Population structure and conservation implications for the loggerhead sea turtle of the Cape Verde Islands

The Cape Verde Islands harbour the second largest nesting aggregation of the globally endangered loggerhead sea turtle in the Atlantic. To characterize the unknown genetic structure, connectivity, and demographic history of this population, we sequenced a segment of the mitochondrial (mt) DNA control region (380 bp, n = 186) and genotyped 12 microsatellite loci (n = 128) in females nesting at three islands of Cape Verde. No genetic differentiation in either haplotype or allele frequencies was found among the islands (mtDNA F _ST = 0.001, P > 0.02; nDNA F _ST = 0.001, P > 0.126). However, population pairwise comparisons of the mtDNA data revealed significant differences between Cape Verde and all previously sequenced Atlantic and Mediterranean rookeries (F _ST = 0.745; P < 0.000). Results of a mixed stock analysis of mtDNA data from 10 published oceanic feeding grounds showed that feeding grounds of the Madeira, Azores, and the Canary Islands, in the Atlantic Ocean, and Gimnesies, Pitiüses, and Andalusia, in the Mediterranean sea, are feeding grounds used by turtles born in Cape Verde, but that about 43% (±19%) of Cape Verde juveniles disperse to unknown areas. In a subset of samples (n = 145) we evaluated the utility of a longer segment (~760 bp) amplified by recently designed mtDNA control region primers for assessing the genetic structure of Atlantic loggerhead turtles. The analysis of the longer fragment revealed more variants overall than in the shorter segments. The genetic data presented here are likely to improve assignment and population genetic analyses, with significant conservation and research applications.     

Natal homing in juvenile loggerhead turtles (Caretta caretta)

Juvenile loggerhead turtles (Caretta caretta) from West Atlantic nesting beaches occupy oceanic (pelagic) habitats in the eastern Atlantic and Mediterranean, whereas larger juvenile turtles occupy shallow (neritic) habitats along the continental coastline of North America. Hence the switch from oceanic to neritic stage can involve a trans-oceanic migration. Several researchers have suggested that at the end of the oceanic phase, juveniles are homing to feeding habitats in the vicinity of their natal rookery. To test the hypothesis of juvenile homing behaviour, we surveyed 10 juvenile feeding zones across the eastern USA with mitochondrial DNA control region sequences (N = 1437) and compared these samples to potential source (nesting) populations in the Atlantic Ocean and Mediterranean Sea (N = 465). The results indicated a shallow, but significant, population structure of neritic juveniles (PhiST = 0.0088, P = 0.016), and haplotype frequency differences were significantly correlated between coastal feeding populations and adjacent nesting populations (Mantel test R2 = 0.52, P = 0.001). Mixed stock analyses (using a Bayesian algorithm) indicated that juveniles occurred at elevated frequency in the vicinity of their natal rookery. Hence, all lines of evidence supported the hypothesis of juvenile homing in loggerhead turtles. While not as precise as the homing of breeding adults, this behaviour nonetheless places juvenile turtles in the vicinity of their natal nesting colonies. Some of the coastal hazards that affect declining nesting populations may also affect the next generation of turtles feeding in nearby habitats.     

Living together but remaining apart: Atlantic and Mediterranean loggerhead sea turtles (Caretta caretta) in shared feeding grounds

Juvenile loggerhead sea turtles (Caretta caretta) from Atlantic nesting populations migrate into the western Mediterranean, where they share feeding grounds with turtles originating in the Mediterranean. In this scenario, male-mediated gene flow may lead to the homogenization of these distant populations. To test this hypothesis, we genotyped 7 microsatellites from 56 Atlantic individuals sampled from feeding grounds in the western Mediterranean and then compared the observed allele frequencies with published data of 112 individuals from Mediterranean nesting beaches. Mediterranean populations were found to be genetically differentiated from the Atlantic stock reaching the western Mediterranean (F(st) = 0.029, P < 0.001); therefore, the possible mating events between Atlantic and Mediterranean individuals are not sufficient to homogenize these 2 areas. The differentiation observed between these 2 areas demonstrates that microsatellites are sufficiently powerful for mixed stock analysis and that individual assignment (IA) tests can be performed in combination with mitochondrial DNA (mtDNA) analysis. In a set of 197 individuals sampled in western Mediterranean feeding grounds, 87% were robustly assigned to Atlantic or Mediterranean groups with the combined marker, as compared with only 52% with mtDNA alone. These findings provide a new approach for tracking the movements of these oceanic migrants and have strong implications for the conservation of the species.     

