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.
It is a fact universally acknowledged that most of the photographs that readers send me are of birds. There are millions of birders out there, but why so few “snailers” or “froggers”? I suppose it’s because birds are beautiful, colorful, and abundant. Their beauty is certainly on tap in these photos sent by reader Damon Williford, who lives in southern Texas.
And readers, bring out your wildlife photos, for the tank is growing quite empty! Damon’s notes are indented:
The Loggerhead Shrike (Lanius ludovicianus), which has declined in parts of its range, is still relatively abundant in southern Texas (I’m not sure what the juvenile in the photo was trying to accomplish).
The Northern Bobwhite (Colinus virginianus) is another grassland species that has declined, mostly due to habitat loss. But, like the Loggerhead Shrike, it’s still fairly common in South Texas, especially during wet years. Bobwhites have become one of my favorite birds, partly because it was the focus of 2 of my dissertation chapters.
The Plain Chachalaca (Ortalis vetula), the only member of Cracidae native to the U.S., is still restricted to the 3 southernmost counties in Texas. The chachalaca is considered a game bird in Texas, and attempts have been made to introduce it into other counties but these have failed.
I’ve included some photos of Reddish Egrets (Egretta rufescens) from previous years, showing both color morphs. [JAC: The first three photos below are of this species.]
JAC: These color morphs are quite distinct; I had trouble believing it was the same species! Wikipedia says this about the morphs:
The sexes are similar, but there are two color morphs. The adult dark morph has a slate blue body and reddish head and neck with shaggy plumes. The adult white morph has completely white body plumage. Young birds have a brown body, head, and neck. During mating, the males plumage stands out in a ruff on its head, neck and back.
I’m sure there has been some speculation about these distinct forms. Their lack of intermediates (or so I gather) suggests a single gene is responsible, but if there’s any adaptive significance to this polymorphism (presence of distinct forms in a population), I don’t know what it is. Perhaps some readers can enlighten us.
The last photo shows juvenile Wood Storks (Mycteria americana). Wood Storks wander northward into Texas after the breeding season ends in Mexico. There hasn’t been a confirmed case of Wood Storks nesting in Texas since 1960.
I was reading the Times Higher Education this morning, and my attention was drawn to a set of articles about how to deal with sullen students. One suggestion, from Tara Brabazon, caught my eye as I had a 10 o’clock lecture this morning. I tw**ted:
Colleagues from around the world goaded me into accepting the challenge, so after much thought I decided to project this tw**et, to the sound of Iggy Pop’s ‘Lust for Life’ (1977), which seemed appropriate for a lecture about speciation and natural selection.
The students seemed amused, though the effect was not as dramatic as Professor Brabazon seems to have found:
Whether the students were really oriented into a learning experience as a result, only time will tell.
I invite readers to comment below with a) examples of lecturers exciting and awakening students with music or *shudder* mime, and b) suitably amusing/interesting music that could be used to preface a lecture on a particular topic. So, for example, my next lecture in this series is on Fitness. What should I play before it? Non-biological lecture topics are welcome in the comments, too!
I have two more days in Dobrzyn before I head to Warsaw and then Sweden. Fall has set in with a vengeance here: the leaves are turning quickly, and the temperature has dropped below freezing. Unfortunately, lack of space in my luggage has prevented me from bringing very warm clothes (plus I’m going to Atlanta, for crying out loud!), and I’m told that Sweden is no warmer than Poland. But I am furry, and will make do. Meanwhile in Dobrzyn, Hili is trying to decide between roaming and eating, but that’s a Hobson’s choice given her consumption of rodents in the wild.
Hili: I was thinking about a walk, but there are food bowls at home…
Cyrus: Well, what can I say…
In Polish:
Hili: Myślałam o spacerze, ale w domu są miski…
Cyrus; Cóż mogę ci powiedzieć..
I suspect that this cartoon, sent to me by Matthew Cobb, expresses both his and my feelings. He’s overworked with lectures and writing; I’m largely done with the work I set myself in Dobrzyn and simply want to cuddle with the Furry Princess of Poland on this very cold morning. Would that bosses could be so understanding!
This is from lunarbaboon, whose site reveals precious few details about the man who draws it, save that he lives in Toronto.
If Steve Pinker is right, and I hope he is, Islam will inevitably be tamed, with the more pernicious aspects of the faith either being ignored (as is happening with Catholicism) or jettisoned outright. But given the large percentage of surveyed Muslims who see the Qur’an as not only the word of God, but literally true*, as well as the many believers who favor sharia law (see below), this taming will take a long time.
