Ecogeographic surveys as tools for analyzing potential reproductive isolating mechanisms: an example using Solanum juglandifolium Dunal, S. ochranthum Dunal, S. lycopersicoides Dunal, and S. sitiens I. M. Johnston

Abstract

An ecogeographic survey was completed for two pairs of South American Solanum species: (1) S. juglandifolium and S. ochranthum, and (2) S. lycopersicoides and S. sitiens. The purpose of this survey was to characterize the distribution, ecology, and phenology of these species and to screen for factors that might constitute premating reproductive isolating mechanisms between each pair. Passport data from 276 herbarium specimens were entered into a database, which was subsequently analyzed to determine the ecogeographic distribution and phenology of the surveyed species. The differences between species uncovered by the survey were then considered in the context of reproductive isolation. As S. juglandifolium and S. ochranthum were found to have overlapping ecogeographic preferences and phenology, it was postulated that postmating isolating mechanisms form the principal barrier to hybridization between the two species. Unlike S. juglandifolium and S. ochranthum, S. lycopersicoides and S. sitiens differed markedly in ecogeographic distribution. The species have been successfully crossed several times artificially, so the differences in distribution found in this survey probably contribute to maintaining species barriers between the two. In summary, this ecogeographic survey provided a useful method for analyzing the potential for interspecific gene flow between closely related taxa.