Scientists are often trying to insert new or modified genes into fruit flies. It’s usually difficult to tell if their gene has been successfully inserted so researchers add their gene next to an obvious marker gene. White vs. pigmented flies provide a good marker so scientists created an artificial white imitator gene called mini-white. Scientists stick the desired gene and the mini-white gene together and then insert them into white fly embryos. Any flies that grow up with dark eyes should also have the test gene. To allow even further control, scientists attach DNA that acts as a heat activated switch to the control gene. They can then turn on their target gene whenever they want by heating up the flies.

Now being able to flip a switch in an animals genetics is already pretty cool but now we get to the interesting part. Unknown to scientists, the heat activated switch activates genes on both sides of it. This means that after heating both the target gene and mini-white suddenly flood into the fly. This influx of mini-white produces some rather odd effects. To quote from Zhang and Odenwald, the scientists that noticed this:

[After heating], transformant males displayed their wings in a spread outward and upward position. Close examination of these males revealed that many had protracted phalli. … Coincident with the extended-wings posture was the onset of vigorous male-male courtship.

The picture to the right shows some of this courtship. The arrow points to a poor ignored female. Again I think the researchers describe the courtship best:

Chain leaders frequently courted members of their own chains, creating courtship circles and lariats. The male-male courtship activities included touching partners with forelegs, unilateral 90° wing extensions (a display that was followed by the extended-wings posture), licking the partner’s genitalia, and curling the abdomen to achieve genital-genital contact. While participants repeated their courtship routines multiple times, no repelling signals were detected-i.e., wing flicking or face kicking.

Since this was a pretty odd phenomenon, Zhang and Odenwald decided to investigate a bit further. As shown in the picture to the left, they looked at heated normal flies (left), heated mini-white flies (middle) and non-heated mini-white flies (right). Only the heated mini-white flies form the conspicious homosexual chains (the arrow points to females hiding in the corner). To test for pheremones, they tried pumping air from the homosexual bottles to the non-homosexual bottles and switching bottles but nothing happened. Interestingly, they found that even non-modified males would eventually join in the homosexual activities if most males (> 80%) in the bottle were participating mini-white flies. But that was likely a behavioral side effect and didn’t really help explain what was going on. They tried adding or removing different target genes to the mini-white and heat switch DNA but that did not change the results. They tested the children of homosexual flies and found that the homosexual trait associated with whichever chromosome had the inserted mini-white gene. They even fed mutagen to mini-white flies that altered the DNA sequence of mini-white and found that these broken mini-white flies did not exhibit homosexuality. So they are pretty sure they know that abnormal production of min-white can trigger homosexual behavior.

But they are unsure why a pigment producing protien could have such obvious behavioral effects. Interestingly, white protien is also important in transporting trytophan (yes the Thanksgiving turkey sleepiness protien [although that's mostly a myth]). A decrease in tryptophan has been observed to cause male-male mounting in rats and rabbits. In addition, serotonin (a product of trytophan) depleted cats also exhibit homosexual behavior. This led Zhang and Odenwald to hypothesize that abnormal influx of white gene expression was causing a depletion of tryptophan and serotonin and leading to homosexual behavior although this still needs further investigation.

So this was a pretty cool and obvious demonstration of how genes, molecular pathways and behaviors are tied together both in a single animal and over quite different species (and how can you not like a paper describing “courtship chains and lariats”).

References

S.-D. Zhang & W. F. Odenwald 1995. Misexpression of the White (w) Gene Triggers Male-Male Courtship in Drosophila. Proceedings of the National Academy of Sciences 92:5525-5529

The sound is half the fun so don’t forget to turn up your speakers. It seems like it must be a part of some research project with the fancy recording set up but I’m not sure who made it. Anyway it seemed pretty cool, so I took a quick look at the literature to see what was going on.

At first glance, it looks like the spider is making the noise with his front legs but it turns out that, according to research by Noordam, he is actually using a specialized hardened region on the bottom of his abdomen to bang on the ground at the same time he moves his arms (At third glance, it looks like he’s not really hitting the ground with his abdomen. See the update below.). If you look closely on the video you can see his tail end moving up and down in time with the sounds.

