Admixture and sexual bias in the population settlement of La Réunion Island (Indian Ocean)

La Réunion, one of the three Mascarene islands located in the Indian Ocean, remained devoid of inhabitants until it was first colonized by the French in the middle of the 17th century. The continuous flow of foreign-born slaves and immigrant workers from Africa, India, Southeast Asia, and China to work on coffee and sugar cane plantations led to the island becoming a melting pot of people of multiple ethnic origins. To establish the impact of the different incoming ethnic groups on the present Reunionese gene pool, we have sequenced both hypervariable regions I and II of the mitochondrial DNA molecule, the 9 bp COII/tRNA(Lys) deletion, and four SNPs located in the coding region in a total of 41 samples of the general population, and a further 18 STRs and 35 SNPs on the Y chromosome in 26 of these samples. Our results show that there was a strong sexual bias (asymmetrical gene flow) in the peopling of La Réunion, where admixture events were mainly between male settlers and females from the incoming slave groups. Most of the Y-chromosome gene pool is of European/Middle Eastern ancestry (85%), whereas the mtDNA gene pool is mainly of Indian and East Asian ancestry (70%). The absence of genetic diversity within these two major components of the mtDNA gene pool suggests these populations may have witnessed strong founder effects during the colonization process.     

Partial self-incompatibility and inbreeding depression in a native tree species of La Réunion (Indian Ocean)

We investigated the reproductive system of the threatened taxon Dombeya acutangula ssp. acutangula Cav. (Sterculiaceae), an endemic tree of the Mascarene archipelago (Indian Ocean). A controlled crossing experiment was performed in two natural populations located in the remnants of the low-elevation dry forest on the island of La Réunion. Active pollination, probably mainly by insects, was necessary for reproduction in this species. Individuals varied in their degree of self-sterility from 0 to 100%. Outcrossing between nearby individuals produced lower seed set than did crosses between more distant individuals within one of the two tested populations. The variation in reproductive success on selfing and in the different types of crosses could result from inbreeding depression causing embryo death, and we provide evidence that progenies from selfing have lower seed size and quality. However, for inbreeding depression to account for the dramatic variation in seed set found in our crossing experiment, the distribution of genetic load and number of lethal factors required appear unrealistic. We favour an alternative interpretation, that D. acutangula possesses an incompatibility system similar to that found in other Sterculiaceae species such as Theobroma cacao L. Such an incompatibility system allows a certain amount of selfing, and different individuals vary in their degree of self-incompatibility. The low success of crosses among close neighbours in one population suggests that there was spatial structure for incompatibility alleles in that population. This could partly explain the decline of the species in fragmented and disturbed habitats, since relatedness at incompatibility loci may increase in small or isolated population and thus reduce mate availability. Received: 2 March 1998 / Accepted: 3 August 1998     

Water velocity dependence of phosphate uptake on a coral-dominated fringing reef flat,La Réunion Island,Indian Ocean

Phosphate uptake (P-uptake) into coral reef communities has been hypothesized to be mass-transfer limited. One method of demonstrating mass-transfer limitation of P-uptake is to show dependence of P-uptake on water velocity. Water velocity across reef flats varies with tides and swell; thus, we measured P-uptake over the entire reef flat on eight different days, representing a range in water velocities. P-uptake was calculated from changes in P concentration of the water column. Changes in P concentration were measured by water sampling at six sites along a 300-m cross-reef transect while simultaneously measuring water velocity. To smooth the variability in phosphate concentrations, peristaltic pumps were used to get time-integrated water samples for 4–6 h at each site. Water velocities were measured in the middle of the transect using an acoustic Doppler current profiler and were averaged to match the time-integrated water sampling. Depth-averaged cross-reef water velocities were 0.031 ± 0.013 m s⁻¹ (mean ± SD), while the root-mean-square water velocities, accounting for oscillatory flow, averaged 3.3 times higher, 0.101 ± 0.021 m s⁻¹ (mean ± SD). Phosphate decreased along all transects. The first-order rate constant for P-uptake (S) was 8.5 ± 2.4 m d⁻¹ (mean ± SD) and increased linearly with root-mean-square water velocity. The Stanton number derived from oscillatory flow, the ratio of the first-order rate constant for P-uptake to the root-mean-square water velocity (S/U _rms), was (9.4 ± 1.2) × 10⁻⁴ (mean ± SD). P-uptake ranged from 0.2 to 1.1 mmol P m⁻² d⁻¹, demonstrating that P-uptake is variable on short time scales and is directly related to P concentration and water velocity.

