Balearic Archipelago Research Articles

Stephos (Copepoda: Calanoida: Stephidae) from Balearic caves (W Mediterranean)

A new species of the calanoid copepod genus Stephos is described from an anchialine cave on Majorca (Balearic Islands). It occurs in sympatry with S. margalefi, another Balearic endemic differing markedly in body size as well as in the morphology of the fifth legs of both sexes. The new species is extraordinary within its family, the Stephidae, and even within the entire superfamily Clausocalanoidea in displaying a paired arrangement of the reproductive system in the female genital double‐somite. No other member of this cluster of 10 families displays such a primitive condition, all exhibiting different degrees of coalescence or reduction of the genital opercula, pores and ducts. We interpret the condition found in Stephos vivesi sp. nov. as secondary, perhaps derived by loss of the operculum concealing the paired apertures and their subsequent migration and separation on the ventral surface. We take advantage of this discovery to amend the diagnosis of S. margalefi, which was inaccurately described and of which the type material has been lost. This species is unique in the genus in expressing the basal exite seta on the maxillule and in having a 4‐segmented (vs. 5‐segmented) male left fifth leg; the latter condition is the result of the failure to express the inter‐segmental articulation between ancestral segments 3 and 4. In addition, it is the only Stephos with the segment 3 of the male left leg 5 (fused to fourth segment) displaying any armature, viz. a tiny spine on the lateral margin, and a pointed process on the medial margin. We tentatively consider S. balearensis, a third cavernicolous species apparently endemic to Minorca, to be a junior synonym of S. margalefi. The disjunct distribution of this apparently stygobiont species, embracing three different islands of the Balearic archipelago, does not pose any biogeographical problem since all three comprised a single island as recently as 17000 yr BP, at the time of the last glacial maximum when a global marine regression of up to 140 m took place.

Factors determining the interaction between common bottlenose dolphins and bottom trawlers off the Balearic Archipelago (western Mediterranean Sea)

Factors determining bottlenose dolphin association with bottom trawlers were studied off the Balearic Islands, western Mediterranean, by studying dolphin distribution around the islands and their interaction with fishing operations. Results showed that bottlenose dolphins avoided the upper shelf (shallower than 50 m) in the warm season, but not in the cold season and that the slope was avoided all year round. Bottlenose dolphins approached most of the trawlers surveyed in the continental shelf, but seldom interacted with those operating in the slope in the warm season. As a consequence, the average depth of trawling operations that attracted dolphins was shallower than those not attracting dolphins. No statistical difference was observed in the average catch of hauls conducted in the presence or in the absence of dolphins. However, discriminant analysis showed differences in catch composition between hauls with and without dolphin presence, but this difference was not attributed to the palatability of the catch, but to influence of trawling depth on the catch. It is concluded that depth is the main factor ruling occurrence of interaction.

Tourism in archipelagos: Hawai’i and the Balearics

Islands and archipelagos pose unique challenges for tourism policy. While tourism development in islands is well studied, little attention has been given to archipelagos and their special challenges. This paper analyzes tourism issues faced by archipelagos. by comparing two successful “sun and beach” mass destinations—the Hawai’ian (USA) and Balearic (Spain) archipelagos. Growth paths since the 1950s are discussed, and comparative policy issues over the last five decades are analyzed. The paper finds similarities and differences in their growth paths. It compares the strengths, weaknesses, opportunities and threats of each archipelago destination, and discusses how each is incorporating sustainability principles to address unique archipelago issues.

Patch dynamics of the Mediterranean seagrass Posidonia oceanica: Implications for recolonisation process

