Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
We’ve had occasion previously to note some dastardly beings that eat lizards, and express dismay at their foul deeds. And now, thanks to Matthew, we have another opportunity to engage in a two minutes hate towards a transgressor.
Wasp spider (Argiope bruennichi) with common lizard (Lacerta vivipara) in (probably) Cheshire, UK, from Phil @Goldenorfephoto.
That’s a wasp spider (Argiope bruennichi), a recent invader of Great Britain from the Continent. The picture was tweeted by Phil @goldenorfephoto. Phil is based in Cheshire, which is up where the NE corner of Wales touches England. So if he took the photo locally, then the spider is expanding its range rapidly (or, as Matthew put it to me when pointing this out, “pdq”), as can be seen from the map below, where it’s still quite a ways from Cheshire.
Distribution of Argiope bruennichi in the UK (from britishspiders.org.uk).
The tragic victim is a common lizard, Lacerta vivipara, one of the two three species of lizard native to Britain (the others being the much rarer sand lizard, Lacerta agilis, and the legless slow worm, Anguis fragilis; lizard count updated thanks to comment below by reader Dave). You can see some less traumatic photos of them here.
The picture reminded me very much of the large American orb weaving spider Nephila clavipes, which I have encountered in the West Indies and Central America, and which also eats lizards. The Nephila I’ve seen in the tropics are more yellow, rather than the orangey Florida ones pictured at the link above. Nephila and Argiope are both orb weavers (I didn’t realize they had big ones in England), and are sometimes placed in the same family.
[JAC: There was some discussion this morning about why so many mammals have light bellies. Greg answered in the comments, but I’d also direct you to this article on countershading (yes, it’s from Wikipedia, but it’s the best I could find). Greg happens to be our resident expert on animal coloration, and decided to add a short post based on a picture he saw in the local paper.]
by Greg Mayer
As the picture below shows, countershading doesn’t always work– sometimes the hawk does spot the chipmunk.
Immature Cooper’s Hawk with chipmunk in Racine, Wisconsin (photo by Diana Hawes, from Journal Times).
I saw this just today in my local paper. As was discussed in the comments on the latest set of readers’ wildlife photos, chipmunks being dark above and light below gives them a “flattened” aspect and makes them harder to see, but no protective coloration is perfect. There have been years when hawks nested in trees on my block quite close to my house, and mangled chipmunk remains would appear frequently below the nest. This year, I haven’t seen any hawks near the house, and chipmunks seem more common than usual.
JAC: My post on the tuatara parietal eye was short and, for some readers, not informative enough. Where did it come from? What does it look like? (By mistake I published a picture of an iguana and not a tuatara.) Greg answers some of the many questions that have surely been tormenting many of you about this bizarre feature.
by Greg Mayer
The tuatara has long been of interest to us here at WEIT, and just the other day Jerry posted a video of one hatching, along with many interesting notes on their biology, especially on the parietal or ‘third’ eye. Jerry included a picture of the parietal which, as Jon Losos, among others, noted, was not, alas (as a simple google image search indicated), that of a tuatara, but rather that of what looks to me to be a common or green iguana (Iguana iguana— which, if you learn no others, is the one scientific name you should commit to memory). Jon remarked to Jerry that good pictures of a tuatara’s parietal would be hard to find. Well, here’s the best I could find.
The parietal eye of the tuatara (Plate 20 from Dendy, 1911).
This is Plate 20 from Arthur Dendy’s classic 1911 monograph describing the pineal organs (including the parietal eye) of the tuatara. The upper figure is a longitudinal section of the parietal eye, and the lens, retina, and pineal nerve (equivalent to the optic nerve) are readily apparent. The two lower figures provide details of the retina.
Dendy studied both adults and embryos; the above figures are of adults. Dendy, an Englishman, resided in a number of the antipodal parts of the British Empire, and in his monograph records his good fortune in not losing some of his histological sections of tuatara embryos, “… for they were, with most of my Australasian collections, shipwrecked in transmission from New Zealand to South Africa. The boxes containing the sections were, however, salved, and reached me after being soaked for weeks in salt water.”
The following figure, from Angus Bellairs’ still useful Life of Reptiles, is based on Dendy’s top figure, and labels some of the parts for clear identification.
The parietal eye of the tuatara (Figure 114 from Bellairs, 1970).
Neither of these pictures, of course, shows the parietal from the outside. I’ve read that the parietal is not externally visible in adult tuatara, but I’ve never checked on the preserved tuatara I’ve seen; Jon has seen tuatara live and up close– perhaps he will stop by again here at WEIT and let us know if he has noticed the eye on the ones he’s seen and held.
