Natural selection for apostasy and crypsis acting on the shell colour polymorphism of a mangrove snail, Littoraria filosa (Sowerby) (Gastropoda: Littorinidae)

Littoraria filosa (Sowerby) is a member of the L. scabra group, found amongst the foliage of mangrove trees in northern Australia. The colour of the shell is polymorphic, showing two discrete ground colours, either yellow or orange-pink, with a variable degree of superimposed brown patterning. At a site on Magnetic Island, northern Queensland, colour frequencies of small snails were similar on different backgrounds. Amongst larger shells yellows were more frequent on Avicennia trees with abundant foliage, and browns on relatively bare trees, suggesting that visual selection for crypsis occurred. There was no evidence of substrate selection by the morphs. Yellow shells were cooler than brown shells, but differences in colour frequencies on sunny and shaded trees, and at different seasons, did not suggest climatic selection. By manipulating the colour frequencies of subpopulations of small snails isolated on individual trees, it was shown that the disappearance of yellow and brown shells was frequency-dependent. This result is consistent with hypotheses of mimicry of background elements by the morphs and of apostatic selection by unknown predators. Only the latter can account for the persistence of the highly conspicuous pink morph at a low frequency.     

Apostasy and selection for crypsis in the marine snail Littoraria filosa: an explanation for a balanced colour polymorphism

The marine snail, Littoraria filosa, is polymorphic for shell colour, with yellow, brown, and pink morphs that correspond in both appearance and frequency to the predominant background colours of its habitat. Previous research on this polymorphism has found indirect evidence of apostatic selection and selection for crypsis by unknown agents, probably crabs, and direct evidence of selection for crypsis by the parasitoid fly Sarcophaga megafilosia. In the present study, we report on field experiments to investigate whether S. megafilosia and shell‐crushing predators exert apostatic selection on L. filosa. For S. megafilosia, seven experimental treatments containing yellow and brown snails in the proportions of 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, and 0.9 of each colour were established on mangrove trees and used to separately quantify the proportions of each colour attacked on grey/brown trunks and yellow/green leaves. The results obtained confirmed an earlier finding of selection for crypsis, but only showed slight, but significant, anti‐apostatic selection by S. megafilosia. For shell‐crushing predators, seven experimental treatments containing yellow and brown snails in the proportions of 0.08, 0.17, 0.33, 0.50, 0.66, 0.83, and 0.92 were established on two types of trees that differed in their background proportions of brown and green: (1) trees which had been pruned of approximately 90% of their foliage and (2) unpruned trees. The results obtained showed both selection for crypsis and apostatic selection. Furthermore, a selectively neutral frequency for yellow L. filosa was found for each background, and was less on pruned trees than unpruned ones (and vice versa for brown L. filosa), which can therefore account for the maintenance of a colour polymorphism where the proportions of each morph tend to resemble and correspond in frequency to the colours of the background. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 62–71.     

Intraspecific variation in limblessness in vertebrates: a unique example of microevolution

Many species of arboreal marine snails in the genus Littoraria are polymorphic for shell colour, with morphs that correspond in both colour and frequency to those predominant in the habitat. Although the combined effects of selection for crypsis and apostasy have been suggested as the most likely reasons for this, they have not been demonstrated directly in the field. We investigated whether two parasitoid flies, Sarcophaga megafilosia and Sarcophaga meiofilosia, select for crypsis in Littoraria filosa . It was possible to compare the proportions that matched and did not match the background between samples of live and dead snails because the shells of individuals killed by these parasitoids, within which the larva and pupa develop, remain attached to the substratum. This comparison was necessary because these snails frequently move among different coloured microhabitats, which will tend to obscure any effect of selection for crypsis if only live individuals are censused. The method appeared reliable since there was no change in background colour and very little loss of shells between larviposition and emergence of flies. S. megafilosia killed a significantly greater than expected proportion of snails that did not match their background. In contrast, there was no evidence of selective attack by S. meiofilosia. These results are discussed in relation to previous work on polymorphisms in Littoraria species. We also suggest that the role of parasitoid insects as selective agents contributing to the maintenance of colour polymorphisms in terrestrial molluscs may have been overlooked.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77, 367−377.     