Patch dynamics of the Mediterranean slow-growing seagrass Posidonia oceanica was studied in two shallow sites (3–10 m) of the Balearic Archipelago (Spain) through repeated censuses (1–2 year −1). In the sheltered site of Es Port Bay (Cabrera Island), initial patch density (October 2001) was low: 0.05 patches m −2, and the patch size (number of shoots) distribution was bimodal: most of the patches had less than 6 shoots or between 20 and 50 shoots. Mean patch recruitment in Es Port Bay (0.006 ± 0.002 patches m −2 year −1) exceeded mean patch loss (0.001 ± 0.001 patches m −2 year −1), yielding positive net patch recruitment (0.004 ± 0.003 patches m −2 year −1) and a slightly increased patch density 3 years later (July 2004, 0.06 patches m −2). In the exposed site of S’Estanyol, the initial patch density was higher (1.38 patches m −2, August 2003), and patch size frequency decreased exponentially with size. Patch recruitment (0.26 patches m −2 year −1) and loss (0.24 patches m −2 year −1) were high, yielding a slightly increased patch density in the area 1 year later (October 2004, 1.40 patches m −2). Most recruited patches consisted of rooting vegetative fragments of 1–2 shoots. Seedling recruitment was observed in Summer 2004 at both sites. Episodic, seedling recruitment comprised 30% and 25% of total patch recruitment in Es Port Bay and S’Estanyol, respectively. Patch survival increased with patch size and no direct removal was observed among patches of 5 shoots or more. Most patches grew along the study, shifting patch distribution towards larger sizes. Within the size range studied (1–150 shoots), absolute shoot recruitment (shoots year −1) increased linearly with patch size ( R 2 = 0.64, p < 4 × 10 −5, N = 125), while specific shoot recruitment was constant (about 0.25 ± 0.05 year −1), although its variance was large for small patches. Given the slow growth rate and the high survival of patches with 5 or more shoots, even the low patch recruitment rates reported here could play a significant role in the colonisation process of P. oceanica.

Phylogenetic Analysis Informed by Geological History Supports Multiple, Sequential Invasions of the Mediterranean Basin by the Angiosperm Family Araceae

Despite the remarkable species richness of the Mediterranean flora and its well-known geological history, few studies have investigated its temporal and spatial origins. Most importantly, the relative contribution of geological processes and long-distance dispersal to the composition of contemporary Mediterranean biotas remains largely unknown. We used phylogenetic analyses of sequences from six chloroplast DNA markers, Bayesian dating methods, and ancestral area reconstructions, in combination with paleogeographic, paleoclimatic, and ecological evidence, to elucidate the time frame and biogeographic events associated with the diversification of Araceae in the Mediterranean Basin. We focused on the origin of four species, Ambrosina bassii, Biarum dispar, Helicodiceros muscivorus, Arum pictum, subendemic or endemic to Corsica, Sardinia, and the Balearic Archipelago. The results support two main invasions of the Mediterranean Basin by the Araceae, one from an area connecting North America and Eurasia in the Late Cretaceous and one from the Anatolian microplate in western Asia during the Late Eocene, thus confirming the proposed heterogeneous origins of the Mediterranean flora. The subendemic Ambrosina bassii and Biarum dispar likely diverged sympatrically from their widespread Mediterranean sister clades in the Early-Middle Eocene and Early-Middle Miocene, respectively. Combined evidence corroborates a relictual origin for the endemic Helicodiceros muscivorus and Arum pictum, the former apparently representing the first documented case of vicariance driven by the initial splitting of the Hercynian belt in the Early Oligocene. A recurrent theme emerging from our analyses is that land connections and interruptions, caused by repeated cycles of marine transgressions-regressions between the Tethys and Paratethys, favored geodispersalist expansion of biotic ranges from western Asia into the western Mediterranean Basin and subsequent allopatric speciation at different points in time from the Late Eocene to the Late Oligocene.

Effects of recreational fishing on three fish species from the &lt;i&gt;Posidonia oceanica&lt;/i&gt; meadows off Minorca (Balearic archipelago, western Mediterranean)

Experimental fishing and visual censuses were conducted at nine Posidonia oceanica sites off Minorca exposed to different levels of fishing intensity to assess the effects of recreational fishing on the species that dominate the catch. Total catch per unit effort (CPUE) was highly seasonal and a statistically significant interaction term existed between the season and the level of fishing intensity. CPUE decreased everywhere at the end of the fishing season (autumn), but such a reduction was more intense at those sites exposed to the highest level of fishing. Visual censuses confirmed that there was a lower abundance of vulnerable fish in autumn. Differences vanished in spring probably because fish reshuffled between the considered sites throughout the winter, when the level of fishing intensity was extremely low. Although the average total lengths of Serranus scriba and Diplodus annularis were unaffected by the level of fishing intensity, the average total length of Coris julis was smaller at the most heavily fished sites. In conclusion, recreational fishing has a relevant impact on most of the exploited species and some of the seasonality reported for the Posidonia oceanica fish assemblages might be caused by the seasonality of the fishery.

