首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary

This paper compares aspects of the reproduction of a semelparous triclad, Dendrocoelum lacteum, with those of an iteroparous triclad, Dugesia polychroa. Cocoon output was less sensitive to ration and possibly temperature for the former as compared with the latter species. Cocoons of D. lacteum were on average bigger and contained more hatchlings than those of D. polychroa. The sizes of hatchlings did not differ between species, but for D. lacteum only, the hatchlings emerging from late cocoons were significantly larger, and less numerous, than those emerging from earlier cocoons. Possible reasons for these differences are considered.  相似文献   

2.
David M. Bates 《Brittonia》1967,19(3):227-236
Reevaluation of the generic limits ofMalvastrum A. Gray requires the transfer of several species. Among these,M. lacteum (Ait.) Garcke andM. subtriflorum (Lag.) Hemsley of Central America and Colombia form a natural alliance differing fromMalvastrum in morphological, cytological, and ecological characteristics and are recognized as a new genus,Kearnemalvastrum. The affinities ofKearnemalvastrum within the tribe Malveae are uncertain. Despite the fact thatK. lacteum andK. subtriflorum occupy similar ecological situations, are fully interfertile, and apparently hybridize to some degree in nature, they do maintain their identity and, therefore, are recognized as species.  相似文献   

3.
Summary The physiological activity and C and N allocation of beech seedlings planted in two different beech forest soils (acid brown earth, rendzina) were studied over 80 days. One adult earthworm Octolasion lacteum (Örley) was placed in half of the containers. Transpiration, CO2, assimilation, chlorophyll synthesis and N incorporation were higher in the acid brown earth than in the rendzina. Fine root production was also higher in the acid brown earth. Production of stems and total N incorporation were higher in the O. lacteum treatments than in the controls. Burrowing activity of O. lacteum did not affect total root production but stimulated the transfer of C and N towards aboveground parts of the plants and shifted the large root to fine root ratio towards large roots. O. lacteum effects were similar in both soils. It is concluded that endogeic earthworms significantly affect resource allocation patterns of beech seedlings over a wide range of soils. This effect can be partly explained by an increased availability of N in soils worked by earth-worms.  相似文献   

4.
Herrmann  Jan 《Hydrobiologia》1986,132(1):273-277
Rapid streams in southern Sweden are often inhabited by the triclad Dendrocoelum lacteum. Outside Fennoscandia, this species is mainly restricted to lentic habitats. The normal food refuge for D. lacteum, the isopod Asellus aquaticus, is seldom found in the stream habitats, and probably the prey here is the amphipod Gammarus pulex. With respect to spatial and trophic niche components, it seems that D. lacteum has taken the place of Crenobia alpina in southern Sweden.Two parameters of reproduction, namely production of cocoons and of hatchlings, both peaked approximately one month later in a stream than in an adjacent lake. This difference was attributed to a low temperature regime in the stream. Number of hatchlings per cocoon and cocoon sterility were higher in the stream than in the lake. Similar cocoon and hatchling output per adult was found in the two habitats, indicating a similar reproductive effort for the two triclad populations. I suggest that D. lacteum, by virtue of its choice of microhabitat, viz., under stones, is not so vulnerable to the more severe stream environment.  相似文献   

5.
By discriminant analysis on data from 115 lakes in South Sweden it was shown that the distribution and abundance of the triclad Dendrocoelum lacteum was predominantly governed by the density of the isopod Asellus aquaticus, its main food. The occurrence of the latter was mainly correlated with the nutrient richness of the lakes, most probably via presence of appropriate detritus, chiefly allochtonous material. As opposed to British oligotrophic lakes, most Swedish nutrient-poor lakes are surrounded by deciduous vegetation, which indirectly promotes the existence of A. aquaticus and consequently D. lacteum. Presence of mat-forming plants generally seemed to depress triclad density, whereas smaller stones promoted their occurrence, at least in nutrient-rich lakes.  相似文献   

