Reproductive interference and sensitivity to female pheromones in males and females of two herbivorous mite species

Abstract

Competitive interaction between sister species can be affected by reproductive interference (RI) depending on the ability of males to discriminate conspecific from heterospecific mates. We study such interactions in Tetranychus evansi and T. urticae. These spider mites co-occur on solanaceous plants in Southern Europe, and cause important yield losses in tomato crops. Previous studies using Spanish populations found that T. evansi outcompetes T. urticae, and that this is due to unidirectional RI of T. evansi males with T. urticae females. The unidirectional RI is attributed to differences in male mate preference for conspecific females between the two species. Also, differences in the propensity of interspecific web sharing in females plays a role. To investigate proximate mechanisms of this RI, here we study the role of female pheromones on male mate preference and female web sharing. We extracted pheromones from females of the two species, and investigated if males and females were arrested by the pheromone extractions in various concentrations. We observed that T. urticae males were more sensitive to the pheromone extractions and able to discriminate conspecific from heterospecific ones. Tetranychus evansi males, on the other hand, were less sensitive. Females from both species were arrested by conspecific pheromone extraction in lower concentrations. In conclusion, heterospecific mating by T. evansi males, which results in RI, can be explained by their lack of discrimination between female pheromones of the two species. Differences in the propensity of interspecific web sharing in females might not be explained by the pheromones that we investigated.

The operational sex ratio experienced by mothers modulates the expression of sons’ alternative reproductive tactics in spider mites

“…Indeed, males mounting teleiochrysalis males are occasionally observed in extremely dense populations but the ART of those males is unknown. Also, mating with incompatible females such as females from different strains and species occurs in T. urticae (Collins and Margolies 1994;Navajas et al 2000;Sato et al 2014a), a phenomenon which can be associated with decreased sensitivity, specificity or lowered acceptance threshold of the sex pheromone (Sato and Alba 2020). However, explanation (ii) seems less plausible to explain our observations because lowered response/acceptance thresholds are commonly assumed to correlate with elevated stress and aggression, which is expected to be a fighter trait.…”

“…It is unclear which mechanism mediates the information transfer from mothers to the sons in the parental effects observed here. However, a faster guarding response to teleiochrysalis females may be brought about by mothers enhancing the sensitivity and/or responsiveness of sneaker males to sex pheromones emitted by teleiochrysalis females (Cone et al 1971;Royalty et al 1992Royalty et al , 1993aRoyalty et al , 1993bRasmy and Hussein 1994;Margolies and Collins 1994;Oku et al 2015;Rodrigues et al 2017;Sato and Alba 2020) although theoretically two alternative explanations are possible. (i) These male-arresting sex pheromones can be extracted from all life stages and both sexes, although the amount is much higher in teleiochrysalis females (Royalty et al 1992;Margolies and Collins 1994).…”

Wolbachiastrengthens the match between pre-mating and early post-mating isolation in spider mites

“…Therefore, post-mating incompatibilities are particularly costly and should select for earlier pre-zygotic barriers through reinforcement. Yet, highly variable degrees of pre-mating isolation can be found both between (Sato et al 2014(Sato et al , 2016Clemente et al 2016;Sato and Alba 2020) and within species (e.g., Murtaugh and Wrensch 1978;Gotoh et al 1993).…”

Competitor Displacement by an Herbivore that Manipulates Plant Defences

“…T. evansi produces a very dense web that prevents competitors or predators to accessing its feeding sites (Renato A Sarmento et al, 2011). In addition, reproductive interference with genetically incompatible congenerics and the overcompensation of oviposition in the presence of competitors aid T. evansi to increase its competitive potential (Sato & Alba, 2020; Sato et al, 2014). Whether these ‘buffering traits’ have evolved along the ability to suppress plant defences in order to protect it from exploitation remains an unexplored possibility that might explain the observed patterns of competitor displacement by suppressing mites (Blaazer et al, 2018).…”