Matching floral and pollinator traits through guild convergence and pollinator ecotype formation

Flowers show important structural variation as reproductive organs but the evolutionary forces underlying this diversity are still poorly understood. In animal-pollinated species, flower shape is strongly fashioned by selection imposed by pollinators, which is expected to vary according to guilds of effective pollinators. Using the Antillean subtribe Gesneriinae (Gesneriaceae), we tested the hypothesis that pollination specialists pollinated by one functional type of pollinator have maintained more similar corolla shapes through time due to more constant and stronger selection constraints compared to species with more generalist pollination strategies. Using geometric morphometrics and evolutionary models, we showed that the corolla of hummingbird specialists, bat specialists, and species with a mixed-pollination strategy (pollinated by hummingbirds and bats; thus a more generalist strategy) have distinct shapes and that these shapes have evolved under evolutionary constraints. However, we did not find support for greater disparity in corolla shape of more generalist species. This could be because the corolla shape of more generalist species in subtribe Gesneriinae, which has evolved multiple times, is finely adapted to be effectively pollinated by both bats and hummingbirds. These results suggest that ecological generalization is not necessarily associated with relaxed selection constraints.

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“…; Newman et al. ; Niet et al. ), especially when reciprocal transplant experiments confirmed these patterns (Newman et al.…”

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Greater pollination generalization is not associated with reduced constraints on corolla shape in Antillean plants

et al. 2018

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“…B 281: 20141420 flowers with highly variable (40-70 mm) tube lengths [31], and their nectar is known to be consumed by long proboscid flies [32 -34] and anthophorid bees [35]. Newman et al [21] suggest that short-and long-tubed populations of T. revoluta are pollinator ecotypes, i.e. populations of the same plant species that are morphologically different because they are functionally specialized on different kinds of pollinator.…”

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confidence: 99%

Intraspecific divergence and convergence of floral tube length in specialized pollination interactions

et al. 2014

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Floral tubes are often thought to be a consequence of adaptive specialization towards pollinator morphology. We explore floral tube length evolution within Tritoniopsis revoluta (Iridaceae), a species with considerable geographical tube length variation. We ask whether tube lengths of T. revoluta populations are associated with pollinator proboscis lengths, whether floral divergence occurs in the presence of different pollinators and whether floral convergence occurs between distantly related populations pollinated by the same pollinator. Finally, we ask whether tube length evolution is directional. Shifts between morphologically different pollinators were always associated with shifts in floral morphology, even when populations were very closely related. Distantly related populations had similar tube lengths when they were pollinated by the same pollinator. Shifts in tube length tended to be from short to long, although reversals were not infrequent. After correcting for the population-level phylogeny, there was a strong positive, linear relationship between floral tube length and pollinator proboscis length, suggesting that plants are functionally specialized on different pollinators at different sites. However, because tube length evolution in this system can be a bidirectional process, specialization to the local pollinator fauna is unlikely to result in evolutionary or ecological dead-ends such as canalization or range limitation.

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“…The most frequently documented of these 'trait -environment' correlations involve ecotypes with differing flower tube length and pollinators of correspondingly variable tongue length (Robertson and Wyatt, 1990;Johnson, 1997;Johnson and Steiner, 1997;Boyd, 2004;Anderson et al, 2010;Nattero et al, 2010;Boberg et al, 2014;Newman et al, 2014;van der Niet et al, 2014). Flowering phenology is another trait that has been investigated with respect to pollinator shifts among forms within a species (Herrera et al, 2002).…”

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confidence: 99%

A pollinator shift explains floral divergence in an orchid species complex in South Africa

Peter

Johnson

2013

Annals of Botany

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Aims Floral diversification driven by shifts between pollinators has been one of the key explanations for the radiation of angiosperms. According to the Grant-Stebbins model of pollinator-driven speciation, these shifts result in morphologically distinct 'ecotypes' which may eventually become recognizable as species. The current circumscription of the food-deceptive southern African orchid Eulophia parviflora encompasses a highly variable monophyletic species complex. In this study, two forms were identified within this complex that differ in distribution, floral morphology, scent chemistry and phenology, and a test was made of whether these differences represent adaptations for different pollinators. † Methods and Results Multivariate analysis of floral and vegetative traits revealed that there are at least two discrete morphological forms in the species complex. Field observations revealed that each form is pollinated by a different insect species, and thus represent distinct ecotypes. The early-flowering coastal form which has long spurs and floral scent dominated by sesquiterpene compounds is pollinated exclusively by the long-tongued bee Amegilla fallax (Apidae, Anthophorinae), while the late-flowering inland form with short spurs and floral scent dominated by benzenoid compounds is pollinated exclusively by the beetle Cyrtothyrea marginalis (Cetoniinae; Scarabaeidae). Choice experiments in a Y-maze olfactometer showed that beetles are preferentially attracted to the scent of the short-spurred form. A spur-shortening experiment showed that long spurs are required for effective pollination of the bee-pollinated form. Although it was initially thought likely that divergence occurred across a geographical pollinator gradient, plants of the long-spurred form were effectively pollinated when transplanted to an inland locality outside the natural coastal range of this form. Thus, the underlying geographical basis for the evolution of ecotypes in the E. parviflora complex remains uncertain, although early flowering in the long-spurred form to exploit the emergence of naïve bees may restrict this form to coastal areas where there is no frost that would damage flower buds. Later flowering of the short-spurred form coincides closely with the emergence of the pollinating beetles following winter frosts. † Conclusions This study identifies a shift between bee and beetle pollination as the main driver of floral divergence in an orchid species complex. Floral scent and spur length appear to be key traits in mediating this evolutionary transition.

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Matching floral and pollinator traits through guild convergence and pollinator ecotype formation

Cited by 70 publications

References 44 publications

Greater pollination generalization is not associated with reduced constraints on corolla shape in Antillean plants

Greater pollination generalization is not associated with reduced constraints on corolla shape in Antillean plants

Intraspecific divergence and convergence of floral tube length in specialized pollination interactions

A pollinator shift explains floral divergence in an orchid species complex in South Africa

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