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.
Peter Klaver sent us something we don’t see here often: underwater photographs—and there are some videos as well. Peter’s captions and notes are indented.
Included below are 5 full sized scuba diving photos and 5 smaller preview pictures of movie clips. With each preview picture connected to a video, I’ve provided the url of the movie clip to link to on the Delft University server, where I put the website of the holiday Rachel Wilmoth and I had ( http://dutsm1219.tudelft.net/Africa2018/ ).
From Tofo and Vilanculos in Mozambique we did scuba diving and snorkeling and saw really beautiful underwater wildlife. I do pretty terrible in my knowledge of the Latin names of the animals; hopefully some readers can fill in the gaps and correct my mistakes.
You’ve surely heard of the bizarre anglerfish. There are actually many such species in the order Lophiiformes, but the most famous are the deep-sea species with fearsome teeth who attract their prey with a luminescent lure. (All anglerfish are carnivorous.) Here’s a picture of ten such species from Wikipedia:
Their huge mouths and distendable stomachs enable them to eat prey twice their size: a useful adaptation in the deep sea, where prey are few and far between. And the reproduction of some species, as shown in the stunning video below, is totally bizarre (see this Mental Floss piece for more information). Males are tiny, and weren’t even known to exist until many females had been caught, many afflicted with “parasites”. Scientists eventually realized that the parasites were actually males whose bodies had become permanently fused to the female. That’s a good mating strategy because finding a female in such sparse populations is a real problem. But it’s almost unique in animals.
When males are born, they have to find a female, and they do so by homing onto her using both her light and species-specific pheromones. Such males can’t feed, and don’t get mature gonads until they attach to a female. When a male does that, he secretes an enzyme that dissolves his head and the female’s body wall, allowing the pair to fuse right down to joining their blood vessels. The male remains attached to the female for life, and can spawn repeatedly until she dies (how the male releases sperm when the female produces eggs is something I haven’t yet found out). As I used to tell my students, to their great delight, “the male anglerfish is simply a parasitic sack of gonads—much like undergraduate men.”
A piece in Science by Katie Langin describes the filming of the first pair of mating anglerfish, made at 800 meters near the Azores by Kirsten and Joachim Jakobsen in a submersible (shown in the video below). They followed the 16-cm animal (about six inches long: the size of an American dollar bill) for 25 minutes, and later identified the species as Caulophryne jordani, or the “fanfin angler”, which has a worldwide distribution.
The short video below, put out by the AAAS, shows several interesting features:
The long whiskers of the females of this species, which likely act as feelers. These structures appear to glow like the bioluminiscent “lure,” but the researchers aren’t sure whether the glow of the whiskers is intrinsic or merely reflections from the submersible.
The male seems to move his body about independent of the female
The female uses little energy swimming, and appears to mostly drift around. That’s probably an energy-saving adaptation in a food-poor environment. After all, why swim when you have nowhere to go, and when your prey comes to you?
Have a gander of one of the world’s truly bizarre creatures, and one of the marvels of natural selection.
We have some New Zealand pictures from reader Michael Hannah, whose notes are indented. Hannah is an associate professor of paleontology and evolution at the School of Geography, Environment and Earth Sciences at Victoria University of Wellington.
Numbers 1 – 6 were all taken at Pukaha Mt Bruce sanctuary– I know you visited there on your NZ trip. Most animals were confined to cages so they were easier to photograph. Numbers 7 and 8 were taken at the NZ fur seal colony at Cape Palliser, on the southern coast of the Wairarapa – about 2 hours drive from Wellington. I’ve also thrown in a couple of photos from a fishing village that the road to Palliser passes through called Ngawi. There are no wharfs: boats are pulled in and out of the water by rusty old tractors – some of which are highly decorated!
2.) Kākā – Nestor meridionalis. This is the north island version of the infamous Kea; it’s not quite as brightly coloured.
3.) Korimako – New Zealand bellbird ( Anthornis melanura):
4.) Tui – (Prosthemadera novaeseelandiae) one of my favourite birds – noisy, aggressive – but with the most beautiful feathers. [JAC: note the white feathered “parson’s collar”.]
6.) Longfin Eel – (Anguilla dieffenbachia). Once a major food source for Māori, but now in decline. Theses had gathered to be hand-fed by visitors to the sanctuary.
