Search

Fruits flies (Diptera : Tephritidae) are serious pests on fruit vegetable crops in most tropical countries. In Réunion Island, four species of Tephritidae cause damages on fruit crops, namely the Mascarenes fruit fly. #Ceratitis catoirii# (Guérin Méneville), the Mediterranean fruit fly,#C. capitata# (Wiedmann) , the Natal fruit fly, #C.rosa# karsh, and the recently invasive peach fruit fly, #Bactrocera zonata# (Saunders). If temperature has strong influence on the survivorship during the pré-impaginal development of these four species (Duyck and Quilici 2002 ; Duyck et al. 2004), the influence of humidity and host fruit has received little attention up to now.

For a long time, population geneticists have had to content themselves with analysing neutral markers to infer selection processes indirectly. The recent improvement of sequencing tools now enables them to analyse the variations of a large number of genes and therefore to spot the genes, or the amino acids, which are under the direct influence of the selection (Yang & Bielawski, 2000). In order to analyse the selection processes acting on the mutations and discriminate the different factors acting on their evolution (genetic selection or drift), it is essential to compare polymorphism data between genomes of the same species/population and divergence data between species/populations (Kimura, 1983). Recently, polymorphism data has become available for a sufficient number of genes (>10) in some model species like humans (Fay et al., 2001; Bustamante et al., 2005), the fruit fly (Bierne & Eyre-Walker, 2004) or the arabis (Bustamante et al., 2002). Some inferences have provided surprising results, suggesting that adaptation holds a more important role in the divergence between two species than the expected neutralist hypothesis (review in Eyre-Walker, 2006). However, other results suggest that the efficient size of populations could be a limitating factor for adaptative evolution (Bustamante et al., 2002), even if its role in non-neutral genetic variation is still not well understood (Gillespie, 1999; Bazin et al., 2006). Finally, the number of polymorphic sites in a given gene is often too small to make gene by gene inferences (except for some fruit fly genes) and only a global estimate can be obtained through the compiling of several genes (Bierne & Eyre-Walker, 2004). If some sequences ultra-dense in polymorphic sites existed, reliable estimates could be made at gene level., Les généticiens des populations ont longtemps dû se contenter de l'analyse de marqueurs neutres pour inférer indirectement les processus sélectifs. Les progrès récents des outils de séquençage permettent aujourd'hui de pouvoir analyser les variations d'un grand nombre de gènes et ainsi de pouvoir détecter les gènes voire les acides aminés qui sont sous l'emprise directe de la sélection (Yang & Bielawski, 2000). Pour analyser les processus sélectifs agissant sur les mutations et discriminer les différents facteurs agissant sur leur évolution (sélection ou dérive génétique), il est essentiel de comparer des données de polymorphisme entre génomes d'une même espèce/population et de divergence entre espèces/populations (Kimura, 1983). Récemment, des données de polymorphisme sont devenues disponibles pour un nombre suffisant de gènes (>10) chez quelques espèces modèles comme l'homme (Fay et al., 2001; Bustamante et al., 2005), la drosophile (Bierne & Eyre-Walker, 2004) ou l'arabette (Bustamante et al., 2002). Certaines inférences ont donné des résultats surprenants, suggérant un rôle bien plus important de l'adaptation dans la divergence entre deux espèces que l'attendu de l'hypothèse neutraliste (revue dans Eyre-Walker, 2006). Cependant d'autres résultats suggèrent que la taille efficace des populations (Ne) pourrait être un facteur limitant de l'évolution adaptative (Bustamante et al., 2002), même si son rôle sur la variation génétique nonneutre est encore mal comprise (Gillespie, 1999; Bazin et al., 2006). Enfin, le nombre de sites polymorphes dans un gène donné est souvent trop petit pour pouvoir faire des inférences gène par gène (mis à part peut être chez certains gènes de la drosophile) et seule une estimation globale peut être obtenue en compilant les résultats de plusieurs gènes (Bierne & Eyre-Walker, 2004). S'il existait des séquences ultra-denses en sites polymorphes, des estimations fiables pourraient être réalisées à l'échelle du gène.

International audience

Invaders have often been said to display traits that favor colonisation (r-traits). However, while these traits may allow a species to reach empty habitats before other species do, they are usually associated with low competitive ability. More competitive species, even if they have lower colonisation ability, may prevent the permanent installation of an r-selected invader. Competition rather than colonisation may therefore limit invasion. The best situations to test this hypothesis are "invasive series", when successive invasions by related taxa occur in the same place. Phylogenetic proximity of the taxa and common environment ensure that trade-offs between colonization- and competition-oriented traits can be detected. We expect biological traits to change from colonisation-oriented to increasingly competition-oriented strategies along the invasive series. This prediction was tested using two different model systems, both of which invade tropical insular habitats: freshwater snails of the Thiaridae family in Martinique and Tephritid flies in La Réunion. In both systems, in consistency with our hypothesis, the first invaders were relatively r-selected, and were later replaced by new genotypes and/or taxa with increasingly lower fecundity and higher investment per offspring.

