Showing papers in "Biological Journal of The Linnean Society in 1982"

Sexual selection, natural selection and quality advertisement

Abstract: In Darwin's and Fisher's theory of sexual selection, females prefer ornamented males; the evolution of larger ornaments is limited by increased mortality, lor example through predation. An adornment of given size should often raise mortality more in low than in high quality phenotypes. Possible consequences for the evolution and optimal size of ornaments are here examined with mathematical models. Fisher suggested that an ormamem may evolve if it initially improves male survival. Female preference then spreads for adorned males. Their consequent mating advantage furthers propagation of the preferred trail. An alternative, the ‘handicap mechanism’, suggests that only those males best able to survive can do so with a large, handicapping ornament. Choosing adorned males, females might therefore bear offspring with high general survivorship, but sons also inherit the handicapping ornament. When it reduces survival more in low than in high quality phenotypes, the handicap mechanism (in conjunction with the Fisherian mating advantage) becomes powerful with lower heritability of fitness than previously supposed. It still requires that fitness has some heritability, for which there is indirect evidence, but field measurements are lacking. In Darwin's and Fisher's theory, both mating advantage and mortality disadvantage increase with ornament size, and balance at its optimal development. If a given adornment reduces survival most in low quality phenotypes, the optimum increases with phenotypic quality. Ornament size then may provide a measure of fitness, and can be used in mate choice. A male can usually not gain fitness by developing larger adornments than other males of the same quality. Ornaments can probably also evoke through direct competition between males, without female preferences for adorned males. Field experiments are needed to clarify this and other aspects of sexual selection. Sexual ornaments form part of the reproductive effort. Certain predictions from life-history theory should therefore apply. One is that ornaments will increase in size over the first few reproductive seasons; this is the case in many species.

The distribution of benthic marine algae in relation to the temperature regulation of their life histories

Abstract: Mainly on the basis of the distribution patterns of 42 species of the recently revised genus Cladopkora (Chlorophyceae) in the north Atlantic Ocean, it appeared possible to distinguish 10 phytogeographic distribution groups of wide applicability. Experimentally determined critical temperatures limiting essential events in the life histories of 17 benthic algal species were used to infer possible phytogeographic boundaries; these appeared to fit closely the phytogeographic boundaries derived from field-distribution data. For a temperate species, at least six different boundaries can be postulated and should be checked in the northern hemisphere: (1) the ‘northern lethal boundary’ (corresponding to the lowest winter temperature which a species can survive); (2) the ‘northern growth boundary’ (corresponding to the lowest summer temperature which, over a period of several months, permits sufficient growth); (3) the ‘northern reproductive boundary’ (corresponding to the lowest summer temperature permitting reproduction over a period of several months); (4–6) the corresponding southern boundaries. Photoperiodic responses may influence the temperature responses. Many phytogeographic boundaries appear to be of a composite nature. For instance, the southern boundary of Laminaria digitata follows the European 10°C February isotherm (which corresponds to the highest winter temperature permitting fertility