7.) and 8.) Young Kekeno – New Zealand fur seals. It was a hot day and everyone was sleepy. Some just wanted to float, neatly folded in a convenient rock pool.
Here are the tractors used to drag the boats out of the water in Ngawi. Those crazy Kiwis! Wikipedia says this:
Ngawi has more bulldozers per capita than anywhere else. The bulldozers are used to haul fishing boats into and out of the water as there is no wharf or other access to the ocean other than the beach, which can be notoriously rough at times.
The location has a large population of fur seals, and is popular not just with commercial but recreational fishermen. The best fish to catch are Paua (a type of abalone which is prized for its iridescent shell as well as the flesh), crayfish (also known as rock lobster), and cod. The place is popular with all types of fishermen, including spearfishers.
Here’s a gorgeous photo of clownfish, which just won the photographer, Qin Ling of Canada, an award in the Behaviour category at the Underwater Photographer of the Year competition (click to enlarge) – you can see all the winners here.
Ling’s photo is entitled ‘Your home and my home’. Look closely at these Nemos. Look at their mouths. Those little eyes peeking out. They are not drawn on, as PCC(E) first suggested, nor are they Photoshopped. And they are not babies. They are isopods (like pillbugs or woodlice), which are parasitic. They eat the fish’s tongue, and then replace it, sitting in there, presumably getting first dibs on the food as it comes in. They occasionally turn up on people’s dinner plates when folk order fish and get a crustacean chaser.
The photography judge said: “Six eyes all in pin-sharp focus, looking into the lens of the author … this was one of my favourite shots of the entire competition.”
Isn’t nature wonderful?
*********
JAC: Let me add two references and two videos. You can read Carl Zimmer’s take on these parasites at National Geographic, or Wikipedia’s entry on Cymothoa exigua, the “tongue-eating louse,” which appears to be the only species that does this.
Here’s a video, which has only one photograph:
Here’s another video with photos; it claims that this is the only case in which one organism replaces another organism’s body part:
The Greenland shark (Somniosus microcephalus), a little known species, rivals the white shark in size. According to Wikipedia, individuals can be as long as 7.3 m (24 ft) and weigh more than 1,400 kg (3,100 lb). Here’s what they look like:
They are mostly fish-eaters, swim slowly for a shark, and live in the area below:
They have poisonous flesh, laced with neurotoxins that aren’t lethal to humans but can make sled dogs temporarily unable to stand. Although they’re carnivores, they haven’t been reported to attack humans. They do, however, eat large animals, though perhaps only after the animals are dead. As Wikipedia notes:
Greenland sharks are some of the slowest-swimming sharks, which attain a maximum swimming speed about half the maximum swimming speed of a typical seal. Therefore, biologists have wondered how the sharks are able to prey on the seals. Greenland sharks apparently search out seals and ambush them while they sleep. Greenland sharks have also been found with remains of polar bear, horses, moose,and reindeer (in one case an entire reindeer body) in their stomachs. The Greenland shark is also known to be a scavenger, but to what extent carrion (almost certainly the origin of the reindeer) figures into the slow-moving fish’s stomach contents is unknown. It is known that the species is attracted by the smell of rotting meat in the water.
The other day I saw some click-baitish post about this shark saying: “This shark eats polar bears!” They didn’t mention that the bears might already have been dead.
It’s been reported from mark-release-recapture studies that the sharks grow only about 1 cm per year (due, no doubt, to their cold habitat), so their large size suggested to some scientists that they might be very old. This suggestion was supported by a new paper in Science by Julius Nielsen et al. (reference below, access probably not free). Using a unique method of dating these sharks, they found that they could be up to 500 years old, attaining sexual maturity only after 150 years. That makes them the longest-lived vertebrate on record, far longer-lived than the previous recordholders, Aldabra tortoises and bowhead whales—a bit more than 200 years each. (See the bottom for the longest lived animals that we know about.)
The way that Nielsen et al. aged the sharks (they sampled 28 females between 2011 and 2013) was to use radiocarbon dating on the proteins in the eye nucleus, whose center forms when the shark is still a fetus. (Note: the sharks weren’t killed for this study: they were “by-catch”, accidentally caught in fishing nets.)
