Plants use a wide variety of methods to attract animals for their benefit including brightly coloured flowers and fragrances but a new study has shown an alternative strategy called acoustic attraction.
As most people know, bats use echolocation to both find prey and ‘see’ objects around them. Well the pitcher plant Nepenthes hemsleyana has used this to its advantage. It has a very particular shape that reflects the calls from a bat back to them which attracts them. The bats can follow their own voice towards the plant and land on it.
The bat, which now has a parasite-free and safe perch, provides the plant with several nutrients in well… the form of poop. Bat guano, as its called, is very high in nitrogen, which is vital for plant growth. This study showed that N. hemsleyana plants receive, on average, 34% more nitrogen by attracting bats. This is certainly a huge advantage to them.
The researchers in this study tested the effectiveness of N. hemsleyana and its closest relative N. rafflesiana at rebounding sonar pings back to the location they came from. N. hemsleyana had a shape that allowed it to be more effective at returning signals than its cousin plant, which does not host bats. The researchers call this shape a reflector.
This study solved a mystery. N. hemsleyana was observed to not host any insects like other closely related pitcher plants so scientists didn’t how this plant was thriving in the wild. They now know how N. hemsleyana obtains its nutrients.
Researchers also examined the calls of the species of bat that are attracted to the pitcher plant, K. hardwickii. They found that this bat has a very high call frequency that allows it to detect the pitcher plant in the cluttered forest. This bat is the only species that is attracted to this particular pitcher plant species.
This is a classical example of yet another mutualistic relationship in nature. Both of these species benefit from the interaction. Natural selection would have favoured N. hemsleyana shapes that efficiently attract bats so it is not hard to see how this symbiotic relationship developed.
The close relatives of N. hemsleyana all feed on insects that get trapped in the pitcher as a source of nutrients but this species has changed it up. By feeding on bat feces, the plant doesn’t even have to digest its food, which saves a lot of energy. This explains why N. hemsleyana is so successful.
The study was published in the journal Current Biology.