Showing papers in "Biological Journal of The Linnean Society in 1980"

The evolutionary ecology of mast seeding in trees

Abstract: The hypothesis that masting by trees is a defensive strategy which satiates seed predators in mast years and starves them in the intervening periods is tested in 59 sets of data on the seed production and pre-dispersal seed-predation of 25 tree species. Twenty-lour of the 59 data-sets support the hypothesis and show a statistically significant positive relationship between the proportion of seeds surviving the pre-dispersal stage and the log10 of the crop size for the same year. Evidence that pre-dispersal seed survival increases with the length of the mast interval is poor. A positive relationship between the strength of the masting habit and the maxintum observed pre-dispersal seed mortality in a sample of 15 tree species suggests that the masting habit is best developed in predator-prone species. A survey of seed crop frequencies in the woody plant flora of Nortli America shows masting species to be under-represented amongst shrubs and amongst trees which disperse their seeds in fleshy dispersal units. The selection pressures and evolutionary constraints which operate on the evolution of masting plants and their seed predators are discussed.

Food, feeding ecology and ecological segregation of seabirds at South Georgia

Abstract: At the sub-Antarctic island of South Georgia 25 of the 29 breeding species are seabirds. Fifteen of these have recently been studied in some detail. By examining the timing of their breeding seasons and their diet and feeding ecology (especially feeding techniques and potential foraging ranges), the nature of their ecological isolating mechanisms, and in particular the way in which they partition the resources of the marine environment, are reviewed. Although breeding season adaptations occur (winter breeding in Wandering Albatross and King Penguin; out of phase breeding in two species-pairs of small petrels) these are less important than dillerences in food and feeding ecology. There is a fundamental distinction between the niche of pursuit-diving species (mainly penguins) and the remainder which are basically surface-feeders. The two abundant krill-eating penguins show clear differences in feeding zones. Three albatrosses and a petrel feed mainly on squid and there are differences in both the species and size of the prey of each. The remaining seabirds chiefly take krill (although the giant petrels are extensive scavengers and some smaller petrels specialize on copepods) and utilize different feeding methods and areas to do so. Various adaptations related to inshore and offshore feeding zones are discussed. Although most species possess a combination of ecological isolating mechanisms additional evidence for the particular importance of dietary differences is presented.

Toe pad morphology and mechanisms of sticking in frogs

Abstract: Sticking ability in frogs was measured on a series of different substrates. Analysis of performance suggests that frogs use two sticking mechanisms: interlocking on rough surfaces and capillarity on smooth surfaces. There is a correlation between morphological specializations of the toe pad and sticking ability, but these morphological features are not unique to arboreal species. Terrestrial species that use leaves as resting sites during times of inactivity have many of the same morphological specializations and stick as well as the strictly arboreal species.

A reappraisal of the concept of metabolic cold adaptation in polar marine invertebrates

Abstract: The concept of ‘metabolic cold adaptation’, namely that polar marine ectotherms are adapted in having an elevated basal metabolic rate, has been examined in the light of recent biochemical, physiological and ecological data for Antarctic marine organisms. It is now clear that marine invertebrates from Antarctic waters are characterized by slow growth rates, low basal metabolism and reduced annual reproductive effort, and there is thus no clear evidence of the traditional view of an elevated metabolic rate. By analogy with fish, protein synthesis rates are probably also low. This suggests that the major feature of cold adaptation is a reduction in the individual total annual energy intake in comparison with ecologically similar organisms from warm water. This allows a high standing crop of suspension feeders to develop, and low temperature is thus a significant factor in the successful widespread adoption of typical K-strategies in Antarctic marine invertebrates.

On the definition of mimicry

Abstract: An operational distinction between crypsis and mimicry is made in terms of the cognitive and perceptual systems of signal-receivers. Cryptic organisms specialize in generating information of the type not attended to or filtered out (reference frame) by the receivers, whereas mimetic organisms specialize in producing information (signals) of the type sought out by and of interest to a receiver. Mimicry is defined in terms of a system of three living organisms, model, mimic and operator (signal-receiver), in which the mimic gains in fitness by the operator identifying it with the model. Some advantages and applications of the definition are briefly discussed.

