30 April 2005

Where were you on the night of 30 August 1820?

A group of explorers, including Thomas Say, camping out somewhere along Arkansas River under the command of Captain Bell were deserted by three soldiers on that night, or perhaps early in the morning of the following day. The deserter took with them not only some horses but also the saddle bags of the rest of the party. The bags contained spare clothing, Indian presents and, most importantly, all the manuscripts of Say and Lieutenant William Swift.

They were with Major Stephen Long's 1819-1820 expedition to the Rocky Mountains, but had separated from Long's party on 24 July. Say was the official zoologist of the expedition. He also studied the customs and languages of the Indian tribes they encountered. Lieutenant Swift was one of the assistant topographers. Say's five lost notebooks contained his records of the manners, habits, vocabularies of Indians as well as notes on the animals he had collected.

The identities of the three deserters were known1: "Nolan, Myers and Bernard". Despite a reward of $200 that was offered for their capture2, neither the three men nor the stolen manuscripts were ever found. Say's biographer Stroud wrote1: "To this day scientists lament the theft [of Say's manuscripts]".

If you ever come across ancient-looking journals while cleaning out your grandparents' attic, hang on to them. They could be Say's lost notebooks.


1. Stroud, P.T. 1992. Thomas Say: new world naturalist. University of Pennsylvania Press.
2. Weiss, H.B. & Ziegler, G.M. 1931. Thomas Say: early American naturalist. Charles C. Thomas.

post revised: 8-viii-08

27 April 2005

Spacious shells 2

In a previous post I explained that in most pulmonate land snails the shell seems to be larger than the snail’s body. I listed three reasons why it would be good for a snail to have a shell larger than its body. One advantage is that a larger shell allows a snail to carry water in its mantle cavity. Another advantage I mentioned is that when a snail loses as much as all of the extra portion of its shell to an injury, it will still have enough shell left to withdraw its entire body into. I will now illustrate the latter argument with real-life examples.

lerosiensis1b

The picture above shows two shells of Albinaria lerosiensis, a clausiliid from southwestern Turkey. The shell on the bottom is an ordinary looking specimen, while the one on top looks peculiar; not only does it have a malformed body whorl, but the shell also appears to be too short for its diameter.

Turning the shells sideways, as in the picture below, reveals what happened to the top shell: it lost at least a whorl. But the snail managed to survive and rebuild its shell. The rebuilt whorl is, however, distorted, perhaps because the snail’s mantle―the organ responsible for secreting the shell―had also suffered an injury.

lerosiensis2b

The second example is a shell of Triodopsis juxtidens, a common species from Maryland forests. The photograph below clearly shows that the snail lost almost a half of its original body whorl. It nevertheless survived and repaired its shell (the repaired section is without the characteristics ribs). However, the repaired shell is slightly smaller than the original one as indicated by the arrows pointing at the remnants of the original lip, which are in front of the rebuilt lip.

tjuxtidens2

We can draw two conclusions from these two examples: (1) these snails were able to survive the loss of substantial portions of the body whorls of their shells, because what was left intact was still large enough for them to withdraw their bodies into for protection; (2) in both cases the rebuilt shells ended up being slightly smaller than the original shells. That the snails could fit into smaller shells shows that the original shells were too large for the snails’ bodies. It is not entirely clear why rebuilt shells are often smaller than the original ones. One disadvantage of this is that the snail now has less space for carrying water.

Do prosobranch land snails also have extra space in their shells? That will be the subject of a future post.

25 April 2005

Mosquitos, alligators, Liguus, mosquitos

Once abundant and widespread throughout southern Florida, Liguus fasciatus, the large colorful tree snail, has lost most of its former habitats and is now listed as a “Species of Special Concern” by the Florida Fish and Wildlife Conservation Commission1. After the American Malacological Society meeting on Sanibel Island last August, I decided to spend an afternoon looking for Liguus in Big Cypress National Preserve on my way back to the Miami airport. I was excited because, although I had heard much about these snails, I had never seen one.

