Polymorphism and population density in Donax mgosus (Lamellibranchiata: Donacidae)

Donax rugosus is a common member of the intertidal fauna on wave-beaten sandy beaches in West Africa. In Sierra Leone, the animals breed during December and the shell grows about 3 mm a year to 24 mm after seven years. All populations studied are polymorphic with respect to shell colour, more so in Sengal than in Sierra Leone. Both the relative frequency of the white form and the total number of forms present in the same population increases with population density. There is little indication of significant differences in the relative frequency of colour forms in different year groups from the same population. The polymorphism is therefore assumed to be fairly stable at least over the short term.     

Visible variation in the dog-whelk, Nucella lapillus

Shell shape and colour variation is common in littoral molluscs. As far as shape is concerned, exposure to wave action acts as a strong agent of natural selection, but only speculation seems to have been directed towards elucidating the determinants of colour variation. In the dog-whelk ( Nucella lapillus (L.)) diet may play some part in producing the pigment for colour. However white and banded forms are often found in otherwise coloured colonies. This study describes the classification for colour and banding of 83,524 whelks from 444 areas around the British Isles and west Atlantic coast. Colour and banding were significantly correlated r =0.45±0.05). Because of the possible involvement of diet in shell colour, attention has been confined to banded forms. No obvious pattern in distribution could be discerned. Possible factors affecting the occurrence and incidence of banding are: climate; geology; exposure to wave action; predation; intra- or interspecific competition; cryptic genetical factors; or intraspecific recognition. The only one which was definitely associated with banding frequency was exposure ( r = 0.33±0.05), but there were so many exceptions to the correlation (e.g. highly exposed populations which were entirely unhanded), that this is unlikely to be causal. The most probable explanation seems to be the local spread of mutant forms (probably linked to fitness traits), which have not attained equilibrium frequencies–even though N. lapillus has apparently occurred in large colonies round much of the British coast since the end of the Pleistocene.     

Shell colour variation in Littorina saxatilis Olivi (Prosobranchia: Littorinidae): a multi-factor approach

The marine snail Littorina saxatilis is highly polymorphic for shell colour. It lives in the heterogeneous intertidal zone, where there are sharp transitions in a number of abiotic factors that may influence the relative fitness of morphs. We investigated the hypothesis of selected variation by relating the colour distribution to five factors (wave exposure, substratum, shore level, sex, snail age), and to interactions between them. We compared patterns from geographical areas in Sweden, Iceland and Russia. Cryptic morphs (tessellated and different dark colours) generally dominated (80–98%) while conspicuous morphs (white, yellow, red and banded) were less common (2–20%). The colour frequencies were often related to wave exposure, substratum and shore level. Frequencies rarely varied with age and never with sex. In order to test the assumption that the different colours are genetically determined we cross-bred snails from Iceland in the laboratory. Both the presence of bands and the ground colours of the shell were inherited, and we have tentative support for a one-locus two-allele model for banding. Our results support a model of selected inherited colour variation, involving a number of different selective agents, the importance of which may vary between populations on local and geographical scales.     

HABITAT CONSTRAINTS ON SHELL-COLOUR VARIATION OF A DESERT LANDSNAIL, TROCHOIDEA SIMULATA

Trochoidea simulata, a landsnail widespread in desert regionsof Israel, varies greatly in shell colour. We have previouslyshown that predator and thermoegulatory mediated selection cannotexplain the maintenance of this colour variation. In this paper,we test the hypothesis that observed morph frequencies are aneffect of habitat variation, and that the colour variation hasno functional significance. Because white snails have thickershells than striped or brown snails, we propose that the colourof an individual snail depends on its access to CaCO₃. We testedthis hypothesis by comparing the frequency of white, striped,and brown snails at 9 locations. Each location consisted ofa paired hillside and loess wadi-bed site with high and lowCaCO₃ content respectively. There were significantly more whitesnails at hillside than loess sites. In addition, these habitatsvaried mostly in abiotic characteristics, and not in terms ofsnail population parameters or vegetation characteristics. Hillsidesites had significantly more CaCO₃ and limestone rocks thanloess sites. Soil CaCO₃ content was the strongest predictorof morph frequency among paired sites. Shell-colour variationin this species may be an effect of individual access to resources,mainly CaCO₃ that is ingested with food. (Received 5 August 1996; accepted 25 October 1996)     