Molecular resolution of marine turtle stock composition in fishery bycatch: a case study in the Mediterranean

Based on an extensive sampling regime from both nesting populations and bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic structure and stock composition of the loggerhead sea turtle, Caretta caretta, in different marine fisheries. The analyses show the following. (i) In drifting longline fisheries working in Mediterranean pelagic habitats 53–55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from this regional stock; (iii) This regional stock contribution to fishery bycatch suggests that the population size of the Mediterranean loggerhead nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discovery of a large rookery in Libya. (iv) Present impact of fishery-related mortality on the Mediterranean nesting population is probably incompatible with its long-term conservation. Sea turtle conservation regulations are urgently needed for the Mediterranean fisheries. (v) The significant divergence of mtDNA haplotype frequencies of the Turkish loggerhead colonies define this nesting population as a particularly important management unit. Large immature and adult stages from this management unit seem to be harvested predominantly by Egyptian fisheries. (vi) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management units sharing immature pelagic habitats throughout the Mediterranean (and possibly the eastern Atlantic), with distinct and more localized benthic feeding habitats in the eastern basin used by large immatures and adults. (vii) Between the strict oceanic pelagic and the benthic stages, immature turtles appear to live through an intermediate neritic stage, in which they switch between pelagic and benthic foods.     

Modelling the niche for a marine vertebrate: a case study incorporating behavioural plasticity,proximate threats and climate change

The integration of satellite telemetry, remotely sensed environmental data, and habitat/environmental modelling has provided for a growing understanding of spatial and temporal ecology of species of conservation concern. The Republic of Cape Verde comprises the only substantial rookery for the loggerhead turtle Caretta caretta in the eastern Atlantic. A size related dichotomy in adult foraging patterns has previously been revealed for adult sea turtles from this population with a proportion of adults foraging neritically, whilst the majority forage oceanically. Here we describe observed habitat use and employ ecological niche modelling to identify suitable foraging habitats for animals utilising these two distinct behavioural strategies. We also investigate how these predicted habitat niches may alter under the influence of climate change induced oceanic temperature rises. We further contextualise our niche models with fisheries catch data and knowledge of fisheries ‘hotspots’ to infer threat from fisheries interaction to this population, for animals employing both strategies. Our analysis revealed repeated use of coincident oceanic habitat, over multiple seasons, by all smaller loggerhead turtles, whilst larger neritic foraging turtles occupied continental shelf waters. Modelled habitat niches were spatially distinct, and under the influence of predicted sea surface temperature rises, there was further spatial divergence of suitable habitats. Analysis of fisheries catch data highlighted that the observed and modelled habitats for oceanic and neritic loggerhead turtles could extensively interact with intensive fisheries activity within oceanic and continental shelf waters of northwest Africa. We suggest that the development and enforcement of sustainable management strategies, specifically multi‐national fisheries policy, may begin to address some of these issues; however, these must be flexible and adaptive to accommodate potential range shift for this species.     

The magnetic map of hatchling loggerhead sea turtles

Young loggerhead sea turtles (Caretta caretta) from eastern Florida, U.S.A., undertake a transoceanic migration in which they gradually circle the North Atlantic Ocean before returning to the North American coast. Hatchlings in the open sea are guided at least partly by a 'magnetic map' in which regional magnetic fields function as navigational markers and elicit changes in swimming direction at crucial locations along the migratory route. The magnetic map exists in turtles that have never migrated and thus appears to be inherited. Turtles derive both longitudinal and latitudinal information from the Earth's field, most likely by exploiting unique combinations of field inclination and intensity that occur in different geographic areas. Similar mechanisms may function in the migrations of diverse animals.     

