Island Lizards Research Articles

Bayesian estimation of post-Messinian divergence times in Balearic Island lizards

Phylogenetic relationships and timings of major cladogenesis events are investigated in the Balearic Island lizards Podarcislilfordi and P.pityusensis using 2675bp of mitochondrial and nuclear DNA sequences. Partitioned Bayesian and Maximum Parsimony analyses provided a well-resolved phylogeny with high node-support values. Bayesian MCMC estimation of node dates was investigated by comparing means of posterior distributions from different subsets of the sequence against the most robust analysis which used multiple partitions and allowed for rate heterogeneity among branches under a rate-drift model. Evolutionary rates were systematically underestimated and thus divergence times overestimated when sequences containing lower numbers of variable sites were used (based on ingroup node constraints). The following analyses allowed the best recovery of node times under the constant-rate (i.e., perfect clock) model: (i) all cytochrome b sequence (partitioned by codon position), (ii) cytochrome b (codon position 3 alone), (iii) NADH dehydrogenase (subunits 1 and 2; partitioned by codon position), (iv) cytochrome b and NADH dehydrogenase sequence together (six gene–codon partitions), (v) all unpartitioned sequence, (vi) a full multipartition analysis (nine partitions). Of these, only (iv) and (vi) performed well under the rate-drift model. These findings have significant implications for dating of recent divergence times in other taxa. The earliest P.lilfordi cladogenesis event (divergence of Menorcan populations), occurred before the end of the Pliocene, some 2.6Ma. Subsequent events led to a West Mallorcan lineage (2.0Ma ago), followed 1.2Ma ago by divergence of populations from the southern part of the Cabrera archipelago from a widely-distributed group from north Cabrera, northern and southern Mallorcan islets. Divergence within P.pityusensis is more recent with the main Ibiza and Formentera clades sharing a common ancestor at about 1.0Ma ago. Climatic and sea level changes are likely to have initiated cladogenesis, with lineages making secondary contact during periodic landbridge formation. This oscillating cross-archipelago pattern in which ancient divergence is followed by repeated contact resembles that seen between East-West refugia populations from mainland Europe.

Convergent exaptation and adaptation in solitary island lizards

Independent evolutionary lineages often display similar characteristics in comparable environments. Three kinds of historical hypotheses could explain this convergence. The first is adaptive and evolutionary: nonrandom patterns may result from analogous evolutionary responses to shared conditions. The second explanation is exaptive and ecological: species may be filtered by their suitability for a particular type of environment. The third potential explanation is a null hypothesis of random colonization from a historically nonrandom source pool. Here we demonstrate that both exaptation and adaptation have produced convergent similarity in different size-related characters of solitary island lizards. Large sexual size dimorphism results from adaptive response to solitary existence; uniform, intermediate size results from ecological filtering of potential colonizers. These results demonstrate the existence of deterministic exaptive convergence and suggest that convergent phenomena may require historical explanations that are ecological as well as evolutionary.

Detective Work in the West Indies: Integrating Historical and Experimental Approaches to Study Island Lizard Evolution

ABSTRACT Evolutionary biology is a historical science, like astronomy and geology. Understanding how and why evolution has occurred requires synthesizing multiple lines of inquiry. Historical studies, such as those that estimate phylogenetic trees, can detail the pattern of evolutionary diversification, whereas studies on living species can provide insight into the processes that affect ecological interactions and evolutionary change. The evolutionary radiation of Anolis lizards in the Greater Antilles illustrates the interplay between historical and modern-day approaches and strongly supports the hypothesis that interspecific interactions drive adaptive diversification. Studies of these species also demonstrate the role that manipulative experiments can play in understanding evolutionary phenomena.

Size evolution in island lizards

ABSTRACTAim The island rule, small animal gigantism and large animal dwarfism on islands, is a topic of much recent debate. While size evolution of insular lizards has been widely studied, whether or not they follow the island rule has never been investigated. I examined whether lizards show patterns consistent with the island rule.Location Islands worldwide.Methods I used literature data on the sizes of island–mainland population pairs in 59 species of lizards, spanning the entire size range of the group, and tested whether small insular lizards are larger than their mainland conspecifics and large insular lizards are smaller. I examined the influence of island area, island isolation, and dietary preferences on lizard size evolution.Results Using mean snout–vent length as an index of body size, I found that small lizards on islands become smaller than their mainland conspecifics, while large ones become larger still, opposite to predictions of the island rule. This was especially strong in carnivorous lizards; omnivorous and herbivorous species showed a pattern consistent with the island rule but this result was not statistically significant. No trends consistent with the island rule were found when maximum snout–vent length was used. Island area had, at best, a weak effect on body size. Using maximum snout–vent length as an index of body size resulted in most lizard populations appearing to be dwarfed on islands, but no such pattern was revealed when mean snout–vent length was used as a size index.Main conclusions I suggest that lizard body size is mostly influenced by resource availability, with large size allowing some lizard populations to exploit resources that are unavailable on the mainland. Lizards do not follow the island rule. Maximum snout–vent length may be biased by sampling effort, which should be taken into account when one uses this size index.

