Pollen-Ovule Ratio, Pollen Size, and Breeding System in Astragalus (Fabaceae) Subgenus Epiglottis: A Pollen and Seed Allocation Approach

Abstract

The correlation between pollenlovule (P/O) ratio and breeding system has generally been accounted for either on the basis that P/O reflects pollination efficiency, or in terms of the sex allocation theory. The following were assessed for taxa belonging to genus Astragalus subgenus Epiglottis: I) Degree of correlation between P/O and the breeding system, measured by means of autofertility; 2) The absence or existence of correlation between P/O and pollen grain size; and 3) The ability of various theories to account for the results obtained. Results showed a minimal correlation between P/O and autofertility, and between P/O and pollen grain size in the taxa studied. Analysis of these results in terms of the sex allocation theory enabled this correlation to be explained as a function of the variation existing between taxa with respect to the resources invested in each pollen grain and in each ovule. The predictive capacity ofthis theory, which has moreover proven valuable in explaining the structural peculiarities of the androecium in these taxa, was also highlighted. The type of self-pollination applicable was also discussed, as was the phenotypic model of selection of self-fertilization considered most plausible for these taxa.

Pollen limitation and inbreeding depression in an ‘old rare’ bumblebee‐pollinated grassland herb

“…The pollen/ovule ratio of A . exscapus was one order of magnitude higher than that of reportedly selfing Astragalus species (Gallardo et al. 1994) and similar to that of other perennial Astragalus species (cf.…”

Pollination mode and life form strongly affect the relation between mating system and pollen to ovule ratios

“…For example, several outcrossing taxa are either associated with unusually low P : O ratios (Vasek & Weng, 1988; James & Knox, 1993; Ng & Corlett, 2000; Wang et al ., 2004; Darrault & Schlindwein, 2005) or with very high P : O ratios (Casper, 1982; Cruden, 2000). Also, inconsistencies between expectations, derived by comparing measured P : O ratios with the values given by Cruden (1977) for different mating system classes and independently derived estimates of the mating system, have been reported frequently (Ritland & Ritland, 1989; Gallardo et al ., 1994; Ramirez & Seres, 1994; Olesen et al ., 1998; Sneddon, 1999; Bosch et al ., 2001; Smissen & Garnock‐Jones, 2002; Parachnowitsch & Elle, 2004; Chouteau et al ., 2006). This substantiates the need for additional factors explaining variation in P : O ratios.…”

“…P : O ratios have been shown to reflect variability in seed weight (e.g. Uma Shanker & Ganeshaiah, 1984; Götzenberger et al ., 2006), pollen size (Gallardo et al ., 1994; but see Götzenberger et al ., 2007), stigmatic area, the pollen‐bearing area of pollinators (Cruden & Miller‐Ward, 1981), the size of the pollen dispersal unit (Harder & Johnson, 2008) and the effectiveness of the pollen vector (reviewed in Cruden, 2000). Although not demonstrated thoroughly, the rewarding strategy is also likely to affect P : O ratios, as plants with flowers that offer nectar as well as pollen, or only pollen as a reward, probably have higher P : O ratios than those only providing nectar for pollination services (Mione & Anderson, 1992; Cruden, 2000).…”

A new species of <i>Astragalus</i> L. sect. <i>Sesamei</i> DC. (Leguminosae) from the southeast of Spain: <i>Astragalus castroviejoi</i>

“…This leads us to think that the whole group is self-fertilising, as is the case with other annual species of Astragalus of the sections Bucerates DC. and Epiglottis Bunge (Gallardo & al., 1994).…”