Fine-scale foraging ecology and habitat use of sympatric green and hawksbill turtles in the Western Indian ocean.

Using stable isotope analysis of carbon and nitrogen of turtle tissues and putative prey items, we investigated the diet of immature green turtles and hawksbill turtles foraging in the lagoon of Aldabra Atoll, a relatively undisturbed atoll in the southern Seychelles. Aldabra offers a unique environment for understanding sea turtle ecology. Green turtles mostly consumed seagrass and brown algae while hawksbill turtles mainly consumed mangroves and invertebrates. Green turtles showed a dietary shift with size (a proxy for age). There was minimal niche overlap between species and evidence of small-scale foraging site fidelity with turtle tissue reflecting site-specific prey. This highlights the ecological importance of seagrass and mangrove habitats and suggests that turtles play a role in controlling algal biomass at Aldabra. This study is the first to closely examine the foraging ecology of these sympatric turtle species in the Western Indian Ocean, a globally important region for both species.

Integration of population genetics with oceanographic models reveals strong connectivity among coral reefs across Seychelles.

Many countries with tropical reef systems face hard choices preserving coral reefs in the face of climate change on limited budgets. One approach to maximising regional reef resilience is targeting management efforts and resources at reefs that export large numbers of larvae to other reefs. However, this requires reef connectivity to be quantified. To map coral connectivity in the Seychelles reef system we carried out a population genomic study of the Porites lutea species complex using 241 sequenced colonies from multiple islands. To identify oceanographic drivers of this connectivity and quantify variability, we further used a 2 km resolution regional ocean simulation coupled with a larval dispersal model to predict the flow of coral larvae between reef sites. Patterns of admixture and gene flow are broadly supported by model predictions, but the realised connectivity is greater than that predicted from model simulations. Both methods detected a biogeographic dispersal barrier between the Inner and Outer Islands of Seychelles. However, this barrier is permeable and substantial larval transport is possible across Seychelles, particularly for one of two putative species found in our genomic study. The broad agreement between predicted connectivity and observed genetic patterns supports the use of such larval dispersal simulations in reef system management in Seychelles and the wider region.

Mate-choice for close kin is associated with improved offspring survival in Lodoicea maldivica, the largest-seeded plant in the world.

We studied spatial patterns of kinship in the offspring of the endangered Lodoicea maldivica, a dioecious palm that produces the largest seed of any plant. Previous research has suggested that restricted seed and pollen dispersal in populations resulted in strong spatial genetic structure. We used microsatellites to genotype young plants and their potential parents at four sites across the species' entire natural range. We determined the most likely parents of each young plant based on the spatial separation of each parent pair, their genetic relatedness, and the level of correlated paternity. We identified both parents (43 female, 54 male) for 139 of 493 young plants. Mean distance between parental pairs was 26.8 m. Correlated paternity was low (0.168), indicating that mother trees were often pollinated by several fathers. Parental pairs were more closely related than expected by chance, suggesting outbreeding depression. Our results highlight the apparent strong mate choice for close kin in parent pairs of surviving offspring. We discuss the alternative biological processes that could lead to this, including the potential for break-up of favourable allelic combinations necessary for the development of the palm's very large seed. Management implications include germinating seeds where they naturally fall, using a diverse range of male plants as pollen donors for hand pollination, and protecting the native community of gecko pollinators.

Envisioning a resilient future for biodiversity conservation in the wake of the COVID-19 pandemic.