On the origin of cultivated rye

Abstract: The origin of cultivated rye has been studied, taking into consideration evidence from various fields. Based on morphological resemblances and cytogenetic affinities, cultivated rye is included in Secale cereale L. emend. Sencer, which also includes annual wild and weedy ryes. Wild populations of 5. cereale, which have evolved from Secale montanum Guss. emend. Sencer, invaded wheat and barley fields during the early days of cultivation and gave rise to weedy ryes with varying degrees of rachis brittleness. Cultivated rye was selected from weedy ryes for non-brittle rachis and bigger caryopsis both unconsciously and consciously by man. The geographic origin of cultivated rye is postulated for the Buyuk Ari Dai (Mt. Ararat) and Lake Van area in eastern Turkey. It spread from this area as a weed in wheat and barley fields towards the north, east and west and imposed itself as a secondary crop under conditions unfavourable for wheat and barley. It thus became a crop in its own right in several places independently, in addition to it being known by the people living in the Caucasus and Transcaucasus from very early agricultural times.

Patterns of morphological and molecular polymorphism in the land snail Cepaea nemoralis

Abstract: In the land snail Cepaea nemoralis, allele frequencies at loci controlling shell polymorphisms often show large areas of remarkable constancy which are separated by steep clines from neighbouring areas with strikingly different allele frequencies. It has recently been claimed that these ‘area effects’ exemplify a general tendency for population differentiation without geographic isolation in a variety of organisms of relatively low mobility. As such they could represent an early phase in the process of speciation. If this is true, population differentiation of shell polymorphisms in Cepaea would be expected to be accompanied by parallel differentiation at other gene loci, such as those detected by gel electrophoresis. We have studied populations of C. nemoralis in North Wales and in the Valle de Aran of the Pyrenees. Levels of molecular heterogeneity are comparable to those found in related animals which show much less visible polymorphism. In spite of some statistical problems inherent in the analysis ol overlapping geographic patterns, there is no clear association between the patterns of geographic variation at the visible and molecular levels. Claims that genetic differentiation in the visible polymorphisms between C. nemoralis populations are a special case of the formation of geographic races are therefore probably not justified.

Reproductive adaptations of Antarctic benthic invertebrates

Abstract: The majority of Antarctic benthic invertebrates so far studied do not produce pelagic larvae, but develop non-pelagically by means of egg capsules, brooding or viviparity. The predominance of protected development in the Antarctic benthos is primarily due to the short period of summer phytoplankton abundance and the low sea temperature. Such conditions make it difficult for a larva to complete pelagic development before food becomes scarce in the surface waters. Prosobranch gastropods illustrate some important aspects of Antarctic benthic invertebrate reproduction. Species which develop non-pelagically have an aseasonal or prolonged spawning period. They produce a small number of large yolky eggs which remain in the benthos and develop slowly, giving rise to large, fully competent juveniles. Conversely, one species with free development has a short, synchronous spawning period during early summer, producing larvae which can benefit from the phytoplankton bloom. Protected development by means of brooding will limit dispersion, but transport on floating algae and by anchor ice may partially compensate for this in the Antarctic.

Electrophoretic investigation of systematic relationships in the marine mussels Modiolus modiolus L., Mytilus edulis L., and Mytilus galloprovincialis Lmk. (Mytilidae; Mollusca)

Abstract: Genetic variation was assayed electrophoretically at 13–16 loci in Modiolus modiolus, Mytilus edulis, and Mytilus galloprovincialis. High genetic distance (D) values were observed between Modiolus modiolus and Mytilus edulis (1.516 ± 0.523) and between Modiolus modiolus and Mytilus galloprovincialis (1.564 ± 0.539), whereas the distance between Mytilus edulis and M. galloprovincialis (0.167 ± 0.118) was rather low. The systematic status ot Mytilus edulis and M. galloprovincialis is discussed in relation to these lindings and the genetic distance values are used to estimate divergence times which in turn are compared with paleontological estimates. The observations of high average heterozygosity in Modiolus modiolus, and high correlations of locus heterozygosity between taxa are discussed briefly.

