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Papers by Josina Tiavouane

Landscape composition was determined by the three levels of the reef typology described ... more Landscape composition was determined by the three levels of the reef typology described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178239#pone.0178239.t002" target="_blank">Table 2</a>. Landscape configuration is determined by habitat fragmentation (0% refers to the initial habitat maps, while 20%, 40%, 60% and 80% refer to reduction levels of habitat area compared to the initial habitat map). The coefficient of correlation is the Mantel coefficient of matrix correlation. We used the dispersal kernel that provided the best congruence between the observed and simulated genetic distances (IBD). Bars are medians and error bars are quantile 95%.</p

A) Observed genetic distances from empirical data, obtained from 15 microsatellite loci.... more A) Observed genetic distances from empirical data, obtained from 15 microsatellite loci. B) Genetic distances simulated by the isolation by distance (IBD) model. C) Genetic distances simulated by the isolation by oceanographic distance (IBOD) model. Genetic distances are Cavalli-Sforza & Edwards’s genetic distances [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178239#pone.0178239.ref053" target="_blank">53</a>], normalized to have maximum of 1.</p

The relative influence of the various input parameters (e.g., habitat distribution and t... more The relative influence of the various input parameters (e.g., habitat distribution and type, dispersal distance or pelagic larval duration) on genetic connectivity can be assessed quantitatively by performing sensitivity analyses of these parameters on the match between observed and simulated genetic divergences.</p

Typologies of reef geomorphology considered in this study.</p

Definitions for the main technical terms used in this study, with references.</p

Des « coquillages » imposants mais encore mal connus Les bénitiers sont des mollusques marins de ... more Des « coquillages » imposants mais encore mal connus Les bénitiers sont des mollusques marins de la classe des bivalves 2tout comme les huîtres, moules, palourdes etc.-habitant les eaux côtières chaudes de la zone Indo-Pacifique. On les trouve préférentiellement dans les faibles profondeurs des lagons et sur les pentes externes des récifs-barrières-jusqu'à 30 m de profondeur selon l'espèce-où ils participent à la construction des récifs coralliens et constituent un substrat physique pour de nombreux organismes récifaux. Exploités depuis des millénaires pour leur chair et leur coquille, ils ont une grande importance économique, vivrière et patrimoniale pour de nombreuses communautés de la zone Indo-Pacifique. Sur une douzaine d'espèces actuellement décrites, sept appartenant à deux genres distincts sont présentes en Nouvelle-Calédonie : Tridacna maxima, T. crocea, T. squamosa, T. derasa et T. mbalavuana, T. noae et Hippopus hippopus. Leur densité et leur distribution varient largement d'une espèce à une autre, en fonction de leurs caractéristiques écologiques, mais aussi en raison des pressions de pêche ciblée sur certaines espèces ou certains récifs.

PLOS ONE, 2017

Previous seascape genetics studies have emphasized the role of ocean currents and geographic dist... more Previous seascape genetics studies have emphasized the role of ocean currents and geographic distances to explain the genetic structure of marine species, but the role of benthic habitat has been more rarely considered. Here, we compared the population genetic structure observed in West Pacific giant clam populations against model simulations that accounted habitat composition and configuration, geographical distance, and oceanic currents. Dispersal determined by geographical distance provided a modelled genetic structure in better agreement with the observations than dispersal by oceanic currents, possibly due to insufficient spatial resolution of available oceanographic and coastal circulation models. Considering both habitat composition and configuration significantly improved the match between simulated and observed genetic structures. This study emphasizes the importance of a reefscape genetics approach to population ecology, evolution and conservation in the sea.

Marine Biodiversity, 2017

Noah's giant clam (Tridacna noae), recently resurrected from synonymy with T. maxima, occurs from... more Noah's giant clam (Tridacna noae), recently resurrected from synonymy with T. maxima, occurs from Christmas Island to the Northern Line Islands and from the Ryukyu Islands to New Caledonia. We used mitochondrial and microsatellite markers to investigate the phylogeographic structure and demographic history of T. noae over most of its geographical range. Results from the two types of markers reveal a consistent population structure, partitioning T. noae into three distinct lineages: (1) eastern half of the Indo-Malay archipelago and Western Australia, (2) Melanesia and Micronesia, and (3) Central Polynesia. Demographic expansion initiated between 300,000 and 400,000 years ago, as was detected for each haplogroup. This pattern, which is congruent with other co-occurring Tridacna species, indicates a shared evolutionary history with expansion from past refuges following late-Pleistocene sea-level changes.

