Nectar uptake in bats using a pumping-tongue mechanism - PubMed (original) (raw)

Nectar uptake in bats using a pumping-tongue mechanism

Marco Tschapka et al. Sci Adv. 2015.

Abstract

Many insects use nectar as their principal diet and have mouthparts specialized in nectarivory, whereas most nectar-feeding vertebrates are opportunistic users of floral resources and only a few species show distinct morphological specializations. Specialized nectar-feeding bats extract nectar from flowers using elongated tongues that correspond to two vastly different morphologies: Most species have tongues with hair-like papillae, whereas one group has almost hairless tongues that show distinct lateral grooves. Recent molecular data indicate a convergent evolution of groove- and hair-tongued bat clades into the nectar-feeding niche. Using high-speed video recordings on experimental feeders, we show distinctly divergent nectar-feeding behavior in clades. Grooved tongues are held in contact with nectar for the entire duration of visit as nectar is pumped into the mouths of hovering bats, whereas hairy tongues are used in conventional sinusoidal lapping movements. Bats with grooved tongues use a specific fluid uptake mechanism not known from any other mammal. Nectar rises in semiopen lateral grooves, probably driven by a combination of tongue deformation and capillary action. Extraction efficiency declined for both tongue types with a similar slope toward deeper nectar levels. Our results highlight a novel drinking mechanism in mammals and raise further questions on fluid mechanics and ecological niche partitioning.

Keywords: Chiroptera; Glossophaginae; Lonchophyllinae; adaptations; animal-plant interaction; nectar feeding; pollination.

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Figures

Fig. 1

Fig. 1. Tongue movement.

(Left) Extended tongues of drinking: (top) G. soricina (Glossophaginae) and (bottom) L. robusta (Lonchophyllinae). Although the tongue of G. soricina is covered by long filiform papillae, the tongue of L. robusta shows a distinct lateral canal. (Right) Movement patterns of the tongue tips of G. soricina (A) and L. robusta (B) drinking at a feeder offering honey water at 20 mm below the opening. The tongue of L. robusta submerges in the fluid at the beginning of the visit and stays there with only small movements, whereas the tongue of G. soricina extends and retracts repeatedly in stereotypic lapping movements. Interruptions of Glossophaga curves near the upper rim of the feeder represent the total retraction of the tongue into the mouth. (Left, center) Phylogenetic relations between the two groups [modified from (14, 27)] (figs. S1 and S2 and videos S1 to S4).

Fig. 2

Fig. 2. Feeding behavior.

(A) The amount of nectar extracted after each visit decreases steadily toward deeper levels. (B) Hovering duration in G. soricina and L. robusta increases when bats have to reach deeper into the feeder. The final decline occurs when bats abort their visit upon reaching the limit of their tongue extension capability. (C) Standardized extraction efficiency in both species decreases at a very similar slope. All figures are presented as mean ±1 SE. (D) L. robusta visiting a bromeliad flower (Werauhia sp.). Photo was taken at the Bocas del Toro Field Station of the Smithsonian Tropical Research Institute on March 2009.

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