Site selection in a polymorphic mangrove snail

Three species of littorinid snail live on mangroves of the genus Rhizophora on the north coast of Papua New Guinea. They have recently been placed in the genus Littoraria. The species are L. scabra and L. intermedia , which are monomorphic and cryptic and live on bark, and L. pallescens which is polymorphic and lives in foliage. Littoraria intermedia was found mostly on mangroves facing on to partially fresh water, while L. scabra occurred only at sites facing on to the sea; L. pallescens occurs at both types of site. When kept together in plastic containers, L. pallescens shows a greater propensity to climb than the other two species. The morphs of L. pallescens are principally yellow, orange or dark. Orange is present at a frequency of 0–9% and yellow at 10–50%. There is little evidence of geographical variation in frequency over 80 km of coast, although one central locality has a significantly higher frequency of yellow than sites to the north or south of it. Throughout the tropics where the species occurs, orange is the rarest and yellow usually the next rarest morph. Larger individuals are on average higher in the foliage than smaller ones, and there is a higher frequency of yellows among larger shells than smaller ones. As the air temperature increases, a progressively larger fraction of a sample was found to be on the under-surfaces of leaves rather than on the upper epidermis or on flower or leaf buds. When over 30% of a sample is situated on lower surfaces there is a significant excess of yellows and a deficiency of darks on the upper surfaces. This indicates that individuals selectively take up different positions depending on morph colour, resulting in a degree of optimal background matching. Such a choice of location may be of direct relevance to the maintenance of the polymorphism. A difference in morph frequency between the same sites examined in 1979 and 1984 is interpreted as being a result of site selectivity.     

Substrate preference in a colonial spider: is substrate choice affected by color morph?

Animals can show preference for a particular background as a way of decreasing visibility. Species with color polymorphism may have morph‐dependent background preference. I test this hypothesis on the orb‐weaving spider Parawixia bistriata. Adult females of P. bistriata present two distinct morphs characterized by brown and yellow opisthosomata. This nocturnal spider can be found in its retreat on the vegetation during the day. In order to examine whether females exhibit substrate preference dependent on their color morph, I first recorded the distribution of color morphs on different substrates (leaf and branch) and then performed a mark and release experiment. Field censuses indicated that the yellow morph was associated with leaves while the brown morph was found on either substrate type. The results of a mark and reciprocal release experiment agreed with the censuses and suggest that the two morphs differ in their association to substrate type: yellow females were associated with the leaf substrate, while brown females showed no association to a particular substrate type. Possible forces behind these differences in substrate choice are discussed.     

Habitat and zonation patterns of Littoraria species (Gastropoda: Littorinidae) in Indo-Pacific mangrove forests

The zonation of 15 species of Littoraria in the scabra group is described, using a transect method, at 13 mangrove localities in Australia, Thailand, Malaysia and Hawaii. At these localities the littorinids occurred only on trees, and showed both vertical and horizontal patterns of zonation, with broad overlaps between co-occurring species. It is suggested that vertical distribution is determined mainly by behavioural responses, while the landward limits of horizontal distribution may be set by physiological tolerance. Several species occurred predominantly on either leaf or bark substrates, but no consistent associations with tree species were found. On the basis of local distribution patterns, Littoraria species can be classified as continental or oceanic in character. Oceanic species may be less tolerant of sediment in the water or on the substrate.     

Temporal morph frequency changes in sand‐dune populations of Cepaea nemoralis (L.)