Mesoscale eddies, surface circulation and the scale of habitat selection by immature loggerhead sea turtles

Here we tested whether the dispersal of loggerhead sea turtles in the western Mediterranean was affected by the pattern of surface currents and whether temporary mesoscale eddies were favoured habitats by comparing the distribution of ten satellite-tracked turtles (average straight carapace length = 46.3 cm; range: 37.1–61.1 cm) with satellite images indicative of the position of mesoscale eddies and the Algerian current. The tracking period averaged 120.9 ± 67.0 SD days. The comparison of turtle tracks with satellite images revealed that only 9.5% of the fixes were associated with mesoscale eddies or the Algerian current. However, 28.3% (range: 0–60.0%) of the maximum longitudinal displacement of each turtle occurred while swimming in the Algerian current. Furthermore, accelerated eastward dispersal with the Algerian current was the most likely reason why turtles did not penetrate deep into the Alboran Sea. Conversely, mesoscale eddies were not involved in any net latitudinal or longitudinal displacement of the turtles. Track analysis revealed that only a few turtles were involved in fine habitat search, as the speed of travel and the cosine of the turning angle seldom correlated once the drift associated with the Algerian current and with mesoscale eddies had been removed from the analysis; only the turtles approaching the limits of the Algerian basin modified their swimming behaviour, thus indicating habitat selection. These observations and the results of the simulation experiments revealed that turtle dispersal within the western Mediterranean was a combination of: (1) passive dispersal within a region limited by physical barriers (the Balearic Archipelago, Sardinia, Corsica, and Sicily) and influenced by a strong current (the Algerian current) and (2) fidelity to regions filled with recent Atlantic water. However, turtles fail to recognise and remain in small, discrete mesoscale eddies, thus suggesting that habitat selection in these turtles appears to occur at the scale of hundreds rather than tens of kilometres.

The diet of pelagic loggerhead sea turtles (Caretta caretta) off the Balearic archipelago (western Mediterranean): relevance of long-line baits

Gut content and stable isotope analyses were used to investigate the feeding habits of loggerhead sea turtles (Caretta caretta) inhabiting the Balearic archipelago. Turtles caught in the pelagic realm (δ13C: -16.0±0.6‰ and δ15N: 8.5±0.9‰) and turtles caught on the continental shelf (δ13C: -16.7±0.6‰ and δ15N: 8.4±1.3‰) did not differ in their isotopic signatures, suggesting that their diets include the same prey types. A mixing model revealed that for the turtles here analysed, squid and the jellyfish Cotylorhiza tuberculata were the most relevant prey, although stomach contents analysis revealed that carnivorous jellyplankton, neuston, fish and other cephalopods were also consumed. Gut content analysis also indicated that most of the prey identified, including all fish and most cephalopods, were of pelagic origin. Thus, loggerhead sea turtles inhabiting central regions of the western Mediterranean appear to seldom exploit benthic prey, even while on the continental shelf.

What genetics tell us about the conservation of the critically endangered Balearic Shearwater?

The Balearic shearwater Puffinus mauretanicus is one of the most critically endangered seabirds in the world. The species is endemic to the Balearic archipelago, and conservation concerns are the low number of breeding pairs, the low adult survival, and the possible hybridization with a sibling species, the morphologically smaller Yelkouan shearwater ( P. yelkouan). We sampled almost the entire breeding range of the species and analyzed the genetic variation at two mitochondrial DNA regions. No genetic evidence of population decline was found. Despite the observed philopatry, we detected a weak population structure mainly due to connectivity among colonies higher than expected, but also to a Pleistocene demographic expansion. Some colonies showed a high imbalance between immigration and emigration rates, suggesting spatial heterogeneity in patch quality. Genetic evidence of maternal introgression from the sibling species was reinforced, but almost only in a peripheral colony and not followed, at least to date, by the spread of the introgressed mtDNA lineages. Morphometric differences were not correlated with mtDNA haplotypes and introgression is probably due to a secondary contact between the two species several generations ago. Overall, results suggested that the very recent demographic decline in this critically endangered species has not yet decreased its genetic variability, and connectivity found among most colonies should help to reduce species extinction risk. Spreading of introgression should be monitored, but the species is not jeopardized at the moment by genetic factors and the major conservation actions should concentrate at enhancing adult survival.

Stable C and N isotope concentration in several tissues of the loggerhead sea turtle &lt;i&gt;Caretta caretta&lt;/i&gt; from the western Mediterranean and dietary implications

The isotopic concentrations of carapace scutes, skin, muscle and blood of loggerhead sea turtles (Caretta caretta) from the Balearic Archipelago were analysed to investigate the pattern of variation between tissues and to assess the position of this species in the trophic webs of the Algerian Basin. Skin showed higher d13C values than muscle or carapace scutes and these showed higher values than blood. Conversely, muscle showed higher d15N values than skin, skin showed higher values than blood and blood showed higher values than carapace scutes. Dead and live sea turtles from the same habitat did not differ in the concentration of stable isotopes. However, some of the tissues of the turtles caught in drifting long-lines in the oceanic realm showed higher d13C values than those from the turtles caught by hand or in trammel nets over the continental shelf, although they did not differ in the d15N. Comparison of the concentration of stable isotopes in the turtles with that of other species from several areas of the Algerian Basin revealed that they consumed planktonic prey and that the trophic level of the sea turtles was higher than that of carnivorous cnidarians but lower than that of zooplanktophagous fish and crustaceans.

