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.
For today’s post we return to the New York City Subway 8th Avenue local (B and C trains) station at 81st-Museum of Natural History,this time for the amphibians.
81st St.-Museum of Natural History station, New York subway, July 17, 2019.
My favorite of the amphibians is this brooding caecilian, curled round its eggs. These legless, short-tailed amphibians are found only in the tropics, and there is no real English vernacular name for them. (You can find a Sicilian in the subway, but I prefer Neapolitan.)
Brooding caecilian. 81st St.-Museum of Natural History station, New York subway, July 17, 2019.
What appears to me to be a reed frog (Hyperolius sp.), an African tree frog of sorts, hangs on the wall next to a station identifying sign.
Reed frog. 81st St.-Museum of Natural History station, New York subway, July 17, 2019.
This looks like a ranid frog to me– a member of the family Ranidae, perhaps intended to be a Rana proper. Many species in this and related genera look much alike the world over. Note the nicely delineated tympanic membrane.
Frog. 81st St.-Museum of Natural History station, New York subway, July 17, 2019.
This generic frog (I won’t even try to name a family for it) is leaping out of the Signal Room. Interestingly, the subway workers here believe in free will, apparently of the libertarian sort. A scratched note on the door reads, “Use other door→ | or this one– up to you”.
Frog. 81st St.-Museum of Natural History station, New York subway, July 17, 2019.
These well-rendered salamanders provide detail enabling specific identification. On the left we have a Marbled Salamander (Ambystoma opacum), a species of eastern North America (including the New York area), and on the right we have a Fire Salamander (Salamandra salamandra), a species widely distributed in Europe. The American Tiger Salamander (Ambystoma tigrinum; found in the New York area) is also black with yellow markings, but the yellow markings (quite variable in both species) look more like Salamandra to me, and the evident parotoid glands at the back of the head (making it look wide) are conclusive. Ambystoma and Salamandra are similar in size and body shape, and are sort of continental ecological analogues.
Salamanders. 81st St.-Museum of Natural History station, New York subway, July 17, 2019.
The Coelacanth (Latimeria chalumnae) is one of the few surviving lobe-finned fishes, and as such is one of the tetrapods closest living relatives, and so is included here as an honorary amphibian. I don’t know why there is a question mark on its tail; in fact I never noticed it there before till just now.
Coelacanth. 81st St.-Museum of Natural History station, New York subway, July 17, 2019.
Finally, we have a group of patently Paleozoic fish. The artist has rendered them neither strictly from above (as though we were looking down on them in the ‘water’ of the paving tile) nor from the side, but in a sort of twisted view, allowing us to see various aspects. The bottom four may be intended to be the same type of fish (I’m not sure what kind), but the top one (which seems to be more of an exclusively side view– see the partly opened mouth) looks like one of those strange Paleozoic sharks, with a spiny first dorsal fin, and a heterocercal tail. You can also see more clearly in this photo how the lighter brown granite-like stone is integrated with the darker paving tile.
Fish on the floor. 81st St.-Museum of Natural History station, New York subway, July 17, 2019.
There are other taxa represented in the tiles (e.g., ants), and other forms of art, including larger tiled murals, and casts of in-situ fossils projecting from the wall. Many of these works are depicted in a gallery at www.nycsubway.org, a subway fan/history site. Some of those depicted I’ve never seen in person, because I always exit the station at the south (Museum) end, not at the north (81st Street) end.
(Looking at one of the pictures in the gallery now, I see the undersea mosaic mural has a coelacanth-shaped gray silhouette in the otherwise colorful tiles; could the question mark noted above be related to the coealcanth’s absence here?)
Big Mouth Billy Bass is an adult toy consisting of a plastic bass that sings music and moves its head and fins (see here for an early example).
This videomaker apparently connected Billy Bass up to an Alexa and managed to synchronize its mouth and head with the words. Ergo, you can ask Billy anything.
I have a bad feeling about running out of photos, so now is the time to send them in!
