Northern French Guiana Research Articles

Phenotypic and life-history diversification in Amazonian frogs despite past introgressions

The advent of genomics in phylogenetics and population genetics strengthened the perception that conflicts among gene trees are frequent and often due to introgression. However, hybridization occurs mostly among species that exhibit little phenotypic differentiation. A recent study delineating species in Anomaloglossus, a frog genus endemic to the Guiana Shield, identified an intriguing pattern in the A. baeobatrachus species complex. This complex occurs in French Guiana and Amapá (Brazil) and comprises two sympatric phenotypes contrasting not only in body size, habitat, and advertisement call, but also in larval development mode (endotrophic vs exotrophic tadpoles). However, molecular and phenotypic divergences are, in some cases, incongruent, i.e specimens sharing mtDNA haplotypes are phenotypically distinct, suggesting a complex evolutionary history. Therefore, we genotyped 106 Anomaloglossus individuals using ddRADseq to test whether this phenotype/genotype incongruence was a product of phenotypic plasticity, incomplete lineage sorting, multiple speciation events, or admixture. Based on more than 16,000 SNPs, phylogenetic and population genetic approaches demonstrated that exotrophic populations are paraphyletic. Species tree and admixture analyses revealed a strikingly reticulate pattern, suggesting multiple historical introgression events. The evolutionary history of one exotrophic population in northern French Guiana is particularly compelling given that it received genetic material from exotrophic ancestors but shows very strong genetic affinity with the nearby endotrophic populations. This suggests strong selection on larval development and mating call after secondary contact and hybridization. The case of A. baeobatrachus represents a striking example of introgression among lineages that are phenotypically distinct, even in their larval development mode, and highlights how high-resolution genomic data can unravel unexpectedly complex evolutionary scenarios.

What is the breeding range and breeding season of Pearly-breasted CuckooCoccyzus euleri? New records and breeding in French Guiana

Summary. Pearly-breasted Cuckoo Coccyzus euleri is a rare South American forest cuckoo and almost nothing is known concerning its breeding biology. It is considered to be a rare austral migrant in northern South America. In French Guiana, it was first documented in 2009 in Nouragues Nature Reserve. We detail seven new records in northern French Guiana in 2010–15, including a pair breeding. We provide information on the nest, nest site and behaviour. The breeding attempt failed during incubation, presumably due to predation. The new records were obtained in primary or old secondary forests contiguous to the primary forest block, between 9 August and 17 September. Most birds were spontaneously vocalising and strongly reacted to playback. These observations, and other known breeding records, raise questions as to the species' status in northern South America.

Predicting tree heights for biomass estimates in tropical forests – a test from French Guiana

Abstract. The recent development of REDD+ mechanisms requires reliable estimation of carbon stocks, especially in tropical forests that are particularly threatened by global changes. Even though tree height is a crucial variable for computing aboveground forest biomass (AGB), it is rarely measured in large-scale forest censuses because it requires extra effort. Therefore, tree height has to be predicted with height models. The height and diameter of all trees over 10 cm in diameter were measured in 33 half-hectare plots and 9 one-hectare plots throughout northern French Guiana, an area with substantial climate and environmental gradients. We compared four different model shapes and found that the Michaelis–Menten shape was most appropriate for the tree biomass prediction. Model parameter values were significantly different from one forest plot to another, and this leads to large errors in biomass estimates. Variables from the forest stand structure explained a sufficient part of plot-to-plot variations of the height model parameters to improve the quality of the AGB predictions. In the forest stands dominated by small trees, the trees were found to have rapid height growth for small diameters. In forest stands dominated by larger trees, the trees were found to have the greatest heights for large diameters. The aboveground biomass estimation uncertainty of the forest plots was reduced by the use of the forest structure-based height model. It demonstrated the feasibility and the importance of height modeling in tropical forests for carbon mapping. When the tree heights are not measured in an inventory, they can be predicted with a height–diameter model and incorporating forest structure descriptors may improve the predictions.

Portelmis guianensis sp. nov. from French Guiana (Coleoptera: Elmidae)

Portelmis guianensis sp. nov. is a new member of the Portelmis gurneyi–group. It was collected in Sinnamary, northern French Guiana. The species is externally similar to the other members of the genus, but males deviate considerably by the shape of the aedeagus. A detailed description and figures are given to facilitate easy identification of the new species. In addition, we have modified the key to species for males of the P. gurneyi–group given in Fernandes et al. (2010) by including the new species. The genus Portelmis Sanderson, 1935 now contains 5 members.