Changes in morph frequency over time in sand‐dune populations of Cepaea nemoralis in the British Isles have been examined using the Evolution Megalab database. Frequencies in colonies on a sand dune at Berrow, Somerset were estimated in 2008–9. This extends a survey started in 1926 by A. E. Boycott and C. Diver and continued in the mid‐20th Century by B. C. Clarke and J. J. Murray. An increase in the frequency of the mid‐banded morph, noted in earlier work, has continued. The apparent decrease in brown was not confirmed but the yellow frequency has increased. At a range of dunes in the British Isles, comparisons between data from the mid‐20th Century and the early 21st Century indicate an increase in yellow and mid‐banded morphs and a decrease in banding and brown morphs. These results differ from the overall trends derived from Europe‐wide comparison of early data with Evolution Megalab data, in which banded and mid‐banded increased in frequency, whereas there was no overall change in yellow. The general pattern of regional variation has been retained, although there is also high heterogeneity between samples, suggesting that a variety of factors are involved in explaining the changes. The mean shifts in frequency are consistent with climatic change over the period. Dunes are probably the most likely habitat in which to detect such a change. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 108 , 315–322.     

Perch color preference in juvenile green tree pythons,Chondropython viridis

Green tree pythons, Chondropython viridis, are polymorphic for color as juveniles, commonly being primarily yellow or brown until becoming mostly green at about 1 year of age. We tested the hypothesis that the different morphs arose as a result of selection for differential background matching, yellow morphs selecting light-colored backgrounds, and brown morphs selecting dark-colored backgrounds. Twelve yellow and eight brown morphs were placed repeatedly in individual testing enclosures and allowed to choose between black and white or yellow and brown halves of a t-perch. Trials showed that both color morphs preferred dark over light perches. We tentatively suggest that individuals chose dark-colored perches for purposes of concealment. © 1994 Wiley-Liss, Inc.     

Regeneration niche of three epiphytic species of Gesneriaceae from Chilean rainforests: implications for the evolution of growth habits in Coronanthereae

Ecological and evolutionary studies of the epiphytic growth habit in angiosperms are limited. In this article, we assess the relationship between growth habit and regeneration niche in Coronanthereae (Gesneriaceae) and discuss its implications for the evolution of epiphytism in this lineage. In the temperate rainforest of southern Chile, we quantified the vertical distribution and experimentally examined the regeneration niche of three endemic species of Coronanthereae. One species was a holoepiphyte, which was more frequent in the upper canopy, and two species were secondary hemiepiphytes, which decreased in abundance with tree height. Seed germination of the holoepiphyte was higher on tree bark substrates and under open canopy than on forest soil and in the shade. In contrast, seed germination of both secondary hemiepiphytes did not differ between substrates (bark vs. soil) or light conditions (light vs. shade). Seedling survival percentage of secondary hemiepiphytes was higher on forest soil and under a closed canopy, thus behaving as shade‐tolerant species. In turn, the holoepiphyte behaved as a shade‐intolerant species. The reconstruction of the ancestral growth habits and regeneration niches on the inferred phylogenetic tree of Coronanthereae revealed that the specialized regeneration niche of Sarmienta repens, characterized by requirements of shade intolerance and germination on tree bark, was coupled with the evolution of the holoepiphytic growth habit. We conclude that differentiation in the regeneration niche is a key process in the evolution of epiphytic growth habits in Coronanthereae. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 79–92.     

Adaptive loss of color polymorphism and character displacements in sympatric <Emphasis Type="Italic">Mnais</Emphasis> damselflies

A geographical survey of two Mnais damselfly species in the Kinki area of Japan showed evidence for character displacements when the two species were found in sympatry. Mnais costalis, a species that has polymorphic male mating types of orange-winged territorial and clear-winged non-territorial morphs (hereafter abbreviated to orange and clear morphs respectively) in allopatry often shifted to having monomorphic orange morphs in sympatry. The mean body size of orange morphs was consistently larger than that of clear morph in allopatry. The mean body size of the sympatric orange morphs was even larger than that of allopatric orange morphs. By contrast, Mnais pruinosa, a species that also has two morphs of large orange and small clear morphs in allopatry, shifted to having monomorphic clear morphs in sympatry. The mean body size of the sympatric clear morphs was smaller than that of allopatric clear morphs. Divergence was also detected in the preference for habitat insolation conditions between sympatric Mnais damselflies. Both species in allopatric regions prefer half-light forest habitats, while in sympatric regions they showed diversified habitat preference: M. costalis preferred sunny habitats while M. pruinosa preferred shady habitats. Multiple character displacements in signal traits and habitat preference emerged in heterogeneous forest light environments are likely to have synergistic effects on the reproductive isolation of the two species.     