in the female gametophyte, i.e. to the ‘southern reproductive boundary’), and the American 19°C summer isotherm (corresponding to the ‘southern lethal boundary’). Thus, experimental evidence supports the validity of eight of the following 10 distribution groups (for distribution groups 2 and 6, such evidence could not be found): (1) the amphiatlantic tropical-to-warm temperate group, with a north-eastern extension (examples: Gracilaria foliifera and Centroceras clavulalum); (2) the amphiatlantic tropical-to-warm temperate group, with a north-western extension (example: Hypnea musciformis); (3) the amphiatlantic tropical-to-temperate group (example: Sphacelaria rigidula =furcigera); (4) the amphiatlantic temperate group: the Cladophora rupestris type (examples: Callithamnion hookeri, Dumontia contorta; Laminaria saccharina is transitional to type 10, I., digitata to types 5 and 10); (5) the amphiatlantic temperate group: the Cl. albida type (examples: Scytosiphon lomentaria, Petalonia fascia); (6) the tropical western Atlantic group; (7) the north-east American tropical-to-temperate group (example: Gracilaria tikvahiae); (8) the north-east American temperate group and the corresponding Japanese temperate group (examples: Campylaephora hypneoides and Sargassum muticum); (9) the warm-temperate Mediterranean-Atlantic group, and the corresponding warm-temperate Californian group (examples: Saccorhiza polyschides, Laminaria hyperborea, I., ockroleuca, Macrocystis pyrifera, Hedophyllum sessile); (10) the Arctic group (examples: Saccorhiza dermatodea and Sphacelaria arctica). Distribution groups 6, 9 and 10 have comparatively narrow temperature ranges with a span of 18 22°C between their lethal boundaries and of 5 12°C between their reproductive or growth boundaries. These narrow temperature ranges limit the species in these groups to the tropics; the temperate coasts on the eastern sides of the north Pacific and north Atlantic Oceans and in the southern hemisphere; and to the Arctic, respectively. The narrow temperature ranges of group 9 make the species in this group unfit for life on the western temperate coasts of the north Pacific and north Atlantic Oceans, where algae must cope with annual temperature fluctuations of more than 20°C. Conversely, algae in group 8 (containing the numerous Japanese endemic species) are characterized by wide temperature spans (e.g. 29°C between ‘lethal boundaries’, 12–19°C between ‘growth and/or reproductive boundaries’) and must be potentially capable of occupying wide latitudinal belts on temperate coasts along the east sides of the north Pacific and north Atlantic Oceans. Algae ‘escaped’ from Japan, such as Sargassum muticum, conform to this picture. Apparently Japanese algae do not have the capacity for long distance dispersal. The corresponding east American coasts (30–45 N) harbour very few endemic species, probably as a result of the adverse nature of these sediment coasts for benthic macroalgae and their functioning as a barrier to latitudinal displacements of the flora during glaciations. The remaining distribution groups (1,2,3,4,5,7) are characterized by wide temperature spans and wide distributions, often in both the Atlantic and Pacific Oceans and in both hemispheres. Six temperate species (in distribution groups 4, 5 and 9) with an amphiaequatorial distribution have similar winter-temperature maxima permitting reproduction and corresponding with winter isotherms of 15–17°C; their upper lethal temperatures are more dissimilar and correspond with summer isotherms of 20–30°C. Their amphiaequatorial distribution can be explained by assuming glacial temperature drops along east Pacific and east Atlantic equatorial coasts in narrow belts of intensified upwelling during the presumably intensified glacial circulation of the ocean gyres.