Multiple Quaternary Refugia in the Eastern Guiana Shield Revealed by Comparative Phylogeography of 12 Frog Species

The Guiana Shield (GS) is one of the most pristine regions of Amazonia and biologically one of the richest areas on Earth. How and when this massive diversity arose remains the subject of considerable debate. The prevailing hypothesis of Quaternary glacial refugia suggests that a part of the eastern GS, among other areas in Amazonia, served as stable forested refugia during periods of aridity. However, the recently proposed disturbance-vicariance hypothesis proposes that fluctuations in temperature on orbital timescales, with some associated aridity, have driven Neotropical diversification. The expectations of the temporal and spatial organization of biodiversity differ between these two hypotheses. Here, we compare the genetic structure of 12 leaf-litter inhabiting frog species from the GS lowlands using a combination of mitochondrial and nuclear sequences in an integrative analytical approach that includes phylogenetic reconstructions, molecular dating, and Geographic Information System methods. This comparative and integrated approach overcomes the well-known limitations of phylogeographic inference based on single species and single loci. All of the focal species exhibit distinct phylogeographic patterns highlighting taxon-specific historical distributions, ecological tolerances to climatic disturbance, and dispersal abilities. Nevertheless, all but one species exhibit a history of fragmentation/isolation within the eastern GS during the Quaternary with spatial and temporal concordance among species. The signature of isolation in northern French Guiana (FG) during the early Pleistocene is particularly clear. Approximate Bayesian Computation supports the synchrony of the divergence between northern FG and other GS lineages. Substructure observed throughout the GS suggests further Quaternary fragmentation and a role for rivers. Our findings support fragmentation of moist tropical forest in the eastern GS during this period when the refuge hypothesis would have the region serving as a contiguous wet-forest refuge.

The impact of climate changes during the Holocene on vegetation in northern French Guiana

The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C4 savannas) occurred in northern French Guiana during the Holocene. We measured variations in the ä13C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C4 savannahs or C4 forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the 13C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties.

Genetic structure of the xerophilous bromeliad Pitcairnia geyskesii on inselbergs in French Guiana – a test of the forest refuge hypothesis

Inselbergs are isolated granitic rock outcrops that provide distinctive ecological conditions. In northern South America they rise above the surrounding rainforest. Among inselberg specialists, Pitcairnia geyskesii (Bromeliaceae) is restricted to these habitats in French Guiana. We studied populations from 12 inselbergs using 7 microsatellite loci to give a “reverse image” of the reduction‐expansion of the rainforest in the context of the refuge hypothesis. Our analyses showed that populations are fragmented with dispersal occurring only over very short distances. Genetic diversity was higher in northern French Guiana, whereas specific alleles were observed in the south. The results point to the occurrence of a dry corridor in the north, as hypothesized by Tardy (1998) based on charcoal analyses, whereas de Granville's (1982) hypothesis of a unique past refuge is not confirmed. Moreover, our data suggests the importance of Oyapock River as a pathway for range expansion, arguing against the potential role of the Inini‐Camopi Mountains as a physical barrier. Finally, in spite of a strongly argued scenario in favour of a north‐to‐south migration history, a clear genetic isolation of P. geyskesii populations living on inselbergs of the Mitaraka archipelago suggests a distinct ancestry of the most southern populations.

Hunting in northern French Guiana and its impact on primate communities

The Guianas contain one of the largest single remaining tracts of undisturbed tropical rainforest in the world, but this forest and its fauna are facing increased threats. In the north of French Guiana both anthropogenic pressures and conflicts between settlements related to the use of natural resources are growing. Based on surveys in 17 forest sites we show that hunting pressure was the main factor determining current primate species richness, masking the effects of logging or forest type. Three of the larger species, the red howler monkey Alouatta seniculus, black spider monkey Ateles paniscus and tufted capuchin Cebus apella, were less abundant in hunted areas. In the areas around four settlements the harvested biomass of primates was low compared to other game species, but the harvests were close to or beyond the maximal sustainable thresholds for the red howler monkey and tufted capuchin. In French Guiana primates are either fully protected by law (the spider monkey and white-faced saki Pithecia pithecia), or their hunting is restricted to subsistence use (howler monkey, tufted capuchin and wedge-capped capuchin Cebus olivaceus). Most hunted meat is, however, destined for sale. Current conservation policy in French Guiana is limited to legal protection for some species and areas, and laws are poorly enforced. Although large areas of forest and its wildlife are protected simply by their remoteness, there is an increasingly urgent need for the legal protection of all primate species, and the establishment of large protected areas and efficient forest management schemes to minimize the impacts of logging and hunting.

THE MAMMALS OF PARACOU, FRENCH GUIANA: A NEOTROPICAL LOWLAND RAINFOREST FAUNA PART 2. NONVOLANT SPECIES

Abstract This report describes the results of nonvolant mammal inventory fieldwork at Paracou, a lowland rainforest locality in northern French Guiana, and concludes the faunal analysis introduced by our previous monograph on the bats of Paracou (Simmons and Voss, 1998). Working within a 3–km radius over the course of 202 sampling dates from 1991 to 1994, we recorded a total of 64 nonvolant species by conventional trapping, arboreal platform trapping, pitfall trapping, diurnal and nocturnal hunting, and interviews with local residents. Included in this total species count are 12 marsupials, 9 xenarthrans, 6 primates, 10 carnivores, 5 ungulates, and 22 rodents. Systematic research with nonvolant mammal specimens collected as voucher material resulted in the discovery of new taxa, documented range extensions of previously described species, and helped resolve many longstanding taxonomic problems: (1) Gracilinanus emiliae (Thomas), herein reported for the first time from French Guiana, is redescribed and its...