6.
Chromosome bands in freshwater triclads   总被引:2,自引:2,他引:0  
Four species of Triclads belonging to three families, Dugesia polychroa and Dugesia mediterranea (Dugesiidae), Planaria torva (Planariidae) and Dendrocoelum lacteum (Dendrocoelidae) were studied for chromosome banding: C-banding for all the species, ASG banding for Dugesia polychroa and G-banding for Dugesia polychroa and Dugesia mediterranea. C-banding results for Dugesia lugubris-polychroa group suggest a high level of heterochromatin evolution in the group. Small bands strictly limited to the centromeric region were seen in Dugusia lugubris and this pattern is similar to the patterns of some species belonging to other families, notably Planaria torva and Dendrocoelum lacteum. This could be considered a primitive character. In contrast numerous heterochromatin bands which are useful to characterize the different karyotypes were seen in Dugesia polychroa and Dugesia mediterranea. Our data suggest that heterochromatin is important in freshwater triclad speciation.  相似文献   

7.
Chemoattractants induce a transient accumulation of cGMP levels in Dictyostelium. Intracellular cGMP levels reach a peak at 10 s and prestimulated cGMP levels are recovered at about 30 s. Intracellular and extracellular cGMP levels were detected simultaneously after stimulation of D. lacteum cells with monapterin and of D. discoideum cells with cAMP. In both species about 20% of the intracellularly accumulated cGMP was secreted. All slime mold species investigated so far contain an intracellular phosphodiesterase specific for cGMP. A mutant of D. discoideum which does not contain this cGMP-specific enzyme shows a strongly retarded decline of intracellular cGMP levels. Secretion of cGMP is in this mutant not sufficient to explain the decline of cGMP levels which indicates the involvement of nonspecific phosphodiesterase in intracellular cGMP regulation. These results show multiple degradation pathways of intracellularly accumulated cGMP. In wild-type cells about 20% is secreted, 10–20% is hydrolyzed intracellularly by non-specific phos-phodiesterase, while the majority (60–70%) is hydrolyzed intracellularly by a cGMP-specific phos-phodiesterase. The relationships of intracellular regulation of cGMP and cAMP levels are discussed.  相似文献   

8.
Earthworms (Aporrectodea caliginosa, Lumbricus rubellus, and Octolasion lacteum) obtained from nitrous oxide (N2O)-emitting garden soils emitted 0.14 to 0.87 nmol of N2O h−1 g (fresh weight)−1 under in vivo conditions. L. rubellus obtained from N2O-emitting forest soil also emitted N2O, which confirmed previous observations (G. R. Karsten and H. L. Drake, Appl. Environ. Microbiol. 63:1878–1882, 1997). In contrast, commercially obtained Lumbricus terrestris did not emit N2O; however, such worms emitted N2O when they were fed (i.e., preincubated in) garden soils. A. caliginosa, L. rubellus, and O. lacteum substantially increased the rates of N2O emission of garden soil columns and microcosms. Extrapolation of the data to in situ conditions indicated that N2O emission by earthworms accounted for approximately 33% of the N2O emitted by garden soils. In vivo emission of N2O by earthworms obtained from both garden and forest soils was greatly stimulated when worms were moistened with sterile solutions of nitrate or nitrite; in contrast, ammonium did not stimulate in vivo emission of N2O. In the presence of nitrate, acetylene increased the N2O emission rates of earthworms; in contrast, in the presence of nitrite, acetylene had little or no effect on emission of N2O. In vivo emission of N2O decreased by 80% when earthworms were preincubated in soil supplemented with streptomycin and tetracycline. On a fresh weight basis, the rates of N2O emission of dissected earthworm gut sections were substantially higher than the rates of N2O emission of dissected worms lacking gut sections, indicating that N2O production occurred in the gut rather than on the worm surface. In contrast to living earthworms and gut sections that produced N2O under oxic conditions (i.e., in the presence of air), fresh casts (feces) from N2O-emitting earthworms produced N2O only under anoxic conditions. Collectively, these results indicate that gut-associated denitrifying bacteria are responsible for the in vivo emission of N2O by earthworms and contribute to the N2O that is emitted from certain terrestrial ecosystems.  相似文献   