Species richness and endemism in the Usambara mountain forests, Tanzania

Abstract: The East Usambara Mountain forests constitute what is probably one of the richest biological communities in Africa in terms of plant and animal species numbers and endemic taxa. This review presents brief accounts of the flora and of three invertebrate and four vertebrate groups and shows the percentage endemic taxa to vary from 2% (mammals) to 95% (millipedes) as a proportion of the true forest species. Notes are given on the geology, soils, climate and present land use of the Usambaras. Biological richness is considered to be due to long periods of isolation and geological stability coupled with periods of species immigration during times of re-establishment of a continuous forest cover. The nature of the endemic elements is briefly discussed. Evidence is given to show that the forests are subject to increasing pressure from legal and illegal encroachment due to agriculture (tea, cardamon, subsistence) and forestry timber operations. Air photograph analysis shows a forest decrease of some 50% in the vicinity of Amani from 1954 to 1976. The low conservation status of most forest reserves and the lack of detailed knowledge on the distribution, status and biology of the endemic species means present conservation efforts are poor and haphazard. This review calls for greatly increased research inputs and a complete halt to all exploitation of natural forest areas until a long term conservation land use plan can be implemented.

Species diversity and reproductive mechanisms in Jamaican trees

Abstract: The flowering and fruiting of the 56 species of tree growing in the forests at c. 1550 m in the western Blue Mountains in Jamaica was studied to see how differences in reproductive biology may relate to maintenance of species diversity. Forty-six of the 56 species have small flowers (log length (mm) × log breadth (mm) 1). Thirty-six are hermaphrodite, 12 dioecious and eight dioecious, monoecious or polygamous. Compatibility tests showed that five (possible seven) of the hermaphrodite species are self-compatible, one hermaphrodite species is probably self-incompatible. Anthesis and individual flower duration are variable within and between species. There is some interspecific temporal separation of flowering over the year, but a peak of species in flower in the drier to early wet season. Pollination syndromes were also studied. Of the 23 important species, 20 are generalist, two wind-pollinated, one bird-pollinated. For all species, 46 are generalist, six wind-pollinated, one, perhaps two, bird-pollinated, and possibly two moth-pollinated. Generalist type flowers are visited by a wide range of potential pollinators and one pollinator, Apis mellifera, visits many different flowers. Dispersal units usually weigh between 10 and 1000 mg, the others are smaller. Of the 23 important species, 18 are adapted for bird dispersal, four for wind dispersal, and one lacks obvious adaptation. For all 56 species 46 are bird-dispersed, eight wind-dispersed, one is ectochoric and one lacks obvious adaptation. Fruiting phenology is markedly seasonal, occurring from June to January, spanning the later drier period and half of the wet season. With one common type of pollination—entomophily, one common type of dispersal—by birds, and little temporal separation over the year in time of flower and fruit production, there seems to be only a small amount of niche separation in the variables studied; and thus the coexistence of many species is not explained by the present observations.

Genetic population structure and breeding systems in arionid slugs (Mollusca: Pulmonata)

Abstract: Electrophoresis and biochemical staining were used to analyse genetic variation in enzymes in nine species of terrestrial slugs of the genus Arion from 58 localities in the British Isles. The species fall into three categories on the basis of the genetic structure of their populations and their breeding systems. Arion lusitanicus, A. hortensis, A. distinctus and A. owenii are highly polymorphic and heterozygous, and apparently reproduce predominantly, if not completely, by outcrossing. Arion circumscriptus, A. silvaticus, and A. intermedius consist of one or a few monogenic strains. Their monogenicity apparently results from an automictic mode of reproduction, most probably self-fertilization. Arion ater and A. subfuscus consist of both a polymorphic, heterozygous form and a monogenic strain, between which hybridization occurs. The monogenic strain and the polymorphic form of A. subfuscus occur in pure populations only in Ireland and England, respectively, but each has been introduced throughout the British Isles. In both A. ater and A. subfuscus, hybrid populations show a marked deficiency of heterozygotes as a result of self-fertilization. The genetic structures and breeding systems of populations of the species of Arion introduced to North America are similar to those of native populations in Britain.

Genetic and morphological divergence between populations of the flatfish Platichthys flesus (L.) (Pleuronectidae)

Abstract: Populations of the flounder, Platichthys flesus, were screened for electrophoretically detectable protein variation at up to 37 loci. Atlantic and North Sea populations (subspecies flesus) were genetically very similar to one another (I>0.99) but different from Adriatic (subspecies italicus) and Black Sea (subspecies luscus) populations. The values for genetic identity between subspecies were around 0.9. Diagnostic loci enabled specimens of flesus, italicus and luscus to be differentiated from one another. Samples of flesus showed two to three times the heterozygosity levels ofitalicus or luscus, consistent with the greater population size offlesus. Morphological comparisons enabled populations to be categorized to subspecies. Platichthys flesus italicus and luscus are valid subspecies: the terms are not synonyms. The genetic distance data provide an estimate of divergence time of the three subspecies at about 2 My ago, an estimate that seems reasonable in the light of present knowledge concerning the recent geological histories of the Mediterranean and Black Sea basins.

Pollination of Androdioecious Xerospermum intermedium Radlk. (Sapindaceae) in a rain forest

Abstract: Xerospermum intermedium, a fairly common understorey species in the West Malesian lowland dipterocarp forest is androdioecious, with delayed self-compatibility. It flowers annually, and has an extended flowering period, with individuals flowering somewhat asynchronously, presenting small flowers with minimal visual lures. The flowers are visited by an unrestricted array of apparently imprecise opportunistic feeders, predominated by trigonid bees and butterflies. Most of these visitors exhibit low fidelity and forage opportunistically on numerous competing tree species. Presentation of nectar in alternating rhythms between the male and hermaphrodite trees appears to induce pollinator movement between them. Out of such alternating visits between the sexes, a low level of short-range inter-tree pollen transfer by trigonids and butterflies seems to occur. Despite the elaborate system which promotes pollinator movement between the sexes, this species has retained a low level of self-compatibility. The physical barriers to pollinator movement in the understorey, and high interspecific competition for pollinators by a large number of tree species, appear therefore to make it difficult to maintain an obligate outbreeding system. Hence, androdioecism may be one of the explanations for the survival of X. intermedium.