Traveling east on Route 41, my first stop was the Big Cypress’s Visitor Center. Despite a friendly ranger’s warning that the trails were flooded from the recent rains, I thought I could go on a hike to get some exercise and to do some nature photography. I walked pass a large ditch full of alligators in front of the Visitor Center and entered the trail. Less than a minute later I was in water up to my ankles when a thought occurred to me: “If there is so much water here, there could also be alligators!” I quickly turned around and went back to the Visitor Center to inquire about Liguus. This time, I followed the friendly ranger's advice who told me exactly where to go to find the snails: the two campgrounds along Route 94, a little side road off Route 41. But she did warn me about the mosquitos.


Alligator near Big Cypress National Preserve Visitor Center.

Consulting a map of Big Cypress, I got back in the car with wet shoes and all—one nice thing about driving a rental car. Soon I was on Route 94 traveling west—away from Miami. For about 10 minutes, I did my best to avoid the deep water-filled potholes that covered the unpaved road, and then, gave up and began to just ignore them—another nice thing about driving a rental car. When I got to the Pinecrest campground, I decided to have a look.

I was expecting mosquitos and had come prepared for them. In addition to a head net, I had with me a pair of long pants and an old long sleeved shirt. But little did I know that a million, wait, no, a billion of them would be waiting for me to try to spoil my day. Despite the stifling heat, I put everything on, grabbed my camera and got out. A fraction of a second later I was covered with mosquitos. Not surprisingly, the campground was deserted, which meant that the mosquitos had no one to go to, but me. I did manage to take a quick walk around the perimeter of the campground, but all I could see was an old empty Liguus shell at the base of a tree. The mosquitos were biting me through my shirt, pants and not letting me take my bare hands out of my pockets. How could there have been so many of them? And whose blood do they suck when there is no one around? While getting into the car, I inadvertently let a bunch of them in and then, spent five minutes trying to kill them before I could get back on the road again.

I noticed on the map that near the end of Route 94 there was a place marked "Tree Snail Hammock Trail". Figuring that I would definitely find Liguus there, I drove for another 20 minutes over many more potholes to reach a road block next to a locked gate in front of an unmarked deserted building. Disappointed, I drove back for another 30 minutes and as I was about to give up and head back to Miami, I saw the sign for the other campground, Mitchell Landing. Mostly out of desperation, I decided to check it out.


At one of the two camp clearings on a tree next to the road, I saw the Liguus on the left. I put on my "protective" gear and got out. After I quickly took some pictures of the snail, I ran along the road keeping my eyes on the trees. Before long, I spotted two more snails on a tree. Trying to ignore the countless mosquitos now covering my hands and biting my face through the net, I managed to get a few more pictures, including the one on the right below.








Having accomplished my mission, I got in the car and drove to Miami; I was happy, despite my itchy hands. At a gas station I tossed my shirt covered with the bloody remains of the slower mosquitos into a trash can.

Nothing can spoil a malacologist’s day.




1. Florida Fish and Wildlife Conservation Commission, 2004. Florida’s endangered species,threatened species, and species of special concern. pdf

23 April 2005

Down among the graves and snails

Whenever I am in Turkey, I like to visit old cemeteries, especially the ones with fallen tombstones and crumbling graves overtaken by a wild assortment of plants. In fact, the older and more unkempt a cemetery is, the more attractive I find it. However, my interest in such cemeteries, far from being morbid or religious, is entirely educational and malacological. I have learned much about the demographics and customs of the late 19th and the early 20th century Anatolia during visits to cemeteries. At the Jewish Askenazi cemetery in Istanbul, for example, one can see intermingling tombstones with writings in Hebrew, German and Turkish, representing the flow of historical change during the course of the 20th century.

heybeli

Besides, graveyards are good places to find snails. I have noted that in the metropolitan Istanbul area, the old cemeteries are among the few remaining places where one can still find native land snail species1. The picture above shows the graves at the Moslem cemetery on Heybeliada in the Sea of Marmara, off Istanbul, where I have collected Mastus carneolus, a native.

Now I have a slowly growing list of “cemeteries to be visited” for my next trip to Turkey.

deniz

Field assistant Deniz with a bag of the remains of the dead (snails, of course) at the cemetery of the Profitis Ilias Greek church, Istanbul.

