Showing papers in "Biological Journal of The Linnean Society in 1989"

A life‐cycle theory of responses to stress

Abstract: Stress is here defined as an environmental condition that reduces Darwinian fitness when first applied. Optimal stress responses (i.e. those that maximize Darwinian fitness) are calculated for different levels of growth and mortality stress, and are found to depend critically on the shape of the trade-off curve relating mortality to growth rate. If the trade-off does not change shape when stress is applied, then the optimal strategy is to spend less on personal defence for both mortality and growth stresses. However, if stress does change the shape of the trade-off the predictions may be modified, or reversed. This optimality analysis is rigorous and easy to apply. What is more difficult, is to establish the shapes and positions of trade-off curves in particular cases. This problem is discussed and some suggestions are made. The theory's predictions are applied speculatively to biogeographical data on marine animals and are found to be qualitatively successful, although some of the needed data are lacking. The applications and testability of the theory in the study of ageing and a variety of other processes are considered.

The tortoise and the hare: ecology of angiosperm dominance and gymnosperm persistence

Abstract: Gymnosperms, and conifers in particular, are sometimes very productive trees yet angiosperms dominate most temperate and tropical vegetation. Current explanations for angiosperm success emphasize the advantages of insect pollination and seed dispersal by animals for the colonization of isolated habitats. Differences between gymnosperm and angiosperm reproductive and vegetative growth rates have been largely ignored. Gymnosperms are all woody, perennial and usually have long reproductive cycles. Their leaves are not as fully vascularized as those of angiosperms and are more stereotyped in shape and size. Gymnosperm tracheids are generally more resistant to solute flow than angiosperm vessels. A consequence of the less efficient transport system is that maximum growth rates of gymnosperms are lower than maximum growth rates of angiosperms in well lit, well watered habitats. Gymnosperm seedlings may be particularly uncompetitive since their growth depends on a single cohort of relatively inefficient leaves. Later, some gymnosperms attain a higher productivity than co-occurring angiosperm trees by accumulating several cohorts of leaves with a higher total leaf area. These functional constraints on gymnosperm growth rates suggest that gymnosperms will be restricted to areas where growth of angiosperm competitors is reduced, for example, by cold or nutrient shortages. Biogeographic evidence supports this prediction since conifers are largely confined to high latitudes and elevations or nutrient-poor soils. Experimental studies show that competition in the regeneration niche (between conifer seedlings and angiosperm herbs and shrubs) is common and significantly affects conifer growth and survival, Fast-growing angiosperms, especially herbs and shrubs, may also change the frequency of disturbance regimes thereby excluding slower-growing gymnosperms. Shade-tolerant and early successional conifers share similar characteristics of slow initial growth and low plasticity to a change in resources. Shade-tolerant gymnosperms would be expected to occur only where forest openings are small or otherwise unsuitable for rapid filling by fast-growing angiosperm trees, lianas or shrubs. The limited evidence available suggests that shade-tolerant conifers are confined to forests with small gap sizes where large disturbances are very rare. The regeneration hypothesis for gymnosperm exclusion by angiosperms is consistent with several aspects of the fossil record such as the early disappearance of gymnosperms from early successional environments where competition with angiosperms would have been most severe. However there are unresolved difficulties in interpreting process from paleoecological pattern which prevent the testing of alternative hypotheses.

Effects of environmental stress on species rich assemblages

Abstract: Selye's widely used model of responses of individual organisms to a stressor (1973, American Science, 61: 692 699) is not appropriate for describing effects at the population or community level. At the ecosystem level a number of functional responses have been suggested by Rapport, Regier & Hutchinson (1985, American Naturalist, 125: 617–640) but detailed analysis shows that, in general, functional responses are not sensitive to the early detection of impending ecosystem damage. Three clear changes in community structure occur in response to stressors. These are reduction in diversity, retrogression to dominance by opportunist species and reduction in mean size of the dominating species. Statistically significant reductions in diversity occur rather late in the sequence of increased stressor impact. The first stages of impact are clearly shown by moderately common species yet most attention has concentrated on the common species. Species which dominate in heavily stressed habitats are often species complexes and the possible genetic mechanisms causing this are considered. Whilst changes in the mean size of the dominant organisms can be shown in experiments there is no clear evidence that recorded reductions in the size of North Atlantic and North Sea plankton are induced by man-made stressors.