Salinity related physiological and genetic differences between populations of Mytilus edulis

Abstract: Aminopeptidase-I, the enzymatic product of the Lap locus, liberates N-terminal neutral and aromatic amino acids from oligopeptides. The enzyme is associated with the brush border of the intestine and the extensive lysosomal system in the digestive tubule cells; the enzyme functions in oligopeptide degradation and possibly amino acid transport. The Lap locus is genetically polymorphic and allele frequencies differ between populations according to environmental salinities. Using cell-free lysosomes, we show salinity related differences in both lysosomal membrane latency and lysosomal and cytosolic free-amino acid concentrations. Differences in the response of the lysosomal aminopeptidase-I enzyme to differences or changes in salinity are discussed. Antibodies against aminopeptidase-I enzyme were used to demonstrate that alleles of the Lap locus exhibit different specific activities per unit enzyme concentration. In oceanic populations, the concentrations of aminopeptidase-I enzyme of individual phenorypes are equal, suggesting that variation of specific activity among phenorypes is due to allele specific differences in catalytic efficiency. In estuarine populations, total enzyme activity is lower, which is partially due to a significantly lower concentration of aminopeptidase-I enzyme of one homozygote genotype. The consequences of a change in environmental salinity can be measured on the biochemical, physiological, and population genetic levels. We discuss the possible mechanisms by which salinity variations are responsible for the genetic polymorphism of aminopeptidase-I.

Genetic differentiation in the molluscan species Littorina rudis and Littorina arcana (Prosobranchia: Littorinidae)

Abstract: Six populations of Littorina rudis and ihree of L. arcana were screened for elcctrophorctically dctci table variation at 21 enzyme loci. These species reproduce by ovoviviparity and oviparily respectively, and both are members of the L. saxatilis species complex. The mean coefficient of genetic identity between the two species was high (0.957) and no diagnostic loci were observed. Allele frequency differences are maintained in sympatric populations of the two species. Intraspecific values of/ ranged from 0.944 to 0.995 and both species showed marked inter-population genetic heterogeneity, a feature consistent with their limited powers of dispersal. Heterozygosity is high in all populations of both species. Populations of I. rudis have higher mean heterozygosities (= 0.153) then L. arcane (H= 0.132).

A comparative study of ordination techniques in numerical taxonomy in relation to racial variation in the ringed snake Natrix natrix (L.)

Abstract: The iniluence ot various types of standardization, similarity coefficient and ordination technique (i.e. non-metric multidimensional scaling, canonical analysis, principal coordinate analysis, Q_and R mode principal component analysis) are tested in relation to the numerical taxonomic analysis of the racial differentiation in the ringed snake, N. natrix. The a priori preferences and various criteria, including portrayal of a ‘known taxonomic model’, indicate that canonical analysis and R mode principal components analysis on column-standardized data (or its dual principal coordinate analysis) are to be recommended. Non-metric multidimensional scaling and lack of appropriate character standardization gave inferior results. SUMMARY Thirty-four numerical taxonomic analyses were run varying the method of data standardization, similarity coefficient and ordination technique (i.e. non-metric multidimensional scaling, canonical analysis, principal coordinate analysis and Q and R mode principal component analysis). These analyses were based on sample populations of both sexes representing the marked racial differentiation within the ringed snake N. natrix. Several a priori preferences are stated and various criteria are discussed for judging the taxonomic performance of the methods. (The methods are compared on the basis of taxonomic performance rather than empirical similarity.) On the basis of the a priori preferences, the similarity of the taxonomic conclusions (robustness) and how well they portrayed a ‘known taxonomic model’, the canonical analysis and principal component-coordinate analyses on data standardized by columns (characters) are to be preferred. The principal component/coordinate techniques on unstandardized data is not recommended neither is the use of non-metric multidimensional scaling.