Today we have the second part of Mark Sturtevant’s February 4 post on a spider that lives on water lilies and eats fish. Have a look at the earlier post first, then this one. Mark’s notes are indented, and you can enlarge the photos by clicking on them.
I had recently introduced the six-spotted fishing spider (Dolomedes triton). This species is widespread, and can be found on floating vegetation on lakes and ponds or on river areas with minimal current. From there they will hunt a variety of prey, including small fish. This will be a special post since it is that latter talent that you will see today.
I had brought home a fishing spider, and she was kept for a time in a glass-bottomed aquarium with water and some lily pads. Here she is again. For scale, her leg span was a bit over 2 inches. They do get larger.
The aquarium was put in my backyard for a time, and I could park myself underneath it to photograph activities from below. One tries not to imagine what the neighbors were thinking. Minnows (fishing spider food) were introduced, and I really had no idea if she would even go hunting for one. But from time to time she would extend her legs out onto the water. As I understand it, this is how they monitor for moving prey below, so that was encouraging.
By the way, all of these pictures from the underside were extensively processed since I had put a screen cover over the aquarium to keep her inside while I was directly below. The screen was plainly visible in the pictures, though, so it had to be digitally removed. That was a lot of work!
Anyway, it took a little while, but then something started to happen. At this point I was freaking out!
The actual attack was very fast, and these are among the few pictures that I have of it. What I saw was that the spider strode out onto the water, and suddenly “clawed down” to gather up the fish before retreating quickly back to the lily pad.
The shadow tells the tale.
Here she is again up top. The photographs were taken through glass which was by now rather steamy with the summer heat, and so the pictures required some de-hazing treatments in post-processing to rescue them.
She was deftly turning her prey over and over with her chelicerae and pedipalps, working in the venom. In just a few minutes the tissue dissolving effect of spider venom was very obvious.
Fishing spider hunting has been captured in video. Here are two examples. They really seem to go after fish! [JAC: don’t miss these videos!]
Stephen Barnard from Idaho is back with some lovely photos—and two videos as lagniappe. His captions and IDs are indented.
The first four are mallards (Anas platyrhynchos) in flight. Migratory mallards are pouring in from Canada and parts north. There will soon be thousands. Duck hunting season, popular here, starts October 19. You’ll be happy to know I don’t hunt ducks or allow it on my property. [JAC: Yes, I am delighted at this!]
Next is a photo of Hitch (Canis familiaris), two more mallards, two Canada geese (Branta canadensis), and a moose (Alces alces). It’s not much as a photo, but funny.
This bald eagle (Haliaeetus leucocephalus) sometimes perches in this tall blue spruce (Picea pungens) in my back yard, scanning the creek for fish. This is probably Lucy.
Rainbow trout spawn in the spring, and brown trout (Salmo trutta) spawn in the fall, which is convenient when they coexist because they use the same spawning beds, called redds. These brown trout are on a particularly nice redd, which is also what anglers call a “prime lie” — a favored spot for fish to feed and rest. They compete with each other, and drive away the rainbows that threaten to eat their eggs. The bird calling in the background is a marsh wren (Cistothorus palustris).
Thanks to the several readers who responded to my plea for wildlife photos. I now have at least a week’s worth.
One of the kind respondents was Stephen Barnard, who hasn’t been here for a while. He sent a batch of lovely photos, and I’ve indented his notes below.
A few “wildlife” photos for you (except for the last).
The wildlife on Loving Creek is micro-seasonal through the summer. Species come and species go, on a weekly or even daily schedule/
The first three photos are, obviously, hummingbirds. I get two species: Black-chinned (Archilochus alexandri) and Rufous (Selasphorus rufus). Both are migrating through and not breeding. The Black-chinned arrive first, but the Rufous come soon after, and fireworks ensue. The Black-chinned are pugnacious and defensive of their territory, but the Rufous eventually overwhelm them with numbers. The first two photos show each in a defensive posture, and the third shows the Black-chinned’s purple gorget. Sadly, they’re all gone now.