Towards a physiological and genetical understanding of the energetics of the stress response

Abstract: We consider stress as an environmental change that results in reduction of net energy balance (i.e. growth and reproduction). Reduced energy balance restricts the environmental range of an organism and may change the environmental optima at which maximum production can be achieved. We emphasize individual differences in net energy balance and the interrelationships among genetic heterozygosity, rate of protein synthesis, efficiency of protein synthesis and whole organism measures of both routine and maintenance metabolic rate. Lastly, we consider the consequences of genetically determined individual differences in metabolic maintenance costs within the context of variable environments and how genetic/environmental interactions can define individual responses to environmental extremes.

Evolution and stress-genotypic and phenotypic components

Abstract: Since stress can be defined as anything which reduces growth or performance, it follows that, if appropriate genetic variability is present, classical evolutionary changes in populations are to be expected in any situation where a consistent stress is occurring. There is now considerable evidence for such evolution, producing constitutive adaptations in plants in response to stress, which are specific to the stress concerned. Stress may however operate in a temporary or fluctuating manner. In these situations, facultative adaptations, able to be produced within a single genotype through phenotypic plasticity, will be more appropriate. Very different specific phenotypic response systems, both morphological or physiological, can be found in plants in relation to different fluctuating stresses, operating over a wide range of time scales. These response systems are under normal genetic control and appear to be products of normal evolutionary processes. They can however have quite complex features, analogous to the behavioural response systems in animals.

Ontogeny of trophic morphology in four sympatric morphs of arctic charr Salvelinus alpinus in Thingvallavatn, Iceland

Abstract: Four coexisting morphs or arctic charr, Salvelinus alpinus (L.), occur in the lake Thingvallavatn, Iceland. They can be identified by their head morphology, which appears to he related to feeding habits, benthivorous or planktivorous-piscivorous. Laboratory-rearing experiments indicate that these morphological differences have a genetic basis with a significant maternal effect and support the suggestion that there are three populations of arctic charr in the lake. The ontogenetic mechanism of these differences most readily explained as development heterochrony, that is the heterochrony that shape reflects embryonic phenotypic characteristics while the planktivorous-piscivorous head shape is more differentiated from the embroyonic phenotype.

The analysis of stress in natural populations

Abstract: Populations usually persist despite environmental variations. Experimental analysis of responses to stress must include distinction between potential stresses (environmental perturbations that might not cause stress) and actual stress (phenomena that cause a response by the population). This is made difficult by large temporal fluctuations in abundances of many organisms. Monitoring can measure this variability but is insufficient to predict the potential impact of most stresses. Experimental analyses of stresses are also made difficult by differences among populations in their inertia (lack of response to perturbation), resilience (magnitude of stresses from which a population can recover) and stability (rate of recovery following a stress). These attributes of populations cause a range of responses to intermittent, temporary and acute (or ‘pulse’) stresses and to long-term, chronic (‘press’) disturbances. The timing, magnitude and order of stresses can cause different responses by populations. Synergisms between simultaneous or successive stresses can also have unpredictable effects on populations and cause complexity in interpretations of patterns of competition and predation. Experimental manipulations are needed to understand the likely effect of environmental disturbances on populations. The appropriate experiments are those designed to measure the effects of different types, magnitudes and frequencies of simulated stresses. These will be more revealing than the more common experimental analyses used to determine why and how observed changes in abundances of populations are caused by existing stresses.