Behavioural fitness component effects of the alba polymorphism of Colias (Lepidoptera, Pieridae): resource and time budget analysis

1. Alba, a white wing colour morph of butterflies of the genus Colias , makes fitness-related changes at several levels of phenotypic organization: physiology, development and behaviour. Two sympatric species of Colias are studied, which differ greatly in their frequency of alba vs its sister yellow/orange morph. How resource and time constraints on Colias interact with the morphs' different patterns of pupal resource allocation to alter the balance of the morphs' fitness components in the two species is discussed.
2. These species, C. alexandra and C. scudderi , differ in melanin-based solar energy absorption, in larval dietary richness and in local adult nectar resources. The two female morphs determine alternate thermal balance, internal resource allocation and behavioural effects in each species, thus changing the morphs' time budgets and fitness-component impacts between the species. In particular, female egg output differences between the morphs appears to reverse between species: alba fecundity is greater than yellow fecundity in C. scudderi , but alba is less than yellow in C. alexandra .
3. These differences are consistent with the large observed differences in alba frequency between the species. Some important questions about the selective regime maintaining a polymorphism here, rather than an alternation of monomorphisms, remain.     

Genetic and Ecological Characterisation of Colour Dimorphism in a Coral Reef Fish

Synopsis Many recognised species of coral reef fishes exhibit two or more colour variants, but it is unknown whether these represent genetically identical phenotypes, genetic polymorphisms or closely related species. We tested between these alternatives for two colour morphs of the coral reef fish, Pseudochromis fuscus, from Lizard Island (Great Barrier Reef). A molecular analysis using mtDNA did not detect any genetic differentiation between co-occurring ‘yellow’ and ‘brown’ colour morphs. A previous study proposed that these two colour morphs are aggressive mimics of yellow and brown damselfishes. Here, a manipulative field experiment was used to evaluate whether the colour dimorphism in P. fuscus is a phenotypic response to the presence of two different model species. Colonies of either yellow or brown damselfish species were established on different patch reefs, and each of the two different P. fuscus morphs was then placed on the different reefs. Contrary to expectations, all yellow individuals that stayed on the reefs changed to brown, regardless of the model species. No brown individuals changed to the yellow colouration. However, P. fuscus were more likely to emigrate from, or suffer higher mortality on, patch reefs where they were not matched with similarly coloured models. Clearly, yellow and brown P. fuscus are members of a single species with sufficient phenotypic plasticity to switch from yellow to brown colouration.     

Empirical evaluation of phenotype–environment correlation and trait utility with allopatric and sympatric whitefish, Coregonus lavaretus (L.), populations in subarctic lakes

Adaptive phenotypic divergence of sympatric morphs in a single species may have significant evolutionary consequences. In the present study, phenotypic impacts of predator on zooplankton prey populations were compared in two northern Finnish lakes; one with an allopatric whitefish, Coregonus lavaretus (L.), population and the other with three sympatric whitefish populations. First, we examined whether there were phenotypic associations with specific niches in allopatric and sympatric whitefish. Second, trait utility (i.e. number of gillrakers) of allopatric and sympatric whitefish in utilizing a pelagic resource was explored by comparing predator avoidance of prey, prey size in environment, and prey size in predator diet. The allopatric living large sparsely rakered (LSR) whitefish morph, was a generalist using both pelagic and benthic niches. In contrast, sympatric living whitefish morphs were specialized: LSR whitefish was a littoral benthivore, small sparsely rakered whitefish was a profundal benthivore and densely rakered (DR) whitefish was a pelagic planktivore. In the lake with allopatric whitefish, zooplankton prey did not migrate vertically to avoid predation whereas, in the lake with sympatric whitefish, all important prey taxa migrated significantly. Trait utility was observed as significantly smaller size of prey in environment and predator diet in the lake with DR whitefish than in the lake with only LSR whitefish.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 561–572.     

