Do bats know what's in the fruits?

Submitted by editor on 13 October 2015.Get the paper!

Fleshy fruits function primarily to attract mutualistic animal seed dispersers, yet they are much more than packages of nutritional rewards. Fruits contain a rich array of secondary metabolites that give them their incredible diversity in flavors, odors, and colors. Some of these metabolites may function as attractants, but many wild fruits also contain metabolites that can be deterrent or even highly toxic to potential dispersers. Several studies have shown that secondary metabolites in fruits can defend against non-dispersing consumers (e.g. insect seed predators and fungal pathogens), but how do they affect the foraging and feeding behavior of mutualists? Our paper, “Chemical trade-offs in seed dispersal: defensive metabolites in fruits deter consumption by mutualist bats” shows that secondary metabolites in fruits can lead to complex trade-offs between seed dispersal and fruit defense.

We conducted a series of behavioral experiments exploring how secondary metabolites affect short-tailed fruit bats (Carollia spp.), which are among the most highly abundant frugivores in neotropical forests. They are the main dispersers of one of the most diverse and dominant genera of understory tropical plants, Piper. Piper fruits are borne on distinct spike-shaped infructescences, and bats generally remove an entire infructescence in flight, carry it to a nearby feeding roost, and consume the fruit from the spike as if it were a mini corn-on-the-cob. Indisputably adorable!

 

 

Carollia perspicillata consuming a ripe infructescence of Piper sancti-felicis

 

Ripe Piper fruits contain a diversity of secondary metabolites, including amides, which are a large class of N-based metabolites with known importance in defense. We captured bats from the field at La Selva Biological Station in Costa Rica and conducted behavioral experiments in flight cages that tested the effects of amides on various aspects of Carollia foraging.

 

 

Video from one of our experiments comparing Carollia preferences for control versus amide-treated Piper fruits. Each bat in the cage is marked with a unique symbol using infrared-reflective tape, which allowed us to later review the videos and assign each removal event to an individual bat.

 

We found that amides have an overall negative effect on both the number of infructescences that bats remove and the proportion of fruit that bats consume from an infructescence once it is removed. However, these effects were variable depending both on the Carollia species and the specific amide involved. Thus, the strength of any negative effects of amides on plant fitness, as mediated through reduced seed disperser preferences, will depend on the ecological context. The Piper/Carollia interaction provides an excellent opportunity to understand the complex effects of fruit secondary metabolites on seed dispersal success as well as frugivore behavior and physiology. We are continuing to explore this topic in future studies, so stay tuned!   

 

<Photo caption> Susan Whitehead (left) and Maria Obando (right) capturing bats in the field at La Selva Biological Station in Costa Rica

 

 

By: Susan R. Whitehead and co-authors

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