Showing papers in "Netherlands Journal of Zoology in 1980"
TL;DR: It is argued that the unique cheek tooth structure allows lagomorphs to apply various combinations of crushing, shearing and grinding forces to their food and remain generalized and adapted to different niches.
Abstract: Jaw muscle activity and mandibular movements were studied in the domestic rabbit by quantitative electromyography and cineradiography. Mandibular movement profile and occlusal interaction depend on the consistency of the food masticated. Minimal vertical and maximal transverse jaw excursions combined with initial edge-to-edge apposition of cheek tooth ridges, followed by an oblique antero-medial shearing movement of the lower teeth into intercuspation characterize hay mastication. This movement is followed by a purely transverse grinding stroke guided by the interlocked ridges and valleys of the teeth. In carrot mastication a vertical, crushing movement predominates. In laboratory pellets, the movement profile is intermediate; occlusal movement is usually confined to a transverse grinding stroke. During chewing jaw closure and deflection toward the working side are caused by simultaneous action of balancing side superficial masseter and medial pterygoid and working side deep masseter and temporalis. The lingually directed power stroke is produced by working side superficial masseter and medial pterygoid and balancing side deep masseter and temporalis. Firing levels are higher on the working than on the balancing side and decrease from hay to pellets to carrot. Transverse muscle force components, generated mainly by the pterygoids also decrease in the series hay-pellets-carrot. The ratio between forces on working and balancing sides allows the balancing side joint to act as a fulcrum; the working side joint remains unloaded. During biting joints are loaded symmetrically. The unique cheek tooth structure allows lagomorphs to apply various combinations of crushing, shearing and grinding forces to their food. By combining strong protractive and transverse muscular forces they can adjust bite force direction. It is argued that this versatility enables them to utilize a wide variety of vegetable matter as food and remain generalized and adapted to different niches.
292 citations
TL;DR: An analysis is made of genetic and non-genetic components in the number of eggs in the completed first clutch of the Great Tit, finding no detectable variation in clutch size that can be attributed to differences in habitat quality.
Abstract: An analysis is made of genetic and non-genetic components in the number of eggs in the completed first clutch of the Great Tit. 1) It is doubtful whether a causal relation between density and clutch size exists. 2) There is hardly a systematic effect of age on clutch size. 3) There is an annual variation in clutch size with similar changes in individual females in the same population, but it is hardly correlated between populations. This emphasizes a lack of genotype-environment interaction. 4) Within populations there is no detectable variation in clutch size that can be attributed to differences in habitat quality. 5) About 40% of the total phenotypic variation in clutch size is genetic variation. Several ways of eliminating a possible resemblance through correlated environments yield the same result. 6) Selection for clutch size is demonstrated in several years. 7) The implications for rapid evolutionary change in mean clutch size are discussed.
125 citations
TL;DR: On the basis of five apomorphic characters it is proposed that the Cichlidae, as presently recognized, is monophyletic.
Abstract: The phyletic status of the speciose and diverse family Cichlidae is investigated. In accordance with the current methods of cladistic analysis a wide range of perciform taxa is included for outgroup comparison. Attention is centred upon the anatomy of the adductor mandibulae muscle, elements of the pharyngeal jaw apparatus and the microbranchiospines. On the basis of five apomorphic characters it is proposed that the Cichlidae, as presently recognized, is monophyletic.
82 citations
TL;DR: Breeding of the bulk of the haplochromine species (phytoplankton/detritus eaters, zooplanktophages and some insectivores) in the sublittoral and littoral waters with a mud bottom appears to be seasonal, and an optimal trawl fishery recommendations based on the present data are discussed.
