Pollination success of animal-pollinated flowers depends on rate of pollinator visits and on pollen deposition per visit, both of which should vary with the pollen and nectar "neighborhoods" of a plant, i.e., with pollen and nectar availability in nearby plants. One determinant of these neighborhoods is per-flower production of pollen and nectar, which is likely to respond to environmental influences. In this study, we explored environmental effects on pollen and nectar production and on pollination success in order to follow up a surprising result from a previous study: flowers of Ipomopsis aggregata received less pollen in years of high visitation by their hummingbird pollinators. A new analysis of the earlier data indicated that high bird visitation corresponded to drought years. We hypothesized that drought might contribute to the enigmatic prior result if it decreases both nectar and pollen production: in dry years, low nectar availability could cause hummingbirds to visit flowers at a higher rate, and low pollen availability could cause them to deposit less pollen per visit. A greenhouse experiment demonstrated that drought does reduce both pollen and nectar production by I. aggregata flowers. This result was corroborated across 6 yr of variable precipitation and soil moisture in four unmanipulated field populations. In addition, experimental removal of pollen from flowers reduced the pollen received by nearby flowers. We conclude that there is much to learn about how abiotic and biotic environmental drivers jointly affect pollen and nectar production and availability, and how this contributes to pollen and nectar neighborhoods and thus influences pollination success.

Les palmiers constituent une famille emblématique de monocotylédones, comprenant 183 genres et environ 2500 espèces distribuées sur tous les continents dans les zones tropicales et subtropicales. Leurs feuilles et leurs stipes, très caractéristiques, les rendent facilement reconnaissables dans la nature. En revanche leurs fleurs passent souvent inaperçues. Elles sont généralement petites (quelques centimètres), trimères, unisexuées, peu colorées (blanches ou vertes) et regroupées sur de grandes inflorescences. Cependant les palmiers présentent une diversité importante au niveau du système sexuel et du nombre d’étamines. Les trois systèmes sexuels principaux des angiospermes : hermaphrodisme, monoécie et dioécie, sont présents chez les palmiers. Le nombre d’étamines varie entre quelques unités (oligandrie) et des dizaines, voire centaines, d’unités (polyandrie) chez certains genres. Nous avons étudié l’évolution du système sexuel et du nombre d’étamines à l’échelle de la famille. Nous avons pour cela utilisé une phylogénie comprenant tous les genres de palmiers, bien résolue, datée et qui a été publiée récemment. Notre étude a montré que l’ancêtre commun à tous les palmiers était probablement monoïque et possédait des fleurs oligandres à 6 étamines. A partir de ces états ancestraux, plusieurs transitions ont eu lieu : vers l’hermaphrodisme et la monoécie d’une part, et vers la polyandrie d’autre part. Dans l’objectif d’initier une recherche sur une éventuelle explication fonctionnelle de l’augmentation du nombre d’étamines, nous avons comparé celui-ci à la production de pollen, en étudiant la quantité totale de pollen produite par les fleurs de 82 espèces. Notre étude a montré que, chez deux sous-familles, les fleurs ont tendance à produire plus de pollen quand le nombre d’étamines est plus élevé. Nous avons également réalisé la phylogénie moléculaire d’une sous-tribu (les Ptychospermatinae) dans laquelle la variation du nombre d’étamines est exceptionnelle. De futures études sur la génétique, le développement, l’écologie et la biologie de la pollinisation sont nécessaires. / Palms (Arecaceae) are an emblematic family of monocots of 183 genera and around 2500 species distributed on all continents, throughout tropical and subtropical areas. Their characteristic leaves and stems make palms immediately recognizable in the field. The inconspicuous palm flowers are usually considered as rather dull. They are usually small (a few centimetres), trimerous, often unisexual, colourless (white or greenish) and grouped into huge inflorescences. However palms exhibit a large diversity in sexual system and in stamen number, diversity that is still poorly understood. The three main sexual systems of angiosperm, hermaphroditism, dioecy and monoecy are present in palms. Stamen number ranges between a few units (oligandry) to several dozens and even several hundreds of units (polyandry) in some genera. We studied the evolution of sexual system and stamen number at the family level. We used as historical framework