Effects of male sterility on reproductive traits in gynodioecious plants: a meta-analysis

Abstract

Female fecundity advantage in gynodioecious plants is required for the spread and maintenance of this reproductive system. However, not all reproductive characters show female advantage in all species. We used a meta-analysis to summarise differences between females and hermaphrodites reported from the literature for several reproductive traits. Further we tested three hypotheses, (1) that female plants of species with many ovules produce more seeds per fruit while those with few ovules produce heavier seeds, (2) that females are more pollen limited than hermaphrodites, and (3) that floral sexual size dimorphism is more pronounced in species with few ovules, either because female reproductive success is less limited by pollen availability in such species or because flowers with few ovules require a smaller floral structure to protect the carpels. Overall, females compared to hermaphrodites produced more but smaller flowers, had higher fruit set, higher total seed production, and produced heavier seeds that germinated better. Species with many versus few ovules differed in female advantage for flower size dimorphism, flower number, fruit set and total seed production. However seed size, seed set per fruit and seed germination differences between females and hermaphrodites did not differ significantly between species with few and many ovules. We also found no evidence for differential pollen limitation between females and hermaphrodites. Degree of floral sexual size dimorphism differed significantly between species with few and many ovules. Though pistillate flowers were generally smaller than those of hermaphrodites, species with many ovules showed less difference in flower size between the sexes, suggesting either that the protective role of the perianth constrains the evolution of sexual size dimorphism in species with many ovules or that selection for adequate pollination in species with many ovules impedes the reduction in flower size of females.

Prolonged stigma and flower lifespan in females of the gynodioecious plant Geranium sylvaticum

“…Females usually have a higher seed output, seeds that germinate better and/or have offspring of a higher quality (reviewed in Shykoff et al, 2003;Dufaÿ and Billard, 2012). Such female reproductive advantage has generally been attributed to three main, non-exclusive, proximal causes (Shykoff et al, 2003;Dufaÿ and Billard, 2012).…”

“…However, we are unaware of any study on gynodioecious plants showing pollination discrimination in favor of female plants. In fact, female flowers are almost always smaller than hermaphrodite flowers (reviewed in Delph, 1996 andShykoff et al, 2003;e.g. Bai et al, 2011;Barr and Fishman, 2011;Cuevas and López, 2011;Griffin and Byers, 2012;Blank et al, 2014;Cuevas et al, 2014) and/or they produce less nectar and pollen, leading to lower pollinator visitation rates (Delph, 1996;Ashman, 2000;Bai et al, 2011).…”

“…Whereas these three mechanisms leading to a female advantage have received a lot of attention in recent studies and reviews (Shykoff et al, 2003;Ashman, 2007;Dufaÿ and Billard, 2012;Vega-Frutis et al, 2013), a mechanism that is rarely discussed is the potential difference in flower and stigma lifespan, which can affect pollination levels. In dioecious and monoecious plants female flowers generally remain open for a longer time than male flowers (Primack, 1985).…”

Cytoplasmic male sterility in Mimulus hybrids has pleiotropic effects on corolla and pistil traits

“…The causes behind this relationship are not understood fully, though there is some support for the idea of selection for greater perianth size in females to protect ovaries (Delph et al, 1996). In contrast, in gynodioecious species with separate male-sterile (female) and male-fertile (hermaphrodite) plants in natural populations, female corollas are almost always smaller than those of hermaphrodites (Baker, 1948;Delph et al, 1996;Eckhart, 1999;Shykoff et al, 2003). Two hypotheses have been proposed for this relationship.…”

“…In gynodioecious taxa, a necessary precondition for the maintenance of male steriles is a fitness advantage, however slight, over male fertiles (Charlesworth and Charlesworth, 1978;Frank, 1989), and in most studies, females make at least as many seeds as hermaphrodites and generally more (Van Damme and Van Delden, 1984;Manicacci et al, 1998;Frank and Barr, 2001;Barr, 2003Barr, , 2004bShykoff et al, 2003). Higher seed set in females is commonly attributed to some kind of reallocation of resources from pollen to seeds, avoidance of inbreeding depression or ability to better deal with ecological stress (Barr, 2003;Meagher, 2007).…”