Individual variation in feeding habitat use by adult female green sea turtles (Chelonia mydas): are they obligately neritic herbivores?

Satellite telemetry and stable isotope analysis were used to confirm that oceanic areas (where water depths are >200 m) are alternative feeding habitats for adult female green sea turtles (Chelonia mydas), which have been thought to be obligate herbivores in neritic areas (where depths are <200 m). Four females were tagged with satellite transmitters and tracked during post-nesting periods from Ogasawara Islands, Japan. Three females migrated to neritic habitats, while transmissions from another female ceased in an oceanic habitat. The overall mean nighttime dive depths during oceanic swimming periods in two females were <20 m, implying that the main function of their nighttime dives were resting with neutral buoyancy, whereas the means in two other females were >20 m, implying that they not only rested, but also foraged on macroplankton that exhibit diel vertical migration. Comparisons of stable carbon and nitrogen isotope ratios between 89 females and the prey items in a three-source mixing model estimated that 69% of the females nesting on Ogasawara Islands mainly used neritic habitats and 31% mainly used oceanic habitats. Out of four females tracked by satellite, two females were inferred from isotope ratios to be neritic herbivores and the two others oceanic planktivores. Although post-nesting movements for four females were not completely consistent with the inferences from isotope ratios, possibly due to short tracking periods (28–42 days), their diving behaviors were consistent with the inferences. There were no relationships between body size and the two isotope ratios, indicating a lack of size-related differences in feeding habitat use by adult female green turtles, which was in contrast with loggerhead sea turtles (Caretta caretta). These results and previous findings suggest that ontogenetic habitat shifts by sea turtles are facultative, and consequently, their life histories are polymorphic.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Genetic diversity and historical demography of Atlantic bigeye tuna (Thunnus obesus)

Bigeye (Thunnus obesus) is a large, pelagic, and migratory species of tuna that inhabits tropical and temperate marine waters worldwide. Previous studies based on mitochondrial RFLP data have shown that bigeye tunas from the Atlantic Ocean are the most interesting from a genetic point of view. Two highly divergent mitochondrial haplotype clades (I and II) coexist in the Atlantic Ocean. One is almost exclusive of the Atlantic Ocean whereas the other is also found in the Indo-Pacific Ocean. Bigeye tuna from the Atlantic Ocean is currently managed as a single stock, although this assumption remains untested at the genetic level. Therefore, genetic diversity was determined at the mitochondrial control region to test the null hypothesis of no population structure in bigeye tuna from the Atlantic Ocean. A total of 331 specimens were sampled from four locations in the Atlantic Ocean (Canada, Azores, Canary Islands, and Gulf of Guinea), and one in the Indian and Pacific Oceans, respectively. The reconstructed neighbor-joining phylogeny confirmed the presence of Clades I and II throughout the Atlantic Ocean. No apparent latitudinal gradient of the proportions of both clades in the different collection sites was observed. Hierarchical AMOVA tests and pairwise phi(ST) comparisons involving Atlantic Ocean Clades I and II were consistent with a single stock of bigeye tuna in the Atlantic Ocean. Population genetic analyses considering phylogroups independently supported gene flow within Clade II throughout the Atlantic Ocean, and within Clade I between Atlantic and Indo-Pacific Oceans. The latter result suggests present uni-directional gene flow from the Indo-Pacific into the Atlantic Ocean. Moreover, mismatch analyses dated divergence of Clades I and II during the Pleistocene, as previously proposed. In addition, migration rates were estimated using coalescent methods, and showed a net migration from Atlantic Ocean feeding grounds towards the Gulf of Guinea, the best-known spawning ground of Atlantic bigeye tuna.     

