We have two more photos from reader Stephen Barnard in Idaho, who appears to still be alive despite his ownership of a new, high-powered sports car. His customary pair of eagles, Desi and Lucy, have returned as well, and appear ready to make more eaglets.
Yet another Red-tailed Hawk (Buteo jamaicensis) in flight:
The bald eagles (Haliaeetus leucocephalus): Lucy (on the left) looks pregnant. It’s about that time. Last year she laid eggs in March. Desi is the male on the right.
From reader Tim Anderson in Oz:
Here are two pictures of sunset looking west towards the town of Tumut, New South Wales:
Reader Joe Dickinson sent some photographs called “More from Moorea.”
Tours to see, touch, and snorkel with stingrays (Himantura fai?) and blacktip reef sharks (Carcharhinus limbatus) are widely offered in French Polynesia. They often are in shallow water on sandy bottoms, so pretty good views are possible without going in the water. A snorkel mask and waterproof camera provide better clarity (photo #2). The rays, in particular, are fully habituated to frequent visitors, so up close and personal contact is easy. Note the remora on the ray’s ventral surface in the second photo. The sharks usually have one or more remoras either swimming just below catching a ride. I like the final photo for the distorted reflections from the surface.
Note that the remora’s “sucker” is on its dorsal (top) side, so the one on the shark is riding upside down, while the one on the ray is upright.
Before we go back to the photos, we have a brief biological announcement, for there’s an evolutionary lesson here.
The “sucker” of the remora is remarkable, for it’s simply a modified dorsal fin. That was first conjectured from its morphology, but is now supported by analyzing its development. The following photos and info are from London’s Natural History Museum.
First, here’s the sucker; isn’t it bizarre?
But it’s a modified fin. The reason we know its evolutionary history is that the “sucker” begins developing just like a normal dorsal fin, which you can see by comparing its development to that of the dorsal fin in a sucker-less fish. Here is a sharksucker (Remora sp.) in early development, with the bones stained red. The sucker begins developing just like a normal fin, complete with the fin spines. Bottom photo is closeup of spines:
And then, as the Museum page notes, the structure begins growing and moving forward:
Then, over a series of small changes, the dorsal fin in the Remora begins to expand andshift towards the head.
By the time the Remora has reached around 30mm in length, the dorsal fin has become a fully formed 2mm sucking disc. It still has the components found in the dorsal fin, the tiny fin spines, spine bases and supporting bones, but the spine bases have greatly expanded.
So, the sucking disc is formed by a massive expansion of the dorsal fin through small changes while the fish is developing. It is not the result of the evolution of a completely new structure.
Here’s the diagram of the dorsal fin of a regular suckerless fish (a bass, Morone sp., top) with that of a remora (bottom). The equivalent (“homologous”) parts are given the same numbers. In the remora, the internal bases of the spines (#1) have gotten much longer, the plates anchoring the spines (#2) have become large platelike structures, and the spines themselves (#3) are the lateral structures in the sucker:
Here’s the adult remora with the bones stained red. You can clearly see the bony spines, homologous to the regular dorsal-fin spines:
So, as is usual in evolution, remarkable and useful new structures don’t arise out of nowhere: they’re simply modifications of things that were there before. One can only speculate about the steps taken by evolution to convert a dorsal fin into a sucker. If this is a product of natural selection, and it surely must be because of its complicated design and usefulness, then each intermediate step in the transition between a normal dorsal fin and the highly modified sucker fin must have been adaptive. I leave it to readers to think about how this might have happened gradually, with each modification conferring a reproductive advantage on individuals in the evolving lineage. (Hint: if you give up, read the article by Carl Zimmer highlighted by reader Glenn Butler in the comments.)
One more point: the sucker is so effective that in some places remoras are used to catch turtles—even large ones. They put a line around the remora’s tail, toss it into the water near a turtle, and it promptly heads for and fastens onto the turtle’s shell. (Remoras hate not being fastened to something.) Small turtles are simply reeled in with the fish, and large ones hauled near the boat where they can be harpooned.