Despite quarantine procedures, many invasions of polyphagous fruit flies (family Tephritidae) have been observed in various parts of the world. These invasions usually result in decreased numbers of, and niche shifts by, established species, be they indigenous or previous invaders. In this study we compare four species of this family: three successive invaders and one endemic species of La Réunion Island with respect to demographic parameters, experimental co-infestations on the same fruit and behavioural interference. The results suggest an interspecific trade-off between K and r traits. Larval competition has a negative effect on pupal weight and larval survival. In behavioural trials, some adult females are able to drive out other females from a fruit. The asymmetry of larval competition and direct interactions among females seems to be correlated with the temporal rank of establishment on the island, the species arrived more recently showing a high performance in larval competition and in driving out other females from the fruit. In optimal conditions, the r-K gradient could be used as a predictor of potential invaders because K-traits may favour both exploitation and interference competition. However coexistence among species is allowed because of the variability in tolerance to climatic conditions (temperature and humidity) and host-plants range. However, the endemic species has lower fecundity and survival parameters than the other species, and moreover has both the climatic and resource axes of its niche included in those of other competing species. We predict the stable coexistence among the three invasive species while the extinction of the endemic species may occur. (Texte intégral)

De nombreuses invasions par des mouches des fruits polyphages (Diptera: Tephritidae) ont été observées dans différentes parties du monde. Les paramètres démographiques de quatre espèces nuisibles aux cultures fruitières à La Réunion (l'une indigène, les trois autres exotiques) suggèrent un trade-off interspécifique entre les traits k et r. Chez les femelles adultes, des comportements d'expulsion loin du fruit par d'autres femelles ont également été observés. L'asymétrie de la compétition larvaire et des interactions directes entre femelles semble corrélée au rang d'établissement sur l'île, l'espèce arrivée la plus récemment ayant de bonnes performances dans la compétition larvaire comme dans l'aptitude à déplacer d'autres femelles d'un fruit. La coexistence entre espèces pourrait cependant être permise par la variabilité de la tolérance aux conditions climatiques. En conclusion, il apparaît important de prendre en compte la communauté envahie dans toute Analyse de Risque Phytosanitaire.

Invasive species have often been said to display r-selected traits. However, when ecologically similar species are already established, interspecific competition rather than the ability to colonize or rapidly grow in numbers at low density could be the limiting factor of invasion, favouring K rather than r traits. We tested this idea using the "invasive series" approach. We define an invasive series as a suite of ecologically and/or taxonomically similar taxa invading the same region, characterised by hierarchical invasive ranks, in terms of ability to competitively displace each other and become numerically dominant in the invaded area. Three species of polyphagous fruit flies (Diptera: Tephritidae) that successively invaded the Reunion Island (initially occupied by a fourth, endemic species) together provide an example of such a series. We characterized life-history traits of these four species in optimal laboratory conditions, at all stages from egg to death in order to test whether invasive ranks were dependent on positions along an r-K gradient. Our results suggest an interspecific trade-off between K and r traits, and that the K lifestyle is associated with higher ranks in the invasive series. The resident endemic species is an exception, as it has low values for both r and K traits. Its competitive exclusion by the three invasive species is therefore explained by some form of maladaptation rather than by a strategy along an r-K trade-off. (Texte intégral)

In Reunion Island, four species of fruit flies (Diptera: Tephritidae) cause damages on fruit crops namely the Mascarene fruit fly, Ceratitis catoirii (Guérin Mèneville), the Mediterranean fruit fly, C. capitata (Wiedemann), the Natal fruit fly, C. rosa Karsch and the recent invasive peach fruit fly, Bactrocera zonata (Saunders). The influence of four important host fruit (guava, Psidium guayava L., strawberry guava, Psidium cattleianum Sabine, mango, Mangifera indica L. and Indian almond, Terminalia catappa L.) on larval development, pupal weight and fecundity of these species has been studied in the laboratory. Larval host had strong effects on survival, developmental times and pupal sizes. Relationships were also observed between developmental times and pupal weight in certain fruit species. Pupal weight (for a given fruit species and among fruit species) had an influence on the fecundity of the emerged females. The relationship between pupal weight and female fecundity was determined for the 4 fruit flies species studied. These results should be useful for a better understanding of the importance of pupal weight as an indicator of female quality. (Texte intégral)

In Reunion Island, four species of fruit flies (Diptera: Tephritidae) cause damages on fruit crops namely the Mascarenes fruit fly, Ceratitis catoirii (Guérin Mèneville), the Mediterranean fruit fly, C. capitata (Wiedemann), the Natal fruit fly, C. rosa Karsch and the recent invasive peach fruit fly, Bactrocera zonata (Saunders). The influence of four important host fruit (guava, Psidium guava L., strawberry guava, Psidium cattleyanum Sabine mango, Mangifera indica L. and Indian almond, Terminalia catappa L.) on larval development and of a range of relative humidity on pupal development and the influence have been studied in the laboratory. Larval host had strong effects on survival, developmental times and pupal sizes (that possibly have consequences on fecundity of the female in the same generation). Humidity, especially low levels (30 and 50% RH), had very important effect on survival depending on the fruit fly species. Indeed, C. capitata and B. zonata showed a high tolerance to dryness contrary to C. catoirii and C. rosa. These fruit fly species live in different ecological niches that can overlap. Results of this study are discussed according to the current distribution of these four fruit flies species in Reunion Island. Predictions can be also made on the future distribution of the invasive peach fruit fly.