The systematics of the Phelsuma madagascariensis species group of day geckos (Reptilia: Gekkonidae) in the Seychelles

Conventional taxonomy of the Seychelles populations of the Phelsuma madagascariensis species group has failed to illustrate the principal patterns of phenetic variation between island populations. The taxonomic history of the populations is discussed critically, and a revised nomenclature is suggested from the results of a recent comprehensive study of the forms using multivariate morphometrics. Three phenetic groups from the granitic islands are referred to as Phelsuma sundbergi sundbergi from the north western islands; P. s. ladiguensis from the north eastern islands; and P. s. longinsulae from the southern islands. Phelsuma abbotti populations from Aldabra and Assumption are considered subspecifically distinct, and not conspecific with the granitic island forms. The other coralline island populations are closely allied to the races from the granitic islands and probably represent recent colonization or introductions by man.     

Identification, morphometries and cytogenetics of green geckos (Phelsuma) from Praslin, Seychelles (with notes on P. longinsulae, Mahé)

The three species of green geckos (Phelsuma) on the granitic Seychelles can be identified by colour pattern, snout shape and the occurrence of keeled belly scales. There is no difference in chromosome number (2n=S6) between species but multivariate morphometries analysis, based on body proportions and scalation, can distinguish between the species on Praslin Island.     

Phylogeography and natural selection in the Tenerife gecko Tarentola delalandii: testing historical and adaptive hypotheses

Combining phylogeographic and matrix correspondence approaches in the analysis of geographical variation provides a fruitful approach to inferring the causes of molecular and morphological evolution within species. Here we present a study on the gecko Tarentola delalandii on the island of Tenerife, Canary Islands, which provides an outstanding model of an exceptionally high degree of phylogeographic differentiation in magnitude and pattern on a small spatial scale. We reconstruct the population history of T. delalandii using phylogeographic information, matrix correspondence tests and estimates of divergence times in conjunction with geological data. It appears that populations differentiated on three precursor islands and secondary contact followed the junction of these islands. The cytochrome b sequence appears to be evolving at least at approximately 1% per million years in this species. Matrix correspondence tests indicate that morphological character systems may reflect ecological selection regimes (colour pattern), history (body dimensions) or both (scalation). The results imply that natural selection can override a historical legacy, but also underline the potential relevance of molecular phylogenetic data for the interpretation of geographical variation in morphology.     

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.     

Geological history and within-island diversity: a debris avalanche and the Tenerife lizard Gallotia galloti

Several processes have been described that could explain geographical variation and speciation within small islands, including fragmentation of populations through volcanic eruptions. Massive landslides, or debris avalanches, could cause similar effects. Here we analyse the potential impact of the 0.8 million-year-ago (Ma) Güimar valley debris avalanche on the phylogeography of the lizard Gallotia galloti on the Canary Island of Tenerife. Distributions of mitochondrial DNA lineages (based on cytochrome b sequences) were analysed on a 60-km southeastern coast transect centred on this area. Three main clades were detected, which can be divided into northern (one clade) and southern (two clades) groups that introgress across the valley. Maximum-likelihood estimates of migration rates (scaled for mutation rate) revealed highly asymmetric patterns, indicating that long-term gene flow into this region from both the northern and the southern populations greatly exceeded that in the opposite directions, consistent with recolonization of the area. The ancestral Tenerife node on the G. galloti tree is estimated at 0.80 Ma, matching closely with the geological estimate for the debris avalanche. Morphological variation (body dimensions and scalation) was also analysed and indicated a stepped cline in female scalation across the valley, although the patterns for male scalation and male and female body dimensions were not as clear. Together these findings provide support for the hypothesis that the debris avalanche has shaped the phylogeography of G. galloti and may even have been a primary cause of the within-island cladogenesis through population fragmentation and isolation. Current estimates of timing of island unification mean that the original hypothesis that within-island diversity is explained by the secondary contact of populations from the two ancient precursor islands of Teno and Anaga is less plausible for this and some other Tenerife species. Large-scale landslides have occurred on many volcanic islands, and so may have been instrumental in shaping within-island diversities.     

