Distribution ecology of pollen tubes: fine‐grained, labile spatial mosaics in southern Spanish Lamiaceae

Abstract

Summary• Patterns of intraspecific variation in the number of pollen tubes per style in naturally pollinated plants are poorly known, yet that information is essential for assessing the frequency of occurrence and evolutionary implications of microgametophyte competition in the wild.• This paper analyses intraspecific variation in the number of pollen tubes per style for six species of southern Spanish insect-pollinated Lamiaceae ( Ballota hirsuta , Lavandula latifolia , Marrubium supinum , Phlomis lychnitis , Rosmarinus officinalis and Teucrium rotundifolium ) differing in growth form, phenology, flower size and pollinators.• Number of pollen tubes exceeded number of fertilizable ovules in 26 -87% of styles, and mean number per pollen tube of other pollen tubes in the same style varied between five and 12. Within-plant variation in pollen tube number was extensive in all species, accounting for 68-92% of total population-level variance. In L. latifolia mean pollen tube number per style differed between populations and between plants within populations, but such differences were not consistent among years.• It is concluded that opportunities for microgametophyte competition and selection on competitive ability are considerable in all species studied, although extreme spatial fine-graininess and marked stochasticity in the variation of pollen tube numbers, including temporal inconstancy of individual differences, will greatly reduce the opportunity for selection on sporophytic characters influencing degree of microgametophyte competition.

Effects of Pollen Load and Donor Diversity on Seed and Fruit Mass in the Columnar Cactus, Pachycereus schottii (Cactaceae)

“…Although aspects of the pollination process can, in some cases, influence variation in seed or fruit size (Waser 1978;Biere 1991;Dogterom et al 2000;Herrera 2004), results of our studies indicate that, rather than pollen load and donor diversity, intra-and interplant effects are the dominant source of variation in seed and fruit mass of senita. In the pollen supplementation experiment, 94% of variation in seed and fruit mass was explained by intra-and interplant effects (table 3).…”

“…Alternatively, any effect of pollen load on variation in seed and fruit size may be mediated by stigma clogging or pollen tube competition (Waser 1978;Herrera 2004). Though not directly examined, such factors may be important in senita, as their stigmas receive thousands more pollen grains than there are ovules (Holland and Chamberlain 2007).…”

Evolutionary and Ecological Consequences of Multiscale Variation in Pollen Receipt for Seed Production

“…For 13 animal-pollinated species, 50.4% to 100% of this variation was attributed to variation among flowers within individuals, whereas the remaining variation occurred among individuals (Herrera 2004(Herrera , 2009). In contrast, for wind-pollinated plants, amongplant variation likely plays a more dominant role than within-plant variation (Friedman and Barrett 2011).…”

“…For monocarpic species, which our model addresses most directly, Knight et al (2006) found that pollen supplementation of all flowers increased seed production, on average, by 13%. According to our model, this response would occur if 60% of the variation in pollen receipt occurs within plants, an estimate consistent with several naturally pollinated plant populations (Herrera 2002(Herrera , 2004(Herrera , 2009.…”

“…Seed production by flowering plants should be particularly susceptible to the magnitude and structure of variation because pollen receipt by stigmas differs extensively among flowers within and among plants (Burd 1995;Herrera 2002Herrera , 2004, owing to heterogeneity in both the number of pollinator visits (Waites and Agren 2004;Ghazoul 2005) and pollen deposition by individual pollinators (Waser and Price 1984;Thomson 1986;Pettersson 1991;Richards et al 2009). Because received pollen cannot be redistributed among a plant's flowers, variable pollination should select for floral and inflorescence traits with variance-reducing properties (Waser and Price 1984;Thomson 1986;Pettersson 1991;Richards et al 2009) as well as specific resource allocations to pollen attraction, ovule production, and seed maturation (Burd 1995(Burd , 2008Rosenheim et al 2010).…”