Ecology and Reproductive Patterns of the Agamid Lizard Japalura swinhonis on an East Asian Island, with Comments on the Small Clutch Sizes of Island Lizards

I describe the habitat use, diet, and the male and female reproductive cycles of Japalura swinhonis, an oviparous agamid lizard inhabiting Orchid Island, a tropical island off the southeastern coast of Taiwan. Ninety percent of lizards (n=126) were observed on tree trunks or at the forest edge. The diet of J. swinhonis on Orchid Island consisted mostly of hymenopterans (53.33%) and orthopterans (16.67%). The mean snout-vent length (SVL) of adult males was 74.58 (n=89) and that of females was 69.31 (n=37) mm. Females exhibited a long vitellogenic period from November to February, with parturition occurring from March to October. The onset of vitellogenesis did not correlate with the mass of the female fat bodies. Females produced two to five eggs per clutch, and clutch size was not correlated with SVL. Two clutches were recorded during a single year in some individuals. Clutch size in J. swinhonis was compared with that in other Japalura species. Clutch sizes of Japalura species are larger in mainland China than on insular Taiwan. Clutch size is also mainly affected by environmental constraints, and smaller clutch sizes are probably affected by predators on Orchid Island.

Highly polymorphic tetranucleotide microsatellite loci for the eastern Canary Island lizard, Gallotia atlantica

AbstractWe describe 10 polymorphic tetranucleotide microsatellite loci from the eastern Canary Island lacertid lizard, Gallotia atlantica. Loci were isolated from a partial genomic library that had been enriched for AAAG repeat sequence. All loci were highly polymorphic (eight alleles or more) with observed heterozygosities from 0.75 to 1.00. At least four loci were successfully amplified and polymorphic in the Gran Canarian lacertid, Gallotia stehlini. These loci will be used to examine correlations between patterns of gene flow and recent volcanism on the island of Lanzarote.

A hump‐shaped density–area relationship for island lizards

We evaluated the density of Anolis lizards as a function of island area, habitat diversity, and topographic diversity on the Grenadines islands. We found a hump‐shaped density–area relationship. Density at sea level increased with island area until an island was sufficiently large to contain multiple habitat types. Beyond this area threshold, average sea level density declined with island area. Increased species interactions on larger islands may explain the density decline.

Climate, competition, and the coexistence of island lizards

Summary The influence of environmental temperatures and competition combine to determine the distributions of island lizards. Neither a bioenergetic model nor simple models of competition alone can account for the distributions. A mechanistic, bioenergetic model successfully predicts how the abundance of a solitary Anolis lizard species will decline along an island's elevation gradient. However, the abundance trends for sympatric lizards diverge from the predictions of the non‐interactive model. Here we incorporate competition in the bioenergetic model and examine how different forms of competition modify the temperature‐based abundance predictions. Applying the bioenergetic model with competition to an island chain tests whether the model can successfully predict on which islands two lizards species will coexist. Coexistence is restricted to the two largest islands, which the model predicts have substantially greater carrying capacities than the smaller islands. The model successfully predicts that competition prevents species coexistence on the smallest islands. However, the model predicts that the mid‐sized islands are capable of supporting substantial populations of both species. Additional island characteristics, such as habitat diversity, resource availability and temporal disturbance patterns, may prevent coexistence.

Mainland colonization by island lizards

AbstractAim We investigate biogeographic relationships within the lizard genusAnolisDaudin, 1802 to test the hypothesis that the mainland (Central and South American) Norops‐clade species descended from a West IndianAnolisancestor. Previous hypotheses have suggested that close island relatives of mainland Norops species (the CubanAnolis sagreiand JamaicanA. grahamiseries) represent over‐water dispersal from a mainland ancestor. These previous hypotheses predict that theA. sagreiandA. grahamiseries should be phylogenetically nested within a Norops clade whose ancestral geography traces to the mainland. If Norops is West Indian in origin, then West Indian species should span the deepest phylogenetic divergences within the Norops clade.Location Central and South America and West Indian islands.Methods The phylogenetic relationships ofAnolislizards are reconstructed from aligned DNA sequences using both parsimony and Bayesian approaches. Hypotheses are tested in two ways: (1) by reconstructing the ancestral geographic location for the Norops clade usingPagel & Lutzoni's (2002)Bayesian approach, and (2) by testing alternative topological arrangements via Wilcoxon Signed‐Ranks tests (Templeton, 1983) and Shimodaira–Hasegawa tests (Shimodaira & Hasegawa, 1999).Results Our evidence supports an origin of mainland Norops anoles from a West Indian ancestor. A West Indian ancestor to the Norops clade is statistically supported, and alternatives to the biogeographic pattern [Cuban (Jamaican, Mainland)] are statistically rejected by Shimodaira–Hasegawa tests, although not by Wilcoxon Signed‐Ranks tests.Main conclusions Our data support the hypothesis of a West Indian origin for mainland Norops. This result contradicts previous hypotheses and suggests that island forms may be an important source for mainland biodiversity.

