28 February 2006

A circularly naked snail

snlinsd
Neohelix albolabris removed from its shell. The red arrow points at the part of the snail's body that fits into the spire of the shell and the blue arrow points at the penis (cut open) with the attached vas deferens. The folded flap of skin visible above the penis normally protects the penis and the other organs located within the foot when the latter is outside the shell.

If a snail is removed from its shell, one can see that the upper whorls of the body (red arrow in the photo), which normally never leave the shell, are unsupported and the organs incorporated in them will be visible behind only a thin membrane. In contrast, the organs within the foot (for example, the lower genitalia, including the penis) are protected by a thick skin.

From this observation, we can conclude that in gastropods with shells large enough to cover at least most of the body, the external shell has evolved to support and protect some of the organs.

Nevertheless, this conclusion, if stated in the following form, could sound like a circular argument: The shell protects the exposed organs and the organs are exposed, because they are protected by the shell. There is no circularity, however, when one realizes that gastropod anatomy and shell have evolved together. If, for example, the ancestral gastropods had lost their shells during their early evolution, this would have taken place concurrently with the movement of their organs to locations within their body cavities.

It follows from these considerations that a snail lineage can’t undergo a drastic reduction in shell size without accompanying changes in its anatomy. This is exactly what has happened during the evolution of slugs from snails: as the shell got smaller and smaller, the organs have migrated further into the body cavity.

27 February 2006

An afternoon at Hirshhorn

darabjerd
Darabjerd III by Frank Stella (1967).

A friend was in town yesterday. I took him to the Hirshhorn Museum in D.C. We had a good time taking pictures and evading the guards at the same time ("Don't use flash!" "No picture taking in this exhibit!" "Don't lean on the wall!"...).

fsh
Fish by Alexander Calder (1944).


137a
Two views of #137 by Hans Breder (1967).
137b

25 February 2006

Double standards of scientific photography

In 1977, Alfred A. Blaker, a professional scientific photographer, wrote1:

"...errors do occur, and besides, it is not always possible to make a single exposure that will be optimal for the entire image. I refer to the solution of this problem as differential printing, though this concept is commonly thought of as two separate procedures called dodging and burning in. Dodging consists of interrupting the light between the lens and a small area of the printing paper so as to give less exposure to that area, whereas burning in is the opposite-interrupting the light to the entire paper except for a small area, so as to give more exposure to that area. These procedures are illustrated in Figure 6. [reproduced below]"


Instructions you will not need anymore. But note the sentence I underlined: "When correctly done, differential exposure is not detectable in the final print." Go explain that to the editors of Nature.


In our age of digital photography, however, the established techniques of scientific film photography that were once completely acceptable would get your manuscripts rejected. Item #5 in Nature's new "Provisional guide for digital images":

"Processing (such as changing brightness and contrast) is appropriate only when applied equally across the entire image and when it is applied equally to controls. Contrast should not be adjusted so that data disappear. Excessive manipulations, such as processing to emphasize one region in the image at the expense of others (for example, through the use of a biased choice of threshold settings), is inappropriate, as is emphasizing experimental data relative to the control."

Differential printing, I suppose even if it is applied equally to controls, is now inappropriate.

I recommend that Nature change the title of their guidelines to "Paranoid guide for digital images".


1. Alfred A. Blaker. 1977. Handbook for Scientific Photography. W.H. Freeman.

24 February 2006

Beaver's dam and lodge

bvrldg3

About a week ago I posted a picture of a beaver dam I had discovered. I went back to the area and did some more exploring. The picture above shows what I think may be the beaver's lodge (there is probably more than one, so I should say beavers' lodge). I could not see any other structures that were similar in appearance to this one.

Here is another picture of the dam taken from the front. Yes, I was standing in the creek (I had rubber boots on). The arrow points at the lodge in the picture above.

bvrdm2

You may be able to tell from the picture that the dam is not straight, but curved. I had a measuring tape with me and estimated the length of the dam as 18 m. I measured 2 sections, 7 and 6 m long, and estimated the length of the last section as 5 m (water along the 5-m section was too deep for my boots).

I was also able to take a closer look at how the dam was constructed. I will save that information for another post.