An integrated approach to environmental stress tolerance and life-history variation: desiccation tolerance in Drosophila

Abstract: The availability of metabolic energy provides a general measure of the environmental stress that can be tolerated by organisms, leading to the hypothesis that increased tolerance to a range of environmental stresses will be associated with a reduction in metabolic rate in Drosophila and many other organisms. This hypothesis makes three predictions about genetic variation for stress tolerance: (1) increased stress tolerance will tend to be associated with decreased metabolic rate; (2) genetic correlations between tolerance of different environmental stresses will tend to be positive; (3) stress tolerance and life-history traits will tend to be genetically correlated; in Drosophila correlations with life-history traits other than longevity will tend to be negative. These predictions were tested by artificially selecting for increased desiccation tolerance in Drosophila melanogaster, using an 85% mortality level. The response to selection was rapid and the mean realized heritability was c. 0.65. The selection response was associated with a decreased rate of water loss, reduced activity and a decrease in metabolic rate in agreement with prediction (1). Selection did not alter body size. Selected lines were relatively more tolerant of starvation and a toxic concentration of ethanol in agreement with prediction (2), and had lower fecundities in agreement with prediction (3).

Strategies of mass change in breeding birds

Abstract: Birds experience strikingly different patterns of mass change during breeding. In some species with uniparental incubation, the incubating parents (mostly females) lose mass and attain their lowest point when the chicks hatch (Incubatory mass loss strategy = IML). In species with shared incubation, or with intense incubation feeding, the incubating parents maintain or increase in body mass without reducing attentiveness levels (Incubatory mass constancy = IMC). In other species, uniparental incubation with IMC is associated with reduced levels of attentiveness. The mobilization of fat stores or its preservation are involved in the two strategies. IML leads to mass increases after hatching of the young, while the opposite is true for IMC. The non-incubating sex in uniparental species does not experience significant mass changes during breeding. Fasting endurance, predation risk and mode of development are proposed as the main selective factors determining strategy. Latitude, climate, diet and food availability interact with the main factors. From a revision of the literature we can deduce that IML is mainly found among large birds with precocial development, while IMC is typical of smaller species with altricial development. Proportional mass losses are positively correlated with body mass in IML-species, as well as in precocial species, where body mass explains more than 70% of the variation in proportional mass change. Incubation periods increase with body mass in uniparental IMC-species, but not in IML-species. IML is thus associated to fast embryonic growth in large species. Successful raising of highly-dependent young in altricial and semialtricial species apparently depends on one of the parents retaining reserves until hatching. Subsequent mass losses may be necessary to maintain the brooding parent through a period when nestlings require heat, insulation and food. Patterns of mass change are not mere consequences of reproductive stress but the outcome of adaptive compromises between different selective factors and constitute an important aspect of the breeding biology and life history of birds.

The eradication of muskrats and coypus from Britain

Abstract: Introduced vertebrates can cause massive environmental damage but most attempts to remove feral populations have failed. This paper discusses the eradication campaigns against feral muskrats, Ondatra Zibethicus and coypus, Myocastor coypus in Britain. Both specks were introduced in the 1920s to be farmed for pelts and feral populations became established following escapes. The risk of environmental damage by muskrats was well known from Europe and;in eradication campaign started promptly in 1932 making use of overseas expertise and a control strategy designed by pest control specialists. The campaign was brought to a successful conclusion in 1939 when at least 4388 muskrats had been killed. In the 1930s, few believed that coypus would cause significant environment damage and early trapping efforts were inadequate. An early campaign achieved only limited success partly because of the lack of biological information. The eradication campaign which started in 1981, was based on a long tem study of population ecology. The effect of trapping and cold weather was quantified and detailed population simulations were used to plan the numbers of trappers, the time needed for eradication arid thus the likely cost of the campaign. An incentive bonus scheme was designed to overcome the problem that trappers would be reluctant to work themselves out of a job. Trapper deployment was planned using capture/trapping effort ratios and progress was checked by Ministry of Agriculture field staff. The muskrat campaigns succeeded because technical information to help plan the work was available and because action was taken quickly. Where an introduced population is well established, as with coypus in Britain, a closely integrated programme involving applied population ecology and a well-planned control organization may he essential for succesful removal.

Sexual dimorphism in snake tail length: sexual selection, natural selection, or morphological constraint?

