Bird–flower interactions in the Macaronesian islands

Aims Several bird‐pollinated or ornithophilous flowers are present on the Macaronesian archipelagos, the Canary Islands and Madeira, but absent from nearby NW Africa and Europe. In Macaronesia, no specialist nectar‐feeding birds are found, but several generalist passerine bird species visit flowers for nectar. Two hypotheses attempt to explain the origin and evolution of ornithophily in the Macaronesian flora. According to ‘the island de novo hypothesis’, bird‐flowers evolved from mainland insect‐pollinated ancestors after island colonization. Alternatively, ancestors of the ornithophilous Macaronesian plant species evolved bird‐flowers before reaching the islands (‘the relict hypothesis’). In this study we first compile information of Macaronesian bird–flower interactions from the literature and our own field observations. Secondly, we discuss the two hypotheses of origin of ornithophily in the light of evidence from recent molecular plant phylogenies, palaeontology, historical biogeography of the African avifauna and flora, and present‐day ecological patterns. Location Madeira and Canary Islands. Results At least eleven endemic Macaronesian plant species from six genera have typical ornithophilous floral traits. These genera are: Canarina and Musschia (Campanulaceae), Isoplexis (Scrophulariaceae), Echium (Boraginaceae), Lotus (Fabaceae) and Lavatera (Malvaceae). These lineages have clear affinities to the Mediterranean region, except for Canarina whose closest relatives grow in East African mountains. Six generalist passerine bird species of Sylvia, Phylloscopus (Sylviidae), Serinus (Fringillidae) and Parus (Paridae) visit this flora for nectar. Main conclusion We suggest that the origin and evolution of ornithophilous traits in these plant species took place mostly in mainland areas prior to island colonization. In Canarina and Lavatera, it is well supported that ornithophily is a relict condition, which originated in mainland areas possibly in association with specialist nectar‐feeding birds. For the remaining plant species except Echium wildpretii bird floral traits probably also are a relict condition. These species may be derived from ancestors, which were visited by specialist nectar‐feeding birds during geological periods when the Mediterranean and the Ethiopian vegetation were intermingled in mainland Africa. Probably, these mainland ancestors went extinct due to severe climatic fluctuations, while their Macaronesian descendants survived in ‘refuge’ on the islands. Finally, the island de novo hypothesis may explain the evolution of a mixed bird/insect‐pollination system in the neo‐endemic red‐flowered Echium wildpretii.     

The origin of bird pollination in Macaronesian Lotus (Loteae, Leguminosae)

The four red-flowered, apparently bird-pollinated Lotus species from the Canary Islands have previously been classified in their own genus, Rhyncholotus. Currently, they are considered as a separate section within genus Lotus, distinct from other herbaceous Canarian congeners which are yellow-flowered and bee-pollinated. A combined analysis of four nuclear regions (including ITS and three homologues of CYCLOIDEA) and three plastid regions (CYB6, matK and trnH-psbA) nests the four bird-pollinated species within a single extant species of bee-pollinated Lotus (L. sessilifolius), in a very extreme example of species paraphyly. Therefore, our data compellingly support the hypothesis that the Macaronesian Lotus species with a bird pollination syndrome are recently derived from entomophilous ancestors. Calibration of the phylogenetic trees using geological age estimates of the most recent islands (La Palma and El Hierro) together with oldest ages of Fuerteventura indicates that bird pollination evolved ca. 1.7 Ma in the Canarian Lotus. These four bird-pollinated species share a most recent common ancestor (MRCA) with L. sessilifolius that dates to about 2.2 Ma. Our analyses further suggest that the evolution of the bird pollination syndrome was likely triggered by the availability of new niches in La Palma and Tenerife as a result of recent volcanic activity.     

