Does Haldane's rule speciation within mimetic Poison frogs?

To explain how populations with distinct warning signals coexist in close parapatry, we experimentally assessed intrinsic mechanisms acting as reproductive barriers within three Ranitomeya poison-frog species. For all species, assortative mating did not occur, nor did a survival disadvantage for inter-population hybrids. However, in Ranitomeya fantastica , these hybrids of the male sex are sterile, an outcome predicted by Haldane’s rule. Our results suggest a possible XY sex determinism in R. fantastica , and show that this process is associated with an extraordinary diversity, leading to speciation.