Abstract: Male snakes typically have longer tails relative to body length than females, but the extent of this dimorphism varies among species. Three hypotheses have been suggested to explain tail dimorphism. The Morphological Constraint Hypothesis proposes that males have relatively longer tails to accommodate hemipenes and retractor muscles. The Female Reproductive Output Hypothesis proposes that females have relatively shorter tails as a secondary result of natural selection for increased reproductive capacity. The Male Mating Ability Hypothesis proposes that sexual selection favours relatively longer tails in males during courtship. These hypotheses make different predictions about the relationships among tail length, body size, male reproductive morphology, female reproductive output, mode of reproduction, and male mating behaviour among and within taxa. Predictions were tested using published data for 56 genera in the family Colubridae and original data for the water snake, Nerodia sipedon. Tail length dimorphism was more male-biased in tam having relatively short tails (r=–0.52, P < 0.001), hemipenes and retractor muscles occupied a greater proportion of the tail in taxa having relatively short tails (r=– 0.71, P < 0.00l and r=– 0.66, P = 0.001, respectively), and tail length dimorphism was more male-biased in taxa in which body size dimorphism was more female-biased (r=– 0.60, P < 0.001). These results support both the Morphological Constraint Hypotheses and the Female Reproductive Output Hypothesis. However, tests of other predictions, including those regarding patterns within N. sipedon, failed to support any of the three hypotheses. Comparisons among taxa suggest several species in which further tests of these hypotheses would be especially appropriate.

Genetic coupling in mate recognition systems: what is the evidence?

Abstract: Genetic coupling and coevolution of male and female components have been seen as alternative solutions to the problem of maintaining coordination between the sexes during evolutionary divergence of mate recognition systems. The evidence supposed to provide a distinction between these alternatives is reviewed. In most cases the data are inadequate, but in two examples coupling is clearly absent and in no case is it firmly established as the explanation for the maintenance of coordination. The distinction may only be useful in systems controlled by a few major loci as opposed to polygenic systems.

Seasonal plasticity in growth and development of the speckled wood butterfly, Pararge aegeria (Satyrinae)

Abstract: Regulation of growth and development by photoperiod was studied in a population of the speckled wood butterfly, Purarge aegeria L. (Lepidoptera: Satyrinae), from southern Sweden. Individuals were reared in a range of photoperiodic regimes (9L. to 22L) and temperatures (13°C to 21° C). Plasticity was found for important life-history traits- generation time, growth rate and final weight and seasonal regulation of development in response to photoperiod was found to occur at two levels. Purarge aegeria hibernates as a third instar larva or in the pupal stage, cantering one of four major developmental pathways in response to photoperiod: (1) direct development in both the larval and pupal stages, (2) pupal winter diapause with or (3) without a preceding larval summer diapause, or (4) larval winter diapause. In addition to this high-level regulation of individual development, larval growth rate and pupal development rate also appear to be finally regulated by photoperiod within each major pathway. As photoperiods decreased from 22 h to 17 h at 17° C, growth rate among directly developing larvae increased progressively, as was the case for larva? developing according to a univoltine life cycle from 17 h to 14 h. At two photoperiods, 13 h and 16 h (corresponding to shifts between major pathways), both larval and pupal development were extremely variable with the fastest individuals developing directly and the slowest developing with a diapause. This indicates a gradual nature of diapause itself, suggesting that the two level may not he fundamentally different.

Leaf domatia and mites on Australasian plants: ecological and evolutionary implications

