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.
Today’s photos come from Larry Powell of Calgary; his captions and IDs are indented, and you can enlarge the photos by clicking on them.
Here are some photos of amphibian and reptile species that are found in Alberta. Most of our species are widely distributed through western North America, and reach their northern (or eastern) range limits here. We don’t have a very diverse herpetofauna, and the species we do have must deal with long cold winters.
Some of these (Prairie Rattlesnake, Greater Short-horned Lizard, Long-toed Salamander) are species that I’ve conducted ecological research on in Alberta, and the others are individuals that I’ve come across during various field projects.
Tiger Salamander (Ambystoma tigrinum) – A large and amiable salamander found over much of Alberta’s prairies, but seldom seen, as it spends most of its time underground. This one was found right at the western margin of its Alberta distribution, at the eastern edge of the Front Range:
Long-toed Salamander (Ambystoma macrodactylum) – This is our other salamander species, found in the mountains. It’s much smaller than the Tiger Salamander, but also spends most of its time underground:
Three Long-toed Salamanders from the same population in the Front Range, showing the great variability in dorsal colouration and pattern. This species exudes a toxic secretion from glands in the skin, and from a ridge of glandular tissue down the dorsal side of the tail, that is both sticky and irritating, so the bright yellow blotching is presumably warning colouration:
Wood Frog (Lithobates sylvaticus) – This is a cold-adapted species found in the boreal forest across Canada. It overwinters by allowing its extracellular fluids to freeze, and limits damage to cellular structures through cryoprotectants. This individual was found in the Front Range:
Leopard Frog (Lithobates pipiens) – This species was formerly widespread and abundant in the Alberta Prairies, but almost disappeared in the late 1970s. There doesn’t seem to be any satisfactory explanation for this. They are still locally common in spots, however – this individual was found in a dugout in the deep southeast of the province, in relatively undisturbed short-grass prairie:
Great Plains Toad (Anaxyrus cognatus) – A handsome and charming toad that reaches its northern limits in southeastern Alberta, where it occurs in great numbers in spots (mainly the sandy areas around the South Saskatchewan River). The breeding call sounds like a miniature jackhammer, and breeding congregations are audible for a long distance:
A Great Plains Toad in the hand:
Bullsnake (Pituophis catenifer sayi) – Bullsnakes are found over the short-grass prairie region of southeastern Alberta, mainly near rivers. They are unusual in being oviparous – most Alberta reptiles are viviparous. This specimen was encountered by the South Saskatchewan River, north of Medicine Hat. Bullsnakes spend a lot of time underground, hunting rodents in their burrows – note the large rostral scale, thought to be used in burrowing:
Prairie Rattlesnake (Crotalus viridis) – Another species of the short-grass prairie in the southeast of the province. Like Bullsnakes, their distribution is associated with drainage channels – they hibernate communally in the bedrock exposed in these situations, and travel considerable distances during the warmer months to and from their dens. This individual is a subadult, encountered on a road at the edge of the Cypress Hills:
Greater Short-horned Lizard (Phrynosoma hernandesi brevirostris) – This is our only lizard, found in scattered locations across the southeast corner of the province. They are remarkably cold-hardy. This is a large adult female I’m holding – males are quite a bit smaller. The species’ viviparity is probably part of the reason for this sexual size dimorphism:
Another Greater Short-horned Lizard – this individual is a member of the northernmost population of this species in the world, located about 30 km north of Medicine Hat. It’s a subadult female:
A frog pollinating a flower? That would be remarkable, and a paper supposedly describing the phenomenon was recently published. It got a lot of attention, including a large piece in (guess where?) Scientific American. I was prepared to write about it based on the publicity, but I needed to see the paper first. When I read it, I was sorely disappointed. The evidence for frog pollination, which would be the very first described case of an amphibian effecting pollination—was as thin as a piece of paper.
The relevant paper, from the journal Food Webs, is not widely available, even through the University of Chicago library. Fortunately, a kind reader somehow got hold of the pdf (you can too, through judicious inquiry), and just a bit of it is online, which you can see by clicking the link below.
I’ll be brief (well, I’ll try). This group of investigators from Brazil report that the tropical treefrog Xenohyla truncata was observed eating fruit, petals of flowers, and sipping nectar during one four-hour observation period. This itself is unusual because frogs are mostly carnivorous and insectivorous. This species (and one congeneric relative) were reported earlier to be omnivorous, eating both fruits and invertebrates.
The popularized result? One (count it, one) frog was found with pollen on its back after sticking itself into a flower to eat. Was it observed pollinating another flower? No. We don’t even know if the plant is self-compatible, so that a frog could even effect cross-pollination on the same plant. Did the frog visit more than one plant, so that cross pollination was possible? No.