23 February 2006

Sex on the grass

ecomyntas

I photographed these 2 eastern tailed blues (Everes comyntas) last September in Germantown, Maryland. They were mating on a grassy strip next to a busy road, completely oblivious to the traffic and to me.

The question of why sex evolved is one of the perennial questions in evolutionary biology. An article by Paland and Lynch1 and an accompanying essay by Nielsen2, both in last week's Science, offer some explanations.

Sexual reproduction allows genetic recombination, that is, the exchange of genetic material between parental chromosomes. In this case, the chromosomes of the male butterfly will recombine with the chromosomes of the female and their offspring will have new sets of chromosomes.

Genetic recombination provides a mechanism for genetic variants that have arisen in different individuals to be combined and tested for fitness in one individual. When a lucky butterfly has several beneficial mutations in its genes, it is more likely to survive and produce its own offspring. As Nielsen summarizes: "genetic recombination is advantageous because it allows natural Darwinian selection to work more efficiently."

The results by Paland and Lynch suggest that asexual populations of the water flea Daphnia pules accumulate deleterious mutations. They conclude: “our results indicate that sexual reproduction enhances the efficiency of purifying selection, supporting the theory that deleterious-mutation accumulation is a leading evolutionary force contributing to the short longevity of asexual lineages.”

Yes, but, what about bdelloid rotifers? They are the largest group of animals that appear to reproduce exclusively by parthenogenesis (they are all females) and they may have been around for quite some time.

Perhaps a more appropriate, but certainly less attention grabbing, title for this post would have been "Recombination on the grass".


1. Susanne Paland & Michael Lynch. 2006. Transitions to Asexuality Result in Excess Amino Acid Substitutions. Science 311:990-992.
2. Rasmus Nielsen. 2006. Why Sex? Science 311:960-961.

22 February 2006

The other ultimate question

Yesterday, someone who was searching the Internet using the phrase "meaning of snails" hit upon this blog.

What is the meaning of snails? Well, my dear reader, that question ranks right up there with "What is the meaning of life?"

Generations of malacologists have tried in vain to find an answer. The legend has it that some even climbed high mountains in their quest for the molluscan truth.

Others went so far as to claim that snails were nothing more than figments of our imaginations.

The first question to ask is: What is a land snail? The answer is that there is not any such thing.
H.B. Baker, 1958

But would it not make a sound if a tree fell on a snail in the forest and crushed it into smithereens? And what about that tenacious slime that coats our fingers when we pick up a slug? The crushing of a snail’s shell may not make a sound (if no one is around to hear it), but do we dare deny the reality of slime?

Well, dear reader, I certainly hope your visit to this blog was enlightening. But, don't despair and don't give up in your quest for meaning. The best thing mortals like you and I can do is to keep searching and asking and asking and asking...

Are snails gastropods? Are gastropods mollusks? How did snails, slugs, clams, octopuses evolve from one common ancestor? Is it octopuses or octopi?


The quote above is from H.B. Baker, 1958. Land snail dispersal. Nautilus 71:141.

Land snails of Turkey: Discus rotundatus

Drotundatus

The first and so far the only published record of the land snail Discus rotundatus in Turkey is from Anadolu Hisari, a 14th century fort on the Asian side of the Bosphorus in Istanbul, where I found it in August 20021. It is certainly an introduced species at least in the Istanbul area.

The native distribution range of D. rotundatus covers western and central Europe. It has also been introduced to other countries, including the U.S.

The shell of D. rotundatus is characterized by a wide umbilicus, prominent ribs and reddish-brown marks. The largest shell I found was 5.4 mm in diameter. (The scale in the picture above is in millimeters.)

The land snail family Discidae, which includes the genus Discus, has native representatives both in Europe and in North America. I will return to the biogeography of the Discidae in a future post.


Archive of the Land Snails of Turkey series.