It turns out that nuclear bomb testing in the 1950s and 1960s created a spike in radioactive carbon (carbon 14) that was absorbed into the marine environment, and then into animal proteins, so you can see a spike in the amount of radioactive carbon occurring in specimens caught beginning around 1960 (figure from the paper):
(from paper): Fig. 1 Radiocarbon chronologies of the North Atlantic Ocean. Radiocarbon levels (pMC) of different origin (inorganic and dietary) over the past 150 years are shown. Open symbols (connected) reflect radiocarbon in marine carbonates (inorganic carbon source) of surface mixed and deeper waters. Solid symbols reflect radiocarbon in biogenic archives of dietary origin. The dashed vertical line indicates the bomb pulse onset in the marine food web in the early 1960s.
The authors found that the highest amounts of radioactive carbon were found in the eye nuclei of smallest sharks, which were presumably born about 50 years ago. They also did radiometric dating of the eye nuclei of the other sharks, which were born before the pulse and could be dated using conventional methods. Because once the eye nuclei are formed in utero the proteins (and the carbon they contain, derived from the environment at that time) do not change further, forming in effect, biological artifacts that can be dated just like ancient wooden artifacts.
The analysis was a bit more complicated than this, but you can read the paper and its references for details. The upshot is that there’s opportunity for error—not only in the radiocarbon dating itself, but in their use of Bayesian statistics, which requires prior assumptions about age and growth rate.
Given this, the authors are still confident that their estimates are pretty accurate within the error limits shown. The figures that everyone wants to know are in bold (my emphasis):
The model estimated asymptotical total length to be 546 ± 42 cm (mean ± SD), a size matching the largest records for Greenland sharks, and the age estimates (reported as midpoint and extent of the 95.4% probability range) of the two largest Greenland sharks to be 335 ± 75 years (no. 27, 493 cm) and 392 ± 120 years (no. 28, 502 cm). Moreover, because females are reported to reach sexual maturity at lengths >400 cm , the corresponding age would be at least 156 ± 22 years (no. 19, 392 cm) (table S2). Amodel was 109.6%, demonstrating that samples are in good internal agreement, implying that the age estimates are reliable.
The error limits put the upper age limit of the biggest shark as 512 years and the lower limit at 272 years, with the point estimate at 392 years. That means the shark was estimated to have been born in 1624, and could have been born as early as 1504 (that’s 60 years before Shakespeare was baptized).The Guardian says this about the point estimate of the oldest female:
She was born during the reign of James I, was a youngster when René Descartes set out his rules of thought and the great fire of London raged, saw out her adolescent years as George II ascended the throne, reached adulthood around the time that the American revolution kicked off, and lived through two world wars. Living to an estimated age of nearly 400 years, a female Greenland shark has set a new record for longevity, scientists have revealed. [JAC: This is a record for vertebrates only. Some animals can be way older, or, technically, even immortal, while plants can live thousands of years.]
Well, that’s one way of looking at it, and, if these dating estimates are accurate (see below), there are certainly older Greenland sharks out there.
Two questions arise:
1.) Are scientists on board with this estimate? Given the assumptions and errors, not everyone accepts these dates. The Guardian quotes a doubter:
But not everyone is convinced that Greenland sharks can live for four centuries. “I am convinced by the idea of there being long lifespans for these kinds of sharks, [but] I take the absolute numbers with a pinch of salt,” said Clive Trueman, associate professor in marine ecology at the University of Southampton.
Trueman agrees that it is possible to get a record of the early life of a vertebrate from eye lens proteins. However, the fact that the proteins in the centre of the eye lenses, and hence the carbon-14 within them, came from nutrients taken in by the shark’s mother adds a number of uncertainties to the calculations, he says.
Campana says while the approach taken by the researchers is sound, he remains unconvinced that Greenland sharks live for almost 400 years. But, he adds, “future research should be able to nail the age down with greater certainty.”
2.) Is this the longest lived animal? No, not by a long shot. Sponges and corals, which are animals, can live millennia, with some Antarctic sponges estimated at 10,000 years old. However, for animals we’re more familiar with, the record longevity known with reasonable certainty is held by a clam. As I mentioned in 2013, a specimen of the ocean quahog Arctica islandica—a clam nicknamed “Ming”—was snatched from the sea floor off Iceland and dated at 507 years old using growth rings. Pity that the heartless scientists killed it, for who knows how long it might have lived? Like the shark above, this is a cold-water organism. Cold environments can put physiological limits on growth rates by slowing down metabolism, and that might have something to do with extreme longevity. Who knows?
