Search

When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.

Premise of research. Floral longevity, the amount of time from anthesis to floral senescence, is a key floral trait that determines the opportunity for pollinator visitation. However, the causes and consequences of variation in longevity have primarily been studied among species, which may not reflect patterns of variation within populations. Methodology. To determine the causes and consequences of within-population variation in floral longevity, we exposed Mimulus guttatus to either an ambient- or reduced-pollination treatment. We measured floral longevity to test whether reduced pollinator access (which simulates pollinator decline) causes a plastic extension in floral longevity. We also measured two traits—flower size and anther-stigma distance—that could cause floral longevity to vary and two traits—daily display size and flowering duration—that could vary in response to longevity. Pivotal results. Floral longevity was not affected by experimentally reducing pollinator access or by anther-stigma distance. However, longevity was reduced in M. guttatus plants with larger flowers. Variation in floral longevity did not affect the flowering duration of M. guttatus plants and (depending on the pollination treatment) had either a negative effect or no effect on daily display size. Conclusions. We found evidence that within-population variation in floral longevity in M. guttatus can be caused by correlations with flower size and can have consequences for daily display size that vary depending on the pollination environment. These results contrast with among-species studies of variation in floral longevity, which have not included display size but have found that longevity either is extended in species with larger flowers or is not related to flower size. Consequently, predictions about the causes of within-population variation in floral longevity based on among-species studies may be misleading. [ABSTRACT FROM AUTHOR]

Although interspecific competition for pollination is hypothesized to result in divergence in floral traits (i.e., character displacement), few studies have tested whether selection on these traits differs in the presence and absence of a competitor for pollination. We measured phenotypic selection on floral traits of Lobelia siphilitica L. growing in the presence and absence of Mimulus ringens L., a potential competitor for pollination. Because L. siphilitica is gynodioecious, we estimated selection separately for female and hermaphrodite plants. The presence of M. ringens did not decrease seed set of L. siphilitica. However, the presence of M. ringens did affect selection on daily display size of female L. siphilitica; there was significant selection for smaller daily displays in the absence of M. ringens, but nonsignificant selection for larger displays in the presence of M. ringens. In addition, selection on flower colour did not differ in the presence and absence of M. ringens, but did differ between female and hermaphrodite L. siphilitica. Consequently, our results suggest that the evolution of floral traits in L. siphilitica, but not the evolution of sexual dimorphism in these traits, can be affected by interactions for pollination with M. ringens. Key words: competition, floral traits, gynodioecy, Lobelia siphilitica, phenotypic selection, pollination, sexual dimorphism. Bien que l'on croit que la competition interspecifique pour la pollinisation conduise a une divergence des caracteres floraux (i.e. deplacements de caracteres), peu d'etudes ont verifie si la selection effectuee sur ces caracteres differe en presence ou en absence d'une competition pour la pollinisation. Les auteurs ont mesure la selection phenotypique des caracteres floraux du Lobelia siphilitica L. venant en presence ou en absence du Mimulus ringens L., un competiteur potentiel pour la pollinisation. Puisque le L. siphilitica est gynodioique, les auteurs ont estime la selection separement chez les plantes femelles et hermaphrodites. La presence du M. ringens n'a pas diminue la mise a graine chez le L. siphilitica. Cependant, la presence du M. ringens a affecte la selection selon l'ampleur de l'offrande quotidienne des fleurs du L. siphilitica; on observe une selection significative pour les offrandes quotidiennes plus petites en absence du M. ringens mais une selection non significative pour les offrandes plus importantes en presence du M. ringens. De plus, la selection selon la couleur des fleurs ne differe pas en presence ou en absence du M. ringens, mais differe entre les L. siphilitica femelles et hermaphrodites. Consequemment, les resultats suggerent que revolution des caracteres floraux chez le L. siphilitica, mais non pas revolution du dimorphisme de ces caracteres, peut affecter les interactions de pollinisation avec le M. ringens. [Traduit par la Redaction] Mots-cles: competition, caracteres floraux, gynodiecie, Lobelia siphilitica, selection phenotypique, pollinisation, dimorphisme sexuel., Introduction Plants species compete not only for abiotic resources, such as nutrients and water, but also for pollination (reviewed in Mitchell et al. 2009). Interspecific competition for pollination should have [...]