Octopods of the Canary Islands. New records and biogeographic relationships

Two octopod species are reported from the Canary Islands (eastern Atlantic Ocean) for the first time: the deep sea four-horn octopus, Pteroctopus tetracirrhus (Delle Chiaje, 1830) and the gelatinous giant octopus, Haliphron atlanticus Steenstrup, 1861. Both female specimens were caught in Tenerife. Haliphron atlanticus is described from fresh remains found floating close to the southwest coast and the second species, P. tetracirrhus, is described from a specimen captured in a shrimp trap at 200 m depth on the southeastern coast of Tenerife. With these two additions the revised and updated list of octopod species of the Canary Islands now comprises eight families and 18 species, all of them incirrate octopods. The zoogeographic relationships of octopod species from other Atlantic regions, including the Mediterranean Sea, were studied. The likely directions of faunal flows were inferred based on affinity indices, showing that Mauritania could be the most probable source of the octopod species of the Canary Islands and the rest of the Macaronesian archipelagos.     

First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche

Few at-sea behavioural data exist for oceanic-stage neonate sea turtles, a life-stage commonly referred to as the sea turtle ‘lost years’. Historically, the long-term tracking of small, fast-growing organisms in the open ocean was logistically or technologically impossible. Here, we provide the first long-term satellite tracks of neonate sea turtles. Loggerheads (Caretta caretta) were remotely tracked in the Atlantic Ocean using small solar-powered satellite transmitters. We show that oceanic-stage turtles (i) rarely travel in Continental Shelf waters, (ii) frequently depart the currents associated with the North Atlantic Subtropical Gyre, (iii) travel quickly when in Gyre currents, and (iv) select sea surface habitats that are likely to provide a thermal benefit or refuge to young sea turtles, supporting growth, foraging and survival. Our satellite tracks help define Atlantic loggerhead nursery grounds and early loggerhead habitat use, allowing us to re-examine sea turtle ‘lost years’ paradigms.     

Patterns of diversity of the north-eastern Atlantic blenniid fish fauna (Pisces: Blenniidae)

This paper presents an analysis of the distributional patterns of blenniids (Pisces: Blenniidae) in the north‐eastern Atlantic. Two peaks of species diversity were found, both in terms of number of species and number of endemics: one in the tropical African coast and another in the Mediterranean Sea. A cluster analysis of similarity values (Jaccard coefficient) among the eastern Atlantic zoogeographical areas, revealed the following groups: a north temperate group, a tropical group formed by the tropical African coast and Mauritania, another group formed by the islands of Cape Verde, a south temperate group (South Africa), and a southern Atlantic group formed by the islands of Ascension and St Helena. Within the north temperate group, the subgroups with higher similarities were: Azores and Madeira, Canary Islands and Morocco, and the Mediterranean and the Atlantic coast of the Iberian Peninsula. Based on affinity indices, the probable directions of faunal flows were inferred. The tropical coast of Africa and the Mediterranean emerged from this analysis as probable speciation centres of the north‐eastern Atlantic blenniid fauna. The Mediterranean may have also acted as a refuge during glacial periods.     

BIODIVERSITY RESEARCH: Fidelity to foraging sites,consistency of migration routes and habitat modulation of home range by sea turtles

Aim Resources can shape patterns of habitat utilization. Recently a broad foraging dichotomy between oceanic and coastal sites has been revealed for loggerhead sea turtles (Caretta caretta). Since oceanic and coastal foraging sites differ in prey availability, we might expect a gross difference in home‐range size across these habitats. We tested this hypothesis by equipping nine adult male loggerhead sea turtles with GPS tracking devices. Location National Marine Park of Zakynthos (NMPZ) Greece, central and eastern Mediterranean (Adriatic, Ionian and Aegean seas). Methods In 2007, 2008 and 2009, Fastloc GPS‐Argos transmitters were attached to nine male loggerheads. In addition, a Sirtrack PTT unit was attached to one male in 2007. Four of the turtles were tracked on successive years. We filtered the GPS data to ensure comparable data volumes. Route consistency between breeding and foraging sites of the four re‐tracked turtles was conducted. Foraging site home range areas and within site movement patterns were investigated by the fixed kernel density method. Results Foraging home range size ranged between circa 10 km² at neritic habitats (coastal and open‐sea on the continental shelf) to circa 1000 km² at oceanic sites (using 90% kernel estimates), the latter most probably reflecting sparsely distributed oceanic prey. Across different years individuals did not follow exactly the same migration routes, but did show fidelity to their previous foraging sites, whether oceanic or neritic, with accurate homing in the final stages of migration. Main conclusions The broad distribution and diverse life‐history strategies of this population could complicate the identification of priority marine protected areas beyond the core breeding site.     