9.
Predators play a fundamental role in prey trophic behaviour, with indirect consequences for species coexistence and ecosystem functioning. Resource quality and availability also influence prey trophic behaviour, with potential effects on predator-prey dynamics. Although many studies have addressed these topics, little attention has been paid to the combined effects of predators and resources on prey species coexistence and nutrient transfer along food chains, especially in detritus-based systems. To determine the influence of predators and resource quality on the movement and P uptake of detritivores, we carried out a field experiment on the River Kelvin (Scotland) using 32P to test the hypothesis of reduced prey vagility among resource patches as a strategy to avoid predation. Thirty leaf sacks containing alder leaves and two detritivore prey populations (Asellus aquaticus and Lymnaea peregra) were placed in cages, half of them with two predator species (Dendrocoelum lacteum and Erpobdella octoculata) and the other half without predators. Five alder leaf bags, each individually inoculated with a different fungus strain to simulate a patchy habitat, were placed inside each leaf sack. One bag in each sack was labelled with 32P, in order to assess the proportion of detritivores using it as food and thus their movement among the five resource patches. Three replicates for each labelled fungus and each predation treatment (i.e. with and without predators) were left on the riverbed for 7 days. The presence of predators had negligible effects on the number of detritivores in the leaf bags, but it did reduce the proportion of 32P-labelled detritivores and their P uptake. The most strongly affected species was A. aquaticus, whose vagility, trophic overlap with L. peregra and P uptake were all reduced. The results confirm the importance of bottom-up and top-down forces acting simultaneously to regulate nutrient transfer along food chains in patchy habitats.  相似文献   

10.
Résumé Les néoblastes de la région postérieure du corps de la PlanaireD. lacteum ont les mêmes propriétés migratrices et histogénétiques que les néoblastes de la région prépharyngienne. En cas de section transversale à quelque niveau que ce soit, les néoblastes du fragment postérieur se déplacent d'arrière en avant pour s'accumuler en un bourgeon de régénération normal. Mais la différenciation de ces cellules ne se produit qu'en cas de section nettement antérieure à la racine du pharynx (alors il y a régénération). Après une section postérieure à la racine du pharynx, les néoblastes dégénèrent.
Neoblasts in the anterior regeneration ofDendrocoelum lacteum, Turbellaria tricladida
Summary Neoblasts of the posterior region of the body in the PlanarianD. lacteum have the same migratory and histogenetic properties as neoblasts of the prepharyngeal region. With transverse cuts at whatever level, neoblasts of the posterior fragment migrate forward to accumulate as a normal regeneration bud. But differentiation of these cells only occurs in ease of a section clearly anterior to the root of the pharynx (regeneration then follows). After a transection posterior to this level, the neoblasts degenerate.
  相似文献   

11.
Sixteen species of cellular slime molds were isolated from Southeast Asian forest soils. Ten of these, Dictyostelium mucoroides Brefeld, D. purpureum Olive, D. polycephalum Raper, D. lacteum van Tieghem, D. rhizopodium Raper and Fennell, D. lavandulum Raper and Fennell, D. vinaceo-fuscum Raper and Fennell, D. coeruleo-stipes Raper and Fennell, Polysphondylium violaceum Brefeld, and P. pallidum Olive have been previously described and are well-recognized species occurring in other parts of the world. Two, one in the genus Dictyostelium and one belonging to the family Guttulinaceae, are considered species by the author but have not been formally described. Four are described in this paper as new: Dictyostelium intermedium, D. multi-stipes, D. bifurcatum, and Acytostelium subglobosum. A new variety papilloideum of D. lacteum is also described. One other discovery of special interest is an isolate of Polysphondylium violaceum which produces abundant macrocysts, now known to be the sexual stage in the life cycle of cellular slime molds.  相似文献   

12.
Recent field research shows that the ubiquitous Lumbricus terrestris and Octolasion lacteum (the large parthenogenetic form) have invaded new habitats in Romania, replacing mostly endemic or rare species of the former earthworm communities which were recorded 20–30 years ago. Seven different cases of earthworm invasion are currently described. Invader species have larger ecological tolerances as compared with the endemic species.  相似文献   

13.
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.  相似文献   

14.
Dynamics of abundance and reproductive cycles of limnophileous triclads (Turbellaria) from little ponds.
  1. Studying 18 little ponds in Lower Southern-Saxonia (West-Germany), in 14 ponds seven triclad-species were found.
  2. Phagocata vitta occurs from October to July in 1–2 generations. In the area the species reproduces by fissipary. Maximum abundances and rates of reproduction are reached in December and January. In the ponds, where P. vitta and Dugesia polychroa live together, there is no competition between the two species.
  3. After dry periods Dendrocoelum hercynicum emigrates from interstitial habitats as facultative inhabitant of surface-waters.
  4. In low abundances Dendrocoelum lacteum lives in one pond only. The breeding period (production of cocoons) lasts from January to March. Low densities of this species are probable caused by interspecific food-competition with Polycelis nigra.
  5. Likewise, Dugesia tigrina inhabits only one pond. The species is competitive to P. nigra at temperatures of about 20°C. High abundances in the months July to October fall together with high fissipareous-rates.
  6. Dugesia polychroa occurs in low densities over the year or dependent on dry-periods. Cocoons are produced between March and May, in low numbers till autumn.
  7. In the stagnant pond Bursfelde Polycelis nigra is the absolute dominant triclad-species with densities of up to 800 individuals/0,I m3. The maximum-abundances are caused by two intense reproductive periods in spring and autumn, together with optimum temperatures and food conditions.
  相似文献   

