Birth of a lichen

Lichens are symbiotic organisms consisting of a highly organized fungal mycelium enclosing algal cells. What's strange about lichens is that without the algae, the fungus just looks like a fungus. Without the fungus, the algae is just algae. They only take on the form recognized as a lichen when the two organisms are in that symbiotic association, and of course, the term itself means "living together". This presents some interesting aspects of reproduction. This illustration is from the November 2014 issue of the American Journal of Botany.  The sexual reproduction of the lichen is fungal in nature, so to form a new lichen, the fungus must capture a compatible algal cell anew.  This illustration shows this very early stage where fungal hyphae (filaments) have found and encircled an algae cell. The proliferation of the hyphae and the division of the algal cell is a demonstration that the symbiotic interaction, the lichenization, has begun. The accompanying article by William Sanders provides illustrated diagrams of the sexual and asexual reproductive cycles of lichens, all very nicely done.

Love those weird interactions

Biologists figured out that chloroplasts were descended from free-living cyanobacteria about 50 years ago, and lots of evidence has been accumulated since then, but many people have trouble understanding how this could occur even after it has been clearly demonstrated that it did occur. Well, at the unicellular level lots of similar interactions are still happening, and here's a newly described species that still operates by keeping its options open by generating a hetertrophic offspring and a photosynthetic autotroph, via a symbiosis, with each cell cycle. One daughter cell keeps the photosynthetic symbiont, the other by necessity returns to a heterotrophic life style, until it happens upon the right photosynthetic prey allowing it to switch back. This will be a great new example of what an intermediate stage in the evolution of chloroplasts was thought to be. HT to Lab Rat.

Symbioses - Bacteria & leaf-cutter ants

Leaf-cutter ants are one of the most fascinating organisms you encounter in the tropical rain forest. Watching a river of little leaf pieces bobbing and weaving along a little path only to disappear underground is an amazing sight. Most people assume leaf-cutter ants are herbivores, plant-eaters, but no, they are fungivores, fungus eaters, and the leaves are used to raise their fungi. Like any other "garden" a fungus garden can get infected and weedy fungi can sprout up. The ants, like all big organisms, harbor an internal community of symbiotic bacteria, and unlike disease organisms, these are part of their biology. You don't like to think about this but you harbor more bacteria within you body than you have cells making up your body. A recent study has found that Streptomyces is one such ant symbiotic bacterium, and just as the name suggests, it can make antibiotics and antifungals used to stop infections and weeds from damaging the crop of fungus. This doesn't surprise me at all because one of our students on our most recent rain forest ecology field trip conducted a nice little experiment that demonstrated that extracts of leaf-cutter ants have strong antibiotic properties. Here's a link for more information on leaf-cutter ants.

Symbioses and the Origin of Life on Land

At least two of the biggest events in the history of life involve symbioses, which are intimate interactions of two organisms literally “living together”. One would be the symbiosis between the eukaryote host cell and the two organisms that became mitochondria and chloroplasts, and the other would be the symbiosis between fungi and liverworts, the most ancient lineage of land plants. The invasion of land by green aquatic organisms was certainly a major event without which our familiar environs would never have appeared. Liverworts are simple bodied land plants, although the one shown here (Conocephalum) is more sophisticated internally than most people would suppose, but they lack roots and leaves although the plant body itself might be considered "leafy" in the sense that it is way broader than deep. The so-called higher fungi appear at about the time life invaded land, and their filamentous bodies invade intercellular spaces and the body cells of modern liverworts functioning much like the mycorrhizal fungi so familiar in association with flowering plants. A recent study has demonstrated that such fungi associated with liverworts can enhance the uptake of critical mineral nutrients, thus providing one of the functions of a root system, especially under conditions where such nutrients are hard to come by. This enhances the photosynthetic output of the liverwort even after “paying off” its debt to the fungus. Such experimental work demonstrates the value of this symbiosis, which would is even more important under harsh terrestrial conditions, and 500 million years ago terrestrial conditions were very harsh because without its familiar mantle of plants and soil, the environmental extremes and weather would have been quite severe.