Analysis of helminth communities of the pine marten, Martes martes, in Spain: Mainland and insular data

AbstractThe present study analyses the helminth communities found in one hundred and two specimens of Martes martes from the Iberian Peninsula and the Balearic Archipelago. The component community is constituted by seventeen helminth species, which frequency and mean abundance show a bimodal pattern. The set of core species is constituted by the trichurids Pearsonema plica, Eucoleus aerophilus and Aonchotheca putorii (72.2% of total helminth individuals found), while the remaining can be considered satellite species. Significant co-occurrences were found among E. aerophilus/A. putorii and E. aerophilus/P. plica. These results demonstrate the great importance of earthworms within the diet of pine marten and contribute to the knowledge of the pine marten’s food ethology, since this kind of prey normally goes undetected in diet studies. Several helminth species, as Sobolevingylus petrowi, Centrorhynchus aluconis, Uncinaria criniformis, Mastophorus muris and Spirura rytipleurites seurati seem to show geographical distributions limited to insular ecosystems. Moreover, helminth communities of M. martes among four Spanish territories, including mainland and insular areas, are characterized and compared.

First data on growth and nucleic acid and protein content of field-captured Mediterranean bluefin (&lt;em&gt;Thunnus thynnus&lt;/em&gt;) and albacore (&lt;em&gt;Thunnus alalunga&lt;/em&gt;) tuna larvae: a comparative study

The waters surrounding the Balearic archipelago are considered to be prime spawning habitats of the bluefin tuna (Thunnus thynnus) and other tuna species such as albacore (T. alalunga) in the Mediterranean. During the 2003 bluefin and albacore spawning season, a tuna larval survey (TUNIBAL 0703) was carried out to assess the distribution of bluefin larvae in relation to hydrographic mesoscale features. Tuna larvae were collected by means of surface plankton tows with a bongo gear with a quadrangular mouth measuring 1 m diagonally. The otolith microstructure of 157 and 71 field-captured larvae of Mediterranean bluefin and albacore, respectively, were analyzed to estimate the daily growth pattern. Furthermore, biochemical analysis to estimate DNA, RNA and protein content was done on another batch of 114 bluefin and 132 albacore larvae. The size range included pre-flexion to post-flexion larvae, from 2.8 to 8.6 mm in body length. bluefin and albacore larvae grew linearly in standard length (0.35 and 0.33 mm/day, respectively) and potentially with respect to dry weight. No significant differences between species were observed in the size-weight relationship, or in the allometric relationship of body size and weight to otolith radius. However, the relationship of DNA and RNA to body size and weight showed a significant difference between species. Bluefin tuna larvae showed a greater nucleic acid content than albacore larvae. Protein content showed no significant differences with respect to body length.

Habitat selection by grey mullets (Osteichthyes: Mugilidae) in Mediterranean estuaries: the role of salinity

A stratified study of microhabitat use by grey mullet on the island of Minorca (Balearic archipelago, western Mediterranean) showed that the distribution of all the species was dramatically affected by salinity. Sites with a salinity level under 15 were positively selected in spring and summer by those species whose growth performance was the best in oligomesohaline water (Liza ramado and Mugil cephalus) but also by a species whose growth was not affected by salinity (Chelon labrosus). Liza aurata concentrated in polyhaline and euhaline sites, where growth was improved, a pattern also exhibited by Liza saliens. Both species avoided fresh water sites all year round. As a consequence, community structure was correlated with salinity. The above reported electivity patterns often disappeared in autumn, when most grey mullets migrate off-shore.