Shell colour polymorphism in a mangrove snail Littorina sp. (Prosobranchia: Littorinidae)

Shell colour polymorphism was examined in populations of a mangrove snail Littorina sp. in Queensland, Australia. Three morphs were recognized, yellow, red and brown, and morph frequencies varied both between widely spaced populations and between islands less than 1 km apart. Morph frequencies also varied with time of year. There was a relationship between shell colour and position on the tree, with yellow snails more often occurring amongst the foliage and brown snails more often on trunks and branches. In some populations yellow snails appeared to survive better than the other morphs, while in other populations there was no difference. The evidence for the maintenance of the polymorphism by natural selection is discussed.     

MICRODISTRIBUTION IN THE FIELD AND HABITAT CHOICE IN AQUARIA BY COLOUR MORPHS OF LITTORINA MARIAE SACCHI & RASTELLI

The microdistributions of yellow and brown morphs of adult andjuvenile Littorina mariae were investigated in the field onFucus plants. On F. vesiculosus in autumn, yellow adults werefound more frequently than expected on laminae and brown adultsmore frequently than expected on stipes. In spring there wasno difference in distribution between adult morphs. There wasno difference in microdistribution betweenjuvenile morphs oneither F. vesiculosus or F. serratus in autumn. Yellow and brown adults were allowed to choose between an artificialbrown and an artificial yellow background, and between stipeand lamina of F. serratus in aquarium experiments. Both morphspreferred the yellow rather than the brown background. In mostcases, the morphs climbed upwards on F. serratus, regardlessof algal orientation (lamina upwards or stipe upwards) or lightregime (lights on or off). A significant difference in microdistributionbetween morphs was found with the lamina placed upwards andthe lights on. Brown snails then preferred stipe, while yellowsnails did not show a preference for either stipe or lamina. (Received 16 June 1994; accepted 31 October 1994)     

Heating properties of morphs of the mangrove snail Littoraria pallescens

The rate of heating and the temperature attained after 10 and 20 min have been examined for shells of the yellow, dark and orange morphs of the mangrove leaf snail Littoraria pallescens. Under the experimental conditions used, heating from 20 to 40C took 5–10 min and thereafter the temperature remained roughly constant for up to 20 min. This represents temperature conditions which the animals are likely to experience in the wild. Large shells heat more slowly than small ones and reach lower temperatures. At around 40C yellows are on average 1.5C cooler than the dark morph, and orange individuals lie between. This difference could account for the observed difference between morphs in their choice of preferred leaf surface. Besides differing in colour, yellows are thinner and less heavy than dark shells, which probably contributes to the fact that they arc less robust.     

Epiphytic lichen is associated with species richness of gall-inducing aphids but not with niche differentiation among them

The presence of epiphytic foliose lichen amplifies the heterogeneity of habitat by creating shelters for insects living on tree bark. It thus should enhance species number and spatial niche segregation among these canopy insects. We studied this hypothesis in a field experiment using four aphid species that induce galls on Pistacia atlantica trees covered with Xanthoria parietina lichen. In autumn 2008, 3 months after aphid fundatrices were oviposited, we marked six branches on each of 29 trees. Two served as a control, whereas the other four were isolated with insect glue; two of them were scraped with sandpaper to remove epiphytic foliose lichens. We therefore obtained three treatments comprising control branches, isolated branches with lichen, and isolated branches without lichen. In summer 2009, we counted all the galls developing on five new annual shoots on each of 174 branches. We observed more cecidogenic aphid species on all the branches with lichens than without, but each species at different proportions. The different frequencies of utilization of the lichen did not lead to habitat partitioning between species. In conclusion, although habitat heterogeneity itself was associated with species richness and population abundance, it did not induce spatial niche segregation. Considering that many economically important insect species, pests and natural enemies, oviposit or spend some portion of their lives in bark cracks, it is possible that some can use lichens too for protection or/and oviposition sites. As a consequence, lichens may affect management of agrosystems and their impacts should be investigated more deeply in such contexts.     

