Variation in reproductive investment and floret gender ratios in two gynodioecious mat daisies (Raoulia, Asteraceae)

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Widespread species could be expected to demonstrate greater among-population variation in reproductive traits than species with limited distributions. We investigated variability in floret gender and capitula number in populations of two gynomonoecious mat daisies, the widespread Raoulia australis and the alpine specialist Raoulia hectori in Central Otago, lower South Island. Gynomonoecy (female and hermaphrodite florets in a capitulum) is common in the daisy family Asteraceae. Varying gender ratios within capitula could allow for plasticity in reproductive investment in relation to environment and life-history stage. We found that the ratio of female to hermaphrodite florets within capitula did not vary significantly among populations or with plant size for either Raoulia species. Instead, the number of capitula produced varied among populations within species, independent of plant size, and showed different patterns in relationship to plant size between the two species. Smaller plants of the alpine specialist R. hectori consistently showed a proportionally greater allocation to reproduction than larger plants, whereas the relationship between plant size and reproductive allocation varied markedly among populations of R. australis. These results suggest that allocation to capitula may be a key component of reproduction in Raoulia species, and is potentially responsive to environment and life-history stage. However, as our study included few populations and did not follow through to seed production, this hypothesis requires further testing. Moreover, our values for floret gender ratios differed from standard species descriptions, so broader geographic variation in floret gender ratios may still exist.

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