Genetic linkage study for bipolar disorders on chromosomes 17 and 18 in families with a high expression of mental illness from the Balearic Islands

Genetically, bipolar disorder is a complex genetic illness, in which both genes and environmental factors play an important role in pathogenesis. Linkage studies have reported suggestive evidence for genomic regions, especially on chromosome 18, but in most cases they have been inconclusive. A total of 12 pedigrees, from the islands of Majorca and Minorca (Balearic Archipelago), with a high expression of mental illness, have been studied. A scan of 29 polymorphic short tandem repeat markers was performed, spanning chromosomes 17 and 18 for bipolar and other affective disorder susceptibility loci. Narrow (only bipolar I disorder) and broad (bipolar plus other affective disorders) diagnosis criteria were employed. The loci D18S63, D18S452, D18S53, D18S61, D18S1161 and D17S831 showed LOD score values of less than -2. Thus, the positive linkage found by other authors on the regions 18p11.2 and 18p11.3 has not been reproduced in the families studied. The data obtained in chromosome 17 suggested two possible regions that could contain a bipolar disorder susceptibility gene: 17q11 (D17S1857, D17S798) and especially 17q24-qter (D17S949, D17S928). The maximum significant linkage was to D17S949 (17q24), following a recessive mode of inheritance. We have also found a positive LOD score value for D18S478 marker located in the region 18q12.

Extensive gene flow blurs phylogeographic but not phylogenetic signal in Olea europaea L.

Genetic structure and evolutionary patterns of the wild olive tree (Olea europaea L.) were investigated with AFLP fingerprinting data at three geographic levels: (a) phylogenetic relationships of the six currently recognized subspecies in Eurasia and Africa; (b) lineage identification in subsp. europaea of the Mediterranean basin; and (c) phylogeography in the western Mediterranean. Two statistical approaches (Bayesian inference and analysis of molecular variance) were used to analyse the AFLP fingerprints. To determine the congruency and transferability of results across studies previous RAPD and ISSR data were analysed in a similar manner. Comparisons proved that qualitative results were mostly congruent but quantitative values differed, depending on the method of analysis. Neighbour-Joining analysis of AFLP phenotypes supported current classification of subspecies. At a Mediterranean scale no clear cut phylogeographic pattern was recovered, likely due to extensive gene flow between populations of subsp. europaea. Gene flow estimates calculated with conventional F-statistics showed that reproductive barriers separated neither populations nor lineages of O. europaea. Genetic divergence between eastern and western parts of the Mediterranean basin was observed only when geographical and population information were incorporated into the analyses through hierarchical analysis of molecular variance (AMOVA). Within the western Mediterranean, the highest genetic diversity was found in two regions: on both sides of the Strait of Gibraltar and in the Balearic archipelago. Additionally, long-lasting isolation of the northern-most populations of the Iberian Peninsula appeared to be responsible for a significant divergence.

Influence of physical environmental factors on the composition and horizontal distribution of summer larval fish assemblages off Mallorca island (Balearic archipelago, western Mediterranean)

Two ichthyoplankton surveys were carried out in two areas off Mallorca island (Balearic archipelago, western Mediterranean) in June 1996 and August 1996, respectively. The aim of both surveys was to assess the influence of physical environmental factors on the horizontal distribution of larval fish assemblages, focusing on larvae of large migratory pelagic fish species. Canonical correspondence analysis (CCA) indicated that in the June survey, the patterns of horizontal distribution offish larvae were mainly conditioned by depth and by the distribution of two surface water masses: the Modified Atlantic Waters (MA W), of recent Atlantic origin, and the older Surface Mediterranean Waters (SMW). The effect of depth gradient was clear in mesopelagic and neritic species, but it was not so evident in the larvae of large pelagic species which presented a highly patchy distribution. Contrastingly, the August patterns of horizontal fish larvae distribution were significantly correlated with the surface salinity gradient resulting from successive MAW inflows, whereas depth did not show any significant effect, probably linked to the bottom topography with a very narrow shelf area. The data obtained highlight that the Balearic Islands constitute an important spawning ground for most of the large pelagic fishes inhabiting Mediterranean waters, both highly migratory and resident species.

Allopolyploid Origin of the Mediterranean Endemic, &lt;I&gt;Centaurium bianoris&lt;/I&gt; (Gentianaceae), Inferred by Molecular Markers

