical distribution of Naididae (Oligochaeta) in Britain

A compilation of records of the geographical location of naidid species in Britain is presented. Many species previously considered rare are shown to be widely distributed.     

Ecology of Naididae (Oligochaeta) from an alkaline bog stream: life history patterns and community structure

Population and community dynamics of naidid oligochaetes were studied from June 1982–December 1983 in a sluggish, alkaline bog stream situated within Cedarburg Bog, Ozaukee County, Wisconsin, USA. Temporal differences in periods of peak abundance were observed for five species studied in detail: Chaetogaster diaphanus (mid-August and September), Chaetogaster diastrophus (mid-May), Dero digitata (mid-September), Dero nivea (mid-October), and Pristina leidyi (mid-October). Several correlations of abiotic and biotic parameters to density and percentage of naidids reproducing asexually were calculated. Mean doubling times (days) for field populations were 12.1, 22.7, 62.4, 19.6, 27.7 for C. diaphanus, C. diastrophus, D. digitata, D. nivea, and P. leidyi, respectively. Asexual reproduction by paratomy was the principal method of population increase. Sexual specimens were observed for Stylaria lacustris during June and October–December, D. digitata in September, C. diastrophus and Nais simplex during October, and C. diaphanus in October–November. Generally, a high proportion of the respective population was sexually mature when this type of reproduction occurred. Naididae community diversity index values using the Shannon-Weaver index ranged from 0.19–3.86.