As the COVID-19 pandemic continues to affect societies across the world, the ongoing economic and social disruptions are likely to present fundamental challenges for current and future biodiversity conservation.We review the literature for outcomes of past major societal, political, economic and zoonotic perturbations on biodiversity conservation, and demonstrate the complex implications of perturbation events upon conservation efforts. Building on the review findings, we use six in-depth case studies and the emerging literature to identify positive and negative outcomes of the COVID-19 pandemic, known and anticipated, for biodiversity conservation efforts around the world.A number of similarities exist between the current pandemic and past perturbations, with experiences highlighting that the pandemic-induced declines in conservation revenue and capacity, livelihood and trade disruptions are likely to have long-lasting and negative implications for biodiversity and conservation efforts.Yet, the COVID-19 pandemic also brought about a global pause in human movement that is unique in recent history, and may yet foster long-lasting behavioural and societal changes, presenting opportunities to strengthen and advance conservation efforts in the wake of the pandemic. Enhanced collaborations and partnerships at the local level, cross-sectoral engagement, local investment and leadership will all enhance the resilience of conservation efforts in the face of future perturbations. Other actions aimed at enhancing resilience will require fundamental institutional change and extensive government and public engagement and support if they are to be realised.The pandemic has highlighted the inherent vulnerabilities in the social and economic models upon which many conservation efforts are based. In so doing, it presents an opportunity to reconsider the status quo for conservation, and promotes behaviours and actions that are resilient to future perturbation. A free Plain Language Summary can be found within the Supporting Information of this article.

Correction: Rapid loss of flight in the Aldabra white-throated rail.

[This corrects the article DOI: 10.1371/journal.pone.0226064.].

The costs of removing the unsanctioned import of marine plastic litter to small island states.

Small island states receive unprecedented amounts of the world's plastic waste. In March 2019, we removed as much plastic litter as possible from Aldabra Atoll, a remote UNESCO World Heritage Site, and estimated the money and effort required to remove the remaining debris. We removed 25 tonnes at a cost of $224,537, which equates to around $10,000 per day of clean-up operations or $8,900 per tonne of litter. We estimate that 513 tonnes (95% CI 212-814) remains on Aldabra, the largest accumulation reported for any single island. We calculate that removing it will cost approximately $4.68 million and require 18,000 person-hours of labour. By weight, the composition is dominated by litter from the regional fishing industry (83%) and flip-flops from further afield (7%). Given the serious detrimental effects of plastic litter on marine ecosystems, we conclude that clean-up efforts are a vital management action for islands like Aldabra, despite the high financial cost and should be integrated alongside policies directed at 'turning off the tap'. We recommend that international funding be made available for such efforts, especially considering the transboundary nature of both the marine plastic litter problem and the ecosystem services provided by biodiversity-rich islands.

Identification of sex-linked markers in the sexually cryptic coco de mer: are males and females produced in equal proportions?

Lodoicea maldivica (coco de mer) is a long-lived dioecious palm in which male and female plants are visually indistinguishable when immature, only becoming sexually dimorphic as adults, which in natural forest can take as much as 50 years. Most adult populations in the Seychelles exhibit biased sex ratios, but it is unknown whether this is due to different proportions of male and female plants being produced or to differential mortality. In this study, we developed sex-linked markers in Lodoicea using ddRAD sequencing, enabling us to reliably determine the gender of immature individuals. We screened 589 immature individuals to explore sex ratios across life stages in Lodoicea. The two sex-specific markers resulted in the amplification of male-specific bands (Lm123977 at 405 bp and Lm435135 at 130 bp). Our study of four sub-populations of Lodoicea on the islands of Praslin and Curieuse revealed that the two sexes were produced in approximately equal numbers, with no significant deviation from a 1:1 ratio before the adult stage. We conclude that sex in Lodoicea is genetically determined, suggesting that Lodoicea has a chromosomal sex determination system in which males are the heterogametic sex (XY) and females are homogametic (XX). We discuss the potential causes for observed biased sex ratios in adult populations, and the implications of our results for the life history, ecology and conservation management of Lodoicea.

Rapid loss of flight in the Aldabra white-throated rail.

