Impact of inbreeding and hybridization in four biological control agents

La consanguinité et l’hybridation sont deux processus génétiques pouvant avoir des effets antagonistes dans les élevages d’auxiliaires de lutte biologique. L’hybridation peut minimiser les risques de dépression de consanguinité (diminution de fitness des individus consanguins), et favoriser l’apparition de phénotypes avantageux. Bien que les mécanismes de la dépression de consanguinité et des conséquences de l’hybridation soient bien connus, très peu d’études ont été réalisées dans le cadre de la lutte biologique. Il convient d’évaluer les effets réels de la consanguinité et de l’hybridation sur la fitness des auxiliaires pour orienter les pratiques de l’industrie de la lutte biologique. Dans le cadre d’une collaboration public-privé, des données ont été produites sur les effets de la consanguinité chez les quatre auxiliaires Allotropa burrelli, Chrysoperla near comanche, Cryptolaemus montrouzieri et Macrolophus pygmaeus. La consanguinité a notamment provoqué une baisse de 30% du succès reproducteur chez M. pygmaeus. Une étude approfondie des conséquences de l’hybridation intra-spécifique a alors été réalisée en utilisant quatre populations de M. pygmaeus. Trois groupes génétiques séparés par un fort isolement reproducteur ont été mis en évidence. Néanmoins, un avantage de fitness pour les individus issus de croisements entre parents génétiquement distants a été mis en évidence au sein de chaque groupe génétique. Ce travail de thèse apporte des données utilisables à court-terme par les entreprises partenaires. Il contribue par ailleurs à créer un corpus de données pour mieux évaluer l’importance réelle des effets génétiques dans les élevages d’auxiliaires.Inbreeding and hybridization are two genetic processes that may have antagonistic effects in biological control agents (BCAs) rearing. Hybridization can minimize the risk of inbreeding depression (decrease in fitness of inbred individuals), and favor the emergence of advantageous phenotypes. Although the mechanisms of inbreeding depression and the consequences of hybridization are well known, very few studies have been carried out in the context of biological control. The actual effects of inbreeding and hybridization on the fitness of BCAs should be assessed to guide the practices of the biocontrol industry. In a public-private collaboration, data were generated on the effects of inbreeding in the four BCAs Allotropa burrelli, Chrysoperla near comanche, Cryptolaemus montrouzieri and Macrolophus pygmaeus. Inbreeding resulted in a 30% decrease in reproductive success in M. pygmaeus. A thorough study of the consequences of intra-specific hybridization was then carried out using four populations of M. pygmaeus. Three genetic groups separated by strong reproductive isolation were identified. Nevertheless, a fitness advantage for individuals from crosses between genetically distant parents has been highlighted within each genetic group. This work brings data usable in the short term by the partner companies. It also helps to create a corpus of data to better evaluate the real importance of genetic effects in BCAs rearing

Impact de la consanguinité et de l’hybridation chez quatre auxiliaires de lutte biologique

Inbreeding and hybridization are two genetic processes that may have antagonistic effects in biological control agents (BCAs) rearing. Hybridization can minimize the risk of inbreeding depression (decrease in fitness of inbred individuals), and favor the emergence of advantageous phenotypes. Although the mechanisms of inbreeding depression and the consequences of hybridization are well known, very few studies have been carried out in the context of biological control. The actual effects of inbreeding and hybridization on the fitness of BCAs should be assessed to guide the practices of the biocontrol industry. In a public-private collaboration, data were generated on the effects of inbreeding in the four BCAs Allotropa burrelli, Chrysoperla near comanche, Cryptolaemus montrouzieri and Macrolophus pygmaeus. Inbreeding resulted in a 30% decrease in reproductive success in M. pygmaeus. A thorough study of the consequences of intra-specific hybridization was then carried out using four populations of M. pygmaeus. Three genetic groups separated by strong reproductive isolation were identified. Nevertheless, a fitness advantage for individuals from crosses between genetically distant parents has been highlighted within each genetic group. This work brings data usable in the short term by the partner companies. It also helps to create a corpus of data to better evaluate the real importance of genetic effects in BCAs rearing.La consanguinité et l’hybridation sont deux processus génétiques pouvant avoir des effets antagonistes dans les élevages d’auxiliaires de lutte biologique. L’hybridation peut minimiser les risques de dépression de consanguinité (diminution de fitness des individus consanguins), et favoriser l’apparition de phénotypes avantageux. Bien que les mécanismes de la dépression de consanguinité et des conséquences de l’hybridation soient bien connus, très peu d’études ont été réalisées dans le cadre de la lutte biologique. Il convient d’évaluer les effets réels de la consanguinité et de l’hybridation sur la fitness des auxiliaires pour orienter les pratiques de l’industrie de la lutte biologique. Dans le cadre d’une collaboration public-privé, des données ont été produites sur les effets de la consanguinité chez les quatre auxiliaires Allotropa burrelli, Chrysoperla near comanche, Cryptolaemus montrouzieri et Macrolophus pygmaeus. La consanguinité a notamment provoqué une baisse de 30% du succès reproducteur chez M. pygmaeus. Une étude approfondie des conséquences de l’hybridation intra-spécifique a alors été réalisée en utilisant quatre populations de M. pygmaeus. Trois groupes génétiques séparés par un fort isolement reproducteur ont été mis en évidence. Néanmoins, un avantage de fitness pour les individus issus de croisements entre parents génétiquement distants a été mis en évidence au sein de chaque groupe génétique. Ce travail de thèse apporte des données utilisables à court-terme par les entreprises partenaires. Il contribue par ailleurs à créer un corpus de données pour mieux évaluer l’importance réelle des effets génétiques dans les élevages d’auxiliaires

Inbreeding depression in a parasitoid wasp with single-locus complementary sex determination.

