RESUMEN
The diversification of angiosperms has largely been attributed to adaptive radiation of their pollination and mating systems, which are relevant drivers of the macroevolution processes. The fig (Ficus, Moraceae) and fig wasp (Agaonidae, Hymenoptera) interaction is an example of obligate mutualism. Passive and active pollination modes have been associated with morphological traits in both partners. However, more information is required to assess the relationship between floral traits and pollination modes, particularly in Neotropical Ficus species. This study evaluates the morphological traits of figs and fig wasps regarding pollination modes in species belonging to Neotropical Ficus sections (three species each of Americanae and Pharmacosycea). Pollination mode was identified by floral morphology, anther/ovule ratio, and specialized structures fig wasps use for pollen transport (pollen pocket and coxal combs). Fig species in sect. Americanae are actively pollinated because pistillate flowers form a synstigma, present anther/ovule ratios <0.11, and their pollinator Pegoscapus fig wasps have pollen pockets and coxal combs. In contrast, species in sect. Pharmacosycea have free pistillate flowers, with anther/ovule ratios >0.27; they are pollinated by Tetrapus wasps, which lack specialized structures to carry pollen. Each species of Ficus was associated with a single morphospecies of fig wasp. The results support previous contributions that consider reciprocal morphological traits between fig species and their pollinating wasps as evidence of a close co-evolutionary history.
RESUMEN
This study tested the hypothesis that self-compatibility would be associated with floral traits that facilitate autonomous self-pollination to ensure reproduction under low pollinator visitation. In a comparison of two pairs of Ipomoea species with contrasting breeding systems, we predicted that self-compatible (SC) species would have smaller, less variable flowers, reduced herkogamy, lower pollinator visitation and higher reproductive success than their self-incompatible (SI) congeners. We studied sympatric species pairs, I. hederacea (SC)- I. mitchellae (SI) and I. purpurea (SC)-I. indica (SI), in Mexico, over two years. We quantified variation in floral traits and nectar production, documented pollinator visitation, and determined natural fruit and seed set. Hand-pollination and bagging experiments were conducted to determine potential for autonomous self-pollination and apomixis. Self-compatible Ipomoea species had smaller flowers and lower nectar production than SI species; however, floral variation and integration did not vary according to breeding system. Bees were primary pollinators of all species, but visitation rates were seven times lower in SC than SI species. SC species had a high capacity for autonomous self-pollination due to reduced herkogamy at the highest anther levels. Self-compatible species had two to six times higher fruit set than SI species. Results generally support the hypothesis that self-compatibility and autonomous self-pollination ensure reproduction under low pollinator visitation. However, high variation in morphological traits of SC Ipomoea species suggests they maintain variation through outcrossing. Furthermore, reduced herkogamy was associated with high potential for autonomous self-pollination, providing a reproductive advantage that possibly underlies transitions to self-compatibility in Ipomoea.
Asunto(s)
Flores , Ipomoea , Cruzamiento , Flores/anatomía & histología , Flores/fisiología , Frutas/anatomía & histología , Frutas/fisiología , Ipomoea/anatomía & histología , Ipomoea/fisiología , México , Fenotipo , Polinización , Reproducción , Semillas/anatomía & histología , Semillas/fisiología , Autofecundación , SimpatríaRESUMEN
Many mistletoe species produce 'bird'-pollinated flowers; however, the reproductive biology of the majority of these species has not been studied. Psittacanthus auriculatus is a Mexican endemic mistletoe, most common in open, dry mesquite grassland. Knowledge of the reproductive biology of P. auriculatus is essential for understanding species formation and diversification of Psittacanthus mistletoes, but it is currently poorly understood. Thus, we studied floral biology and phenology, nectar production and breeding system and pollination of this species. The hermaphroditic red-pink flowers open from the middle to the tip and petals are curly, but remain partially fused forming a floral tube of ca. 20-mm long. Flowers are partially protandrous, produce large amounts of nectar, last 2 days, and stigma receptivity is highest during the second day. We recorded hummingbirds (Cynanthus latirostris, Hylocharis leucotis, Amazilia beryllina, A. violiceps, Calothorax lucifer, Archilochus colubris) and less commonly butterflies (Agraulis vanillae, Anteos clorinde, Papilio multicaudatus, Phocides urania, Phoebis sennae) as floral visitors. P. auriculatus flowers are self-compatible. However, this mistletoe is an obligate animal-pollinated species, as the sensitive stigma avoids self-pollination. Under natural conditions, reproductive success was higher than in manually selfed or cross-pollinated flowers, likely due to the traplining foraging behaviour of hummingbirds. We suggest that the apparent efficient foraging behaviour of hummingbirds maintains gene flow among P. auriculatus, promoting outcrossing.