1. Örstan, A. 2003. The first record of Discus rotundatus from Turkey. Triton, No. 7, p. 27. pdf

21 February 2006

Return of the skull eaters

A previous post mentioned that we have a collection of assorted deer bones in our backyard left from the days when my son had an interest in bones. I also mentioned that some unknown animals frequently scatter the bones around. One of those bones is a deer skull that I have been keeping as a decoration of sorts on a large flat rock. I have often found that skull displaced from its location, but it wasn't until yesterday that I noticed how much of it had been eaten away. The picture below compares it (top) with another skull that has been kept indoors.

deersklls

Top of the snout is completely gone and the braincase seems to have caved in. Close inspection reveals what seem to be teeth marks at several places on the skull (below). Perhaps someone experienced with such marks can identify the animal that has been using this skull as its calcium source. In any case, we are keeping our eyes open to photograph the beast in action.

deerskll

20 February 2006

An upside down butterfly

smelinus1

This is a gray hairstreak (Strymon melinus). The only time I had a chance to photograph this species was last August in my backyard. If you look closely, you will notice that this individual is missing a small portion of its hindwing, including one of the pair of hair-like tails it had. In a previous post I had a picture of a butterfly with wings in much worse condition.

smelinus2

Beth at Fireforest Blog notes that these butterflies seldom leave their wings open when they are nectaring. Nevertheless, she was able to photograph one with its wings partially open.

18 February 2006

Harbors far from the sea

LakeBafa3

This satellite photo from Google Earth is of the area in western Turkey where the Meander (Büyük Menderes) River empties into the Aegean Sea. The course of the river, which as it approaches the sea divides into several channels, is my approximation (see below for a close up). A previous post had a picture of the delta I had taken from Mount Mycale on Dilek Peninsula. Lake Bafa is a shallow, brackish water lake.

During the last ice age an enormous quantity of water was tied up as snow and ice. This resulted in a shortage of liquid water and consequently, the global sea level was about 100 m or more lower than the present level. The continental shelf was exposed along the coastlines and many coastal islands became connected by dry land to each other or to the mainland.

After the ice age ended, about 10,000 years ago, the sea level gradually rose, islands became islands again and coastal areas got flooded. This is known as the postglacial transgression. The image below is my recreation of what the Meander Delta may have looked like about 2500 years ago. I don't think it is known how far inland the sea went. So, the location of the end of the embayment is a wild guess.

Latmian

Along the shores, there were 3 well-known Ionian harbor cities, Priene, Miletus and Heracleia. The small island northwest of Miletus acquired its share of fame by giving its name to the Battle of Lade between the Ionian Greek and the Persian navies that took place near the island in 494 B.C.E.

But gradually, with the silt it was carrying, the river filled up its own delta, which moved towards the sea. This is known as progradation. One by one, the coastal cities were cut off from the sea and the Latmian Gulf became a brackish water lake. The diagram below shows the approximate dates of the coastline throughout the history.

prgrdtn3
Map from Göney, S. 1975. Büyük Menderes Bölgesi. [M.Ö.=B.C., M.S.=A.D.] Another scheme is given by Müllenhoff et al. (link below).


The Island of Lade is now a hill surrounded by cotton fields. Ships must surely have sunk during the Battle of Lade. I have always wondered if one dug deep enough in the fields, if one would find the remains of those ships.

delta


More information on the progradation of the Meander Delta:
Marc Müllenhoff, Mathias Handl, Maria Knipping & Helmut Brückner. 2004. The evolution of Lake Bafa (Western Turkey) – Sedimentological, microfaunal and palynological results. Coastline reports 1:55-66.
pdf

17 February 2006

A beaver dam


This is the largest beaver dam I have seen. According to the only authoritative source I have on beavers, E. R. Warren's 1927 book The Beaver, beaver dams could be from a few feet to thousands of feet long. He mentions one dam that was 2140 feet (about 700 m) long.

Warren explains that in the beginning of a dam, beavers lay the sticks and brushes longitudinally. Only after a dam is completed may they put sticks on it transversely. In this dam most sticks appear to be positioned longitudinally.

This dam is in Black Hill Regional Park in Germantown, Maryland, in an area where beavers have been active for several years. I will be posting more beaver-related pictures in the future.

16 February 2006

Today's good word: meander

mndr2

Meanders are semicircular bends in stream channels. The meander in this picture is in a creek near my house.

