Mother Nature’s Kama Sutra, Part 2

KSBlogImage2Female worker bees find their food in the nectar of flowering plants. I see them flitting flower to flower sucking zealously. Most flowers have both male and female elements, leading us to think they can fertilize themselves. Mother Nature, however, blocked that mechanism in many specimens by superimposing a complicated incompatibility system to prevent the male pollen from getting to the female ovary. The only way these plants can complete the sexual act is by cross-fertilization following the matching rules of coupling between molecules with the required characteristics. The bottom line? Such plants cannot self-fertilize but can successfully fertilize most other members of the species, thus achieving outbreeding with a mix of genomes in successive generations.

Gregor Mendel, the father of inheritance—bee keeper, gardener, and monk—wanted to know how discernable traits are passed on from one generation to the next. Fortuitously, he first chose peas rather than bees for study. He cross-bred, by taking pollen from one known parent and depositing it on the tip of the tube leading to the bulbous female ovary of another. By scoring expression of certain parental traits, such as flower color and peapod shape, in the offspring of these crosses, he showed that defined characteristics of each parent were passed on from one generation to the next. Mendel tried working with bees for comparable studies. Alas the data from bees did not jibe with those of peas, due to the then unknown, unorthodox ways of sexual reproduction in bees.

Filled with the fragrance of pretty spring flowers, I turn again to that lily-padded frog pond and think of smaller creatures hidden therein—the microscopic fungi and algae. I pause to ponder the possible presence of tiny swimming spores coming from a little fresh water mold called Achlya ambisexualis, the subject of my master’s thesis many years ago. I and my mentor, John (Red) Raper fell in love while sampling small ponds in the hinterlands around Chicago to make collections of this wee critter for study back in the lab. We nurtured the spores on freshly cut hemp seeds and watched them develop into full-grown colonies of threadlike cells called hyphae. We paired the grownup colonies to look for evidence of mating.

Achlya ambisexualis is aptly named. It goes frogs, birds, fish, bees, and peas one better. It can be either male or female depending upon the partner it happens to meet. A supreme opportunist, this little mold spends no energy making fertilizing organs before they are needed. If you were one of its members, you could go either way depending upon the relative sexuality of the nearest possible partner. You could behave as male if your neighbor bears stronger female tendencies than you and vice versa.

Let’s say your male potential is stronger than that of your neighbor. She behaves as female and initiates the dalliance by sending you a signal to develop long finger-like appendages in readiness for genomic delivery. Then, and only then, do you release a message in response, telling that female to make her little nucleated egg sacks in order to receive your nuclei. She, in turn, signals your fertilizing elements hither to deliver your genes to hers within the encapsulated eggs. Voila!

My thesis aimed towards concentrating enough of a strong female’s message to determine its nature. I failed in this, but others succeeded by using better, more modern techniques. Amazingly, these later investigators defined the attracting signals of both sexes as two different steroid molecules resembling human sex hormones. The regulating genes remain unknown.

My love of the fungi persists from that time.

Moving on to the fringe of the woods, I  spot a light brown, dome-shaped mushroom hanging from a white birch tree. It must be Polyporus betulinus, a fungus studied by friend Abe Flexer, a fellow researcher in Red Raper’s lab. Abe discovered its sex life and found two sexes back in the nineteen seventies, but later investigators found more—as many as 33. How can that be?

KSBlogImage1Walking further, with mushrooms on my mind, I find a group of fan-shaped forms anchored to a log half-rotted. I kneel up close and cock my head. Each resembles a scallop shell, small as a fingernail, with irregular ridges of spore-bearing gills scoring the concave underside. It is Schizophyllum commune, my favorite mushroom-bearing fungus, with not just three dozen sexes but thousands.