Sex choice in plants: facultative adjustment of the sex ratio in the perennial herb Begonia gracilis

Abstract

Sex allocation theory predicts that reproducing individuals will increase their fitness by facultatively adjusting their relative investment towards the rarer sex in response to population shifts in operational sex ratio (OSR). The evolution of facultative manipulation of sex ratio depends on the ability of the parents to track the conditions favouring skewed sex allocation and on the mechanism controlling sex allocation. In animals, which have well‐developed sensorial mechanisms, facultative adjustment of sex ratios has been demonstrated on many occasions. In this paper, we show that plants have mechanisms that allow them to evaluate the population OSR. We simulated three different conditions of population OSR by manipulating the amount of pollen received by the female flowers of a monoecious herb, and examined the effect of this treatment on the allocation to male vs. female flowers. A shortage of pollen on the stigmas resulted in a more male‐skewed sex allocation, whereas plants that experienced a relatively pollen rich environment tended to produce a more female‐skewed sex allocation pattern. Our results for Begonia gracilis demonstrate that the individuals of this species are able to respond to the levels of pollination intensity experienced by their female flowers and adjust their patterns of sex allocation in accordance to the expectations of sex allocation theory.

Two's Company, Three's a Crowd: Experimental Evaluation of the Evolutionary Maintenance of Trioecy in Mercurialis annua (Euphorbiaceae)

“…Because M. annua hermaphrodites are self compatible and not pollen-limited when grown in the absence of males [34], this observation is not likely to have been the result of enhanced seed production via higher levels of pollen deposition. Instead, these results appear to be similar to those from Begonia gracilis , a monoecious plant that increases its allocation to female function in response to higher levels of pollen deposition [35]. For the hermaphrodites in our experiment, such responses have the potential to be adaptive, because they enable facultative adjustment of sex allocations in response to the operational sex ratio during mating [36].…”

Inter-genotype variation in reproductive response to crowding among Daphnia pulex

“…If daphnids were able to distinguish between infochemicals emitted by males and females then they could conceivably adjust their offspring sex ratios or reproductive behaviour accordingly, as some monoecious plants do depending on the amount of pollen they detect (Lo´pez & Domı´nguez, 2003). The population demographics experienced by a mother, however, may not reliably predict those her offspring will experience at sexual maturity, which may be a reason why some bird species, for instance, do not employ this strategy (Bensch et al, 1999).…”

Morfología floral y embriología de Begonia gracilis (Begoniaceae): su relevancia en la monoecia

“…Otra explicación posible dada ELIZABETH CHÁVEZ-GARCÍA Y SONIA VÁZQUEZ-SANTANA por Castillo-Gámez (1999) y López y Domínguez (2003 es que los polinizadores no son del todo efi cientes en el movimiento de polen, ya que cuando se realizan polinizaciones manuales, la producción de frutos aumenta considerablemente, hasta siete veces más. No obstante, nuestras observaciones registran una gran cantidad de tubos polínicos sobre la placenta y cerca del saco embrionario, lo cual sugiere que el número de tubos polínicos podría no ser la causa de la poca producción de semillas en B. gracilis.…”

“…Generalmente las de aparición temprana son las fl ores masculinas y las tardías son las femeninas, lo cual favorece la xenogamia. Se propone que en esta especie, algunos individuos producen sólo fl ores femeninas, como respuesta a un ambiente con abundante polen (producido por otros individuos), lo que sugiere que este tipo de infl uencia ambiental puede ser un factor básico para entender la evolución de los sistemas reproductivos en plantas (Harder et al, 2000), en particular en B. gracilis (Castillo-Gámez, 1999;Castillo et al, 2002;López y Domínguez, 2003).…”

“…y mariposas (Lycaenidae sp., Castillo-Gámez, 1999). Esta especie puede alterar sus patrones de asignación sexual, en respuesta a las variaciones en los niveles de polinización, lo cual puede ocurrir por: (1) la diferenciación de un mayor número de meristemos fl orales de uno de los dos sexos o (2) por medio de la aborción en el meristemo fl oral de los primordios de los estambres o de los carpelos (López y Domínguez, 2003;López-Mendoza, 2004;Chávez-García, 2009). Pero no se sabe cómo ni cuándo se establece la unisexualidad, es por esto que consideramos necesario estudiar las fases de desarrollo que defi nan cuál es el patrón de desarrollo unisexual en B. gracilis, ya que en otras especies hay reminiscencias de uno de los verticilos sexuales.…”