Plant mimicry: evolutionary constraints

Abstract: Because plants are sessile and their flowers and fruits are aggregated, plant mimics are less likely to be mistaken for their models than animal mimics which are mobile and dispersed among their models. Therefore, operator species are more likely to be deceived by animal mimics than plant mimics. In addition, the autonomy of plant appendages implies that warning mimicry provides less advantage to plants than to animals because plants suffer less from sampling by naive operators. Therefore, the advantage of warning mimicry is much greater for animals than plants. These reasons may explain why plant mimicry is less common than animal mimicry, based on attraction of rather than avoidance by operator species, and limited to the class of aggressive mimicry.

Genetic divergence in four species of the genus Raphanus: Implications for the ancestry of the domestic radish R. sativus

Abstract: Four species of radish of the genus Raphanus were examined by electrophoresis of water soluble proteins. This technique was used to provide information about the degree of genetic differentiation of the species over a range of gene loci coding for various enzymes. These results give genetic distance estimates showing all four radish species to be closely related. From this data a simple dendrogram is constructed to show the possible interrelationships and evolutionary divergence of these species. The domestic radish Raphanus sativus shows the greatest genetic similarity when compared with an Italian population of R. landra.

Diet choice, resource depression, and the regular nest spacing of birds of prey

Abstract: The hypothesis is suggested that resource depression is one important factor behind the observed regular nest spacing of many birds of prey. It predicts that the proportion of evasive prey in the predator's diet should be reflected in the degree of regularity in its nest spacing. The idea is tested on data from 24 raptorial bird populations of 19 species. The proportion of supposed evasive prey (birds and large mammals) in the diet was positively correlated with the degree of regularity in spacing of the nests, considering all populations or species. No such significant correlation was found for the six highly territorial species, whereas the correlation was highly significant for the other 13 species. Thus, the hypothesis seems most applicable to species with widely overlapping home ranges. However, resource depression could be one reason for territoriality.

Size and shape as ecological discriminants in successional communities of Heteroptera

Abstract: Three stages in a temperate, secondary succession are represented by a recently harrowed field, an area of mixed grassland with forbs and a predominantly birch woodland. In these, four plant communities are recognized ruderal, early, mid and late successional. The Heteroptera associated with these four successional plant communities have been sampled over a 4-year-period (1977–1980). The form (size and shape) of individual insect species is described in several ways although a multivariate analysis provides the most precise description. The range in size and shape of Heteroptera increases with the successional age of the community and exhibits a similar trend to the structural diversity of the green plants.

Competition, niche specialization and the evolution of brain size in the genus Peromyscus

Abstract: Previous studies of relative brain size in mammals have suggested an association with complex habitats and with low reproductive rate. In order to examine the causal relationships more thoroughly, a detailed examination of relative brain size variation in the genus Peromyscus was undertaken. Endocranial volumes were used to estimate brain weight for 32 species including 161 subspecies, and relative brain size calculated as the species deviation from the allometric relationship between brain and body size. The intrageneric allometric coefficient was higher than most values previously reported from low taxonomic levels, but intraspecific coefficients were generally lower than this. Island species, and relict species isolated on mountain tops, which may be ecological ‘islands’, had consistently small relative brain sizes, but peninsular species were large brained. Among the remaining species there were significant correlations between litter size and relative brain size, and between the number of competitor species and relative brain size. Species with many competitor species have relatively large brains and small litters. It is concluded that the nature of the geographical distribution, the pattern of species formation and habitat complexity all influence relative brain size in existing forms.

A theoretical analysis of the morph frequency variation in the peppered moth over England and Wales

Abstract: The migration-selection model for the spatial and temporal variation of morph frequencies of Biston betularia over England and Wales (Cook & Mani, 1980) has been extended to include effects due to non-visual selection. The parameters for non-visual selection were chosen from the recent determination by Mani (1980) and by Creed et al. (1980). The morph frequencies over England and Wales were obtained through computer simulation and the results were compared with data along the Manchester-Yorkshire, Central Wales-East Anglia and South Wales-London transects. Best fits to the data were obtained by using the non-visual selective values of Mani for carbonaria and modified values of Creed et al. for insularia. It is concluded that the observed polymorphism could be well explained through a balance of migration and visual and non-visual selections.