Bird-pollinated Macaronesian Lotus (Leguminosae) evolved within a group of entomophilous ancestors with post-anthesis flower color change

We analyzed the evolution of red/orange flowers in four putatively bird-pollinated species of Macaronesian Lotus, with the aim of investigating whether this floral trait evolved from a similar trait found in some entomophilous Lotus species, namely the ability to modify flower color to red after anthesis. First, we mapped the ability to modify flower color in this group on a well-resolved and densely sampled phylogenetic tree of the Macaronesian Lotus. Secondly, we determined differences in light reflectance and pigment composition between petals of (1) prechange and postchange flowers in bee-pollinated species and (2) between bee and putatively bird-pollinated species. Post-anthesis flower color change evolved three times within Macaronesian Lotus, and putatively bird-pollinated species evolved within a clade with this ability to change flower color to red after anthesis. The evolutionary transition to red/orange flowers in the putatively bird-pollinated species involved biochemical changes similar to those of the developmental transition to red postchange flowers. In both cases there are changes in the composition of flavonols and anthocyanidins within the same metabolic pathways, especially in the cyanidin branch of pigment production, but not the activation or inactivation of additional branches of this pathway. Post-anthesis color change in Lotus, from yellow to red, is thought to be an adaptation to reduce bee visits to already pollinated flowers. Our results are consistent with the hypothesis that constitutive red coloration for bird-pollination evolved from facultative red flower color change in Lotus. As red post-anthesis coloration is widespread in plants, this may possibly represent a widespread exaptive mechanism for the evolution of bird pollination.     

Patterns of ecomorphological convergence among mainland and island Anolis lizards

Differing selective pressures on islands versus the mainland may produce alternative evolutionary outcomes among closely related lineages. Conversely, lineages may be constrained to produce similar outcomes in different mainland and island environments, or mainland and island environments may not differ significantly. Among the best‐studied island radiations are Caribbean Anolis lizards. Distinct morphotypes, or ‘ecomorphs’, have been described, and the same ecomorphs have evolved independently on each Greater Antillean island. The mainland Anolis radiation has received much less attention. We use a large morphological data set and a novel phylogenetic hypothesis to show that mainland Anolis did not evolve the same morphotypes as island Anolis, despite some island species being more closely related to mainland species than to island species that share their morphotype. A maximum of four of the six Caribbean ecomorphs were found to exist on the mainland, and just 15 of 123 mainland species are assignable to a Caribbean ecomorph. This result was insensitive to differing taxon samples and alternative phylogenetic hypotheses. Mainland convergence to a Caribbean ecomorph occurs only among species assigned to the grass‐bush ecomorph. Thus, the ecomorphs that have evolved convergently multiple times in the Caribbean have not evolved in parallel on the mainland. These results are consistent with the hypothesis that mainland and island environments offer different selective pressures. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 852–859.     

Lobelia vivaldii (Campanulaceae: Lobelioideae), a remarkable new species of sect. Tylomium from Isla de Mona,Puerto rico

A new species ofLobelia (Campanulaceae: Lobelioideae) is described from Isla de Mona, a Caribbean island not previously known to harbor the genus. The small woody rosette-plants were collected in 1988 and 1992 at the northeastern corner of the island, where they grew from crevices in the vertical limestone cliffs, approximately 60 m above the sea. The new species,Lobelia vivaldii, belongs to sect.Tylomium, a group of approximately 36 suffruticose and woody species endemic to the Caribbean basin. Within that section, it is most similar to and apparently derived fromL. cirsiifolia, a less woody rain forest species found at higher elevations on several islands in the Lesser Antilles.     

Variation in dispersability among mainland and island populations of three wind dispersed plant species

Reduced dispersability of species living on islands relative to mainland has been documented in both plants and animals. One evolutionary scenario explains this trend by strong selection against dispersal, once the species has reached the island, to reduce dispersal out to sea. In this study, we compare the dispersal ability of three wind dispersed plant species (Cirsium arvense, Epilobium angustifolium, and E. hirsutum) from populations on mainland and three islands. Dispersal ability was estimated directly as drop time of diaspores, and indirectly using a morphological measure relating the weight of the diaspore to the size of the pappus (Cirsium) or seed hairs (Epilobium). Positive correlation between the morphological measure of dispersal ability and drop time of diaspores were found for all study species. Dispersal ability varied significantly among mainland and islands, and among species. C. arvense showed a significant reduction in dispersal ability on islands compared to mainland, whereas the reverse was found for the two Epilobium species. Overall Epilobium diaspores had a 2–4 times higher dispersability than C. arvense, indicating that degree of isolation of islands vary among study species. Significant differences in dispersability among plants within populations were detected in all species suggesting that this trait may have a genetic component.     