Rypstra, Wieg, Walker, Persons found female spiders are more likely to copulate if the male does more arm and body shakes. On the other hand, the male is more likely to work harder at his jitterbug if he can detect pheromones indicating the female has not yet mated. Next time I see a couple spiders together, I’m going to be looking for dancing.

Update

Dale Hoyt left a helpful comment that points out that the abdomen isn’t actually touching the ground when when the sounds are being made. I had assumed it was a trick of the lighting but looking closer now, there really doesn’t appear to be any contact. Luckily he suggested the search term “stridulation” (a shrill grating, chirping, or hissing sound made by rubbing body parts together) that produced much better results from the literature. The video may have been from (or based on a) study by Elias, Mason, Maddison and Hoy where they studied the vibrational aspects of spider dancing. Their experimental setup sounds a lot like what’s in the video:

The arena substrate floor for courtship was a sheet of graph paper attached to a square cardboard frame (60 cm×45 cm). Females were tethered as above [anesthetized with CO2 and attached to a wire with low melting point wax], and the male’s seismic signals recorded using a piezo-electric sensor placed directly underneath the tethered female.

Didn’t seem to bother the male much that she was unconscious and restrained. Anyway, the researchers found three different types of seismic signaling and labeled them (using highly technical terminology): thumps, buzzes and scrapes. They made a really cool figure that demonstrates each of the types:

Top panels show body positions, with numbers (1–5) illustrating movements of the forelegs and abdomen. Middle panels show the position of one of the forelegs (mm above the substrate). Bottom panels show the oscillograms of the seismic signals.

Thump signal: Front legs come down (1–2), contact the substrate and quickly move back up (2–3). Shortly afterwards the abdomen is pulled back and released, and the abdomen ‘rings’ at 58.3 Hz (4–5). Thumps are broadband signals with peak frequencies at 203 Hz and 1203 Hz. Production of signal corresponds with the percussive contact of the front legs against the substrate (1–2) and movements of the abdomen (4–5).

Scrape signal: Abdomen moves up (1–2) and shortly afterwards the front legs come down (2–3). Scrapes occur in groups with a frequency of 5.7 Hz. Scrapes are broadband signals with peak frequencies at 230 Hz and 550 Hz. Production of seismic signal corresponds to movements of the abdomen.

Buzz signal: Front legs come down (1–2) as the abdomen oscillates at 65 Hz (1–2). This signal has a fundamental frequency at 65 Hz with several harmonic frequencies (130 Hz, 195 Hz and 260 Hz). Production of seismic signal corresponds with movements of the front legs and abdomen.

[Edited slightly]

Elias et al. found that thumps came from the front legs impacting the ground, scrapes were produced by rubbing together a set of bristles between the head and body, and buzzes were made by the spider vibrating its body. They note that their research species (Habronattus dossenus) is the only species known to produce all three of these signals. It sounds like the spider in the video does all three of these so I guess that means it’s a H. dossenus.

In a follow up study, Elias, Hebets, Hoy and Mason investigated the results of muting the males by using wax to connect the spider’s head and body. They found females were more likely to mate and waited less time before mating with vibrating males. In addition, many of the muted males were eaten before getting a chance to mate.

I’m glad I finally tracked down the rest of the story (I hope). It turns out that some spiders bang their abdomens against the ground but the spider in the video is actually do a much more complex dance. Spider sure have some interesting mating patterns.

References

A. P. Noordam. 2002. Abdominal percussion and ventral scutum in male Euophrys frontalis (Araneae: Salticidae). Entomologische Berichten, Amsterdam. 62:17-19

A. L. Rypstra, C. Wieg, S. E. Walker & M. H. Persons. 2003. Mutual mate assessment in wolf spiders: differences in the cues used by males and females. Ethology. 109:315-325

D. O. Elias, A. C. Mason, W. P. Maddison & R. R. Hoy. 2005. Seismic signals in a courting male jumping spider (Araneae: Salticidae). Journal of Experimental Biology, 206:4029-4039

D. O. Elias, E. A. Hebets, R. R. Hoy & A. C. Mason. 2005. Seismic signals are crucial for male mating success in a visual specialist jumping spider (Araneae: Salticidae). Animal Behaviour. 69:931–938

Thanks to Harley for showing me the video

(Another) Update: TheBrummel confirms that the video came from Dr. Madisson or his group and points to a bunch of additional courtship videos of jumping spiders.