Bullia digitalis (Gastropoda) actively pursues moving prey by swash-riding

An individual's success at locating resource items is largely determined by the manner in which it searches. Studies on the movement trajectories of individuals have therefore been useful in elucidating mechanisms by which animals find their resources. Studies thus far have concentrated on animals that live in physically stable environments and search for stationary food items. Several of these studies revealed a surprising ineptitude of individuals in locating their resources. Our study on the other hand focuses on an animal living in a highly turbulent environment that needs to locate moving food items. We studied Bullia digitalis , a whelk that lives in the surf and swash zones of sandy beaches. In spite of constraints imposed by wave action on its movement and obvious difficulties in using positive chemotaxis in a turbulent environment, B. digitalis appears to be most efficient in tracking its prey through the surf. It uses wave-generated flow in a form of locomotion called swash-riding which is commonly used by a wide variety of sandy beach invertebrates.     

Supergenes in polymorphic land snails. I. Partula taeniata.

The general colour of the shell in Partula taeniata is controlled by at least two loci. One of these (C) has a series of six alleles which determine the yellow (Y) and neutral brown (N) series of colours. Alleles for darker colours are dominant to those for lighter colours, but dominance is not always complete. The pink (P) colours are determined by a second locus (P) which modified the expression of the lighter alleles of the C locus. Orangeshell colour segregates with yellow but its allelic relationship is unknown. Colour of the lip is controlled by a locus (L) with pink lip dominant to white lip. The colour of the spire is determined by a locus (S) with dark (N4) spire dominant to light spire. An intermediate spire colour shows the same pattern of inheritance and may represent the effect of another allele. Banding of the shell is dominant to absence of bands, with two loci (B1 and B2) determining the type of banding. An allele at B1 produces the frenata pattern; an allele at B2 produces zonata; together they produce lyra. All the loci for which linkage data are available are linked so strongly that the whole array may be considered a supergene. Self-fertilisation takes place primarily during early reproductive life. About 20 per cent of the young of the first mating of an individual are produced by selfing, but over the whole reproductive span the frequency is only about 2-5 per cent. There is inconclusive evidence for heterozygote advantage of banded individuals.     

SHELL COLOUR IN CALLIOSTOMA ZIZYPHINUM (L.) FROM STRANGFORD LOUGH, N. IRELAND

Shells of Calliostoma zizyphinum taken from Strangford Lough,N. Ireland are divisible into three distinct colour forms: white(=var lyonsi) intermediate (a pale variegated form) and purple(a dark variegated form). The predominance of white and paleshelled individuals within and the absence of white Calliostomaoutside the lough was confirmed. The proportions of animalswith white and variegated shells at selected sites were almostidentical with those previously documented, suggesting a temporalstability of colour form ratios. No differences in shell thicknessand pedal adhesion were demonstrated between these forms. Snails with white shells reflect radiant heat better, have lightercoloured feet, move more rapidly, show a greater incidence ofshell repair and are more frequently exposed on weed at lowtide, than those with either intermediate or purple shells.Increased proportions of white individuals may be associatedwith high population densities. Under such circumstances, itis suggested that increased mobility may, by increasing dispersion,reduce intraspecific competition. In the event of exposure atlow tide a white shell would help minimize thermal stress. (Received 9 February 1987;     

Shell colour polymorphism associated with substrate colour in the intertidal snail Littorina saxatilis Olivi (Prosobranchia: Littorinidae)

Littorina saxatilis Olivi (1792), the rough winkle, is highly polymorphic in shell colour. Shell colour frequencies were studied at six locations in south-western Wales, U.K., each at a geological contact between red sandstone and grey limestone or volcanic rock. At each site shell colour frequencies were determined in samples from the contact zone and on red or grey rock on either side. Highly significant associations were found between shell colour frequencies and substrate colour. Grey shells were always more common on grey rock than on red rock, and brown shells were usually more common on red than on grey rock, suggesting selection for cryptic colouration. Shell colour frequency differences were also found between replicate samples taken only 5 m apart from the same kind of rock, and between samples from the same kind of rock at the six study sites. These latter differences suggest that selection for camouflage is not the only factor involved in maintaining shell colour polymorphism in this species.     