Abstract: Ecological investigations on the haplochromine Cichlidae from the Mwanza Gulf of Lake Victoria revealed that more than 140 species are living in the habitats fished with bottom trawlers (i.e. all major habitats except rocky bottoms, dense plant stands and very shallow water). These species can be classified into 9 trophic groups. The phytoplankton/detritus eaters and the zooplanktophages (both belonging to the smaller species) form the dominant group in the sublittoral waters with a mud bottom, while insect eaters dominate in shallower water, especially over sand. Most haplochromine species appear to be strongly habitat-restricted throughout life. Breeding of the bulk of the haplochromine species (phytoplankton/detritus eaters, zooplanktophages and some insectivores) in the sublittoral and littoral waters with a mud bottom appears to be seasonal. Spawning takes place at the end of the rainy season. However, some species of the littoral sand habitat breed throughout the year. A discussion is given of the factors by which the seasonal breeding pattern might be imposed. For an optimal trawl fishery recommendations based on the present data are discussed.
79 citations
TL;DR: The ecology and taxonomy of the haplochromine cichlids from the Mwanza Gulf of Lake Victoria (East Africa) have been studied by the Haplochromis Ecology Survey Team (HEST), which resulted in the recognition of 150+ new species.
Abstract: The ecology and taxonomy of the haplochromine cichlids from the Mwanza Gulf of Lake Victoria (East Africa) have been studied by the Haplochromis Ecology Survey Team (HEST). The research area and the fishing techniques are described as basic information for following publications. Taxonomic studies resulted in the recognition of 150+ new species. The results of the ecological research on these species-including factors which influence species distribution, breeding and migration-are summarized.
73 citations
TL;DR: Patches with a reduced quality for the host are less attractive for the parasitoid which spends less time and searches less intensely on such patches than on patches with a better quality forThe host.
Abstract: We studied three factors affecting the allocation of patch time and the intensity of searching by the larval parasitoid Asobara tabida Nees. We found that: 1. A. tabida reacts to a water-soluble kairomone, produced by its host Drosophila melanogaster Meigen in that a) time spent on a patch (yeast patch in which D. melanogaster larvae had crawled and fed) increased in a S-shaped fashion with increasing kairomone concentration. b) the searching intensity by the parasitoid increased with increasing kairomone concentration until it levels off at higher concentrations. 2. A. tabida recognized areas previously searched by a conspecific and spent less time and searched less intensely on such patches as compared to unsearched patches. 3. Patches with a reduced quality (reduced amount of living yeast) for the host are less attractive for the parasitoid which spends less time and searches less intensely on such patches than on patches with a better quality for the host. The response of the parasitoid to these three factors contributes to the optimization of time allocation. The increase in search intensity can eventually cause a sigmoid functional response and may enhance population stability.
62 citations
TL;DR: The development of the adductor-muscles of the lower jaw is studied and described in relation with the development of vision, which sheds a new light on a kinematical construction and its emergence.
Abstract: This study of vision during growth of Haplochromis elegans 1 is a functional morphological analysis of the eye as a changing functional component (DULLEMEIJER, 1974). Retinal development is described. Retinal parameters, like densities and distributions of visual cells are determined throughout the span of life of H. elegans. Optical properties of the eye-lens have been measured. A physical model, using ray-tracings, composition of the eye-lens and optical properties of the eye-protein, calculates correctly the chromatic aberration of the eye-lens as a function of lens-radius. Defect of focus of the eye during buccal development is determined. Its influence on resolving power of the eye as an optical instrument is calculated, using diffraction theory. The same theory is used to calculate the influence of chromatic aberration on resolving power as a function of lens-radius. Scotopic vision is analysed numerically, by calculating scotopic retinal visual acuity and convergence during growth. In photopic conditions, the retina appears to be a limiting factor in resolving power from the moment the retina becomes functional (determined by electron-micrographic studies) till the maximum eye-size is reached. The eye-size for which retinal visual acuity is the same as optical visual acuity predicts correctly the maximum eye-size found in H. elegans. The development of the adductor-muscles of the lower jaw is studied and described in relation with the development of vision, which sheds a new light on a kinematical construction and its emergence. A comparison between three haplochromine species of different trophic types demonstrated a variation in photopic and scotopic visual acuity as well as in convergence. The fish feeder has a high convergence and a high scotopic visual acuity. The insect feeder has a high photopic visual acuity. The mollusc feeder has a moderate degree of convergence. A comparison between the eyes of Perca fluviatilis and H. elegans demonstrates that the existence of a yellow cornea in the perch is necessarily connected to the dispersive power of its eye-lens protein.
