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.
Be sure to send in your good wildlife photos for possible posting here. The level in the tank is okay, but its drop has made me a bit nervous.
Today we have some photographs taken by reader Damon Williford and sent to me on November 23. His notes:
Attached are some photos that I took this weekend. The first batch are from Estero Llano Grande State Park in the Lower Rio Grande Valley of Texas. Two are tyrant flycatchers, Tropical Kingbird (Tyrannus melanocholicus), and a Vermilion Flycatcher (Pyrocephalus rubinus, male). The other photos are a sleepy Yellow-crowned Night-heron (Nyctanassa violacea), Long-billed Thrasher (Toxostoma longirostre), and spiny softshell turtle (Apalone spinifera),
These photos are from the Santa Ana National Wildlife Refuge on the Texas-Mexico border, including a roseate skimmer (Orthemis ferruginea), rosebelly lizard (Sceloporus variabilis), and Texas indigo snakes (Drymarchon melanurus erebenus). I saw more indigo snakes on that refuge last Sunday than I have seen any where else. I found a total of 4. The head shot was of a small individual (2-3 ft). The second photo is the last indigo snake I came across that day and looked like it was 4-5 feet long. These snakes come across as very camera shy.
Yesterday we claimed that a headline involving frogs was the best headline in the history of the world. This piece of hyperbole was soon disputed on Tw*tter:
Social insect colonies rely heavily on chemical signalling to identify members of the colony, and conversely to detect intruders. These communication systems are generally very effective, but as that great scientist Professor Ian Malcolm put it, ‘Life will find a way’. If there’s a locked system, somewhere a pesky but perspicacious parasite will find a way to crack it.
Caterpillars of the Maculinea genus – also known as Alcon butterflies – hatch on the ground near Myrmica ant nests, and are picked up by the workers. The ants take home what tastes/smells like one of their babies, except this is a carnivorous cuckoo that will munch its way through their larvae…
An unusual example of such chemical camouflage was discovered in 2013 by a group of German and Swiss researchers, led by Mark-Oliver Rödel of the Museum für Naturkunde Berlin. It’s unusual because, as the title of this post indicates, it involves a frog.
The West African Rubber Frog (Phrynomantis microps) is found throughout west Africa, and can often be found living in the underground nests of the ponerine ant Paltothyreus tarsatus (aka the African stink ant).
These are pretty aggressive ants about 2 cm long, which pack a nasty bite and an even more powerful sting. They can be found pretty much throughout sub-Saharan Africa, where they play a very important ecological role. Most ponerine ants have quite small nests of a few hundred individuals, but in a paper published in 2013 my pal Christian Peeters found that some P. tarsatus nests can be as large as 5,000 individuals.
Here’s a rather small picture of Christian with a box of these alarmingly large ants:
Although the ants are notoriously aggressive, they don’t seem to bother about the Rubber Frog, as shown by this photo:
You can see how the ants seem rather bemused by the frogs in this video stitched together from the Rödel paper by a YouTube user – the first part shows ants with an adult frog, the final section with a froglet:
Other frogs, and other arthropods, are immediately attacked by the ants when they encounter them. However, when dead mealworms or live termites were covered in extracts from the frog’s skin, they were generally ignored by the ants, or at least it took much longer for the first bite to be administered:
Figure 1. Time from first ant, Paltothyreus tarsatus, contact with termites (left; inlet A) or mealworms (right), coated with the skin secretion of Phrynomantis microps, until stinging (inlet B). Control groups are termites or mealworms coated with water. Boxplots show the median and the interquartiles of time from first ant contact with a termite or mealworm until stinging. Coated insects were stung significantly later than control insects. Taken from here.
When Rödel’s group examined the chemical composition of the frog’s skin, they found it contained two novel peptides – short proteins, each 9 or 11 amino acids long – with a proline-phenylalanine pair at the end. When termites were covered with either or both of these peptides, the ants took significantly longer to attack them, suggesting these are indeed the active ingredients on the frog’s skin:
Figure 2. Effect of the two peptides from the skin secretion of Phrynomantis microps applied to termite, Macrotermes bellicosus, soldiers and delaying the aggressive behaviour and stinging of Paltothyreus tarsatus ants. Maximum observation time was 20. Taken from here.
This finding is doubly surprising – most instances of chemical camouflage involve cuticular hydrocarbons, which many arthropods use for communicating (for example, these are involved in the case of the Alcon Blue caterpillars described above). In the case of Phrynomantis microps, not only were novel peptides involved, no hydrocarbons could be detected on the frog’s skin, even though the animals were living in a hydrocarbon-rich environment in the ants’ nest.
What’s in it for the frog? Protection from predators (you’d have to be very foolhardy to take on the ants) and possibly protection from dessication during the dry season. They may also eat some of the ant larvae, although that is speculation on my part.
What’s in it for the ants? Probably nothing. If the frogs found a way to hack their chemical communication system, but at low or zero cost to the ants, then it won’t matter. If there’s a substantial cost to the ants, then you would expect a chemical arms race to begin – any ant nest that used a slightly different system of communication would not sustain the cost of the frog in the room.
The final point about this rather neat piece of biology, which flowed from a field observation, is that it’s opened up a new area of study in chemical communication in ants, and potentially a way of placating aggressive insects.
Peeters C, U. Braun U & Hölldobler B (2013) Large Colonies and Striking Sexual investment in the African Stink Ant, Paltothyreus tarsatus (Subfamily Ponerinae) African Entomology, 21(1):9-14. (Abstract)
We have some photos from a new contributor, Christina Pfaff; her notes are indented:
I’ve been looking at the wildlife pictures for a long time, but only recently got a camera that I felt took good enough pictures to send in. Near the end of October, my husband and I went camping at Council Bluff Lake in southern Missouri to enjoy one of the last weekends of fall color. As with many MO lakes, it’s man-made via a dam across the Big River which was constructed about 30 years ago. The first picture I included was shot from the Lakeshore Trail looking down one of the many fingers of the lake.