Importance of conspicuous colours in warning signals: the great tit’s (Parus major) point of view

Few studies have dealt with the importance of colours per se in warning signalling, with the use of a broader array of different colours. We tested the reactions of great tits (Parus major) to colour modifications (red, orange, yellow, white, blue, violet, and green) of the warning signal of the red firebug (Pyrrhocoris apterus), preserving its typical black pattern. We used the edible Guyana spotted roach (Blaptica dubia) as the prey, each of which carried a paper sticker shield of a particular colour on its back. With such prey, the effects of the other traits of the red firebug (e.g. shape of the legs and antennae or chemical signals) on the birds’ reactions were removed. All of the conspicuous forms of the prey, possessing a black pattern, were protected against great tits better than the non-patterned brown control form. The level of protection decreased from those forms with colours similar to the model and commonly occurring in warning signals in nature (red, orange, yellow), through other conspicuous colours rarely occurring in warning signals in nature (white, violet, blue), to the colour which usually occurs as cryptic in nature (green). In the green form, repeated encounters were necessary to reach avoidance. Avoidance learning came to pass despite the fact that the presented prey was neither inedible nor distasteful.     

Massive polymorphism and natural selection in Donacilla cornea (Poli, 1791) (Bivalvia: Mesodesmatidae)

We describe a massive polymorphism for shell colour and pattern in Donacilla cornea , a shallow-burrowing bivalve which inhabits the mid-littoral of sandy and stony beaches in southern and western Europe. Of the four sites studied, the one where the substrate was a mixture of small stones and sand contained the highest densities of Donacilla. At this site the densities of stones and animals and the frequencies of shell and stone colour phenotypes are both highly correlated. Although the four populations sampled comprise a similar range of phenotypes, the frequencies of most morphs and population diversity indices differ significantly between sites. At two sites the similar range of colour and pattern variation between shells and substrate suggests selection for crypsis and masquerade. On the other hand, at two other sites, one or two common phenotypes (and a number of rare ones at all sites) fail to mimic any aspect of the background. We therefore suggest that if frequency-dependent selection by predators is responsible for the maintenance of polymorphism in Donacilla , then the mechanisms involved include crypsis and masquerade in some cases and selective advantages from being different in others.     

Visual selection of shell colour in two littoral prosobranchs

The rough periwinkle Littorina “saxatilis” exhibits a wide range of shell colours. In current literature it is claimed that these colours are not related to the environment, that they arise randomly as genetic accidents and that they have little positive survival value. In a previous paper it has been shown that, in Wales, “saxatilis” consists of four separate, fully sympatric species. This paper reports an investigation as to whether the colour of two of these species, nigrolineata and rudis, is related to the colour of the background. Because of difficulties in quantitatively describing the colour of the background it was decided to concentrate mainly upon one aspect: whether or not the frequency of red shells is larger upon shores consisting of red sandstone than elsewhere in Wales. In both species the association between red shells and red sandstone is highly significant. All nigrolineata samples in which red was found at a frequency above 15% are from red sandstone. On red sandstone, red shells of this species were found mainly upon sheltered shores, their frequency decreasing and that of white shells increasing with exposure. This may be because barnacles, which occupy the same vertical zone as nigrolineata, are more abundant upon exposed shores. Partly covering the red rock, barnacles create a white background upon which white shells, rather than red, are cryptic. Yellow shells are found mainly on sheltered shores, where the brown alga Fucus is abundant. It was observed that when the tide is in and the algae spread out, a yellow shell situated beneath them is well concealed. Yellow is also found upon barnacles which because of fungal and lichen infections, are dirty yellow. It is suggested that a striped (“nigrolineated”) pattern breaks up the shape of the shell. It also resembles the colour of the dark rock and the dark sutures between barnacle plates. In rudis 80% of the samples containing over 25% red are from red sandstone. Contrast to nigrolineata, in this species the relative frequency of red decreases on sheltered shores. This could be because the brown alga Pelvetia, which occupies the same vertical zone as rudis, is more abundant in sheltered conditions and its colour partly covers over that of the rock beneath. The fact that in both species red shells are more frequent upon red sandstone than elsewhere in the study area, suggests that visual selection is restricting their distribution to the background that they match most. Rock pipits and shore-crabs prey upon winkles. They have colour perception and could be partly responsible for this selection.     

