Showing papers in "Biological Journal of The Linnean Society in 1975"

The role of photosynthesis in the nutrition of the mollusc Elysia viridis

Abstract: Experiments were carried out on the changes in weight, chlorophyll content and photo-synthetic capacity of Elysia viridis over periods of up to 8 weeks when incubated in light or dark, with and without its source of chloroplasts, the seaweed Codium fragile. It was concluded that photosynthesis is of considerable importance in the nutrition of the animal. Animals starved in the dark lost weight much more rapidly than those starved in the light. Rates of photosynthesis are of the right order to account for these differences in weight. The animal seems to have an annual life-cycle, an important consideration in analysing the results of long term experiments carried out on animals collected at different times of the year.

Ecology of cotton stainers (Heteroptera: Pyrrhocoridae) in southern Ghana

Abstract: An account is given of the ecology of four species of Dysdercus in southern Ghana. Succession of host plants, host preference and migration is studied. Colony structure is examined. Natural enemies are investigated. Mimetic resemblance of the resident predator to a particular species of host Dysdercus is studied. Experiments on the palatibility of Dysdercus species to mammalian predators are discussed.

Convergent evolution in aquatic fungi: the tetraradiate spore

Abstract: Fungi are mostly terrestrial. Less than 2% of the species are aquatic. These include primitive species with zoospores (Chytridiomycetes and Oomycetes) and re-migrant types mostly in Ascomycetes and Fungi Imperfecti (including Hyphomycetes) with a very few in Basidio-mycetes. Aquatic Hyphomycetes are abundant on decaying leaves (especially of broad-leaved trees) in well-aerated streams and rivers. Their conidia are hyaline and mostly of unusual form. In many the conidium is tetraradiate consisting of four long arms diverging from a common point. In the different genera the tetraradiate conidium develops in very different ways. In some it is a phialoconidium; in others a thalloconidium. In some attachment to the conidiophore is by the tip of one of the four arms; in others near their point of divergence. In some all arms develop simultaneously; in others in succession. The wide range of developmental geometry suggests convergent evolution. The tetraradiate aquatic spore also occurs in Basidiomycetes. The only two higher Basidiomycetes (both marine) with submerged sporophores have tetraradiate basidiospores. The world-wide distribution of aquatic Hyphomycetes is discussed. Their general ecology is also considered. Concentrations of 1000 to 10,000 conidia per litre may be reached in small rivers in autumn. Attention is paid to the possible biological value of the tetraradiate aquatic spore. The evidence suggests that this is connected with the problem of initial anchorage in the turbulent conditions of a stream.

Natural enemies of Toxoptera aurantii (Boy.) (Homoptera: Aphididae) on cocoa in Ghana

Abstract: Natural enemies of the black citrus aphid, Toxoptera aurantii (Boy.), on cocoa in Ghana are identified. Biology of some of the natural enemies is followed. Behaviour of the coccinellid and syrphid predators is studied in detail. Effectiveness of the predators in reducing the aphid populations is discussed.

A study of two physiological races of the heather psyllid, Strophingia ericae (Curtis) (Homoptera: Psylloidea)

Abstract: Evidence is presented that Strophingia ericae, a small homopteran feeding on Calluna has two physiological races. One of these occurs from sea level up to about 200 m altitude, and the other above this altitude.

Shell polymorphism in the snail Cochlicella acuta (Müller) and some data on its genetics

Abstract: The principal shell variation in the snail Cochlicella acuta is described in terms of banding, extra-band opacity and ground colour. A nomenclature like that used for Cepaea is adopted for the banding and a simple descriptive one, using the terms continuously opaque and discontinuously opaque, for extra-band opacity. Ground colour is either lacking, a condition which produces shells of white appearance, or present which makes them amber coloured. The results of breeding experiments are reported, which show that much of the shell polymorphism is controlled by genes located at closely linked loci. The shell polymorphism in Cochlicella acuta is compared with that in Cepaea. Possible factors determining supergene frequencies in Cochlicella acuta are discussed. Visually selective predation by rooks, Corvus frugilegus is suggested as the influence responsible for the evolution of morphs that are cryptic in certain environments. Direct evidence of such evolutionary change is reported from sub-fossil material collected from successive strata below the present surface of fixed dunes at a site in Cornwall.

