Within-island microgeographic variation in the colour pattern of the skink,Chalcides sexlineatus: Pattern and cause

The colour pattern of the Gran Canarian skink is described with eight independent colour pattern characters. Significant geographic variation occurs in each character. There are generally high levels of congruence between the patterns of geographic variation in each character although some differences exist. In canonical variate analyses, the first canonical variate expresses most of the among-locality variation in colour pattern, indicating a largely unidimensional pattern. Patterns of geographic variation in the colour pattern are portrayed by contouring. This reveals north-east/south-west clines for seven of the individual characters and the generalized pattern (CV1). Four causal hypotheses were erected which predicted four different unidimensional patterns of geographic variation. Mantel tests and partial correlation analyses were used to compare the observed patterns of microgeographic variation with the four hypothesized patterns. This method suggests differential selection occurring between ecotones as the cause of the microgeographic variation. Microgeographic variation in some aspects of the colour pattern can be explained by selection for different anti-predator strategies in the hot, arid southern areas vs the cooler, lusher northern areas.     

Within-island microgeographic variation in body dimensions and scalation of the skink Chalcides sexlineatus, with testing of causal hypotheses

Correlations, univariate analyses, multiple group principal component analyses, canonical analyses, contours and transects arc used to describe microgeographic variation in body dimensions and scalation of the scincid lizard Chalcides sexlineatus within the island of Gran Canaria. Patterns of geographic variation in both character systems show similar north-east/south-west clines, scalation variation is also altitude-related. Canonical variate analyses showed that the generalized patterns of geographic variation in scalation and body dimensions were largely unidimensional. Four hypotheses, each one predicting a unidimensional pattern of microgeographic variation, were tested simultaneously against each described pattern using partial correlation. This method did not reject north/south differences in climate and/or vegetation as a cause of the microevolution in body dimensions. Similarly, altitude and north/south differences in climate/vegetation were not rejected for scalation. Partial correlation rejected the hypothesis that there are two species of Chalcides with different ranges within Gran Canaria. Mantel tests rejected the altitude hypothesis alone as a cause of the generalized geographic variation in body dimensions but did not reject any of the proposed hypotheses as being causal for the generalized geographic variation in scalation. A consideration is made of how habitat variation could cause differential selection and comparisons drawn with a parallel pattern of microgeographic variation found in the colour pattern, scalation and size of a lizard on a neighbouring island.     

Climatic variability and body size variation in the muskrats (Ondatra zibethicus) of North America

Summary Patterns of geographic variation in nine morphological characters of adult muskrats (Ondatra zibethicus) are investigated by multiple regression and canonical correlation analysis. Three variables describing the annual precipitation regimen account for 16 to 33% of the variance in each of the skeletal measurements. Highly variable precipitation patterns result in low rates of germination and survivorship for preferred aquatic food plants which in turn reduces average total food availability for muskrats. In large individuals nutritive demands may exceed supply, thus selection favors smaller body size in areas of low food availability.After removing the variation attributable to three precipitation variables, the residual variation in the morphological variables is exposed to canonical correlation analysis with a set of 10 environmental and geographic variables. A canonical variate loaded for climatic seasonality accounts for 60% of the variance in a canonical variate of the morphological residuals which load as a general body size variate. It is argued that seasonality is a major factor selecting for large body size in muskrats and other organisms. During seasonal periods of resource abundance natural selection favors individuals with rapid growth to a large size, while concurrently enhancing survivorship through oncoming periods of resource shortage.     

Juvenile colour polymorphism in the red rock crab,Cancer productus: patterns,causes, and possible adaptive significance

