I can’t brain today, which is lucky because there’s nothing substantive to write about—and I have other work to do. So enjoy these photographs from Robert Clark’s new photo book: Evolution: A Visual Record. I’ve selected a few photographs from a longer selection in the December 8 Washington Post. The notes at flush left are mine but are informed by the Post‘s captions. All photos are by Clark himself.
Below is a gynandromorph (half male, half female) of the Palawan Birdwing butterfly (Trogonoptera trojana): guess which half is male. What probably happened here is that one sex chromosome in a male embryo was lost at the two-cell stage, so that the left half remained ZZ in sex-chromosome constitution, while the right half was ZO. (In birds and butterflies, unlike mammals and flies, males have two identical sex chromosomes, ZZ, and females have unlike sex chromosomes ZW. If you’re ZZ and lose a Z, you’re ZO, probably a female—and very probably sterile.) [Note added in proof: actually, this speculation isn’t correct; as reader Arnaud Martin pointed out in a comment on this site, Lepidopteran gynandromorphs are produced in a genetically different way. But the stuff about flies below is correct.]
This beautiful specimen is certainly sterile, with its body split right up the middle. Notice the longer antennae of the male as well as its shorter hindwing. It’s a direct way of comparing the traits that are sexually dimorphic, but in a single individual.
I sometimes found flies just like this, though the gynandromorphs were caused by a loss of the X chromosome in females, causing one half (or bits) of the body to be XX (female) and the other half to be XO (phenotypically male). Sometimes the loss of the X occurs later in development, so that only a portion of the body is male.
My undergraduate student Ryan Oyama and I used genetic tricks to make lots of these gynandromorphs (with the male parts identified by bearing a yellow body-color mutation), trying to find out where in the body the male cuticular hydrocarbons, which act as sex pheromones, were made. (Males and females have different pheromones.) I found that it was only when the abdomen was male did the gynandromorph produce male pheromones, so that area, I concluded, was where the hydrocarbons were made. (Each gynandromorph, carefully scored for where and how much was male vs female, was then assessed for its hydrocarbons using gas chromatography.) This location was later confirmed by others who directly found the hydrocarbon-producing cells—right under the surface of the abdomen.
Here’s the table from my PNAS paper with Ryan clearly showing that the abdomen must be male for the fly to have male pheromone, and female to have the female pheromone (female pheromone is 7, 11-HD or 7,11-heptacosadiene, male is 7-T, or 7-tricosene). The “H”, “T” and “A” in the first three columns refer, respectively, to the sex identification (F for female, M for male) of the gynandromorphs (“mosaics”) we produced. n is the sample size.
I was just reminded that Matthew had a post–a really good one–on this site about Lepidopteran gynandromorphs as well as gynandromorphs affecting behavior in Drosophila. The first comment on that post, by Arnaud Martin, corrects both Matthew and me in our speculations about the source of the gynandromorphism.
The orchid, from Madagascar, was described by a French botanist in 1798, but came to be named “Darwin’s Orchid” because Darwin speculated that the flower, which had a long nectar spur—27–43 cm, or 10.6–16.9 in—must have been pollinated by a moth that could stick its very long proboscis all the way into the spur. (By so doing, the moth pollinated the orchid by pressing its head against the opening of the flower. Flowers produce nectar as a way to get their genes into the next generation through pollination.) Here’s the orchid (photo by B. J. Ramsay):
Darwin’s idea was ridiculed by some of his colleagues, but then the moth was discovered in 1903. Darwin, as usual, was right, though he didn’t live to see his vindication—at least about the moth.
Here’s how Wikipedia describes the pollination:
The fertilization of A. sesquipedale has been observed to proceed as follows. The moth approaches the flower to ascertain by scent whether or not it is the correct orchid species. Then the moth backs up over a foot and unrolls its proboscis, then flies forward, inserting it into a cleft in the rostellum which leads to the spur while gripping the labellum. After the moth has finished drinking the nectar, which usually takes about 6 seconds, it instinctively raises its head while removing its proboscis from the spur, and in doing so causes the viscidium to adhere to its proboscis usually about 4 to 9 mm (0.16 to 0.35 in) from its base.Attached to the viscidium via the caudicle is the pollinia. Upon removing its proboscis from the flower, the pollinarium stalk will be straight and parallel with the moth’s proboscis. Then after leaving the orchid the caudicle will eventually dry out, causing its angle relative to the moth’s proboscis to change by 90° so that it is at the correct angle to attach to the stigma of the next orchid the moth visits. The moth then repeats this process at another A. sesquipedale orchid and simultaneously fertilizes it. Once the flower has been fertilized, it quickly stops producing its powerful scent.
I believe it was my friend Phil DeVries who first actually photographed the pollination event, which takes place at night (video at link).
You can buy a lovely print of the pollination event from Official Website Artist™ Kelly Houle.
I’ll add two more photos because Matthew, who called the Post piece to my attention, said they were his favorite pictures of the lot. I’ve used the Post‘s own captions here.
And this is amazing, though there are much older hominin footprints (the Laetoli footprints, which date back 3.7 million years and were probably made by Australopithecus afarensis). Both show humans walking bipedally, and the A. afarensis footprints are direct confirmation of what was surmised only from anatomy.
Go see the other photos at the Post site.
h/t: Matthew Cobb