Meeting Abstract
Interspecific reproductive barriers (IRBs) prevent hybridization and establish species integrity. Recent research has suggested that molecular mechanisms of interspecific incompatibility in plants are intimately related to that of gametophytic self-incompatibility, a mating system that establishes obligatory outcrossing between individuals of the same species via pollen-pistil interactions. We investigated the presence and direction IRBs among closely related species in the wild tomato clade (Solanum section Lycopersicon). We conducted reciprocal crosses between self-incompatible (SI) S. arcanum and self-compatible (SC) population of mostly SI S. peruvianum which lacks the expression of the female determinant gene of SI (S-RNase), and measured fruit and seed set. Additionally, we conducted crosses between SI S. arcanum and SC S. pimpinellifolium which is polymorphic in functionality of pollen-side SI factor (Cullin1). We found that SI S. arcanum and SC population of S. peruvianum were compatible only in one direction. Crosses between SC S. peruvianum (dam) and SI S. arcanum (sire) resulted in an average of 46.9% fruit set, while the reciprocal cross failed to set any fruit. However, there were associated fitness costs of hybridization in the fruits produced. Unlike the results for crosses between SI S. arcanum and SC S. peruvianum, crosses between SI S. arcanum and SC S. pimpinellifolium were compatible in both directions regardless of Cullin1 functionality. The variation of IRBs shown here complicates assumptions about how mating systems can predict the outcomes of interspecific incompatibilities and suggests that the establishment of IRBs involves uncharacterized complexities. This study contributes to the integration of molecular mechanisms and evolutionary consequences of interspecific interaction.