Geographic variation in Pemphigus populicaulis (Insecta: Aphididae) in Eastern North America*,†

Abstract: The geographic variation of 33 morphological characters of the gall-forming aphid Pemphigus populicaulis is studied for 118 localities east of 100oW longitude. Variation can be partitioned into within-gall, among-gall and among-locality components. Among localities variation ranges from 26 to 54%, being significant for all characters. Variation among galls within localities ranges from 24 to. 56%, that within-galls from 8 to 4796. The design of the study permits computation of character correlation matrices within and among localities. Gall size is correlated with tnorphometric characters only on an interlocality but not on an intralocality basis. Interlocalily correlations are a function of intralocality correlations, confirming earlier predictions. There is little correlation between characters of stem mother and alate morphotypes within localities, whereas among localities such correlation is appreciable. This phenomenon may be caused by aspects ol the environment that vary among localities but remain reasonably constant through the earlv life cycle of the aphid. When subjected to factor analysis both correlation matrices yield four factors. Multiple discriminant analysis of the data set results in five interpretable significant axes. Maps are furnished for characters representing the independent dimensions of variation and for discriminant function scores. The patterns of variation can be shown to be significantly nonrandom by Mantel's test and by spatial autocorrelation analysis. All variables are significantly positively autocorrelated at 200 km, many at 400 km and a few at 600 km; few general statements can be made about significant autocorrelations at higher distances. The positive autocorrelation at relatively short distances may be related to the pool of clones from which the genotypes of any one locality sample are taken. There are three correlogram patterns that can be associated with four clusters of variation patterns of characters. The separate patterns presumably cannot be explained by a single microevolutionary process.

Criteria for the identification of potential colonizers

Abstract: Man's interference with the environment encourages colonization by species that are often undesirable, hence a technique by which potential colonizers can be identified is urgently required. It can be developed when general prerequisites for successful colonization are identified. These prerequisites can then serve as criteria to distinguish potential colonizers from non-colonizers. The proposed relevant prerequisites are associated with two problems encountered by all colonists: small founding populations and a difference in the environmental conditions between the source area and the target, making the target rather unpredictable. Both these features increase the risk of random extinction, which can be overcome by possessing a potential for rapid population growth (high r) and for rapid adaptation to environmental conditions (high genetic variability). The parameters associated with meeting these prerequisites can serve for the identification of potential colonizers and for ranking species as to their colonization ability. The proposed technique may best be tested by comparing the intrinsic growth rate and the electrophoretic variability of species that have recently colonized with closely related species that have not done so under similar circumstances. The colonization of the eastern Mediterranean by Red Sea species immigrating via the Suez Canal created an appropriate system for such a test.

A phylogenetic analysis of the land plants

Abstract: Phylogenetic systematics (cladistics) is a theory of phylogeny reconstruction and classification widely used in zoology. Taxa are grouped hierarchically by the sharing of derived (advanced) characters. The information is expressed in a cladogram, a best estimate of a phylogeny. Plant systematists generally use a phenetic system, grouping taxa on overall similarity which results in many groups being formed, at least in part, on the basis of shared primitive characters. The methods of phylogenetic systematics are used to create a preliminary cladogram of land plants. The current classification of land plants is criticized for its inclusion of many groups which are not monophyletic. Objections to the use of phylogenetic systematics in botany, apparent convergences within major groups and frequent hybridization, are shown to be invalid. It is concluded that cladistic analysis presents the best estimate of die natural hierarchy of organisms, and should be adopted by plant systematists in their assessment of plant interrelationships.

Experimental manipulation of patterns of resource allocation in the growth cycle and reproduction of Smyrnium olusatrum L.

Abstract: Plants of the monocarpic (normally biennial) Smyrnium olusatrum (Umbel]iferae) were grown in pots in soil at a high or low nutrient regime. Some plants receiving full nutrients were grown in a heated glasshouse with 16 h days. The remainder were grown without supplementary lighting or heat and included control plants and others which received surgical treatment after ten months growth: deradication (removal of half of the root stock); defoliation; deradication and defoliation. The distribution of plant biomass and of phosphorus were analyzed at the time of seed set. Patterns of allocation of dry matter and phosphorus were quite different and were significantly altered by treatments, which produced a range of allocation to reproductive structures ranging from 21 to 74% of total phosphorus and 12 to 35% of dry matter. Distribution patterns of total phosphorus are discussed in terms of the potential demands being made by alternative structures and functions over the life cycle of the plants.

