Tadpole Conundrum, the Philippines
It’s always interesting to see how people adjust to life in camp when first arriving in the field. I am particularly intrigued by what appeals to new students—what interests them, which animals they like, what questions develop. It’s a finer point, but these initial impressions can have a profound impact on someone’s life. It is that passion for the organism that not only has the potential to inspire someone to take up a career in biology, but which may also sustain them for five or six years of graduate school or whatever higher training they may undertake.
This year, as we embark on the 100th year anniversary of herpetological collaboration between the University of Kansas and the National Museum of the Philippines (actually titled the Philippine Bureau of Science when Dr. E. H. Taylor first travelled to the archipelago in 1912), I am accompanied by a new student, Kerry Cobb, who has just earned his bachelor’s degree from KU and has been excitedly looking forward to this trip (his first time out of the States) for the last several months.
Kerry is already an accomplished field biologist who has done very hard-core, months-long, back-country fieldwork on salmon ecology in major parks in the western U.S. He wasted no time fitting right in to the group social dynamic of our all-Filipino field team, going out every night to catch amphibians and reptiles with the herper, cracking jokes with the mammalogist, poking fun at the parasitologist for their study of very gross things, and in general staying amused and in good spirits. On our second day he discovered that the nearby river was full of tadpoles and went back to his tent with a purpose, produced a pair of swimming goggles, and spent the next couple of hours swimming back and forth across one of the larger pools. He then triumphantly came back to camp with several goldfish bags of tadpoles and spent another hour or two sorting the larvae into batches corresponding to species. A day later, after he had time to think about it a bit, he did the math and perceptively pointed out that although we had encountered six or seven species of frogs in the area, there were nine species of tadpoles present in the site. What could be going on here?
As it turns out, the idiosyncratic reproductive cycles of the various frog species present at any given site and time is always in flux. Clearly there were two or three additional species breeding here a month ago, and while we have not yet encountered the adults, we know they were here because of the presence of their larvae in the river. Perhaps the adults have dispersed back into the forest at this point, may have gone under ground or up into the tree canopy…we just don’t know. “Well, how do we identify them?” Kerry asked, “And are there any published papers that we can use to key out the tads?” Unfortunately, the state of knowledge of vertebrate biodiversity is so underdeveloped in this part of the country that those kinds of resources do not yet exist. The best we can do is sort the tadpoles to apparent species, preserve a few of each kind for future studies back in the museum, and take tissue samples for subsequent DNA identification. When we get back to the lab in several months, we can sequence the DNA of all the adults and tadpoles for a common gene fragment. Then we can match them up and identify the tadpole of each resident species….but the mystery tads will remain a mystery until an adult (possibly from another part of the island, or the next island over) can be sequenced and matched to their genotype. Doing this systematically for the country, trying to match all the larvae with all the adults (there are more than 110 frog species in the Philippines), would be a great first step for a graduate project and constitute a major contribution to Philippine herpetology. Hopefully a bright student with a passion for tadpoles will emerge. I can see the first kernel of curiosity in Kerry; hopefully someone like him will be inspired to take on the Philippine tadpole challenge. —Rafe