Bryophyte Evolution And Geography

Abstract: The three extant Divisions comprising the bryophytes extend, as fossils, well back into Palaeozoic time. Bryophyte origin is part of the rise of terrestrial, vascularized, plants with sporopollenin-walled spores in the Silurian. Before the end of Carboniferous time, bryophyte lines were widely present. Separation of Gondwana and Laurasia by the Permian Tethys Sea and subsequent widespread desert episodes fragmented an already diversified bryoflora subjecting it to intense selective pressure. The cool, mesic climate of southern Gondwana provided a refugium for austral bryophytes. Warmer and drier climates of the Permo-Triassic Laurentian-Laurasia favoured drought-adapted or niche-specific groups creating marked systematic discontinuities. The Angaran wet, probably cool, temperate region provided refuge for basic stock for much of today's rich holarctic and wet ‘tropical’ bryofloras. Climatic changes, correlated with tectonic events and the rise of angiosperms, opened habitats favourable for a diversity explosion. Despite demonstrated potential for long-distance dispersal, modern distributions are mostly linked with total floras or establishment on islands prior to niche saturation. Remnants of Gondwanan bryoflora persist in high southern latitudes as disjunctions with the possibility that the folded ranges of the African Cape have been an insular fragment at higher latitudes becoming attached shortly after angiosperm diversification. Floras of southern India and east Africa have common features but the Himalayan flora shows evidence that the Gondwanan flora of the Indian plate was lost during the movement through desert and tropical latitudes; neotropical and palaeotropical floras are distinctive. Much of the northern Australian bryoflora is recently Malesian-derived while the southeast shows strong austral influence and commonality with New Zealand. Tropical Pacific island floras are mostly Malesian-derived but with both holarctic and austral elements present as in Hawaii and the Society Islands. Holarctic bryoflora is circum-polar with temperate areas of Euro-American and far eastern elements floristically bound by disjunct and vicariad species. Kroeber Coefficients of Correlation differ as Pacific island floras are compared and Guttman-Lingoes Smallest Space Coordinates indicates floristic subgroups within Polynesia. Although these and other mathematical treatments yield potentially promising results, the methods are yet unrefined and there is some uncertainty whether characteristics of numbers or of organisms are implicit in the summations.

A field study of the association between the stinkhorn Phallus impudicus Pers. and the British fungal-breeding Drosophila

Abstract: Emergence records for three species of Drosophila breeding in the stinkhorn (Phallus impudicus) are presented. These are D. phalerata, D. subobscura and D. cameraria. The numbers of stinkhorn present in one woodland (0.114 km2) have been estimated for a two-year period. In 1976, the total number of these fungal breeding sites during the summer was approximately 8000 and in 1977 it was 5300. Utilizing the estimates of breeding site numbers, Drosophila emergence data and estimates of adult survival from laboratory populations, density estimates for D. phalerata and D. subobscura are calculated.

The Psocoptera of East Africa—a taxonomic and ecological survey

Abstract: The ecology of 62 species of Psocoptera obtained in a survey carried out in the dry season in East Africa is discussed. Twenty-eight new species are here described: Thylacella angustipennis; Lepinolus fuscus; Trogium apterum; Hemiseopsis obscurus; Liposcclis pleswpuber; Caecilius aequalis, frater, proxmus and uirgalus; Paracaecilius copiosus and lucidus; Harpezoneura indotata; Lcchesilla acutiloba, cornistema, keniensis and rectigladia; Heterocaecilius aequabilis; Pseudoscottiella maculata; Elipsocus ignobilis; Lesneia niger and pulchra; Haplophallus afruanus; Mesopsocus acutilobus, alatus, difiilis, nitidifrans and propinquus. Redescriptions are given of Caecilius inquinatus Enderlein, Paracaecilius pallidus (Pearman), Harpezoneura pallens Pearman, Pseudocaecilius morstatti Enderlein and Mesopsocus montinus Enderlein. Keys are given to the African species of Paracaecilius Badonnel and to the East African species of Mesopsocidae. A checklist of the Psocoptera known from East Africa is provided.

