Temporal variation in the pollen:ovule ratios of Clarkia (Onagraceae) taxa with contrasting mating systems: field populations

Abstract

Among plants, pairs of selfing vs. outcrossing sister taxa provide interesting systems in which to test predictions concerning the magnitude and direction of temporal changes in sex allocation. Although resource availability typically declines towards the end of the growing season for annual taxa, temporal changes in mating opportunities depend on mating system and should change less in selfing taxa. Consequently, given that the pollen:ovule (P:O) ratio of flowers reflects the investment in (and potential fitness pay‐off due to) male vs. female function, we predicted that the P:O ratio should also be less variable among and within selfers than in closely related outcrossers. To test these predictions, we measured temporal changes in sex allocation in multiple field populations of two pairs of sister taxa in the annual flowering plant genus Clarkia (Onagraceae). In the outcrossing Clarkia unguiculata and the selfing Clarkia exilis, ovule production declined similarly from early to late buds, whereas pollen production remained constant or increased in the outcrosser but remained constant or decreased in the selfer. Consequently, the P:O ratio increased within unguiculata populations but marginally increased or stayed constant in exilis populations. In all populations of the selfing Clarkia xantiana spp. parviflora and the outcrossing C. x. spp. xantiana, both ovule and pollen production per flower declined over time. The effects of these declines on the P:O ratio, however, differed between subspecies. In each xantiana population, the mean P:O ratio did not differ between early and late flowers, although individuals varied greatly in the direction and magnitude of phenotypic change. By contrast, parviflora populations differed in the mean direction of temporal change in the P:O ratio. We found little evidence to support our initial predictions that the P:O ratio of the selfing taxa will consistently vary less than in outcrossing taxa.

Physiological Performance in Clarkia Sister Taxa with Contrasting Mating Systems: Do Early-Flowering Autogamous Taxa Avoid Water Stress Relative to Their Pollinator-Dependent Counterparts?

“…The outcrossing and relatively widespread xantiana occupies rocky hillsides in the southern Sierra Nevada, the Tehachapi Mountains, and the Western Transverse Ranges; parviflora is typically restricted to rocky slopes in the eastern portion of the species' range (Hickman 1993). 1032 INTERNATIONAL JOURNAL PLANT SCIENCES Dudley et al (2007) and Delesalle et al (2008) provide additional information about these four taxa.…”

The effect of flower position on variation and covariation in floral traits in a wild hermaphrodite plant

“…This intra-inflorescence variation in floral allocation has been attributed to the effects of resource competition [21-23], architectural effects [20,24,25] or mating environments [26,27]. Although the ability to adjust sex allocation over time is one potential advantage of modularity in hermaphrodites [26,28,29], there are few empirical studies that examine temporal variation in floral traits [30,31], particularly considering trait correlations among sequentially blooming flowers.…”

Sistema Reproductivo de Trichloris (Poaceae, Chloridoideae, Chlorideae)

“…Diversos autores han señalado numerosos caracteres morfo-funcionales asociados a las especies autógamas. Entre estos se destacan: a) tamaño reducido de las estructuras florales (Goodwillie et al, 2010, Kalisz et al, 2012, b) elevada superposición temporal de las funciones masculina y femenina (Delesalle et al, 2008, Mazer et al, 2009, c) ciclos florales de corta vida (Runions & Geber, 2000, Mazer et al, 2010, d) estructuras masculinas y femeninas próximas entre sí (Webb & Lloyd, 1986, Herlihy & Eckert, 2007 y, e) baja relación polen/óvulo (Cruden, 1977). Muchos de estos caracteres están presentes en las especies de Trichloris, reforzando su condición de autógamas.…”