Does biodiversity beget biodiversity?  Alfred Wallace suggested that high tropical diversity is due to the “complex influences of organism upon organism”: an increased number of biotic interactions increases the number of specialized niches available, accelerating adaptation and speciation in a positive feedback loop.  The Muchhala Lab conducts research in evolutionary ecology addressing the role of such interactions, especially mutualism and interspecific competition, in structuring communities and driving diversification.  We focus on plants pollinated by bats and hummingbirds, and integrate various approaches including molecular phylogenetics, mathematical modeling, and field experiments. Three specific questions we are particularly interested in include:

     1) What selective pressures favor specialization in pollination systems?  

     2) What are the evolutionary and ecological consequences of competition for pollination?

     3) How do pollinators influence plant speciation?  

     A common theme in angiosperm diversification involves repeated evolution of suites of traits, termed pollination syndromes, that adapt a flower to a certain type of pollinator ( Lagomarsino et al. 2017, Clark et al. 2015).  But why specialize to a given pollinator, when generalizing (e.g., Lagomarsino & Muchhala 2019) ought to allow many more opportunities for successful pollination per unit time?  Work with the genus Burmeistera (Campanulaceae) showed that most species are specialized to either bats or hummingbirds (Muchhala 2006a), and experiments demonstrated that an adaptive tradeoff in floral form (wide flowers fit bat heads better while narrow flowers fit hummingbird bills better) is strong enough that generalist flowers are suboptimal (Muchhala 2007).  We are continuing to explore the traits that adapt flowers to bat pollination, such as increased pollen production (e.g. Muchhala et al. 2010), and olfactory, visual, and echo-reflectance cues (reviewed in Muchhala & Tschapka 2020).

Specialization in pollination systems (continued)

     The majority of flowers are pollinated by more than one species, and pollinators typically visit many species of flowers, thus pollination syndromes are examples of either one-sided evolution (plants evolving to pollinators) or, at best, diffuse coevolution.  True reciprocal coevolution can only occur in highly specialized interactions.  One example of this is the nectar bat Anoura fistulata (Muchhala et al. 2005), which can launch its tongue 1.5 times its body length (double that of other bats and longer than any other mammal). Unique adaptations allow it to store its tongue in its rib cage (Muchhala 2006b).  Experiments suggest that this pair is involved in a coevolutionary race with the 9-cm-long flowers of Centropogon nigricans; longer tongues allow bats to reach more nectar, while longer flowers maximize pollen transfer (Muchhala & Thomson 2009).  We plan to continue to study the geographic mosaic of the interaction between this bat and the flowers it pollinates throughout its range, as well as the ‘trigger’ behind the coevolutionary race – that is, why exactly do long flowers receive more pollen?