Ocean currents mediate evolution in island lizards.

Islands are considered to be natural laboratories in which to examine evolution because of the implicit assumption that limited gene flow allows tests of evolutionary processes in isolated replicates. Here we show that this well-accepted idea requires re-examination. Island inundation during hurricanes can have devastating effects on lizard populations in the Bahamas. After severe storms, islands may be recolonized by over-water dispersal of lizards from neighbouring islands. High levels of gene flow may homogenize genes responsible for divergence, and are widely viewed as a constraining force on evolution. Ultimately, the magnitude of gene flow determines the extent to which populations diverge from one another, and whether or not they eventually form new species. We show that patterns of gene flow among island populations of Anolis lizards are best explained by prevailing ocean currents, and that over-water dispersal has evolutionary consequences. Across islands, divergence in fitness-related morphology decreases with increasing gene flow. Results suggest that over-water dispersal after hurricanes constrains adaptive diversification in Anolis lizards, and that it may have an important but previously undocumented role in this classical example of adaptive radiation.

Status and relationships of the extinct giant Canary Island lizard Gallotia goliath (Reptilia: Lacertidae), assessed using ancient mtDNA from its mummified remains

Ancient mitochondrial DNA sequences (378 base pairs of cytochrome b and 368 of 12S rRNA) extracted from a mummified extinct giant lizard, Gallotia goliath, from eastern Tenerife, Canary Islands, were used to assess the species status and relationship of this form within the genus. G. goliath is clearly a member of the G. simonyi group of the western Canary islands (Tenerife, La Gomera, El Hierro and La Palma) and is not closely related to the giant G. stehlini of Gran Canaria. Contrary to recent opinion, it is phylogenetically distinct, within the G. simonyi group, from the extant G. simonyi of El Hierro and also from the recently discovered live G. gomerana on La Gomera and from G. intermedia in north-western Tenerife. It may be the sister taxon of either all the other members of the G. simonyi group or of G. intermedia. The phylogenetic distinctness of G. goliath makes Tenerife unique among oceanic islands in having had one giant and two medium-sized lizard species that were probably substantially herbivorous, the others being G. intermedia and G. galloti. Gallotia shows great community differences on other islands in the Canaries, two having a single small species, one a single giant, and three a giant and a medium-sized form.

Lizards as pollinators and seed dispersers: an island phenomenon

Although it is well established that many insects, birds and mammals serve as important pollinators and seed dispersers of flowering plants, the role of lizards in these processes has traditionally been considered as rare and less important. However, recent work shows both that their role as mutualistic agents has been underestimated and also reveals a striking pattern – that pollination and seed dispersal by lizards is most common on islands. We argue that this island phenomenon occurs because island lizards reach very high densities (density compensation) and experience a lower predation risk than do those on the mainland and, consequently, can expand their diet to include nectar, pollen and fruit. Although further empirical evidence is needed to confirm this explanation, such relationships could be ideal systems with which to study fundamental ecological problems, such as niche shifts, ecological release and competition.

Reproductive Characteristics of the Island Lacertid Lizard Podarcis lilfordi

We report reproductive characteristics (clutch frequency, clutch size, egg and hatchling sizes) of the island lizard Podarcis lilfordi, studied in the laboratory. Individual females produced two or three consecutive clutches, composed of 2-4 eggs with an average mass of 0.63 g. Both clutch size and average egg mass were independent of female body length, and did not differ between the first and subsequent annual clutches. Among-clutch differences in egg mass were negatively correlated with clutch size, and this trade-off is independent of female size. Larger clutches were also composed of less elongated (i.e, rounder) eggs than are smaller clutches, suggesting that limitations posed by the females' body volume, rather than by restrictions of energy availability, induce the phenotypic trade-off between egg size and numbers. Egg shape was also related to female size: larger females laid shorter but wider eggs than smaller individuals, suggesting that egg width is constrained by the width of the female's pelvic girdle. Relative to other Eu- ropean lacertids with similar adult female body length, P lilfordi produces clutches that are composed of very few, but extremely large eggs. Comparative studies of life histories explore patterns of covariation among life history char- acteristics and search for relationships between trait complexes and ecological conditions. Many studies address these issues in reptiles, espe- cially lizards (e.g., Tinkle, 1969; Tinkle et al., 1970; Dunham and Miles, 1985; Dunham et al.,

