Nectar Bat Morphology: Adaptations for Specialization

Nectar bats are a highly specialized group of micro bats occupying the subfamilies Glossophaginae, Lonchophyllinae, Phyllonycterinae, and Bracyphillinae in the family Phyllostomidae (Kunz and Fenton 2003). They are found primarily in Central and South America and feed almost entirely on flower nectar, with some species occasionally exhibiting opportunistic feeding on pollen, fruit, and even insects. However, millions of years of natural selection since the Eocene epoch (approximately 55 Ma)  have resulted in the extreme specialization of some bats to obligate nectarivory, and they have the adaptations to show for it.

Bats in the subfamilies Lonchophyllinae and Glossophaginae show the most dramatic adaptations with regard to nectarivory. They possess an extremely long tongue, with hair-like papillae at the tip to facilitate nectar feeding through capillary action (Figure 1). For example, Glossophaga soricina is, on average, only 60mm in total body length, but can boast a tongue of up to 48mm (Tschapka and Dressler 2002). In addition to their long tongues, specialized nectar bats are characterized by a highly elongated skull and rostrum and noticeably diminished dentition. These adaptations allow the bat to easily reach inside flowers for nectar and withdraw from the flower quickly and efficiently (Figure 2; Tschapka and Dressler 2002).


 Figure 1. Cooper, M. 2006. A tube-lipped nectar bat (Anoura fistulata) sips nectar from a tube. Note extreme length of the tongue, which is more than half of the bat's total body length. This adaptation allows for quick and efficient nectar feeding. http://www.newscientist.com/article/dn10721-the-bat-with-the-incredibly-long-tongue.html; retrieved 29/3/2015.




 
Figure 2. Schneeberger, K. 2012. Elongated rostrum of an orange nectar bat (Lonchophylla robusta) adapted for easy access to nectar inside flowers. http://commons.wikimedia.org/wiki/File:Lonchophylla_robusta_head.jpg; retrieved 29/3/2015.


Whereas these specialized nectar bats clearly show some incredible morphological adaptations, many nectar bats also display physiological and behavioral adaptations to aid in nectar feeding. These evolutionary phenomena will be discussed in detail in future posts, along with the counter-adaptations shown by many of the plant species these bats visit.


References

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

TSCHAPKA, M. and DRESSLER, S., 2002. Chiropterophily: On Bat–Flowers and Flower Bats. Curtis's Botanical Magazine, 19(2), pp. 114.

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.

Bats and Plants: Introduction

Bats and Plants: An Introduction

Bats are a group of mammals in the taxonomic order Chiroptera (meaning "hand wing" in Latin). It is one of the most diverse orders of mammals (second only to Rodentia), with nearly 1,200  total species from 19 families (Kunz and Fenton 2003). Bats are subdivided into two suborders: Megachiroptera (Old World flying foxes) and Microchiroptera (micro bats). All bats are nocturnal, emerging at dusk and foraging for a range of foods including insects, fruit, pollen, nectar, fish, and even other bats in some species (Kunz and Fenton 2003). Whereas there is clearly a high diversity of diets among bat species, this blog will focus on fruit and nectar bats and the coevolutionary relationships that have developed between bats and plants over time. 

(Image reprinted from batworlds.com)

Both clades of bats, Megachiroptera and Microchiroptera, contain species that have converged towards a frugivorous and/or nectarivorous diet over evolutionary time. In total, nearly 300 bat species feed at least partially on fruit, and an additional 50 species on nectar (Kunz and Fenton 2003). Fruit bats feed primarily on ripe fruit and excrete nearly intact seeds, allowing for germination of new plants from that digested fruit (Becker et al. 2010). Similarly, nectar bats come in physical contact with plants when feeding and often gather pollen on their fur. These bats then travel from plant to plant, dropping off and picking up pollen and allowing for cross pollination (Fleming et al. 2009). These behaviors of fruit and nectar bats are ecosystem services, and have important implications for conservation biology.

(Copyright Marco Tschapka)

Because of the aforementioned behaviors, fruit and nectar bats have developed highly specialized morphological and behavioral adaptations to accompany their diets. Concurrently, plants have evolved to complement these traits and enhance the efficiency of bat-plant mutualisms. This is an incredible example of coevolution, and will be further discussed in future posts. 

References

BECKER, N.I., ROTHENWÖHRER, C. and TSCHAPKA, M., 2010. Dynamic feeding habits: Efficiency of frugivory in a nectarivorous bat. Canadian journal of zoology, 88(8), pp. 764-773.

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., 2005; 2003. Bat ecology. Paperback edn. Chicago: University of Chicago Press.