bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the effects of abnormally high water levels on the ecology of fish in certain shallow regions of Lake Victoria
Authors: Welcomme R. L. 
Published: August 2009

Between 1961 and 1964 the water levels of Lake Victoria increased abruptly. This increase produced changes around the shoreline of the lake, creating new habitats in the form of lagoons. Such lagoons were cut off from the main lake by differing widths of floating vegetation. Chemically and physically these new regions resembled small tropical fish ponds, with a nocturnal reduction in both dissolved oxygen and temperature.The lagoons were occupied shortly after their appearance by characteristic groups of fishes, which depended for their species composition on the degree of isolation of the different bodies of water from the main lake. It was generally found that the more isolated the lagoon, the more impoverished it was in numbers of species. The most successful colonizers of these waters were Tilapia leucosticta and Haplochromis nubilus, which were present in all lagoons.Populations of these two species showed a tendency to stunt, which was more marked in the more isolated populations. This, together with the population changes associated with isolation, suggests that the mat of floating vegetation, by reason of the de‐oxygenated conditions that exist under it, acts as a form of biological filter. Thus fish from the lake can only penetrate to the nearer lagoons, the populations in the more isolated waters remaining more or less segregated.
Some aspects of adaptation in a polymorphism for breeding colours in the Threespine stickleback (Gasterosteus aculeatus))
Authors: Semler David Edward 
Published: August 2009

Polymorphism in the nuptial colouration of male Threespine sticklebacks (Garterosteus aculeatus L.) was studied. In Lake Wapato in Eastern Washington, approximately 14% of the breeding males develop typical red nuptial colouration while others develop various colours which were grouped into a non‐red category. The hypothesis was tested that red males are adaptive in Lake Wapato as a result of sexual selection and differential egg predation.In a series of mate preference tests, females demonstrated a significant preference for red males over non‐red males. In a second experiment, using artiticially coloured non‐red males, it was shown that the females are responding to the red colouration alone. This evidence suggests that one of the selective pressures maintaining the red morph is sexual selection.In a stomach analysis of male and female sticklebacks collected from a breeding colony it was found that 51 % of the fish examined had stickleback eggs in their stomachs. Both male and female sticklebacks eat a large number of eggs; however, males eat significantly more eggs than females. Eggs were found to be most susceptible to predation during their first four days of development. Given that red ventral colouration has threat value, red males may also be adaptive because of a reduction in egg predation within their territories in contrast to non‐red males.One of the selective forces against red males is probably differential predation by trout (Salmo gairdneri). This trout predation has been shown to be extensive in Lake Wapato. The opposing selective forces discussed in this paper cannot maintain the polymorphism; they are only components of fitness of the colour morphs.
Limb posture and locomotion in the Virginia opossum (Didelphis marsupialis) and in other non‐cursorial mammals
Authors: Jenkins Farish A. 
Published: August 2009

Past studies of mammalian posture and locomotion have been made principally on cursorial species and current concepts are stereotyped accordingly. Mammalian limbs are usually characterized in terms of vertical orientation and parasagittal excursion; the assumption prevails that this type of stance and limb movement is typical of the class.In the present study, walking movements in eight mammalian species (Tachyglossus aculeatus, Didelphis marsupialis, Tupaia glis. Mesocricetus auratus, Rattus norvegicus, Mustela putorius, Heterohyrax brucei, and Felis domestica) were studied cineradiographically with particular attention given to limb posture and excursion relative to the parasagittal and horizontal planes. Only the cat and, to a lesser degree, the hyrax conform to the postural and locomotory pattern that has been regarded as characteristic of most terrestrial, quadrupedal mammals. In the other six species, the humeri and femora usually function in positions more horizontal than vertical and at angles oblique to the parasagittal plane. Furthermore, the excursion pattern of these species have interspecific differences; some patterns are more variable than others. The classical conception of “mammalian posture” and “mammalian locomotion” is inaccurate both as a description of the features possessed in common by living terrestrial mammals and as a hypothetical approximation of the condition in ancestral mammals. At present, non‐cursorial mammals such as the opossum and tree shrew are more realistic models on which to base deductions concerning posture and locomotion in eatly mammals.
Pituitary control of ovarian activity in the lizard, Agama agama
Authors: Eyeson K. N. 
Published: August 2009

