In this year's butterfly research news, the last two Atrophaneuras on the alphabetical list, A. varuna and A. zaleucus, were declared to be subspecies of a single species. Though easy to tell apart on sight, since zaleucus has white spots on its hindwings and varuna has none, they can crossbreed easily enough to be regarded as local variations of the same animal.
Adam White's original description of Atrophaneura varuna, 1842:
Photo anonymously donated to GBIF. The base color of the fore wings is dark, but in some light the inside corners can iridesce white.
In 1847 Westwood argued that some, not all, individuals from northern India looked different from typical southern specimens of varuna He admitted that the differences between varuna and astorion are hard to quantify when visible and aren't always visible.
On the surface zaleucus appeared to be a distinct, though similar, species, with a distinct pattern of wing markings. At least on some individuals it was distinct. On others it was not. Debate has gone back and forth about whether to count zaleucus as a separate species. Currently most sources seem to be counting it as a subspecies.
If you search long enough Google will pull up a document detailing how the species classification of Red-bodied Swallowtails is currently done. "De-tailing" is the word. The tail segments of dead individuals show more reliable species variations than the wing size and colors of living butterflies do, so, for an official species identification, the butterfly's hindmost segments may have to be viewed under a microscope. Living butterflies just go by scent, but they can smell, and see and hear and taste, an almost completely different range of things than we do. I'm not interested in detailed drawings of butterflies' back ends, but the drawings are online for those who want them.
Suffice it to say that the reproductive parts of butterflies of different species usually don't fit together well. Crossbreeding is physically awkward or impossible. Subspecies within a species, however, can and do crossbreed. Hybrids between varuna and Atrophaneura aidoneaus are not found. Hybrids between varuna and zaleucus are.common in places where both types are found.
Photo donated to GBIF and iNaturalist by SL Liew (licensed under http://creativecommons.org/licenses/by-nc/4.0/) ..Often varuna looks solid black; the head except for the eyes and a patch between them, and the underside of the body, have red-to-pink-to-white color, but look black when backlighted.
As the same individual approaches a flower, the independent movement of his wings can make them look as if they were damaged, as if the butterfly were falling. This is a trait all the Red-Bodied Swallowtails share. Their big wings have better coordinated steering abilities than most butterflies have.
Photo by Uajith. Pictures of male varuna often look as if the body were impossibly wide and thick, for a butterfly. If you click to enlarge this photo, or study the larger photo studies of this species by Joel Sartore, you see that the extra skin at the butterfly's sides is actually part of the wings. Many butterflies have folds of skin, sometimes covered with hair not scales, on the wings alongside the body, from which their species-specific scent drifts into the air as they fly. Usually the scent is not noticed by humans. The males of Atrophaneura varuna have especially generous scent folds that can be unfolded to show little round "pouches" on museum specimens. Humans can smell them. The most charitable word I found used to describe these butterflies' odor was "musky."
In other species of Atrophaneura females have no scent folds. Their hind wings have straight or concave inside edges. In varuna, however, females often do show scent folds, smaller than males' but big enough to form convex lines on the inner edges of museum specimens' hind wings. Humans recognize them, too, as having an unmistakable odor. It's not a faint whiff of jasmine or papaya, either.
Atrophaneura varuna, A.v. astorion, and A.v. zaleucus are found in most of southeast Asia in the right times and places. Their sizes vary from 3.5 to 5.5 inches, and the plain dark color of varuna and astorion can be confused with other species, but the varuna group can be identified by the scent folds and by the fact that both male and female butterflies in this species have an odor humans recognize. Humans describe it as strong, rank, and disagreeable. This species are the biggest stinkers in the Atrophaneura group, though some other male Atrophaneuras have distinctive odors that humans can smell, sometimes described as musky.
This museum collection shows the exaggerated scent folds of some males and the conspicuous ones of some females:
The "nominate" subspecies, Atrophaneura varuna varuna, may be the least common of the three. While most of the earliest recognized Atrophaneuras were named after literary characters associated with funerals, because of their black and white "funereal attire," varuna was named after a Hindu god primarily associated with the sky--probably because males often glisten with an iridescent bright blue like the sky on a starry night.
The other subspecies' names are harder to account for. Zaleucus, probably a real Greek judge and lawgiver, was remembered for his wisdom more than for his funeral, although he was certainly missed. "Astorion" may have been a misspelling of Asterion, a minor river god in Greek mythology, or may have been meant as a tribute to the wealthy Astor family.
Wherever Common Batwings are found, they seem likely to be tagged as that place's Batwing. The subspecies astorion is especially identified with Sylhet while zaleucus may be "the" Burmese Batwing, but Common Batwings have been identified with several places depending on where they were found.
As with most Atrophaneuras,males are most likely to look glossy and iridescent, females faded and brownish, but there are no guarantees. In many swallowtail butterfly species some females look different from males and some don't. The butterflies recognize one another primarily by scent, so it's hard to say what purpose this variability serves.
A question even scientists ask about varuna is what purpose its odor serves. Many swallowtail butterflies are primarily composters, and live on things that smell foul to humans, but the butterflies' scent is not noticeable to humans. Varuna is a pollinator species. Why should a pollinator species smell "worse" than the composters? Varuna spend most of their time in deep woods, whetre they are well camouflaged; do they need the additional protection they get by smelling unpleasant, and if so, from what? That the butterflies probably like the way they smell means less to adherents of Evolutionism than it does to the rest of us. We can see how animals might select for especially strong odors just because they like the way their mates smell, but it's a tenet of Evolutionism that taste evolves to fit biological needs. Varuna favors flowers in the genus Lantanai that also have an odor many humans dislike. To one another they probably smell like delicious flower nectar, even if it's a flavor nobody else seems to like.
