Évolution du rapport des sexes de populations de Rumex acetosella le long d'une succession postculturale

Abstract

The sex ratios of natural populations of Rumex acetosella L. have been recorded during two growing seasons, along a successional gradient of abandoned agricultural fields of various ages (from 6 months to 15 years old), south of Paris. At the same time, male and female ramets have been collected to determine the resource allocation pattern of the different organs. We have observed that females of Rumex acetosella L. were more frequent than males at the younger stages, and that males predominated at the older ones. Concomitantly, there was a decrease in aboveground biomass and in the reproductive effort of the two sexes in the field, with increasing community maturity. The decrease in reproductive effort was confirmed, in controlled conditions, in the female genets only. Females always produced a higher reproductive effort and a higher aboveground biomass than males, which may explain why they were more abundant in the younger successional stages. Otherwise, our results show that sexual reproduction represented a high energetic cost which tended to consume root resources. Females, and mainly those of the younger stages which presented a high reproductive effort, may suffer more than males. The latter, which were more vigorous in vegetative reproduction and less affected by flower production than females, prevailed at older stages.

Water stress effects on successional populations of the dioecious herb, Rumex acetosella L.

“…In the present work, non-fiowering youngfield females were found to out-perform males in relation to water stress. This may explain the slight female biased sex ratio observed in recently abandoned old-fields (Escarre et al, 1987). However, as succession proceeds, females may be selectively eliminated due to their greater energy allocation to fruits to the detriment of vegetative reproduction, this reducing their competitive ability in crowded conditions and resulting in a greater sensitivity to stress.…”

“…The main purpose was to determine whether the sexes differed in tbeir physiological responses, which may in turn influence changes in the sex ratio along a successional gradient. This was achieved by quantifying variation in drought tolerance and the capacity to recover after water stress, both in the sexes and in populations of different successional age which represent extremes of the post-cultural gradient and in wbicb biased sex ratios have been previously recorded (Escarre et al, 1987). Clearly, the use of only two populations means that differences interpreted as being linked to successional habitat variation may in fact be influenced by others factors.…”

“…Rumex acetosella L. (Polygonaceae) is a dioecious herb in which an excess of females has been observed in successionally young habitats, whereas a male biased sex-ratio was found in more stable, latesuccessional environments (Harris, 1968;Escarre, Houssard & Briane, 1987). Furthermore, variation in leaf size and shape associated witb drought stress has suggested 'a physiological rather than a morphological basis of drought tolerance' in tbis species (Farris, 1984).…”

Sexual dimorphism in clonal growth forms and ramet distribution patterns in Rumex acetosella (Polygonaceae)

“…Previous studies have proposed that these features arose as a consequence of the higher reproductive efforts observed in females (reviewed in Lloyd and Webb 1977;Bullock and Bawa 1981;Cipollini et al 1994;Obeso 1997;Purrington and Schmitt 1998;Nicotra 1998;Delph 1999)or because of mating competition among males (Bullock 1982;Bond and Midgley 1988;Menges 1990;Carr 1991;Vasiliauskas and Aarssen 1992;Machon et al 1995;Purrington and Schmitt 1998;reviewed in Freeman et al 1997;Eckhart 1999). In clonal dioecious species, biomass allocation patterns differ between sexes; male plants commonly allocate more resources to clonal structures, such as creeping roots in Rumex acetosella (Putwain and Harper 1972;Escarre´et al 1987;Houssard et al 1992) and runners in the dioecious strawberry (Darwin 1877;Hancock and Bringhurst 1979). Males of Xanthoxylum americanum allocate more biomass to clonal propagation than females in open field sites, but in forest sites where seed production is prone to failure, both sexes exhibited similar biomass allocation patterns (Popp and Reinartz 1988).…”

Evolution of Dioecy in Buchloe Dactyloides (Gramineae): Tests for Sex‐specific Vegetative Characters, Ecological Differences, and Sexual Niche‐partitioning

“…The males and females ofa dioecious species may sometimes show differences in growth rates, biomass allocation, and other vegetative characters, or in their spatial distribution or use of resources (Freeman, Klikoff, and Harper, 1976;Grant and Mitton, 1979;Hancock and Bringhurst, 1980;Conn and Blum, 1981;Fox and Harrison, 1981;Gross and Soule, 1981;Meagher and Antonovics, 1982;Vitale and Freeman, 1985;Escarre, Houssard, and Briane, 1987;Agren, 1988;Popp and Reinartz, 1988;Boecklen, Price, and Mopper, 1990). Such observations have led to suggestions that these differences played key roles in the success of separate sexes, or even in the evolution of dioecy (Freeman, Harper, and Ostler, 1980;Cox, 1981;Lovett Doust, O'Brien, and Lovett Doust, 1987;Armstrong and Irvine, 1989).…”