The principal ovarian structures in Agama agama are non‐yolky and yolky follicles, corpora lutea and atretic follicles. Hypophysectomy affects all stages of vitellogenesis and follicular atresia results. Atresia involves resorption and digestion of yolk by the granulosa cells, which eventually undergo a fatty degeneration. Immature follicles and corpora lutea are not affected by hypophysectomy.Injections of 0.2 mg FSH (NIH‐FSH‐S3 ovine) on alternate days for 14 days not only maintain vitellogenesis in hypophysectomized animals, but also tend to overstimulate the small follicles to synthesize yolk. A similar dose of LH(NIH‐LH‐SII ovine) fails to maintain vitellogenesis in hypophysectomized animals, while a higher dose of 0.4 mg LH tends to overstimulate the small follicles. An unusual rupture of yolky follicles in FSH injected lizards is reported and a possible development of such follicles into corpora lutea is discussed.
Associations of Cladocera in the zooplankton of the lake sources of the White Nile
Authors: Green J. 
Published: August 2009

Thirty‐one species of Cladocera are recorded from the lake sources of the White Nile. An account is given of the seasonal occurrence of the main planktonic species at eight stations in Lake Albert. The horizontal distribution of species in Lake Albert was studied by means of vertical hauls taken at intervals along the length of the lake, and along transects from the shore to the middle of the lake. It is possible to distinguish an inshore group, consisting of Moina micrura and the helmeted form of Daphnia lumholtzi, and an offshore group with Ceriodaphnia reticulata and the monacha form of Daphnia lumholtzi. The validity of these groups is demonstrated by analyses of percentage co‐occurrence, correlation and regression. Diaphanosoma excisum and Ceriodaphnia cornuta overlap these two groups. These distributions can be explained by the combined operation of two major factors: the presence inshore of the zooplanktivorous fish Alestes baremose, and competition between cladoceran species of similar sizes. The overlapping of the inshore and the offshore groups by Diaphanosoma excisum and Ceriodaphnia cornuta can be explained by their sizes differing from the other main species sufficiently to reduce competition.Similar transects on Lake Edward again reveal Moina micrura as an inshore form and the monacha form of Daphnia lumholtzi as an offshore form. Ceriodaphnia reticulata is replaced in Lake Edward by the similarly sized C. dubia. The helmeted form of Daphnia lumholtzi was not found in the samples from Lake Edward, but it is apparently replaced by Daphnia longispina, although this species also increases in abundance offshore. In Lake Victoria both the helmeted form of D. lumholtzi and D. longispina are found, but their distributions have not been studied. Lake George has D. barbata as the only species of the genus, and the samples from Lake Kyoga lacked the genus completely.In most of the planktonic Cladocera from the lake sources of the White Nile the size of the eye is related to the size of the carapace, but the horned form of Ceriodaphnia cornuta from Lake Victoria has a relatively smaller eye than the unhorned form from Lake Albert. This may be caused by selection pressure exerted by the small planktivorous fish Engraulicypris argenteus.Within one lake the numbers of Cladocera under one square metre increase with the depth of the station. This implies utilization by the Cladocera of an environmental resource related to total depth. This resource may simply be space. When the numbers per unit volume are calculated there is no apparent relationship to the depth of the station. With the exception of Lake Kyoga the lakes can be arranged in a series of increasing conductivity and increasing numbers of Cladocera per unit volume.
Ecological studies on crater lakes in West Cameroon Zooplankton of Barombi Mbo, Mboandong, Lake Kotto and Lake Soden
Authors: Green J. 
Published: August 2009