Floral scent in bird- and beetle-pollinated Protea species (Proteaceae): Chemistry,emission rates and function

Evolutionary shifts between pollination systems are often accompanied by modifications of floral traits, including olfactory cues. We investigated the implications of a shift from passerine bird to beetle pollination in Protea for floral scent chemistry, and also explored the functional significance of Protea scent for pollinator attraction. Using headspace sampling and gas chromatography–mass spectrometry, we found distinct differences in the emission rates and chemical composition of floral scents between eight bird- and four beetle-pollinated species. The amount of scent emitted from inflorescences of beetle-pollinated species was, on average, about 10-fold greater than that of bird-pollinated species. Floral scent of bird-pollinated species consists mainly of small amounts of “green-leaf volatiles” and benzenoid compounds, including benzaldehyde, anisole and benzyl alcohol. The floral scent of beetle-pollinated species is dominated by emissions of linalool, a wide variety of other monoterpenes and the benzenoid methyl benzoate, which imparts a fruity odour to the human nose. The number of compounds recorded in the scent of beetle-pollinated species was, on average, greater than in bird-pollinated species (45 versus 29 compounds, respectively). Choice experiments using a Y-maze showed that a primary pollinator of Protea species, the cetoniine beetle Atrichelaphinis tigrina, strongly preferred the scent of inflorescences of the beetle-pollinated Protea simplex over those of the bird-pollinated sympatric congener, Protea roupelliae. This study shows that a shift from passerine bird- to insect-pollination can be associated with marked up-regulation and compositional changes in floral scent emissions.     

The impact of insularity on the thermoregulation of a Mediterranean lizard

The overall biology of ectotherms is strongly affected by the thermal quality of the environment. The particular conditions prevailing on islands have a strong effect on numerous features of animal life. In this study we compared mainland and island populations of the lizard Lacerta trilineata and hypothesized that insularity would affect the thermoregulatory strategy. Continental habitats were of lower thermal quality, experiencing more intense fluctuations and had higher values of operative temperatures. Nevertheless mainland lizards selected for higher body temperatures in the lab and showed more effective thermoregulation during summer than their island peers. Lizards achieved similar body temperatures in the field in both types of habitat, underlining the importance of predation as a potential factor to mainland lizards that failed to reach their higher thermal preferences. Both island and mainland populations of L. trilineata have been adapted to their thermal environment, supporting the labile view on the evolution of thermal physiology for this species.     

Evolution and island endemism of morphologically cryptic Baetis and Cloeon species (Ephemeroptera,Baetidae) on the Canary Islands and Madeira

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Spiders on a Hot Volcanic Roof: Colonisation Pathways and Phylogeography of the Canary Islands Endemic Trap-Door Spider Titanidiops canariensis (Araneae,Idiopidae)