Shell colour polymorphism in the chiton Ischnochiton striolatus (Gray, 1828) (Mollusca: Polyplacophora) and habitat heterogeneity

Shell colour polymorphism was examined in a population of the polyplacophoran Ischnochiton striolatus (Gray, 1828) living on intertidal rocks in Búzios, Rio de Janeiro State, Brazil. Nine shell colours were identified: green (most common), grey, pink, cream, brown, orange, white, black and purple. The species habitat was also examined using three rock characteristics: volume; turnover frequency, caused by hydrodynamic disturbance; and chromatic composition. Chitons were most frequently encountered on the undersides of rocks of intermediate volume which experienced medium-intensity hydrodynamic disturbance, and which harboured a chromatically rich biotic community. These findings were in agreement with the Intermediate Disturbance Hypothesis. As chitons depend on the biotic community on rocks for food and shelter, a greater variety of colours could increase the chances of camouflage of the morphs against the background, favouring crypsis. It is likely that the frequency at which intermediate-volume rocks are overturned − thus exposing the chitons on them to light − would be sufficient for visual predators to act as selective agents.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 543–548.     

Colour morph related performance in the meadow grasshopper Chorthippus parallelus (Orthoptera,Acrididae)

Abstract 1. Polymorphism has been described for a number of herbivorous insects, but little is known about whether differences in body colour cause fitness differences. In Chorthippus parallelus, three main colour morphs occur, namely brown, green, and dorsally striped. 2. The present study examined colour morph abundances and morph‐related differences in body size, oviposition rate, and offspring numbers in females of C. parallelus collected in 15 montane grasslands. The study also examined the effect of plant species richness, composition, community productivity, and solar radiation on colour morph frequency and fitness. 3. The relative frequencies of the three colour morphs was 31.7% (brown), 33.1% (green), and 35.2% (dorsally striped), but the morphs were not evenly distributed across the 15 sites. 4. There was no effect of the habitat variables on the distribution of the green and the striped morph in the study sites, however 80% of the variation in the abundances of the brown morph was explained by plant species richness and composition. 5. Grasshopper size was equal among the morphs. Brown females laid significantly more egg pods than the green and dorsally striped morphs. There were no significant differences in offspring numbers among the colour morphs. 6. Body colour in C. parallelus seems to be a fitness‐relevant trait, raising the question of the evolutionary maintenance of polymorphism.     

Variability in Penicillium janthinellum Biourge, a producer of the antibiotic janthinellin, under the action of nitrosomethylurea]

Variation of the janthinellin-producing organism P. janthinellum was induced by nitrozomethylurea (NMU). The following concentrations of NMU were tested: 0.5; 0.25, 0.125 per cent at the exposure time of 15 minutes, 1 and 10 hours. The conidia survival had back dependence on the concentration and exposure time. The morphological variation was evident from the presence of forms with changed colour of the colony surface mycelium, light green, brown, light yellow, yellow-pink and white conidia and forms differing in the rate of the mycelium development and sporulation. The reverse surface of the colonies of both cultures was light brown to brown because of pigmentation. The feature of pigmentation was stable and no apigmented froms were obtained under the effect of NMU. Formation of variants producing higher yields of janthinellin (400, 2000 units) as compared to the activity of the control variant was noted. Plus variants were detected among the morphologically unchanged cultures.     

The seasonal forms and reproductive potential of the common pistachio psylla, Agonoscena pistaciae (Hem., Psylloidea)

Abstract:  Two distinct seasonal forms were found for the common pistachio psylla, Agonoscena pistaciae , the most serious insect pest of cultivated pistachio trees, Pistacia vera in Iran. The two forms are different morphologically as well as biologically. The summer form is of light colour and readily mates and starts egg laying 1–2 days after emergence, whereas, the winter form is larger, generally darker and in reproductive diapause. The first form is observed under long photoperiod, while the second form is induced under a combination of short photoperiod and low temperature. The combination of long photoperiod and warm temperature enhanced post-emergence ovarian development in the winter form, showing a close inverse correlation between pre-oviposition period and increasing temperatures. Both forms of A. pistaciae are adapted to a wide temperature range of 20–30°C for reproduction, and the fecundity of psyllid adults of either summer- or winter forms was found to be very high under experimental conditions.     