The zooplankton of four crater lakes in North‐west Cameroon has been studied by means of vertical hauls from the bottom to the surface. Two of the lakes are deep, with sparse phytoplankton, while the other two are shallow with dense blooms of blue‐green algae. All the lakes are without planktonic Cladocera. In Lake Kotto, Mboandong and Barombi Mbo the dominant zooplankter is Mesocyclops (Thermocyclops) hyalinus, which is replaced in Lake Soden by Mesocyclops leuckarti. Larvae of Chaoborus are present in all the lakes. In the two deep lakes, Soden and Barombi Mbo, the dominant rotifer is Polyarthra dolichoptera, but in the two shallow lakes, Kotto and Mboandong, three species, Hexarthra mira, Brachionus fakatus and B. caudatus, make up the bulk of the rotifers.In Barombi Mbo during the daytime most of the zooplankton was in the top 20 m, but most of the Chaoborus larvae were below 20m.The standing crops of zooplankton in these lakes are low compared with those of lakes in the Kigezi District of Uganda.The most remarkable feature of the zooplankton in these lakes is the occurrence of dwarfed forms. Both species of cyclopoid copepods and the eight identifiable species of Rotifera are smaller here than in most other localities. Factors which may be associated with this dwarfing are low latitude with constant high temperature, low phytoplankton availability, and the low ratio of drainage area to lake area.
The syrinx in family Columbidae
Authors: Warner Robert W. 
Published: August 2009

The pigeon syrinx is markedly different to that organ in most other birds, and although basically a simple structure, shows a number of unique modifications, the significance of which cannot readily be fully assessed. The tracheal rings are dorsally cartilaginous, but are thickened and ossified over their ventral surfaces; the sternotrachealis muscles are asymmetrically inserted on to the trachea. There is an extensive unsupported area in the external walls of the syrinx, resembling an external tympaniform membrane, but which does not appear to be a sound source. The tracheolateralis muscles insert directly on to this area, not on to the adjacent rings. There is no rigid pessulus.The sound‐producing mechanism of the Columbidae is different to that found in other non‐passerine birds. The anatomy of the syrinx is described in detail, and the mechanism of sound‐production is discussed.
An interpretation of morphometric and gravimetric differences shown by adult Steganacarus magnus (Acari: Cryptostigmata)
Authors: Elmes G. W. , Webb N. R. 
Published: August 2009

The weights and lengths of about a thousand individuals of Steganacarus magnus (Nic.) have been analysed and found to have a bimodal distribution. It is suggested that this can be used as an aid to separating the sexes in this species.Summary:An analysis of the weight distributions of adult Steganacarus magnus (Nic.) showed them to be bimodal. Small individuals, without eggs and pre‐larvae had a mean weight of 159 μg and large individuals with eggs and pre‐larvae had a mean weight of 335 μg. It is suggested that these two weight classes represent male and female individuals.
A study of the internal parasites of small rodents from woodland areas in Surrey
Authors: Lewis J. W. , Twigg G. I. 
Published: August 2009

The occurrence of helminth parasites and leptospires from the Long‐tailed field mouse, Apodemus sylvaticus, the Bank vole, Clethrionomys giareolus and the Short‐tailed vole, Microtus agrestis has been studied from four woodland areas in Surrey. The composition of the helminth fauna of these rodents, particularly A. sylvaticus and C. giareolus, differs from that of previous studies carried out in the British Isles in consisting largely of cestodes and fewer species of digeneans and nematodes. On the other hand the degree of infection of the rodents with nematodes as in the case of A. sylvaticus infected with the trichostrongylid Nematospiroides dubius and theoxyurid Syphacia stroma and of C. giareolus with thecap‐illarid Capillaria muris sylvatici is greater than the cestode and digenean infections and is probably linked with the monoxenous nature of the nematode life cycles.Differences in the number, incidence and degree of infection of mice and voles with species of helminths is undoubtedly linked with differences in the feeding habits of the respective hosts but the present study has also confirmed that infection levels in both leptospires and helminths are influenced by the age/sex relationships of the host together with season and habitat. The relationship between the distribution of rodents infected with leptospires and some helminths suggests similarities in the mode of their transmission.
Allometric growth in two species of Ectobius (Dictyoptera: Blattidae)
Authors: Brown Valerie , Davies R. G. 
Published: August 2009

