Camera Tips from an Engineer

I’ve been wondering if companies (and consumers) have been concentrating too much on megapixels. This engineer thinks yes.

Explorer 1

It was the 50th anniversary of the US’s first satellite. I didn’t know they sent a Geiger counter up in it.

Happy Face on Mars

Not a whole lot more to it just a pretty cute picture.

Asteroid Almost Hits Mars

An asteroid almost hit Mars but didn’t. Now we don’t know where it is (although this was expected).

More Mercury Images

Some new pictures from the MESSENGER flyby. I especially like the annotated image to help out people (like me) that can never seem to find what people are talking about.

Henry Rollins on Evolution

Nice to see the Liar Liar guy seems to have his head on straight.

18′ Shark Surprise

Pretty cool video of a big six-gill shark.

Potential Presidential Science Debate

Sounds like a good idea and it’d be in Philadelphia so maybe I could go.

Evolving Virtual Creatures

Interesting examples of applying evolution to create virtual creatures that fulfill tasks like fast movement, grabbing a ball and fighting each other.

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

When females of a species mate with several males, evolution can develop some pretty weird adaptations in males competing to fertilize the egg. More numerous, faster or cooperative sperm can improve the chances of their sperm reaching the egg first. Another alternative is to try to prevent other males from mating with that female.

As a way to interfere with other males, many species develop sticky semen to form copulatory plugs blocking other sperm access to the egg. I had heard of this before but what I didn’t know was that some insects have taken this method to an extreme and actually leaves pieces of their genitals behind in the female. These pieces had been shown to protect the males’ sperm against competition by blocking rivals from mating with the female. Similar genital breakage had been observed in spiders but since spider females like to eat their mates and males have two penis-like organs, called pedipalps, scientists debated whether a spider sacrificing one of his genitalia could be a sort of quick release to allow the males to live another day and mate again.

So the authors of this paper (Nessler, Uhl and Schneider) set about solving this question. They figured that if genital damage was a survival tactic then virgin males, who have a second pair of genitals in reserve, should damage their pedipalps more often than males who had already lost one genitalia and have nothing to gain (evolutionarily speaking) by surviving with no genitalia. On the other hand, if broken genitals function as copulation blockers then duration or probability of mating should decrease after a female mates and is stuck with male genital pieces inside her.

Virgin males did appear to be trying harder to escape post-copulatory predation with virgin males cut and running after about 6 seconds and one-genitalia males sticking it out for a lengthy 25 seconds. This resulted in 35% of virgins escaping while only 5% of their more seasoned counterparts avoided post-coital dining. Yet even with these differences in behavior, the researchers still found that genital damage was not significantly different between virgin and one-pedipalp males. This suggests that sacrificing one’s genitals does not make one more likely to escape a cannibalistic female.

On the other hand, the researchers found that males mating with females containing pieces of genitalia copulated about half as long and were 75% less likely to break off their genitals as males mating with either virgin or genitalia-free mated females. Since longer matings increase the chance of that males sperm being successful, genital breakage appears to be a form of copulation plug that increases the evolutionary fitness of that male.

For the curious, the article also included a picture of a) female spiders, b) male pedipalp genitalia, c) a piece of male genitalia stuck in a female, and d) a close-up view of the male pedipalp showing the part that breaks off.

I was surprised to see how small the broken piece of pedipalp was. It’s kind of amazing that losing that little piece of tip results in sterility for that genitalia and blocks other males. Then again, I suppose any genital breakage is too much genital breakage.

References

S. H. Nessler, G. Uhl and J. M. Schneider. 2007. Genital damage in the orb-web spider Argiope bruennichi (Araneae: Araneidae) increases paternity success Behavioral Ecology 18:174-181

I had always pictured sperm as little tadpoles but it turns out that rodent sperm actually have some rather nasty looking hooks on their heads. Scientists were not sure what the purpose of these hooks was. Some guessed they were just for aerodynamics while others had observed sperm using their hooks to link up and form cooperative groups.

This paper theorized that sperm cooperation would occur more in mice and rats where the sperm of different fathers had to compete against each other. In rodents where females were promiscuous, sperm from the same father, since they are on average 50% genetically identical (the same as brothers), would be evolutionarily selected to cooperate with each other. Promiscuous females present many problems to males trying to pass along their genetic material. One other ways that males compete is by volume of semen and number of sperm (the more players in the game, the better the chance of winning). This means that males in species where many males mate with one female will tend to be selected for big testicles. The authors of this study used testicle size as an index of female promiscuity and found that in more sexed-up species sperm are in fact hookier and more cooperative.

To back up their results, the scientists measured the speed of sperm trains vs. individual sperms. They found that in rats sperm trains are about 30% faster but in mice the sperm trains are slower. They guess that sperm trains also provide greater thrust to help move through viscous fluid so mice sperm may still perform better in trains.

A pretty cool study and a nice quick read at only 3 pages. Before today, I had no idea sperm cooperated. That’s why I like biology, there’s always something surprising and interesting to learn yet it’s all still tied together by evolution. Now if you’re anything like me, you probably want to see one of these sperm conga lines. I know I would have been pretty disappointed if the article didn’t have any pictures. So here’s the money shot:

If pictures aren’t enough, there’s also a video.

References:

By Hook or by Crook? Morphometry, Competition and Cooperation in Rodent Sperm. S. Immler, H.D.M. Moore, W.G. Breed, T.R. Birkhead. PLoS. 2007.