The most famous meandering river in history was the Meander River in western Turkey, now known by its Turkish name as the Büyük Menderes (Big Meander). The word meander derives via Greek from the name of this river in the antiquity, Maiandros. Maiandros is neither Turkish nor Greek; it appears to be a very old Anatolian word with an obscure meaning.

To the north of the Büyük Menderes is the Küçük Menderes (Little Meander), the ancient Cayster (Caystros).

The next posts in this series will be about the colorful (mostly, turbid brown, actually) histories of the Meander and the Cayster rivers.

15 February 2006

A twisted snail


Recently I had a post on Subulina octona, a land snail introduced to Florida. This is another photo of the same individual caught during an act of contortion with its body turned around almost 180° relative to the opening of the shell.

Snails can do that without any trouble because their bodies are attached to their shells by only one muscle, the columellar, that twists around the axis of coiling, the columella. The lower portion of a snail's body, including its foot, is not attached to its shell. If that weren't the case, I don't think a snail would be able to go in and out of its shell so easily and quickly.

14 February 2006

High above the Aegean

mycale

In a previous post I had a picture of the delta of the river Büyük Menderes, the ancient Meander River, taken from Mount Mycale on Dilek Peninsula in western Turkey. In response to a reader's inquiry, I am posting more pictures of the area.

Mount Mycale (Dilek Tepe) is the highest peak on Dilek Peninsula reaching about 1230 m. We climbed it on 1 July 2004 during our land snail survey of the peninsula. Four of us (Francisco Welter-Schultes, Tim Pearce, Zeki Yildirim and I) started the climb together, but along the way we got separated; it's not a safe practice, but it happens with us frequently when people start making unscheduled stops to look for snails.

Towards the end of the climb I was with Francisco when we reached a relatively flat area and stopped to collect snails. I looked under some rocks and found one species we were looking for: Gallandina annularis. I yelled at Francisco to let him know, but he didn’t respond. Then I realized that he had left and that I had been all alone. I was just a few meters from a deep chasm separating me from 2 almost vertical cliffs. I remember having a peculiar sensation not only from being alone in an unfamiliar wild place right at the edge of a cliff (I have a fear of heights, actually), but also from viewing such an awesome sight and realizing that I would probably never see it again. That's when I took out my camera and snapped the picture above.

D45

After I grabbed my bag and started off for the peak, I saw Francisco and Tim way ahead of me. If you look carefully you may notice them (arrows) in the picture above. Soon we all got together again, including Zeki, who was the slowest among us because of a knee surgery he had had a few months earlier. The peak of Mycale was about 60 m above us. We had done enough collecting and the sun was setting, so we decided to descend rather than climb further up. We were at 1170 m when I took this picture of Francisco with the delta of the river Büyük Menderes below him.

FWSD45>

Gallandina annularis, in the family Vitrinidae, is limited in its distribution to such high altitudes. Most members of the Vitrinidae are known as semislugs, because they have a reduced shell into which they cannot withdraw completely (G. annularis can, however, withdraw completely into its shell). The vitrinids are closely related to some full slug families, including the Limacidae. The interactions of semislugs with slugs provide important clues to the evolutionary mechanisms responsible for the origin of slugs from snails. As I already mentioned in another post, Berhard Hausdorf1 has proposed that the European vitrinids are limited to cold mountain habitats, because they are displaced from lower and warmer habitats by the more successful slugs, their distant relatives.

gannularis
Shells of Gallandina annularis. The ruler is in millimeters.


1. 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.

13 February 2006

Snow crystal photography


Following Saturday nite's heavy snow fall, Sunday morning offered plenty of opportunities to photograph the usual snowy day subjects, including neighbor's dogs in the snow, snow covered trees and my wife shoveling the driveway. (My excuse was: "But honey I am taking pictures and you look so cute with the shovel in your hand".)

Then I tried something that I had tried once before a long time ago and failed: taking pictures of snow crystals.

I quickly learned that the crystals, being transparent and colorless, are best spotted along the upper edge of a mound of snow and against a dark background. It would be pretty difficult to see them by looking directly at the surface of the snow.