Evidence for an asymmetrical size exchange of loggerhead sea turtles between the Mediterranean and the Atlantic through the Straits of Gibraltar

The permanent eastward current at the Straits of Gibraltar may trap small Atlantic loggerhead sea turtles (Caretta caretta) inside the western Mediterranean until their swimming and diving skills improve enough to allow them counter-current swimming abilities through the current. A captivity experiment with twelve loggerhead sea turtles (straight carapace length or SCL range: 25.3-48.0 cm) revealed that the average critical velocity of this species within the considered length range was 0.38 ± 0.16 m s^− 1 or 1.01 ± 0.24 bl s^− 1. As a consequence, loggerhead sea turtles are predicted to require a minimum SCL of 36.0 cm to swim counter-current through the Straits of Gibraltar, where the water velocity ranges 0.31-0.37 m s^− 1. Genetic analysis of 105 specimens using one mitochondrial marker and seven microsatellites, as well as the recapture of three tagged individuals, support this conclusion; all Mediterranean individuals found in the Atlantic side of the Straits were not smaller than 36.0 cm SCL and the average length (47.3 cm SCL) was significantly higher than that of the Mediterranean turtles in the Mediterranean side of the Straits (31.6 cm SCL). Furthermore, the average length of the turtles of any origin moving from the Mediterranean to the Atlantic was much larger than 36.0 cm (SCL: 54.5 cm SCL), which may indicate the intervention of a different, yet unidentified mechanism restricting east-westward movement. The Algerian current, running along northern Africa, may at least partially explain the delayed departure of loggerhead sea turtles from the Mediterranean Sea to the Atlantic Ocean, as it would force the eastward drift of loggerheads occupying the southwestern Mediterranean. Exchange through the Straits is asymmetrical, and Atlantic turtles are found to enter the Mediterranean at a length of about 20.5 cm. However, once in the Mediterranean they would be retained there for up to 7.9 years, due to the surface circulation pattern. This increases the time span at which turtles are exposed to a high mortality rate, caused by fishing.     

Spatial variability of the mesozooplankton biomass and ichthyoplankton in the Canary region, in autumn 1991

In this paper, we study whether the variability introduced inthe Canary region by the Canary Islands on perturbing the generalflow of the Canary Current and trade winds, and by the NorthwestAfrican upwelling, is manifested in the mesozooplankton biomassdistribution and ichthyoplankton population. Two transects weresampled and two stations were occupied for 24 h during the firstpart of the cruise Canarias 9110. One transect and one stationwere located to the north, upstream of the Canary Islands, inthe ‘non-perturbed’ zone, and the other transectand station were to the south, downstream of the islands, inthe ‘perturbed’ zone. Oceanographic conditions,as represented by the vertical temperature structure, changedboth latitudinally, between upstream unperturbed and downstreamperturbed conditions, and longitudinally, between upwellingand oceanic situations. However, differences were evident onlyin mesozooplankton biomass and in the latitudinal sense. Likewise,the results obtained suggest that (i) there is an interconnectionbetween the neritic fish populations of the Macaronesian archipelagos,in a north–south sense and in a southerly direction, bymeans of the transport of fish larvae by the Azores and Canarycurrents, and (ii) this interconnection could affect both thosespecies whose larvae are well adapted for a long survival inthe pelagic environment, possessing morphological specializations,and those whose larvae do not present these characteristics.     

