No evidence for reproductive isolation through sexual conflict in the bulb mite Rhizoglyphus robini

Abstract

Sexual conflict leading to sexual antagonistic coevolution has been hypothesized to drive reproductive isolation in allopatric populations and hence lead to speciation. However, the generality of this speciation mechanism is under debate. We used experimental evolution in the bulb mite Rhizoglyphusrobini to investigate whether sexual conflict promotes reproductive isolation measured comprehensively to include all possible pre- and post-zygotic mechanisms. We established replicate populations in which we either enforced monogamy, and hence removed sexual conflict by making male and female evolutionary interests congruent, or allowed promiscuity. After 35 and 45 generations of experimental evolution, we found no evidence of reproductive isolation between the populations in any of the mating systems. Our results indicate that sexual conflict does not necessarily drive fast reproductive isolation and it may not be a ubiquitous mechanism leading to speciation.

Figure 1. Schematic representation of the design of Assay I.

Schematic representation of the design of Assay I and the way of calculating pre-zygotic isolation mechanisms under male competition index on the example of a female’s line 1. Procedures are described in the text.

Figure 2. Schematic representation of the design of Assay II.

Schematic representation of the design of Assay II and the way of calculating mate choice and post-zygotic reproductive isolation on the example of a male’s line 1. Procedures are described in the text.

Figure 3. Pre-zygotic isolation indexes measured under male competition for monogamous and promiscuous mating system.

Pre-zygotic isolation indices measured under male competition for monogamous and promiscuous mating system calculated from the mean indices for female lines. Indices values lower than 0.5 indicate that a male from the same line as a female fertilizes on average more eggs than a rival from different line. Bars indicate 95% confidence intervals.

Figure 4. Mate choice and post-zygotic isolation indexes for monogamous and promiscuous mating system.

Mean mate choice and post-zygotic isolation indices for monogamous and promiscuous mating system calculated from the mean indices for male lines. Indices values lower than 0.5 indicate that a female from the same line as a male produces on average more offspring than a female from a different line. Bars indicate 95% confidence intervals.