Tag Archives: sex

Twisted wings, twisted sex

Some time ago, I wrote a post on here. It was reasonably popular, but I deleted it for foolish reasons. However, I no longer care about those reasons, so now I’ve edited it slightly and it’s back! Enjoy? ENJOY!

If you’re the type of person who frequents animal behaviour blogs, you probably love yourself some animal sex posts (I sometimes feel like I should put some sort of “it’s science so it’s not weird OKAY” disclaimer or something here, but you should be used to it by now… and also I get so many hits from people googling ‘dolphin rape’ that I don’t think it would really make any difference). Such a predilection for tales of animal mating systems will mean you’re most likely well acquainted with the ornaments, weapons and displays that males (for the most part) of a huge variety of shapes, sizes, and species use to improve their chances of mating. Perhaps you’ve tired of pictures of peacock trains and scarab beetle horns; those videos of jumping spiders shaking their curiously colourful buttflaps (erm, you should get used to this level of technical terminology) or bowerbirds prancing around their ornately decorated nests just don’t cut it for you these days.

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(I’m really sorry to the people who took the original photographs that I have ruined there)

Even Stephen Stearns doing his sage grouse impression isn’t enough.

Give us more, you cry: we need more sexual dimorphism! More weird behaviours! Different body shapes! Life histories! Displays, weapons, ornaments, EVERYTHING!

Well, I was flicking through my copy of Thornhill and Alcock’s seminal (hurr hurr) work, ‘The Evolution of Insect Mating Systems’, and happened upon a short passage describing the Strepsipteran order of insects. ‘Strepsiptera’ translates as ‘twisted wing’, but the curious wing shape that gives these insects their name is not the main reason that they piqued my interest. No, it’s because the sub-order Stylopidia has some extreme sexual dimorphism going on: only the males actually grow wings, legs, antennae, mouthparts, eyes, or any of the traits that we associate with adult insects; the females, meanwhile, have none of these features. Male flight is required because they need to find a female to mate with, and quick, because these guys only live for a few hours after emerging as adults.

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Male (left) and female (right) Xenos vesparum.

So while males are flying around in a desperate sexual frenzy, what are their rather curious female counterparts doing? And where are the females, if they have no means of locomotion? The Strepsiptera are ‘obligate parasites’, meaning that some part of their life cycle must take place within a host animal. Hosts include a whole variety of different insects, including silverfish, crickets, stink bugs, wasps, bees, flies… In one particular family, the Myrmecolacidae, males parasitise ants while females parasitise Orthopteran insects. Female Strepsipterans never leave their hosts, instead sitting pretty – at least, about as pretty as a wingless, eyeless, mouthless parasite can get – and waiting for a male to come along. To move things along, virgin females help out by releasing a pheromone that males can use to home in on a potential mate before suffering an early death.

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Females poking out from betwixt the thoracic segments of a Polistes wasp.

Well, you may say, that is some fairly intense sexual dimorphism. But is that all? Males have wings and fly about? It’s not really setting the world on fire. I mean, there are those huge beetles which climb giant trees and throw each other off branches in order to reach the demure, hornless female at the top – it’s not even as good as that, is it?

Oh, ok. I get it. People are immune to weird sexual dimorphisms in insects these days. Fur and feathers, that’s what you want. Maybe if it were a lion with wings flying around briefly in search of a weird giant worm thing to hump, then you’d be impressed? Also, the giant no-face lion-worm would probably live in a giraffe’s bum. Then you’d care. Then you’d ALL care. You want to know something else about the Stylopidae? Well, there’s some controversy over how they mate, but one of the main hypotheses is that mating occurs via TRAUMATIC INSEMINATION.

…also known as HYPODERMIC INSEMINATION.

Why is it called that? Well, males have a pointed, hook-like aedaegus, which is an appendage used to transfer sperm to the female. It’s a bit like a penis, although in deference to this particular method of reproduction, let’s just call it a STABBYCOCKDAGGER*. The male, without so much as a by-your-leave, simply shunts his STABBYCOCKDAGGER straight into the female, releasing sperm into her body cavity.