Colour polymorphism in Ephippiger ephippiger (Orthoptera, Tettigoniidae)

Colour in the Ephippiger ephippiger complex varies with the geographical distribution and with rearing density. In the W European subspecies E. e. vitium , wild insects from northern and eastern parts of the range tend to have green tergites with relatively inconspicuous banding, whereas those from S France have conspicuously pale banded dark-green or brown tergites. These forms represent the ends of a continuum and there is no zone of distinction. However, the E Pyrenean subspecies, E. e. cunii , lacks the broad banding of its neighbouring E. e. vitium. The tergites of laboratory cultured insects of these stocks when reared in isolation are distinctly green but when reared together become progressively brown. The darkness of the brown is density dependant, so that at high densities the tergites may become almost black. These colour changes are irreversible. Adult insects also become darker with sexual maturity and after contact on mating. Wild-caught E. e. ephippiger from Italy and Yugoslavia have green tergites without obvious banding. Colour changes have not been found or induced in this subspecies. The significance of the colour change is considered and although firm data are wanting, circumstantial evidence suggests a deliberate shift to an aposematic or pseudoaposematic colour pattern.     

Microclimatic adaptation and differences in food consumption and assimilation efficiency of different shell colour morphs of the land snail Arianta arbustorum

Food consumption and assimilation efficiency of different shell colour morphs adapted to various microclimatic conditions were determined. Five-factor analysis of variance (adaptation temperature, relative humidity, phenotypic shell colour, age class and time of acclimatization) was used. There are differences between different levels of adaptation temperature and relative humidity in the effect on food consumption in the two morphs. The interaction of these two factors is also significant. There is no effect of the phenotypic shell colour on the food consumption, but there is a relation between shell colour and adaptation temperature. Food consumption is greater in the juveniles. The interactions between age class and adaptation temperature or relative humidity are relevant. Acclimatization to these conditions shows a highly significant effect on the food consumption. The brown and yellow morphs of Arianta arbustorum consumed different amounts of food in relation to the adaptation temperature.
Assimilation efficiency is independent of temperature but declines at high relative humidity. There is a relation between adaptation temperature and relative humidity, but not between the phenotypic shell colour and age class factors. The yellow morphs show higher assimilation efficiencies than the brown morphs during cold adaptation to 5 °C and at the highest level of relative humidity (98%).     

Gene frequency changes in Cepaea snails on the Marlborough Downs over 25 years

In 1985 we resurveyed the sites on the Marlborough Downs in southern England at which Cain and Currey in 1960/61 sampled Cepaea snails and thence introduced the term 'area effects' to describe large areas of uniform morph frequency. Some sites no longer harboured Cepaea and at others the species composition had changed, with a general spread of Cepaea hortensis at the expense of Cepaea nemoralis. The majority, however, permitted comparison of morph frequencies between the two surveys. In C. nemoralis, we detected a significant overall decrease in the frequency of the brown morph and estimate selection as 5–9% per generation. There was no apparent change in frequencies of banded morphs. In C. hortensis we detected a significant overall increase in the frequency of unbanded shells (1–3% selection per generation) and an almost significant decrease in the frequency of fusions within the banded class. There was insufficient colour polymorphism in C. hortensis to allow analysis of colour morph frequencies. These changes—all in the direction of reduced absorption of solar energy—resemble others detected in both species at other localities in southern England. Possible explanations include large-scale climatic effects and changes in vegetation.     

The use of an EGG agar medium with neutral red for the differentiation betweenM. Tuberculosis and acid-fast saprophytes

Summary Differentiation between acid-fast saprophytes andM. tuberculosis is possible by the addition of neutral red to the B medium. Acid-fast saprophytes split amylum and produce a violet colour, whereasM. tuberculosis do not split amylum, so that the brown colour is maintained.     

The pale brown allele in Cepaea nemoralis

The pale brown colour morph in Cepaea nemoralis appears to be determined by an allele at the C (colour) locus ( C ^{P B}). Pale brown is dominant to yellow, codominant with pink and recessive to dark brown. It is linked to the B locus (which controls the presence or absence of banding on the shell), but not to the U locus, which determines whether there is one band or five. In segregations of pale brown and yellow there is a significant deficiency of pale brown, suggesting that there are differences in viability between the morphs.