One of the most species-rich families of plants in Hawai`i is the Rubiaceae, or coffee family. Several of these will be apparent as you walk along the boardwalk in the Alaka`i Swamp. While 22 species of the rubiaceous genus Hedyotis are listed in the Manual of the Flowering Plants of Hawai`i (Wagner et al. 1999, Bishop Museum, Honolulu), one species, Hedyotis terminalis (manono), has dozens of subspecies and varieties listed. The Manual says that this species "is probably the most polymorphic species among Haaiian flowering plants except perhaps Metrosideros polymorpha" [ohi`a, described in Part 1].

You can say that again. As I began my research project, I brought specimens of most of the plants to the botanists at the National Tropical Botanical Garden in Lawa`i for identification. After a few months I had learned the local species well enough, but in the process I believe I brought specimens of H. terminalis to one botanist at least four times. It got to be a bit embarrassing, but eventually I got a feel for the gestalt of this species.

Which brings me back to the end of Part 1, in which I suggested that the word 'species' itself may be inadequate to describe the current state of Hawaiian plants along the evolutionary continuum. The Manual admits there is no easy way to classify either H. terminalis or M. polymorpha into multiple species. Similar problems exist in some insect groups. Those doing DNA analysis of island endemics usually find similar genetic variation within a species to that between related species, which means it is nearly impossible to find genetic markers to distinguish species. Only by doing an analysis of multiple genes and seeing where an individual insect falls out on a plot of other known insects is it possible to identify it genetically. As I did with some plants, I had similar problems recognizing with certainty one moth species, Scotorythra rara, the most common one in the swamp. Once again, with the help from an expert in that genus, I understood the range of variation in that species enough to recognize it on site.

But given these difficulties, how do we know these moths or plants are all in the same species? Morphology is certainly useful, and in many insects, genitalia structure is key for separating species. But is it definitive? I'm not sure. For most Hawaiian insects, some major information is missing - their ecology and behavior. Entomologists in the islands work almost entirely with dead specimens, knowing little about how they live their lives. Among the hundreds of insects I reared and called S. rara, there were not only dozens of food plants, but multiple morphologies of the larvae (which are inchworms). When I first began rearing the insects, I assumed all these would be different species. And no one has a clue about their mating behavior, which is theoretically crucial to the actual definition of a species - if two individuals can interbreed and produce fertile offspring, they are usually (but not always, especially in plants!) considered the same species.

There is another genus of moths that positively exploded in its radiation in Hawai`i, called Hyposmocoma. There are over 300 described species of Hyposmocoma, and many in description limbo. I would not be surprised if there are actually over a thousand (as there are of a more studied fly genus in Hawai`i, Drosophila). Unfortunately, these are tiny moths, and even less is known about their life histories than about Scotorythra. An eminent entomologist I worked with on occasion at the British Museum of Natural History had tried to work on the taxonomy of the group, and had simply given up. Many specimens he studied with similar genitalia had different wing morphology, and vice versa. The larvae are case bearers, meaning they hang out in a little silken bag, and for some species the structure of the case seemed to be distinctive. But for most, it is apparently not.

Why are species so hard to separate in Hawai`i? Evolution is a continuous process, that has no endpoint. But because the Hawaiian Islands are so recent in geological time, and it is so rare for any living thing to arrive there on its own over vast expanses of ocean, I believe we are still witnessing the messy sorting out of niche-filling. The traits of different species drift and become more distinct from each other through several processes, including physical separation (via geological events, for example) and assortative mating (in which more similar individuals mate and reproduce). In Hawai`i, we have to ask, who knows what a species is? because we have not found a way to actually watch how individuals from all of these different groups interact with each other, and the environment. Speciation is not an instantaneous process, and in Hawai`i, along the boardwalk of the Alaka`i Swamp, we are watching it happen.

The plants and insects of the swamp are finding their way. Unfortunately, the evolutionary process can no longer stay on its natural course in Hawai`i, because of the habitat destruction and thousands of alien species that are invading the natural areas like the swamp and creating selection pressures that would not have been there without humans. I feel fortunate to live during the time that I do, that I had a chance to see a glimmer of what Hawai`i was really like. Of course, I don't know an ecologist there who doesn't wish we could go back in time a couple hundred years before Europeans came, or even a couple thousand years before humans were there at all. We have to be content with the few slivers of the real Hawai`i that are left, and do our best to protect them, although the future looks bleak. When I am in the Alaka`i Swamp, I forget about the continuing destruction below me. As I peer through the mist, all I think about is the wonder of evolution.

For more about the moths and plants of the Alaka`i Swamp, click here.

Labels: environment, evolution, Hawaii, invasive species