Abstract: Leaf domatia, specialized chambers in the vein axils on the underside of leaves of many plant species, have remained an enigma for over a century. In this study we show a strong association between foliar domatia and mites in 37 plant species in Australasia. Overall, mites accounted for 91% of the arthropods observed in domatia. Across all species, a median of 51% of domatia were occupied and 71% of leaves showed mite evidence in domatia. The level of mite association did not depend on domatia type (pit, pouch, pocket, or tuft) or provenance (Papua New Guinea, Queensland, Victoria, or New Zealand). Mite association with domatia commonly varied between plant species, between individuals within species, and between shoots within individuals. The leaf developmental stage probably explains much of the variation in association for many of these species. The presence of a variety of life history stages of mites within domatia indicates that these structures act as shelters for development and reproduction. Furthermore, in 12 of 13 plant species examined, domatia concentrate mites in particular locations on the leaf. Mite taxa that we classify as largely predaceous (e.g. phytoseiids, stigmaeids and tydeids) or fungivorous (e.g. acarids and oribatids) were most common in domatia and dominated the association in 21 of 24 plant species in which the relative abundance of herbivorous, fungivorous and predaceous groups was quantified. We evaluate hypotheses that explain the role of leaf domatia, including non-functional hypotheses (e.g. architectural constraints), physiological function (e.g. gas exchange and water uptake), bacterial symbiosis and antagonistic and mutualistic associations with mites. Our quantitative results confirm anecdotal accounts of mite association with leaf domatia and are most consistent with Lundstroem's century-old hypothesis of plant-mite mutualism in which leaf domatia billet predaceous and fungivorous mites that prey on plant enemies. Leaf domatia are widespread among woody angiosperms and abundant in many temperate and tropical regions of Australasia. Mites, an ancient group of arthropods whose diversity and abundance parallels that of insects, are likely to be important selective agents on terrestrial plants. Our results (1) indicate that mite-domatia association represents a relationship of comparable scope to plant-ant associations mediated by specialized plant structures such as extrafloral nectaries, food bodies and specialized domatia; (2) suggest that sociality is not a necessary prerequisite for widespread and diverse mutualisms between arthropods and plants; and, (3) extend the diversity of organisms that produce specialized mite ‘houses’ from lizards, and wasps and bees to woody angiosperms.

The stress debate: symptom of impending synthesis?

Abstract: Opposition to use of the word ‘stress’ and other terms of wide ambit in ecology and evolutionary biology often signifies a commitment to programmes of detailed research and narrowed focus. This approach is justified where the objective is to analyse the demographic, genetic or biochemical mechanisms of contemporary populations. However, concepts employing ‘stress’ are vital to those forms of research that seek to obtain a broader perspective by recognizing ecological and evolutionary patterns with a high degree of repetition (sensu MacArthur, 1968 in R. C. Lewontin, Population Biology & Evolution). It is argued that there are recurrent types of evolutionary response to stress and that these provide important clues to the structure and dynamics of communities and ecosystems. Such patterns can assist our understanding of phenomena as widely divergent as the decline or expansion of populations within the British flora and fauna and the persistence of radionuclides in unproductive terrestrial ecosystems.

Patterns of pollen removal and deposition in tristylous Pontederia cordata L. (Pontederiaceae)

Abstract: In tristylous Pontederia cordata (Pontederiaceae), conspicuous differences in the size of pollen grains and discrete variation in the length of reproductive organs provide a suitable experimental system for the study of fine-scale pollination events. At a population of P. cordata at Pothole Lake, Ontario, the majority of flowers are visited by bumble bees which remove on average 45% of the pollen during single visits to previously unvisited flowers. The amount and proportion of pollen removed are significantly different among floral morphs and stamen levels. Deposition of the three pollen types on the bodies of Bombus spp., Apis mellifera and Melissodes apicata is non-random: large- and medium-size pollen tends to remain in greatest concentrations where it is initially deposited, whereas small-size pollen is displaced from the proboscis to more posterior body parts, probably as a result of grooming activities. Stigmatic pollen loads of individual flowers following single bumble bee visits indicate that the mid-styled morph captures the largest total pollen load, and the short-styled morph the smallest. The largest proportion of compatible pollen grains is deposited on stigmas of the long-styled morph. Pollen load data from “single visit” flowers is in general agreement with previously published population surveys involving multiply-visited flowers.