Biology and immature stages of cotton stainers (Heteroptera: Pyrrhocoridae) found in Ghana

Abstract: Biology and immature stages of four species of Dysdercus found in Ghana are studied in detail. Complete life cycles of the species are followed in the laboratory. The larval stages are fully described for the first time. Keys to distinguish the larvae and adults are constructed. Relationship between measurements of successive instars is discussed.

Gene frequencies, genetic background and environment in Pyrenean populations of Cepaea nemoralis (L.)

Abstract: Microgeographical genetic differentiation of populations of the polymorphic land snail Cepaea nemoralis (L.) has been the subject of intensive investigation. The importance of environmental selection acting at the loci which control the shell polymorphism in determining the distribution of genes in this species remains a matter of considerable controversy. Some populations of C. nemoralis in the central Pyrenees show striking local associations of morph frequency (and particularly of the frequency of unhanded shells) with topography which have been ascribed to the action of natural selection. In the Ter valley (eastern Spanish Pyrenees) populations described here, however, the pattern of association of the frequencies of the shell morphs with topography is quite different from that found in the central Pyrenees. In particular, the distribution of unhanded shells is almost the inverse of that found in some previously studied populations. The general picture of variation in relation to topography in Pyrenean C. nemoralis populations is now seen to be one of great local consistency within valley systems, but of considerable differences between valley systems. This variation in population structure may be due either to cryptic and undetected environmental differences between valley systems or to evolutionary divergence between their C. nemoralis populations. The difficulty of deciding between these two conflicting hypotheses emphasizes the limitations of the technique of simply examining the distribution of individual genes in natural populations as a method of analysing their evolutionary history.

Factors controlling the distribution in Jamaica of Pachodynerus nasidens (Latr.) (Hymenoptera: Eumenidae)

Abstract: Pachodynerus nasidens (Latr.) is an inquiline in the disused cells of Sceliphron assimile Dahlbom (Sphecidae) and Eumenes colona Saussure (Eumenidae) in Jamaica. Within the area of distribution of its hosts it is virtually absent where the essential resources of water and of leaf-mining, flower-feeding or leaf-rolling caterpillars on bushes are further than 80 m from the nesting site. Its use of host cells is reduced where mean annual precipitation is less than 1200 mm and where altitude is less than 100 m. In trap-nests it can be collected only in shaded and (less frequently) in partly-shaded localities. Of six other inquilines also found, only Trypoxylon texense Saussure (Sphecidae) was sufficiently numerous to be an important competitor for host cells but evidence shows its competition was unimportant to Pachodynerus nasidens. High percentage mortality resulting from Melittobia chalybti Ashmead (Eulophidae) on P. nasidens did not limit utilization of host cells. During drought, fecundity of P. nasidens dropped from 14.0 (± 2.9) to 7.0 (± 1.4) eggs per female and this may have brought about local extinction and hence low utilization of host cells. Drought reduced longevity and the rate of oviposition, but had no effect on the speed of provisioning.

The Hookers and the development of the Royal Botanic Gardens, Kew*

Abstract: Following the recommendations of an investigating committee headed by John Lindley, responsibility for the maintenance of the neglected royal estates at Kew was assumed by the State in 1840. Sir William Jackson Hooker, who had long coveted the post, was appointed the first Director. Under his able supervision, the Royal Botanic Gardens rapidly expanded and were imaginatively landscaped, new greenhouses, including the famous Palm House, were erected, and three museums of economic botany were opened. Hooker's own extensive collections formed the nucleus of the Herbarium and Library which made Kew an important centre of taxonomic research. Joseph Dalton Hooker who succeeded his father as Director, although continuing to improve and develop the Gardens, concentrated his efforts on essentially scientific activities particularly in the fields of systematics and phytogeography. To a great extent the international reputation enjoyed by the Gardens today is due to the vision, determination and energy of the two Hookers.