Studies conducted on volcanic islands have greatly contributed to our current understanding of how organisms diversify. The Canary Islands archipelago, located northwest of the coast of northern Africa, harbours a large number of endemic taxa. Because of their low vagility, mygalomorph spiders are usually absent from oceanic islands. The spider Titanidiops canariensis, which inhabits the easternmost islands of the archipelago, constitutes an exception to this rule. Here, we use a multi-locus approach that combines three mitochondrial and four nuclear genes to investigate the origins and phylogeography of this remarkable trap-door spider. We provide a timeframe for the colonisation of the Canary Islands using two alternative approaches: concatenation and species tree inference in a Bayesian relaxed clock framework. Additionally, we investigate the existence of cryptic species on the islands by means of a Bayesian multi-locus species delimitation method. Our results indicate that T. canariensis colonised the Canary Islands once, most likely during the Miocene, although discrepancies between the timeframes from different approaches make the exact timing uncertain. A complex evolutionary history for the species in the archipelago is revealed, which involves two independent colonisations of Fuerteventura from the ancestral range of T. canariensis in northern Lanzarote and a possible back colonisation of southern Lanzarote. The data further corroborate a previously proposed volcanic refugium, highlighting the impact of the dynamic volcanic history of the island on the phylogeographic patterns of the endemic taxa. T. canariensis includes at least two different species, one inhabiting the Jandia peninsula and central Fuerteventura and one spanning from central Fuerteventura to Lanzarote. Our data suggest that the extant northern African Titanidiops lineages may have expanded to the region after the islands were colonised and, hence, are not the source of colonisation. In addition, T. maroccanus may harbour several cryptic species.     

Parasite island syndromes in the context of nidicolous ectoparasites: Fleas (Insecta: Siphonaptera) in wild passerine birds from Azores Archipelago

Island syndrome, previously established for isolation process of insular vertebrates' populations, have been adapted to insular parasites communities, termed parasite island syndromes. In this work, were studied for the first time the insular syndromes for nidicolous ectoparasites of the bird species, Turdus merula, Sylvia atricapilla, Fringilla coelebs and Erithacus rubecula from Azores and the mainland Portugal. Flea species were only recorded on Azorean birds, namely Dasypsyllus gallinulae and Ctenocephalides felis felis, known as not host-specific parasites. In the absence of shared flea species between mainland and islands birds, a comparison among our fleas prevalence to Azores Islands and mainland fleas prevalence, recorded to others European studies, showed that Azorean host populations undergo higher prevalence than the mainland one. This result was consistent with parasite island syndromes predictions recorded to ectoparasites, hippoboscid flies and chewing lice, that fleas have higher prevalence on the Azores Islands compared to mainland Portugal. However, our results provide a new perspective to parasite island syndromes assumptions, namely in the context of nidicolous ectoparasites that spend only brief periods on the hosts' body.     

Bermuda as an Evolutionary Life Raft for an Ancient Lineage of Endangered Lizards

Oceanic islands are well known for harboring diverse species assemblages and are frequently the basis of research on adaptive radiation and neoendemism. However, a commonly overlooked role of some islands is their function in preserving ancient lineages that have become extinct everywhere else (paleoendemism). The island archipelago of Bermuda is home to a single species of extant terrestrial vertebrate, the endemic skink Plestiodon (formerly Eumeces) longirostris. The presence of this species is surprising because Bermuda is an isolated, relatively young oceanic island approximately 1000 km from the eastern United States. Here, we apply Bayesian phylogenetic analyses using a relaxed molecular clock to demonstrate that the island of Bermuda, although no older than two million years, is home to the only extant representative of one of the earliest mainland North American Plestiodon lineages, which diverged from its closest living relatives 11.5 to 19.8 million years ago. This implies that, within a short geological time frame, mainland North American ancestors of P. longirostris colonized the recently emergent Bermuda and the entire lineage subsequently vanished from the mainland. Thus, our analyses reveal that Bermuda is an example of a “life raft” preserving millions of years of unique evolutionary history, now at the brink of extinction. Threats such as habitat destruction, littering, and non-native species have severely reduced the population size of this highly endangered lizard.     