Photographed head-on, this astorion's scent folds make his hind wings look thick. Atrophaneura aidoneus has generous scent folds too, but a few other features allow Asian butterfly watchers to tell them apart without dissecting them, explains Sebastien Delongtee:
For those new to this web site, we recognize the fact that populations of living things evolve in response to environmental conditions, within a range of what's possible for their species. (Conditions allow men to evolve from an average healthy weight of about 100 pounds to an average healthy weight closer to 200 pounds, but in no human population have men ever evolved to an average healthy weight over 200 pounds--as it might be with an average height of nine feet. We evolve to the large or small end of the spectrum, and there we stop.) The difference between the plain black wings of varuna and the white-splashed wings of zaleucus is produced by DNA. Different environmental conditions, or just chance, may have caused the genes for white spotting to disappear in varuna and astorion populations while becoming universal or near-universal in zaleucus populations. That is how subspecies and races evolve. In some animal species, genetic variations can even develop in such a way that crossbreeding becomes unsuccessful--crossbred offspring may not survive, or may be sterile.
The evolution of different physical types within species is a fact; gardeners rely on it to raise the kinds of food and flowers they want. Evolutionism is a different thing--a quasi-religious cult that insists that all living things must have evolved from amoebae, because if they didn't they would have to have been created by God, and the Evolutionists don't want to admit that there is any Higher Power than themselves. Evolutionism seems to me to require a great deal more faith than believing that a Creator made the different kinds of living things we see on Earth and gave them the ability to evolve.
Did varuna and astorion gradually lose their spots? Did zaleucus gradually develop their white spots? Did the populations separate from an ancestral population in which some individuals had spots and some had none? We will never know. Fossil ecords don't document butterflies' colors. We do know that zaleucus don't always have big splashy white spots like the one shown. The white spots can be reduced to bars along the edges of the hind wings or to pin-dots in the middles. This museum collection shows the range of variations zaleucus can have, especially in places where the subspecies can crossbreed.
Like other Atrophaneuras and large butterflies generally, they fly slowly, often along streams or rivers in search of lantana flowers. They are found in hill country rather than high mountains. Nyok Lin Liew notes that males may occasionally join other male butterflies at puddles, not mentioning any specific preference for polluted puddles. Our Eastern Tiger Swallowtails would never gather at the clear water beside a stream if they could find a puddle left by a dog or filmed by an oil slick or, if possible, both. Liew finds a Common Batwing and a Common Rose sipping companionably at a stream.
Butterflies are easiest to photograph while sipping water at puddles, so puddle behavior tends to be well documented.
Liew also documents that they are "seasonal," but not tied to a particular season. Liew's population chart can be read in either of two ways. Either the life cycle is short, with multiple generations per year, and the butterflies move to different places for each generation; or the life cycle is long and irregular, with some nine-month and some eighteen-month generations.
Generally varuna is considered a species of least concern to conservationists, Some local populations have, neverehelss, been described a endangered. Local populations are sad to be endangered in Bangladesh, declining in Nepal, and already extinct in Singapore.
Mating can be a simple matter of standing back to back, or a more athletic display in which both butterflies hang vertically, one supporting the other's weight and one flying upside down. Whatever the frequency with which the butterflies choose positions, photographers are madly attracted to the one that looks strenuous. This position is well documented at GBIF, INaturalist, and ifoundbutterflies.
The food plants of many swallowtail butterflies are in the genus Aristolochia. These vines are best known as big, fast-growing vines that can survive being the food plants of very hungry caterpillars. Here, however, is the flower of the host of Artophaneura varuna:
Eggs are little orange beads, textured with tiny drops of aristolochic acid. Caterpillars eat Aristolochia leaves and share the same wonderfully unappetizing look other Atrophaneura caterpillars have. They hatch out pinkish white, already covered in bumps and hairs that make them look hard to swallow or digest.
Still in its first skin, this baby has eaten enough of its host plant to give itself a healthy blackish-red color that warns birds that it will not taste good.
Each of the five skins through which they grow is slightly different in color and is bumpy, with a mix of red, black, white, and a purplish-brown combination of those, suggesting something incompletely digested by a bird who was probably very sorry it had tried to eat the thing. The caterpillars are in fact disgusting and indigestible to birds; a bird that eats one will probably survive, but won't eat another one. They show different combinations of reddish black and blackish red, with the white "belt" marking many Atrophaneura caterpillars show. The thoracic segments are slightly wider than the segments ahead and behind, and contain an osmeterium or "stink horns," a fork of flesh that seems meant to look like a snake's tongue. The osmeteria of most Swallowtail caterpillars release species-specific odors, which, if noticed by humans at all, are usually described as sweet and fruity. Varuna are not described as smelling sweet at any stage in life.
Pupae have the usual Aristophaneura dead-leaf shape, and may show a distinct blackish-grayish patterm on the back.
Nicholas Kong used time-lapse photos of two caterpillars to document their life cycle in a four-minute video:
This finishes our study of the Red-bodied Swallowtails. Next week we'll consider the peculiar genus Baronia.
No comments:
Post a Comment