Allometric growth of the postembryonic stages of Ectobius lapponicus (Linn.) and E. panzeri Stephens is described and analysed. Alternative methods of computing the allometric growth equation are discussed and applied, with the necessary significance tests, to a large number of skeletal structures in all developmental stages of each sex. The validity of Dyar's Law and its modifications are assessed quantitatively.Summary:The growth in linear dimensions of 74 exosketetal structures has been studied quantitatively in all instars of both sexes of Ectobius lapponicus and E. panzeri.Almost all the investigated structures show some statistically significant degree of allometric growth, but relatively few of them grow by simple allometry. Some possible reasons for this are indicated.Well‐defined growth gradients exist in the appendages and along the main axis of the body. Allometric growth contours, showing sexual and specific differences, express the temporal and spatial variations in the allometric growth ratio.The limitations of Dyar's Law and Przibram's Rule are discussed and it is shown that conformity with Dyar's Law is not improved by allowing for differences in the duration of the instars.It is emphasized that allometric growth studies should involve the choice of a suitable reference dimension and the selection of an appropriate statistical model to which the growth data are fitted. The estimation of the allometry parameters a and b, as well as the appropriate significance tests, depend on the model chosen, though the two models compared in this study do not yield appreciably different estimates.
Some effects of X‐irradiation on the activity of the thyroid and pituitary glands of Xenopus laevis (Amphibia) during metamorphosis
Authors: Chopra D. P. , Hamilton Louie 
Published: August 2009

A histological study of irradiated thyroid and pituitary glands of metamorphosing Xenopus tadpoles was made. Both glands shrink, reaching a minimum nine hours after irradiation and recover by 24 hours. It is suggested that sudden release of hormones may explain a reported hastening of metamorphosis in irradiated tadpoles.Summary: Xenopus larvae received 2500 rads of whole body X‐rays.Nine hours after irradiation both pituitary and thyroid volumes were significantly less than the controls. From 24 hours after, the volumes had returned to control levels.The mitotic incidence in irradiated thyroids fell within five hours to one tenth of the control value and remained suppressed for at least three days.
A comparative study of territory in the Reed warbler (Acrocephalus scirpaceus) and Sedge warbler (A. schoenobaenus)
Authors: Catchpole C. K. 
Published: August 2009

Various aspects of territoriality were studied comparatively in a marked population of Reed and Sedge warblers at the Attenborough Nature Reserve, Nottinghamshire. Differences in arrival patterns, establishment of territory and particularly territory size were detected. In view of the dynamic nature of territory boundaries, a method is described for obtaining measures of mean territory size for comparative purposes. The sympatric species were largely separated by different breeding and feeding habitats, but there was also a degree of interspecific competition in some areas and interspecific territorialism was found to occur. Adults of both these migratory species were found to exhibit strong site fidelity, and there was some evidence to suggest that early post‐fledging experience may influence initial selection of a particular area and territory for first breeding.The adaptive significance of territory is discussed in relation to the findings presented and current hypotheses. There was some evidence which suggests that reduction of predation pressure and intraspecific interference through spacing out, as well as provision of a nest‐site may be important functions of territory in these species, but no evidence that food supply or population regulation are involved. The significance of interspecific territorialism is considered in relation to interspecific competition. The various factors effecting territory size and the patterns of nesting dispersion are also considered in an attempt to account for the striking interspecific differences found between these closely related species. It is concluded that although a multiplicity of factors may well be interacting in complex fashion, the more important of these stem from contrasts in the physical properties of the two habitats.
Fine structure of the respiratory organs of the Climbing perch, Anabas testudineus (Pisces: Anabantidae)
Authors: Hughes G. M. , Munshi J. S. Dutta 
Published: August 2009

