Gender-specific floral and physiological traits: implications for the maintenance of females in gynodioecious Lobelia siphilitica

Abstract

A common gender dimorphism in angiosperms is gynodioecy, in which hermaphrodites and females co-occur. Females are at an inherent disadvantage because they can transmit their genes only through ovule production. One mechanism by which females can compensate for the loss of male function is by producing more seeds than hermaphrodites. As such, females should: (1) increase resource uptake to support higher seed production; and (2) allocate resources saved by the loss of male function to seed production. To test this hypothesis, we measured physiological and floral traits of gynodioecious Lobelia siphilitica, controlling for both environmental and genetic variation through a comparison of greenhouse-grown siblings. Pre-reproductive females had 14% higher area-based (Z=2.14; P=0.04) and 32% higher mass-based (Z=1.96; P=0.05) photosynthetic rate than hermaphrodites, suggesting that they have increased carbon acquisition by altering photosynthetic physiology. Female L. siphilitica produced flowers with 4-8% smaller corollas than hermaphrodites (all P<0.05), suggesting that females allocate resources away from floral structures used for pollinator attraction. The genetic correlation between genders for four floral and four physiological traits was significantly less than one but greater than zero, indicating that the evolution of gender dimorphism in response to sex-differential selection will be constrained. The allocation of resources saved by the loss of male function has been viewed as the most important mechanism allowing females of gynodioecious species to support higher seed production. Our data suggest that increased resource acquisition by females at pre-reproductive stages can also contribute to the maintenance of gender dimorphism in gynodioecious species.

An angiosperm-wide analysis of the gynodioecy–dioecy pathway

“…Some papers refer to gynodioecy as the second most frequent reproductive system in angiosperms after hermaphroditism (e.g. Collin et al 2002;Bailey et al 2003;Caruso et al 2003;Chang, 2006), while others consider gynodioecy an extremely rare system (e.g. Charlesworth, 2002).…”

Effect of genotype, Cr(III) and Cr(VI) on plant growth and micronutrient status in Silene vulgaris (Moench)

“…This increase in female fitness has been observed in most gynodioecious species, but the few studies that investigated physiological differences between genders in gynodioecious species have produced inconsistent results (Poot et al, 1996;Caruso et al, 2003;Schultz, 2003).…”

“…Comparison of physiological traits between genders is scarce for gynodioecious species, and the results are generally inconsistent, with some suggesting that females have higher photosynthetic rates (Caruso et al, 2003) and others suggesting the opposite (Schultz, 2003). At least three physiological mechanisms might underlie such sex differences: i) higher carbon demand in developing fruit; ii) greater nitrogen demand in developing seeds and iii) greater rate of active translocation of resources from leaves to developing fruit.…”

Sexual differences in response to simulated herbivory in the gynodioecious herb Geranium sylvaticum

“…Additionally, in the absence of differences in life-history parameters, females producing higher amounts of seeds should theoretically either have larger photosynthetic area or higher physiological activities that make large resource flux to seeds possible. Although rarely studied, sexspecific physiological differences are documented in some gynodioecious species: photosynthesis rate is reported to be different in the two gender morphs in the gynodioecious Lobelia siphilitica (Caruso et al 2003) and Schiedea salicaria (Culley et al 2006).…”