When a Flower isn’t a Flower

There is an evolutionary trend in flowering plants for single flowers to cluster into groups, and then for dense groups to take on the appearance of single flowers. (Think of Hydrangea arborescens with larger flowers on the outside of each inflorescence.) One extreme of this trend is seen in Asteraceae, with plants like asters and daisies where the “flower” is actually a cluster of reduced flowers.

Euphorbia is another extreme of flower clustering and reduction. In fact, it’s more extreme than Asteraceae! Each Euphorbia flower seems to consist of an ovary surrounded by stamens, like a normal single flower. However, the “petals,” if present, are bracts (modified leaves).  Each stamen is a flower, and so is each ovary. If you take a close look at the stamen, you’ll see that its stalk has a tiny joint, a node, which is where the pedicel (flower stalk) meets the male flower, reduced to a single stamen. It’s easier to tell something weird is happening with the ovary. Not only does it have a joint, but as the fruit matures the flower stalk elongates and grows out of the “flower.” Very strange.

Is the actual genetic code the best of all possible codes?

Is our genetic code the best of all possible codes? A 2000 article concludes that maybe it is, depending on what “best” and “possible” mean in this context. Although the article goes well beyond my expertise, I attempt to explain.

The genetic code in question is DNA’s “language” of 3-base-pair-long codons, each specifying an amino acid for building proteins.

What would the “best” genetic code be? The authors hypothesize that the best code might be the one that produces the fewest faulty proteins if a mutation changes one of the base pairs in the codon. In this code, a change in DNA would either produce specify the same codon or a physiochemically similar one. But how do we measure amino acid physiochemical similarity? There are several plausible possibilities. The authors test a few. The actual genetic code scores extremely well on one, and they go with that, hopefully not circularly.

How does one measure how good a code is at inserting the same or similar amino acids after point mutations? There are several ways to measure that, too. Authors choose one for reasons that are probably plausible, though I wouldn’t know. Along the way they explain that people using other methods found that there could be many better codes only because they used the wrong method.

Now that they have defined “best” and “similar”, what is “possible”?  The authors briefly explain what random assignment of amino acids to codons would produce a LOT of errors and choose “possible” to mean either “arangements that remain synonymous codon block structure [of real DNA] for all variants” or organized according to a plausible hypothesis of evolution of the code.  Thus they have two different sets data to analyze.

After solving a last problem – how to measure optimality – the authors are ready to report their results.

Results and conclusions:  The code is adaptive and apparently the result of selection for minimizing protein errors after mutation errors. Its apparent excellence is not a result of the analytical methods used. Its excellence is not a result of optimizing treatment of a few extreme amino acids, but of how it treats the entire set. The code is not a result of stereochemic limitations. If the possibilities are restricted to those considered evolutionarily likely and if a realistic transition bias is included, the code is 95-100% optimized. It is possible that no better code could develop under these restrictions.

Under any assumptions, the actual code is extremely good and equally good or better codes are extremely rare. Nonetheless, there theoretically can be a few better codes. Most of these probably can’t evolve given plausible evolutionary starting points for the code. Only under evolutionarily plausible restrictions may the actual code be the best of all possible codes.

Source: Freeland, Stephen J., Robin D. Knight, Laura F. Landweber, and Laurence D. Hurst. 2000. Early Fixation of an Optimal Genetic Code. Molecular Biology and Evolution 17(4): 551-518. DOI: 10.1093/oxfordjournals.molbev.a026331

Sheep Fescue, not native to North America

Sheep Fescue (Festuca ovina) is not native to North America. Here’s a little history.

Festuca ovina was originally described about 250 yearas ago from Scandinavian specimens. In 1880, European grass expert Hackel wrote an influential monograph on fescues. He worked to show the differences among fescues while at the same time recognizing their similarities. He placed most of the fine-leaved fescues within a few variable “species.”

One of those species was Festuca ovina, Sheep Fescue. Within Sheep Fescue Hackel included fine-leaved bunchgrass fescues from Europe, Asia, and North America. These fescues varied in structure and ecology. Hackel recognized these variation as subspecies, varieties, and subvarieties of F. ovina. Although all “F. ovina” shared the overall look, the subtaxa differ in habitat as well as leaf structure, awn length, lemma length, leaf color, and a host of other details.  Also, many of these forms fail to produce fertile offspring when crossed.  Hackel’s F. ovina species concept was gradually rejected as overly broad.

As botanists and agronomists became more familiar with the fescues, they began separating the more distinct units as species in their own right. At one time, Festuca ovina included such North American fescues as Idaho Fescue (F. idahoensis), Roemer’s Fescue (F. roemeri), Western Fescue (F. occidentalis), Rocky Mountain Fescue (F. saximontana), Alpine Fescue (F. brachyphylla), and Tiny Fescue (F. minutiflora). However, these fescues differ greatly in ecology and their structural differences are real though easily overlooked. By 1969 when Hitchcock et al. published Vascular Plants of the Pacific Northwest, only a few alpine and arctic fescues remained within what was left of the broad Festuca ovina concept.

Since then, further surgery has been performed on the Festuca ovina species concept. Now, the name Festuca ovina is restricted to an arctic/alpine bunchgrass of northern Europe. It is not native to North America.