Background:
Inbreeding depression represents the reduced fitness of individuals originating from matings
between related individuals compared to those originating from matings between unrelated
individuals. Bottlenecks in population size can purge deleterious alleles responsible for
inbreeding depression under certain demographic conditions and for a certain range of
mutation effects (i.e. strongly deleterious and highly recessive alleles, Glémin 2003). Such
purging has been demonstrated empirically in artificially bottlenecked populations
(Crnokrak & Barrett 2002, Avila et al. 2010) and in several invasive species (Mullarkey
et al. 2013, Fountain et al. 2014), including the ladybird Harmonia axyridis (Facon et al.
2011). Rather than posing a barrier to invasion, bottlenecks and inbreeding that follows
introduction events can indeed enhance invasion ability by purging deleterious alleles (Estoup
et al 2016). Under such circumstances, inbred individuals can have a fitness as high as non
inbred ones (Facon et al. 2011). More studies using both phenotypic and genomic
approaches are needed in order to assess whether purging is an important factor for
successful invasions.
Project description:
Drosophila suzukii is an insect species historically distributed in Southeast Asia (Asplen et al.
2015).This species is invasive in the USA and Europe since 2008 (Asplen et al. 2015).
Unlike most drosophilid species (including its relative Drosophila melanogaster), D. suzukii
females display a large serrated ovipositor (Atallah et al. 2014) allowing them to lay eggs in
ripening fruits. As such, this pest poses a major threat to the agricultural production of stone
fruits and berries (Lee et al. 2011). The invasion routes of D. suzukii have been recently
uncovered by researchers at CBGP (Fraimout et al. 2017). Building on these findings, this
master project aims at gaining further insights into the evolutionary factors associated with the
invasion success of D. suzukii. The master student will test whether inbreeding depression is
reduced in invasive compared to native populations.
Methods:
To investigate whether deleterious alleles have been purged in the course of invasion, the
student will perform controlled crosses in the laboratory and will quantify the level of
inbreeding depression in both native and invasive populations (see Facon et al. 2011).

Internship supervisors: Arnaud Estoup (DR1), Laure Olazcuaga (PhD student), Nicolas
Rode (Postdoc)
Contacts: [email protected], [email protected], [email protected]

Lab: Centre de Biologie pour la Gestion des Populations, INRA, Montferrier sur Lez, France

References:
Asplen MK, Anfora G, Biondi A, Choi DS, Chu D, Daane KM, Gibert P, Gutierrez AP,
Hoelmer KA, Hutchison WD, Isaacs R, Jiang ZL, Kárpáti Z, Kimura MT, Pascual M,
Philips CR, Plantamp C, Ponti L, Vétek G, Vogt H, Walton VM, Yu Y, Zappalà L,
Desneux N. 2015. Invasion biology of spotted wing Drosophila (Drosophila suzukii): a
global perspective and future priorities. J Pest Sci. 88: 469–494.
Atallah J, Teixeira L, Salazar R, Zaragoza G, Kopp A. 2014. The making of a pest: the
evolution of a fruit-penetrating ovipositor in Drosophila suzukii and related species.
Proc R Soc B. 281: 20132840–20132840.
Avila, V., Amador, C., & García‐Dorado, A. (2010). The purge of genetic load through
restricted panmixia in a Drosophila experiment. Journal of evolutionary biology, 23(9),
1937-1946.
Crnokrak P, Barrett SCH. 2002. Perspective: Purging the genetic load: a review of the
experimental evidence. Evolution 56:2347–58.
Estoup A, Ravigné V, Hufbauer RA, Vitalis R, Gautier M, Facon B (2016) Is there a genetic
paradox of biological invasion? Annual Review of Ecology, Evolution, and Systematics,
47, 51-72. doi: 10.1146/annurev-ecolsys-121415–032116.
Facon B, Hufbauer RA, Tayeh A, Loiseau A, Lombaert E, Vitalis R, Guillemaud T, Lundgren
JG, Estoup A 2011. Inbreeding depression is purged in the invasive insect Harmonia
axyridis. Curr. Biol. 21:424–27.
Fountain T, Duvaux L, Horsburgh G, Reinhard K, Butlin RK. 2014. Human–facilitated
metapopulation dynamics in an emerging pest, Cimex lectularius. Mol. Ecol. 23:1071–
84
Fraimout A, Debat V, Fellous S, Hufbauer AR, Foucaud J, Pudlo P, Marin J-M, Price DK,
Cattel J, Chen X, Deprá M, Duyck P-F, Guedot C, Loeb G, Kenis M, Kimura MT,
Loiseau A, Martinez-Sañudo I, Pascual M, Polihronakis Richmond M, Sheare, P, Singh
N, Tamura T, Xuéreb A, Zhang J, Estoup, A (2017) Deciphering the invasion routes of
Drosophila suzukii by means of ABC random forest. Molecular Biology and Evolution,
34, 980-996.
Glémin S. 2003. How are deleterious mutations purged? Drift versus nonrandom mating.
Evolution 57:2678–87
Lee JC, Bruck DJ, Curry H, Edwards D, Haviland DR, Van Steenwyk RA, Yorgey BM. 2011.
The susceptibility of small fruits and cherries to the spotted-wing drosophila,
Drosophila suzukii. Pest Manag Sci. 67: 1358–1367.
Mullarkey AA, Byers DL, Anderson RC. 2013. Inbreeding depression and partitioning of
genetic load in the invasive biennial Alliaria petiolata (Brassicaceae). Am. J. Bot.
100:509–18.

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