47 citations
TL;DR: The primary, solitary parasitoids Asobara tabida Nees and Leptopilina heterotoma and Pseudeucoila bochei Weld are sympatric, show seasonal overlap and share the same hosts, viz. larvae of Drosophila species.
Abstract: The primary, solitary parasitoids Asobara tabida Nees (Braconidae: Alysiinae) and Leptopilina heterotoma (Thomson) (= Pseudeucoila bochei Weld): Eucoilidae) are sympatric, show seasonal overlap and share the same hosts, viz. larvae of Drosophila species. Discrimination between unparasitized hosts and hosts parasitized by the other species was studied. No differences were found in their behaviour towards the two kinds of hosts: these were accepted equally well for parasitization.
39 citations
TL;DR: It is suggested that for many insects the high dispersal capacity is the more decisive factor in determining whether the species will survive in unpredictable environments.
Abstract: This study concerns the distribution, both of populations in a landscape and of individuals in a population, and the annual cycle of two species of beetles of the forest floor, Pterostichus oblongopunctatus and Philonthus decorus. The distribution pattern ofpopulations of Pt. oblongopunctatus in a given landscape changes very little from year to year, and less than Ph. decorus. This comment holds also within the population. Pt. oblongopunc- tatus has a more stable pattern of favourable places within its habitat than has Ph. decorus. So individuals of the latter species have to cope with a more unpredictable environment than the former. A description of the preferred habitats is given. The habitat of Pt. oblongopunctatus is determined more strictly by a number of structural and physical properties of the environment than is the case for Ph. decorus. Although density fluctuations differ considerably in each population in the landscape, they run parallel in the various places within the habitat of one population. Absolute densities have been established by means of mark recapture techniques. Mortality is lower for Pt. oblongopunctatus and its life span may be more than 4 years as opposed to 2 years for Ph. decorus. The relative locomotor activity has been measured throughout the reproduction period. It is found to be positively correlated with temperature. However, the quantitative relation changes with time: Pt. oblongopunctatus becomes progressively less active at all temperatures from April till July, culminating in aestivation, and Ph. decorus may become increasingly active at all temperatures. The form of the "activity" curve, based on pitfall catches, can be explained by the mortality rate and changes in locomotor activity. The reproductive cycle and the dispersal capacity of the species have been studied by dissecting specimens. For Staphylinids flight muscle dimorphism may be a partial alternative for the wellknown wing dimorphism in Carabids. Results of the various studies are discussed in terms of life strategies. As the distribution pattern within a population is rather fixed, conditions for triggering the mechanism of the "spreading of risk", i.e. making use of the heterogeneity of the environment and thus levelling off fluctuations in density, are not fulfilled. The climatic stability of the forest floor and self-regulation of the density of the species must account for the relatively stable populations. Development of the dispersal capacity is set against high reproduction capacity. Both may make conflicting demands on the resources of the animals. It is suggested that for many insects the high dispersal capacity is the more decisive factor in determining whether the species will survive in unpredictable environments.
34 citations
TL;DR: Statistical analysis of gall midge provenance data showed S. betulae to predominate in B. pendula-like birches and S. tarda to be more common inB.
Abstract: The host plant relations of three species of Semudobia Kieffer, viz., S. betulae (Winnertz), S. tarda Roskam and S. skuhravae Roskam are studied. These gall midge species are sympatric and induce galls in fruit catkins of birches, viz., Betula pendula Roth, B. pubescens Ehrhart and intermediate forms (putative hybrids). No intermediate forms of the gall midge species are known. They may be found in the same birch specimen and often occur in the same fruit catkin. S. skuhravae induces galls in the fruit scales of birches; the other two species infect the fruits. Statistical analysis of gall midge provenance data showed S. betulae to predominate in B. pendula-like birches and S. tarda to be more common in B. pubescens-like specimens. Although both species occupy similar niches, there is a different occurrence on a 'hybrid index' scale of the host plant species.
32 citations
TL;DR: Investigation of the mortality of larvae of Pterostichus oblongopunctatus and Philonthus decorus found that cannibalism is an important factor in the regulation of the density of both species.