Chemistry of cerambycid host plants. Part I: Survey of Leguminosae—A study in adaptive radiation

Eighty wood samples representing 51 taxa in 33 genera of Leguminosae were collected in the Sinnamary River Basin in Northern French Guiana and evaluated for their fauna of longhorned beetles (Cerambycidae) and their phytochemical constituents. The cerambycid fauna was assessed using cut branches and trunks that were continuously observed for emerging beetles. Phytochemical patterns were determined in partially purified methanolic extracts that were obtained from wood and bark of the same branches and trunks using thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC). It was found that small groups of taxonomically related and often phytochemically similar plant species serve as host plants for small and well-defined longicorn guilds. Members of longicorn guilds are usually not taxonomically related. Host-plant chemistry appears to play a role in resource allocation among longicorn guilds in this lowland neotropical rainforest. These findings are discussed in reference to theories on coevolution and adaptive radiation in plant-insect associations.

Disturbance, selective logging and bird diversity: a neotropical forest study

The composition and structure of bird communities, and the damage to forest structure were surveyed in northern French Guiana (northeastern Amazonia) one year and ten years after selective logging and compared with the situation in a similar undisturbed primary forest. A point-count method was used in which 937 0.25ha sample plots were censused for 20 minutes each, and their vegetation structure was measured. On average, 38% of the forest undergrowth was destroyed, then invaded by dense regrowth, and up to 63% of the canopy was substantially opened as a result of selective logging. Hunting pressure also increased due to access roads opened for logging. Among the 256 species recorded, overall bird species richness and abundance were depressed by 27–34% in the logged areas compared to primary forest. The most vulnerable guilds, which decreased by 37–98% in abundance, were mature forest understorey species, especially terrestrial ones and mixed flocks of insectivores. Hummingbirds, small gaps, vine tangles and canopy species did not decrease, nor increase significantly after logging. Only species naturally associated with dense second growth, forest edges and large gaps actually increased. Habitat specialization was the major determinant of vulnerability to logging, and, to a lesser degree, size (large) and diet (insectivorous), but foraging behaviour and rarity had little effect. Bird sensitivity to changes in logged forest structure may involve physiological intolerance, reduced food categories, increased exposure to predators, too dense understorey for their specific foraging behaviour and/or avoidance of gaps. Suggested improvements of current forest management and logging techniques for the maintenance of a higher proportion of the original biodiversity include minimizing logging damages, long rotations (>50 years) between cuts, and keeping unlogged forest patches within logging concessions.

Is the equatorial atlantic discordant?

The equatorial Atlantic is often considered discordant because the margins of South America and Africa, which elsewhere follow the trends of Late Proterozoic mobile belts, here intersect those mobile belts at high angles and apparently truncate Archean and Early Proterozoic cratons. The Amazonian and São Luís Cratons of northern French Guiana and Brazil, however, exhibit Early and Late Proterozoic structures which are parallel to and concordant with the coastline. In Gondwana reconstructions, the clash between these structures and discordant structures of the West African Craton implies that the equatorial Atlantic coincides with a major Proterozoic structural boundary. One thousand km of dextral offset observed between lithologic/geochronologic provinces and major fault zones of the two continents agrees with the offset in Proterozoic paleopoles from Venezuela and Liberia. We propose three models to account for this offset. Our preferred model includes the São Luís Craton with the Amazonian, rather than the West African Craton, and accommodates motion along a zone parallel to the northern margin of South America. Movement must have been completed between the Amazonian/Eburnean (2.2-1.9 Ga) and the Brazilian/Pan-African orogenies (600-500 Ma). This zone of weakness was reactivated during the Cretaceous as the site of the equatorial Atlantic fracture zones.

Etat actuel de nos connaissances sur la geologie de la Guyane francaise

Abstract A summary of the geology of northern French Guiana includes brief discussions of the stratigraphy, tectonics, dolerite dikes, Quaternary deposits and mineral resources. Precambrian rocks, which constitute a major part of the area, are represented by a discordant series ranging between 4000 and 1800 m.y. in age, which have been metamorphosed by successive granitization and intrusions of basic rocks. Two tectonic depressions, oriented in an ESE-WNW direction, occupy part of the area, one in the north extending halfway into Surinam, the other in the central region. Dolerite dikes up to 70 km long strike NNW-SSE. Transgressions and regressions in the Quaternary resulted in the deposition of three series of sediments on fossiliferous Eocene beds. Gold deposits, the basic resource of the country, seem to be related to the Caribbean granitization. A table correlates the stratigraphy of French Guiana, Guyana, and Surinam.