Final course: ‘Coffee’… *

Or, rather, something to ponder as you finish your meal, maybe with a coffee. Whatever your food(s) of choice, you need the right equipment – e.g. teeth – to cope with it (unless it’s a liquid or intravenously-introduced diet…). Although this item is a slightly offbeat ‘nutrition and teeth’ one, it’s a good one. Rather than eat out in the open – where they may themselves be food for another predator, ants of the genus Melissotarsus chew and tunnel through wood beneath the bark of living trees. But, they don’t consume the woody material they excavate so skilfully; instead the galleries that result are colonised by the source of food that the ants do exploit. Wood is tough material to chew through and this activity requires more than dental appropriateness.

How these tiny insects – 2–2.5 mm long – are adapted to accomplish this feet has been uncovered by Adam Khalife et al.. Using a combined approach including, histology, scanning electron microscopy, X-ray spectrometry, X-ray microcomputed tomography (micro-CT), and 3-D modelling, Khalife et al. show that Melissotarsus worker ants have developed a specialized morphology eminently suited for excavating their intriguing ecological niche. In particular, their large head is furnished with huge mandible closer, and unusually large opener, muscles, which maximize force output for slow but powerful closing and opening motions. And the design of their mid and hind legs braces the body while chewing and tunnelling. However, these adaptations for tunnelling have been achieved at the expense of normal walking and foraging; the ants are confined to the tree tunnels that they excavate. But, if these ants don’t feast upon the wood they chew through, upon what do they feed? [Ed. – And where’s the plant nutrition dimension to this Plant Cutting?]

Their nutritional needs are supplied by a scale insect – albeit a species, Morganella conspicua, that doesn’t produce the characteristic external scale structure – with which the ants enjoy a mutually beneficial symbiosis [or mutualism]. In this arrangement the ants feast upon the waxes and proteins secreted by their mutualist partner that would normally be used to build their shields, as well as live individuals, ‘exuviae’ [the scale insects’ scales – some individuals in this partnership occasionally produce a scale], and “excretions from the Malpighian tubules”. In turn, the ant’s tunnel-creating activities provide the scale insect with a safe environment under the bark, and – importantly! – close to the parenchyma tissues that they feed on. So, there is a plant dimension to this dietary arrangement after all!

There’s also a farming dimension to this item because the ants are arguably creating the necessary conditions that favour survival of the shield insects which are exploited as a food source, in much the same way that humans might keep cattle. The animal husbandry and domestication apparently involved in this relationship, and the leaf-cutting exploits of more vegetarian ants, have led other commentators to suggest that ants are amongst the Earth’s first farmers, thereby beating puny human’s 10,000 years old endeavours in the area of animal and plant domestication by tens of millions of years.

* This is the last in a 5-item series of articles. The preceding article can be found here. The first article is here.