Phylogenetic systematics and the evolution of mating systems in Lithospermum (Boraginaceae)

Studies pertaining to the evolution of mating systems have lacked a phylogenetic framework from which proposed models could be tested. Ecological studies also examining mating system dynamics have proceeded in a species by species manner and have as a result been unable to provide a synthesis between sex allocation and a particular type of mating system. Phylogenetic systematics provides framework from which evolutionary and ecological questions concerning mating systems can be address, however until recently this tool has been rarely used, and certainly not used to test hypotheses concerning the evolution of heterostyly. To test hypotheses proposed for heterostyly's development and to initiate studies concerning mechanisms influencing heterostyly's development, a phylogenetic analysis of Lithospermum (Boraginaceae) was conducted. Several questions were addressed all of which pertain to the intrageneric relationships in Lithospermum and the position of heterostylous taxa within the lineage.;Phylogenetic analysis and comparative resource allocation among heterostyly taxa determined that heterostyly was derived on four separate occasions within the lineage. The phylogeny also supports Darwin's hypothesis for heterostyly's development that morphological differentiation in stigma and anther heights occur first and self-incompatibility is secondarily derived. The expression of this mating system in terms of resource allocation is different among the heterostylous taxa with similar patterns of resource allocation appearing only among closely related heterostylous taxa. The analysis also indicated that one species Lithospermum cobrense exhibits a form of heterostyly that is more stable when compared to L. multiflorum. The less developed form of heterostyly provided an opportunity to examine mechanisms influencing stigma/anther positions within the heterostylous floral morphs.;Preliminary studies concerning the effects of herbivory on seed production indicate that Lithospermum multiflorum is not affected by early season herbivory. The compensatory response by the plants is to produce more flowers per plant. The increased number of flowers available to pollinators may exert a pressure on floral morphology, specifically stigma and anther height, such that successful pollinations and seed production is more likely to occur among individuals that have optimal stigma and anther heights between the heterostylous morphs.;This studies intent was to integrate ecology and phylogenetic systematic methodologies to test hypotheses for heterostyly's development and to begin to examine mechanisms that influence this mating system. The results represent the first time support for a particular hypothesis and provide a framework from which comparative studies can be initiated.