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Evolution may improve the invasiveness of populations, but it often remains unclear whether key adaptation events occur after introduction into the recipient habitat (i.e. post-introduction adaptation scenario), or before introduction within the native range (i.e. prior-adaptation scenario) or at a primary site of invasion (i.e. bridgehead scenario). We used a multidisciplinary approach to determine which of these three scenarios underlies the invasion of the tropical ant Wasmannia auropunctata in a Mediterranean region (i.e. Israel). Species distribution models (SDM), phylogeographical analyses at a broad geographical scale and laboratory experiments on appropriate native and invasive populations indicated that Israeli populations followed an invasion scenario in which adaptation to cold occurred at the southern limit of the native range before dispersal to Israel. We discuss the usefulness of combining SDM, genetic and experimental approaches for unambiguous determination of eco-evolutionary invasion scenarios.

Recent papers have promoted the view that model-based methods in general, and those based on Approximate Bayesian Computation (ABC) in particular, are flawed in a number of ways, and are therefore inappropriate for the analysis of phylogeographic data. These papers further argue that Nested Clade Phylogeographic Analysis (NCPA) offers the best approach in statistical phylogeography. In order to remove the confusion and misconceptions introduced by these papers, we justify and explain the reasoning behind model-based inference. We argue that ABC is a statistically valid approach, alongside other computational statistical techniques that have been successfully used to infer parameters and compare models in population genetics. We also examine the NCPA method and highlight numerous deficiencies, either when used with single or multiple loci. We further show that the ages of clades are carelessly used to infer ages of demographic events, that these ages are estimated under a simple model of panmixia and population stationarity but are then used under different and unspecified models to test hypotheses, a usage the invalidates these testing procedures. We conclude by encouraging researchers to study and use model-based inference in population genetics.

Background: Approximate Bayesian computation (ABC) is a recent flexible class of Monte-Carlo algorithms increasingly used to make model-based inference on complex evolutionary scenarios that have acted on natural populations. The software DIYABC offers a user-friendly interface allowing non-expert users to consider population histories involving any combination of population divergences, admixtures and population size changes. We here describe and illustrate new developments of this software that mainly include (i) inference from DNA sequence data in addition or separately to microsatellite data, (ii) the possibility to analyze five categories of loci considering balanced or non balanced sex ratios: autosomal diploid, autosomal haploid, X-linked, Y-linked and mitochondrial, and (iii) the possibility to perform model checking computation to assess the "goodness-of-fit" of a model, a feature of ABC analysis that has been so far neglected. Results: We used controlled simulated data sets generated under evolutionary scenarios involving various divergence and admixture events to evaluate the effect of mixing autosomal microsatellite, mtDNA and/or nuclear autosomal DNA sequence data on inferences. This evaluation included the comparison of competing scenarios and the quantification of their relative support, and the estimation of parameter posterior distributions under a given scenario. We also considered a set of scenarios often compared when making ABC inferences on the routes of introduction of invasive species to illustrate the interest of the new model checking option of DIYABC to assess model misfit. Conclusions: Our new developments of the integrated software DIYABC should be particularly useful to make inference on complex evolutionary scenarios involving both recent and ancient historical events and using various types of molecular markers in diploid or haploid organisms. They offer a handy way for non-expert users to achieve model checking computation within an

The biology of most invasive species in their native geographical areas remains largely unknown. Such studies are, however, crucial in shedding light on the ecological and evolutionary processes underlying biological invasions. 2. The present study focuses on the little fire ant Wasmannia auropunctata, a species native to Central and South America that has been widely introduced and which has become invasive throughout the tropics. We characterise and compare several ecological traits of native populations in French Guiana with those in one of its introduced ranges, New Caledonia. 3. We found ecologically heterogeneous populations of W. auropunctata coexisting in the species' native geographical area. First, we found populations restricted to naturally perturbed areas (particularly floodplains) within the primary forest, and absent from the surrounding forest areas. These populations were characterised by low nest and worker densities. Second, we found dominant populations in recent anthropogenic areas (e.g. secondary forest or forest edge along road) characterised by high nest and worker densities, and associated with low ant species richness. The local dominance of W. auropunctata in such areas can be due to the displacement of other species (cause) or the filling-up of empty habitats unsuitable to other ants (effect). With respect to their demographic features and ant species richness, the populations of native anthropogenic habitats were to a large extent similar to the invasive populations introduced into remote areas. 4. The results point to the need for greater research efforts to better understand the ecological and demographic features of invasive species within their native ranges. © 2009 The Royal Entomological Society., SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published

