Friday, March 30, 2007

Are There Really More Female Than Male Telescope Shiners?

At the end of a hectic week, we sat down this afternoon and finished removing and weighing the gonads from the March 3 collection of telescope shiners. Out of 37 fish, 23 are female and 14 are male (if I counted correctly). The same pattern was present in our February collection, but I wasn't as sure of the accuracy of our count because it was harder to tell males from females from lack of gonadal development. We were talking about whether or not we somehow discriminated against males while seining for them. I know that the net's mesh is fine enough so that only fish smaller than about 15 mm could possibly slip through, and adult telescopes are at least 30 mm long in our experience. We also didn't throw back any fish and thus possibly discriminate against smaller males, because we were having a hard enough time catching fish that we kept all that we caught. So it may be a property of at least this population of telescope shiners in Hurricane Creek that there is a significant skew in the M:F ratio. I can't tell you what this means, or if it's adaptive in some fashion; but I hope further evidence leads to some working hypothesis as to what the hell's going on with this population (or is it a species-wide phenomenon?).

I sacrificed two scarlet shiners that I've kept in an aquarium since last August. One of them was brilliantly colored, and had tubercles on his head. Currently they're in a freezer. Next week we hope to extract carotenoid pigments from them and look for any relationship between carotenoid concentration and sexual display (coloration). Carotenoid pigments are the basis of red/orange color in many fishes, and in principle an alpha scarlet shiner that's very red should have a lot of carotenoids in its body. Carotenoids are also part of an animal's anti-oxidation mechanism, as is Vitamin E, for instance. Our protocol for extracting carotenoids will involve grinding up the whole body, rather than merely a surface extraction. So we'll get the whole count, hopefully. As usual, if I knew what was going to happen it wouldn't be an experiment, so we'll see.

I was just listening to a really grungy swamp-rock version of the song "John the Revelator" on WWOZ out of Nawlins. Somehow it was the perfect soundtrack for writing this entry. Now it's cut to an even swampier version of "If You Walk With Jesus" sung by a guy who sounds like Tom Waites. Well, I guess that's why I listen to the station. . . . .

Sunday, March 25, 2007

Hiking In And Out Of The Walls Of Jericho

I spent the day yesterday hiking in and out of the Walls of Jericho tract, from the parking lot on Highway 79, to the Walls, and back to the parking lot. This was the first organized, themed hike organized by Nick Sharp, the Land Steward. Over 100 people showed up which was truly amazing. The leader of the hike was Jim Lacefield, a retired biologist/geologist from the University of North Alabama who pointed out features on the property speaking to the great age of the geology, back to the Carboniferous Period. In short, as on much of the Cumberland Plateau, there's a layer of sandstone that weathers slowly overlying deeper limestones that can weather quickly if the sandstone is removed or broken. That explains the deep valleys of the tributaries of the Paint Rock River as they flow south from Tennessee into Alabama, e.g. Hurricane Creek on the Walls property and Estill Fork to the west. We all made it to the Walls, proper, and below is a picture of Turkey Creek flowing away from the springs that emerge at the Walls on the way to joining Hurricane Creek. In the background, on the left, you can see the cliffs of exposed limestone that are slowly retreating.

I made it in and out with no injury or heat stroke, I'm proud to say. The trailhead is 1000 feet higher in elevation than Hurricane Creek, so at the end of the day we all climbed the two mile trail and gained 1000 feet. Forget about jogging, this kind of hiking is a full body workout. Today I'm only a little bit achy.

I stopped along Turkey Creek and caught a few small fish with an aquarium handnet I brought with me. I've always noticed these small fish in Turkey Creek but never had a chance to net them. The three I caught were all juvenile creek chubs, which makes sense. Turkey Creek is almost intermittent depending on the rate of spring flow at the Walls. Creek chubs are often the last fish to hold out in a shrinking creek so I'd guess that for much of Turkey Creek the only fish present is the creek chub. I still want to bring a seine net up to the Walls this summer and seine the big, deep pool there; I'm convinced there are other species present in this more permanent pool.