Abstract: A description is given of a number of experiments, in the field as well as in the laboratory, in which the mortality of larvae of Pterostichus oblongopunctatus and Philonthus decorus was investigated. Mortality during the larval stage was found to be very high. This applied, at least in Pterostichus, to all three instars. In Philonthus significantly more larvae survived when they were able to find their first meal shortly after hatching. The same tendency was found in Pterostichus. Survival of larvae is strongly influenced by their density and by the availability of food. Probably many larvae do not succeed in finding enough food and die from starvation. Larvae of both species are cannibalistic. Although this cannibalism is reduced when alternative food is available, it does not disappear entirely. Cannibalism occurs even at very low densities (for example in Pterostichus at a density of 15-20 larvae per m 2 ), so it is very likely that under natural conditions (3 _ 8 adults in our study area) cannibalism is an important factor in the regulation of the density of both species.
TL;DR: In urodeles, the mechanism which allows primordial germ cells to differentiate from mesoderm cells remains to be discovered, and in anurans, whether germ plasm is the determinant and if so, how and when it acts, has yet to be determined.
Abstract: In urodele embryos, primordial germ cells arise epigenetically from the region of the ventral mesoderm, as a result of inductive influences from the ventral endoderm. In contrast, primordial germ cells in anuran embryos originate from cells which are in the endoderm and which contain germ plasm. In urodeles, the mechanism which allows primordial germ cells to differentiate from mesoderm cells remains to be discovered. Similarly, in anurans, whether germ plasm is the determinant and if so, how and when it acts, has yet to be determined.
TL;DR: The host-searching and oviposition behaviour of three Aphytis species was studied to obtain information about the presence of the ability to distinguish parasitized hosts from unparasitized ones in gregarious parasites, and it was suggested that these species are able to distinguish un parasitized from parasitizedhosts.
Abstract: 1. The host-searching and oviposition behaviour of three Aphytis species (A. coheni, A. lingnanensis and A. melinus; Hymenoptera, Chalcidoidea, Aphelinidae), ectoparasites of armoured scale insects (Homoptera, Coccoidea, Diaspididae) was studied to obtain information about the presence of the ability to distinguish parasitized hosts from unparasitized ones in gregarious parasites. 2. Analysis of frequency distributions of parasite eggs over the hosts showed that extreme care must be exercised when dealing with such indirect results, because differences in host distribution patterns (i.e. hosts occurring in clusters versus isolated hosts) resulted in large differences in the frequency distribution of parasite eggs per host. These differences in egg distributions may prevent detection of the parasite's discrimination ability. 3. Careful analysis of these data suggested, however, that the three Aphytis species are able to distinguish unparasitized from parasitized hosts, and direct observation of the oviposition behaviour confirmed this suggestion. 4. Furthermore, the data indicate that Aphytis adults are able to 'count' the number of parasite eggs present on a previously parasitized host and that they prefer to lay on hosts containing the lowest number of parasite eggs when meeting parasitized hosts. 5. Females of the three Aphytis species apply an external mark on the scale cover of their hosts after parasitization, and they are also able to detect internal changes within a previously parasitized host. Rejection of parasitized hosts usually occurs when the parasite perceives the external mark while she is drumming with her antennae on the scale cover; however, if she provisionally accepts a parasitized host, rejection can still occur when she detects the internal change with the ovipositor inserted into the host's body. 6. When third stage oleander scales are used as hosts, the number of eggs laid per host visit is usually 1 for A. coheni and A. lingnanensis, and about 2 for A. melinus. The first two species are more or less solitary parasites, A. melinus is a gregarious species, usually laying two or more eggs per host visit. More than one parasite may develop per host in A. melinus without a reduction in size of the resulting adult. If more than one parasite develops per host in A. coheni and A. lingnanensis, a reduction in size of the parasite adults occurs. 7. The ability to discriminate is important for both the solitary and gregarious Aphytis species, because it prevents the wasting of parasite eggs, it saves time (rejecting a host takes only a fraction of the time necessary for an entire oviposition sequence) and it may enable the parasite to determine the condition of a patch with hosts (i.e. to leave a site where only parasitized hosts are present).