Juveniles of the common red rock crab of the Northeastern Pacific, Cancer productus, display a stunning diversity of colours and patterns, while adults all have the same drab colouration. Although this is widely known, key questions remain: (1) Does the frequency of different juvenile colours or patterns vary among collection sites or seasonally? (2) Does juvenile colour polymorphism reflect genetic heterogeneity or phenotypic plasticity in response to variable environmental conditions? (3) Do juveniles of different colours or patterns prefer substrata of different heterogeneity or brightness? We therefore: (i) described the variation in colour and pattern of juvenile C. productus; (ii) tested for associations between colour/pattern morphs and crab size, collection site, and season, in the field; (iii) conducted preliminary tests for habitat preferences (background colour, substratum type, light level) of different colour/pattern morphs in laboratory experiments, and (iv) tested the effect of diet (mussels versus shrimp) and feeding rate (high versus low) on juvenile colour/pattern. We describe 30 phenotypes that embrace a wide range of colour and pattern variants. The proportions of these phenotypes did not vary significantly among four collection sites, but they did vary significantly with season: over the summer and fall, juvenile colour and pattern variation was gradually replaced by the uniform adult colouration. The number of crabs displaying adult colouration also increased with crab size. Laboratory experiments suggest no significant preferences of different juvenile morphs for different backgrounds, substrata, or light levels. Diet (mussels versus shrimp) and feeding frequency had no effect on colour/pattern. Collectively, these results, although limited in scope, are not consistent with two likely hypotheses that could explain the extensive colour and pattern variation in juvenile C. productus: (i) selection for background matching by different cryptic forms and (ii) direct effects of diet or feeding rate on colour or pattern. Most probably, the large variety of different juvenile morphs is a result of frequency-dependent selection in which abundant variants are attacked disproportionately often and rarer forms are favoured. Juvenile colour polymorphism in C. productus may reduce the vulnerability to visual predators, impede the formation of a search image, and consequently decrease the risk of predation during the juvenile stages.     

Colour pattern divergence in reef fish species is rapid and driven by both range overlap and symmetry

Signal divergence is an important process underpinning the diversification of lineages. Research has shown that signal divergence is greatest in species pairs that possess high geographic range overlap. However, the influence of range‐size differences within pairs is less understood. We investigated how these factors have shaped signal divergence within brightly coloured coral reef butterflyfishes (genus: Chaetodon). Using a novel digital imaging methodology, we quantified both colouration and pattern using 250 000 sample points on each fish image. Surprisingly, evolutionary age did not affect colour pattern dissimilarity between species pairs, with average differences arising in just 300 000 years. However, the effect of range overlap and range symmetry was significant. Species‐pair colour patterns become more different with increasing overlap, but only when ranges are similar in size. When ranges differ markedly in area, species‐pair colour patterns become more similar with increasing overlap. This suggests that species with small ranges may maintain non‐colour‐based species boundaries.     

Geographic variation in scalation of the lizard Gallotia stehlini within the island of Gran Canaria

The lacertid lizard ( Gallotia stehlini ), an endemic of Gran Canaria, shows no visually obvious geographic variation, yet all seven scalation characters that were examined exhibit significant geographic variation. The number of collar scales, scales along the ventral trunk and femoral pores are correlated with habitat type, while the number of femoral pores is correlated negatively with altitude. Mantel tests were used to compare simultaneously an observed pattern with three hypothesized patterns (habitat type, altitude and proximity). They indicate that, while several individual characters are significantly associated with the putative causal factors of habitat type and altitude, there is no association between an overall scalation distance matrix and habitat type, or altitude when the effect of proximity is removed. Consequently, one should consider the individual characters as well as the multivariate generalized distances. Some of the observed patterns of geographic variation in scalation are very similar to those of the small scincid lizard Chalcides sexlineatus on Gran Canaria and also parallel the altitudinal and latitudinal variation in the scalation of the Tenerife lacertid ( Galotia galloti ). The low level of congruence in patterns of geographic variation in individual characters (i.e. some vary with latitude, some with altitude and one varies with longitude) is consistent with the hypothesis that ecogenetically caused geographic variation may result in lower inter-character congruence than phylogenetically caused geographic variation.     

Complex clines: the predictivity of complicated patterns of geographic variation portrayed by multivariate analysis