Clinical Pathology Reference Intervals for an In-Water Population of Juvenile Loggerhead Sea Turtles (Caretta caretta) in Core Sound,North Carolina,USA

The loggerhead sea turtle (Caretta caretta) is found throughout the waters of the Atlantic, Pacific, and Indian Oceans. It is a protected species throughout much of its range due to threats such as habitat loss, fisheries interactions, hatchling predation, and marine debris. Loggerheads that occur in the southeastern U.S. are listed as “threatened” on the U.S. Endangered Species List, and receive state and federal protection. As part of an on-going population assessment conducted by the National Marine Fisheries Service, samples were collected from juvenile loggerhead sea turtles in Core Sound, North Carolina, between 2004 and 2007 to gain insight on the baseline health of the threatened Northwest Atlantic Ocean population. The aims of the current study were to establish hematologic and biochemical reference intervals for this population, and to assess variation of the hematologic and plasma biochemical analytes by season, water temperature, and sex and size of the turtles. Reference intervals for the clinical pathology parameters were estimated following Clinical Laboratory Standards Institute guidelines. Season, water temperature, sex, and size of the turtles were found to be significant factors of variation for parameter values. Seasonal variation could be attributed to physiological effects of decreasing photoperiod, cooler water temperature, and migration during the fall months. Packed cell volume, total protein, and albumin increased with increasing size of the turtles. The size-related differences in analytes documented in the present study are consistent with other reports of variation in clinical pathology parameters by size and age in sea turtles. As a component of a health assessment of juvenile loggerhead sea turtles in North Carolina, this study will serve as a baseline aiding in evaluation of trends for this population and as a diagnostic tool for assessing the health and prognosis for loggerhead sea turtles undergoing rehabilitation.     

Bottom or midwater: alternative foraging behaviours in adult female loggerhead sea turtles

Intrapopulational polymorphism in habitat use is widely reported in many animal species. The phenomenon has recently also been recognized in adult female loggerhead sea turtles Caretta caretta , with small females tending to inhabit oceanic areas (where water depths are >200 m) while presumably feeding pelagically and large females tending to inhabit neritic areas (where depths are <200 m) while presumably feeding benthically. In this study, dive recording satellite telemetry units were used to verify their foraging and diving behaviours in these habitats. Two females that nested on Yakushima Island, Japan, were tracked for 124 and 197 days. The small female wandered in the oceanic Pacific, and spent most of the time at 0–25 m depths regardless of day or night, implying that she foraged pelagically at the surface and shallow depths. Her mean dive durations were significantly longer at night than during the day. The large female moved into the neritic East China Sea, and spent most of the time over the continental shelf at 100–150 m depths during the day and at 0–25 m depths at night, suggesting that she alternated between diurnal benthic foraging and nocturnal resting within the depths where she could attain neutral buoyancy. Her mean dive durations were not significantly different between day and night. The increase in dive duration for both turtles coincided with a seasonal decrease in water temperature. The small female sometimes showed midwater dormancy at 0–25 m depths with a duration of >5 h that was in contrast with bottom dormancy by sea turtles inhabiting other regions. The diving behaviours observed during this study were consistent with their estimated main feeding habits, which demonstrated resource polymorphism in a marine reptile.     

Gastrointestinal helminth community of loggerhead sea turtle Caretta caretta in the Adriatic Sea