     

An Assessment of Habitat Diversity and Transformation on La Réunion Island (Mascarene Islands,Indian Ocean) as a Basis for Identifying Broad-scale Conservation Priorities

Most natural habitat in the Mascarene Islands (Mauritius, La Réunion and Rodrigues) has been transformed. Although urbanisation, agriculture and alien plant invasions have transformed large areas in La Réunion, the island has by far the greatest area of intact habitats in the Mascarenes, but remaining natural areas are under threat. We propose a protocol for defining a system of habitat types and for using these to provide a preliminary assessment of conservation priorities for La Réunion. The protocol draws on existing data and expert knowledge to map habitat types, assesses the extent of habitat transformation, and quantifies heterogeneity between habitat types based on climate, topography and geology. The pattern of habitat transformation was uneven among the nineteen habitat types identified. While three habitats have lost > 95% of their original area, four still retain> 80% of their original extent. Habitat types could be grouped into the following categories: (i) transformed habitats with low levels of plant endemism, (ii) habitats confined to homogenous geology with high levels of plantendemism, and (iii) species-rich heterogeneous habitats on diverse geological types. Priority habitats were also identified using municipalities as a basis for implementation. Urgent action is required for several habitat types where a large part of the original extent has been transformed. Three municipalities which contain more than 10 habitat types should receive conservation priority. The analysis provides the basis for setting conservation priorities in La Réunion at the regional and local scale. Implications of the results are discussed with reference to requirements for finer-scale conservation planning.     

La Réunion and Mayotte cockroaches: impact of altitude and human activity

Competitive displacement is the outcome of interspecific competition between invading and native species. Alien insect species invade not only cultivated areas but also natural habitats. We prospected the cockroach fauna on two oceanic islands (Mayotte and La Réunion) to investigate the impact of altitude and anthropic disturbance on the distribution of these species. Most invading cockroach species seem to benefit from cultivation of land whereas endemic species occupy more specific and reduced habitats that are threatened by human impact.     

Zoogeography of Pacific Ocean islands: a comparison of the rotifer faunas of Easter Island and the Galápagos archipelago

During September 1990, an extensive sampling of the freshwaters of Easter Island was conducted. The resulting list of rotifer species, supplemented by taxa present in samples collected during a previous trip to the island, is compared with that of another oceanic island of volcanic origin, namely Santa Cruz, Galápagos archipelago. In spite of less research, Santa Cruz has a richer rotifer fauna which, unlike Easter Island, includes endemic species. Possible causes for the faunal poverty of Easter Island are: large source-to-target distance, small target size, uniformity of the target island's ecosystems and limited age of its aquatic biotopes.     

Elver Invasion, Population Structure and Growth of Marbled eels Anguilla marmorata in a Tropical River on Réunion Island in the Indian Ocean

Winter skates, Leucoraja ocellata, exposed to 80% and 50% seawater (SW) exhibited rapid and significant weight gains followed by a slight recovery to new steady state levels within 8 days. Skates were acclimated at each salinity (100% SW [N = 16], 80% SW [N = 8], 50% SW [N = 8]), anesthetized (MS222) and bled from the caudal vein. In 100% SW, skate plasma (930mOsm/kg) was slightly hyperosmotic to the external medium (922mOsm/kg). Plasma osmolality decreased with seawater dilution, but became increasingly hyperosmotic to the bathing media. The environmental dilutions resulted in significant, but disproportionate changes in plasma Cl^–, P^–, Na⁺, Ca⁺, Mg⁺, trimethylamine oxide (TMAO) and urea concentrations. Mean corpuscular [Hb] and milliliter RBC water measurements suggest that skate red cells swelled less at each dilution than predicted for a passive erythrocyte osmometer. Concentrations of the major RBC solutes K⁺, urea, TMAO and Cl^– decreased by 8, 25, 5 and 21%, respectively in 80% SW. In 50% SW, K⁺, urea, TMAO and Cl^– concentrations decreased by 9, 47, 36 and 15%, respectively. Quantitatively, the other measured intracellular electrolytes (Mg⁺, Na⁺, P^– and Ca⁺) also exhibited disproportionate changes in concentration. Our results indicate that L. ocellata is a euryhaline elasmobranch that can tolerate significant reduction in the external salinity through the release of both ions and urea from the extracellular compartments while retaining electrolytes at the expense of urea in the intracellular compartment.     

