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Morph specific selection in Proc B

posted May 24, 2018, 12:38 AM by Bruno Buzatto   [ updated May 24, 2018, 12:40 AM ]

Today Proc B published a paper I wrote with Huon Clark and Joe Tomkins (both at UWA) about our ambitious artificial selection experiment with the mite Rhizoglyphus echinopus. The experiment ran for about a year and a half, so we put a lot of our work (and lives!) into that experiment. The goal was simple — I wanted to test whether selection acting exclusively on one male morph (males of this species can conditionally be one of 2 morphs: fighters or scramblers) would affect the evolution of the other morph. Phenotypic plasticity theory predicts some level of developmental decoupling between morphs, and therefore potential for independent evolution, but we suspected the story was a bit more complicated than that. So we imposed selection for thicker (and thiner) legs on 6 lines of mites, always applying selection to fighter males only, focusing on their fighting legs.

After 9 generations we found that scrambler males (and females!) presented correlated evolution in the same direction as shown by fighters. This is not very surprising, as we already knew there were genetic correlations for this trait between male morphs and sexes. However, our approach is a powerful demonstration of a genetic constraint for the evolution of dimorphisms (between sexes and morphs), and goes one step beyond predicting correlated evolution through genetic correlations — we showed that correlated evolution in the lab! Now we know that, despite these constraints, the morphs did evolve (prior to the experiment!) very different morphologies, so what we demonstrated just shows that somehow male morphs overcame the genetic constraints (that are truly there!) to evolve divergent morphologies. But now we need to figure out how!