Pollinator shifts drive increasingly long nectar spurs in columbine flowers

Abstract

Directional evolutionary trends have long garnered interest because they suggest that evolution can be predictable. However, the identification of the trends themselves and the underlying processes that may produce them have often been controversial. In 1862, in explaining the exceptionally long nectar spur of Angraecum sesquipedale, Darwin proposed that a coevolutionary 'race' had driven the directional increase in length of a plant's spur and its pollinator's tongue. Thus he predicted the existence of an exceptionally long-tongued moth. Though the discovery of Xanthopan morgani ssp. praedicta in 1903 with a tongue length of 22 cm validated Darwin's prediction, his 'race' model for the evolution of long-spurred flowers remains contentious. Spurs may also evolve to exceptional lengths by way of pollinator shifts as plants adapt to a series of unrelated pollinators, each with a greater tongue length. Here, using a species-level phylogeny of the columbine genus, Aquilegia, we show a significant evolutionary trend for increasing spur length during directional shifts to pollinators with longer tongues. In addition, we find evidence for 'punctuated' change in spur length during speciation events, suggesting that Aquilegia nectar spurs rapidly evolve to fit adaptive peaks predefined by pollinator morphology. These findings show that evolution may proceed in predictable pathways without reversals and that change may be concentrated during speciation.

Low functional diversity promotes niche changes in natural island pollinator communities

“…Owing to the usually intimate associations between long-tongued pollinators and flowers with specialized floral organs, such as long corolla tube and spur ( [31,32]; figure 1), declines in long-tongued pollinators can lead to such plants becoming pollinator-limited [16,19,20,33]. However, few studies of natural ecosystems have investigated the impacts of long-tongued pollinator declines and the resulting niche changes on a whole flower community (but see Brosi & Briggs [17] and Kadoya & Ishii [22]).…”

Pollinators and nectar robbers cause directional selection for large spur circle in Impatiens oxyanthera (Balsaminaceae)

“…3). Selection for long spurs has been reported in previous publications (Johnson and Steiner 1997;Whittall and Hodges 2007;Brunet 2009;Boberg and Å gren 2009;Ellis and Johnson 2010;Å gren 2010, 2011). Flowers with large spur circle probably had higher pollination efficiency.…”

“…The evolution of nectar spurs represents a key innovation that has facilitated speciation (Hodges and Arnold 1995;Hodges 1997;Whittall and Hodges 2007). Spur shape (spur length and curvature) usually experiences selection from pollinators and nectar robbers.…”

“…Spur shape (spur length and curvature) usually experiences selection from pollinators and nectar robbers. On one hand, long and curly spurs increase the contact between flowers and pollinators and therefore enhance reproductive success (Travers et al 2003;Whittall and Hodges 2007;Young 2008;Brunet 2009;Boberg and Å gren 2009;Ellis and Johnson 2010;Sletvold and Å gren 2011). Yet, these traits incur nectar robber visitation which counteract selection on long and curved spurs by pollinators (Pan 1999;Temeles and Pan 2002;Young 2008;Navarro and Medel 2009).…”

Trait evolution in the slipper orchidPaphiopedilum(Orchidaceae) in China

“…1,3 Mapping these traits onto phylogenies is one of the most popular methods for studying potential pathways of adaptive evolution. 1,4,5 This approach is particularly appropriate for orchid plants because fossil records have provided few insights into the origins of their specific relationships. 6 Species from the genus Paphiopedilum, within Orchidaceae, vary in their leaf morphology and floral and ecological characters.…”