Effects of floral herbivory, limited pollination, and intrinsic plant characteristics on phenotypic gender in Sanicula arctopoides

Abstract

Sexual expression in hermaphroditic plants is often a function of environmental factors affecting individuals before or during flowering. I tested for the effects of floral herbivory and lack of pollination in early umbels on the relative proportions of hermaphroditic and staminate (male) flowers produced on later umbels by Sanicula arctopoides, a monocarpic, andromonoecious perennial. Neither floral herbivory or lack of early pollination had a significant effect on the ratio of the two floral morphs, but the probability of producing staminate flowers on late umbels was strongly and positively related to plant size measured just prior to floral initiation and prior to herbivory. Plant size was also negatively correlated with flowering date. I suggest that producing staminate flowers on late umbels should benefit large early-blooming plants more than small late-blooming plants because more mating opportunities occur during the period when these flowers release pollen. Although herbivory did not cause labile changes of sex, whole plant phenotypic gender was still strongly affected by various forms of treatment. Sex-biased herbivory or lack of pollination rendered plants more or less phenotypically male, depending on which tissues were affected. Deer and pollen-feeding mites preferentially remove male tissues while hymenopteran seed predators preferentially remove female tissues. I conclude that combinations of herbivores could have counteracting or compounding effects on plant gender, and these effects may change the rankings of male and female reproductive success within populations.

The Role of Herbivores in the Evolution of Separate Sexes From Hermaphroditism

“…In contrast to herbivory on sources, damage to sinks (buds, flowers, and fruit) in hermaphrodite plants routinely induces a plastic shift in sex allocation toward femaleness. Destruction of flowers resulted in an increase in the proportion of hermaphrodite flowers (i.e., those with female function) in three of four andromonoecious species studied, Heracleum lanatum [Hendrix 1984], Pastinaca sativa [Hendrix and Trapp 1981], and Isomeris arborea [Krupnick and Weis 1998] but not Sanicula arctopoides [Lowenberg 1997]. Additionally, anther smut disease eliminates male function, but only slightly reduces female function of hermaphrodites in gynomonoecious Dianthus silvester (Shykoff et al 1997).…”

Sex choice in plants: facultative adjustment of the sex ratio in the perennial herb Begonia gracilis

“…Furthermore, although little is known about the sex allocation mechanisms of monoecious species (Dellaporta & Calderon‐Urrea, 1993), it is well known that plants with this reproductive system are capable of facultative adjustments in response to a variety of physical and biological stimuli (Freeman et al. , 1980; Charnov, 1982; Cid‐Benevento, 1987; Lowenberg, 1997).…”

“…Evidence of facultative adjustments also exists in species in which sex is chromosomally determined although the mechanisms remain controversial. Plant literature has plenty of examples showing that in many species sex allocation responds to environmental or intrinsic conditions varying as a function of age, size, herbivore damage, disease, weather, nutritional condition and light (Freeman et al, 1980(Freeman et al, , 1981Charnov, 1982;Cid-Benevento, 1987;Delph & Lloyd, 1991;Sakai & Weller, 1991;Wells & Lloyd, 1991;Klinkhamer et al, 1997;Lowenberg, 1997;McKone et al, 1998;de Jong et al, 1999). Most of the studies have concentrated on sex-allocation shifts in response to environmentally induced variation in spatial or parental resources.…”

“…Monoecious species (individuals are characterized by the presence of both male and female flowers) are particularly useful to test this kind of hypothesis as male and female investments are separated in different flowers. Furthermore, although little is known about the sex allocation mechanisms of monoecious species (Dellaporta & Calderon-Urrea, 1993), it is well known that plants with this reproductive system are capable of facultative adjustments in response to a variety of physical and biological stimuli (Freeman et al, 1980;Charnov, 1982;Cid-Benevento, 1987;Lowenberg, 1997).…”

Linking herbivory and pollination : costs and selection implications in Centrosema virginianum Bentham (Fabaceae: papilionoideae)

“…Male function is often negatively affected by leaf damage through reducing flower traits such as flowers size (Frazee and Marquis 1994, pollen number , Lowenberg 1997, and pollen size (Delph et al 1997, Lehtilae and.…”