The Evolution of Bat Pollination

Plants rely on a number of different methods of pollination, including wind, water, and animal-mediated pollen dispersal. In some tropical rainforests, however, up to  99% of angiosperm species are pollinated solely by animal species, many of which are bats (Fleming et al. 2009). In fact, there are some tropical plant species that rely almost exclusively on bats for pollination, and both parties have developed very interesting morphological and chemical adaptations to accommodate this mutualism (Kunz and Fenton 2003). Whereas bat pollination is not nearly as common as insect or bird pollination, at least 300 species of bats visit flowers and serve as an important pollination vector for many tropical plant species. Knowing this, some basic questions about bat and plant evolution arise: How and when did bats evolve to pollinate plants? How many times did bat pollination evolve in angiosperm lineages? What are the consequences and adaptations associated with bat pollination? In this blog, I aim to address these questions and outline the incredible evolutionary history of bat-plant mutualisms. 

Fig 1. Tuttle, M.D. 2014. A pollen-gilded bat (Phylonycteris poeyi) emerging from a flower, covered in pollen. http://ngm.nationalgeographic.com; retrieved 20/3/2015. 

There are two families of bats that have evolved to pollinate flowers: the Pteropodidae (Old World flying foxes) and the Phyllostomidae (New World leaf-nosed bats). These two families are in different suborders (Pteropodidae in Megachiroptera, Phyllostomidae in Microchiroptera) and have completely different geographic distributions, so pollination of flowers appears to have evolved separately in these two clades (Simmons et al. 2005). Pteropodidae evolved approximately 56 million years ago with frugivory as its basal feeding mode (Simmons et al. 2005). According to molecular analyses, specialized nectarivory within the Pteropodidae evolved independently three separate times (twice in Asia/Australasia, once in Africa), resulting in a significant radiation of specialized bat pollinators thereafter (Simmons et al.2005). 

The Phyllostomidae evolved approximately 39 million years ago and, in contrast to the originally frugivorous Pteropodidae, displayed a basal insectivorous diet (Fleming et al. 2009). This means that frugivory and nectarivory are both derived characters along the evolutionary track of phyllostomids, suggesting a long history of coevolution between New World microbats and their flower counterparts. Most likely, ancient phyllostomids evolved opportunistic frugivory and nectarivory, and slowly developed specific adaptations and radiated into the more specialized subfamilies of Glossophaginae, Phyllonycterinae, and Brachyphyllinae (Fleming et al. 2009). 

The different patterns of evolution between the Pteropodidae and Phyllostomidae resulted in radiation of more specialized, obligate nectarivores and frugivores. Fleming et al. (2009) postulates that this specialization sparked a counter-radiation in plants pollinated by bats; that is, the speciation of flower-visiting bats in turn caused speciation of the flowers they visited (Figure 2). This is an incredible example of coevolution, and resulted in some of the amazing morphological and chemical adaptations seen in both modern bat and angiosperm species. 

Fig. 2. Fleming et al. 2009. Angiosperm cladogram showing patterns of diversification as a result of pollination by frugivorous and nectarivorous bats. http://aob.oxfordjournals.org/; retrieved 20/3/2015. 

References

FLEMING, T.H., GEISELMAN, C. and KRESS, W.J., 2009. The evolution of bat pollination: a phylogenetic perspective. Annals of Botany, 104(6), pp. 1017-1043.

KUNZ, T.H. and FENTON, M.B., 2003. Bat ecology. Paperback edn. Chicago: University of Chicago Press.

SIMMONS, N.B., WILSON, D. and REEDER, D., 2005. Order Chiroptera. Mammal species of the world: a taxonomic and geographic reference, 1, pp. 312-529.