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

Abstract

• 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 com- petition 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 selec- tion 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.