We analysed the intestinal helminth community of 70 loggerhead sea turtles Caretta caretta with a curved carapace length ranging from 25 to 85.4 cm, recovered dead in neritic foraging habitats in the Adriatic Sea in 1995 to 2004. The overall prevalence of infection was high (70.0%), with a mean abundance of 36.8 helminth parasites per turtle. Helminth fauna comprised 5 trematodes (Calycodes anthos, Enodiotrema megachondrus, Orchidasma amphiorchis, Pachypsolus irroratus, Rhytidodes gelatinosus) and 3 nematodes (Sulcascaris sulcata, Anisakis spp., Hysterothylacium sp.), with 6 taxa specific for marine turtles. In terms of infection intensity and parasite abundance, O. amphiorchis was the dominant species (mean intensity: 49.8; mean abundance: 12.8), followed by R. gelatinosus (30.5 and 8.3, respectively) and P. irroratus (23.5 and 7.0, respectively), while larval Anisakis spp. exhibited the highest prevalence (34.3%). The intensity of helminth infection ranged from 1 to 302 (mean: 52.6 ± 69.1) and was not correlated with the size of turtles; this relationship held for all species, except R. gelatinosus (rS = 0.556, p < 0.05). In comparison to other marine habitats, the helminth community of Adriatic loggerheads is characterised by higher species diversity (Shannon-Wiener H' = 1.58) and evenness (E = 0.76), and lower dominance values (Berger-Parker d = 0.35), which can be attributed to the life history and feeding ecology of sea turtles in recruited neritic grounds and the diversity of their benthic prey.     

GLOBAL PHYLOGEOGRAPHY OF THE LOGGERHEAD TURTLE (CARETTA CARETTA) AS INDICATED BY MITOCHONDRIAL DNA HAPLOTYPES

Restriction-site analyses of mitochondrial DNA (mtDNA) from the loggerhead sea turtle (Caretta caretta) reveal substantial phylogeographic structure among major nesting populations in the Atlantic, Indian, and Pacific oceans and the Mediterranean sea. Based on 176 samples from eight nesting populations, most breeding colonies were distinguished from other assayed nesting locations by diagnostic and often fixed restriction-site differences, indicating a strong propensity for natal homing by nesting females. Phylogenetic analyses revealed two distinctive matrilines in the loggerhead turtle that differ by a mean estimated sequence divergence p = 0.009, a value similar in magnitude to the deepest intraspecific mtDNA node (p = 0.007) reported in a global survey of the green sea turtle Chelonia mydas. In contrast to the green turtle, where a fundamental phylogenetic split distinguished turtles in the Atlantic Ocean and the Mediterranean Sea from those in the Indian and Pacific oceans, genotypes representing the two primary loggerhead mtDNA lineages were observed in both Atlantic–Mediterranean and Indian-Pacific samples. We attribute this aspect of phylogeographic structure in Caretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats around southern Africa. These results demonstrate how differences in the ecology and geographic ranges of marine turtle species can influence their comparative global population structures.     

Drivers of diversity in Macaronesian spiders and the role of species extinctions

Aim To identify the biogeographical factors underlying spider species richness in the Macaronesian region and assess the importance of species extinctions in shaping the current diversity. Location The European archipelagos of Macaronesia with an emphasis on the Azores and Canary Islands. Methods Seven variables were tested as predictors of single‐island endemics (SIE), archipelago endemics and indigenous spider species richness in the Azores, Canary Islands and Macaronesia as a whole: island area; geological age; maximum elevation; distance from mainland; distance from the closest island; distance from an older island; and natural forest area remaining per island – a measure of deforestation (the latter only in the Azores). Different mathematical formulations of the general dynamic model of oceanic island biogeography (GDM) were also tested. Results Island area and the proportion of remaining natural forest were the best predictors of species richness in the Azores. In the Canary Islands, area alone did not explain the richness of spiders. However, a hump‐shaped relationship between richness and time was apparent in these islands. The island richness in Macaronesia was correlated with island area, geological age, maximum elevation and distance to mainland. Main conclusions In Macaronesia as a whole, area, island age, the large distance that separates the Azores from the mainland, and the recent disappearance of native habitats with subsequent unrecorded extinctions seem to be the most probable explanations for the current observed richness. In the Canary Islands, the GDM model is strongly supported by many genera that radiated early, reached a peak at intermediate island ages, and have gone extinct on older, eroded islands. In the Azores, the unrecorded extinctions of many species in the oldest, most disturbed islands seem to be one of the main drivers of the current richness patterns. Spiders, the most important terrestrial predators on these islands, may be acting as early indicators for the future disappearance of other insular taxa.