TL;DR: The present paper deals with the taxonomic description and eco-morphology of the two (new) species of haplochromine cleaner fishes from Lake Victoria, and deduced that one species feeds mainly and the other partly on carplice and leeches.
Abstract: In addition to the many trophic groups of haplochromine cichlids already known from Lake Victoria, two new ones (ie zooplanktophages and cleaner fishes) have been discovered by the Haplochromis Ecology Survey Team which operates in the Mwanza Gulf of the Lake The present paper deals with the taxonomic description and eco-morphology of the two (new) species of haplochromine cleaner fishes Cleaning symbiosis has been described mainly for marine fishes Among cichlids only juvenile Etroplus maculatus were known as (facultative) cleaners 1 The cleaning behaviour of the Victoria haplochromines is deduced from their stomach contents which revealed that one species feeds mainly and the other partly on carplice and leeches No other cleaner fishes are known to feed on these kinds of parasites which in Lake Victoria occur externally on smooth-skinned fishes (Protopterus aethiopicus, Bagrus docmac, Synodontis sp and Clarias sp) The preference for firmly attached, flat parasites correlates with the scraper-like teeth of the haplochromine cleaners Virtually all other cleaner fishes have teeth with pronounced, pointed cusps and feed on mobile parasites or (elongate) parasites which are only proximally attached to their hosts
TL;DR: Experiments have been performed showing that the ichneumon wasp Poecilostictus cothurnatus, a parasitoid of the advanced larvae of the pine looper, Bupalus piniarius, is able to locate the host by following the trail left on the needles by the crawling caterpillars.
Abstract: Experiments have been performed showing that the ichneumon wasp Poecilostictus cothurnatus, a parasitoid of the advanced larvae of the pine looper, Bupalus piniarius, is able to locate the host by following the trail left on the needles by the crawling caterpillars. Artificial trails can be prepared by moving the skin of a caterpillar over a sheet of paper, showing that one or more chemicals present in the cuticular layer function as signals (kairomone) for the wasp. When no caterpillar is found when she arrives at the end of the trail, the wasp shows a characteristic behaviour known as area-restricted searching. This type of behaviour has been found in several other species of parasitoids, but in all these cases it was performed immediately after having parasitized a host. The observations suggest that in a pine forest host finding is accomplished by alternating short flights with landings on twigs. After a landing there is a short search for the presence of a trail, and, coming across one, the wasp will try to find the host. If this is found and parasitized she flies away, and will probably soon make a new landing elsewhere.
TL;DR: Evidence is put forward that a fixed sex-regulation system exists during oviposition and a fertilization/oviposition system is found that favours the presence of one♂ and a certain number of ♀♀ per Diopsis egg.
Abstract: In Malawi, during the study period eggs of the rice-borer Diopsis macrophthalma were mainly parasitized by Trichogramma kalkae and Trichogramma pinneyi and further by Trichogrammatoidea simmondsi and a Paracentrobia species. Data are presented on rates of parasitism, locations and sizes of parasitized eggs, fecundity, longevity, development time, number of exit holes, clutch size per host egg, sex-ratio, emergence rate,alternative hosts and super- and multiple parasitism. Relations are discussed between 1) development time and clutch size, 2) number of ♂♂ per host egg and exit holes, 3) oviposition rate and host egg size and 4) sex-ratio and clutch size. In the first three parasitoids mentioned a fertilization/oviposition system is found that favours the presence of one♂ and a certain number of ♀♀ per Diopsis egg. Evidence is put forward that a fixed sex-regulation system exists during oviposition. T. kalkae was the most important egg parasitoid of D. macrophthalma, followed by T. pinneyi. No other hosts were found for T. kalkae, whereas T. pinneyi had one alternative main host and some hosts of lesser importance. In competition for eggs of D. macrophthalma T. kalkae was in various ways superior to T. pinneyi. This latter species seems more adapted to smaller host eggs.
TL;DR: It is believed that webs may function as a physical barrier to host searching females of competing Encarsia species, or that they may serve as an intraspecific host-marking device.