The stability of complex patterns of geographic variation was investigated by assessing the congruence between multivariate ordinations derived from randomly chosen real characters. Two series of populations were analysed representing two situations with complex patterns of geographic variation. The first, a ‘Eurasian’ series of populations, showed a strongly structured hierarchical pattern, the second, an ‘eastern’ series of populations, showed a more subtle complex pattern of smooth clines and steps. The characters were selected from a total of 81 (Eurasian) or 61 (eastern) within-population independent characters from six different systems. The congruence between ordinations of the geographical populations was measured by the rotational fit statistic, R². Three procedures were used to compare ordinations based on from two to up to 80 characters randomly chosen to give: A, completely independent character sets; B, subsets compared to the total set; and C, potentially overlapping sets. All three procedures showed that congruence between the ordinations was asymptotic in relation to character number. This relationship was described by one of two mathematical models (procedure B did not result in a hyperbolic model as found with simple patterns of geographic variation). Generally speaking, once a sufficient number of characters are used, the complex patterns of geographic variation are stable, reliable and predictive and not substantially influenced by character choice. The strongly structured hierarchical pattern required 15 or so characters to achieve reliability whilst the more subtle patterns required 20 or so characters. However, the addition of further characters does improve reliability in both cases. The greater percentage of variance portrayed by three-dimensional ordinations compared to two-dimensional ordinations is achieved at the cost of lower congruence when a sufficient number of characters are used. If case studies of geographic variation were to adopt these procedures (preferably using completely independent character sets; procedure A) the reliability of their results would be indicated).     

Fine nanostructural variation in the wing pattern of a moth <Emphasis Type="Italic">Chiasmia eleonora</Emphasis> Cramer (1780)

Butterflies and moths possess diverse patterns on their wings. Butterflies employ miscellaneous colour in the wings whereas moths use a combination of dull colours like white, grey, brown and black for the patterning of their wings. The exception is some of the toxic diurnal moths which possess bright wing colouration. Moths possess an obscure pattern in the dorsal part of the wings which may be a line, zigzag or swirl. Such patterns help in camouflage during resting period. Thus, the dorsal wing pattern of the moth is used for both intra- as well as inter-specific signal communication. Chiasmia eleonora is a nocturnal moth of greyish black colouration. The dorsal hindwing possesses yellow and black colour patches. A white-coloured oblique line crosses both left and right fore- and hindwings to form a V-shaped pattern across the dorsal wing. This V-shaped pattern possesses a UV signal. Closer to the body, the colour appears darker, which fades towards the margin. The fine nanostructural variation is observed throughout the wings. This study elucidates the wing pattern of the geometrid moth C. eleonora using high-resolution microscopy techniques that has not been described in previous studies.     

Quantitative handling of characters useful in snake systematics with particular reference to intraspecific variation in the Ringed Snake Natrix natrix (L.)

This paper is based on the numerous characters used in a biometric study of the intraspecific variation of Natrix natrix (L.). These characters are drawn from the internal morphology, scalation, colour pattern, body proportions, dentition and dermal sense organs. The criteria involved in selecting these characters for taxonomic work are considered.
The alternative methods for quantifying the above features are discussed and so are the theoretical problems involved in coding the continuous characters.
The value of the characters in studying the geographic variation, ontogenetic variation and sexual dimorphism in N. natrix is indicated.
The use of a wider range of characters than just the scalation and colour pattern is urged when diagnosing the lower taxonomic levels of ophidians. The neglected internal morphology may well be able to supply characters to this end.     

Nuclear and mitochondrial data reveal different evolutionary processes in the Lake Tanganyika cichlid genus <Emphasis Type="Italic">Tropheus</Emphasis>

Background  

Cichlid fishes are notorious for their wealth of intra- and interspecific colour pattern diversity. In Lake Tanganyika, the endemic genus Tropheus represents the most impressive example for geographic variation in the pattern and hue of integument colouration, but the taxonomy of the over 100 mostly allopatric colour morphs remains to a large degree unresolved. Previous studies of mitochondrial DNA sequence data revealed polyphyly of the six nominally described species and complex phylogeographic patterns influenced by lake level fluctuations and population admixture, and suggested the parallel evolution of similar colour patterns in divergent evolutionary lineages. A gene tree of a rapidly radiating group may be subject to incomplete and stochastic lineage sorting, and to overcome this problem we used multi-locus, nuclear AFLP data in comparison with mtDNA sequences to study diversification, migration and introgression in Tropheus colour morphs in Lake Tanganyika.     