Background: Environmental parental effects can have important ecological and evolutionary consequences, yet little is known about genetic variation among populations in the plastic responses of offspring phenotypes to parental environmental conditions. This type of variation may lead to rapid phenotypic divergence among populations and facilitate speciation. With respect to density-dependent phenotypic plasticity, locust species (Orthoptera: family Acrididae), exhibit spectacular developmental and behavioural shifts in response to population density, called phase change. Given the significance of phase change in locust outbreaks and control, its triggering processes have been widely investigated. Whereas crowding within the lifetime of both offspring and parents has emerged as a primary causal factor of phase change, less is known about intraspecific genetic variation in the expression of phase change, and in particular in response to the parental environment. We conducted a laboratory experiment that explicitly controlled for the environmental effects of parental rearing density. This design enabled us to compare the parental effects on offspring expression of phase-related traits between two naturally-occurring, genetically distinct populations of Locusta migratoria that differed in their historical patterns of high population density outbreak events. Results: We found that locusts from a historically outbreaking population of L. migratoria expressed parentally-inherited density-dependent phase changes to a greater degree than those from a historically non-outbreaking population. Conclusion: Because locusts from both populations were raised in a common environment during our experiment, a genetically-based process must be responsible for the observed variation in the propensity to express phase change. This result emphasizes the importance of genetic factors in the expression of phase traits and calls for further investigations on density-dependent parental effect

Background: Environmental parental effects can have important ecological and evolutionary consequences, yet little is known about genetic variation among populations in the plastic responses of offspring phenotypes to parental environmental conditions. This type of variation may lead to rapid phenotypic divergence among populations and facilitate speciation. With respect to density-dependent phenotypic plasticity, locust species (Orthoptera: family Acrididae), exhibit spectacular developmental and behavioural shifts in response to population density, called phase change. Given the significance of phase change in locust outbreaks and control, its triggering processes have been widely investigated. Whereas crowding within the lifetime of both offspring and parents has emerged as a primary causal factor of phase change, less is known about intraspecific genetic variation in the expression of phase change, and in particular in response to the parental environment. We conducted a laboratory experiment that explicitly controlled for the environmental effects of parental rearing density. This design enabled us to compare the parental effects on offspring expression of phase-related traits between two naturally-occurring, genetically distinct populations of Locusta migratoria that differed in their historical patterns of high population density outbreak events. Results: We found that locusts from a historically outbreaking population of L. migratoria expressed parentally-inherited density-dependent phase changes to a greater degree than those from a historically non-outbreaking population. Conclusion: Because locusts from both populations were raised in a common environment during our experiment, a genetically-based process must be responsible for the observed variation in the propensity to express phase change. This result emphasizes the importance of genetic factors in the expression of phase traits and calls for further investigations on density-dependent parental effect

Microsatellite null alleles are commonly encountered in population genetics studies, yet little is known about their impact on the estimation of population differentiation. Computer simulations based on the coalescent were used to investigate the evolutionary dynamics of null alleles, their impact on FST and genetic distances, and the efficiency of estimators of null allele frequency. Further, we explored how the existing method for correcting genotype data for null alleles performed in estimating FST and genetic distances, and we compared this method with a new method proposed here (for FST only). Null alleles were likely to be encountered in populations with a large effective size, with an unusually high mutation rate in the flanking regions, and that have diverged from the population from which the cloned allele state was drawn and the primers designed. When populations were significantly differentiated, FST and genetic distances were overestimated in the presence of null alleles. Frequency of null alleles was estimated precisely with the algorithm presented in Dempster et al. (1977). The conventional method for correcting genotype data for null alleles did not provide an accurate estimate of FST and genetic distances. However, the use of the genetic distance of Cavalli-Sforza and Edwards (1967) corrected by the conventional method gave better estimates than those obtained without correction. FST estimation from corrected genotype frequencies performed well when restricted to visible allele sizes. Both the proposed method and the traditional correction method have been implemented in a program that is available free of charge at http://www.montpellier.inra.fr/URLB/. We used 2 published microsatellite data sets based on original and redesigned pairs of primers to empirically confirm our simulation results.