As I began to hike out I stopped on a big rock as I crossed Hurricane Creek at the mouth of Turkey Creek (see picture below). Sitting on the rock in the middle of the creek I was able to watch black darters spawning in the gravel and cobbles just upstream from this natural ford. Some of the aggregations of darters were surprisingly large, a dozen or more at a time. Large males were chasing each other and any other smaller darters that came near (and weren't receptive females, I guess). On the edge of these aggregations were small schools of striped shiners, maybe looking for eggs? I didn't see any active egg predation, that's also just a guess.

My next trip to Hurricane Creek is Saturday, April 7. My truck is being fixed up with a new timing belt, etc., so we should be ready to go.

Tuesday, March 20, 2007

Telescope Shiner, Yet More! And Jail Might Help Studying.

Besides the February and March collections of telescopes being significantly different in length and mass, I've found that in the March collection the males are a lot smaller than the females; significantly so. We haven't looked at all of the fish yet, but looking at 20 suggests that there is sexual size dimorphism. My next task is to sit down with the ovaries we've removed and characterize their maturation. It's advanced, but not quite mature; small immature eggs <1 mm can be seen with the naked eye. I would say that they're showing signs of exogenous vitellogenesis, probably late stage.

It looks like I'm going on a hike through the Walls of Jericho tract this Saturday. I just heard that a geologist will be leading a hiking group to explain the geologic history and structure of the Walls. His name escapes me, but I'm game. It's been announced on the local NPR radio station as "a strenuous five hour hike requiring good shoes". Ha! I could've told them that! It should be fun, and I need a good workout like that.

As an odd observation, two students in my intro biology lecture section were in jail separately just before my last exam. One was in for five days, the other for three. Both of them did significantly better on this exam compared to the first exam; they both said they did nothing but study while being held. It sounds harsh, but maybe undergraduates should be held in the county jail for several days before an exam for their own good?

Tuesday, March 13, 2007

Two Months Of Telescope Shiner Size Data

I've been so wrapped up in teaching obligations that I've let this blog slide for twelve days, more than I meant to do. But I have some interesting data to post.

Our trip to Hurricane Creek at the Walls of Jericho went well. My new truck made it in and out with no problems. The most challenging part of the ride was driving down about 500 meters of road that often floods and becomes part of the creek; that was the story on March 3, two days after heavy rains in the southeast. The road had about 15-20 cm of water running in the road, but we were able to negotiate it with problems (much to the students' relief). We collected our quote of telescope shiners from high, fast water, and only two of the students fell in to any degree. Good thing, because the water was 11 deg. C. But everyone survived. We also collected a single adult flame chub, which seems to be my daily allocation at this site.

The attached graph shows the length-weight relationships of telescope shiners from February and March at Hurricane Creek. The March fish are statistically significantly longer and heavier, not a big surprise since they've had a month of eating the increasing number of aquatic insects available. We've dissected the five largest of these March fish, and all turned out to be female with well-developed ovaries. Their stomachs were full of aquatic-stage insect larvae so they're apparently well-fed and putting on weight. The average GSI of these five fish is 3.5, up from the 1.2 of the February fish.

We'll do more dissections on Friday, so I'll post more data as it becomes available.

Thursday, March 01, 2007

Western Blots To Quantify NMDA Receptors In Scarlet Shiner Brains

Enrique and Rebecca have begun to set up Western blots of treated brain tissues from scarlet shiners to quantify the presence of NMDA receptors. These receptors are clusters of proteins in the cell membranes of brain cells, cells that facilitate both learning and sexual activity in fishes as primary signalling conduits between clusters of brain cells. Our interest in these receptors is to examine probable differences in brain structure between dominant males, subdominant males, reproductive females, and juveniles. Studies of other fish species have shown that males have a relatively high, steady number of these receptors in key brain areas, while females show strong seasonal and age variability in receptor number. This is of interest to us because scarlet shiners are both seasonal breeders and sexually dimorphic; that is, males become brightly colored during breeding season as the result of increased circulating levels of different types of testosterone. Reproductive hormones like testosterone and estrogen also have a strong influence on brain structure and function, so understanding different levels of NMDA receptors is a key part of understanding the neurobiology of scarlet shiner reproductive ecology.

I have to admit that I've never worked with Western blots before; my co-investigator, Amy, has done lots of work with this electrophoretic technique and her lab is set up for running Westerns. What we're doing is really a form of interdisciplinary research between a neuroscientist (Amy) and an aquatic ecologist (me). So far this collaboration is producing strong results, and of course I'll keep you posted on this site. See ya!