The costs of sex in seaweeds

Abstract: The brown seaweeds (Fucales) include dioecious and hermaphrodite species and genera with one, two, tour or eight eggs per oogonium. The costs of gamete production, measured as biomass, are very small. Eggs represent only 0.1–0.4% of body weight. Females of dioecious species do not produce more eggs per gramme of tissue than hermaphrodites. Hermaphrodites occupy upper shore zones and dioecious species the biotically richer submerged zones. Neither egg size nor number correlate with habitat or sexuality. Some of these observations are hard to reconcile with theoretical concepts of the costs of sex.

Seasonal fluctuations in microbial activity in Antarctic moss peat

Abstract: The Signy Island terrestrial reference sites epitomize unpolluted maritime Antarctic tundra The extreme transition from the harsh Antarctic winter to the milder summer facilitates studies of the effects of freeze-thaw cycles on microbial activity in moss peat Seasonal monitoring of peat oxygen uptake showed a transient spring peak at c 0oC, attributed to microbial utilization of dissolved organic carbon (DOC) After a more gradual temperature-linked summer increase, autumnal freeze-thaw cycles stimulated a final pre-winter peak The transient climaxes were associated with blooms of saccharolytic yeasts and microfungi The bacterial population stabilized after a spring increase but then diversified as DOC became rate-limiting Effects of pre-monitored spring freeze-thaw cycles on late-winter peat cores were simulated in a Gilson respirometer In vitro perturbations demonstrated the regulatory effects of DOC availability, water content and temperature on peat respiration and microflora! composition Comparative respirometry and loss in tensile strength of interred cotton strips showed a difference in decomposer activity beneath a relatively dry Polytrichum-Chorisodontium turf and a wet Cattiergon-Cephalozielta carpet This was associated with water content and anaerobiosis Cellulolysis accelerated during the growing season and increased with depth, despite anaerobic conditions Estimates of annual bryophyte decomposition are presented for use in an Antarctic ecosystem model

Population structure and social organization of Southern Elephant Seals, Mirounga leonina (L.)

Abstract: The population structure and social organization of the Southern Elephant Seal, Mirounga leonina, were studied at South Georgia principally by extensive field census work and determination of age and reproductive history from sections of teeth taken from samples of bulls and cows. The adult males of the South Georgia population were exploited from 1910 to 1964, mainly at the maximum sustainable yield for this population. The present data are compared with similar information obtained from studies at South Georgia in 1951 during the exploitation phase and at Macquarie Island in the 1950's where sealing ended in 1919 and the population had stabilized. Changes have been noted in the time of bull haul out, number of bulls ashore, cow: bull ratio, harem size and the age of harem bulls. These changes can all be attributed to the ending of exploitation. In contrast, the structure of the cow herd has not changed appreciably in the same period. In addition, differences in growth, body size and population structure still persist between the South Georgia and Macquarie Island populations and it is likely that most of them may reflect differences in food availability at the two locations.

Dietary and morphometric variation in some Peruvian rodent communities: the effect of feeding strategy on evolution

Abstract: This study examines the relationship between feeding strategy and the evolutionary radiation of three genera of broadly sympatric cricetid rodents (Phyllotis, Akodon, Calomys) found in the Andes of southern Peru. Stomach contents from 13 species reveal that although food habits are variable, both intra- and interspecifically, there are two general feeding strategies: diurnal insectivory and nocturnal herbivory-omnivory. Intraspecific variation in diet was sometimes correlated with altitude. Patterns which might suggest competitive exclusion or ecological release were generally not observed. Interspecific dietary variation is related to morphological variation in both size and shape as revealed by regression and discriminant function analyses. There is a significant negative relationship between the degree of insectivory and body size (wt). The existence of correlated patterns of dietary variation with environment and morphology supports the hypothesis that feeding strategy is adaptive and has been a factor in the evolutionary radiation of these groups. We propose that both phyllotines and akodonts arose from small, insectivorous ancestors. In conjunction with shifts toward herbivory, most phyllotines have evolved larger size plus tooth and jaw modifications. Calomys sorellus is atypical of other phyllotines; it is small, and insectivorous. Most Peruvian Akodon are also small and insectivorous; A. jelskii is an exceptional akodont being large and principally herbivorous.