1. Örstan, A. 2004. Cemeteries as refuges for native land snails in Istanbul, Turkey. Tentacle, No. 12, pp. 11-12. pdf

21 April 2005

Falcons hunting pigeons: yet another demonstration of natural selection

An interesting study by Palleroni et al., published in today’s Nature1 shows that peregrine falcons (Falco peregrinus) are less likely to catch the feral pigeons with the so-called “wild” plumage, characterized by a white rump, than those with other plumage types. These results were based on observations of 1485 attacks on feral pigeons by five falcons in Davis, California. To confirm these results, the authors switched the rump feathers of a large number of wild and blue-barred (another plumage type) pigeons. After plumage transfer, the manipulated wild phenotype suffered predation at the same rate as the unmanipulated blue-barred type, whereas the manipulated blue-barred type had rates of predation as low as the unmanipulated wild type.

This paper reminded me of a recent study by Pole et al.,2 that demonstrated that in Zimbabwe, African wild dogs (Lycaon pictus) selectively prey on those individuals of impala (Aepycerus melampus) that are in poorer condition.

However, there is an interesting difference between the results of these two studies. In the Palleroni et al., study what determined the likelihood of a pigeon getting caught by a falcon was its plumage, regardless of its health; whereas, in the Pole et al., study it was the physical condition of an impala that dictated its chances of survival. In other words, sometimes even a very healthy animal may be more likely to get eaten if it has the wrong plumage, or the wrong fur color, or some display on its body that attracts the predators’ attention.

Another key point these studies reinforce is that survival is to some extent a matter of chance. The healthier or better camouflaged individuals are not guaranteed to survive; they only have better chances to do so.


1. Palleroni, A., Miller, C.T., Hauser, M., Marler, P. 2005. Predation: Prey plumage adaptation against falcon attack. Nature 434:973-974.
2. Pole, A., Gordon, I.J., Gorman, M.L. 2003, African wild dogs test the ‘survival of the fittest’ paradigm. Proc. R. Soc. Lond. B (Suppl.) (
Biology Letters) 270:S57.

20 April 2005

Spacious shells 1

Most pulmonate land snails seem to have quite a bit of extra space in their shells. One way to demonstrate this is to hold a snail that has been dormant for a while against a bright light and to try to make out the outline of the snail’s body within the body whorl (this will work only if the shell is translucent). The picture on the right shows an individual of Neohelix albolaris that I collected in Maryland in February 2001. The snail had been dormant for a while as indicated by the multiple membranous epiphragms (short arrows) it had formed as it withdrew deeper and deeper into its shell possibly as the weather got colder and colder. The long arrow is pointing at the edge of snail's body.

Considering that the body whorl makes up the bulk of the shell volume, it is obvious from this picture that the volume of extra space in the body whorl is a significant fraction of the total volume. Building a shell is both a time consuming and a costly process in terms of the raw materials and energy it takes. Why don't the snails build shells that are just big enough for their bodies?

I can think of three advantages in having a shell that is larger than its occupant. First, a larger shell allows a snail to carry water in its mantle cavity1. This water in turn allows the snail to be temporarily independent of the water fluctuations in its environment and to visit places that may be on the dry side.

Second, when the snail is dormant the extra space in the body whorl provides additional security against both biotic (predators, parasites) and physical dangers by letting the snail withdraw from the shell aperture and fill the intervening space with multiple epiphragms.

Third, if a snail with extra space in its shell loses a portion of its shell starting at the lip, it may still have enough shell left to withdraw its entire body into. In another post, I will demonstrate with examples that this indeed happens.

Spacious shells 2

1. Blinn, W.C. 1964. Water in the mantle cavity of land snails. Physiological Zoology 37:329-337.


18 April 2005

Slug's shell: a flimsy evidence for evolution

Dreticulatum
Deroceras reticulatum is a European slug that has been introduced into the U.S. It is now common in gardens, abandoned farm fields and parks in the eastern states. This individual was 50 mm long. The hump with the breathing pore behind the head is the mantle.