The next two photos are action macros. The flower in the first photo is Cleome serrulata, commonly known as Rocky Mountain beeplant/beeweed, stinking clover, bee spider-flower, skunk weed, Navajo spinach, and guano. “Navajo spinach” is problematical, so please don’t tip Titania off. Sadly, all the flowers and bees are gone now.
Next three are trout-themed photos. Loving Creek gets several different mayfly “hatches”. The Tricos are the most impressive in numbers and biomass. Sadly, they’re over. Happily, the Callibaetis are thriving. The first photo is a Callibaetis “dun” — a recently emerged mayfly, drifting on the surface drying its wings, vulnerable to a trout, or even a swallow. The third photo is a rainbow trout (Oncorhynchus mykiss) consuming a Callibaetis “spinner” — a spent fly that’s fallen dead in the water.
Finally, not wildlife, but some cows. I’m trying to rejuvenate the soil with a varied cover crop and grazing.
I’m happy to report that Stephen Barnard is back with a spate of pictures—of fishing. Stephen’s notes are indented:
During the seemingly endless pandemic I’ve been doing little more than fly fishing and farm chores, and photographing fish. All these are rainbow trout (Oncorhynchus mykiss). The exceptions are mayflies: a Callibaetis dun and a comparision of an artificial fly and a natural Trico spinner. Anglers refer to newly emerged adult mayflies as a “duns”, and to the spent insects that fall into the water after mating and egg-laying as “spinners”. One photo is of a oddly colored trout that I’ve been seeing for at least three years, and that I’ve caught three times. I used to think it had an abnormally dark head, but after bringing it to hand I realized it had an abnormally light body, but only on one side.
JAC: A very realistic fly!
When I pointed out that I liked the second photo best, with the fish’s head above the water, Stephen replied:
That’s what they do when they take tricos on the surface. There are so many mayflies that they kind of sweep their heads around to take as many insects as possible. Here’s another photo of a fish eating a callibaetis dun.
Here’s an amazing paper—though the striking part isn’t sufficiently emphasized—reporting artificial hybridization between two long-diverged species, and the resulting appearance of viable hybrids despite what must be substantial genetic divergence between the components of a hybrid genome.
Here are the two species involved, the Russian sturgeon (Acipenser gueldenstaedtii), a source of meat and caviar, and a member of the fish family Acipenseridae.
From Wikipedia
The other species is the American paddlefish (Polyodon spathula), a member of the fish family Polyodontidae, and the only living species in that genus (the Chinese paddlefish, Psephurus gladius, which is in a different genus, has been pronounced extinct). Note the different morphology: the “paddle” on the fish below, which it uses for filter feeding (the Russian sturgeon is a predator on crustaceans, molluscs, and smaller fish), and the lack of bumpy protuberances on the paddlefish’s back. The fin shapes and placement also differ. These species are strikingly divergent in morphology, behavior, and, of course, in time.
How long since these two species had a common ancestor? If you go to the great site Timetree, which gives divergence times of many species calculated from the literature (you can enter any pair and will usually get an answer), you find a median divergence time of 136 million years and an estimated time of about 158 million years. That is a very long time! (The paper below, using older data, says the divergence time is longer: about 184 million years.)
For comparison, the divergence between our species and the Virginia opossum occurred about 160 million years ago, so the sturgeon/paddlefish hybrids are equivalent, with respect to divergence time, to getting a viable hybrid between a human and a possum!
The hybridization is reported in the new paper below from the journal Genes (click on screenshot to go to paper and get the pdf; reference at bottom).
The results can be stated briefly. During an experiment designed to get Russian sturgeon offspring without a father’s genes (“gynogenesis”), the researchers did a control cross between female Russian sturgeon and male American paddlefish (sturgeon eggs were put in a solution of diluted paddlefish sperm). There were five such crosses. They showed a hatching rate of 78-85%, and a survival rate of hybrids at 6 months from 49-68%—comparable to survival in artificial fertilization experiments in pure species.