Morphological and genetic analysis of fish of a Carassius complex (Cyprinidae) in Lake Kasumigaura with reference to the taxonomic status of two all-female triploid morphs

The classification of the Carassius complex (Cyprinidae) including all-female triploids, called ginbuna in Japanese, is so confused that three sympatric morphs of crucian carp in Lake Kasumigaura are categorized into two different subspecies within a species. We examined them in order to explain the coexistence of more than one subspecies and determine the founder of the triploid lineages in the crucian carp fauna in the lake. Principal component analysis proved that the three sympatric morphs had a morphometric basis distinguishable from each other. Ploidy was determined by flow cytometry which showed triploids in two morphs and diploids in the other morph. Stepwise discriminant analysis using only meristic characteristics could separate the diploids from the triploids. Phylogenetic analysis using mitochondrial DNA inferred two lineages in which one was composed of a triploid morph and the other was a diploid–triploid mixture. Disagreement between the taxonomic status and the phylogenetic status is explicable by assuming that the triploids in the Carassius complex had independent origins leading to the different subspecies. C. auratus langsdorfii appears to show genetic complexities that traditional taxonomic classification can not unravel.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 351–357.     

Difference in habitat selection by different morphs of the land snail Arianta arbustorum

The behaviour of morphs of Arianta arbustorum has been investigated using a new technique involving a paint which fades in daylight. The technique was used to study the response of different morphs to exposure to sunlight at a homogeneous woodland habitat and a heterogeneous open habitat. The yellow morph showed a significantly higher rate of fading than the brown morph. A mark, release and recapture programme was used to analyse the association between frequencies of different morphs recaptured and not recaptured. In both habitats, there was a general tendency for the frequency of recapture to increase with increasing age in both morphs. Habitat selection resulting from different behaviour of different morphs of A. arbustorum is discussed. Morph frequencies can be related to habitat, the brown morphs of A. arbustorum are significantly less frequent in the open habitat. The behavioural responses of Cepaea hortensis , present with A. arbustorum in two other populations, to the exposure of sunshine were also studied. Climatic selection by solar energy associated with different morphs, species and habitat are also discussed.     

Change and stability in a steep morph‐frequency cline in the snail Cepaea nemoralis (L.) over 43 years

Populations of the polymorphic land snail Cepaea nemoralis (L.) from Deepdale, Derbyshire, UK, sampled in 1965–67, showed a pattern of area effects, with steep clines among groups of populations differing in shell colour and banding morph frequencies. In 2010, most of these populations were resampled. In particular, a continuous transect made in 1967 of 42 quadrats (18.34 × 18.34 m) across a steep cline in several morph frequencies was completely resampled. In the dale as a whole, yellow shells had increased in frequency. In the transect, the frequencies of banding morphs showed no significant changes, although colour morphs showed some changes. Pink shells had increased in frequency in a section in which scrub had developed, and brown shells had increased in frequency in the area in which they had originally been at the highest frequency. In each case, the selection coefficients were of the order of 4%. Yellow had increased elsewhere. Nevertheless, both in the dale as a whole and in the transect, the pattern of geographical change in morph frequencies had remained essentially the same. Estimates of migration based on previous studies of marked snails and on modelling of the effect of drift and migration suggest that, regardless of whether the cline is a product of differential selection or of the gradual merging of previously separate founding populations, it has been in existence for a long time, and that migration occurs over greater distances than estimated from direct observation on marked snails. Although we can demonstrate that selection has occurred, the origin and maintenance of the cline and others similar to it remain in doubt; the development and maintenance of polymorphism in this species may require consideration of several processes operating on different time scales. © 2012 The Linnean Society of London