Incomplete reproductive barriers and genomic differentiation impact the spread of resistance mutations between green- and red-colour morphs of a cosmopolitan mite pest.

Pesticide resistance represents a clear and trackable case of adaptive evolution with a strong societal impact. Understanding the factors associated with the evolution and spread of resistance is imperative to develop sustainable crop management strategies. The two-spotted spider mite Tetranychus urticae, a major crop pest with worldwide distribution and a polyphagous lifestyle, has evolved resistance to most classes of pesticides. Tetranychus urticae exists as either a green- or a red-coloured morph. However, the extent of genetic divergence and reproductive compatibility vary across populations of these colour morphs, complicating their taxonomic resolution at the species level. Here, we studied patterns of genetic differentiation and barriers to gene flow within and between morphs of T. urticae in order to understand the factors that influence the spread of resistance mutations across its populations. We derived multiple iso-female lines from Tetranychus populations collected from agricultural crops. We generated genomic and morphological data, characterized their bacterial communities and performed controlled crosses. Despite morphological similarities, we found large genomic differentiation between the morphs. This pattern was reflected in the incomplete, but strong postzygotic incompatibility in crosses between colour morphs, while crosses within morphs from different geographical locations were largely compatible. In addition, our results suggest recent/on-going gene flow between green-coloured T. urticae and T. turkestani. By screening the sequences of 10 resistance genes, we found evidence for multiple independent origins and for single evolutionary origins of target-site resistance mutations. Our results indicate that target-site mutations mostly evolve independently in populations on different geographical locations, and that these mutations can spread due to incomplete barriers to gene flow within and between populations.

Vasorelaxant effect of taurine is diminished by tetraethylammonium in rat isolated arteries.

Although the vasorelaxant effects of taurine have been studied in rabbit ear artery, rat isolated aorta and mesenteric artery, its pharmacological properties in other vascular beds and underlying mechanism(s) are still not well clarified. The present study was designed to observe the effects of taurine on the contractions induced by depolarization and phenylephrine in rat isolated aortic, renal and mesenteric arterial rings, and to get an insight into its mechanism(s). Arterial rings were suspended in organ baths and tension was recorded isometrically. Taurine 20-80 mM produced concentration-dependent relaxations of rat isolated aortic rings precontracted by 30 mM potassium chloride and 1 microM phenylephrine; the maximal relaxation was 17.17+/-3.18% and 22.23+/-1.83% respectively. The relaxation was not affected by 0.1 mM NG-nitro-L-arginine methylester ester (a nitric oxide synthetase inhibitor), 10 microM indomethacin (a cyclooxygenase inhibitor), 1 mM 4-aminopyridine (a K(V) blocker), 10 muM glibenclamide (a K(ATP) blocker), 1 mM barium chloride (BaCl(2), a K(IR) blocker), and 100 nM iberiotoxin (a BK(Ca) blocker), but was nearly abolished by 10 mM tetraethylammonium (TEA, a non-selective potassium channel blocker). Preincubation with taurine 20-60 mM did not affect the basal tone but inhibited the contraction induced by phenylephrine, and the inhibitory effect was attenuated by TEA in isolated renal and mesenteric arterial rings. Present experiments show that taurine relaxes contracted rat aorta and inhibits the phenylephrine-induced contraction of renal and mesenteric arteries, and suggest that a mechanism related to potassium channel opening may be involved in the action of taurine.