Biology subjects

Lombaert, E.

Publications and source records attributed to Lombaert, E..

4 recordsLinked to original sources

bioRxiv2018

Inference of the worldwide invasion routes of the pinewood nematode, Bursaphelenchus xylophilus, using ABC analysis on microsatellite data

AO_SCPLOWBSTRACTC_SCPLOWPopulation genetics have been greatly beneficial to improve knowledge about biological invasions. Model-based genetic inference methods, such as approximate Bayesian computation (ABC), have brought this improvement to a higher level and are now essential tools to decipher the invasion routes of any invasive species. In this paper, we performed ABC random forest analyses to shed light on the pinewood nematode (PWN) worldwide invasion routes and to identify the source of European populations. Originating from North America, this microscopic worm has been invading Asia since 1905 and Europe since 1999, causing tremendous damage on pine forests. Using microsatellite data, we demonstrated the existence of multiple introduction events in Japan (at least two involving individuals originating from the USA) and China (one involving individuals originating from the USA and one involving individuals originating from Japan). We also found that Portuguese samples had a Japanese origin. We observed some discrepancies between descriptive genetic methods and the ABC method, which are worth investigating and are discussed here. The ABC method helped clarify the worldwide history of the PWN invasion, even though the results still need to be considered with some caution because the features of the PWN and the genetic markers used probably push the ABC method to its very limits.

genetics↗

bioRxiv2018

When higher carrying capacities lead to faster propagation

This preprint has been reviewed and recommended by Peer Community In Ecology (https://dx.doi.org/10.24072/pci.ecology.100004). Finding general patterns in the expansion of natural populations is a major challenge in ecology and invasion biology. Classical spatio-temporal models predict that the carrying capacity (K) of the environment should have no influence on the speed (v) of an expanding population. We tested the generality of this statement with reaction-diffusion equations, stochastic individual-based models, and microcosms experiments with Trichogramma chilonis wasps. We investigated the dependence between K and v under different assumptions: null model (Fisher-KPP-like assumptions), strong Allee effects, and positive density-dependent dispersal. These approaches led to similar and complementary results. Strong Allee effects, positive density-dependent dispersal and demographic stochasticity in small populations lead to a positive dependence between K and v. A positive correlation between carrying capacity and propagation speed might be more frequent than previously expected, and be the rule when individuals at the edge of a population range are not able to fully drive the expansion.

ecology↗

bioRxiv2017

Colonization History Of The Western Corn Rootworm (Diabrotica virgifera virgifera) In North America: Insights From Random Forest ABC Using Microsatellite Data

First described from western Kansas, USA, the western corn rootworm, Diabrotica virgifera virgifera, is one of the worst pests of maize. The species is generally thought to be of Mexican origin and to have incidentally followed the expansion of maize cultivation into North America thousands of years ago. However, this hypothesis has never been investigated formally. In this study, the genetic variability of samples collected throughout North America was analysed at 13 microsatellite marker loci to explore precisely the population genetic structure and colonization history of D. v. virgifera. In particular, we used up-to-date Approximate Bayesian Computation methods based on random forest algorithms to test a Mexican versus a central-USA origin of the species, and to compare various possible timings of colonization. This analysis provided strong evidence that the origin of D. v. virgifera was southern (Mexico, or even further south). Surprisingly, we also found that the expansion of the species north of its origin was recent - probably not before 1100 years ago - thus indicating it was not directly associated with the early history of maize expansion out of Mexico, a far more ancient event.

evolutionary biology↗

bioRxiv2016

A simulation-based evaluation of STRUCTURE software for exploring the introduction routes of invasive species

Population genetic methods are widely used to retrace the introduction routes of invasive species. The unsupervised Bayesian clustering algorithm implemented in STRUCTURE is amongst the most frequently use of these methods, but its ability to provide reliable information about introduction routes has never before been assessed. We used computer simulations of microsatellite datasets to evaluate the extent to which the clustering results provided by STRUCTURE were misleading for the inference of introduction routes for two invasive populations independently introduced from a native population. For this simple scenario of independent introductions, the assumption of two clusters (i.e. K=2) would not be expected to result in STRUCTURE assigning the native population to one cluster, with both invasive populations assigned to the second cluster. We investigated the influence of two demographic parameters (effective size and bottleneck severity) and different numbers of loci on the type and frequency of misleading results. We showed that misleading STRUCTURE results were obtained for 10% of our simulated datasets and at a frequency of up to 37% for some combinations of parameters. Our results highlighted two different categories of misleading output. The first occurs in situations in which the native population has a low level of diversity. In this case, the two introduced populations may be very similar, despite their independent introduction histories. The second category results from convergence issues in STRUCTURE for K=2, with strong bottleneck severity and/or large numbers of loci resulting in high levels of differentiation between the three populations.

evolutionary biology↗