Inbreeding and inbreeding depression are key processes in small or isolated populations and are therefore central concerns for the management of threatened or (re)introduced organisms. Haplodiploid species of the order Hymenoptera have a particular status with regard to inbreeding depression. Although recessive deleterious alleles that are expressed in males should be purged, an alternative form of inbreeding depression exists in species with single-locus complementary sex determination (sl-CSD). Under sl-CSD, genetically-related parents have a high probability of producing sterile sons instead of fertile daughters. In this article, we study inbreeding depression in Venturia canescens (Hymenoptera: Ichneumonidae), a parasitoid wasp with sl-CSD. We used a crossing design to manipulate relatedness according to three levels: within-family, between-family and between-population. For each level, several fitness components were measured on parents and female offspring. We found a 20% reduction in egg load at emergence for inbred crosses. Inbred crosses also yielded a higher proportion of males, as expected in a species with sl-CSD. Mating probability, presence of daughters among offspring, body size, symmetry and longevity were unaffected by inbreeding

M. pygmaeus, une punaise auxiliaire pleine de ressources

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No inbreeding depression in laboratory-reared individuals of the parasitoid wasp Allotropa burrelli

Inbreeding depression is a major concern in almost all human activities relating to plant and animal breeding. The biological control of pests with natural enemies is no exception, because populations of biocontrol agents experience a series of bottlenecks during importation, rearing, and introduction. A classical biological control program for the Comstock mealybug Pseudococcus comstocki (Hemiptera: Pseudococcidae) was initiated in France in 2008, based on the introduction of an exotic parasitoid, Allotropa burrelli Mues. (Hymenoptera: Platygastridae), a haplodiploid parasitoid imported from Japan. We evaluated the sensitivity of A. burrelli to inbreeding, to optimize rearing and release strategies. We compared several morphological and life-history traits between the offspring of siblings and the offspring of unrelated parents. We took into account the low level of genetic variability due to the relatively small size of laboratory-reared populations by contrasting two types of pedigree: one for individuals from a strain founded from a single field population, and the other generated by hybridizing individuals from two strains founded from two highly differentiated populations. Despite this careful design, we obtained no evidence for a negative impact of inbreeding on laboratory-reared A. burrelli. We discussed the results in light of haplodiploid sex determination and parasitoid mating systems, and classical biological control practices

Boxplot of sex ratios for the three cross types.

<p>The bottom and top limits of the box are the 0.25 and 0.75 quartiles, respectively, and the bold black line indicates the median. Whiskers represent the minimum and maximum values. Asterisks show represent the predictions of the model with for the type of cross as fixed effect and maternal and paternal families as random effects. Different letters indicate a significant difference of least-square means (within-family/between-family: z = −2.91, <i>p</i> = 0.0102; within-family/between-population: z = −6.47, <i>p</i><0.0001; between-family/between-population: z = 4.03, <i>p</i> = 0.0002).</p

Egg load (A) at emergence and (B) at death as a function of body size for the three cross types.

<p>Circles represent observed values and lines represent the predictions of the fixed part of the model with cross type, body size and their interaction as fixed effects and maternal and paternal families as random effects for egg load at emergence, body size as fixed effect and maternal families and block as random effects for egg load at death.</p

Means ± SEM of egg load at emergence and at death.

<p>Means and SEM are calculated for observed values minus the predictions for random effects of a model with cross type, body size and their interaction as fixed effect and paternal and maternal populations as random effects (egg load at emergence) or a model with body size as fixed effect and maternal population and block as random effects (egg load at death). Means for within-family, between-family and between-population crosses are represented by black, grey and empty circles, respectively. For egg load at emergence, least-square means were higher for between-family crosses than for other crosses (within-family/between-family: z = 2.92, <i>p</i> = 0.0097; within-family/between-population: z = −0.26, <i>p</i> = 0.9627; between-family/between-population: z = 3.14, <i>p</i> = 0.0049).</p

Generalized linear models and generalized linear mixed model for (A) mating probability, (B) presence of daughters among progeny, and (C) offspring sex ratio.

<p>Details are provided in parentheses for each response variable: error distribution, variance components (VC) for the random effects selected (M = maternal family; P = paternal family), number of observations (N) and number of levels for random effects (n_M =  number of maternal families; n_P = number of paternal families).</p

Generalized linear models for (A) body size and (B) symmetry.

<p>For each response variable, details are given in parentheses: error distribution and the number of observations (N).</p