Testing multivariate patterns of within-island differentiation in Podarcis dugesii from Madeira

Podarcis dugesii is a polymorphic species found on the ecologically-heterogeneous Atlantic island of Madeira. Patterns of geographic variation in size-free body dimensions (body shape), scalation, and size were portrayed on maps with isophene contours. There was no dominant pattern of among-site variation as seen in several other island lizards, although some linear combinations of morphological variables showed evidence of clines towards the east coast. Multivariate statistical techniques were developed to evaluate whether morphological variation contained an ecology-related spatial pattern, after removal of the effects of statistical non-independence of studied populations. Specifically, a partial correlation matrix comparison method provided evidence to support a proposed elevation model of among-site divergence in scalation and body size, with both an alternative rainfall model and spatial non-independence held constant. Similar divergence in scalation has been observed in other lizard species on other island archipelagos as well on some continental areas. The rainfall model was rejected for both body shape and scalation. The degree of within-population polymorphism in body shape and scalation showed no clear geographic trends in general, although the elevation and rainfall models could not be rejected for female scalation.     

Within-island geographic variation of the dangerous Taiwanese snake, Trimeresurus stejnegeri, in relation to ecology

Multivariate analysis shows that geographic variation occurs in the scalation and body proportions of the dangerously venomous snake Tritneresurus stejnegeri , within the island of Taiwan. Canonical correlation analysis reveals a high correlation between constellations of morphological characters and ecological factors. Numerical hypothesis testing, using partial Mantel tests, provides evidence of a causal relationship with ecology. Head shape was found to be primarily associated with mean annual temperature and altitude, and head scalation with the annual range of temperature. Body scalation was found to be influenced by altitude, mean annual temperature and mean annual rainfall. Tail length is primarily associated with the range of temperature and rainfall and secondarily with the mean annual temperature and altitude. Geographic proximity was found to be less important in the explanation of the observed geographic pattern than some ecological factors, supporting the hypothesis of an ecogenetic origin of morphological variation.     

Reconstructing an island radiation using ancient and recent DNA: the extinct and living day geckos (Phelsuma) of the Mascarene islands

Mitochondrial (12SrRNA and cyt b, 1086 bp) and nuclear (c-mos, 374 bp) DNA sequences were used to investigate relationships and biogeography of 24 living and extinct taxa of Phelsuma geckos. Monophyly of Phelsuma and sister relationship to the SW African Rhoptropella is corroborated. Phelsuma originated on Madagascar and made multiple long-distance invasions of oceanic islands including the Mascarenes, Aldabra, Comores, Seychelles, Andamans, and perhaps Pemba. The Mascarenes were probably colonised once, about 4.2-5.1Ma, and here Phelsuma rosagularis and Phelsuma inexpectata are newly recognised as species, as are three lineages of Phelsuma cepediana. Mascarene relationships are: Phelsuma edwardnewtoni, Phelsuma gigas (Phelsuma guentheri ((((P. cepediana A (P. cepediana B, C)) P. rosagularis) Phelsuma borbonica) ((Phelsuma ornata, P. inexpectata) Phelsuma guimbeaui))). The two recently extinct species, P. edwardnewtoni and the giant secondarily nocturnal Phelsuma gigas, differentiated on Rodrigues while on Mauritius the large nocturnal P. guentheri separated from a small diurnal form that radiated into six species, a likely result of volcanic activity. Two small-bodied lineages from Mauritius invaded the more recent island of Réunion producing two more species. Outside the Mascarenes, two mainly Madagascan assemblages are substantiated: Phelsuma serraticauda (Phelsuma lineata, Phelsuma laticauda, Phelsuma quadriocellata); (Phelsuma m. kochi (Phelsuma m. grandis, Phelsuma abboti)) (Phelsuma astriata, Phelsuma sundbergi). Their relationships to the Mascarene clade, and to Phelsuma mutabilis, Phelsuma standingi and Phelsuma andamanensis are unresolved.     

Multivariate phenotypic evolution among island and mainland populations of the ornate day gecko, Phelsuma ornata

Interpopulation variation in morphology, such as that among small island populations, plays a key role in speciation and diversification. There are two approaches to investigating evolution of morphological characters: comparing patterns of trait variances and covariances within and among populations, and testing particular adaptive scenarios. Here, we combine both approaches to infer the role of natural selection in shaping morphological variation in body size, head color pattern, and body shape among 10 populations of a day gecko, Phelsuma ornata, and its close relative, P. inexpectata, in the Mascarene Islands. We find that local populations are morphologically distinct, and that natural selection has likely influenced phenotypic diversification in the group. Lizards on small outer islands tend to be larger than lizards on the mainland of Mauritius. For body shape and head color pattern, comparisons of variation within and among populations reveal that differences among populations for some variables are too great to be explained by neutral processes alone, although we cannot identify the causal agents for this selection. These results reveal that the forces shaping different sets of organismal traits may be distinct, such that a variety of statistical approaches are needed to investigate selection in natural populations.     