The upshot s that all the publicity given to this frog is comes from the observation of a single individual exiting a flower with pollen on its back. That says virtually nothing about whether it is a pollinator, and even less about whether it’s an important pollinator.
Here are the data described in the paper:
We conducted in situ observations of a breeding population of X. truncata on 15 December 2020, in a Restinga vegetation area in the municipality of Búzios, state of Rio de Janeiro, southeastern Brazil (22◦46′13.94”S, 41◦57′4.47” W; WGS84; 2 m a.s.l.), for approximately four hours (from 6:00 to 10:00 pm). Air temperature was 25.8 ◦C. We observed five individuals of X. truncata in feeding activity on two plant species between 7:00 and 9:00 pm.
. . .Around 8:00 pm we observed other X. truncata individuals leaving bromeliads and climbing a Brazilian milk fruit tree [JAC: Cordia taguahyensis] full of fruits and flowers. Three individuals (sex undetermined) clustered around a ripe fruit and began a dispute to get close to the fruit, pushing each other away as they tried to bite the fruit (Fig. 1D; Video S2). After approximately five min, two individuals gave in and remained perched on branches close to the fruit, while the third began to nibble the fruit, increasing a pre-existing hole to gain access to the pulp (Fig. 1D). While this individual fed on the fruit, the others no longer disturbed it. The same individual remained nibbling and sucking the fruit pulp for about 10 min, the others eventually approaching to feed. x
. . . On the other side of the same tree, we observed a X. truncata individual that climbed a branch and entered an open flower (Fig. 1E), where it remained for approximately 5 min performing suction-like movements (Video S3). Upon leaving, pollen grains were adhered to its back (Fig. 1F).
This is the first report of a frog species actively feeding on nectar and flowers in nature and the first evidence that it may act as pollinator.
Here are the two pictures mentioned above, along with their captions from the paper:
X. truncata within a Cordia taguahyensis flower (E)
. . . and coming out of it with pollen grains (red arrow) on the back (F). Photographs by C. H. de-Oliveira-Nogueira.
The frog was also observed feeding on an “alien” (THEIR WORD) species, the beareded Iris, Iris x germanica (see video below; the “x” indicates the species is of hybrid origin).
So what’s the evidence that this frog actually effected any pollination? None that I can see. What is the evidence that it’s a regular and important pollinator of the native milk fruit tree? None, nada, zippo. Now it is possible that this frog could still pollinate other flowers on the same tree (if it’s self-compatible) or on other trees, but we don’t have that evidence. What we have is the authors’ speculation, eagerly and breathlessly snapped up and regurgitated by the press. More from the paper (my emphasis)
As mentioned, the relationship between X. truncata and the native C. taguahyensis is remarkable. The flower structure of C. taguahyensis allows X. truncata to enter and exit the flower, and to carry pollen grains after the visit. In this case, X. truncata could act as a pollinator of this species, or even of other plant species with similar floral structure. However, to play the pollinator role of C. taguahyensis, this frog should visit another flower or another plant individual on the same night. We lack information about the breeding system of C. taguahyensis, but some Cordia species are self-compatible, whereas others are self-incompatible (Opler et al., 1975; Machado and Loiola, 2000; Mcmullen, 2011; Wang et al., 2020). As X. truncata wanders from one plant to another before it settles in a bromeliad for daytime shelter (our pers. obs.), it is likely that the above mentioned scenario about its pollinator role actually occurs.
How likely is it? We don’t know.
Species in the genus Cordia are visited by a wide variety of invertebrates, such as bees, butterflies, beetles, wasps and flies (Opler et al., 1975; Machado and Loiola, 2000; Lopes et al., 2015), as well as vertebrates such as bats (Alvarez and Quintero, 1970) and birds (Opler et al., 1975; Dalsgaard, 2011; Wang et al., 2020). Thus, C. taguahyensis is likely pollinated by multiple animal species and the treefrog X. truncata is now a potential pollinator candidate.
“May”, “might”, “seems likely”, and so on it goes. To show pollination, you need to show pollination, not speculate that it’s likely. One way to do this is dust a flower with fluorescent pigment, like those used in making black-light posters, and then see if any fluorescent pollen makes its way to another flower (and, of course, that the flowers are reproductively compatible). This wasn’t done (we used this method to mark Drosophila in the wild.) Ergo, while we have new evidence that X. truncata is omnivorous and eats petals and nectar, and that pollen adheres to its back, that’s all we have. It’s possible that a cross pollination occurs occasionally, but even that is speculation, and doesn’t show that the frog, as opposed to the many insects that visit the plant, is of any importance as a pollinator. As the authors say, “the treefrog X. truncata is now a potential pollinator candidate.”
