Éditeur(s) : Public Library Science
Résumé : Changes in phenology, the timing of seasonal activities, are among the most frequently observed responses to environmental disturbances and in marine species are known to occur in response to climate changes that directly affects ocean temperature, biogeochemical composition and sea level. We examined nesting seasonality data from long-term studies at 8 green turtle (Chelonia mydas) rookeries that include 21 specific nesting sites in the South-West Indian Ocean (SWIO). We demonstrated that temperature drives patterns of nesting seasonality at the regional scale. We found a significant correlation between mean annual Sea Surface Temperature (SST) and dates of peak nesting with rookeries exposed to higher SST having a delayed nesting peak. This supports the hypothesis that temperature is the main factor determining peak nesting dates. We also demonstrated a spatial synchrony in nesting activity amongst multiple rookeries in the northern part of the SWIO (Aldabra, Glorieuses, Mohéli, Mayotte) but not with the eastern and southern rookeries (Europa, Tromelin), differences which could be attributed to females with sharply different adult foraging conditions. However, we did not detect a temporal trend in the nesting peak date over the study period or an inter-annual relation between nesting peak date and SST. The findings of our study provide a better understanding of the processes that drive marine species phenology. The findings will also help to predict their ability to cope with climate change and other environmental perturbations. Despite demonstrating this spatial shift in nesting phenology, no trend in the alteration of nesting dates over more than 20 years was found.
Plos One (1932-6203) (Public Library Science), 2012-10 , Vol. 7 , N. 10 , P. 1-13

Droits : 2012 Dalleau et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
http://archimer.ifremer.fr/doc/00098/20940/18558.pdf
DOI:10.1371/journal.pone.0046920
http://archimer.ifremer.fr/doc/00098/20940/

Éditeur(s) : Elsevier
Résumé : The gametogenic cycle and the reproductive effort of the blacklip pearl oyster, Pinctada margaritifera, cultivated in Takapoto lagoon were studied for a 1-year period (March 1997-April 1998) by bimonthly observations of gonadal sections, dry tissue weights and gonadal index in a population of pearl oyster composed of three age-groups. pearl oysters attained sexual maturity in the end of their first year (height approximate to 40 mm), implying that P. margaritifera is a late-maturing species in comparison with other Pteriidae. This species was also confirmed to be a marked protandrous successive hermaphrodite in culture, with 100 % of males at first maturity and 75 % in older pearl oyster (height > 120 mm). The general pattern of gametogenic activity, fairly synchronous in both sexes, was comparable with that of other tropical bivalves: reproduction occurs continuously throughout the year with a maximal activity during the warm season (November-May). No resting period was observed. Quantitative growth data showed that P. margaritifera exhibits an annual synchronised polymodal spawning pattern, with two spawning peaks in age-group I (height approximate to 70 mm) and five in age-groups II (height approximate to 100 mm) and III (height approximate to 120 mm). Spawning was sometimes incomplete, nevertheless a clear relationship between gamete production (P-R, g) and size (height H, mm) was obtained: P-R = 5.26 x 10(-7) H-2.91 (R-2 = 0.99, p < 0.05). Estimation of P-R was used to calculate the annual reproductive effort in P. margaritifera. Reproductive effort (%) was similar to those calculated for temperate species and showed a progressive increase with the age of pearl oyster, from 7 % in age-group I to 38 % in age-group III. This study showed that, in a fairly stable tropical environment such as the Takapoto lagoon, P. margaritifera is a multiple spawner, which uses an opportunistic reproductive strategy, allowing investment all year around, of any surplus energy into gamete production. Surplus energy is ensured by the high pumping rates developed by this non-symbiotic bivalve to succeed in low seston conditions. (C) 2000 Ifremer/Cnrs/Inra/Ird/Cemagref/Editions scientifiques et medicales Elsevier SAS.
Le cycle et l'effort de reproduction de l'huître perlière à lèvres noires, Pinctada margaritifera, cultivée dans le lagon de Takapoto, ont été étudiés sur une période annuelle (de mars 1997 à avril 1998), par un suivi bimensuel des stades de maturation et des indices gonadiques, sur une population en élevage composée de trois groupes d'âge (1, 2 et 3 ans). Cette étude a confirmé que P. margaritifera est une espèce qui se reproduit tardivement par rapport aux autres Ptériidés (elle atteint sa maturité sexuelle à la fin de sa première année, pour une hauteur approximative de 40 mm). Par ailleurs, elle présente, en élevage, une protandrie marquée (100 % de mâles à première maturité, 75 % pour des huîtres âgées de trois ans). Le schéma général de sa gamétogenèse, relativement synchrone dans les deux sexes, est comparable à celui des autres bivalves tropicaux : la reproduction est quasiment continue (aucune période de repos sexuel) avec une activité accrue en saison chaude (de novembre à mai). L'analyse des variations du poids de la gonade suggère l'existence de deux pics d'émission de gamètes chez les huîtres de un an et cinq pics chez les huîtres de 2 et 3 ans (cycle de reproduction de type polymodal). Bien que ces émissions de gamètes soient parfois incomplètes, une relation entre la production de gamètes (PR, en g) et la taille de l'huître perlière (hauteur, H, en mm) a été établie : PR = 5,26 x 10-7 H2,91 (R2 = 0,99, p < 0,05). Ces résultats ont permis de calculer l'effort de reproduction de P. margaritifera à Takapoto et sur un bilan annuel : il augmente avec l'âge de l'huître perlière de 7 % pour le groupe d'âge I à 38% pour le groupe d'âge III. Ces valeurs annuelles sont similaires à celles calculées chez les bivalves de milieux tempérés. Cette étude a donc montré que, dans un environnement tropical assez stable tel que celui du lagon de Takapoto, P. margaritifera présente une reproduction continue, avec plusieurs pics d'émission de gamètes par an. Cette stratégie « opportuniste » permet l'investissement, de tout surplus d'énergie en production de gamètes, tout au long de l'année. Malgré la faible concentration du milieu en nourriture, ces surplus d'énergie sont assurés par les fortes capacités de filtration développées par cette espèce tropicale non-symbiotique.
Aquatic Living Resources (0990-7440) (Elsevier), 2000 , Vol. 13 , N. 1 , P. 37-48