These 2 shots are the best ones out of several I took with my Olympus E-500 with a Zuiko 35 mm macro lens at or near its highest magnification of 1:1. The camera was handheld at 1/250 s (f10 and f13 at ISO 400); a tripod would have been too cumbersome. These crystals were about 2 mm across and quite fragile and ephemeral. As I was focusing on one crystal thru the viewfinder, I saw its top break and blow away before I could photograph it.

The best crystals are probably present while it's snowing. I suppose one could sit outdoors when it's snowing under a tent-like structure to keep the camera dry and bring snow covered objects under the tent for photography. However, under such conditions there may not be enough light for good photography. Next time it snows I will try again.

12 February 2006

Happy Birthday Charles!


Charles Darwin (12 February 1809-19 April 1882)

Next day I started for Cambridge to see Henslow, and thence to London to see Fitz-Roy1, and all was soon arranged. Afterwards, on becoming very intimate with Fitz-Roy, I heard that I had run a very narrow risk of being rejected, on account of the shape of my nose! He was an ardent disciple of Lavater, and was convinced that he could judge of a man's character by the outline of his features; and he doubted whether any one with my nose could possess sufficient energy and determination for the voyage. But I think he was afterwards well satisfied that my nose had spoken falsely.

Charles Darwin, Autobiography


1. Robert Fitz-Roy (or FitzRoy or Fitz Roy) was the captain of the Beagle, the ship on which Darwin sailed for 5 years (1831-1836).

10 February 2006

What are these butterflies doing?


Here is a series of pictures of a couple of butterflies from last August. I suspected this was some sort of mating related activity, but I wasn't sure what exactly was going on. I e-mailed the pictures to Torben Larsen (whose book on butterfly collecting I reviewed here) and asked for his help. Torben kindly provided his opinion.


He thought that the male, the one in the air, was attempting to mate with the female on the flower. The female, however, appears to have been reluctant. Torben indicated that the purpose of the raised abdomen of the female was to physically prevent the male from mating if it succeeded in landing next to the female.


I also wasn't sure what the species was. I have difficulty telling these sulphurs apart. My choices were either Colias philodice or C. eurytheme. Torben's pick was C. eurytheme.


It will be another couple of months before we start seeing butterflies here in Maryland (they are predicting snow for tomorrow). But Firefly Forest Blog tells us that down in Arizona Great Purple Hairstreak (Atlides halesus) is already out.

09 February 2006

Papers read this week

Musical accompaniment: Complete Works of Scott Joplin played by Richard Zimmerman.

This week I review 2 papers on fossil invertebrates.

Paul A. Selden, José A. Corronca, Mario A. Hünicken. 2005. The true identity of the supposed giant fossil spider Megarachne. Biology Letters 1:44-48.
In 1980, Argentine palaeontologist Mario Hünicken described Megarachne servinei, a Permo-Carboniferous1 fossil, as the largest spider that had ever lived. Its leg-span2 was estimated to be 50 cm. This paper, with Hünicken as a coauthor, revises the identity of this fossil as a “bizarre eurypterid”, a water scorpion (Eurypterida). The animal apparently lived in a lake environment.


With the disqualification of Megarachne, the largest spider title returns to the extant tarantula Theraposa leblondi, whose leg-span, according to the authors, is 30 cm. Water scorpions (along with giant earthworms) and the question of what evolutionary factors may limit the sizes of terrestrial invertebrates were the subjects of a previous post of mine.

1. I suppose this means it was from the boundary of the Permian and the Carboniferous, which would make it about 290 million years old. A geologic time scale is available here.
2. If my understanding is correct, there is apparently no standard way to measure spider leg-span; it can be measured from the tip of leg 1 to the tip of leg 4 diagonally or on the same side.


Di-Ying Huang, Jun-Yuan Chen, Jean Vannier, J. I. Saiz Salinas. 2004. Early Cambrian sipunculan worms from southwest China. Proceedings of the Royal Society: Biological Sciences 271:1671-1676.
Sipunculans (peanut worms) form a small phylum (Sipuncula) of non-segmented marine worms. According to this paper there are about 150 species of sipunculans, but according to the University of California Museum of Paleontology website, there are about 320 species.