Survival strategies in polar terrestrial arthropods

Abstract: Three components of the survival strategy of a terrestrial Antarctic mite, Alaskozetes antarcticus (Acari: Cryptostigmata) are considered: overwintering survival, energetics and life history. Supercooling is an important feature of its cold tolerance, whilst elevation of standard metabolism allows activity at low temperatures, both of which contribute tcTa long development and maximum survival of individuals in the population. These are facets of the overall survival strategy evolved by such a species in response to the Antarctic terrestrial environment, but which may be widespread in polar invertebrates.

A comparative study of life history and resource allocation in selected Umbelliferae

Abstract: A comparison was made of the allocation of biomass during the life cycles of five species of Umbelliferae. At maturity, the monocarpic ‘biennial’Smymium olusatrum allocated 25–39% of biomass and 60% of total plant phosphorus to reproductive tissues. The first season's growth is dominated by development of a massive storage root system. In contrast the perennial Oenanthe crocata allocates 30% of total biomass to root tubers and 8–9% to reproductive structures. The more extreme perennial, Conopodium majus lacks clonal growth and c. 70% of total biomass is present as a persistent conn at the time of fruiting when only 7% of biomass is represented by ripe fruits. The life cycles of Anthriscus sylvestris and Pastinaca sativa represent allocation patterns intermediate between these extremes. Analyses of allocation represent an approach to the quantitative description and comparison of the life cycles of higher plants and pose problems about the appropriate ‘currency’ in which to measure allocation.

Pre‐adult viability differences of melanic Biston betularia (L.) (Lepidoptera)

Abstract: Departures from mendelian ratios have been analysed in all published family data for the peppered moth, Biston betularia. No distinction was made between different insularia alleles; thus carbonaria is top dominant while insularia is dominant over typical. Viabilities of five of the six genotypes were calculated by a simple algebraic method; a maximum likelihood method gave viabilities for all six genotypes together with their standard errors. Carbonaria homozygotes (and possibly also insularia homozygotes) have enhanced viability while the viability of insularia/carbonaria heterozygotes is reduced. The significance of these findings is discussed in relation to phenotype frequencies found in the wild.

Historical and environmental influences on hedgerow snail faunas

Abstract: In three areas of the English Midlands, composition and diversity of hedgerow snail faunas are influenced both by historical and environmental differences between hedges. Soil aciditv and climate are the most important environmental factors. Hedges originating in or near woodland have richer faunas than those planted in open fields, and some snail species are indicators of woodland origin. Snail diversity also increases with the age of the hedge, but this effect is slight in hedges over 100 years old. It is suggested that these differences are primarily due to the poor dispersal of snails rather than to existing environmental differences between hedges of differing age and origins, and the results are compared with the very similar ones obtained for plants. Historical influences on the distribution ol slow-dispersing organisms may be of very general importance, even in comparisons of adjacent habitats with considerable temporal stability.

The role of escape in mimicry and polymorphism: I. The response of captive birds to artificial prey

Abstract: The effectiveness of active escape as an alternative to chemical and physical irritants in defensive mimicry was tested. Philaenus spumarius is a polymorphic insect used to illustrate the hypothesis that an efficient escape mechanism could be associated with conspicuousness by potential predators causing them to avoid this type of prey. Tile experiment used robins (Erithacus rubecula) as predators and mealworms {Tenebrio mulilur), with colour bands of either green, orange or blue, as prey. To simulate escape the prey was offered from a lunged platform which could be dropped allowing the mealworm to roll away and out ol'sigln of the bird before it could be pecked. During the first half of the experiment (day 1–10) only one of the tin ee colours of mealworm was allowed to be caught, within a 180 s time limit. This was a cryptic non-mimetic (blue) form. The other two were the cryptic (green) and conspicuous (orange) escaping models. In the second half of the experiment (day 11–17) the platform was not lowered within the lime limit. The three forms of prey remain available; the models thus becoming the mimics. During the first part of the experiment the birds took the non-mimetic form Ireely and learned to avoid the conspicuous and to a lesser degree the cryptic models. Throughout the second pan of the experiment the conspicuous form continued to be avoided more than the cryptic, illustrating the greater efficiency of conspicuous colour combined with escape.

