Evol Ecol Res 10: 835-848 (2008)     Full PDF if your library subscribes.

Spatial and temporal female frequency variation in a plant with joint nuclear and cytoplasmic sex determination

Camille M. Barr

Division of Biological Sciences, University of Montana, Missoula, Montana, USA

Correspondence: C.M. Barr, Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA.
e-mail: camille.barr@mso.umt.edu


Questions: A population’s sex ratio is a trait that can have profound effects on fitness and is thus under strong selection. Despite the presence of predicted population-level sex ratios that optimize individual fitness, many plant population sex ratios have been theorized to be driven by gene-level processes that are expected to result in both spatially and temporally unstable sex ratios. Do sex ratios in Nemophila menziesii vary spatially and temporally, and does the temporal variation follow predictions based on theoretical models?

Study system: The annual plant Nemophila menziesii Hook. & Arn. in 16 California populations at various spatial scales over a period of 5 years.

Methods: I measured spatial and temporal variation in sex ratio for a gynodioecious plant with cytoplasmic male sterility over a period of 5 years. I used Moran’s I to estimate the spatial scale at which the sex ratio varied the most. I used Mantel tests and regression analyses to detect sex-ratio variation among years.

Results: Spatial autocorrelation in sex ratio was highest at small (0.25 m2) spatial scales. Temporal variation in sex ratio was most apparent at the within-population scale, and did not follow expectations based on simple models of cytoplasmic male sterility. These results provide rare small-scale spatial and long-term temporal evidence of sex-ratio variation and indicate that some recent information on the complicated inheritance and expression of cytoplasmic male sterility may be important in determining sex-ratio dynamics in natural populations.

Keywords: cytoplasmic male sterility, genomic conflict, gynodioecy, nuclear–cytoplasmic sex inheritance, sex ratio.

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