I’m not as savvy with species names as many of your readers, but I enjoy finding and photographing critters we find on our hiking adventures. I do my best to identify species on the internet, but probably make mistakes sometimes. One of our first sightings on the trail was an Eastern Chipmunk (Tamias striatus), who thought he was doing a very good job of hiding from us in a log. I know chipmunks are a dime a dozen, but this was one of the better shots I’ve ever taken of one.
Can you spot the rodent?
The next two photos are Eastern American Toads [(Anaxyrus americanus americanus). Although they’re very common, they come in so many size and color varieties that they’re always a joy to see on the trail. They usually amble off in a mixture of hopping and tumbling as soon as they hear us coming.
Another common companion on the trail are turtles (fifth photo). I believe this guy is a Three-Toed Box Turtle (Terrapene carolina triunguis) and he was just waiting for us in the middle of the trail. He retracted his limbs a bit into his shell as we walked past, but otherwise seemed unconcerned by our presence.
The last three photos are some of the insects we found along the trail. The Horned Passalus (Odontotaenius disjunctus) is the only Missouri member of the Bess beetle family. The forest around the lake would provide plenty of rotted and decaying wood for them to survive on.
The Banded Woolly Bear is the caterpillar form of the Isabella Tiger Moth (Pyrrharctia isabella). While we found many in the forest, there were even more creeping along the highways on our drive home. I imagine the moth population will be booming come spring!
Finally, we found a Carolina mantis (Stagmomantis carolina) in a picnic area near the lake. She appears to be a female since her wings only extend part-way down the abdomen.
We have photos from a new contributor, Rachel Wilmoth. Her notes:
I’m (mainly) a lurker on your website, and was inspired by the readers’ wildlife photos posted yesterday, Oct. 19. My fiance and I went to South Africa, Namibia, Botswana, and Zimbabwe last month. The wildlife and scenery were astounding. I’d like to share some photos.
The herd of African elephants (Loxodanta africana), lazing lion, zebras, elephants eating, and giraffes drinking were all in Etosha National Park, in Namibia.
The sand dune is Dune 45, and is located in the Sossusvlei, in Namibia:
The penguins are African penguins (Spheniscus demersus), and the photo was taken at Boulders Beach, in Zuid-Afrika. I was lucky to get the shot I did, as they started squabbling two seconds later:
The great white pelicans (Pelecanus onocrotalus) were at Walvis Bay, in Namibia. They look large, but only weigh 3-6 kilos:
There was a large colony of Cape Fur Seals (Arctocephalus pusillus) at Cape Cross. They’re loud (and the young ones sound like goats). They also reek to high heaven. The picture is of a seal pup:
The small frog was found in the Okavango Delta. [Readers: any IDs?]
The pictures hippo (Hippopotamus amphibius) and the sunset were taken from the Chobe river:
The photos big male lion and the prides of lionesses, as well as the water buffalo, and antelope (possibly a kudu, but I’m not 100% certain) were all taken in Chobe national park. Some lionesses were eating an elephant that had died of illness. By the way the antelope was just running to run, no predators were hot on its heels.
Finally, the last picture is of an aerial shot over the Zimbabwe side of Victoria Falls. The flow of water from the Zambezi was nearing its annual low point.
National Geographic reports the discovery that the hawksbill sea turtle (Eretmochelys imbricata), the most endangered of all marine turtles, is biofluorescent: it absorbs blue light from the ocean and, after that light is transformed into different light by photosensitive molecules, it’s reflected back as a panoply of different colors. This differs from bioluminescence, which is the emission of nonreflected endogenouslight produced wholly by chemical reactions. Bioluminescence is found in many organisms, including fish, jellyfish, and marine microorganisms, while biofluorescence has been seen only in fish, corals, and now this turtle. Here’s what the fluorescent hawksbill looks like, filmed by the discoverer, marine biologist David Gruber. The colors are the reflection of the camera’s blue light, which matches wavelengths found in the ocean.
We have no idea why the turtle does this, or even whether it’s an adaptation. Perhaps it’s only a byproduct of some other aspect of the turtle’s metabolism or morphology. Gruber and Alexander Gaos (a researcher on turtles not involved in the discovery) speculate that the fluorescence helps camouflage the turtle at night, but of course we don’t know for sure:
“[Biofluorescence is] usually used for finding and attracting prey or defense or some kind of communication,” says Gaos. In this instance, it could be a kind of camouflage for the sea turtle. (See pictures of insects that are masters of camouflage.)
The hawksbill’s shell is very good at concealing the animal in a rocky reef habitat during the day, Gaos explains. “When we go out to catch them, sometimes they’re really hard to spot.”
The same could be true for a habitat rife with biofluorescing animals—like a coral reef.
In fact, Gruber pointed out that some of the red on the hawksbill he saw could have been because of algae on the shell that was fluorescing. The green is definitely from the turtle though, he says.
The problem I see with the “camouflage” explanation is twofold. First, as far as I know nothing preys on adult hawksbills except humans. Perhaps the camouflage is there to protect babies against predators, but that wasn’t suggested. Further, the prey of hawksbills isn’t likely to avoid them when they’re camouflaged, because their prey is largely sessile or nonvisual (the main diet of this turtle is sponges, supplemented with jellyfish). There’s not much need, then, to hide yourself from such prey. I could swell the suggestions by speculating that it’s a mate-recognition adaption, enabling males and females to find each other in the dark, but that too is pure speculation.