In the interim, the dictates of sharia law, including death for gays, adulterers, and apostates, continue to be enforced in many places, either publicly or by vigilante justice. Is there anyone brave enough among the readers to claim that Islam has nothing to do with these beastly deeds?
If so, first read the piece on Gay Star News about ISIS’s latest execution of four gay men in Mosul by hurling them from buildings, two onto a pile of cement bricks. (This seems to be a regular event in Mosul: 9 were killed in a single day last August). Here’s a photo from last weekend’s killing, a photo that is disturbing but, I think, important in understanding what’s really happening.
Then look at these data, from the recent Pew Survey of worldwide Muslim beliefs (summary here), and try to argue that religious dictates played no role in the tragic and brutal deaths of these men. Note that Pew did not survey Muslim attitudes in countries like Saudi Arabia and Syria, where, says the Pew survey, “political sensitivities or security concerns prevented opinion research among Muslims.”
While we’re at it, let’s look at the survey’s report on men’s attitudes towards women. This cannot be due to colonialist oppression, so you decide what role religion might play:
____________
*From the Pew Survey; data taken only from sub-Saharan Africa:
“Across most of the African nations surveyed, more than nine-in-ten Muslims say the Quran is the word of God, and solid majorities say it should be taken literally, word for word. Only in two countries in the region – Guinea Bissau (59%) and the Democratic Republic of the Congo (54%) – do smaller percentages think the Quran should be read literally. The results in those two countries are similar to the United States, where 86% of Muslims said in a 2007 survey that the Quran was the word of God, including 50% who said it should be read literally, word for word. (For more U.S. results, see Appendix A.)”
Mimicry is a recurring subject on this site, mainly because I’m fascinated by the precision with which natural selection can mold animals and plants to look like things they’re not. We’ve also seen examples of plants mimicking animals before, as in the orchids that mimic bees and wasps, fooling randy insect males into trying to copulate with the flowers (this deception promotes pollen transfer). But I think the following example is unique, for it involves plants whose seeds mimic animal feces. And the mimicry involves both the shape, size, and odor of the seeds.
What does the plant gain from this mimicry? It fools dung beetles, who apparently mistake the seeds for antelope dung. And dung beetles, as we all know, roll the dung balls away, bury them, and lay eggs in them, providing sustenance for their larvae. By fooling the beetles, the plant gets insects to not only disperse the seeds, but bury them, hiding them from seed predators and destructive fires, giving them a head start in germination.
This fascinating mimicry is described in a new article in Nature Plants (reference below, free access at link) written by a team of investigators from the Universities of Cape Town and of KwaZulu Natal in South Africa. Here’s the duplicitous plant, Ceratocaryum argenteum, a rush-like angiosperm native to Cape Province, South Africa (photo from Rosa Rubicondior).
The plant is unusual in having large rough seeds (nuts), which, as you can see in figures a-c below, are about 1.5 cm (0.6 inches) across. They’re not only large, but, to the investigators, smelled distinctly like animal feces.
(From the paper): a–c, Vertical (a) and side (b) views of a C. argenteum seed as well as one that has been cracked open (c) showing the endosperm and thick woody inner seed-coat layer and the outer tuberculate layer which together form the husk.
While studying what animals might eat these seeds, the team discovered that while de-husked seeds were eaten by the area’s main mammalian seed-eater, the striped field mouse (Rhabdomys pumilio), those mice avoided whole, husked seeds and didn’t cache or bury them. But in the course of these observations, the authors realized something else: hard seeds like these often have no odor, and in fact hard seed coats may have evolved in part to protect predators from smelling the inner seed and eating it. Thus the pungent fecal odor of C. argenteum suggested that maybe the odor was adaptive for the plant.
Sure enough, they observed individuals of the dung beetle Epirinus flagellatus treating the seeds exactly as if they were spherical pieces of animal dung: the beetle rolled away the seeds and buried them. Here’s the beetle; it’s a small one, about 1 cm. long:
Here, from Science News, is a video of the hapless beetle rolling and burying a C. argenteum seed. This is the Sisyphus of the animal world, laboriously rolling a heavy object to no avail.
To see how many of these seeds got buried, the authors put out 195 of them in 31 locations. They found that 27% of the seeds were buried whole (presumably by dung beetles) within a day, under what they call “optimal moist conditions.” That’s a pretty good way to get your seeds moved to new habitat where they don’t have to compete with other seeds, and even planted underground. One can see how a plant tricking a beetle in this way could substantially increase the spread of the plant’s genes.