Abstract: After oviposition the uniparental hyperparasite Signiphora coquilletti Ashmead was observed to spin a web over her host, Trialeurodes vaporariorum (Westwood) previously parasitized by Encarsia formosa Gahan. Signiphora coquilletti was subsequently reared from webbed T. vaporariorum pupae and from webbed pupae of Tetraleurodes mori (Quaintance), T. stanfordi (Bemis), Aleuroplatus coronatus (Quaintance), and A. gelatinosus (Cockerell). Oviposition and web-spinning behavior of S. coquilletti are described, and the ultrastructure of the webs is discussed. We believe that webs may function as a physical barrier to host searching females of competing Encarsia species, or that they may serve as an intraspecific host-marking device. Two additional hypotheses are that webs afford protection against predation of Signiphora immatures in host pupae, or that they reduce mortality of Signiphora by tying host pupae to leaf surfaces.
TL;DR: The most notable difference between the two species flocks is that many species from Lake Malawi have restricted distributions within the lake whereas there is, as yet, no evidence for this in Lake Victoria.
Abstract: Comparisons can be made between data collected by HEST in the Mwanza Gulf of Lake Victoria and that accumulated from Lake Malawi by the Fisheries Research Unit of the Malawi Fisheries Department. Although the sampling programmes differ the data available are sufficient to show many similarities between the ecology of the two species flocks. In each lake distribution and abundance of species are shown to be strongly influenced by both depth and bottom type, though the degree of association with the substrate varies between species. Well marked and comparable trophic groups are present in both lakes though in Lake Malawi it has been found that even species with highly specialised trophic mechanisms can be facultative feeders. This has not been demonstrated in Lake Victoria. A gradation from discrete breeding seasonality to continuous breeding appears to be a feature of the haplochromines of both lakes. Seasonality may be related to food supply or other factors such as weather conditions. The most notable difference between the two species flocks is that many species from Lake Malawi have restricted distributions within the lake whereas there is, as yet, no evidence for this in Lake Victoria.
Journal Article•
TL;DR: The closely related species and forms of the plant-hopper genus Muellerianella have been studied and intra- and inter-specific morphological differences in males and females are described in detail, including geographic variation.
Abstract: The closely related species and forms of the plant-hopper genus Muellerianella have been studied. In Western Europe this complex consists of three bisexual species and a number of triploid forms which reproduce by gynogenesis. M. extrusa Scott 1871 appears to be a distinct species which lives on Molinia caerulea. It is here taken out of synonymy from M. fairmairei Perris 1857, which lives on Holcus lanatus. The third species, M. brevipennis Boheman 1847, lives on Deschampsia cespitosa. Intra- and inter-specific morphological differences in males and females are described in detail, including geographic variation. Triploid forms, which are usually associated with M. fairmairei cannot be distinguished from bisexual females of this species. Distribution maps are given for each bisexual species and for the triploid forms which are based on an evaluation of literature data, museum collections and on 150 new samples taken all over Europe.
TL;DR: Evidence for a cytoplasmic clock regulating the cycle of DNA synthesis and cytokinesis in early cleavage in Xenopus eggs is reported, as well as on further experiments on the mechanism of cell cycle changes in the midblastula period.
Abstract: Following fertilization in Xenopus eggs, the dorsal-ventral asymmetry of the egg is established and a rapid cell cycle is begun In the mid to late blastula period this initial asymmetry is translated into differentiation of the dorsal mesoderm initiated by the vegetal dorsalizing center; as suggested by experiments of Nieuwkoop About this time the cell cycle undergoes a modification coincident with several events including the onset of cell motility We report here on experiments describing how the dorsal-ventral asymmetry is produced in the early period In particular we discuss the role of the sperm, its associated aster, the cortex, and redistribution of cytoplasmic contents This analysis furthers our understanding of UV effects on dorsalization and the mechanism of twinning We report also on evidence for a cytoplasmic clock regulating the cycle of DNA synthesis and cytokinesis in early cleavage, as well as on further experiments on the mechanism of cell cycle changes in the midblastula period
TL;DR: It is demonstrated that the two species plus the two colour forms can be distinguished from each other on the basis of (small) morphological differences (other than male colouration) and the two Mwanza forms are described as new species.