Reproductive Characteristics of the Lacertid LizardPodarcis atrata

Abstract We report reproductive characteristics (timing of sexual maturity, clutch frequency, clutch size, egg and hatchling sizes) of the Island Lizard Podarcis atrata. Reproductive performance was related to female size. The larger females initiate reproductive activities early in the season and produce two to four clutches annually, whereas the smaller individuals postpone reproduction until the season is well advanced and lay only a single clutch. Clutch size increased with female length and was slightly lower for clutches laid during June–July than for those produced during May. Among-clutch differences in egg mass were negatively correlated with clutch size, and this relationship is independent of female size. Larger clutches are also composed of less elongated (i.e., rounder) eggs than are smaller clutches, suggesting that the phenotypic trade-off between egg size and numbers is induced by limitations posed by the females' body volume, rather than by restrictions of energy availability. Comparison ...

Mitochondrial DNA evolution and population history of the Tenerife skink Chalcides viridanus

Recent studies of island lizards have suggested that historical vicariance as a result of volcanism may have played an important role in shaping patterns of within-island genetic diversity. The skink, Chalcides viridanus, shows variation in morphology within the volcanic island of Tenerife. Two mitochondrial DNA (mtDNA) fragments (from the 12S and 16S rRNA regions) were sequenced in individuals from 17 sites to evaluate the relationship between current phylogeography and the geological history of the island. Three main clades were detected. The two most basal clades were restricted to areas representing the ancient precursor islands of Teno and Anaga in the northwest and northeast of Tenerife, respectively. The third clade showed a widespread geographical distribution and provided evidence of a recent rapid expansion after a bottleneck. Within-island cladogenesis appears to have taken place during a recent period of volcanic activity and long after the ancient islands had been united by the eruptions that led to the formation of the Canadas edifice. Evidence of similar biogeographical histories are found in other species in the Canary archipelago, supporting the volcanism scenario as a potentially widespread cause of within-island differentiation in reptiles.

Endemism, gigantism and extinction in island lizards: the genus Gallotia on the Canary Islands

Endemism, gigantism and extinction in island lizards: the genus Gallotia on the Canary Islands

Endemism, gigantism and extinction in island lizards: the genus Gallotia on the Canary Islands

AbstractIn the Canary Islands five extant and two extinct giant lacertid lizards belonging to the endemic genus Gallotia are known. A comparative study of the living and subfossil specimens from the Western Canary Islands demonstrates that the extinct giant species Gallotia goliath and Gallotia maxima are synonymous with the living Gallotia simonyi. Characters formerly used in the diagnosis of the extinct species and subspecies fall within the range of intraspecific variation (ontogenetic and individual) of the living species. The only significant difference between living and subfossil populations of G. simonyi is size, and there is strong evidence to suggest that the reduction in size in living populations reflects shorter life expectancy, a factor that should be taken into account in the current conservation projects on this species.

Contingency and determinism in replicated adaptive radiations of island lizards

The vagaries of history lead to the prediction that repeated instances of evolutionary diversification will lead to disparate outcomes even if starting conditions are similar. We tested this proposition by examining the evolutionary radiation of Anolis lizards on the four islands of the Greater Antilles. Morphometric analyses indicate that the same set of habitat specialists, termed ecomorphs, occurs on all four islands. Although these similar assemblages could result from a single evolutionary origin of each ecomorph, followed by dispersal or vicariance, phylogenetic analysis indicates that the ecomorphs originated independently on each island. Thus, adaptive radiation in similar environments can overcome historical contingencies to produce strikingly similar evolutionary outcomes.

For Island Lizards, History Repeats Itself

If one could start with similar organisms in similar environments, would evolution repeat itself to produce the same results? On page 2115, evolutionary ecologists report that anole lizards on four different islands of the Greater Antilles independently evolved into strikingly similar creatures. Although examples of convergent evolution, such as wings on bats and birds, are well known, researchers say these lizards have evolved a remarkable degree of similarity on all four of the islands.

Species patterns: evolution's competitive edge.

Phylogenetic analyses of island lizard faunas suggest that patterns in species distributions and body size evolution are the result of resource competition.