Sex-ratio variation and the function of staminodes inAralia nudicaulis¹This article is part of a Special Issue entitled “Pollination biology research in Canada: Perspectives on a mutualism at different scales”.

Abstract

Aralia nudicaulis L. is a clonal dioecious herb common to forested ecosystems in eastern North America. Across 15 sites, the frequency of female ramets ranged between 5% and 95%. This variation was used to examine hypotheses involving the life history and pollination biology of A. nudicaulis. Because female reproductive function is thought to incur greater resource costs than male function, we predicted that female ramets should (i) be more common where resources (and light in particular) are more abundant and (ii) have lower rates of survival than male ramets. However, there was (i) no significant association between light availability (measured as canopy closure) and female frequencies across sites and (ii) ramet ages were skewed towards older ages for females, not males. Female A. nudicaulis produce staminodes that render female inflorescences visually similar to male inflorescences. We experimentally manipulated the presence-absence of staminodes and found that pollen receipt by females without staminodes was substantially lower than for plants with intact staminodes. Finally, pollinators tend to prefer visiting male over female flowers. We were interested in evaluating whether such preferences might scale up to the population level, with higher pollinator abundances at male-dominated sites. However, we instead found a strong positive association between pollinator abundances and female frequencies. Although there is unlikely to be a causal relationship between them, the identification of a common variable underlying variation in female frequencies and pollinator abundances might reveal key insights into the factors regulating the life history and pollination of forest understory plants.Résumé : L'Aralia nudicaulisL. est une plante clonale herbacée dioïque des écosystèmes forestiers de l'est de l'Amérique du Nord. Sur les 50 sites observés la fréquence des genets femelles va 5 à 95 %. Les auteurs ont utilisé cette variation pour examiner des hypothèses impliquant le cycle vital et la biologie de la pollinisation de l'A. nudicaulis. Parce que l'on croit que la fonction reproductive femelle nécessite un coût plus élevé en ressources que la fonction mâle, les auteurs ont prédit que les genets femelles devraient (i) être plus communs là où les ressources (et en particulier la lumière) sont plus abondantes et (ii) avoir des taux de survie plus faibles que les genets mâles. Cependant, il n'y a pas (i) d'association significative entre la disponibilité de la lumière (mesurée comme fermeture de la canopée) et les fréquences des femelles sur l'ensemble du site et (ii) les âges des genets présentent une curtose des âges avancés en faveur des femelles et non des mâles. Les femelles de l'A. nudicaulis produisent des staminodes qui rendent les inflorescences femelles visuellement similaires aux inflorescences mâles. Les auteurs ont manipulé expérimentalement la présence/absence des staminodes et ont constaté une réduction substantielle de la quantité de pollen reçu par les plantes femelles sans staminodes par rapport aux ...

Sexual system variation in the legumes (Fabaceae): prospects for morphological, evolutionary and genomic study

“…Despite not participating in the production of gametophytes, vestigial and sterile reproductive organs may still participate in reproduction, e.g. staminodes attracting pollinators in mimosoid legumes and other plants (Nicholls and Dorken 2012). Staminodes and pistillodes may be very small, and in these cases, just recording their presence (or absence) may be sufficient.…”

Evolution of the staminode in a representative sample of Scrophularia and its role as nectar safeguard in three widespread species

“…In the Scrophulariaceae s.str., approximately 30 % of the genera possess a staminode (e.g., Scrophularia). However, there are very few experimental studies on functional diversification of the staminode in asterids (Walker-Larsen and Harder 2001;Cabrera 2001, 2002;Hawk and Tepedino 2007 in Penstemon; Vieira et al 1992;Bittencourt and Semir 2006;Yanagizawa and Maimoni-Rodella 2007;Guimarães et al 2008;Maués et al 2008; Alves et al 2010 in Jacaranda;Nicholls and Dorken 2012 in Aralia nudicaulis) and none in the family Scrophulariaceae s.str. These cited studies reported different functions for the staminode, which are generally related to pollination (e.g., visual orientation, smell guiding, mediate pollinator contact with reproductive organs, guide to reach the anthers, secondary pollen presentation, visual indicator of flower senescence, and avoidance of pollen robbing).…”