Abstract: The endemic haplochromine cichlids from Lake Victoria are estimated to comprise 200 to 250 species. This estimate is mainly based on collections from two opposite ends of the Lake, i.e. the area around Jinja (Uganda) in the north and the area around Mwanza (Tanzania) in the south. An ecological and taxonomic survey of the haplochromines from the Mwanza area was recently started by the Haplochromis Ecology Survey Team (HEST). The collection of HEST contains several species groups of which the members closely resemble each other as well as their congeners known from the northern part of the Lake. One such case, the "H." empodisma group, has been analysed in this paper. The study was focussed on two new colour forms of this group, which were discovered in the Mwanza area, and on two previously described species, "H." empodisma and "H." obtusidens, which closely resemble them. It is demonstrated that the two species plus the two colour forms can be distinguished from each other on the basis of (small) morphological differences (other than male colouration). The two Mwanza forms are described as new species. The species rank is corroborated by ecological data.
TL;DR: Le processus d'eclosion en presence of lumiere indique une convergence adaptative entre l'eClosion des oeufs dormants du Rotifere epizoique et ceux de son support naturel (Daphnies).
Abstract: Deux mecanismes declenchent l'eclosion des oeufs de duree de B. rubens. Apres un seuil minimal de latence obligatoire de deux semaines, les oeufs dormants eclosent s'ils sont exposes a la lumiere, dans un intervalle de temperature compris entre 10 et 20° C. Dans ces conditions, le taux d'eclosion peut atteindre 80% en un temps bref variant en fonction de la duree de conservation des oeufs de duree a l'obscurite mais non de la photoperiode a laquelle ils sont ensuite soumis. En absence de lumiere, aucune eclosion n'a lieu, quelle que soit la temperature. Neanmoins, ce blocage est leve apres plusieurs mois, meme a basse temperature. A 5° C, a l'obscurite, les premieres eclosions interviennent apres 4 mois et se poursuivent ensuite a intervalles reguliers mais espaces. Les implications ecologiques de ces mecanismes sont discutees en conclusion. Le processus d'eclosion en presence de lumiere indique une convergence adaptative entre l'eclosion des oeufs dormants du Rotifere epizoique et ceux de son support naturel (Daphnies).
TL;DR: Der Ameisenlowe, die Larve der Ameisenjungfer Euroleon nostras Fourcr.
Abstract: Der Ameisenlowe, die Larve der Ameisenjungfer Euroleon nostras Fourcr., erwirbt seine Beute als Lauer-Rauber in selbst gegrabenen Trichterfallen. Das Bauprinzip folgt einem angeborenen Verhaltensmuster, fur das die Schleuderbewegung und das Ruckwartslaufen charakteristisch sind; beide Bewegungen werden naher beschrieben. Die differenzierten Wurfe werden durch die besondere Beweglichkeit der Intersegmentalhaute des Thorax ermoglicht. Die Dimensionen des Trichters sind einerseits vom Alter und Larvenstadium abhangig, andererseits werden sie durch abiotische Faktoren, insbesondere durch die Beschaffenheit des Baumaterials bestimmt. Der Sattigungsgrad der Larve hat keinen signifikanten Einflus auf die Trichtergrose.
TL;DR: It is shown that Puntius melanampyx singhala (Duncker, 1911) is identical to juvenile stages of P. filamentosus (Val., in Cuv. & Val., 1844).
Abstract: It is shown that Puntius melanampyx singhala (Duncker, 1911) is identical to juvenile stages of P. filamentosus (Val., in Cuv. & Val., 1844). The taxonomic relationship between the latter species and P. melanampyx (Day, 1865) is briefly discussed. The argument of the present paper is not influenced if the generic name Barbus is adhered to instead of Puntius. Synonymy Barbus singhala Duncker, 1911: 263. Puntius singhala; Deraniyagala, 1930: 11. Puntius melanampyx singhala; Deraniyagala, 1949: 17. Puntius melanampyx sinhala; Deraniyagala, 1949: 4; 1952: 33; Munro, 1955: 43. Puntius filamentosus (Val., in Cuv. & Val., 1844).