Evidence for rapid faunal changes on islands in a man-made lake

Summary Few studies of island biogeography have been made on islands in which the time of insularization is precisely known. We tested the effects of island formation on ant species diversity in a man-made lake in South Africa, to determine whether island effects are detectable after only 16 years of insularization. The number of ant species observed at trap-line censuses on islands was significantly correlated with island size (r=0.608; P<0.05) and ant species diversity was generally low compared with similar mainland habitats. Mean species number for all islands, including landbridge islands, was 5.5±3.3 species, and on mainland sites was 7.9±2.85 species. Island effects were more marked on islands <20 ha, which had a mean of 3.3±2.5 species per island. Species number on islands was inversely related to densities of the aggressive Anoplolepis custodiens and A. steingroeveri. These two species were only patchily distributed on mainlands, but these ants were nearly ubiquitous on small islands. Several lines of evidence suggest that this single species domination may be responsible for island effects. Island sites also differed in the number of ant species in different trophic groupings, tending to have fewer granivorous species than the mainland sites, but species in other diet groups were similar in both island and mainland habitats. We conclude that there have been marked changes in the ant faunas on islands smaller than 20 ha apparently due to changes in abundance of the dominant ant species. However, the causes of these changes are unknown.     

Evolutionary assembly of island faunas reverses the classic island–mainland richness difference in Anolis lizards

Aim Islands are widely considered to be species depauperate relative to mainlands but, somewhat paradoxically, are also host to many striking adaptive radiations. Here, focusing on Anolis lizards, we investigate if cladogenetic processes can reconcile these observations by determining if in situ speciation can reduce, or even reverse, the classical island–mainland richness discrepancy. Location Caribbean islands and the Neotropical mainland. Methods We constructed range maps for 203 mainland anoles from museum records and evaluated whether geographical area could account for differences in species richness between island and mainland anole faunas. We compared the island species–area relationship with total mainland anole diversity and with the richness of island‐sized mainland areas. We evaluated the role of climate in the observed differences by using Bayesian model averaging to predict island richness based on the mainland climate–richness relationship. Lastly, we used a published phylogeny and stochastic mapping of ancestral states to determine if speciation rate was greater on islands, after accounting for differences in geographical area. Results Islands dominated by in situ speciation had, on average, significantly more species than similarly sized mainland regions, but islands where in situ speciation has not occurred were species depauperate relative to mainland areas. Results were similar at the scale of the entire mainland, although marginally non‐significant. These findings held even after accounting for climate. Speciation has not been faster on islands; instead, when extinction was assumed to be low, speciation rate varied consistently with geographical area. When extinction was high, there was some evidence that mainland speciation was faster than expected based on area. Main conclusions Our results indicate that evolutionary assembly of island faunas can reverse the general pattern of reduced species richness on islands relative to mainlands.     

Repeated range expansion and niche shift in a volcanic hotspot archipelago: Radiation of C4 Hawaiian Euphorbia subgenus Chamaesyce (Euphorbiaceae)

Woody perennial plants on islands have repeatedly evolved from herbaceous mainland ancestors. Although the majority of species in Euphorbia subgenus Chamaesyce section Anisophyllum (Euphorbiaceae) are small and herbaceous, a clade of 16 woody species diversified on the Hawaiian Islands. They are found in a broad range of habitats, including the only known C₄ plants adapted to wet forest understories. We investigate the history of island colonization and habitat shift in this group. We sampled 153 individuals in 15 of the 16 native species of Hawaiian Euphorbia on six major Hawaiian Islands, plus 11 New World close relatives, to elucidate the biogeographic movement of this lineage within the Hawaiian island chain. We used a concatenated chloroplast DNA data set of more than eight kilobases in aligned length and applied maximum likelihood and Bayesian inference for phylogenetic reconstruction. Age and phylogeographic patterns were co‐estimated using BEAST. In addition, we used nuclear ribosomal ITS and the low‐copy genes LEAFY and G3pdhC to investigate the reticulate relationships within this radiation. Hawaiian Euphorbia first arrived on Kaua`i or Ni`ihau ca. 5 million years ago and subsequently diverged into 16 named species with extensive reticulation. During this process Hawaiian Euphorbia dispersed from older to younger islands through open vegetation that is disturbance‐prone. Species that occur under closed vegetation evolved in situ from open vegetation of the same island and are only found on the two oldest islands of Kaua`i and O`ahu. The biogeographic history of Hawaiian Euphorbia supports a progression rule with within‐island shifts from open to closed vegetation.     