Spiders males are often cannibalized by their mates after sex. Spiders have two penis-like organs, called pedipalps, which usually break during sex meaning male spiders can only have sex twice. I wasn’t going to write about anymore spider sex but I came across a couple articles about the adaptations that can occur since males with no remaining pedipalps males are evolutionary useless. Often females help their mates find purpose by using the male as dinner. Scientists had thought that this was an example of competition between the sexes with the large female taking advantage of the undersized male (like the picture to the left). Sort of a male spiders are from Mars, female spiders are from Cannibal World Centauri 6. But in 1996 M. C. B. Andrade noticed that males of the redback spider actually perform a difficult somersault maneuver just to position their bodies in prime eating position (her video).

This self sacrifice was at odds with the common idea that the females were taking advantage of the unfortunate male. Perhaps there was some sort of evolutionary benefit to make the male want to be eaten. One possibility was that by feeding the female the male is helping his future children. But after Andrade calculated that males were only 1.5% of the mass of a female and only 2.5% the mass of an egg sac and found no increase in egg sac mass after cannibalistic matings, this possibility seemed unlikely. The other possibility was self-sacrifice either increased the male’s proportion of the offspring or prevented other males from mating. Female spiders appear to be the deciding partner for when copulation stops (being 50 times larger will do that). Andrade found that female spiders began eating their mate at the beginning of sex and continued chewing on him throughout. This snacking distraction allowed the sex to last more than twice as long as with non-suicidal males (25 minutes if you’re curious). Since longer sex results in fathering higher proportions of the offspring, this longer sex should result in sacrificial males fathering approximately two times as many children. In addition, virgin females who ate their mate were less likely to accept a second suitor.

These benefits to a male for offering himself up for sacrifice during sex were good but since female spiders have two sperm receiving organs, male spiders that sacrifice themselves on their first mating are potentially leaving other males a crack at half of the offspring. Andrade (with Gu and Stoltz) noticed that many male redback spiders constricted their abdomens prior to mating and thought that this might be an additional adaptation to make their self-sacrifice even more effective. Pictures from the article show the constriction in action:

On the left is an unconstricted male prior to courtship, the middle shows a constricted male with W indicating a decrease in width and L indicating length, and on the right is a wounded male with haemolyph (spider blood) dripping from a wound. Line 1 indicates the usual amount of abdomen eaten after one mating and line 2 indicates the amount after two matings. Arrows in all pictures indicate the location of the constriction and the black scale bar represents 1 mm.

To see what the effect of this constriction was, the researchers teased males with a female until their abdomen constricted. Then they grabbed the males and cut off pieces from their abdomen corresponding to the amount a female would eat after one mating (below the constriction) or after two matings (above the constriction). A control group had pieces amputated without any preparation. Many of the control group and constricted males cut above the constriction died quickly. Constricted males cut below the constriction were able to survive longer. When presented with a female, only about 20% of unconstricted males and males injured above the constriction were able to perform while 73% of the constricted males with one mating’s worth of damage managed to mate. The redback spider appears to have developed a specialized internal tourniquet for sacrificial mating and can even mate again after having half it’s abdomen chewed off. That’s one determined spider lover.

Foellmer and Fairbarn found an even more suicidal spider, Agriope aurantia. They observed that males of this spider die after their second mating even if the female does not attack them. To rule out fatalities caused by pedipalp breakage, the researchers chopped off spiders’ pedipalps themselves but did not observe this spontaneous death. All their spiders’ hearts appear to stop after their second pedipalp is inflated. In fact, they even observed one desperate male returning for a second round of spider loving who mistook the corpse of a mealworm stuck in the web for the female and copulated with the carcass. Even this confused spider died after its bout of misguided sex. Foellmer and Fairbarn suggest that the dead male carcass may form a copulatory plug preventing or delaying other males from mating.

