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

Abstract

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.

The role of common ancestry and gene flow in the evolution of human‐directed play behaviour in dogs

“…Inferences about evolutionary processes have traditionally been made based on the observed interspecific variance of phenotypes (Darwin, ). Phenotypic diversity accumulated at the intraspecific level is also important to consider for a better understanding of processes behind geographical differentiation and adaptation, and to establish a connection between micro‐ and macroevolution (Roitberg et al, , Anderson, Ros, Wiese, & Ellis, , e.g. Bertin, Ruiz, Figueroa, & Gouin, , Jaffe, Campbell‐Staton, & Losos, , Tsuboi et al, ).…”

Evolutionary ecology of specialization: insights from phylogenetic analysis

“…Models of the evolution of specialization that incorporate environmental heterogeneity and associative mating indicate that these variables can result in a decrease in gene flow between environments and contribute to speciation [7]. Anderson et al [41] examined pollinators in different parts of a plant species' range and found a close association between floral traits and the traits of the pollinators in the region but did not find strong evidence that these patterns greatly influenced gene flow and dispersal. Presumably, if selection pressures were consistent for generations, speciation could occur, yet pollinators may be too variable between years [57].…”

“…For example, if spatial heterogeneity is such that the abundance of a commonly used host changes rapidly over space (beta-diversity is high), this should accelerate the evolution of specialization [41]. Much of the work in this area is done with herbivorous insects, with some studies suggesting that generalization is positively associated with large range size [55] and others finding cases where a specialist can have a much larger range if its host species is widespread [56].…”

“…In contrast to the idea that shifts in specialization result in speciation ( pollinator shifts), Abrahamczyk et al [40] find more evidence favouring biogeographical shifts spurring the process of lineage splitting. In Tritoniopsis revoluta (Iridaceae) Anderson et al [41] report that pollinators vary geographically across the plant's range and are closely associated with variation in floral traits, suggesting a strong role of distribution and range in how biotic specialization influences speciation (see Range extent, specialization, and diversification).…”

Evolutionary dynamics of mimetic rings in heterogeneous ecological communities

“…One striking example of community level patterns shaped by species interactions is the phenotypic convergence of mutualistic partners. Phenotypic convergence emerges in different mutualistic interactions such as plant-pollinator interactions (Anderson et al, 2014), plant-seed disperser interactions (Jordano, 1995), cleaning symbiosis in marine ecosystems (Stummer et al, 2004) and Müllerian mimicry,in which the per-capita predation risks of unpalatable individuals from different species with similar warning signals decay because they share costs of predators learning warning signals (Müller, 1879;Kapan, 2001;Ruxton et al, 2004;Meyer, 2006;Rowland et al, 2007;Elias et al, 2008). There are theoretical and empirical evidences that reciprocal selection imposed by mutualism can result in convergence between species (Guimaraes Jr et al, 2011;Thompson, 2006;Marek & Bond, 2009;Nuismer et al, 2013;Pinheiro et al, 2016).…”