Hidden inside the slug Deroceras reticulatum is a clue that betrays the slug's roots; a clue that exposes the identities of its ancestors. The clue is a shell buried under the slug's mantle. But unlike the familiar spiraling shells of snails, this one is only a thin, fragile membrane of calcium carbonate that is barely noticeable. It hardly deserves to be called a shell.

But what an evidence it is. It reveals wonderfully that slugs evolved from shell-bearing snails. The slug's shell is a vestige of a distant past. It is a perfect example for Darwin's1 exquisite logic: "Rudimentary organs may be compared with the letters in a word, still retained in the spelling, but become useless in the pronunciation, but which serve as a clue in seeking for its derivation. On the view of descent with modification, we may conclude that the existence of organs in a rudimentary, imperfect, and useless condition, or quite aborted, far from presenting a strange difficulty, as they assuredly do on the ordinary doctrine of creation, might even have been anticipated, and can be accounted for by the laws of inheritance."

Derocerashell
The shell of Deroceras reticulatum revealed under its mantle. The concentric growth lines are vaguely visible on the shell.

1. Darwin, C. 1859. On the Origin of Species by Means of Natural Selection. Full text


14 April 2005

Darwin’s snails

"No facts seem to me so difficult as those connected with the dispersal of Land Mollusca."
Charles Darwin, letter to J. D. Dana, 29 September 1856

Darwin appears to have spent considerable effort to understand the dispersal mechanisms of animals, especially land snails, that live on isolated islands. This subject comes up repeatedly in his letters. For example, in his letter of 23 May 1855 to W. D. Fox, he announced his plans to test the survival of land snails immersed in sea water1: "I am going to try land-snail shells & their eggs also. in [sic] sea-water." Two years later, in another letter to Fox dated 8 February 1857, he reported his results1: "I have just had a Helix pomatia withstand 14 days well in Salt-water; to my very great surprise." And then again to Charles Lyell three days later1: "I have just had Helix Pomatia quite alive & hearty after 20 days under sea-water; & this same individual about six-weeks ago had a bath of 7 days."

The subject was still on his mind when he wrote to Alfred Russel Wallace on 1 May 18571: "One of the subjects on which I have been experimentising & which cost me much trouble, is the means of distribution of all organic beings found on oceanic islands & any facts on this subject would be most gratefully received: Land-Molluscs are a great perplexity to me."

In On the Origin of Species2, he proposed two plausible mechanisms by which land snails could be dispersed: on birds and on driftwood. Of course, he didn't forget to mention the results of his experiments: "And I found that several species in this state [hibernation] withstand uninjured an immersion in sea-water during seven days: one of these shells was the Helix pomatia, and after it had again hybernated I put it in sea-water for twenty days, and it perfectly recovered. As this species has a thick calcareous operculum, I removed it, and when it had formed a new membranous one, I immersed it for fourteen days in sea-water, and it recovered and crawled away: but more experiments are wanted on this head."

Land snails do get around. In 1883, the island of Krakatau was devastated by a volcanic eruption. The five species of land snails that had been recorded on the island before the eruption has not recolonized it, but two other species were first recorded on the island in 19083. One of these was the tree snail Amphidromus porcellanus that had probably rafted to the island. Darwin would have been fascinated.


1. Burkhardt, F. (editor) 1996. Charles Darwin's Letters. A Selection 1825-1859. Cambridge University Press.
2. Darwin, C. 1859. On the Origin of Species by Means of Natural Selection. Full text
3. Thornton, I. 1996. Krakatau. Harvard University Press.

13 April 2005

Cast from the past: Thomas Say’s male and female pulmonates

While everyone is busy reading what got published today, I will turn my gaze back to the early 19th century. The pioneering American naturalist Thomas Say was a member of an expedition from Philadelphia to Florida in 1817. One result of that expedition was a paper Say published about a year later in the then fledgling Journal of the Academy of Natural Sciences of Philadelphia1.