Flight loss has evolved independently in numerous island bird lineages worldwide, and particularly in rails (Rallidae). The Aldabra white-throated rail (Dryolimnas [cuvieri] aldabranus) is the last surviving flightless bird in the western Indian Ocean, and the only living flightless subspecies within Dryolimnas cuvieri, which is otherwise volant across its extant range. Such a difference in flight capacity among populations of a single species is unusual, and could be due to rapid evolution of flight loss, or greater evolutionary divergence than can readily be detected by traditional taxonomic approaches. Here we used genetic and morphological analyses to investigate evolutionary trajectories of living and extinct Dryolimnas cuvieri subspecies. Our data places D. [c.] aldabranus among the most rapid documented avian flight loss cases (within an estimated maximum of 80,000-130,000 years). However, the unusual intraspecific variability in flight capacity within D. cuvieri is best explained by levels of genetic divergence, which exceed those documented between other volant taxa versus flightless close relatives, all of which have full species status. Our results also support consideration of Dryolimnas [cuvieri] aldabranus as sufficiently evolutionary distinct from D. c. cuvieri to warrant management as an evolutionary significant unit. Trait variability among closely related lineages should be considered when assessing conservation status, particularly for traits known to influence vulnerability to extinction (e.g. flightlessness).

Trophic interactions between larger crocodylians and giant tortoises on Aldabra Atoll, Western Indian Ocean, during the Late Pleistocene.

Today, the UNESCO World Heritage Site of Aldabra Atoll is home to about 100 000 giant tortoises, Aldabrachelys gigantea, whose fossil record goes back to the Late Pleistocene. New Late Pleistocene fossils (age ca. 90-125 000 years) from the atoll revealed some appendicular bones and numerous shell fragments of giant tortoises and cranial and postcranial elements of crocodylians. Several tortoise bones show circular holes, pits and scratch marks that are interpreted as bite marks of crocodylians. The presence of a Late Pleistocene crocodylian species, Aldabrachampsus dilophus, has been known for some time, but the recently found crocodylian remains presented herein are distinctly larger than those previously described. This indicates the presence of at least some larger crocodylians, either of the same or of a different species, on the atoll. These larger crocodylians, likely the apex predators in the Aldabra ecosystem at the time, were well capable of inflicting damage on even very large giant tortoises. We thus propose an extinct predator-prey interaction between crocodylians and giant tortoises during the Late Pleistocene, when both groups were living sympatrically on Aldabra, and we discuss scenarios for the crocodylians directly attacking the tortoises or scavenging on recently deceased animals.

Tracing coco de mer's reproductive history: Pollen and nutrient limitations reduce fecundity.

Habitat degradation can reduce or even prevent the reproduction of previously abundant plant species. To develop appropriate management strategies, we need to understand the reasons for reduced recruitment in degraded ecosystems. The dioecious coco de mer palm (Lodoicea maldivica) produces by far the largest seeds of any plant. It is a keystone species in an ancient palm forest that occurs only on two small islands in the Seychelles, yet contemporary rates of seed production are low, especially in fragmented populations. We developed a method to infer the recent reproductive history of female trees from morphological evidence present on their inflorescences. We then applied this method to investigate the effects of habitat disturbance and soil nutrient conditions on flower and fruit production. The 57 female trees in our sample showed a 19.5-fold variation in flower production among individuals over a seven-year period. Only 77.2% of trees bore developing fruits (or had recently shed fruits), with the number per tree ranging from zero to 43. Flower production was positively correlated with concentrations of available soil nitrogen and potassium and did not differ significantly between closed and degraded habitat. Fruiting success was positively correlated with pollen availability, as measured by numbers and distance of neighboring male trees. Fruit set was lower in degraded habitat than in closed forest, while the proportion of abnormal fruits that failed to develop was higher in degraded habitat. Seed size recorded for a large sample of seeds collected by forest wardens varied widely, with fresh weights ranging from 1 to 18 kg. Synthesis: Shortages of both nutrients and pollen appear to limit seed production of Lodoicea in its natural habitat, with these factors affecting different stages of the reproductive process. Flower production varies widely amongst trees, while seed production is especially low in degraded habitat. The size of seeds is also very variable. We discuss the implications of these findings for managing this ecologically and economically important species.