First record of troglobitic Hemiptera (Fulgoromorpha: Cixiidae) from La Réunion Island

A new species of troglobitic Cixiidae (Hemiptera: Fulgoromorpha), Brixia briali n. sp. is described from a lava tube on La Réunion Island. Information on its ecology, distribution, and comments on its tentative systematic placement into the genus Brixia is provided. The new discovery from La Réunion is placed into the context of cavernicolous Fulgoromorpha of the world, their zoogeography, ecology and biology.     

Impact of human activity on the distribution of native and non-native cockroach species (Dictyoptera) in La Réunion and Mayotte

Establishment of non-native species and human-driven alteration of habitats are major causes of the decline of native faunas. Interference between native and non-native cockroach species was evaluated here by comparing their distribution areas in two oceanic islands: Mayotte and La Réunion. A factorial correspondence analysis showed that their presence is related to environmental parameters among which human activity, humidity and altitude are the three most important. Human activity and humidity favour establishment and development of non-native species, whereas altitude limits their presence. Non-native species form guilds (up to seven species). Their distribution areas overlap and illustrate their colonizing capacities. On the contrary, distribution areas of native species never overlap, although some co-occur with non-native species. Native species are more endangered when they are established in cultivated areas than when they are in protected natural areas.     

Botryosphaeriaceae associated with Acacia heterophylla (La Réunion) and Acacia koa (Hawaii)

Acacia koa and A. heterophylla are commonly occurring native trees on the Hawaiian Islands and La Réunion, respectively. A recent phylogenetic study suggested that A. heterophylla renders A. koa paraphyletic, and that the former likely arose from the Hawaiian Islands around 1.4 million years ago. An intriguing question is whether their microbiota is similar, although they occur naturally in two very distant geographical locations. In this study, we compared the fungi in the Botryosphaeriaceae isolated from natural populations of A. koa and A. heterophylla. These fungi were chosen because they commonly occur on woody plants and some are important pathogens. They are also known to have been moved globally on asymptomatic plant materials. Isolates were identified based on comparisons of DNA sequence data for the rDNA-ITS, TEF1-α and β-tubulin loci. Ten Botryosphaeriaceae species were identified, of which four species were specific to A. koa from the Hawaiian Islands and five to A. heterophylla in La Réunion. Only one species, Neofusicoccum parvum, which is known to have a wide global distribution, was common to both hosts. The overall results of this study suggest that although A. koa and A. heterophylla share a recent evolutionary history, they have established independent microbiota, at least in terms of the Botryosphaeriaceae.     

Clonal plants: beyond the patterns—ecological and evolutionary dynamics of asexual reproduction

More than 25 years have passed since publication of the first comprehensive multi-authored landmark volume on the population biology and evolution of clonal organisms (Jackson et al. 1985). Since then, no less than eight symposium volumes or special issues have appeared in scientific journals reporting on advances in the field of clonal plant research, indicating that the study of clonal organisms has remained an important topic in ecological research. The three most recent overviews were published in special issues of this journal (Stuefer et al. 2000; Tolvanen et al. 2004; Sammul et al. 2008), and these are now supplemented with a fourth special issue of Evolutionary Ecology. The articles published here reflect some of the most important contributions to a workshop on clonal plant biology held in Leuven (Belgium) in July 2009 and they illustrate some major advances that have been made over the last few years. In the following paragraphs, we first summarize some representative contributions to the current issue, and second, we put forward some personal ideas about promising and underexplored research lines in clonal plant research.     

