Floral specialization for different pollinators and divergent use of the same pollinator among co-occurringImpatiensspecies (Balsaminaceae) from Southeast Asia

Abstract

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co‐occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee‐pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee‐ and lepidopteran‐pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar‐producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co‐occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species‐specific pollen‐placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non‐homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.

New insights into plants co‐existence in species‐rich communities: The pollination interaction perspective

“…Since pollinators tend to visit nearby plant species, spatially aggregated co‐flowering species are likely to experience stronger competition for pollinators and potentially suffer higher pollen loss and fitness decrease due to heterospecific pollen transfer (Fang & Huang, ; van der Kooi et al., ). Adaptations to minimize competition and pollen loss may include all those changes that reduce the sharing of pollinators, such as specialization on different pollinators (Kipling & Warren, ; Muchhala et al., ; Ruchisansakun, Tangtorwongsakul, Cozien, Smets, & van der Niet, ), shifts in flowering time (Devaux & Lande, ; Gleeson, ), a segregated spatial distribution (Kipling & Warren, ; Mosquin, ; Pleasants, ); or divergence in floral traits such as the anther position, which allows pollinator‐sharing species to avoid pollen loss by placing pollen on different parts of pollinators’ bodies (Ruchisansakun et al., ).…”

Impatiens tanintharyiensis (Balsaminaceae), a new species from Southern Myanmar

“…The presence of a large floral chamber with a wide entrance are traits associated with bee pollination in Southeast Asian Impatiens (Ruchisansakun et al 2016). Based on the traits of the new species, we hypothesize that the new species is also bee-pollinated.…”

“…Pollination ecology:-A recent comparative study of floral morphology and pollination ecology demonstrated that the closely related and morphologically similar I. daraneenae, is pollinated by bees (Ruchisansakun et al 2016). The presence of a large floral chamber with a wide entrance are traits associated with bee pollination in Southeast Asian Impatiens (Ruchisansakun et al 2016).…”

Three new species of Impatiens (Balsaminaceae) from Myanmar

“…This prediction is based on the strong similarity in floral features, including flower size, between I. decurva and I. muscicola. For the latter species autonomous self-pollination was experimentally confirmed (Ruchisansakun et al 2016). Phenology:-Flowering and fruiting in September.…”

“…However, based on the possession of a long, broad spur, we predict that this species is pollinated by both bees and butterflies (cf. Ruchisansakun et al 2016). Proposed IUCN conservation assessment:-Critically Endangered B1ab (i, ii, iii).…”