Physiological effects of temperature do not explain prevalence of females in populations of gynodioeciousLobelia siphiliticagrowing in warmer climates.
OBJECTIVE
Gynodioecy is a sexual polymorphism whereby female and hermaphroditic plants co-occur within populations. In many gynodioecious species, stressful abiotic environments are associated with higher frequencies of females. This association suggests that abiotic stress affects the relative fitness of females and hermaphrodites and, thus, the maintenance of gynodioecy.


METHODS
To test whether abiotic stress affects the fitness of females and hermaphrodites, we grew open-pollinatedLobelia siphiliticafamilies in temperature regimes characteristic of the southern portion of the species' range (where females are common) and the northern portion of the range (where females are rare). We measured physiological and phenological traits that are indicative of heat stress, and fitness components of females and hermaphrodites that could affect the maintenance of gynodioecy.


RESULTS
Contrary to expectations if growth at high temperatures is stressful, we found that the hot treatment increased leaf chlorophyll content, decreased the percentage of plants that delayed flowering initiation, and did not affect the quantum efficiency of photosystem II. Growth at high temperatures did not affect the magnitude of the difference in rosette size (a correlate of flower number) between females and hermaphrodites, or the variance in pollen viability among hermaphrodites.


CONCLUSIONS
We found that growing-season temperatures typical of high femaleL.siphiliticapopulations were not stressful and did not affect either the fitness of females compared to hermaphrodites or variation in fitness among hermaphrodites. Consequently, further research is necessary to explain correlations between abiotic environmental factors and the frequency of females in this and other gynodioecious species.
Department of Biology, Providence College, Providence, Rhode Island 02918, USA mbailey9@providence.edu.
Maia F
MF
Bailey
Department of Biological Sciences, Kent State University, Kent, Ohio 44242, USA.
Andrea L
AL
Case
Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Christina M
CM
Caruso
D002734:Chlorophyll / Q000378:metabolism; D002980:Climate; D035264:Flowers / Q000254:growth & development / Q000502:physiology; D029746:Lobelia / Q000254:growth & development / Q000502:physiology*; D010641:Phenotype; D011058:Pollen / Q000254:growth & development / Q000502:physiology; D054817:Pollination; D012098:Reproduction; D012744:Sex Ratio; D013312:Stress, Physiological; D013696:Temperature
D002734:Chlorophyll
abiotic stress; breeding system; cost of restoration; female advantage; gynodioecy; reproductive compensation; sex ratio