a well-supported and dated phylogeny, published recently. Our study showed that the putative ancestor of palms was monoecious and bore oligandrous flowers with 6 stamens. From these ancestral states, several transitions occurred: towards hermaphroditism and dioecy and towards polyandry respectively. In order to initiate a research on a possible functional significance of increase in stamen number, we investigated the relationship between stamen number and pollen production, by extracting the total pollen content from flowers of 82 species. Our study showed a tendency towards higher pollen production when the number of stamen increases in two subfamilies. We also produced molecular phylogeny of a subtribe (Ptychospermatinae) in which the range of variation in stamen number is exceptional. Further investigations into genetic, developmental, ecology and pollination biology are needed.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O pÃlen apÃcola à um produto das abelhas Apis mellifera que possui alto valor nutricional, indispensÃvel para a manutenÃÃo de suas colÃnias. AlÃm disso, representa uma importante fonte de renda para apicultores de diversos paÃses. Mas, a falta de conhecimento sobre a flora polinÃfera e sua contribuiÃÃo no valor nutricional ainda sÃo entraves para a expansÃo da produÃÃo do pÃlen apÃcola. Nesse sentido, o presente estudo teve como objetivo analisar o potencial da produÃÃo, a variaÃÃo temporal, a origem botÃnica e o valor nutricional do pÃlen apÃcola produzido por A. mellifera em Floresta Estacional Semidecidual na Serra da Meruoca (FESSM). Para isso foram coletadas 15 amostras de pÃlen mensalmente em cada colÃnia (n=10), durante 12 meses. Cada amostra foi dividida em duas partes, sendo uma destinada à anÃlise bromatolÃgia e a outra à anÃlise da origem botÃnica. A dieta de A. mellifera na FESSM foi composta por 74 tipos polÃnicos distribuÃdos em 58 gÃneros e 27 famÃlias. As famÃlias botÃnicas mais representativas em nÃmero de espÃcies foram Leguminosae (n= 16), Asteraceae (11) e Rubiaceae (6). O gÃnero Mimosa (Leguminosae) apresentou o maior nÃmero de espÃcie (n=7) em floraÃÃo durante o perÃodo de estudo. Ao longo do ano dois picos produtivos de pÃlen apÃcola foram encontrados, um no perÃodo seco e outro no perÃodo chuvoso, com valores mais elevados no perÃodo chuvoso. A anÃlise do valor nutricional considerando, proteÃna bruta, carboidratos, extrato etÃreo e matÃria mineral variaram ao longo do perÃodo estudado. Sendo a matÃria seca influenciada pela precipitaÃÃo. Alguns grupos taxonÃmicos apresentaram relaÃÃo positiva com os nutrientes. Embora a dieta do A. mellifera seja amplamente diversificada, essa espÃcie de abelha direciona a maior parte de seu esforÃo no forrageamento de pÃlen em espÃcies do gÃnero Mimosa e em Attalea speciosa. Este estudo mostra que a FESSM apresenta espÃcies de plantas altamente nutritivas e um elevado potencial para a produÃÃo de pÃlen apÃcola. / Bee pollen is a product of Apis mellifera with high nutritional value, indispensable for the maintenance of its colonies. It is also an important source of income for beekeepers in different countries. However, the lack of knowledge about the polliniferous flora and its contribution to the nutritional value is an obstacle to increase the production of bee pollen. In this sense, this study analyzed the potential of production, the temporal variation, the botanical origin and the nutritional value of bee pollen produced by A. mellifera in a seasonal semideciduous forest at Serra da Meruoca (FESSM). Once in a month, we collected 15 pollen samples in each colony (n= 10) over a period of 12 months. Each sample was divided into two parts, one for chemical analysis and another for botanical origin analysis. The diet of A. mellifera consisted of 74 pollen types distributed in 58 genera and 27 families. The botanical families Leguminosae (n= 16), Asteraceae (11) and Rubiaceae (6) were the most representative in number of species. Mimosa (Leguminosae) had the highest number of species (n= 7) contributing pollen during the study period. As for the production of bee pollen, we found two production peaks, with higher values in the rainy season. Results of the nutritional value considering crude protein, carbohydrates, lipids and mineral matter indicated changes over the study period, with influence of rainfall on the dry matter content. Some taxonomic groups showed a positive relationship with nutrients. Although the diet of A. mellifera is broadly diversified, this species uses most of its pollen foraging effort in the genus Mimosa and the species Attalea speciosa. This study shows that FESSM presents species of highly nutritious plants and a high potential for the pollen production.