Evolution can bring about some funny adaptations but it’s interesting to see researchers piecing together what the underlying causes are. I guess if you have to go, you might as well go happy (and while increasing your evolutionary fitness) although I wouldn’t mind skipping the being eaten alive by my mate part.

References

M. C. B. Andrade. 1996. Sexual selection for male sacrifice in redback spiders. Science. 271: 70-72

M. C. B. Andrade, L. Gu and J. A. Stoltz. 2005. Novel male trait prolongs survival in suicidal mating. Biology Letters 1: 276-279

M. W. Foellmer and D. J. Fairbarn. 2003. Spontaneous male death during copulation in an orb-weaving spider. Proceeding of the Royal Society of London B. (Suppl.) 270:S183-185

When fertile, females of this species wait outside the nest each night waiting for a flying male to show up. When a male flies in, he courts her a bit and then they mate. After the successful coupling, the two remain stuck together while the female drags her suitor inside the nest. She then curls around and bites the males abdomen in half, leaving the male to die while she walks off with his genitals and the lower half of his body. Since this seems like a rather strange thing to do, two researchers (Moonin and Peeters) decided to investigate whether this amputation acted as a rather gruesome copulation plug preventing other males from mating. They found that other males were unable to mate while the severed body of their rival was blocking access and that by the time the female removed the male pieces about a half hour later she was no longer interested in sex. The female ants were never observed mating again.

While this may at first glance seem pretty detrimental to the male, males have little chance of finding another fertile female and the payoff for a successful mating is offspring for the entire life of the female so the male is well rewarded in the evolutionary sense although he doesn’t look too happy in this sketch of the female about to separate him from his lower half.

The sketches in the article were interesting but I had been hoping for pictures. Luckily, Monnin (the lead author) has a website covering his many studies of the queenless ant and includes the pictures the paper’s sketches were based off of and many other cool pictures.

If you were wondering what exactly is going on in the picture above, the biologists Allard, Gobin, Ito, Tsuji and Billen set out to answer your question. They decided to catch a similar species of ants in the act, cut a thin section out of the center of them and see how everything was connecting.

Their caption left me looking for a dictionary so I’ve inserted definitions in []‘s:

Longitudinal section through copulating pair of Diacamma sp. showing male aedeagus [the whole male reproductive parts on the end of the abdomen] inserted inside female genital tract, and spermatophore (SP) [a packet of sperm] inside oviduct [passage from ovaries to outside]. Arrow points at strand connecting spermatophore to male gonopore [hole where sperm comes out]. Note cross section of sting (S), which is directed sideways by female during copulation. Scale bar: 1 mm.
Fig. 2. Schematical representation of fig. 1.
Fig. 3. Detail showing volsellar digitus (D) [bottom part of claspers for holding onto female] and cuspis (C) [top part of claspers for holding onto female] of male clasping the last sternite [the tail end of the abdomen] of female (arrow) during copulation. Scale bar: 100 um.
B: bursa copulatrix [insect vagina]; C: cuspis; D: digitus; P: inflated penis; PV: penis valves; S: sting; SP: spermatophore; VS: vesicula seminalis [sperm storage].

You may be wondering how they could cut such a thin slice out of a pair of ants. It turns out they fix the ants in place by submerging them in a clear plastic and then cut a tiny section through them with a double bladed saw. Reminds me of undergrad, when I had to do something similar when sectioning fish ear bones for aging.

If you were still curious, they also extracted the ant penis. I’m not too sure what the purpose of that was but if a trivia question ever asks how many lobes an ant penis has, we’ll now know the answer is 2.

The letters correspond to P: inflated bilobe penis; PA: paramere [case for penis when not in use]; PV: penis valve.

References

Monnin T. & Peeters C. 1998. Monogyny and regulation of worker mating in the queenless ant Dinoponera quadriceps Animal Behaviour. 55:299–306

Allard, D., Gobin, B., Ito, F. Tsuji, K. & Billen, J. 2002. Sperm transfer in the Japanese queenless ant Diacamma sp. Netherlands Journal of Zoology. 52:77-86