Now back to our regular program: the blacktip sharks photographed by Joe:
Fascinating about the remoras, though must say they are ugly suckers🐸
The sucker fish is closely related to the Mahi Mahi? I did not know that but will look further.
Evolution is cool, and all the photos are great too. I’m a sucker for pics of undersea life.
As I read about the remora I was wondering how on earth the sucker could have evolved! What advantage would half a sucker be? It sure wouldn’t stick properly, would it? I read on hoping for some enlightenment. Then, I see this question is left to the reader. Boy that sucks!
What advantage would half a sucker be?
Carl Zimmer to the rescue.
I’d completely forgotten about Carl’s piece, though I’d read it (and the original paper). I’ve highlighted the link above, thanks!
Carl answers with a reasonable response to ‘what good is half a sucker’. The earlier form was: ” only part-way down the road to ridiculousness”.
Thanks for the link.
Suspect that fishing with a remora is like life itself. Sometimes you get the remora and a turtle back, other times you get half a remora.
Well put:-)
It probably looks different if you’re the remora. Come back alive, to be thrown back ; come back in installments after being pulled in two (refer to the Sepoy Mutiny and occasional records of Ghengis Khan getting all mediaeval on someone’s ass) ; or don’t come back at all unless you too can “do a Jonah”.
Looks like there’s a missing photo, for me anyway, called “sharks & rays5”.
The correct image link is:
whyevolutionistrue.files.wordpress.com/2015/02/sharks-rays51.jpg
I like how the Eagles appear to be engaged in conversation.
Lucy: “Did you remember to gather fresh sticks for the nest?”
Desi: “Uh, Just a sec, I’ll be right back!”
https://www.youtube.com/watch?v=2KfhFzH0aPg
I love Lucy, and Desi too!
Uh oh… sorry, PCC, about the embedment!
That reminded me of a recent article I saw but didn’t read before now:
“Remoras don’t suck: Their iconic clinch is far more complex
How does the hitchhiking, flat-headed remora fish attach to surfaces so securely yet release so easily? Suction was thought to be the easy answer, but Brooke Flammang, a biologist at the New Jersey Institute of Technology (NJIT), has proved this long-held conclusion to be only partly true.”
“Using footage captured by GoPro cameras at SeaWorld’s Discovery Cove in Orlando, Flammang and NJIT researchers found that the adhesive disc on the remora’s head used to attach to sharks, rays and other pelagic hosts is actually a complex mechanism that includes a modified fin structure with teeny spikes (called lamellar spinules) that generate friction to adhere to the host. Remora head anatomy also differs from other fish in having unusually-structured blood vessels that may be the secret to how they maintain adhesion for hours at a time.”
[ http://www.sciencedaily.com/releases/2015/02/150212183610.htm ]
So FWIW. But presumably a hefty dose of remaining friction adhesion supports Carl Zimmer’s proposed pathway.
What use is half a sucker? Ask the remora, it has one. =D
An interesting thought…might be there any evolved features of any sharks that make attachment easier for remoras? That is, any signs of symbiosis?
b&
Perhaps the shark’s raspy skin makes it easier for a remora to “stick”. Though I doubt it is an example of coevolution.
Even if it wasn’t initially, it’s not difficult to imagine it being enough to start a coevolutionary path.
Are there sharks that are superficially similar but remoras prefer one variety over another? Might be interesting to compare….
b&
Yes, not difficult to imagine at all.
Good question in regards to a remora’s shark preference.
I’m trying to think of how the remora would benefit the shark…
Maybe the remora removes parasites? Like a traveling cleaning station. A personal assistant.
Remoras do exactly that.
b&
Nice pics! I had no idea the remora’s sucker was a modified dorsal fin. Thanks for the learnings.
Beautiful sunset in Oz.
The Cobra hasn’t been delivered yet, which explains why I’m still alive.
When it comes, I’d love to see a photo of Deets behind the wheel. 😀
Great photos and science info.
sub
The comment that the remora hates not being attached to something reminds me of something I was wondering: Do clownfish enjoy being among anemone tentacles or do they fear not being in them? Or is it something else? With a fishy brain scan, it might even be possible to tell which path evolution has taken in shaping their brains…