One complication: Russian sturgeon are “polyploid”, that is, their ancestors underwent a complete duplication of their genomes, so they have four copies of each chromosome (i.e., they are “tetraploid”). Most modern fish are polyploid in this way. Paddlefish, however, diverged so long ago that they are “diploid,” that is, like most modern vertebrate species, they have only two copies of each chromosome.
Because of this difference, two kinds of hybrids were produced. “SH hybrids” were “triploids”, with three sets of each chromosome: two from the sturgeon egg and one from the paddlefish egg (total chromosomes around 165). They also obtained “pentaploid” hybrids, called LH, apparently resulting from the fusion of a sturgeon egg that had a full set of maternal chromosomes plus one set of paddlefish chromosomes (total chromosomes around 300).
You can see the two types of hybrids below. (a) is the Russian sturgeon, and (the caption is wonky), the rest of the pictures show hybrids, without a picture of the paddlefish itself). (c) is the LH hybrid with a full sturgeon genome (four copies of each chromosome) and half a paddlefish genome. That’s why it looks mostly sturgeon-y, with a bit of a paddle in front.
(d) is the “LH” triploid hybrid, which has half a sturgeon genome less than (b). That’s why it looks more paddlefish-y.
I’m assuming that these pictures are labeled correctly in the paper; but it could be that (b), unlabeled in the graph, is an SH hybrid, (c) the LH hybrid (it has a longer “paddle”), and (d) the pure paddlefish. If there’s a labeling error, it should be fixed.
Regardless, the surprising thing is that viable and apparently vigorous hybrids were produced. Were they fertile? No data on that are reported, but, given the difference in ploidy level between the parents, I doubt it: the different numbers of chromosomes from each species would play hob with meiosis—the chromosome-pairing process that is required for the formation of sperm and eggs.
But still, despite about 150 million years apart, the genomes can still work together to produce a viable and functional individual. That is simply amazing; like I said, it’s sort of like getting a viable offspring between a human and a possum. (What a monstrosity that would be: a furry anthropoid with huge teeth and a prehensile tail!)
But why could such long-diverged species still have their genes function fairly harmoniously in a single individual? Well, we don’t know, but there are several possibilities.
1.)While the two species could be long diverged, the function of the diverged genes hasn’t changed much, so they don’t screw up development. In other words, adaptive evolution in these species has been slow since they shared their common ancestor. (This isn’t true for non-coding bits of the genome, for that’s the way they estimated the great divergence time of the species.) I’m not that keen to embrace this possibility since the fish are so different in appearance and behavior, and in ways that seem adaptive.
2.) The species have an “open” developmental system that will tolerate errors or disharmonies more readily, compensating for them by producing a functional individual. This used to be the explanation for why animals like frogs could produce viable hybrids between long-diverged species, while mammals couldn’t. But saying the developmental system is “open” is just another way of saying that “long-diverged genes still function together”, and is thus a bit tautological. To really test whether the individual species are more tolerant of screwups, one could, I suppose, look at the effects of mutations in these species that usually wreck development in fish. If sturgeon and/or paddlefish are less disrupted by such mutations than are other fish, one might have something to go on.
3.) The polyploidy of the sturgeon genome somehow buffers development against screwup. That is, having two or four copies of the sturgeon genome in hybrids can somehow override the detrimental effects of genome incompatibility. I’m not sure exactly how this would work, but perhaps it would be through a “dosage” effect: if you have a full dose (at least two copies) of one species’ genes, you can override any effects of other-species’ genes that act to “poison” development.
Well, we don’t know the answer. What is remarkable is the resilience of the genome, and the development it induces, in the face of ancient divergence. Remember, this is about 22 times the temporal divergence between humans and chimpanzees, and we cannot produce hybrids with chimps (it’s been tried; see Why Evolution is True).