When they dug up the seeds, they found no beetles or eggs associated with them (beetles tend to go underground with their dung balls, laying eggs in them and nomming some of the dung). This suggests that the beetles discover their mistake only after rolling away the seeds and burying them. I guess they just give up and return aboveground, searching for real dung.
What are the seeds’ adaptations to facilitate beetle dispersal? First, their shape. As the authors note:
C. argenteum seeds look similar in size, shape and dark brownish colouration to the dung of local small antelope (Fig. 1g). [JAC: this is feces from the bontebok, Damaliscus pygargus]. Seeds are remarkably circular (ratio of widest to narrowest seed dimension = 1.02; Fig. 1a,b) whereas scatterhoarded nuts tend to be flattened (L. sessileratio = 1.86; Fig. 1h, i). This circularity would facilitate rolling. Seeds of most of the other Ceratocaryum and closely related Cannomois species are unscented, smaller, smooth, black and have elaiosomes for ant dispersal (Fig. 1j).
Here are the figures (a and b are above; note similarity of bontebok feces in shape and size to the plant seed).
Finally, the mimicry involves, as noted above, not just size and shape but odor as well. Using gas chromatography and mass spectrometry, the authors compared the amount and composition of volatile chemicals emitted by both old and fresh C. argenteum seeds with those of other seeds in the family, and also with the dung of elands, elephants, gemsboks, impalas, and bonteboks. (The main antelopes in the area are elands and bonteboks.)
C. argenteum seeds emitted a tremendously higher amount of volatiles than did other seeds in the family (a 300-fold difference). Further, as you can see from the figure below, the chemical composition of C. argenteum seeds resembled that of dung, while related but non-rolled seeds did not. As the authors note:
Compounds emitted from the seeds that are also emitted by eland and/or bontebok dung include various acids, the benzenoid compounds acetophenone, phenol, p-cresol and 4-ethyl-phenol, as well as the sulphur compound dimethyl sulphone (Supplementary Tables 2 and 3). Most of these compounds are well known as components of the scent of herbivore dung(see also Supplementary Table 3). Similarity in scent is not due to bontebok feeding on C. argenteum as this plant is unpalatable and bontebok feed instead on various grasses (Poaceae).
(From paper): Similarity in the composition of volatile blends of seeds and animal droppings is based on non-metric multidimensional scaling. Symbols for other Restionaceae (Methods, Supplementary Table 3) that overlap are slightly offset for clarity. The composition of scent sampled from Ceratocaryum seeds is very similar (R = 0.75, P = 0.33) to that of dung of local herbivores (eland and bontebok), but differs markedly (R = 1.0, P = 0.028) from that of seeds of other Restionaceae (nested ANOSIM permutation test).
One final point: the habitat of C. argenteum is one swept regularly by fire, and, unlike many plants, this species can’t re-sprout after a fire. Thus, the ability to get its seeds buried away from the flames is highly adaptive!
This is a very nice paper that reveals a heretofore unknown kind of mimicry. And the mimicry involves not just shape and size, but odor.
The resemblance of C. argenteum seed odor to that of animal dung was obvious to the investigators, but of course what matters is the resemblance of the smells to beetles. And we can’t say that the dung smells the same to humans as it does to beetles: all we can say is that beetles and humans probably detect the same chemicals. The perception of odor, after all, is subjective.
There are probably many other cases of animal and plant mimicry that also involve odor, but aren’t so easy to detect because the odors are perceptible to insects or other beasts whose odor receptors differ from ours. After all, it was discovered only recently that the bee-and-wasp-resembling orchids have also evolved a scent resembling the mating pheromones of bees. There must be many aspects of mimicry that—as humans whose range of senses differs from that of many creatures who are duped—we simply cannot yet detect.
CODA: I was a young graduate student when I took my first trip to the tropics: a two month Organization for Tropical Studies course in ecology in Costa Rica. (It was a fantastic experience.) Before I went, one of my naturalist friends, the late Ken Miyata, gave me some advice. If you want to learn some biology, he said, go out in the forest by yourself and defecate. Then just sit near your leavings and watch them for a while. So I did it, and sat nearby for over an hour. Within a matter of five minutes, all manner of insects had descended on the pile, and soon the dung beetles came, rolling bits of scat into balls and trundling them away. Within an hour the pile was completely gone—eaten or sequestered by all kinds of beasts. Dung is a rich resource, and the rapidity of its disappearance shows not only its value to many species, but how well adapted they are at finding a small lump of excrement in the deep forest. In the tropics, nothing edible goes uneaten.
