Style length variation in male and female figs: development, inheritance, and control of pollinator oviposition

Abstract

AbstractFig trees (Ficus spp., Moraceae) depend on female fig wasps to transport their pollen and as a reward provide nutrition for pollinator fig wasp larvae. Most pollinators are host specific, but natural plant hybrids occur if atypical hosts are pollinated. Female fig wasps lay their eggs into ovaries of female flowers in receptive figs by inserting their ovipositors through the styles, and relative style and ovipositor lengths are believed to largely determine their ability to oviposit. In dioecious fig trees, flowers in receptive male figs have short styles and support larval development, whereas flowers in receptive female figs have long styles and only develop into seeds. Using the dioecious fig tree species Ficus montana Burm. f. and Ficus asperifolia Miq., we recorded the comparative ontogeny of style lengths to determine whether style growth in the two sexes is coordinated with the attraction of pollinators, and how maximum style lengths relate to the ovipositor lengths of their pollinators. F1 hybrids between these species produce viable seeds, but no pollinator offspring. We examined style lengths in F1s and backcrosses, relative to those of their parents, and whether coordination of style growth with pollinator attraction is disrupted. The ovipositor of Kradibia tentacularis (Grandi) (Hymenoptera: Agaonidae), the pollinator of F. montana, could reach some of the ovaries in female figs, but fails to lay eggs there. Styles in male F1 figs were intermediate in length between those of the two parents, but in female F1 figs styles grew longer than in either parent. Maximum style lengths in F1s were partially decoupled from receptivity, especially in female figs. Our results illustrate how timing of stigmal growth is coordinated with pollinator attraction, and that this coordination can be disrupted in hybrid individuals.