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.     

GEOGRAPHIC VARIATION WITHIN AN ISLAND: UNIVARIATE AND MULTIVARIATE CONTOURING OF SCALATION,SIZE, AND SHAPE OF THE LIZARD GALLOTIA GALLOTI

Microgeographic variation of the vegetarian lizard Gallotia galloti within the island of Tenerife is described using univariate analysis, correlation, multiple group principal component analysis, canonical analysis, transects, and contours. The size varies locally in a mosaic pattern while head shape shows a WNW–ESE cline in the south. The scalation (scale and femoral pore counts) has two facets to its geographic variation, both of which are incongruent with the primary variation in the size and shape. The scalation shows categorical variation (stepped cline) between northern and southern populations and also a strong clinal relationship with altitude. The possible causes of this variation are considered and adaptation to current ecological conditions appears to be implicated for at least the altitudinal variation, although the pertinent factors are not obvious. It is apparent that vertebrate populations distributed across small islands do not necessarily offer the advantage of a discrete homogeneous unit for evolutionary studies but can offer the opportunity for studying microgeographic variation.     

The dynamics of natural selection and vicariance in the Dominican anole: patterns of within-island molecular and morphological divergence

The larger islands of the Lesser Antilles are ecologically and geologically complex and are inhabited by single, but morphologically variable, Anolis species. Although earlier work has indicated that a large part of the morphological variation in Anolis oculatus from Dominica can be attributed to selection, a history of recurrent volcanic activity over the last few million years suggests that vicariance may have also played a significant role. We report a study of variation in the cytochrome b gene of mitochondrial DNA across the island to address this issue. We uncovered a very high degree of polymorphism, with an overall gene diversity of 0.97 and a nucleotide diversity of 0.04. Sequences, on average, differ by 3.82% and the maximum pairwise divergence (corrected for multiple hits) is 9.29%. Most haplotypes are restricted to single localities (a pattern not changed by increasing the sample size). Phylogenetic analysis revealed the presence of two distinct lineages on the island with strong phylogeographic structure. One of these is geographically restricted to a relatively small part of the central Caribbean coast. Sublineages were also discernible within the other more widely distributed lineage, but resolution within and support for these sublineages was poor. The phylogeographic pattern is not congruent with generalized body shape and scalation, but is significantly correlated with color pattern. Even when correcting for this lineage effect with partial Matrix correspondence tests, the relationship between color pattern and vegetation is reaffirmed, suggesting that although both vicariance and selection have played a role in the morphological differentiation of this species, selection for current environmental conditions has been more important. We discuss the causes of the phylogeographic structure in light of the volcanic history of the island and highlight the exceptional instance of congruence between all morphological character systems and lineage boundaries, which occurs at the transition between the northern and southern Caribbean ecotypes.     

The ecology of lizards on Praslin Island, Seychelles

Ecological studies of five species of lizards were carried out on the island of Praslin, central Seychelles between July and September 1976. Quadrat sampling within four vegetation types revealed distinct habitat preferences between species. Phelsuma sundbergi occurred at highest densities in coastal vegetation, particularly coconuts Cocos nucifera , whilst Phelsuma astriata occurred at highest densities in intermediate forest, particularly in endemic palms such as Lodoicea maldivica. Within each vegetation type, both species preferred particular tree species. In coastal coconuts and Lodoicea in intermediate forest, the two species tended to occur in different sized trees. Calculations of niche breadth indicated greatest values for P. sundbergi in coastal vegetation and for P. astriata in intermediate forest. Both Phelsuma species showed a diurnal pattern of activity with some indication of temporal displacement between species in lowland and intermediate forest. Ailuronyx sechellensis was nocturnal with a relict distribution on Praslin, occurring in the quadrats on only three endemic palm species in intermediate forest. Mabuya sechellensis was by far the commonest and most widespread of the two skink species, with highest density in intermediate forest where it was probably favoured by the high proportion of palm leaf litter. Scelotes gardineri was only recorded in lowland and intermediate forest, where it occurred at low densities. Both species were diurnal, although the latter was never recorded after midday. Intermediate forest had the highest lizard biomass and species diversity whilst eroded land had the lowest. The possible origins and relationships of the two closely related Phelsuma species are discussed, together with the roles that habitat modification, predation, and interspecific competition may play.     

