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Reproductive modes in Leiothrix (Eriocaulaceae) in south-eastern Brazil: the role of microenvironmental heterogeneity.

BACKGROUND AND AIMS
The genus Leiothrix (Eriocaulaceae) is restricted to South America and contains 37 taxa. The genus is most species-rich in the mountains of Minas Gerais, where 25 species occur, 19 of them in the Serra do Cipó. Leiothrix taxa that inhabit different microhabitats exhibit a number of reproductive modes. Rhizomatous taxa produce seeds plentifully; therefore, this group were defined as rhizomatous seed-producing. The pseudoviviparous reproductive mode was divided into canopy-forming and rooted. In the first, ramets remain attached to a parental rosette suspended by scapes, whereas in the second, ramets take root and may or may not remain attached to a parental rosette. In this study, it is proposed that microenvironmental heterogeneity is an important factor generating and maintaining reproductive modes in Leiothrix.


METHODS
Soil analyses and vegetation cover estimates were performed for five Leiothrix taxa occurring in 19 areas along the Serra do Cipó. In these 19 points of the Serra do Cipó, soil data were collected from 27 populations of each species, and vegetation cover data were collected from 20 populations, due to fire that occurred in the region and destroyed most of the vegetation. For each population, three replicates were made. A discriminant function analysis was performed, in an attempt to test the effect of microhabitat features in the differentiation of the reproductive modes.


KEY RESULTS
Discriminant function analyses separated the three groups of reproductive modes based mainly on percentage vegetation cover. The pseudoviviparous canopy-forming group occurs under densely crowded conditions, while the pseudoviviparous rooted and rhizomatous seed-producing groups occur in areas with sparse vegetation cover. However, the group pseudoviviparous rooted occurs in soils constituted of exposed sand, while the rhizomatous seed-producing group occurs, frequently, on mat-forming mosses.


CONCLUSIONS
Microenvironmental heterogeneity, specifically heterogeneity in percentage cover of vegetation, appears to have influenced the generation and maintenance of reproductive modes in Leiothrix. Reproductive variation within Leiothrix taxa occupying different microenvironments results from a response to fine-scale habitat variation. Therefore, it is proposed that ecological speciation is an important process in adaptive radiation in this genus.