Structured population models: a tool for linking effects at individual and population level

Abstract: We address the problem of relating information on the effects of a particular stress on individuals to possible effects at the population level. Structured population models aim to predict population dynamics from a careful specification of the dynamics of individuals; however, in spite of major mathematical advances, there are only a few cases where such models have made significant contributions to ecological understanding. This paper reports progress to date on a project in which we construct both individual and population models of Daphnia. We present a model of individual growth and development which has been tested against results from several laboratories on D. pulex. We propose a simple, stage-structured population model and give a preliminary report of some of its properties.

Copulation behaviour in mammals: evidence that sperm competition is widespread

Abstract: We review information on copulation behaviour and sperm competition in mammals using data primarily from the literature Female mammals of many species regularly copulate with more than one male during each oestrous period Such multi-male copulations are reported more often in social, compared with solitary species In addition, the mates of males of polygynous species experience multi-male copulations as often as the mates of males or monogamous species Male mammals attempt to increase their certainty of paternity through a number of reproductive tactics Copulation frequency is higher in specks with multi-male copulations compared with other species Consortships, which can br regarded as a form of mate guarding, are often absent from species in which more than one male copulates with each female during her oestrous period Most solitary burrow-living small mammal species copulate in the open, whereas social species often copulate inside their burrows Insurance copulations may occur in many species since high copulation rates occur in four circumstances: (i) when mates are reunited, (ii) when a new male takes over a female, (iii) when a strange male steals a copulation, and (iv) when an audience of males is present

Genetic anomalies associated with Cerion hybrid zones: the origin and maintenance of new electromorphic variants called hybrizymes

Abstract: Natural hybrid zones involving the West Indian pulmonate land snail Cerion are characterized by the occurrence, in low to moderate frequencies, of allozymes that are unique to interspecific hybrid zones. As such electrophoretically detected genetic anomalies havr also becn reported in hybrid zones involving mammals, birds, reptiles, amphibians, and insects this appears to be a general phenomenon. These unexpected allozymes are inappropriately called ‘rare alleles’ and the term hybrizyme is introduced. The origins of hybrizymes are discussed in terms of suppressor-mutation systems, transposon-induced hybrid dysgenesis and intragenic recombination, but available evidence will not resolve this issue. Similarly, it is not clear whether the relatively high frequencies of particular hybrizymes are due to selection or genetic drift or some combination of these agents. Finally, the evolutionary significance of hybrizymes and the possible role of hybridization in introducing new genetic variation into populations are discussed.

Population changes of Greater horseshoe bats studied near Bristol over the past twenty-six years

Abstract: Capture censuses of Greater horseshoe bats involving about 35 hibernacula were consistently carried out over twenty-six years in two separate areas. Hibernacula were visited three times per winter. A control area (reduced disturbance) was visited once annually. Censuses showed similar trends in all three areas, and counts of bats at a breeding site showed similar trends to those hibernacula, hut much greater stability. All numbers fell sharply to about 50%, of the original level between the winters or 1962/3 and 1966/7, then more-or-less stabilized until the mid 1970s; rose in the late 1970s and early 1980s, and finally declined precipitiously in all areas in 1986 to about 30% of the 1962/3 figure. Numbers of juveniles born annually showed no relationship to the numbers reaching hibernacula during the subsequent winter, but was negatively related to the mean birth time in July. The final forearm length of juveniles is negatively related to birth time. A population control mechanism based on birth timing and subsequent growth is postulated and supported by reproductive studies.

The incidence of sperm displacement in insects: four conjectures, one corroboration

Abstract: The paper tests, by the comparative method, four hypotheses to explain why the degree of sperm displacement differs in different insect species. It summarizes evidence for 57 species. Here are the four hypotheses: species with mating plugs should show low sperm displacement, and species without plugs high displacement (Boorman & Parker); species with spheroid spermathecas should show low displacement, species with elongate spermathecas high displacement (Walker); species with low paternal investment should show low sperm displacement, species with high paternal investment high displaycement (Gwynne); and species with low natural mating frequencies should show low displacement, species with high mating frequencies high displacement (this paper). The spermathecal shape hypothesis is of limited theoretical plausibility; but the other ideas are theoretically possible. The evidence, if numbers of species are counted, generally fits all four theories; but, in a statistically more rigorous cladistic test, it significantly supports only the mating frequency theory.

