engleski

Sexual dimorphism in gynodioecious Sidalcea hirtipes (Malvaceae). I. Seed, fruit, and ecophysiology

Gynodioecy is a stable dimorphism of female and hermaphrodite individuals. Females often exhibit a higher seed or fruit set. This difference in reproductive investment is hypothesized in models of sex allocation theory to result in compensatory sex differences in vegetative traits, such as leaf physiological function, and in microhabitat. To investigate this possibility in gynodioecious Sidalcea hirtipes in two Oregon coastal populations, I compared the two sex morphs in several physiological and ecological variables, including fruit and seed set, spatial dispersion, instantaneous gas exchange, water use efficiency, and water potential. Several significant sex differences were found: Hermaphrodites exhibited a lower CO2 compensation point, day respiration rate, predawn water potential, and seed set per fruit. Hermaphrodites had slightly higher rates of carbon assimilation across the range of supplied CO2 concentrations, significantly for low CO2 values. Both sex morphs showed some spatial clumping at the level of the nearest neighbor but no significant pattern at any other spatial scale. These results indicate that sex dimorphism in photosynthetic gas exchange can occur in gynodioecious species and may result from a physiological trade-off against seed production. Secondary sex differences, however, were more subtle than typically observed in dioecious species, which perhaps reflects the less evolutionarily derived state of gynodioecy.

gynodioecy; male sterility; carboxylation; electron transport; respiration; photosynthesis

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