This paper describes 3 fossil sipunculans of Lower Cambrian age (about 520 million years old). The fossils were identified as sipunculans based on their morphological similarities to extant sipunculans. But then, the authors say that the fossil forms have "striking similarities" to modern sipunculans, and conclude that “most typical features of extant sipunculans have undergone only limited changes since the Early Cambrian, thus indicating a possible evolutionary stasis over the past 520 Myr.” Isn't this a circular argument or am I missing something? The point is if there were Lower Cambrian sipunculans that were very different than extant species, would they be identified unequivocally as sipunculans?

08 February 2006

The matter of the 3 hydrogen bonds


Dotted lines show the 3 hydrogen bonds that form between the bases cytosine and guanine on adjacent strands of a DNA molecule. Copied from Lehninger, A. Biochemistry, Worth Publishers, 1975; original from Pauling, Linus and Robert B. Corey. 1956. Specific Hydrogen-Bond Formation Between Pyrimidines and Purines in Deoxyribonucleic Acids. Archives of Biochemistry and Biophysics 65:164-181.

A hydrogen atom attached to an oxygen or a nitrogen atom by an ordinary chemical bond (a covalent bond) can also form a second and much weaker bond with an oxygen or a nitrogen atom on a nearby molecule. Such bonds are known as hydrogen bonds. Hydrogen bonds are very common between biologically important molecules. They are the main bonds that hold the 2 complementary strands of a DNA molecule together; the bases adenine and thymine form 2 hydrogen bonds with each other and guanine forms 3 hydrogen bonds with cytosine.

However, if you look at the earliest papers of Francis Crick and James Watson, the duo who discovered the helical structure of DNA, you will notice that their figures show only 2 hydrogen bonds between guanine and cytosine.

GC2
This figure from Watson & Crick (1953)1 shows only 2 hydrogen bonds between guanine and cytosine. Missing is the 3rd hydrogen bond between the hydrogen of the -NH2 group of guanine on the left and the oxygen of cytosine on the right. [Red dotted lines mine.]

This omission by Crick and Watson was the subject of an essay in last week's Nature2. The author, Simon Wain-Hobson, points out that it was Linus Pauling who first determined that guanine and cytosine could definitely form 3 hydrogen bonds and that this was published by Pauling and Corey in 1956 (figure and citation above). Watson and Crick had apparently considered but rejected this 3rd hydrogen bond, because they had thought that the hydrogen of the -NH2 group of guanine and the oxygen of cytosine were not aligned properly and that a hydrogen bond between them would be very weak.

Coincidentally, just a couple of weeks ago I was looking thru the collection of Crick's correspondence at the National Library of Medicine when I came upon a letter from Pauling to Crick, dated 18 feb 1963.


Obviously, this was still an issue, at least in Pauling's mind, almost 10 years after Crick and Watson's first papers on the structure of the DNA and 6 years after Pauling and Corey's paper. Pauling was apparently hoping that Crick would include some sort of correction about the number of hydrogen bonds between guanine and cytosine in the published version of his Nobel lecture presented less than 2 months earlier. However, the printed version of Crick's lecture was not directly about the structure of the DNA molecule, but was about the genetic code and he did not mention hydrogen bonds at all.

Curiously, I could not find a response from Crick to Pauling when I searched Crick's correspondence archive between 1963 and 1966.

What makes hydrogen bonds biologically significant is that they are much weaker than ordinary chemical bonds that hold atoms together in molecules. And exactly because of the relative weaknesses of the hydrogen bonds between the base pairs along its 2 strands, a DNA molecule can come apart easily to be copied.

In a sense, then, life on earth exists and evolution has been possible because of those 3 hydrogen bonds between guanine and cytosine and the 2 between adenine and thymine.


Learn more about hydrogen bonds here and here (more advanced).


1. Watson & Crick 1953. Genetical implications of the structure of deoxyrbonucleic acid. Nature 171:964. pdf
2. Simon Wain-Hobson. The third bond. Nature 439:539 (2 February 2006).


07 February 2006

An alien in Florida: Subulina octona


Subulina octona is one of the land snail species that have been widely distributed as a result of human activities. I am not quite sure where the species originated. Pilsbry1 implied that the original range of S. octona was tropical America and indicated that it was introduced in Africa, Ceylon, East Indies and elsewhere. Schileyko gave the range of the genus as tropical Africa, Comora Islands, Central America and tropical South America.