Patterns of Genetic and Reproductive Traits Differentiation in Mainland vs. Corsican Populations of Bumblebees

Populations on islands often exhibit lower levels of genetic variation and ecomorphological divergence compared to their mainland relatives. While phenotypic differentiation in characters, such as size or shape among insular organisms, has been well studied, insular differentiation in quantitative reproductive traits involved in chemical communication has received very little attention to date. Here, we investigated the impact of insularity on two syntopic bumblebee species pairs: one including species that are phylogenetically related (Bombus terrestris and B. lucorum), and the other including species that interact ecologically (B. terrestris and its specific nest inquiline B. vestalis). For each bumblebee species, we characterized the patterns of variation and differentiation of insular (Corsican) vs. mainland (European) populations (i) with four genes (nuclear and mitochondrial, 3781 bp) and (ii) in the chemical composition of male marking secretions (MMS), a key trait for mate attraction in bumblebees, by gas chromatography-mass spectrometry (GC-MS). Our results provide evidence for genetic differentiation in Corsican bumblebees and show that, contrary to theoretical expectations, island populations of bumblebees exhibit levels of genetic variation similar to the mainland populations. Likewise, our comparative chemical analyses of MMS indicate that Corsican populations of bumblebees are significantly differentiated from the mainland yet they hold comparative levels of within-population MMS variability compared to the mainland. Therefore, insularity has led Corsican populations to diverge both genetically and chemically from their mainland relatives, presumably through genetic drift, but without a decrease of genetic diversity in island populations. We hypothesize that MMS divergence in Corsican bumblebees was driven by a persistent lack of gene flow with mainland populations and reinforced by the preference of Corsican females for sympatric (Corsican) MMS. The impoverished Corsican bumblebee fauna has not led to relaxation of stabilizing selection on MMS but to consistent differentiation chemical reproductive traits on the island.     

Genetic differentiation of continental and island populations of Bombus terrestris (Hymenoptera: Apidae) in Europe

Ten microsatellite loci and a partial sequence of the COII mitochondrial gene were used to investigate genetic differentiation in B. terrestris, a bumble bee of interest for its high-value crop pollination. The analysis included eight populations from the European continent, five from Mediterranean islands (six subspecies altogether) and one from Tenerife (initially described as a colour form of B. terrestris but recently considered as a separate species, B. canariensis). Eight of the 10 microsatellite loci displayed high levels of polymorphism in most populations. In B. terrestris populations, the total number of alleles detected per polymorphic locus ranged from 3 to 16, with observed allelic diversity from 3.8 ± 0.5 to 6.5 ± 1.4 and average calculated heterozygosities from 0.41 ± 0.09 to 0.65 ± 0.07. B. canariensis showed a significantly lower average calculated heterozygosity (0.12 ± 0.08) and observed allelic diversity (1.5 ± 0.04) as compared to both continental and island populations of B. terrestris. No significant differentiation was found among populations of B. terrestris from the European continent. In contrast, island populations were all significantly and most of them strongly differentiated from continental populations. B. terrestris mitochondrial DNA is characterized by a low nucleotide diversity: 0.18%± 0.07%, 0.20%± 0.04% and 0.27%± 0.04% for the continental populations, the island populations and all populations together, respectively. The only haplotype found in the Tenerife population differs by a single nucleotide substitution from the most common continental haplotype of B. terrestris. This situation, identical to that of Tyrrhenian islands populations and quite different from that of B. lucorum (15 substitutions between terrestris and lucorum mtDNA) casts doubts on the species status of B. canariensis. The large genetic distance between the Tenerife and B. terrestris populations estimated from microsatellite data result, most probably, from a severe bottleneck in the Canary island population. Microsatellite and mitochondrial DNA data call for the protection of the island populations of B. terrestris against importation of bumble bees of foreign origin which are used as crop pollinators.     