The parietal eye is also found in many lizards (which, together with snakes, are the tuatara’s closest living relatives, so the sharing of this features is not anomalous.) In vertebrates, there can be a number of evaginations (together known as the pineal complex) from the region of the brain called the epithalamus. One of these forms the pineal gland or organ, while another forms the parietal organ. Both can be photoreceptive. In lizards and tuatara, the parietal organ can have a lens and a retina, forming the parietal eye. The eye is overlain by a translucent scale, easily visible in many lizards. It cannot, as far as is known, form an image. In lampreys, both the the pineal and parietal can be eye-like, so that some authors refer to them having a pineal eye and a parietal eye (which is why the median eye of lizards and tuatara, though sometimes called the pineal eye, is better called the parietal eye). In lampreys the position of the median eyes is indicated by a whitish, unpigmented, oval on the otherwise dark skin of the middle of the head, In birds and mammals, the parietal organ is absent, and the pineal organ (now called the pineal gland) is buried deep in the head, and has endocrine functions.
The pineal complex was present in some of the earliest fishes, as indicated by the presence of a single median foramen [JAC: small opening in the bone] in the skull of ostracoderms, placoderms, and others. It is most eye-like in the parietal eye of lizards and tuatara, which suggests that a fully eye-like parietal or pineal was not present in early vertebrates, so that the parietal eye did not evolve from a “real” eye.
Bellairs, A. 1970. The Life of Reptiles. 2 vols. Universe Books, New York.
Dendy, A. 1911. On the structure, development and morphological interpretation of the pineal organs and adjacent parts of the brain in the tuatara (Sphenodon punctatus). Philosophical Transactions of the Royal Society of London 201:227-331, pls. 19-31. pdf (Dendy’s interpretations of homology are no longer all accepted, but the morphological and histological work remains fundamental.)
Well, it’s not that hard to spot, but you can see how the wood frog (Rana sylvatica) is aptly named.
Wood frog, near Lake Superior, Minnesota, 10 June 2014.
My Minnesota correspondent found this fellow along Caribou Trail (a road) and Jonvick Creek near Lutsen, Cook County, Minnesota, about a half mile from the north shore of Lake Superior, on 10 June 2014. The region is mixed spruce and maple forest; the frog was in a “mapley” area. The great herpetologist Robert C. Stebbins thought the species’ distribution tracked, for much of its range, pretty closely to the distribution of spruce.
The distribution of wood frogs is interesting for at least two reasons. First, they are the most northerly distributed of any North American amphibian (or reptile, for that matter), and extremes are always interesting. They can survive for weeks at temperatures below freezing, in part through elevated levels of blood glucose acting as an “anti-freeze”.
Range of the wood frog (Rana sylvatica), from USGS via Wikipedia.
They’re not immune to freezing though—I once found, during an early spring field trip near Northampton, Massachusetts, a dead female who had laid her eggs in a small pond. She was perfectly intact, and I suspected she had frozen, as contact with ice crystals (from the pond) makes them more vulnerable to freezing.
Second, there are a number of outlying populations to the south of the main range (which, as shown above, crosses northern North America from the Bering Strait to the North Atlantic, descending into eastern North America along the Appalachians). In particular, note the outliers in Colorado and Wyoming. These are almost certainly relicts from cooler glacial times when the frog occurred further south in the Rockies; it moved northward as the glaciers retreated, leaving behind populations in some favorable southern localities. The isolated Colorado-Wyoming population was named as a distinct species (maslini), but currently it is not recognized, not even as a subspecies.
Wood frogs are are also famous for another “non-subspecies”: cantabrigensis, a short-legged form from the northwestern part of the range, versus the longer legged ones to the east. While the variation in leg size is real, there is a gradual cross-continental gradient (a cline, in technical terminology), with no break in leg size, and most systematists do not distinguish such clinal patterns of geographic variation with nomenclatural recognition. So cantabrigensis is not recognized either, and the wood frog has become a classic case of clinal variation.
Bagdonas, K.R. and D. Pettus. 1976. Genetic compatibility in wood frogs (Amphibia, Anura, Ranidae). Journal of Herpetology 10:105-112 (jstor)
Costanzo, J.P., M.C.F. do Amaral, A.J. Rosendale and R.E. Lee. 2013. Hibernation physiology, freezing adaptation and extreme freeze tolerance in a northern population of the wood frog. Journal of Experimental Biology 216:3461-3473. (pdf)
Dodd, C.K. 2013. Frogs of the United States and Canada. Johns Hopkins University Press, Baltimore (publisher) (Google books)
Porter, K.R. 1969. Evolutionary status of the Rocky Mountain population of wood frogs. Evolution 23:163-170. (jstor)
Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians. 3rd ed. Houghton Mifflin, Boston. (publisher)
In a serendipitous coincidence for Chicago hockey fans, my Florida correspondent has sent me today this photo of a defiant young hawk.
