What's in your dinner?

Insectivorous bats use echolocation to move around their surroundings and to locate prey. In response, some insects use hearing-based defences to detect and evade echolocating bats. Furthermore, some arctiid moths produce ultrasonic clicks in response to bat echolocation calls and thus deter bat attacks or advertise their unpalatability. Therefore, there is always a constant evolutionary arms race going on between predator and prey.

To infer predator-prey relationship is not easy, especially when predation is hard to document or observed directly. Traditionally, identification of digested prey remains is by using visual morphological analysis. This can be of a problem, because insectivores chew up their prey rapidly and thoroughly, and of course when the prey goes through the digestive system, nothing much remain except for exoskeletal parts. Therefore, in the past, morphological identification rarely went lower than orders. Thus, molecular techniques can come in quite handy when morphological identification fails.

With the improvement in technology, molecular approaches have provided new opportunities to characterise predator-prey relationship in complex food webs. The techniques have assisted in prey identification, often very accurately to species level. Furthermore, this is considered a non-invasive sampling method, as it is only a small part of the study subject that is taken, and in this case, bat guano.

Eastern red bats (Lasiurus borealis) range across most of eastern North America. They frequently forage around streetlights where there is a large concentration of insects. These bats have extremely robust jaws, similar to other bats species that specialise in Coleoptera (beetles) prey, which have a hard case to protect against predators. Furthermore, the bats also emit echolocation calls between 30-65 kHz, making them audible to tympanate insects.

Clare et al (2009) employed molecular techniques to describe the diet of the eastern red bat, Lasiurus borealis, and test several existing hypothesis about the prey of these bats. This is the first time Polymerase Chain Reaction (PCR) and sequence-based approaches for dietary analyses have been done on bats. The results were compared with the North American arthropod database present in the Barcode of Life Data System.

What they found from the study was, despite having an extremely robust jaw, L. borealis’s diet consists of a wide range of insects, but mainly of soft-bodied Lepidoptera species (butterfly and moths). They also identified insects from other orders that were not detected from previous studies using just morphological identification. More surprisingly was that most of the Lepidopterans that were preyed on were tympanate species, which means they had “ears” they use to detect echolocation used by hunting bats. It would seem like the bats are winning the arms’ race!!

This goes to show that by looking at the morphology or behaviour of predator species alone is not enough to infer the range of prey that they take. The authors also reported that several economically important pest species were found in the bat’s diet. This might be an important implication for pest management as it would be interesting to see how much of the pest species constitute the bat’s diet. Also, this type of study could also be used to infer relative abundance of pests.

Molecular technology breakthrough can provide a whole new level of understanding of the evolutionary and ecological principles underlying food web relationships.

Click here for more details and in-depth reading about the Eastern Red Bats and their diet