In that paper, Say established the genus Polygyra and described three Polygyra species. What is most interesting about Say’s descriptions is that for two of the species, P. auriculata and P. septemvolva, he gave separate dimensions for the shells of what he claimed were female and male snails. Obviously, in 1818 Say didn’t know that those particular species he was describing were, in modern terminology, simultaneous hermaphrodites, that is, they can produce both sperm cells and ova at the same time and have both female and male genitalia.

But how did Say distinguish between "female" and "male" Polygyra? Say didn’t say, but a clue emerges from the dimensions he gave. For both species, his females are larger than his males. We also know that the dimensions of the shells of Polygyra species tend to be quite variable. So it appears that Say noticed and attributed this variability to sexual dimorphism and decided that "female" snails were larger than "males".

When and how did Say wise up? That will be the subject of another post.

auriculata

1. Say, T. 1818. Account of two new genera, and several new species, of fresh water and land shells. Journal of the Academy of Natural Sciences of Philadelphia, 1:276-284. Full text


11 April 2005

Deadwood is good

Rotting trees in forests are a very significant source of food and habitat for many organisms, including snails. In one of the first papers I published on land snails1, I had a sentence about the importance of not removing the fallen trees from wooded areas. I had been influenced not only by my own observations, but also by a USDA publication on the subject2.

An organism that lives in or on rotting organic matter is called a saprophyte. Many saprophytes can survive nowhere but on dead trees. I don't know if there are any snail species that are strictly saprophytic, but many do hang around rotting tree trunks, because that is where they can find food (the fungi that grow on dead wood), moisture and shelter. However, in most cases the species that can be collected from rotting trees have also been observed eating live plants in the wild and will eat fresh vegetables in captivity.

In most wooded parks that I have visited in the U.S. I have seen plenty of rotting trees. I hadn't realized that this wasn't generally the case in European forests until I read a recent publication by the World Wildlife Fund3. According to the WWF, “Average forests in Europe have less than 5 per cent of the deadwood expected in natural conditions.” Perhaps because of this shortage of deadwood, WWF also reports that the species associated with deadwood is the largest single group of threatened species in Europe.

Even if you can't do anything else, you may consider keeping a small log or two in a secluded spot in your yard to help some saprophytes survive4. Many people seem to think that rotting wood is an ugly sight. That is not necessarily the case. In fact, I consider many saprophytic fungi rather pretty on their own terms. They are also good subjects for photography, because they don't move much.

fungus

1. Örstan, A. 1999. Land Snails of Black Hill Regional Park, Montgomery County, Maryland. Maryland Naturalist, 43(3-4):20-24. pdf (from Aydin’s Library)
2. Maser, C., & Trappe, J.M. 1984. The seen and unseen world of the fallen tree. General Technical Report PNW-164. U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station, Portland, Oregon.
3. Dudley, N. & Vallauri, D. 2004. WWF Report. Deadwood - living forests. The importance of veteran trees and deadwood to biodiversity. pdf (from WWF)

4. Keep such logs away from your house to avoid potential termite infestations.

09 April 2005

Meet my namesake Metafruticicola oerstani



I have recently had a new land snail species named after me1. This is certainly an honor for me, especially since the new species is endemic to Turkey, where I am originally from. For this, I thank the authors Bernhard Hausdorf, Zeki Yıldırım and Burçin Gümüş. I personally know and have worked with Zeki and Burçin. I have exchanged many e-mails with Berhard Hausdorf, but haven't yet had the pleasure of meeting him in person.

So, what's the big deal with M. oerstani, besides being my namesake? Its type location on Barla Mountain, the only place where it has so far been found, has an altitude of 2550 m. The other new species Hausdorf et al., described in the same paper, Metafruticicola dedegoelensis, is likewise known only from a spot at an altitude of 2350 m on Dedegöl Mountains. Zeki has been collecting snails in that area for quite some time, and if either of these species lived at much lower altitudes, he would most likely have encountered them by now. So, it looks like these two species are restricted to high altitudes.

This tells us two things. First, there are probably many more unknown species that remain to be discovered on the mountains of Turkey. We have started surveying the Turkish mountains and are now planning future high-altitude expeditions.