An electron microscopic study has been made of the three respiratory organs of climbing perch. The gill structure is similar to that of the other telcosts but the thickness of the water/blood barrier is much greater, being as great as 20 μm in some specimens. The increased thickness is due to a multilayered epithelium which is thinner (3.5–7 μm) over the marginal channel of the secondary lamellae. The other two main layers, basement membrane and pillar cell flange, are relatively thin (about 1 μm).The pillar cells have a typical structure, but in certain regions they are contiguous with one another and line well‐defined blood channels. Some of the columns of basement membrane material in such regions may be common to adjacent pillar cells.The air‐breathing organs are (a) the lining of the suprabranchial chambers, and (b) the labyrinthine plates attached to the dorsal region of branchial arches. Electron microscopy showed that their structure is well adapted for gas exchange, the air/blood barriers being only 0.12–0.3 μm, comprising an epithelial layer, basement membrane, and thin capillary endothelium. The many parallel blood channels of the respiratory islets of both organs are separated by pillar‐like structures which differ from the pillar cells of the secondary lamellae. Thus the hypothesis that the air‐breathing organs represent modified gills is not supported by this study.The fine structure of the non‐respiratory region of the air‐breathing organs is similar to that of the skin, and includes chemoreceptor‐like cells. Evidence concerning the possible homology of pillar cells with plain muscle cells is discussed.
Ecological studies on crater lakes in West Cameroon The blood of endemic cichlids in Barombi Mbo in relation to stratification and their feeding habits
Authors: Green J. , Corbet Sarah A. , Betney Elaine 
Published: August 2009

The West Cameroonian crater lake Barombi Mbo is stratified, with no detectable oxygen below 20 m. Of the endemic cichlid fishes in this lake Konia dikume is exceptional in having a mean haemoglobin concentration of 16.55 g/100 ml, while the other ten endemic cichlids range from 5.55 to 8.70 g/100 ml blood. The erythrocyte count is also higher in K. dikume than in the other species.The phytoplankton in the lake is most abundant between 10 and 15 m from the surface.The single species of cyclopoid copepod and the rotifers in the zooplankton remain in the top 20 m throughout the day and night, but the larvae of Chaoborus spend the daytime at depths below 20 m, mostly between 30 and 70 m. At night these larvae ascend into the upper layers, and feed on rotifers. Konia dikume feeds on the larvae of Chaoborus, and the high concentration of haemoglobin in the blood of this fish, coupled with a large blood volume, appears to be an adaptation for the storage of oxygen. This would enable the fish to dive into the deoxygenated hypolimnion and extend the time available for feeding when the Chuoborus larvae are ascending at dusk and descending at dawn. Konia dikume appears to be a visual feeder, and in the short tropical twilight any extension of the feeding period could be of survival value.
Spermatophore formation in the pseudoscorpion Chthonius ischnocheles (Chthoniidae)
Authors: Legg G. 
Published: August 2009

The reproduction of pseudoscorpions involves indirect sperm transfer by means of spermatophores. The spermatophores are the product of the male genital atrium. A functional interpretation of spermatophore formation in Chthonius ischnocheles is based on evidence from (a) a morphological study of the genital atrium, the associated accessory glands and the musculature (b) males sectioned during spermatophore production (c) histochemical tests on the glands and their secretions (d) biochemical analyses of one gland (posterior dorsal) and its secretion (e) the behaviour of males during this process and (f) the structure of the spermatophore.The anterior region of the genital atrium is concerned with the production of the sperm packet. The encysted sperm and the seminal fluid from the prostatic reservoir are encapsulated in a sperm packet by a secretion from two pairs of anterior glands. The posterior region of the genital atrium is responsible for the formation of the spermatophore stalk and its distal elaboration, the two lateral collars. These parts of the spermatophore arise from the fibroin secretion of the posterior dorsal gland; the shape of the spermatophore collars is correlated with their mould, the medial diverticula. In addition the lateral glands secrete a light oil which accumulates on a thickening of the spermatophore stalk proximal to the collars. This suggested that this secretion acts as a pheromone to attract females to the spermatophore since in this species males produce their spermatophores in the absence of females.