Mating strategies in flowering plants: the outcrossing–selfing paradigm and beyond

Abstract

Comparisons of the causes and consequences of cross-and self-fertilization have dominated research on plant mating since Darwin's seminal work on plant reproduction. Here, I provide examples of these accomplishments, but also illustrate new approaches that emphasize the role of floral design and display in pollen dispersal and fitness gain through male function. Wide variation in outcrossing rate characterizes animal-pollinated plants. In species with large floral displays, part of the selfing component of mixed mating can arise from geitonogamy and be maladaptive because of strong inbreeding depression and pollen discounting. Floral strategies that separate the benefits of floral display from the mating costs associated with geitonogamy can resolve these conflicts by reducing lost mating opportunities through male function. The results from experiments with marker genes and floral manipulations provide evidence for the function of herkogamy and dichogamy in reducing self-pollination and promoting pollen dispersal. Evidence is also presented indicating that increased selfing resulting from changes to floral design, or geitonogamy in large clones, can act as a stimulus for the evolution of dioecy. The scope of future research on mating strategies needs to be broadened to include investigations of functional links among flowers, inflorescences and plant architecture within the framework of life-history evolution.

Temporal variation in pollen dispersal and breeding structure in a bee-pollinated Neotropical tree

“…In animal-pollinated species, pollen presentation and behavioral differences of animal pollinators and their flight capacity determine pollen carryover and thus the distances over which the pollen is dispersed (Barrett and Harder, 1996;Barrett, 2003). Ecological factors, such as population spatial distribution and density and flowering phenology, may also affect the foraging behavior of pollinators, and in turn, the distance of pollen dispersal (Handel, 1983;Ghazoul, 2005).…”

Quantifying inbreeding in natural populations of hermaphroditic organisms

“…First, selfing substantially affects the distribution of genetic variation within and among populations, and therefore the response of populations to selection (review in Jarne, 1995;Charlesworth, 2003). Second, the evolution of the selfing rate itself is a topic of central importance (review in Jarne and Charlesworth, 1993;Uyenoyama et al, 1993;Barrett, 2003;Goodwillie et al, 2005). Precise estimates are required to understand the evolution of selfing in relation to reproductive traits (for example, floral traits, copulatory behavior) and inbreeding depression, as well as to test a central prediction of genetic models of mating system evolution, that distributions of selfing rates across species should be U-shaped (Jarne and Auld, 2006, in animals;Goodwillie et al, 2005, in plants).…”

Biología floral y reproductiva de Escallonia pulverulenta (Ruiz et Pav.) Pers. (Escalloniaceae) y su relación con los visitantes florales

“…El sistema reproductivo de las plantas influye en la estructura genética de las poblaciones y en su potencial reproductivo (Barrett 2003). Diferentes estudios han encontrado relación entre la proximidad espacial y el nivel de consanguinidad de los individuos, producto de una dispersión a corta distancia de polen y/o semillas, lo que resulta en poblaciones espacialmente estructuradas (Glaettli et al 2006).…”

“…Este mecanismo obliga a que la fecundación se produzca solo si el transporte del polen por vectores se realiza a distancias donde pueda ocurrir variación genética efectiva entre individuos no emparentados, reduciendo la endogamia y asegurando la adecuación biológica de la planta (Schmitt & Gamble 1990). En general, las plantas leñosas y longevas tienden a ser autoincompatibles mientras que las herbáceas anuales tienden a ser autocompatibles (Arroyo & Squeo 1990, Barrett 2003.…”

“…Atributos de la biología floral, como el período de floración, el tiempo de receptividad del estigma, el despliegue floral, la maduración de las anteras y la longevidad floral, influyen en la transferencia de polen por los polinizadores, en las tasas de geitonogamia y en el tipo de polinizador asociado (Primack 1980, 1985, Zimmerman 1988, Lloyd & Schoen 1992, Harder & Barrett 1995, Barrett 2003. Por ejemplo, especies protándricas son frecuentemente polinizadas por abejas o moscas, mientras que las protoginias son polinizadas por escarabajos o por el viento (Sargent & Otto 2004).…”