Carnivorous plants in Borneo act as hotels (and bathrooms) for tiny bats

In Borneo, carnivorous pitcher plants and 4-centimeter-long bats have teamed up for what's possibly nature's most heavy-metal-album-cover-friendly mutualistic relationship. The bats take shelter in the pitcher plants, and the plants feast on the bats' nitrogen-rich guano in turn.

The pitcher plants of Borneo catch and digest insects to make up for the lack of nitrogen in the soil. These plants entice arthropods using attractive patterns, aromas, and nectar. Researchers noticed that a specific kind of pitcher plant, N. rafflesiana elongata, wasn't as adept at catching the bugs — the enlongata variety had a thinner pitcher and didn't have the alluring scents. The team discovered that the narrow pitchers acquired nitrogen from a more novel source. From their findings, which are posted today in Biology Letters:

At first view, carnivorous pitcher plants of the genus Nepenthes seem to be highly unlikely candidates for mutualistic interactions with animals, as they form dimorphic terrestrial and aerial pitchers that trap arthropods and small vertebrates. Surprisingly, however, the aerial pitchers of Nepenthes rafflesiana variety elongata are poor insect traps, with low amounts of insect-attractive volatile compounds and low amounts of digestive fluid [...] N. rafflesiana elongata gains an estimated 33.8 per cent of the total foliar nitrogen from the faeces of Hardwicke's woolly bats (Kerivoula hardwickii hardwickii) that exclusively roost in its aerial pitchers. This is the first case in which the faeces-trapping syndrome has been documented in a pitcher plant that attracts bats and only the second case of a mutualistic association between a carnivorous plant and a mammal to date.

The team tracked the bats using tiny radio transmitters and discovered that the aerial pitcher plants were roomy enough to accommodate both mother bats and their young. Additionally, these daytime roosts protect the bats from blood-drinking parasites. The researchers do note that bat feces aren't the pitcher plants' sole supply of nitrogen, as a bat tenant is by no means a guarantee:

[...] Giving up the insect-capturing strategy completely may be risky from an evolutionary perspective, since the probability of attracting a bat to a particular individual aerial pitcher was only 22.8 per cent in our study area. Instead, it should be beneficial for pitcher plants to pursue a dual strategy by retaining the ability to trap insects, especially if bats are absent from some habitat patches. Such conditional asymmetries in interspecific interactions are common. Our study shows that the interaction is mutualistic, with the bat possibly more dependent on the pitcher plant than vice versa.

So yes, somewhere on this planet, a grizzled biker's completely insane tattoo is an accurate depiction of Borneo's ecosystem.

[BBC; photo via Holger Bohn]