Proximate and ultimate responses to stress in biological systems

Abstract: Environmental stress causes reductions in survival probability, growth rates and reproductive outputs. Under these circumstances, however, some genotypes may be less influenced by stress than others and these resistant forms will be favoured by stress acting as a selection pressure. Following Mayr (Science, 134: 1501–1506), these two effects can be described as proximate and ultimate respectively. The ultimate, evolutionary response can lead to direct adaptations that are either fixed or facultative, or to indirect life-history adaptations. Several attempts to classify stressful selection pressures are reviewed and relationships between these are considered. A model that potentially allows proximate and ultimate, direct and indirect adaptations to be treated within the same framework is described.

Estimation of migration from a perturbation experiment in natural populations of Drosophila buzzatii Patterson & Wheeler

Abstract: In order to estimate migration and gene flow, allele frequencies in populations at two sites separated by 120 m were differentially perturbed by the continuous release over 413 days of flies homozygous at particular allozyme loci. The effects of perturbation were determined by genotype assay at two collections prior to, thirteen during and nine after the perturbation period. Maximum likelihood methods were developed to estimate migration into the two populations from the homozygous releases, and migration between the two populations. The successful perturbation of allele frequencies in a natural population is demonstrated. A plateau in allele frequencies during perturbation and a return to original frequencies following cessation of perturbation was most likely due to selection during development against recessive alleles concurrently introduced into the populations by the released flies. There is unequivocal evidence for short distance gene flow between the two populations. The migration rates estimated at ten times over a nine month period were extremely variable, but with higher population density at one site positively related with migration from that site to the other.

Causes of variation in wing loading among Drosophila species

Abstract: We examined influences on wing and body size in 11 species (12 strains) of Drosophila. Six measures of wing length and width were closely correlated with wing area and suggested little variation in wing shape among the species. Among ten species wing loading, an important factor in flight costs and manoeuvrability, increased as body mass increased at a rate consistent with expectations from allometric scaling of wing area and body mass to body length. Intraspecific variation in wing loading showed similar relationships to body mass. Density and temperature during larval development influenced wing loading through general allometric relations of body size and wing area. Temperature during the pupal stage, but not during wing hardening after eclosion, influenced wing area independently of body size. Wing area increased as growth temperature decreased. Individuals reared at cooler temperatures thus compensated for a potential allometric increase in wing loading by differentially enlarging the wing area during pupal development.

Symptoms of pathology in the Gulf of Bothnia (Baltic Sea): ecosystem response to stress from human activity

Abstract: An extensive review of the data now accumulated on the response of the Gulf of Bothnia ecosystem to stress from human activity provides abundant evidence for incipient ecosystem pathology. Signs of ‘ecosystem distress' appear at local, coastal and basin-wide scales. Symptoms include early signs of eutrophication in local and coastal waters, formation of local abiotic zones, reduction in species diversity, reduction in genetic diversity (particularly in salmonids), reduced size of biota, increased dominance by opportunistic species, increased disease prevalence and bio-accumulation of toxic substances (e.g. PCBs, DDT, heavy metals). Pathology may propagate between local, coastal and basin-wide regions by several different pathways. Despite reductions in loadings of some toxic substances in recent years (e.g. PCBs, DDT), stress from human activities on the Gulf of Bothnia continues to impact the ecosystem at all spatial scales.

Microgeographic variation in the colour pattern of the lizard Gallotia galloti within the island of Tenerife: distribution, pattern and hypothesis testing

