Data from: Testing for reproductive interference in the population dynamics of two congeneric species of herbivorous mites

When phylogenetically close, two competing species may reproductively
interfere, and thereby affect their population dynamics. We tested for
reproductive interference (RI) between two congeneric haplo-diploid spider
mites, Tetranychus evansi and Tetranychus urticae, by investigating their
interspecific mating and their population dynamics when they competed on
the same plants. They are both pests of tomato, but differ in the host
plant defences that they suppress or induce. To reduce the effect of
plant-mediated interaction, we used a mutant tomato plant lacking
jasmonate-mediated anti-herbivore defences in the competition experiment.
In addition, to manipulate the effect of RI, we introduced founder females
already mated with conspecific males in mild RI treatments or founder,
virgin females in strong RI treatments (in either case together with
heterospecific and conspecific males). As females show first-male sperm
precedence, RI should occur especially in the founder generation under
strong RI treatments. We found that T. urticae outcompeted T. evansi in
mild, but not in strong RI treatments. Thus, T. evansi interfered
reproductively with T. urticae. This result was supported by crossing
experiments showing frequent interspecific copulations, strong postmating
reproductive isolation and a preference of T. evansi males to mate with T.
urticae (instead of conspecific) females, whereas T. urticae males
preferred conspecific females. We conclude that interspecific mating comes
at a cost due to asymmetric mate preferences of males. Because RI by T.
evansi can improve its competitiveness to T. urticae, we propose that RI
partly explains why T. evansi became invasive in Europe where T. urticae
is endemic.