Centaurium bianoris (Gentianaceae) is restricted to Majorca, the main island of the Balearic Archipelago. This tetraploid species is characterised by salmon-coloured corollas (var. bianoris), but pink (var. roseum) and yellow (var. sulfureum) varieties have also been described. An allopolyploid origin has been proposed between the diploids C. maritimum (yellow flowers) and C. tenuiflorum var. acutiflorum (pink flowers), both occurring on Majorca and in other places of the Mediterranean basin. In this study, we tested the proposed hybrid origin of C. bianoris by using RAPD fingerprinting, and both direct and cloned sequences of the nuclear ribosomal ITS, and the chloroplast trnLF regions. Our molecular data confirmed the hypothesis of an allotetraploid origin of C. bianoris via hybridisation between C. tenuiflorum and C. maritimum, the latter being the maternal parent. The so-called varieties roseum and sulfureum appeared to be only floral morphs that may have arisen via genomic processes such as gene silencing. Hybridisation is probably the cause of the ITS sequence polymorphism observed in C. bianoris, whereas backcrosses with either parent may be responsible for the apparent bidirectional homogenisation observed in ITS clones. Finally, the polyphyletic behaviour of C. bianoris on the ITS cladogram, combined with the differential rates of homogenisation observed in ITS sequences, may denote a recurrent origin for that taxon. This result contrasts with the narrow distribution of C. bianoris, compared to that of its diploid parents, suggesting instead a single origin for this hybrid.

Differential maternal and paternal contributions to the genetic pool of Ibiza Island, Balearic Archipelago

We report on a comparison of the genetic diversity between Ibiza and the population of the other Balearic islands and also between the archipelago with respect to circum-Mediterranean populations. For such a comparison, autosomal and Y-chromosome STRs, as well as mtDNA sequence data analyzed from the same individuals, were studied. Analysis of 14 autosomal STRs showed that Ibiza had significant differentiation with respect to other Balearic populations and also with respect to insular and continental populations from the Mediterranean area. Nevertheless, the results obtained from the analysis of eight Y-STRs showed a high level of genetic homogeneity for eight western Mediterranean populations. On the other hand, these populations did not show a compacted group when mtDNA diversity was analyzed, since they showed genetic differentiation among them. The analyses of haplotypes shared between populations indicated that mtDNA haplotypes have drifted to higher frequencies than the Y chromosome. This fact could be due to a shared recent history between Ibiza and other western Mediterranean populations, with numerous male displacements originated by wars and, especially, commercial relations. The results of mtDNA from the Ibiza population could be due to a maternal Carthaginian/Phoenician founder effect, together with genetic drift, in accordance with the historical and demographic data of the area.

Two sibling species sympatrically breeding: a new conservation concern for the critically endangered Balearic shearwater

Two Puffinus shearwater species are endemic to the Mediterranean region: the Yelkouan shearwater P.␣yelkouan breeding in the central and eastern, and the critically endangered Balearic shearwater P.␣mauretanicus in the western, exclusively breeding at the Balearic archipelago. All individuals caught in Minorca, a Balearic breeding site, showed phenotypic traits of Yelkouan shearwaters. Ten birds from that colony were sampled and genetically analysed. A fragment of 857 base pairs of the cytochrome b was sequenced and compared to published sequences of both species obtained from GenBank. A Neighbor-Joining (NJ) reconstruction distinguished two clades with high bootstrap support, showing that both species bred sympatrically in that colony. This result was unexpected since shearwaters do not usually form mixed colonies. New conservation concerns arise also from our study: at first, breeding population of Yelkouan shearwaters is even smaller than previously thought; additionally, other potential threats emerge, such as hybridization and ecological competition.

Mitochondrial DNA HVRI variation in Balearic populations

The Balearic archipelago (Majorca, Minorca, and Ibiza islands and the Chuetas, a small and inbred community of descendants of Sephardic Jews) and Valencia were studied by means of the sequencing of a 404-bp segment of hypervariable region I (HVRI) mtDNA in 231 individuals. In total, 127 different haplotypes defined by 92 variable positions were identified. The incidence of unique haplotypes was very low, especially in Ibiza and the Chuetas. A remarkable observation in the Chueta community was the high frequency (23%) of preHV-1, a Middle Eastern lineage that is closely related, though not identical, to many others found at high frequencies in different Jewish populations. The presence of this haplogroup convincingly supported the Jewish origin of the Chueta community. The studied populations showed a reduced African contribution, and no individuals were detected with North African haplogroup U6, indicating a lack of maternal contribution from the Moslem settlement to these populations. Only Ibiza showed a lower diversity, indicating a possible genetic drift effect, also supported by the historical information known about this island. The variability in the sequence of mtDNA hypervariable region I correlated well with the existing information from the populations, with the exception of that of the Y-chromosome, which could indicate a differential contribution of the maternal and paternal lineages to the genetic pool of the Balearic Islands. The phylogenetic trees showed the intermediate position of the Chueta population between the Middle Eastern and Majorcan samples, confirming the Jewish origin of this population and their Spanish admixture.