Phenotypic selection on flowering phenology and size in two dioecious plant species with different pollen vectors

Abstract

Dioecious plants may be pollinated biotically by animals or abiotically via wind or water currents. It has been hypothesized that these two types of pollen vectors might impose contrasting selective pressures on plant flowering phenology. In the present study we describe the flowering phenology of two sympatric dioecious species with contrasting pollination modes: Mercurialis perennis (wind-pollinated) and Tamus communis (insectpollinated). We estimated selection differentials and gradients for flowering time and flowering synchrony. As flowering time might depend on the accumulation of enough internal resources, we also estimated direct and indirect selection on plant size. Both species have male-biased sexual ratios, and males are bigger and produce larger flower displays than females, but only in T. communis do males bloom earlier and for longer than females. Selection gradients suggest that selection tends to favor early-flowering females of T. communis. There is no evidence of direct current selection on the flowering phenology of M. perennis. Intersexual differences in phenology fit with sex allocation and sexual selection theories. As we hypothesized, phenology of the animal-pollinated species is under stronger selection than that of the wind-pollinated species and we discuss the potential role of pollen vectors in shaping the flowering phenologies of the study species.

Reproductive biology of Vasconcellea quercifolia A. St.-Hil. (Caricaceae), a moth-pollinated ‘highland papaya’

“…Furthermore, insect pollinators responded to increased male attractiveness by visiting males more frequently than females. Our results coincide with studies in sexually dimorphic species that have shown allocation to attractive structures beneficing male function more than female function (Conner et al 1996;Vaughton and Ramsey 1998;Munguia-Rosas et al 2011).…”

Flowering phenology of Catopsis compacta (Bromeliaceae), a dioecious epiphyte in an oak forest

“…With respect to the difference in the number of flowers between female and male individuals, in dioecious species it is common for male plants to produce more flowers per individual than female plants (Bram & Quinn 2000, Espírito-Santo et al 2003, Munguia-Rosas et al 2011, Barrett & Hough 2012. Male plants allocate more resources to produce more flowers because their fitness is directly linked to the number of pollen grains released.…”

Tree size and its relationship with flowering phenology and reproductive output inWildNutmeg trees

“…Among these factors, size of individual plants has been found to influence their flowering phenology (Schmitt ; Dieringer ; Ollerton and Lack ; Torimaru and Tomaru ; Munguía‐Rosas et al. a), and probably its reproductive performance as well, mediating the attraction of animal vectors dispersing the pollen (Klinkhamer et al. ).…”

“…The focus has been on species or population mechanisms and despite variation in flowering phenology among individuals within a population has been well documented, few studies have analyzed the factors affecting it (Primack 1980;Dieringer 1991;Ollerton and Lack 1998). Among these factors, size of individual plants has been found to influence their flowering phenology (Schmitt 1983;Dieringer 1991;Ollerton and Lack 1998;Torimaru and Tomaru 2006;Mungu ıa-Rosas et al 2011a), and probably its reproductive performance as well, mediating the attraction of animal vectors dispersing the pollen (Klinkhamer et al 1989). Plant size can influence the acquisition of resources, especially in forest ecosystems where light incidence decreases considerably from canopy to understory strata.…”