Effects of inbreeding on a gregarious parasitoid wasp with complementary sex determination

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.

Effect of mass rearing on the genetic diversity of the predatory mite Amblyseius swirskii

“…Long-term laboratory rearing of the codling moth parasitoid, Mastrus ridens (Horstmann), resulted in lower genetic diversity and higher occurrence of diploid males, most likely as an effect of the reduced allelic diversity on a complementary sex determination locus (Retamal et al, 2016). In inbred lines of this parasitoid, the sex ratio of males to females and the proportion of diploid males was higher, and fewer daughters were produced compared to outbred lines (Zaviezo et al, 2018). Also, inbred populations of the mass-reared parasitoid Trichogramma pretiosum (Riley) produced fewer offspring than genetically variable populations (Guzm an-Larralde et al, 2014).…”

Life‐history traits of the Whiting polyploid line of the parasitoid Nasonia vitripennis

“…In particular, Hymenoptera are prone to polyploidy, often as a consequence of a type of sex determination that is common in the order, the 'complimentary sex determination' (CSD) mechanism (Cook, 1993;van Wilgenburg et al, 2006;Heimpel & de Boer, 2008). This results in a so called 'diploid male vortex' and eventual extinction (Zayed & Packer, 2005;Hein et al, 2009;Zaviezo et al, 2018). Males develop from unfertilized eggs and have genomes of maternal origin only, whereas females develop from fertilized eggs and inherit complete chromosome sets from both parents.…”

The implications of rapid eco‐evolutionary processes for biological control ‐ a review

“…Island populations especially, which can be small given the constrained size of their habitat, experience strong inbreeding depression (Frankham, 1998). Often those agents are hampered by inbreeding depression (Fauvergue et al, 2015;Bueno et al, 2017;Zaviezo et al, 2018), but not always (Trevisan et al, 2016;Quaglietti et al, 2017). Often those agents are hampered by inbreeding depression (Fauvergue et al, 2015;Bueno et al, 2017;Zaviezo et al, 2018), but not always (Trevisan et al, 2016;Quaglietti et al, 2017).…”

“…Several groups have studied biocontrol systems with a focus on hymenopterans, many with complimentary sex determination. Often those agents are hampered by inbreeding depression (Fauvergue et al, 2015;Bueno et al, 2017;Zaviezo et al, 2018), but not always (Trevisan et al, 2016;Quaglietti et al, 2017). Low fitness in biocontrol agents in introduced populations relative to native ones, as in Aphidius ervi (Haliday) (Hufbauer, 2002), might be explained by fixation of deleterious alleles through either drift or inbreeding during the introduction.…”