Sex allocation in Carex (Cyperaceae): effects of light, water, and nutrients

Abstract

Sedges of the genus Carex L. are mostly wind-pollinated, self-compatible, monoecious herbs in which female flowers are receptive before pollen is released (protogyny). One hypothesis was examined for the adaptive importance of the monoecious sexual system, namely that having two flower types permits flexibility in allocation of resources to male and female reproductive functions in the face of changing environmental conditions. Fourteen greenhouse experiments were conducted on a total of six Carex species in which I manipulated one or more of three environmental variables: nutrients, water, and light. These variables had small effects on the proportion of female flowers, though the effects were significant for at least one variable in 8 of the 14 experiments. High nutrient and light levels were generally associated with increased femaleness, while high water levels were associated with increased maleness. Increased female allocation in response to enhanced resource availability has been demonstrated in many species and is thought to reflect the greater potential fitness gains via the female function than via the male function when resources are plentiful. The opposite effects of water are anomalous and contrary to results in the literature. Because the effects of environmental manipulations on sex allocation are modest, the evolution and maintenance of monoecy in sedges probably reflect advantages other than flexible sex expression, at least in part. Selection for avoidance of self-pollination may have been particularly important in favoring the combination of protogyny and monoecy in Carex.Résumé : Les espèces du genre Carex L. sont des herbacées surtout pollinisées par le vent, auto-fertiles et monoïques chez lesquelles les fleurs femelles sont réceptives avant que le pollen ne soit relâché (protogynie). L'auteur examine une hypothèse portant sur la signification adaptative du système sexuel monöique, à savoir que le fait de posséder deux types de fleurs permet une flexibilité dans l'allocation des ressources aux fonctions mâles et femelles, en regard de conditions environnementales changeantes. L'auteur a conduit 14 expériences en serres, sur un total de six espèces de carex, chez lesquelles il a manipulé une ou plus de trois variables environnementales : nutriments, eau, lumière. Ces variables ont des effets minimes sur la proportion des fleurs femelles, bien qu'on observe des effets significatifs sur au moins une variable dans 8 des 14 expériences. Des apports élevés en nutriments et en lumière sont généralement associés à une augmentation de la féminisation, alors que les apports élevés en eau sont généralement associés à une augmentation des mâles. On a dé-montré une augmentation de l'allocation femelle en réaction à une plus grande disponibilité en ressources, chez plusieurs espèces, et on croit que ceci reflète un plus grand potentiel d'adaptation via la fonction femelle que via la fonction mâle, lorsque les ressources surabondent. Les effets contraires de l'eau sont anormaux et contredisent la littératu...

Male flowers are better fathers than hermaphroditic flowers in andromonoecious Passiflora incarnata

“…Typically, female function is prioritized when resources are ample and male function is expressed more often under stress, limited resource conditions or when female function is already fulfilled (e.g. Diggle, 1993;Steven et al, 1999;Bertin, 2007;Lazaro & Mendez, 2007). Studies of the effect of herbivory on gender expression support this idea with the finding of fewer male flowers when fruit production is reduced by herbivory, possibly to accommodate the need for increased female function (Krupnick & Weis, 1998;Wise & Hebert, 2010).…”

Sexual lability during an individual's life: the case of the sedge Carex secalina

“…Male allocation may be limited when an increase in pollen production results in only a few more additional pollinations because the local environment is already pollen saturated (Bertin 2007). This situation probably occurs in populations of C. secalina, which are characterised by low densities of individuals with a high mortality rate (Żukowski et al 2005(Żukowski et al , Lembicz et al 2006.…”

Spatial Genetic Structure of the Sedge Carex Nigra Reflects Hydrological Conditions in an Alpine Fen

“…The wind-pollinated and perennial sedge Carex nigra (L.) Reichard is native to European and Siberian wetlands (Tutin et al, 1964). Sedges are typically self-compatible (Bertin, 2007) and high selfing rates have recently been shown in several Carex species (Friedman and Barrett, 2009). Unfortunately, for our specific study species, the selfing rate has not yet been determined.…”