Well, at least there’s a video of the cute little frog eating from a flower (but the “alien” plant, not the milkfruit flower); this comes from IFL Science. Cute little bugger, isn’t it? The nectar and plant material may be a valuable supplement to the diet of this frog.
The journals that mentioned this paper as a possible case of amphibian pollination include Science, the New York Times, IFL Science, and other places. But the first place that comes up when you google “pollinating frog” is Scientific American.
Sofia Quaglia at the NYT gives the most critical take on this paper, saying this:
But more observations are needed to say the frogs really are pollinating plants.
“We cannot say that these frogs are actually pollinators,” said Felipe Amorim, a pollination ecologist at São Paulo State University who was not involved in the research. “They are flower visitors, they are flower-visitor frogs. We have a lot to learn about this novel interaction.”
For instance, the mucus secreted by the frog’s skin needs to be tested to confirm it doesn’t spoil the pollen before it gets to its destination. Scientists also need to work out whether the pollen is ever delivered to other flowers and if it does successfully fertilize and germinate them. It’s also still unclear why this frog species has developed a liking for flora over fauna in the first place.
And at least Sci. Am. mentions some of these problems. But really, the publicity given this observation, which has an interesting part (some frogs eat flowers and nectar) and a not-so-interesting part (one frog got pollen on its back) far exceeds its scientific novelty. This is what happen when either a university publicity machine goes into action or journalists copy each other’s content. Two colleagues to whom I sent the paper both found the claims of possible pollination by the press (and by the authors, too) wildly exaggerated.
Today we have a lovely selection of photos of red-eyed frogs taken by reader Mike Canzoneri. His notes are indented, and you can enlarge the photos by clicking on them.
The Red-Eyed Tree Frog (Agalychnis callidryas) is probably the most photographed frog in the world, and it’s not difficult to see why. These colorful frogs have a unique personality and are incredibly photogenic.
The Red-Eyed Tree Frogs shown here are all from my property on the Southern Pacific coast of Costa Rica and are less colorful than the populations found on Costa Rica’s Caribbean coast. In fact, the coloration varies significantly from one isolated population to the next, and this year we are likely going to see the species get reclassified and split up into several separate species based on geographic population throughout its range. The color morph that I have around me lacks the vivid blue bars on the side of the body (mine are more bluish-gray) and the bright yellow/orange on the legs and feet that you find on the population on the Caribbean coast. A large percentage of the ones I see also have one or more white spots on their backs as can be seen in the 1st photo below.
Since moving to my house and rain forest property in the Golfito area, I’ve watched the A. callidryas population increase, though not nearly as sharply as some other frog species around me. The main reason for this is that I started keeping the lagoon in front of my house filled with water through the dry season (it normally dries up after the rains stop and rainy season ends) and I’ve added several more year-round tanks of water. Not only do the late rainy season tadpoles now make it to the frog phase, but reproduction for many species continues year-round around my house. Below is a common sight (A. callidryas in amplexus) on practically any night around the lagoon and tanks. After a pair spends time in amplexus they will eventually move to the underside of a large leaf over-hanging some water to deposit and fertilize eggs in a golf ball sized gelatinous egg mass. When the eggs hatch, 7 to 10 days later, the new-born tadpoles drop into the water below.
With an increased population of A. callidryas, I’ve also seen an increase in the populations of their predators, most notably the Northern Cat-Eyed snake (Leptodeira septentrionalis), which feeds on frog egg masses (primarily those of A. callidryas) and also on the frogs themselves (any species they can fit in their mouth) and even tadpoles. Here I noticed a Red-Eyed Tree Frog on the same leaf as a Northern Cat-Eyed snake. The snake eventually moved on and the frog was unharmed.
An interesting sight I caught a couple weeks ago was two male A. callidryas fighting, likely over territory. I had never seen this behavior before from this species (plenty of other species show aggression between males) and it was surprising because these guys are typically low-energy frogs and at night you frequently see them sleeping, even the males during mating. These two were wrestling on a leaf and when the one on the bottom rolled over to the top, they both rolled off the leaf…at the last instant, the feet of one of them caught the base of the leaf and they hung, upside-down, still grappling. Eventually they separated and both climbed back onto the leaf.
And finally, here are some sleepy Red-Eyed Tree Frogs. Notice the gold nictitating membrane that covers each of their eyes…it obscures the bright red eyes that could catch the eyes of a predator while still allowing the frog to see what is going on around it.
