Complex sentence: It has been revealed in captivity studies, that most of the hybrids do not follow Haldane's Rule, but sometimes hybrid females die before they reach sexual maturity this underscores the case for the american black duck being a distinct species.
Split into simpler sentences: It has been revealed in captivity studies that most of the hybrids do not follow Haldane's Rule, but sometimes hybrid females die before they reach sexual maturity. This underscores the case for the american black duck being a distinct species.