Parasite makes ant mimic fruit

Parasites frequently modify the behavior of their hosts to encourage the infection of new hosts. For example, see this video (taken from the Planet Earth documentary) of the fungus Cordyceps that makes insects climb to the top of grass stems, and then erupts its fruiting body from the host's body, and disperses its spores over more hapless hosts from this elevated position. Yanoviak et al. (Am Nat 2008. Vol. 171, pp. 536–544; DOI: 10.1086/528968) describe a case of parasite-induced mimicry in the ant Cephalotes atratus. A nematode infection causes the gasters (rear portion of the abdomen) to become bright red and swollen, resembling a berry fruit, where normally it is black and inconspicuous. The infected gasters are also full of parasite eggs. Birds that feed on berries would then pop off these packets of parasite propagules, and pass out the eggs in their faeces. Ants congregate around bird faeces, which represent food resources to them, and collect them to feed to their brood, completing the cycle.

Here's the lesson from all this, kids: don't eat dung.

Fungal Endophytes

Is a leaf all that it seems to be -- just a leaf? It turns out that fungal endophytes - fungi that live inside plants without harming them - are common and to be found in almost all leaves of tropical forest plants. It seems that the more we learn about organisms and their interactions, the more the idea of the 'free living organism' turns out to be a big lie! Not only are all organisms dependent upon others in obvious ways such as for food and nutrient cycling, but virtually all macroscopic creatures seem to have microscopic organisms living in them too (and frequently even the microscopic ones are hosts to yet smaller ones.)

We commonly understand fungi to adopt a saprobiontic lifestyle, acting as decomposers in the soil, in wood, in leaf litter, or perhaps as pathogens and parasites such as rusts and smuts. But the diversity of these lifestyles may be matched by the diversity of fungal endophytes, which live in the leaf tissues of plants without showing any symptoms or substantially impairing host productivity. They offer benefits to their hosts' fitness, such as preventing pathogenic infection, and possibly making leaves less palatable to herbivores. At the same time the leaves offer a substrate for the fungi to grow upon and provide food substances for their growth and reproduction. Most of these endophytes are transmitted horizontally rather than vertically, though the most well-studied case, that of grass endophytic fungi, are vertically transmitted.

Check out the webpage of Betsy Arnold from the University of Arizona. Her lab does a lot of work on fungal endophyte diversity and interactions with their host plants. Their diversity is still barely understood, especially in the tropics, and culture methods are relatively simple. This could be a pretty cool project for those of you living in places where the leaves aren't all falling off the trees!