Geographic differentiation and speciation in Cerion–a preliminary discussion of patterns and processes

Abstract: Cerion's exuberant morphological diversity (600 described ‘species’) combined with the extreme rarity of reproductive isolation among morphotypes (only one unambiguous case of sympatry in the Bahamas) has long made this genus an object of fascination for evolutionists and of frustration for taxonomists. We have pursued an integrated approach of genetic and morphometric study based on field investigations of ecology and biogeography in the Bahamas. Cerion's morphotypes are not distributed haphazardly, but show definite patterns of correlation with habitat and geography. Although all morphotypes interbreed, hybrid zones tend to be narrow and characterized by highly local genetic anomalies–unique alleles present in neither parental population. Different patterns of covariance in ontogeny, and habitat preferences, also indicate mat the morphotypes are distinctive, non-amalgamating entities (despite little difference in the frequencies of structural genes among them) that may be called species once a definition based on strict reproductive isolation is abandoned. Variation in structural genes, anatomy and morphology is non-concordant, but orderly for each criterion. Similar morphologies are often polyphyletic and evolved repeatedly as one possible ontogenetic route within a developmental program common to all Cerion. Although we cannot always distinguish among competing causes for observed patterns, we can establish genetic, morphological, anatomical, and biogeographic criteria for decisions when adequate evidence is available. The species of Cerion will be reduced by more than an order of magnitude from a list currently described.

Evolution of Antarctic lake ecosystems

Abstract: Antarctic lakes present a wide variety of physical, chemical and biological conditions, and are not always the simplified systems imagined by earlier workers. The volume of data on lakes of various ages now allows informed speculation on the evolution of the Antarctic lake ecosystem.

Cepaea on Salisbury Plain: patterns of variation, landscape history and habitat stability

Abstract: Patterns of variation in Cepaea nemoralis and C. hortensis on Salisbury Plain are related to its landscape history. Areas of arable or mixed farming, with hedgerows and woods, show patterns of variation with habitat and topography. Areas of downland, until recently heavily grazed by sheep, show area effects. Cepaea populations in these downland areas would have been much rarer, and more isolated when grazing was intense. This pattern is repeated in other parts of southern England, showing that area effects in Cepaea are strongly associated with areas of habitat instability, where Cepaea survived as small and isolated populations until recently. This evidence enhances the plausibility of explanations of area effects involving isolation, founder effect or local selection, and co-adaptation.

Aspects of Scotia Sea zooplankton

Abstract: Information on small scale distributions of three species of Antarctic zooplankton is reviewed. Aggregations of the euphausiid Euphausia superba, the tunicate Salpa thompsoni, and the amphipod Parathemisto gaudichaudii are compared, and the manner in which such aggregations mav arise is discussed. A possible relationship between swarming and feeding activity in E. superba is suggested in which krill are thought to be dispersed whilst feeding but that on repletion they swarm. It is thought that this may account for this species' irregular spatial distribution as recorded bv previous expeditions. A further consequence of this theory is that during the Winter swarming will be minimal.

Sexual behaviour and evolution of sexual dimorphism in body size in Jaera (Isopoda Asellota)

Abstract: Individuals o( the genus/aera do not mate at random. In the species from the Mediterranean group. J. italica and./, nordmanni, large males and medium sized females are at an advantage and their sizes are positively assorted. These effects are attributable to sexual competition between males. In the Ponto-caspian species J. istri, no advantage of large males exists, but sexual selection could be the cause for a long passive phase prior to copulation and for normalizing selection upon female size at pairing. In the Atlantic speciesj. albifrons, no selection can be ascertained. Differential mating success in males appears as one of the causes of the evolution of sexual dimorphism in bodv size, which makes males larger, of equal size, or smaller than females according to the species. The reason for this reversal in dimorphism seems to differ in the two sexes. Sexual selection provides an explanation for the evolution of male size, while the interspecific changes in female length are more likely due to ecological factors.