Development of 12 polymorphic microsatellite loci for the endangered Seychelles palm Lodoicea maldivica (Arecaceae).

PREMISE OF THE STUDY: The evolutionarily and ecologically distinct coco de mer palm Lodoicea maldivica (Arecaceae) is endemic to two islands in the Seychelles. Before colonization of the islands by man, the endangered palm formed large monodominant stands, but its natural range is now restricted to four main populations and several patches of isolated individuals. Microsatellite markers were designed to investigate the genetic structure of the remaining natural populations of L. maldivica. METHODS AND RESULTS: We developed 12 polymorphic and three monomorphic microsatellite markers for this species, with a mean number of alleles per locus of 13.2 (range 5-21) and expected heterozygosity values ranging from 0.31-0.91 for the polymorphic loci. CONCLUSIONS: These markers enable us to study the patterns of genetic diversity, contemporary seed dispersal, and the fine-scale spatial genetic structure of this important conservation flagship species.

The nutrient economy of Lodoicea maldivica, a monodominant palm producing the world's largest seed.

The iconic Lodoicea maldivica palm appears to invest heavily in reproduction, with females bearing the world's largest seeds and males producing copious pollen. We asked how these palms, which grow in extremely poor soils, obtain sufficient nutrients to support such high levels of reproductive function. Our study site was the Vallée de Mai UNESCO Site on Praslin, Seychelles. We measured the trees' allocations of dry matter, nitrogen (N) and phosphorus (P) to aboveground growth and reproduction, quantified stemflow and throughfall, and measured availabilities of N and P in the soil. We show that the nutrient costs of reproduction are very high in male and female plants, and for P far exceed those of vegetative growth. We describe how the palm leaves form a huge funnel that intercepts particulate material, especially pollen, which is flushed to the base of the trunk when it rains. In this way, Lodoicea improves its nutrient supply and that of its dispersal-limited offspring. Lodoicea shares many functional characteristics with dominant trees of other monodominant forests in the humid tropics. It also exhibits unique features, including its huge seed, effective funnelling mechanism and diverse community of closely associated animals, suggesting a long evolutionary history under relatively stable conditions.

Persistence of distinctive morphotypes in the native range of the CITES-listed Aldabra giant tortoise.

Understanding the extent of morphological variation in the wild population of Aldabra giant tortoises is important for conservation, as morphological variation in captive populations has been interpreted as evidence for lingering genes from extinct tortoise lineages. If true, this could impact reintroduction programmes in the region. The population of giant tortoises on Aldabra Atoll is subdivided and distributed around several islands. Although pronounced morphological variation was recorded in the late 1960s, it was thought to be a temporary phenomenon. Early researchers also raised concerns over the future of the population, which was perceived to have exceeded its carrying capacity. We analyzed monthly monitoring data from 12 transects spanning a recent 15-year period (1998-2012) during which animals from four subpopulations were counted, measured, and sexed. In addition, we analyzed survival data from individuals first tagged during the early 1970s. The population is stable with no sign of significant decline. Subpopulations differ in density, but these differences are mostly due to differences in the prevailing vegetation type. However, subpopulations differ greatly in both the size of animals and the degree of sexual dimorphism. Comparisons with historical data reveal that phenotypic differences among the subpopulations of tortoises on Aldabra have been apparent for the last 50 years with no sign of diminishing. We conclude that the giant tortoise population on Aldabra is subject to varying ecological selection pressures, giving rise to stable morphotypes in discrete subpopulations. We suggest therefore that (1) the presence of morphological differences among captive Aldabra tortoises does not alone provide convincing evidence of genes from other extinct species; and (2) Aldabra serves as an important example of how conservation and management in situ can add to the scientific value of populations and perhaps enable them to better adapt to future ecological pressures.