Morphological variation in Gallotia atlantica from the volcanic island of Lanzarote: subspecies designations and recent lava flows

A detailed uni‐ and multivariate analysis of within‐island geographical variation in scalation and body dimensions of the lacertid lizard, Gallotia atlantica, from Lanzarote (and two neighbouring offshore islets) was carried out. Two main morphological groupings were detected: four populations clustered within a putative malpaís group, i.e. from relatively recent volcanic lava fields (seven populations were sampled from these areas), while the other 19 populations (including the three remaining malpaís populations, and those from the offshore islets of Montaña Clara and Alegranza) also clustered together. Thus, while there is a tendency for occupation of malpaís areas to be related to morphological variation, this model does have some inconsistencies. The differentiated malpaís group comprises populations from two geographically isolated areas, one from the central‐western part of the island (Timanfaya) and the other from the north (Malpaís de la Corona). The divergence of these populations is considered to have arisen recently, rather than their being relicts of an ancient, formerly widespread, lineage. The morphological variation partially supports the previous use of two different subspecies to describe the within‐island variation. However, if such a scheme were applied then one of the subspecies would need to encompass populations from the geographically separated southern Timanfaya and Malpaís de la Corona areas, as opposed to just the latter. We reject previous observations that either malpaís individuals in general, or those corresponding to the north‐eastern subspecies, are larger than individuals from other areas. The pattern of morphological variation of G. atlantica within Lanzarote is less pronounced but shows some similarities with patterns of morphological variation in lizards from neighbouring islands. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 395–406.     

The ‘Island Rule’ Acting on Anuran Populations (Bufonidae: Rhinella ornata) of the Southern Hemisphere

Darwin and Wallace, in the mid‐nineteenth century, were the first to document examples of natural selection acting on island dwellers. A century later a pattern of morphological differences among organisms on islands was coined the ‘island rule’, which states that on islands species with small individuals tend toward gigantism and large individuals tend toward dwarfism. Selective pressures such as limited resources and increased intraspecific competition modulate the size of organisms in these environments. Of the several works that have tested vertebrates for adherence to the island rule only two have addressed amphibians. This work is the third record of body size variation of island amphibian populations, and the first for the Southern Hemisphere. The islands investigated were once continuous with mainland, and now are isolated as a result of sea level fluctuations that took place in the Pleistocene and Holocene. This study compared morphometric variation in populations of Rhinella ornata (Bufonidae) occurring on three islands of the Costa Verde to populations on five continental areas in Rio de Janeiro, Brazil. We measured 18 morphometric variables of 177 individuals. There was a shift toward smaller body size (dwarfism) in two of the three island populations studied. We attribute this general pattern to geographic factors, verifying the expression of the island rule in tropical frogs populations (insular dwarfism) operating inversely in relation to those of temperate environments (island gigantism).     

Patterns and causes of morphological population differentiation in the Tenerife skink, Chalcides viridanus

Recent studies indicate that differential selection between mesic and xeric habitats is the most plausible explanation of within-island geographic variation in the Gran Ganarian skink, Chalcides sexlineatus. The island of Tenerife shows mesic/xeric heterogeneity similar to that on Gran Canaria, so we tested the prediction of parallel geographic patterns of morphological population differentiation in the Tenerife skink, Chalcides viridanus. Geographic variation was found to be complex; patterns of differentiation in body dimensions and scalation show evidence of both mosaic and latitudinal facets. Using randomization and regression methods, significant relationships were found between a hypothesized xeric/mesic model of population differentiation and geographic variation in female body dimensions, as well as with substantial proportions of the geographic variation in male and female scalation and, to a lesser extent, body dimensions. Matrix comparisons based on the entire morphological distance matrices show that the patterns of variation are not concordant with an alternative hypothesis of historical secondary contact, or with an isolation-by-distance model. It is argued that a substantial component of the geographic variation in body dimensions and scalation of C. viridanus is due to differential selection along an aridity gradient.     