To close, here’s an email exchange I had with Matthew about this paper:
Matthew: And why don’t most vertebrates live for a long time anyway, Mr Professor?
Me: Antagonistic pleiotropy? How the hell do I know?
Matthew: He he. The more you know, the more you realise we know nothing about anything.
Me: Nothing about anything? Not how many hydrogen atoms in a normal water molecule? Not when we split off from the ancestors of chimps? Not how old the universe or the Earth are?
Matthew: You know what I mean. Don’t be a curmudgeon
My Okinawa correspondents spent Boxing Day at the Okinawa Churaumi Aquarium, and sent me a bunch of pictures. The aquarium is a sprawling complex on the coast in northwestern Okinawa, and includes large areas of gardens and park land, and a recreation of traditional Okinawan homes and buildings, as well as the aquarium proper.
Okinawa Churaumi Aquarium
It reminded me, as I’m sure it did many of you, of the Sausalito Cetacean Institute. That’s Ie Shima island in the background.
Okinawa Churaumi Aquarium
One of the main attractions at the Aquarium is the Kuroshio Sea Tank. It’s enormous.
Kuroshio Sea Tank
When my correspondents told me they were going to the Aquarium, they mentioned something about “whale sharks”, but I didn’t query them further. It turns out the Aquarium actually has whale sharks (Rhincodon typus), the world’s largest species of fish!
A whale shark
And not just one!
Two whale sharks
Although whale sharks are, for sharks, specialized feeders– they feed on plankton– they are “typical shark” shaped.
Sharks are cartilaginous fishes (Chondrichthyes), which are of two main types: the Holocephali, comprising the ratfishes and chimaeras (we’ve mentioned them here before at WEIT), and the Elasmobranchi, comprising sharks and rays. Most people have a good idea of what sharks and rays look like. Here are some more typical sharks (I don’t know what species– any shark people out there?) Note that the gill slits are on the side of the head; the fellow in the middle is male, as you can tell by the large claspers medial to the pelvic fins.
Typical sharks
And here’s a typical ray (again, no ID). Note the flattened shape, and the spiracles (whitish bits) behind the eyes– these are the vestigial first pair of gill slits. The flat body of the ray is mostly the greatly enlarged pectoral fins.
A ray
Most people also know the manta ray (Manta birostris). It’s a little unusual for a ray, being pelagic and filter feeding, so the mouth is at the front tip of the body– and, it’s got those crazy cephalic fins or “horns”, from whence it gets the alternative vernacular name “devil fish”. Do note that the gills are on the bottom of the head.
A manta ray
There is more diversity among sharks and rays than most people realize. Sawfish, which look a lot like sharks with a saw strapped to their snout, are actually rays, but shouldn’t be confused with the similar looking saw shark, which is a shark. There are also angel sharks, which look a lot like rays, and guitarfish, which are rays that look a lot like sharks– in fact, more shark-looking than angel sharks.
I’ve never seen either angel sharks or guitarfish in any aquarium, and thus was delighted to find that Okinawa Churaumi has guitarfish (which, remember, are rays). Here’s a guitarfish surrounded by three sharks, with a typical ray off to the right (and a shadowy form below and to the right). If you look carefully, you can see the spiracle (again, whitish looking) on top of the head, behind the eye.
A guitarfish with three sharks (one only a tail), a typical ray, and a shadowy form below and to the right.
In the following picture, we get a really good view of why it’s a ray. Note that the gill slits are on the bottom of the head, as is the mouth (the latter is typical, but not diagnostic, of rays). And, the pectoral fin is joined seamlessly to the head– at a point above, in fact, of the gill slits (which is why the slits are on the bottom of the head). The spiracle, already spatially distant from the other gill slits in sharks, is thus, in rays, separated from the other slits by the interposition of the enlarged pectoral fin.
The underside of a guitarfish’s head
In the next (and last) picture, note that the dorsal, caudal, and pelvic fins all are at least passably shark-like, but that the enlarged pectoral fin is being flapped for locomotion in the manner of a ray. (Also, it’s a male– you can see the free distal ends of the claspers below the second dorsal.)