15.
The influence of light and different concentrations of ATP on cell aggregation in cyclic AMP sensitive (Dictyostelium mucoroides, D. purpureum) and cyclic AMP insensitive species (Polysphondylium violaceum, P. pallidum, D. lacteum) of the cellular slime molds was observed in small and in large amoebal populations.Both light and ATP (optimal concentration:10-5M) accelerated cell aggregation and increased the number of aggregating centers in large populations. For cyclic AMP sensitive species the effect of ATP in large populations was more pronounced than for the species that do not react to cyclic AMP.A possible explanation for the similar effect of light and ATP has been discussed.  相似文献   

16.
The organization of the nervous system ofDendrocoelum lacteum (Tricladida, Paludicola, Dendrocelidae) andPolycelis tenuis (Tricladida, Paludicola, Planariidae) was studied by immunocytochemical double staining, using neuropeptide RFamide and serotonin (5-HT) antisera on cryosections. The study confirmed the status of the main nerve cords (MCs) as the most important and stable of the longitudinal cords and supported the hypothesis of a common phylogenetic origin of the MCs in flatworms. The ganglion-like structures along the MCs at the beginning of transverse commissures and laterla branches showed a close contact with ventral fibres of the submuscular nerve plexus indicating an origin from crossing points of insunken ring commissures. The distributional pattern and morphology of the RFamide-IR cell bodies inD. lacteum corresponded to that of neurosecretory cells. Most RFamide-IR cells were unipolar and rounded while 5-HT-IR cells were uni- bi- and multipolar. The neutropile consisted of a dense RFamide-IR and a loose 5-HT-IR network. RFamide dominated in all parts of the genital plexus.  相似文献   

17.
SUMMARY.
  • 1 L 266 degree-days, above a threshold of 1.0°C, were required for cocoons from the triclad Dendrocoelum lacteum to hatch. The relation is described by ln D=6.12–1.17 1nr (D=number of days, T= temperature).
  • 2 Laboratory and field cocoon deposition reached a maximum in late April; peaks of hatchling occurrence were 2 weeks later. The number of hatchlings per cocoon and eocoon viability declined as spring proceeded. Cocoon deposition ceased in June, coincident with regression of the reproductive organs of the adults.
  • 3 Newly hatched triclads in the field are thought to avoid stones for their first weeks.
  • 4 It is suggested that the earlier and more abundant offspring production in South Sweden than in Britain could be attributed to differences in spring temperature conditions.
  相似文献   

18.
The food niches of four species of triclads and three species of non-parasitic leeches living in the littoral zone of British lakes of different trophic status were investigated, over one year, using a serological technique. Antisera against ten potential prey groups were employed. The basic data were adjusted to compensate for differences in predator size and seasonal changes in field temperatures. Data on two of the leech species have been presented elsewhere, but comparisons of the diet of all seven predator species are made in this paper. Much overlap in diet between the various predator species occurs, but, with one exception, each of the genera has a major food resource. The Polycelis spp. feed extensively on oligochaetes, Dugesia polychroa on molluscs, Dendrocoelum lacteum on Asellus, Erpobdella octoculata on chironomids and Glossiphonia complanata on molluscs. Helobdella stagnalis is a generalist feeder. Problems of coexistence of the leech species, and of the leech and triclad species are discussed.  相似文献   