ALLOZYME DIFFERENTIATION AND GENETIC STRUCTURE IN ISLAND AND MAINLAND JAPANESE POPULATIONS OF CAMPANULA PUNCTATA (CAMPANULACEAE)

Allozyme variation was investigated in 17 Japanese populations of Campanula punctata, ten from the Izu Islands and seven in the mainland (Honshu). The data indicate that there are two groups, a mainland group and an island one, and that the systematically problematic Oshima Island (northernmost Izu island) populations are closely related to those of the other islands. Nei's genetic identity values among islands and among mainland populations were 0.95 and 0.97, respectively, while the value between island and mainland populations was 0.84, suggesting that the island populations are an independent species. Total genetic variation was nearly the same among island and mainland populations. However, the apportionment of variation within and among populations was considerably different; 14% of gene diversity exists among mainland populations, while 31% of the diversity exists among island populations. Mean outcrossing rates of self-incompatible mainland and Oshima populations are 0.62–0.79, supporting xenogamy; those in self-compatible island populations are 0.37–0.57 in the northern islands, indicating a mixed mating system, and 0.16–0.25 in southern ones, indicating dominant inbreeding. Total genetic diversity in each island population decreased with distance from the mainland. Genetic and geological data suggest that the ancestors of insular populations were founded on northern islands in a relatively ancient period and that they dispersed progressively to the southern ones. Chromosome number (2n = 34) and isozyme numbers indicate gene duplications in this species, which suggests it is an ancient polyploid.     

Phylogenetic relationships of the Chalcides skink species from the Chafarinas Islands with those from mainland North Africa

Species whose geographical distribution encompasses both mainland and island populations provide ideal systems for examining potential isolation and genetic divergence. This has also interest from a conservationist point of view, as it is important to protect “evolutionarily significant units”. We report a phylogenetic mitochondrial DNA analysis comparing the populations of the three Chalcides skink species from the Chafarinas Islands (NW Africa) with specimens of the same species from the nearest mainland. We tested for the potential genetic distinctiveness of the skink island populations. However, the results of the comparison of the genetic variability of the mitochondrial coding gene cytb were conclusive showing that the genetic divergence between continental and island Chalcides species was either non-existent or extremely low. We discuss how genetic divergence may be lower than expected if separation time of the islands with the mainland has not been long enough or if the island skink populations were currently communicated via ocean rafting with individuals coming from the mainland ones.     

Convergence in reduced body size,head size,and blood glucose in three island reptiles

Many oceanic islands harbor diverse species that differ markedly from their mainland relatives with respect to morphology, behavior, and physiology. A particularly common morphological change exhibited by a wide range of species on islands worldwide involves either a reduction in body size, termed island dwarfism, or an increase in body size, termed island gigantism. While numerous instances of dwarfism and gigantism have been well documented, documentation of other morphological changes on islands remains limited. Furthermore, we lack a basic understanding of the physiological mechanisms that underlie these changes, and whether they are convergent. A major hypothesis for the repeated evolution of dwarfism posits selection for smaller, more efficient body sizes in the context of low resource availability. Under this hypothesis, we would expect the physiological mechanisms known to be downregulated in model organisms exhibiting small body sizes due to dietary restriction or artificial selection would also be downregulated in wild species exhibiting dwarfism on islands. We measured body size, relative head size, and circulating blood glucose in three species of reptiles—two snakes and one lizard—in the California Channel Islands relative to mainland populations. Collating data from 6 years of study, we found that relative to mainland population the island populations had smaller body size (i.e., island dwarfism), smaller head sizes relative to body size, and lower levels of blood glucose, although with some variation by sex and year. These findings suggest that the island populations of these three species have independently evolved convergent physiological changes (lower glucose set point) corresponding to convergent changes in morphology that are consistent with a scenario of reduced resource availability and/or changes in prey size on the islands. This provides a powerful system to further investigate ecological, physiological, and genetic variables to elucidate the mechanisms underlying convergent changes in life history on islands.