Defiant baby hawk, Fort Myers, Fla., May 2014.
Like its Chicago confreres, it refuses to go down without a fight. The hawk is in the correspondent’s front yard; she thinks “the wind wrecked the nest. There is a second baby up in the tree. ”
I don’t know what species it is; perhaps readers can provide an ID.
I love “Meerschweinchen” (“little ocean pig”) as the name for guinea pig. Where did that come from? And “Lazy animal” for “sloth” is great.
Which reminds me of a story: A city girl was visiting a farm for the first time, and, given a tour, saw a group of pigs around their trough, noisily slurping their slop. “Ewww!”, she said. “No wonder they call them pigs!”
Islands that have never been connected to a continent, often called oceanic islands, must receive their flora and fauna over water, by what Darwin termed “occasional means of transport”. Such means include floating (e.g. coconuts), wind (e.g. spiders), rafting (e.g. iguanas), ice floes (e.g. arctic foxes), and, of course, flying (e.g. birds and bats). Because the ability to disperse is rather unevenly distributed across a continental fauna, the animals of oceanic islands are usually a rather distinctive subset of what is found on the nearest continents. Insular faunas have bats and birds, often lizards and snakes, occasionally mice and rats, but only very rarely amphibians or larger terrestrial mammals.
Another feature of insular faunas is that they are rich in endemics (forms peculiar to the island), because of the rarity of gene flow from the mainland. Unfortunately, these endemic forms, having evolved in isolation with an unusual fauna around them (lacking in predators, for example), often succumb to the environmental changes wrought by man when their islands are discovered and colonized. There have been some cases where island species thought extinct have been rediscovered alive, most famously perhaps the case of the giant lacertid lizards of the Canary Islands. A case from the Revillagigedo Islands in the Mexican Pacific poses an interesting twist on the rediscovery story.
Clarion nightsnake (Hypsiglena ochrorhyncha unaocularus) on Clarion Island by Daniel Mulcahy.
In a paper in PlosOne, Daniel Mulcahy and colleagues from the Instituto de Ecología in Xalapa, Veracruz, México and the U.S. National Museum (including my old friend and mentor George Zug) report the rediscovery of an extant population of the Clarion Island nightsnake (Hypsiglena ochrorhyncha unaocularus). The only previous specimen known had been collected by the intrepid naturalist William Beebe in 1936, and had been scientifically described as an endemic form on the basis of this specimen by Wilmer Tanner in 1944.
What makes this case different from the more usual rediscovery is that in 1955, because no further specimens had been found, Bayard Brattstrom suggested that the original specimen had come from the Mexican mainland, and that the locality data on Beebe’s specimen was in error. Thus the Clarion nightsnake disappeared not into the roll of the extinct, but into the roll of the never existed! So, for nearly 80 years, until 2013, no one had found a Clarion nightsnake, and for most of that time no one thought there even was such a thing.
Mulcahy and colleagues did two things. First, rereading Beebe’s writings about his Clarion expedition, it was clear to them that Beebe had not made an error in labeling where his snake was from– he was very explicit about having found the snake on Clarion, and not the mainland. Second, in 2013 they went to Clarion, and armed with Beebe’s book, they quickly found the right place, and the snakes. They found eleven in all, collected five, and took blood samples and photos of the rest. Thus, knowing the right place and time of day to look, the species proves to be locally common.
Clarion Island, by Daniel Mulcahy.
Based on their morphological and DNA analyses, Mulcahy and colleagues have raised the Clarion snake from a subspecies to a species, but as we’ve discussed before on WEIT the ranking of divergent allopatric forms is a judgment call, and not really the take home message here. Rather it’s a genuine rediscovery (not a shift in taxonomic rank) of an island endemic, which is potentially threatened by several factors, including introduced animals. Mulcahy and colleagues make several recommendations to help insure the snake’s survival.
Beebe, C.W. 1938. Zaca Venture. Harcourt, Brace, New York.
Brattstrom, B.H. 1955. Notes on the herpetology of the Revillagigedo Islands, Mexico. American Midland Naturalist 54:219-229.
Mulcahy, D.G., J.E. Martínez-Gómez, G. Aguirre-León, J.A. Cervantes-Pasqualli, and G.R. Zug. 2014. Rediscovery of an endemic vertebrate from the remote Islas Revillagigedo in the eastern Pacific Ocean: the Clarión nightsnake lost and found. Plosone 9(5): e97682 (8 pp). pdf
Tanner, W.W. 1944. A taxonomic study of the genus Hypsiglena. Great Basin Naturalist 5: 25–92. pdf