19.
S. Scheu 《Oecologia》1990,84(3):351-358
Summary Microbial biomass, nutrient (N and P) status, and carbon and nutrient limitation of the microflora were investigated in soils from five different sites (field, 5-, 12-, and about 50-year-old fallow, beechwood), which represent different stages of a secondary succession from a wheat field to the climax ecosystem of a beechwood on limestone. In addition, the effect of faeces production by the substrate feeding earthworm species Octolasion lacteum (Örley) on the nutrient status of the soil microflora of these sites was studied. Humus had accumulated in the soil of the third fallow site, with an enhanced biomass of microflora. However, in the beechwood soil, which had the highest humus content, microbial biomass was lower than in the soil of the third fallow site and similar to that of the field and the two younger fallow sites. In general, soil microbial biomass was little affected by the passage of soil through the gut of O. lacteum. The soil microflora of the field, the 5-, 12-, and about 50-year-old fallow was limited by carbon, whereas in the beechwood soil phosphorus limited microbial growth. NItrogen availability to the soil microflora was low in the two younger fallow sites and high in the field and the third fallow. In the beechwood soil nitrogen supply did not affect microbial carbon utilization. Application of phosphorus stimulated glucose mineralization in the soil of the field, the third fallow, and the beechwood, but not in the two younger fallow sites. Therefor, the nutrient status of the soil microflora seems to have changed during secondary succession: presumably, during the first phase the availability of nitrogen decreased, whereas during the second phase microbial phosphorus supply became more important, which resulted in phosphorus limitation of the soil microflora in the climax ecosystem. The passage of soil through the gut of O. lacteum caused an alteration in the microbial nutrient status. Generally, microbial growth in earthworm casts was limited by carbon. The relative effect of the gut passage of the soils on microbial carbon utilization seems to increase during succession. Therefore, the effect of decomposer invertebrates on microbial nutrient supply seems to increase during secondary succession. In general, nitrogen did not limit microbial carbon utilization in earthworm casts. Phosphorus requirements of the soil microflora were lowered by the gut passage of the soil of the third fallow site and the beechwood, which indicates an increased phosphorus supply in earthworm casts. Howerver, this additional supply was not sufficient to enable optimal carbon utilization by the soil microflora. The results indicate that the effect of decomposer invertebrates on the soil microflora depends on the nutrient status of the ecosystem.  相似文献   

20.
1. Three species of leeches, Erpobdella octoculata, Glossiphonia complanata and Helobdella stagnalis, and four species of triclads, Polycelis nigra, P. tennis, Dugesia polychroa and Dendrocoelum lacteum, commonly coexist on stony shores in productive British lakes. All species are food limited and there is much overlap in their diet. For both leech and triclad communities, coexistence of species is through the occurrence of food refuges. Leeches are more successful than triclads at capturing live prey, whereas both groups feed on damaged prey, comprising incapacitated, live or dead animals that are leaking body fluids. If triclads are better than leeches at exploiting damaged prey, this could be a mechanism for their coexistence. 2. Laboratory experiments investigated the comparative speeds at which leeches and triclads responded to crushed prey. Young and adult predators were offered a crushed specimen of the oligochaete Tubifex tubifex, the snail Lymnaea peregra, the crustacean Asellus aquaticus or the chironomid Chironomus sp., and their reaction times recorded. These four prey groups constitute the main diet of the predators in the field. Only D. polychroa and D. lacteum showed a significantly different reaction time between young and adults to crushed prey, and the reason for this is unclear. All predators, except H. stagnalis and D. polychroa, showed a difference in reaction time to the four types of prey, presumably a consequence of differences in both the ‘quality’ and ‘concentration’ of the different prey fluids, and there were some differences between predators in their speed of reaction to the same prey type. The following sequence, from fastest to slowest, in general reaction time to prey was obtained: E. octoculata, D. polychroa, P. tenuis, D. lacteum, P. nigra, H. stagnalis and G. complanata. 3. The location of the damaged food by the predators can be explained partly in terms of their foraging behaviour, with E. octoculata, D, polychroa and P. tenuis exhibiting a more seek-out strategy than other species which have a more sit-and-wait behaviour, and partly on the level of sophistication of their chemosensory system used to detect leaked prey fluids. This system is highly developed in triclad species but poorly developed in leeches. 4. In a second type of experiment in which prey, L. peregra, A. aquaticus or Chironomus sp., were offered at different time intervals after crushing to H, stagnalis and P. tenuis, few predators fed on food crushed for 24 h or longer, although a few leeches fed on Chironomus crushed for up to 72 h. 5. It is concluded that coexistence of leech and triclad species on stony shores in lakes is assisted by partitioning of food on a damaged or live basis.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号