Sexual reproduction can be thought of as a cooperative process in whichtwo individuals come together to produce a new individual. It can alsobe viewed as a process in which two parties with differing interests,investment, and background interact to produce a new individual. Fromthe former perspective, parental interests are unified (both wish toproduce vigorous offspring), while the latter suggests possibleconflict. This conflict can occur before or after fertilization. Beforefertilization, the mother has an interest in picking the best suitedfather from a larger pool, while all fathers have an interest in beingpicked. After fertilization, fathers have an interest in maximizingmaternal investment in their progeny, while mothers will have aninterest in carefully partitioning resources among progeny to maximizetheir combined success.
A new study in the September issue of The American Naturalist arguesthat with increased self-fertilization, parental conflict decreases.Consequently, parents from frequently selfing groups should becompetitively inferior with respect to this parental conflict. YanivBrandvain and David Haig examine crosses between selfing andoutcrossing pairs and find that, in most cases, there are pre- andpost-zygotic symptoms of outcrossers being "stronger" than selfers withregard to parental conflict. They contend that this competitiveimbalance can explain a common pattern of unilateral incompatibility,in which pollen from self-incompatible populations can successfullyfertilize ovules of self-compatible individuals, but the reciprocalcross fails. Since both pre- and post-zygotic consequences of thisimbalanced conflict can perturb successful fertilization anddevelopment, they provide barriers to hybridization and may facilitatespeciation.
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Yaniv Brandvain and David Haig, "Divergent mating systems andparental conflict as a barrier to hybridization in flowering plants"166:3 September 2005.
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