Swimming medusoid gonophores in two species of Sertularella (Cnidaria,Hydrozoa, Sertulariidae) from Réunion Island,Indian Ocean

Summary

Two life cycle patterns predominate in thecate hydroids, those with alternating polyp and medusa stages, and those with fixed gonophores. Relatively few species release short-lived medusoids, also called swimming gonophores, that carry the gametes. In the family Sertulariidae, with its large number of taxa, this mode of metagenesis has been documented previously for only two species. It is described here for two others, Sertularella diaphana (Allman, 1885) and Sertularella n. sp., from the coastal waters of Reunion Island. Freshly collected fertile male and female colonies released medusoids near dawn, one per gonotheca. Strong contractions of the bell in the swimming movements induced the shedding of gametes. Once gametes were shed, medusoids quickly degenerated and died. The medusoids were similar morphologically in these two related species, and no obvious sexual dimorphism was noted. They were ovoid in shape, the spadix was eccentric, and a velum was present; but they lacked a mouth, tentacles, sense organs, and radial and circular canals as described earlier in Amphisbetia operculata (Linneus, 1758) and Sertularia marginata Kirchenpauer, 1864. However, the medusoids described here lacked exumbrellar nematocysts. Moreover, the spadix with its dense mass of gametes was different from all other described in being stuck from base to top on one side of the subumbrella in spite of hanging freely in the subumbrellar cavity. The hypothesis that this unusual reproductive mode in sertulariids has been underestimated is confirmed by these findings.     

Mycorrhizal colonizations of ferns and lycophytes on the island of La Réunion in relation to nutrient availability

Very little is known about the degree and ecological correlates of mycorrhization of lycophytes and ferns, although mycorrhizae are believed to be crucial for the majority of land plants. We screened the degree of mycorrhizal colonization for all 75 fern species recorded in nine survey plots across a wide range of soil conditions on the island of La Réunion, including five plots on lava flows of different age. Overall, 66% of all samples had mycorrhizae, but ground-dwelling species had significantly higher colonization levels (78%) than epiphytes (58%). Among ground-dwelling species, 98% of the individuals belonged to species with mycorrhizae, which was significantly higher than at the species level. Most samples had glomeromycetes as fungal partners, but septate endophytes were found in 41% of the colonized samples. While we found no significant relationship between the percentage of fern species with mycorrhizae per plot and seven ecological parameters, the percentage of fern individuals with mycorrhizal colonizations per plot significantly increased on shallow soils with high pH values and high base-saturation. This supports the idea that mycorrhizal colonizations confer an ecological advantage to colonized individuals, and that this advantage is more pronounced on nutrient-deficient sites. Our study thus provides evidence for an ecological advantage of mycorrhizae for ferns, but raises the question why, despite this advantage, species level mycorrhization among ferns (68%) is so much lower than the average for land plants (85%).     

CNP budgets of a coral-dominated fringing reef at La Réunion,France: coupling of oceanic phosphate and groundwater nitrate

Productivity, nutrient input, nutrient uptake, and release rates were determined for a coral-dominated reef flat at La Réunion, France, to assess the influence of groundwater nitrogen on carbon and nutrient budgets. Water samples were collected offshore in the ocean, at the reef crest and back reef for nutrients, picoplankton, pH, and total alkalinity. Volume transport of ocean water across the reef flat was measured using both current meters and drogues. Groundwater advected onto the reef flat and mixed with incoming ocean water. Metabolic rates for the reef community were determined to be: gross primary production = 1,000 mmol C m⁻² d⁻¹, community respiration = 960 mmol C m⁻² d⁻¹, and community calcification = 210 mmol C m⁻² d⁻¹. Across the reef flat, silicate behaved conservatively, there was net uptake of phosphate (0.06 mmol P m⁻² d⁻¹) and net release of nitrate, ammonia, dissolved and particulate organic nitrogen (total 7.0 mmol N m⁻² d⁻¹). Groundwater nitrate contributed 37% of the increase in nitrate plus ammonia. The first-order mass transfer coefficient of phosphate was 3.3 m d⁻¹, and for nitrate plus ammonia, 5.9 m d⁻¹. Gross N and P uptake from estimates of mass transfer and uptake of particles were 0.37 mmol P m⁻² d⁻¹ and 7.2 mmol N m⁻² d⁻¹, respectively giving an N:P uptake ratio of 20:1. Thus, the elevation of nitrogen across the reef flat maintains a high N:P flux, enhancing algal growth downstream of the transect. We conclude that net community production (40 mmol C m⁻² d⁻¹) was sustained by net uptake of phosphate from the ocean and net uptake of new nitrogen from groundwater.

