Balancing in- and out-breeding by the predatory mite Phytoseiulus persimilis

Demet Atalay,Peter Schausberger

doi:10.1007/s10493-018-0225-3

Abstract

In- and out-breeding depressions are commonly observed phenomena in sexually reproducing organisms with a patchy distribution pattern, and spatial segmentation and/or isolation of groups. At the genetic level, inbreeding depression is due to increased homozygosity, whereas outbreeding depression is due to inferior genetic compatibility of mates. Optimal outbreeding theory suggests that intermediate levels of mate relatedness should provide for the highest fitness gains. Here, we assessed the fitness consequences of genetic relatedness between mates in plant-inhabiting predatory mites Phytoseiulus persimilis, which are obligatory sexually reproducing but haplo-diploid. Both females and males arise from fertilized eggs but males lose the paternal chromosome set during embryogenesis, dubbed pseudo-arrhenotoky. Phytoseiulus persimilis are highly efficacious in reducing crop-damaging spider mite populations and widely used in biological control. Using iso-female lines of two populations, from Sicily and Greece, we assessed the fecundity of females, and sex ratio of their offspring, that mated with either a sibling, a male from the same population or a male from the other population. Additionally, we recorded mating latency and duration. Females mating with a male from the same population produced more eggs, with a lower female bias, over a longer time than females mating with a sibling or with a male from the other population. Mating latency was unaffected by mate relatedness; mating duration was disproportionally long in sibling couples, likely indicating female reluctance to mate and sub-optimal spermatophore transfer. Our study provides a rare example of in- and out-breeding depression in a haplo-diploid arthropod, supporting the optimal outbreeding theory.

Highlights

Inbreeding, the mating or breeding between genetically closely related individuals is common in small, fragmented or isolated populations
The level of genetic relatedness affected the mating duration (GLM; Wald χ2 = 6.305, df = 2, P = 0.04), which was unaffected by population (Wald χ2 = 0.623, df = 2, P = 0.73) and the interaction between the level of genetic relatedness and population (Wald χ2 = 4.358, df = 2, P = 0.11) (Fig. 2): sibling (S) couples mated longer than WP and BP couples (LSD; P ≤ 0.05), while WP and BP couples mated long (P > 0.05)
We assessed excessive in- and outbreeding in P. persimilis by comparing the behavioral and reproductive performance of couples having one of three levels of genetic relatedness, that is, mating between siblings, between individuals of the same population and between individuals of different populations

Summary

Introduction

Inbreeding, the mating or breeding between genetically closely related individuals is common in small, fragmented or isolated populations (for review Charlesworth and Charlesworth 1987, 1999; Frankham et al 2002; Henter 2003). At the genetic level, inbreeding depression is associated with increased homozygosity. Two major hypotheses of the causal mechanisms of inbreeding depression have been put forward, i.e. the partial dominance hypothesis and the over-dominance hypothesis (Charlesworth and Charlesworth 1999; Wright et al 2008; Charlesworth and Willis 2009). Both hypotheses assume that increased homozygosity reduces fitness. The partial dominance hypothesis states that fitness reduction arising from inbreeding depends on the genetic load of recessive deleterious alleles. Inbreeding increases the expression of deleterious recessive alleles by increasing the frequency of deleterious homozygous combinations (Waller 1993; Shultz and Willis 1995). The overdominance hypothesis states that heterozygotes generally have a superior fitness than either homozygote (Charlesworth and Willis 2009)

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Results

Conclusion