A multivariate analysis of geographic variation in morphology inPersoonia mollis (Proteaceae)

This study highlights the utility and limitations of multivariate procedures for the analysis and taxonomic interpretation of geographic variation within a complex species. Morphological data from herbarium specimens ofPersoonia mollis (Proteceae) were analyzed by two ordination procedures, multidimensional scaling (MDS) and canonical variate analysis (CVA). Support for the earlier recognition of nine infraspecific taxa was found. However, plots of canonical variate scores against latitute or longitude across parapatric subspecies boundaries revealed unexpected phenetic homogeneity within subspecies with sharp transitions between subspecies. The geographic variation in morphology withinP. mollis can be best described as a mosaic of nine recognisably distinct and internally homogeneous allopatric or parapatric taxa, where neighbouring taxa share surprisingly narrow zones of morphological transition at ecotones. The utility of these procedures was highlighted by the recovery of unexpected patterns of variation. However, questions of rank remain unresolved by phenetic analysis alone.     

Multivariate analysis of morphometric differentiation within the Laonice cirrata-group (Polychaeta, Spionidae)

Principal component, and canonical variate analysis based on six characters show that there are morphological differences between three Laonice forms (L. bahusiensis, L. sarsi, and Laonice sp.). This supports Söderström's division of L. cirrata into four species; a decision often questioned by other taxonomists. We cannot exclude the possibility that the morphological differences are caused by polymorphism or seasonal variation within a single species. There is, however, no information to vindicate this and we conclude that the three forms should be regarded as separate species until this hypothesis can be rejected.     

Size and shape variation in a Lesser Antillean anole, Anolis oculatus (Sauria: Iguanidae) in relation to habitat.

The anole fauna of the Lesser Antilles is depauperate in relation to that of the Greater Antilles, where complex communities characterized by adaptive specialization and convergent structure are present. Much of this adaptation is the result of changes in body size and shape, probably as a result of interspecific competition. Here we present data on variation in size and shape within a solitary Lesser Antillean species occupying an ecologically heterogenous island, and test the hypothesis that natural selection for varying environmental conditions is the cause of this variation. Univariate (analysis of variance), bivariate (analysis of covariance) and multivariate (multiple-group principal component analysis, canonical variate analysis) analysis showed that there is considerable geographic variation in size and shape within Anolis oculatus on Dominica. Partial Mantel tests rejected the null hypothesis of no association between size and shape and environmental variation. The possible proximate and evolutionary mechanisms responsible for these patterns are discussed. Despite these overall associations, a considerable amount of variation in shape appears to be unrelated to environmental variation.     

Population differentiation in scalation of the Iberian rock lizard (Lacerta monticola)

The rock lizard Lacerta monticola is a climatic relict confined to three mountain ranges and one coastal region of the Iberian peninsula. Scalation was studied in specimens from localities encompassing all major parts of its range. Population differentiation was analysed using analyses of variance, z-transformations of within-locality character-correlations, canonical variate analyses, principal components analysis, and matrix association tests. Substantial differentiation was found between Pyrenees specimens and those from other localities, supporting a recent study which indicated that the Pyrenees populations could represent a different species. Considerable geographic variation is also found among populations from the remaining parts of its range, the pattern of which is not compatible with existing racial categories designated for this species.     

The colouration of the venomous coral snakes (family Elapidae) and their mimics (families Aniliidae and Golubridae)

The bright coloured, highly venomous coral snakes, Leptomicrurus, Micrurus and Micruroides (family Elapidae) and a series of harmless or mildly toxic mimics form an important component of the snake fauna of the Americas. Coral snake patterns are defined as any dorsal pattern found in any species of venomous coral snake and/or any dorsal pattern containing a substantial amount of red, pink or orange distributed so as to resemble that of some species of venomous coral snake. The components of coral snake colouration are described and four principal dorsal patterns are recognized: unicolour, bicolour, tricolour and quadricolour. The tricolour patterns may be further clustered based on the number of black bands or rings separating the red ones as: monads, dyads, triads, tetrads or pentads. A detailed classification of all coral snake colour patterns is presented and each pattern is illustrated. The taxonomic distribution of these patterns is surveyed for mimics and the 56 species of highly venomous coral snakes. Among the latter, the most frequent encountered patterns are tricolour monads, tricolour triads and bicolour rings, in that order. No venomous coral snakes have a tricolour dyad, tricolour tetrad or quadricolour pattern. As many as 115 species of harmless or mildly toxic species, c. 18% of all American snakes, are regarded as coral snake mimics. The colouration and behavioural traits of venomous coral snakes combine to form a significant antipredator defence of an aposematic type. The mimics in turn receive protection from predators that innately or through learning avoid coral snake colour patterns. The precise resemblances in colouration between sympatric non-coral snakes and venomous coral snakes and the concordant geographic variation between the two strongly support this view. Batesian mimicry with the highly venomous coral snakes as the models and the other forms as the mimics is the favoured explanation for this situation. It is further concluded that a number of species in the genera Elaphe, Farancia, Nerodia and Thamnophis, although having red in their colouration, should not be included in the coral snake mimic guild.     