Subulina octona is quite common in gardens, parks and alongside roads in Florida. I have found it in Pinellas County, north of Tampa and further south near Fort Myers. The snail pictured above was from the latter location. Elsewhere in the U.S., the species has been recorded from greenhouses. It has also been introduced to the Samoan Islands and was recently found in greenhouses in Prague, Czech Republic.



An empty shell of Subulina octona characterized by, in Pilsbry’s1 words, a "distinctly but not abruptly truncate columella [arrow]".



1. Pilsbry, H.A. 1946. Land Mollusca of North America (north of Mexico ). Vol. 2, part 1.
2. Schileyko, A.A. 1999. Treatise on Recent Terrestrial Pulmonate Molluscs. Part 4. Ruthenica, Supplement 2.

04 February 2006

Papers read this week

Musical accompaniment: Ravi Shankar & Philip Glass: Passages.

Note: To see the Turkish characters properly please set the encoding of your browser to UTF-8. (Instructions are here.)

UĞUR KAYA, İ. ETHEM ÇEVİK, UĞUR C. ERİŞMİŞ. 2005. Population status of the Taurus Frog, Rana holtzi Werner (1898), in its terra typica: is there a decline? Turkish Journal of Zoology 29:317-319. pdf
The Taurus frog (Rana holtzi) , included in the IUCN Red List of Threatened Species, is known from only one location, Maden Lake in the Taurus Mountains, Turkey. The authors did a mark-recapture study of the frogs in 2003 and estimated the population size of the Taurus frog in Maden Lake as 725 to 1432. The species is believed to have been more abundant in the 1960s, although no quantitative data are available from that period. The authors speculate that the introduction of the common carp (Cyprinus carpio) may have been responsible for the population decline of the frogs.

JORDI FIGUEROLA, ANDY J. GREEN and LUIS SANTAMARÍA. 2003. Passive internal transport of aquatic organisms by waterfowl in Doñana, south-west Spain Global Ecology & Biogeography 12:427–436. pdf
Transport of invertebrates, especially snails, by birds has become a recurring theme on this blog (previous posts on this subject are here, here and here). In this paper, the authors recovered intact plant seeds and aquatic invertebrate eggs from 386 faecal samples of 11 species of migratory waterfowl in southwest Spain. Seeds were of at least 7 genera of plants and invertebrate eggs were of crustaceans, bryozoans and Corixidae (aquatic bugs, Heteroptera). The authors conclude that "waterfowl play an important role in the dispersal of organisms in aquatic environments by internal transport." I have one serious objection to the interpretation of their results: they did not check to see if the recovered seeds and eggs were viable! Their conclusion is weakened by their own disclaimer: "We provide data on the presence of apparently viable propagules in the droppings rather than the results of germination assays, thus our data overestimate true viability."

02 February 2006

Happy Marmota monax Day!

groundhog

It’s sunny here where I am in Maryland. So if the groundhog (there is only one?) comes out today, it will most likely see its shadow.

More info on groundhogs:

Woodchuck

Mammalian Species #591


01 February 2006

What the devil is a msat?

My mother was visiting us (she left today). She likes to do word-search puzzles. At her age, late 70s, such activities help keep her mind as sharp as possible. The other day I was flipping thru one of her puzzle books when a sequence of letters she had circled attracted my attention: LIVE DNA IN A MSAT. Live DNA? Msat? "Mom is onto something" I said to myself.

Then, it dawned on me that it was meant to be read backwards: TASMANIAN DEVIL.

I got curious and did a Google search for "live dna" and got almost 2500 hits, but most of which appeared irrelevant. The very first hit was a news item from Cleveland: "Coroner's office seeking live DNA". Of course, a DNA molecule is not alive, so there is no such thing as "live DNA". If I am understanding it correctly, what they mean is DNA from living people.


Note added 2 February: Speaking of the devil, today's Nature reports that progress is being made to control a deadly facial cancer that has been decimating Tasmanian devils (Sarcophilus harrisii).