Abstract: This study of the microgeographic variation in the colour pattern of the lizard, Gallotia galloti, within Tenerife has three facets. One, an analysis of the population distribution and density in relation to physical conditions; two, univariate and multivariate descriptions of the pattern of geographic variation; and three, formal testing of a range of causal hypotheses for these geographic patterns. The range is not divided into separate allotheses high- and low-altitude populations by a inaptitude ring of ground-level cloud although there is a drop in population-density in the middle altitudes. Multiple regression indicates that, or the factors measured, this is primarily due to a decrease in insolation. The pattern of geographic variation in the six independent colour pattern characters is portrayed by contouring the 67 locality means. There is generally good congruence among these patterns and a canonical analysis indicates that the generalized pattern of geographic variation is largely unidimensional and can therefore be represented adequately by (and portrayed by contouring) the first canonical variate. Seven causal hypotheses, from a range of possible and previously suggested causes, are considered. The procedure for testing these hypotheses should depend on their dimensionality and that of the observed pattern. Since all the observed and hypothesized patterns are basically unidimensional the seven hypothesized patterns were simultaneously tested against each observed pattern (individual characters and canonical variate) by partial correlation. All the previously suggested ‘phylogenetic’ hypotheses based on divergence in allopatry are rejected. The hypotheses that the geographic variation in the colour pattern is caused by the topographically determined climate cannot be rejected. The character state changes can be explained by a balance between sexual selection for ‘attractive’ colouration and natural selection, via predation, for cryptic colouration.

Frequency‐dependent selection on aposematic prey: some experiments

Abstract: Experiments to measure the strength of frequency-dependent selection on dimorphic populations of distasteful, brightly coloured prey were carried out, using pastry cylinders as prey and wild birds as predators. When the two forms were haphazardly intermingled, the birds took a relative excess of whichever form happened to be the rarer if all prey in the population were distasteful but selected the forms independently of frequency if they were all neutral in flavour. They did not take an excess of the rarer form from populations of distasteful prey when that form was distributed in a single clump rather than evenly dispersed among the commoner form. This confirms the expectation that rarer forms of aposematic animals are at a frequency-dependent disadvantage when they are intermingled with commoner forms but not when they occur in clusters.

Butterfly wing morphology variation in the British Isles: the influence of climate, behavioural posture and the hostplant-habitat

Abstract: Gradients (isophenes) in modifications of butterfly wing morphology (colour, pattern, size) to the north and west of Britain are shown to correlate closely with contemporary environmental gradients, whereas their alleged formation as infra-specific units in Devensian refugia off western Britain is unsubstantiated. A model is described which explains the transformation in phenotypes in relationship to climate, especially ambient temperatures and radiation levels. In cooler, less predictable summer conditions to the north and west, selection has favoured modifications in adult phenotypes that maintain efficiency in thermoregulation, mate advertisement and predator escape. The form that wing modifications take depends mainly on basking posture (lateral, dorsal-absorption and reflectance), which determines the allocation and interaction of functions on different wing surfaces. It is also dependent on hostplant-habitat structure, which influences thermal stability and the milieu of predators and conspecifics, and other behavioural norms (mate-locating behaviour) and biological attributes (size, robustness, speed and mode of flight, chemical defences) which affect their relationships with predators and conspecifics. The significance of Quaternary palaeoenvironments to phenetic transformations is discussed as is the relevance of the model to the development of phenotypes in arctic endemic butterflies. Differences in phenotypes of butterflies which occupy arctic and temperate montane environments are also predicted by the model.

Selective forces in the emergence of the seed habit

Abstract: The evolution of the seed is one of the major events in the history of land plants. In this paper, we consider the suite of characters that define the seed habit, and discuss the probable selective pressures that produced each character. Our major conclusion is that most characters are a direct consequence of the origin of heterospory and of natural selection for propagules with larger food reserves. Seeds are traditionally defined by the possession of integuments. However, some heterosporous pteridophytes possess integument-like structures. Therefore, integuments cannot explain the evolutionary success of seed plants. Rather, we believe that the decisive character in this success is related to pollination. Seed plants differ from other heterosporous lineages in the capture of microspores before dispersal of the 'megaspore'. Modern gymnosperms all possess mechanisms whereby the maternal sporophyte withholds resources from potential propagules that have not been pollinated and/or fertilized. This represents an increase in efficiency over Pteridophytic reproduction. Wind-pollination means the propagule is vulnerable to pathogens that mimic pollen, and pathogen pressures may have contributed to some seed characters.