Large‐scale geographic variation in iridescent structural ornaments of a long‐distance migratory bird

Iridescent colours produced during moult likely play an important role in pair formation in birds. We sought to quantify geographic variation in such colouration in a duck species, Eurasian teal Anas crecca, in winter (when mating occurs) to evaluate whether this variation reflects birds’ breeding origins or differential individual migration strategies in both males and females. We combined information on feather production region and individual attributes (body size, sex and age) of Eurasian teal from 82 wintering sites in France. Feather production region (moult site or natal origin) was inferred using feather deuterium values (δD_f). We performed spectral measurements to evaluate speculum colour and brightness contrasts for 1052 teal collected over four years. Colouration differed strongly among wintering regions, with birds wintering in eastern France exhibiting higher colour contrast than those wintering in the west. Body size and colouration were positively related. There were no differences in cohort‐specific δD_f values between separate wintering regions in France, indicating that within a winter quarter teal originated from areas across the entire breeding range. Overall, patterns of spatial variation in feather colouration were related most closely to body size which was consistent with predictions of a differential migration hypothesis, with larger and more colour‐contrasting birds wintering closer to their breeding grounds. Because moult speed is also known to affect colour production, early breeders or individuals that skipped reproduction may have invested more or earlier in their feather quality to gain potential advantages in monopolizing future mates.     

Hybridization and transgressive exploration of colour pattern and wing morphology in Heliconius butterflies

Hybridization can generate novel phenotypes distinct from those of parental lineages, a phenomenon known as transgressive trait variation. Transgressive phenotypes might negatively or positively affect hybrid fitness, and increase available variation. Closely related species of Heliconius butterflies regularly produce hybrids in nature, and hybridization is thought to play a role in the diversification of novel wing colour patterns despite strong stabilizing selection due to interspecific mimicry. Here, we studied wing phenotypes in first‐ and second‐generation hybrids produced by controlled crosses between either two co‐mimetic species of Heliconius or between two nonmimetic species. We quantified wing size, shape and colour pattern variation and asked whether hybrids displayed transgressive wing phenotypes. Discrete traits underlain by major‐effect loci, such as the presence or absence of colour patches, generate novel phenotypes. For quantitative traits, such as wing shape or subtle colour pattern characters, hybrids only exceed the parental range in specific dimensions of the morphological space. Overall, our study addresses some of the challenges in defining and measuring phenotypic transgression for multivariate traits and our data suggest that the extent to which transgressive trait variation in hybrids contributes to phenotypic diversity depends on the complexity and the genetic architecture of the traits.     

Morphometric variation in a hybrid zone of two subspecies of Gerris costae (Heteroptera: Gerridae) in the Maritime Alps

Two morphologically distinct subspecies of Gerris costae form a contact zone extending from the Maritime to the Western Alps. Within this area canonical trend surface analysis revealed a geographic pattern of morphometric variation consistent with topography. From North to South, and from high to low elevation there was a transition from G. c. costae-like phenotypes to phenotypes resembling pure G. c. fieberi. The same pattern was confirmed with canonical variate analysis not taking geographic location into account; it is therefore not an artifact of trend surface analysis. Comparisons of the pattern of morphometric variation of laboratory-reared offspring with the pattern of their parents sampled from natural populations show that geographic variation is mostly determined genetically. Intermediate individuals from field populations probably are natural hybrids between the two subspecies, because laboratory-reared hybrids were intermediate between the offspring of pure strains. We did not find increased morphometric variation within the contact zone. This suggests unimpeded introgression and is in contrast with an increase in size variability that is predicted to be associated with a transition between uni- and bivoltine forms.