Abstract
Inbreeding and inbreeding depression are processes in small populations of particular interest for a range of human activities such as animal breeding, species conservation, or pest management. In particular, biological control programs should benefit from a thorough understanding of the causes and consequences of inbreeding because natural enemies experience repetitive bottlenecks during importation, laboratory rearing, and introduction. Predicting the effect of inbreeding in hymenopteran parasitoid wasps, frequently used in biological control programs, is nonetheless a difficult endeavor. In haplodiploid parasitoids, the purge of deleterious alleles via haploid males should reduce genetic load, but if these species also have complementary sex determination (CSD), abnormal diploid males will be produced, which may jeopardize the success of biological control introductions. Mastrus ridens is such a parasitoid wasp with CSD, introduced to control the codling moth, Cydia pomonella (L.). We studied its life history traits in the laboratory under two conditions: inbred (full‐sib) and outbred (nonsib) crosses, across five generations, to examine the consequences of inbreeding in this species. We found that in inbred lines, nonreproducing females live less, the number of daughters produced was lower, and sex ratio (proportion of males) and proportion of diploid males were higher. Diploid males were able to produce fertile daughters, but fewer than haploid males. Lineage survival was similar for inbred and outbred lines across the five generations. The most significant decrease in fitness was thus a consequence of the production of diploid males, but this effect was not as extreme as in most other species with CSD, due to the fertility of diploid males. This study highlights the importance of determining the type of sex determination in parasitoid wasps used for biological control, and the importance of maintaining genetic diversity in species with CSD when importation or augmentation is the goal.
Highlights
The biology of small populations has important applications in areas such as species conservation (Hedrick & Kalinowski, 2000), animal breeding (Douglas, 1999), or pest biological control (Fauvergue, Vercken, Malausa, & Hufbauer, 2012)
We investigated the effects of inbreeding on Mastrus ridens, a gregarious parasitoid with single-locus complementary sex
Inbreeding depression is generally lower in haplodiploid species (Henter, 2003; Werren, 1993) because some deleterious alleles can be purged via hemizygous males, a range of effects on phenotypic traits, from insignificant to considerable, have been found in hymenopteran species (Antolin, 1999)
Summary
The biology of small populations has important applications in areas such as species conservation (Hedrick & Kalinowski, 2000), animal breeding (Douglas, 1999), or pest biological control (Fauvergue, Vercken, Malausa, & Hufbauer, 2012). Gregarious immature development may increase the probability of sib-m ating, and viability of diploid males along with monandry may lower the fitness of sib-m ated females as well as females mating with diploid males (Godfray, 1994; Thiel & Weeda, 2014; Thiel, Weeda, de Boer, & Hoffmeister, 2013; Zayed & Packer, 2005) This puts strong pressure on Hymenoptera with CSD to develop ways to decrease sib-m ating, for example, through behavioral mechanisms (Metzger, Bernstein, Hoffmeister, & Desouhant, 2010; Ode, Antolin, & Strand, 1995; Van Wilgenburg, Driessen, & Beukeboom, 2006). The offspring will be constituted by fewer daughters and more sons (including diploids), leading to a more male-biased sex ratio (larger proportion of sons) In this case, any negative effects of inbreeding would increase during the first few generations, as a consequence of the loss of CSD alleles, but would remain stable once the lowest possible number of CSD alleles (two) is reached. Our results should serve the optimization of rearing protocols and release strategies in biological control programs using parasitoids with CSD, starting with the particular case of M. ridens against the codling moth
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