Evolution and character congruence in some western Indian Ocean Phelsuma: Numerical analysis of biochemistry, shape and scalation

The evolution of five island populations of Green gecko, representing inter- and intra-specific divergence, was studied using biochemical data, scalation and shape. The data were numerically analysed using ordination analyses for the phenetic classification and Wagner trees to hypothesize the phylogeny. These studies revealed three phenetic groups corresponding to three mono-phyletic lineages. The numerical analysis of morphological data agreed with the numerical analysis of biochemical data. It is concluded that the classification based on biochemical affinities differed from the previous classification based on conventional analysis of morphology due to methodological and philosophical differences rather than differences between morphological and biochemical evolution.
The ordination analyses were very congruent between data sets (biochemical, shape, scalation, total) and the Wagner trees were generally congruent between data sets. Some Wagner trees based on scalation data were incongruent. The phenetic and cladistic classifications corresponded to each other but differed from the conventional classification. The phylogenetic analysis of the total data set indicated that the three specific lineages showed relatively equal anagenesis. However, anagenic divergence differed markedly between character types. It is suggested that a range of character types be used when studying anagenesis.     

Chloroplast DNA variation in dactylis glomerata L. taxa endemic to the macaronesian islands

In the Dactylis glomerata infraspecific polyploid grass complex, restriction fragment length polymorphisms (RFLPs) of chloroplast DNA (cpDNA) were studied in diploid and tetraploid populations of several taxa endemic to Macaronesia (Madeira and the Canary islands) and in populations from the African and European continental areas closest to Macaronesia. Two chlorotypes, which differed by a single 290-bp length mutation, were observed in the Macaronesian and the continental populations. Chlorotype I, which is predominant in the whole D. glomerata complex, was found in the majority of continental populations. It was also observed in the most western Macaronesian islands, in the two diploid taxa endemic to the lowland scrub and the high elevation heath of Tenerife, respectively, and in tetraploids endemic to Madeira and La Palma. These island populations were growing under the influence of humid trade winds. Chlorotype II was found in the eastern part of the Archipelago (closer to Africa), which experienced subarid Mediterranean climate conditions, and in very few diploid and tetraploid Mediterranean populations growing at high elevation on the continent. This geographical and climatic distribution of chlorotype variation in Macaronesia is consistent with that reported previously for morphological, allozyme and phenolic variation in the same plant material. Chlorotype II was, however, also observed in tetraploid populations from La Gomera island and in one of the seven tetraploid populations analysed from Madeira, which all showed clearly subtropical characters for morphology, allozymes and phenolic compounds. This result suggests that cpDNA introgression has occurred more than once from the Mediterranean material into the subtropical one and may indicate that colonization between the mainland and islands, or among the islands, probably played a major role in the geographical pattern observed for that marker.     

Testing the ‘island rule’ for a tenebrionid beetle (Coleoptera,Tenebrionidae)

Insular populations and their closest mainland counterparts commonly display body size differences that are considered to fit the island rule, a theoretical framework to explain both dwarfism and gigantism in isolated animal populations. The island rule is used to explain the pattern of change of body size at the inter-specific level. But the model implicitly makes also a prediction for the body size of isolated populations of a single species. It suggests that, for a hypothetical species covering a wide range of island sizes, there exists a specific island size where this species reaches the largest body size. Body size would be small (in relative terms) in the smallest islets of the species range. It would increase with island size, and reach a maximum at some specific island size. However, additional increases from such a specific island size would instead promote body size reduction, and small (in relative terms) body sizes would be found again on the largest islands. The biogeographical patterns predicted by the island rule have been described and analysed for vertebrates only (mainly mammals), but remain largely untested for insects or other invertebrates. I analyse here the pattern of body size variation between seven isolated insular populations of a flightless beetle, Asida planipennis (Coleoptera, Tenebrionidae). This is an endemic species of Mallorca, Menorca and a number of islands and islets in the Balearic archipelago (western Mediterranean). The study covers seven of the 15 known populations (i.e., there are only 15 islands or islets inhabited by the species). The populations studied fit the pattern advanced above and we could, therefore, extrapolate the island rule to a very different kind of organism. However, the small sample size of some of the populations invites some caution at this early stage.     

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).