The migratory locust, Locusta migratoria, is an agricultural pest of major importance in large areas of the Ancient world. Nine geographical taxa of L. migratoria with different propensities to display outbreaks were described, and considered as subspecies. Whether the population dynamics associated with outbreak events influence the genetic diversity within and between populations is still unknown. This question was addressed by analysing the genetic diversity at microsatellite loci in two sets of populations characterized by contrasted patterns of outbreak events. In the north-west Mediterranean area, only uncommon and low intensity outbreaks have been reported. This area, which includes the subspecies L. m. cinerascens and L. m. migratoria, is hence considered as a non-outbreaking area. In Madagascar, frequent and intense outbreak events have been recorded over the last century (36 years of pullulation vs. 64 years of remission). Madagascar (L. m. capito subspecies) is thus considered as a frequently outbreaking area. Nine and twelve populations were sampled over a similar geographical scale in the north-west Mediterranean area and in Madagascar respectively, and analysed at 14 polymorphic microsatellite markers. A similar level of within population diversity was observed in both areas (mean number of alleles: 13.039 vs. 13.232 and mean expected heterozygosity: 0.843 vs. 0.833 in north-west Mediterranean and in Madagascar respectively). This suggests that effective sizes in non-outbreaking subspecies are similar to the harmonic means of effective population sizes in outbreaking subspecies. On the other hand, genetic differentiation between populations was significantly lower in the Malagasy outbreaking subspecies (global Fst = 0.002) than in the north-west Mediterranean subspecies (global Fst = 0.058). Altogether, these results suggest a higher effective migration rate in the outbreaking subspecies than in non-outbreaking subspecies.

News, SCOPUS: no.j, info:eu-repo/semantics/published

The migratory locust, Locusta migratoria, is an agricultural pest of major importance in large areas of the Ancient world. Nine geographical taxa of L. migratoria with different propensities to display outbreaks were described, and considered as subspecies. Whether the population dynamics associated with outbreak events influence the genetic diversity within and between populations is still unknown. This question was addressed by analysing the genetic diversity at microsatellite loci in two sets of populations characterized by contrasted patterns of outbreak events. In the north-west Mediterranean area, only uncommon and low intensity outbreaks have been reported. This area, which includes the subspecies L. m. cinerascens and L. m. migratoria, is hence considered as a non-outbreaking area. In Madagascar, frequent and intense outbreak events have been recorded over the last century (36 years of pullulation vs. 64 years of remission). Madagascar (L. m. capito subspecies) is thus considered as a frequently outbreaking area. Nine and twelve populations were sampled over a similar geographical scale in the north-west Mediterranean area and in Madagascar respectively, and analysed at 14 polymorphic microsatellite markers. A similar level of within population diversity was observed in both areas (mean number of alleles: 13.039 vs. 13.232 and mean expected heterozygosity: 0.843 vs. 0.833 in north-west Mediterranean and in Madagascar respectively). This suggests that effective sizes in non-outbreaking subspecies are similar to the harmonic means of effective population sizes in outbreaking subspecies. On the other hand, genetic differentiation between populations was significantly lower in the Malagasy outbreaking subspecies (global Fst = 0.002) than in the north-west Mediterranean subspecies (global Fst = 0.058). Altogether, these results suggest a higher effective migration rate in the outbreaking subspecies than in non-outbreaking subspecies.