     

Multidisciplinary prospective study of mother-to-child chikungunya virus infections on the island of La Réunion

Background

An outbreak of chikungunya virus affected over one-third of the population of La Réunion Island between March 2005 and December 2006. In June 2005, we identified the first case of mother-to-child chikungunya virus transmission at the Groupe Hospitalier Sud-Réunion level-3 maternity department. The goal of this prospective study was to characterize the epidemiological, clinical, biological, and radiological features and outcomes of all the cases of vertically transmitted chikungunya infections recorded at our institution during this outbreak.

Methods and Findings

Over 22 mo, 7,504 women delivered 7,629 viable neonates; 678 (9.0%) of these parturient women were infected (positive RT-PCR or IgM serology) during antepartum, and 61 (0.8%) in pre- or intrapartum. With the exception of three early fetal deaths, vertical transmission was exclusively observed in near-term deliveries (median duration of gestation: 38 wk, range 35–40 wk) in the context of intrapartum viremia (19 cases of vertical transmission out of 39 women with intrapartum viremia, prevalence rate 0.25%, vertical transmission rate 48.7%). Cesarean section had no protective effect on transmission. All infected neonates were asymptomatic at birth, and median onset of neonatal disease was 4 d (range 3–7 d). Pain, prostration, and fever were present in 100% of cases and thrombocytopenia in 89%. Severe illness was observed in ten cases (52.6%) and mainly consisted of encephalopathy (n = 9; 90%). These nine children had pathologic MRI findings (brain swelling, n = 9; cerebral hemorrhages, n = 2), and four evolved towards persistent disabilities.

Conclusions

Mother-to-child chikungunya virus transmission is frequent in the context of intrapartum maternal viremia, and often leads to severe neonatal infection. Chikungunya represents a substantial risk for neonates born to viremic parturients that should be taken into account by clinicians and public health authorities in the event of a chikungunya outbreak.     

Spatial and Temporal Variability in Territoriality of a Tropical Benthic Damselfish on a Coral Reef (Réunion Island)

The relationship between length of individual Stegastes nigricans and size of the territory that they defend, and both the spatial and temporal variation in territoriality were investigated monthly on a fringing coral reef of Réunion Island over the course of one year. Length of individual S. nigricans was correlated positively with size of the territory. Most small individuals were found separate from adults, in areas with low algal turf cover. This is probably due to strong intra-specific competition for access to algal food resources and shelter availability, and/or differences in habitat preference. Both abundance of individuals and surface defended showed seasonal fluctuations. Densities were slightly higher in austral summer than in winter, and the surface defended by individuals larger than 8cm increased in winter. A permanent redistribution of territories also occured between individuals over time.     

Images of the natural (and social) universe in Rétif De La Bretonne’s La découverte australe

As many cultural historians of the sciences have recently indicated, eighteenth-century illustrations of natural historical works represent an important source that can be used to explore the ways in which nature and the study of nature were regarded in the period. Naturalistic illustrations, however, are not the only genre of images that may help the historian in this investigation. Another interesting source is represented by images of nature and natural objects connected with fictional literature. Yet, little attention has been devoted so far to this genre of images. In this paper I analyse some of the engravings which illustrate Rétif de la Bretonne’s imaginary voyage La Découverte australe par un homme volant (1781). My aim is to show that these illustrations convey a well-defined image of the natural universe, and that their analysis may contribute to our understanding of the various significances and roles attached to Nature in the period—particularly bringing to the fore its moral and political uses. Further, by analysing the ways in which they connect and integrate a variety of artistic and discursive traditions related to fiction, travel, and natural history, I hope to suggest some of the ways in which this genre of images may be used to shed light on the eighteenth-century interplay between spheres of knowledge later assigned to such distinct disciplines as ‘science’, ‘literature’, or ‘art’.     

A new morphological character for the identification of Stomoxys calcitrans and S. niger (Diptera: Muscidae). Comparison of La Réunion island populations

On La Reunion Island (France), two morphological closely related species of stable flies (Diptera: Muscidae), living in the same environment, Stomoxys calcitrans and S. niger, are involved in the transmission of blood parasites to the livestock. To facilitate a rapid identification of both species in the field conditions, we highlighted a diagnostic morphological character not yet described: the length of the maxillary palpus. The study of three populations of S. calcitrans and two populations of S. niger, collected at various elevations, showed that the maxillary palpi of S. niger were significantly longer than in S. calcitrans, independent of sex. This character, easily visible in the field with a simple magnifying glass, has been confirmed on individuals of both species from West Africa.