Droits : 2000 Ifremer/Cnrs/Inra/Ird/Cemagref/Éditions scientifiques et médicales Elsevier SAS
http://archimer.ifremer.fr/doc/2000/publication-1391.pdf
DOI:10.1016/S0990-7440(00)00135-2
http://archimer.ifremer.fr/doc/00000/1391/

Éditeur(s) : HAL CCSD Wiley Open Access
Résumé : 11 pages
International audience
The loss of regulating agents such as parasites is among the most important changes in biotic interactions experienced by populations established in newly colonized areas. Under a relaxed parasite pressure, individuals investing less in costly immune mechanisms might experience a selective advantage and become successful colonizers as they re-allocate resources to other fitness-related traits. Accordingly, a refinement of the evolution of increased competitive ability (EICA) hypothesis proposed that immunity of invasive populations has evolved toward a reduced investment in innate immunity, the most costly component of immunity, and an increased humoral immunity that is less costly. Biogeographical approaches comparing populations between native and expansion ranges are particularly relevant in exploring this issue, but remain very scarce. We conducted a biogeographical comparison between populations of Spectacled Thrush (Turdus nudigenis) from the native area (South America) and from the expansion range (Caribbean islands). First, we compared haemosporidian prevalence and circulating haptoglobin (an acute-phase protein produced during inflammation). Second, we challenged captive birds from both ranges with Escherichia coli lipopolysaccharides (LPS) and measured postchallenge haptoglobin production and body mass change. Birds from the expansion range showed lower haemosporidian prevalence and lower levels of haptoglobin than birds from the native range. In addition, the inflammation elicited by LPS injection and its associated cost in terms of body mass loss were lower in birds from the expansion range than in birds from the native range. In accordance with the enemy release hypothesis, our results suggest that range expansion is associated with a reduced infection risk. Our study also supports the hypothesis that individuals from newly established populations have evolved mechanisms to dampen the inflammatory response and are in accordance with one prediction of the refined EICA hypothesis, proposed to understand biological invasions.
ISSN: 2045-7758

hal-01403291
https://hal.archives-ouvertes.fr/hal-01403291
DOI : 10.1002/ece3.2486