Second, there must have been some pretty fascinating evolutionary events that resulted in the restriction of the ranges of these snails to cold and low-oxygen mountain tops, when their close relatives are enjoying an easier life in the warm meadows below. Not too long ago, Bernhard Hausdorf2 compared the altitudinal distributions of vitrinid semislugs (snails with rudimentary shells outside their bodies) with those of limacoid slugs (fully developed slugs with or without vestigial shells inside their bodies). He noted that the ranges of the most European semislugs are limited to altitudes above 500m and attributed this to their ecological displacement from the lower altitudes by the better adapted slugs.

A question immediately comes to my mind: could something like that have happened and still be happening on the Turkish mountains?

Incidentally, the above drawing of M. oerstani was done by Hülya Korkmaz, a talented student of Zeki.


1. Hausdorf, B., Gümüş, B. A. & Yıldırım, M. Z. 2004. Two new Metafruticicola species from the Taurus Mountains in Turkey (Gastropoda: Hygromiidae). Archiv für Molluskenkunde 133:167-171.
2. Hausdorf, B. 2001. Macroevolution in progress: competition between semislugs and slugs resulting in ecological displacement and ecological release. Biological Journal of the Linnean Society 74:387-395.

Evolution is inevitable

Things are bound to evolve if two conditions are satisfied:

1. There is a set of instructions (the genotype) that determines the morphology (the phenotype) of the things.
2. The instructions are copied and passed on to every new thing as it is starting to form.

These two seemingly innocuous conditions lead to evolution, because it is physically almost impossible to repeatedly copy of a set of instructions without -sooner or later- introducing an error. If anything, there is enough random, incessant thermal motion in the universe to mess things up, even if it is going to be one bit at a time. Once the genotype starts to change, the phenotype follows. And the rest is history.

That's it folks. Everything else follows from this. Natural selection? That is what happens when one phenotype is more successful in the present environment. That phenotype tends to stay around longer and is likely to leave more offspring. So, the successful phenotype soon becomes the dominant one until the environment starts to change and so on. But things could evolve even if natural selection didn't operate, although it would be hard to come up with a scenario without natural selection.

You can't avoid, pass up or ignore evolution. Well, I suppose if one tried hard and was foolish enough, one could ignore evolution and pretend that it was not happening. But once the environment has changed so much and you have been left behind to go extinct, there is usually no turning back. And no one will care enough to feel sorry for you. As Richard Dawkins1 said "nature is not cruel, only pitilessly indifferent."



1. Dawkins, R. 1995. Chapter 4 in River out of Eden. Basic Books.

The dissection selection: Philomycus carolinianus

The pulmonate land snails have evolved all sorts of complicated genitalia and unusual mating rituals. The largest group of pulmonate land snails is the Stylommatophora, in which the eyes are located on the tips of the upper (longer) tentacles. Several families in the Stylommatophora, including the Helicidae, Zonitidae and Philomycidae, have evolved darts to stab each other with during mating. The presence of darts in many distantly related families of the Stylommatophora strongly suggests that darts were also present in the ancestors of the Stylommatophora1.

The Philomycidae is a family of slugs that are native to the United States. One member of the family, Philomycus carolinianus, a common slug in northeastern forests, has a thick, curved dart kept in a muscular sac. The top picture on below shows the components of the hermaphroditic reproductive system of P. carolinianus, while that on the bottom shows its dart, which was about 2.7 mm (the ruler, in millimeters, is for the left photo). The head of the dart broke while I was trying to remove it, but now we can see the shape of its cross-section.



Glenn Webb2 once dissected a pair of these slugs that he had killed while they were still mating and published, to my knowledge, the only account of how the dart functions during the mating of these slugs: "...the dart was found to have been thrust sufficiently far into the proximal or basal part of the inserted penis to form a definite wound..." Talk about painful sex!



1. Barker, G. M. 2001. Gastropods on Land: Phylogeny, Diversity and Adaptive Morphology. In The Biology of Terrestrial Molluscs, edited by Barker, G. M. CABI Publishing.
2. Webb, G. R. 1968. Observations on the Sexology of Philomycus carolinianus Bosc. Gastropodia 1:62.