The comparative distribution and population dynamics in Trinidad of Sceliphron fistularium (Dahlbom) and S. asiaticum (L.) (Hymenoptera: Sphecidae)

Abstract: Two sphecid wasps, Sceliphron asiaticum (L.) and S. fistularium (Dahlbom), which build mud nests and capture spider prey, had overlapping but distinctly different distributions in Trinidad. Sceliphron asiaticum was associated with drier ( 50° mortality of the females between emergence and starting to nest. The regulation of numbers of these wasps in relation to that of S. assimile (Dahlbom) in Jamaica is discussed.

The entomology of the Isle of Rhum National Nature Reserve.

Abstract: Entomological records for the Island of Rhum have been brought together to form an inventory of 2158 species of insects. It is the result of intense surveys conducted in the 1960s combined with casual collecting by visiting and resident entomologists and includes documented records since 1895. The diversity of insects recorded is, perhaps, greater than might have been anticipated in a bleak and windswept Hebridean island. Man-made habitats in the form of mixed woodland, farmland and gardens support the greatest range of species present though most of the resident insect rarities occur in coastal or upland habitats. The island is a National Nature Reserve owned by the Nature Conservancy Council whose management policies include a large scale woodland restoration programme aimed at recreating forest formations composed of native trees and shrubs, as well as studies on the effects of red deer Cervus elaphus and other grazing animals on existing vegetation communities outwith the planting areas. This catalogue serves as a baseline by which changes resulting from these management activities, as well as cyclical population changes, can be measured.

Phenotypic variation with respect to fitness: the basis for rank-order selection.

Abstract: Having argued that phenotypic variation with respect to the component of fitness involved in withstanding density stress is useful for the persistence of populations through time, the sources of such variation are described. Age differences and differences caused by the accidental encounters of dissimilar microenvironments are non-genetic in origin. Genetic bases for phenotypic variation can either be proximate (each individual having a unique genotype) or ultimate. The latter case is one in which the genotypes of individuals are such that the progeny they produce are phenotypically variable. Selection favouring such genotypes can be shown to be Darwinian; group selection is not required. A means for revealing instances of the ultimate genetic control of phenotypic variation is suggested: measures of what should be error variance prove to be larger than those which should, under normal circumstances, include error variance. The last increment of variation that causes what might otherwise be repetitive structures to differ can be ascribed to decisions that are genetically pre-set within developmental programmes.

Shell shape variation in dog‐whelks (Nucella lapillus (L.)) from the West Coast of Scotland

Abstract: European populations of the common dog-whelk, Nucella lapillus (L.), usually show a neat and precise pattern of shell shape variation with the exposure of their habitat to wave action. Whilst this is the case along much of the west coast of Scotland, there are a number of instances where unusually elongated shells occur, somewhat reminiscent of the form described for the Severn Estuary. There are no obvious environmental or geographical correlates to explain the occurrence of these forms and a genetical interpretation is sought.

Hybridization studies in the Schistocerca americana complex: II. The Peruvian locust

Abstract: A culture of swarming locusts from Peru was hybridized with locusts from Argentina and Mexico. The sex ratio and fertility of the hybrids was measured and male meiosis observed. It is concluded that the Peruvian locust is a subspecies of the Central American locust and a separate species from the Argentinian.

Leaf demography and the plastochron index.

Abstract: The recently developed techniques of leaf demography are compared with those of the plastochron index. Data derived from the plastochron index that are relevant to leaf demography can be found in morphological and physiological literature. These are presented and show the usefulness of both concepts in the measurement and description of plant growth, productivity and morphology.

Variation in Nymphon brevirostre (Hodge), and the status of N. rubrum (Hodge) (Arthropoda: Pycnogonida)

Abstract: A series of morphometric analyses conducted on specimens of Nymphon brevirostre Hodge and Nymphon rubrum Hodge from British waters has shown that the characteristics variously used in the past to distinguish these two species are invalid. In this material these characteristics range from the extreme of the typical N. brevirostre form to that of the typical N. rubrum form, with most of the specimens exhibiting an intermediate morphology. Multivariate analyses showed no significant splitting of the material into two groups which might correlate to Hodge's two species. Protonymphon larvae from males of both typical extreme forms were morphologically identical. It is concluded that N. rubrum is a junior synonym of N. brevirostre, a variable species whose morphology tends towards the rubrum form as the animal grows.