ICES Journal of Marine Science, 2016

Despite major advances in our capacity to measure marine larval connectivity (i.e. the pattern of... more Despite major advances in our capacity to measure marine larval connectivity (i.e. the pattern of transport of marine larvae from spawning to settlement sites) and the importance of these measurements for ecological and management questions, uncertainty in experimental estimates of marine larval connectivity has been given little attention. We review potential uncertainty sources in empirical larval connectivity studies and develop Bayesian statistical methods for estimating these uncertainties based on standard techniques in the mark-recapture and genetics literature. These methods are implemented in an existing R package for working with connectivity data, ConnMatTools, and applied to a number of published connectivity estimates. We find that the small sample size of collected settlers at destination sites is a dominant source of uncertainty in connectivity estimates in many published results. For example, widths of 95% CIs for relative connectivity, the value of which is necessar...

Marine Biodiversity, 2016

The Devil Clam, Tridacna mbalavuana Ladd 1934, previously known as T. tevoroa Lucas, Ledua, Brale... more The Devil Clam, Tridacna mbalavuana Ladd 1934, previously known as T. tevoroa Lucas, Ledua, Braley 1990, was described on the barrier reefs of Tonga and the Lau islands of Fiji. Here, we report two individuals found on the northeastern barrier reef of New Caledonia. While its known geographic range has expanded, its rarity and hence vulnerability persists.

Marine Biodiversity, 2014

Previously confused with the small giant clam Tridacna maxima, the recently-resurrected Noah's gi... more Previously confused with the small giant clam Tridacna maxima, the recently-resurrected Noah's giant clam, Tridacna noae has been reported from the Taiwanese and the Ryukyu archipelagoes. Our recent underwater observations now extend its distribution to Dongsha (

Journal of Experimental Marine Biology and Ecology, 2014

ABSTRACT Finding a suitable habitat that will maximize the likelihood of settlement is one of the... more ABSTRACT Finding a suitable habitat that will maximize the likelihood of settlement is one of the greatest challenges faced by coral reef species. This is the case for giant clams, which exhibit high sensory abilities coupled with a fast decline in locomotion after settlement that may curtail subsequent searches for an optimal environment. The goal of this study was to evaluate the ability of early giant clams to use and discriminate contrasted reef signals. We investigated the chemosensory ability and subsequent locomotion of the widely-distributed giant clam Tridacna maxima, ranging from five-day-presettlement larvae to six-month-old juveniles. Choice experiments were conducted to investigate the response of larvae and juveniles to chemical cues that were potentially associated with conspecifics, and with “favorable” and “unfavorable” reef habitats. Our results suggested that T. maxima may rely on both conspecific and habitat cues to detect suitable reef areas. Both larvae and juveniles showed a strong preference for and actively moved towards conspecific effluents. Two- to six-month-old juveniles were capable of efficiently discriminating effluents from “favorable” vs. “unfavorable” reefs, even without the presence of conspecifics, offering the first direct support for active habitat selection based on chemotaxis in giant clams. Our results expand the range of giant clam species known to exhibit post-settlement locomotion and demonstrate that juveniles (up to six months in the present study) have unexpectedly retained their locomotive ability. Despite a marked reduction in displacement occurring between four and six months, the ability of juveniles to move away from unsuitable areas using effective chemotaxis has positive implications for conservation-oriented initiatives, such as clam restoration projects.

Malgre leur role fonctionnel au sein des ecosystemes coralliens, les populations de benitiers (Tr... more Malgre leur role fonctionnel au sein des ecosystemes coralliens, les populations de benitiers (Tridacninae) sont en declin a travers le monde en raison de leur surexploitation. En Nouvelle-Caledonie, 1 a 9 tonnes sont prelevees par an. Dans ce contexte, cette these a pour principaux objectifs de fournir des indications quant aux connectivites demographiques et evolutives des populations de deux especes de benitiers en Nouvelle-Caledonie, Tridacna maxima et Hippopus hippopus afin d'estimer les echelles spatiales de dispersion larvaire, comprendre leur dynamique et proposer des mesures de conservation adaptees. La connectivite des populations a ete estimee via l'analyse de marqueurs genetiques microsatellites specifiquement developpes pour ces deux especes. L'echantillonnage a permis l'identification de deux nouvelles especes en Nouvelle-Caledonie. A l'echelle d'un recif et de quelques kilometres, les tests de parente montrent des taux d'auto-recrutement va...