TL;DR: Analysis of video-tape recordings of the feeding of sticklebacks shows however, that handling time in this "variable attack rate model" is not in accordance with the actual behaviour.
Abstract: (1) The functional response of the three-spined stickleback to changes in prey density was determined by presenting individual sticklebacks (for 15 seconds) with different densities of Daphnia. (2) The observed response, at first sight a type II, could not be adequately described by the existing type II models, i.e. Holling's "disc equation" and Rogers's "random predator equation". (3) The above mentioned models assume that the predator is unable to search for new prey while handling. This is claimed not to be true in the case of the stickleback-Daphnia interaction. (4) A modification of the random predator equation has been developed, which is based upon a biological explanation of the predation process, and gives an adequate description of the data. Two components of handling are distinguished: external and internal handling. Searching can again take place during the internal handling time. From this the possibility arises that the predator finds new prey before the handling of the previous prey has finished. This would result in a "waiting time". (5) The new model has been compared with a model in which the attack-rate increases as prey density increases, which also gives a good fit to the data. Analysis of video-tape recordings of the feeding of sticklebacks shows however, that handling time in this "variable attack rate model" is not in accordance with the actual behaviour. (6) Similarities between the feeding behaviour of the sticklebacks and that of mites and damselflies have been discussed. The "waiting time" resembles the "bottleneck-effect" found in the feeding behaviour of the latter two.
TL;DR: An upper last premolar recently dredged from the Schelde estuary represents either Dicerorhinus etruscus (Falconer) or Dicer orhinus jeanvireti Guerin, a new element to the Pretiglian "black bones" fauna of the Netherlands.
Abstract: An upper last premolar recently dredged from the Schelde estuary represents either Dicerorhinus etruscus (Falconer) or Dicerorhinus jeanvireti Guerin, a new element to the Pretiglian "black bones" fauna of the Netherlands.
TL;DR: The length distribution of the early larval stages in the stomach shows a bimodal size distribution in autumn, winter and spring, indicating that O. filiformis is inhibited in the host B. bufo in a specific stage of development.
Abstract: Fourty males and thirtytwo females of B. bufo were collected before and after spawning at two field stations for examination for the presence of O. filiformis. From one of these places another fifty males and twenty females of B. bufo were collected and placed in outdoor enclosures. The seasonal fluctuation of developmental stages of O. filiformis was followed from March 1978 till March 1979. The infection percentage with O. filiformis is almost 100%. The intensity of the infection varied from 0-102 helminths; in the field 10-20 parasites were frequently found as opposed to 20-30 in the experimental plots. There was no correlation between the intensity of the infection and the length of the host; not could a clear difference be demonstrated in intensity of infection between males and females of B. bufo. Early parasitic stages of O. filiformis are localised in the mucosa of the stomach and must be collected by digestion of this organ in a pepsin-HCl solution. Later on the parasite migrates to the upper intestine. Overwintering hosts harbour different parasitic developmental stages of O. filiformis. During hibernation the development is interrupted and the parasite burden does not change. Resumption of development is not correlated with the spawning activity of the host but seems to be dependent on the rise of temperature in spring. During this development older adult worms and possibly a part of L4 and L5 stages are lost with the faeces. In the experimental plots the infection in May-July was small. The level of infection was lowest in early August. From the middle of August on the infection increases and reaches a maximum in November. The length distribution of the early larval stages in the stomach shows a bimodal size distribution in autumn, winter and spring, indicating that O. filiformis is inhibited in the host B. bufo in a specific stage of development. The seasonal fluctuation of the developmental stages of O. filiformis, the inhibition of development and some facts of the life cycle are discussed.
TL;DR: The ontogenetical histories of pigment patterns in 3 Asiatic species of Barbus are presented in drawings and described and their taxonomic significance is discussed.
Abstract: The ontogenetical histories of pigment patterns in 3 Asiatic species of Barbus are presented in drawings and described. Their taxonomic significance is discussed. On the basis of the data presented, the species are allocated to sub-groups of the genus which have been proposed earlier (KORTMULDER, 1972).