Curious naturalists can ask different kinds of questions about what we see. The most basic kinds consist of the usual, descriptive Who/What/When/Where/How? For instance, some years ago, a colleague and I noticed a small plant with clusters of white flowers and iris-like leaves, growing in muskegs. It was known then as Tofieldia glutinosa, but is now placed in the genus Triantha. An obvious feature of this plant was the array of sticky hairs on the flowering stem, which tended to accumulate little insects.
In this case the Who is the name of the plant, the What is the sticky hairs and the little bugs stuck there, the Where is the flowering stem, and the When is during flowering time. All of that depends just on direct, descriptive observation. And it can be tempting to stop at that point. The answer to the How question lies in the physiology of digestion outside the main body of the organism; details obtained by study of other insectivorous species.
But those kinds of observations lead naturally to a further question: Why? Why does the plant have sticky hairs on the flowering stem? Asking the Why question is important to understanding what we observe and augments the basic observations. We thought of two kinds of possible functions.
Maybe the sticky hairs deter insects that could seriously damage the seeds. If any of those tiny bugs happened to be harmful, they would clearly be put out of action. But a common major seed predator is a looper caterpillar, and our later observations showed that the caterpillars were quite capable of clambering up the sticky stem and chewing on the seeds.
Maybe those sticky hairs caught the little bugs to digest them enzymatically, as well-known insectivorous plants such as sundews, also growing in nutrient-poor soils, regularly do. We tried a little experiment, putting isotope-labelled fruit flies on the stems and then having a laboratory test the plant and seeds to see if the isotope label appeared there, indicating that the labeled fly had been digested. Our small sample failed to show that digestion happened, but a later, more rigorous study on a closely related Triantha species showed that isotopic-labelled nitrogen was taken up from the labelled fruit flies, appearing in leaves mostly in the (!!)following year (after storage in the rhizome). Although the effects of extra nitrogen uptake on survival and reproduction were not reported, positive effects of extra uptake have been recorded for other insectivorous plants and probably occurred here too. So there is the probable answer to Why — it is a feeding mechanism.
However, three unusual aspects of this plant should be noted. It is not even closely related to other insectivorous plants, and the habit of insectivory has evolved independently in this genus. Other insectivorous plants seldom bear their insect traps on reproductive parts, such as the flowering stem. And, unlike the others, the isotope marker shows up not in the same year but mainly in the next year after initial digestion. Of course, these anomalies call for more questions…(another time, perhaps).
Now take a more complicated example: We observe that coho salmon swim upstream in fall, using particular streams. The Who is coho salmon, the What is swimming upstream, the When is the fall season, and the Where is what streams are used. And How do they do it? By what means do they find their particular streams? That question generated numerous research projects dealing with physiology (e.g. hormones) and sensory systems (olfactory, etc.). They probably navigate in the sea using the earth’s magnetic field and they can identify the waters of their home streams by smell.
The next question is Why? This can have two levels of answer. The proximate, obvious answer is “to spawn.” But a deeper answer considers how the behavior patterns may have originated. What were the conditions that may have fostered the evolution of the behaviors that we observe?. What made the behavior (swimming upstream in fresh water) advantageous, giving better success in reproduction and passing on genes to the next generation, such that the behavior became established in the population? (That’s natural selection in action.) Why do adults die after spawning? And why do the young ones go out to sea? What is the advantage of that behavior? In other words, how did natural selection lead to the observed behavior patterns? Finding answers to such questions is how the continuing process of science can back up the plain natural history and add dimensions to it.
Even further: Why did this behavior pattern evolve in some species but not in others? What were the likely historical circumstances under which it evolved? Although genetic and historical-geological data can help resolve such additional questions, some uncertainly usually remains.
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.