If you found this interesting and enjoyed the photos, I can do another piece on some of the other frog species that inhabit the same environment around my house. Feel free to ask me anything about any of these photos or about the frogs around me in Costa Rica. For the photographers: all of these shots were taken at night, in-situ, with a Lumix (Panasonic) G9 20MP Micro 4/3 camera and an Olympus 12-40mm f/2.8 zoom lens and with a Godox V860ii speedlight mounted on the camera and a custom flash diffuser made by Erick Mesen here in Costa Rica.
I want to see more frogs, so please urge Mike to send more photos!
Today we have a new contributor: Gerfried Ambrosch, who sends us lovely pictures of herps. Gerfried’s notes and IDs are indented, and you can enlarge the photos by clicking on them.
I took all of these photos on my iPhone. Most of the amphibians depicted are nocturnal. Only the picture of the Alpine newt was taken during the day. Interestingly, some of the most important European green toad populations are found in urban areas, which is why they’re sometimes considered a synanthropic species. However, one main reason this endangered, steppe-dwelling species of toad now mainly populates these secondary habitats is that its primary habitats have mostly been destroyed. Once common, the European tree frog – Central Europe’s only tree-climbing frog – is now also a threatened species. Fortunately, there are many wildlife-protection and biodiversity projects (some of which I’m involved with) in Austria and Germany that work hard to mitigate these problems.
I’m taking a break from wildlife photos today as I’m conserving them and am also tired. But reader Pradeep has contributed a “spot the” picture. In this pile of rocks, there is a frog. Can you spot it? If you do (or don’t), just say “I did” or “I didn’t” in the comments so to allow readers to look for themselves. The reveal will be at noon Chicago time.
Click to enlarge the photo. I’d call this “medium hard”.
Today we have photos from regular Mark Sturtevant. His notes and IDs are indented, and you can enlarge the photos by clicking on them. I’ll remind readers to send in your good photos, as we’re running low.
Mark:
Here are some pictures of mainly arthropods, taken in 2021 as the weather began to finally warm near my habitat in eastern Michigan.
An early opportunity was a European paper wasp (Polistes dominula) that emerged from hibernation on the front porch. It was still quite cold, so she was motionless most of the time. After a long winter, I was glad to see her even though the species is invasive and problematic in the U.S. because it has reduced populations of the native paper wasps. These pictures are focus stacked from about 100 pictures each, taken with the assistance of a Helicon Fb tube. That is a device that lets you do rapid focus bracketing with a DSLR camera.
Next is a ground spider (Gnaphosidae), a family of free roaming spiders that include some ant mimics. This is Zelotes fratris. This too is focus stacked, but from a few pictures taken by hand. Note the red velvet mite photo bomb.
Here is a very young green frog (Lithobates clamitans), only recently transformed from a tadpole. Often mistaken for the closely related bullfrog, green frogs can be identified by the dorso-lateral ridge that you can see here. This youngster may one day grow to be the size of both of your fists put together.
The big event for the early part of the 2021 season was a possibly once-in-a-lifetime chance to photograph 17-year cicadas,Magicicada septendecim. Cicadas spend most of their lives as nymphs living underground, where they feed on sap from tree roots. “Periodical” cicadas include a 13-year species and the 17-year species. After those many years, the nymphs emerge en masse in biblical plague numbers, mate, lay eggs, and die over a period of several weeks. It is believed their reproduction cycle evolved to overwhelm predators who cannot grow their population in response. The 2021 season was due to have “Brood X” of the 17-year cicadas, which is the largest population of this species. Brood X extends over multiple states in the US, and one edge of this group extends into southern Michigan. So, with the help of the internet, which provided records about their last emergence, I made the long drive to a likely park to see this marvel. The trip was well rewarded with high thousands of cicadas.
Here are various pictures showing perching cicadas, and a bush with quite a few of them. Cicadas were flying everywhere, and collisions with them were pretty frequent. Males are especially distinct with their bright red eyes.
The eerie sound of thousands of cicadas filled the air over the field. But it was evident that there were far more of them in the trees that surrounded the park, since the trees were fairly deafening with their shrill, spooky music. Accounts from other areas of the Brood X emergence described even heavier population densities, where pretty much everything gets covered by them.
It’s the males who sing, and they do so by forcing air past a stack of vibrating membranes under a pair of “tymbal” plates on the abdomen. This picture showing the plates is blurry because the male was continually squalling in protest.
Here is a wide angle macro picture of a cicada posing with my good friend Gary Miller. Gary is an excellent macro photographer in his own right. It was not even summer, and this is one of my favorite pictures of the entire season.
I wanted to find a video that conveys what this natural wonder is like. This amateur recording is a very good match to what the emergence was like in this field, right down to the screaming trees in the distance:
Readers in the eastern U.S. may have direct experience with seeing a periodical cicada mass emergence, and if you’d like to make plans for seeing one, here is a map that can get people started.