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STABBYCOCKDAGGER

This isn’t controversial because of the process itself – after all, traumatic insemination is well-characterised in various other species (in particular, the Cimicidae – or bedbug – family: one of the most interesting talks I’ve ever seen was Mike Siva-Jothy presenting some of his work on bedbugs at the ESEB conference in Tuebingen, 2010) – but more due to the lack of detail as to how or why this might have evolved. The reasons for such an adaptation include the following: bypassing ‘mating plugs’ (in many species, a male can inject a secretion into the female’s reproductive tract, ‘gluing’ it closed, or can even break off its penis – or STABBYCOCKDAGGER – in the female so as to block access by rivals); getting round female resistance to mating; eliminating any time that would otherwise be required for courtship; or even in terms of sperm competition, by enabling males to deposit their sperm closer to female ovaries. However, studies indicate that short-lived Stylops males are unlikely to encounter many competitors, and the females stop producing the attractive pheromone just a few days after mating (so the period during which she may attract males is reasonably brief). A study using scanning and transmission electron microscopy in Xenos vesparum failed to either support or rule out traumatic insemination as a mating strategy, but did provide further evidence (adding to studies dating back to the 1840s) that males could simply be using their STABBYCOCKDAGGER to spread sperm fluid into the female’s ‘ventral canal’, which sounds like a much more soothing process. In fact, a ‘spread into a ventral canal’ sounds like a nice holiday that you might take in the Cotswolds. It is possible that this latter method was actually the ancestral form of mating, and that traumatic insemination has developed more recently – potentially so as to bias paternity.

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Yes, I know that isn’t a face, it’s the female’s ventral canal. POETIC LICENCE, YEAH?

Are you happy now?

Happy?, you might ask, happy that you just did the text-based equivalent of screaming STABBYCOCKDAGGER in my face, over and over again?

Oh. Well, then you might be interested to hear about ‘hemocelous viviparity’. Doesn’t sound so bad, right? It’s just that the eggs hatch inside the female, and the offspring eat their mother from the inside out; the larvae then escape from the host and use tiny little legs to run around and find new hosts.

Also, in the case of X. vesparum, the host is a wasp named Polistes dominulus; parasitised female wasps become sterile, inactive, and leave their colony to form aggregations where the parasites can perform their curious mating. Cappa et al. describe them memorably as “idle, gregarious ‘zombies’”. There is also evidence that ants parasitised by other Strepsipterans tend to linger on the tips of grass stems, even in bright sunlight, which may increase the chances of males finding a mate, or even just give the males a good start when emerging from their own host. Such behaviours may be due to our twisted little parasites somehow manipulating their hosts to their own ends.

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To conclude: extreme sexual dimorphism, traumatic insemination, cannibalisation of their own parents, and turning hosts into sterile zombies? Safe to say these strange little flies do a little bit of everything. And maybe, just maybe, you’re glad that creatures the size of lions don’t behave like this after all.

*I asked on Twitter whether people had a preference towards either ‘STABBYCOCKDAGGER’ or ‘STABBYCOCKNEEDLE’. The results were overwhelmingly in favour of ‘STABBYCOCKDAGGER’.

References

Wojcik, D.P. (1989). Behavioral interactions between ants and their parasites. Florida Entomologist, 72(1), 43-51.

Hughes, D. P., Kathirithamby, J., Turillazzi, S., Beani, L. (2004). Social wasps desert the colony and aggregate outside if parasitized: parasite manipulation? Behavioral Ecology, 15(6) 1037-1043.

Beani, L., Giusti, F., Mercati, D., Lupetti, P., Paccagnini, E., Turillazzi, S. and Dallai, R. (2005). Mating of Xenos vesparum (Rossi) (Strepsiptera, Insecta) revisited. J. Morphol., 265: 291–303. doi: 10.1002/jmor.10359

Beani, L. (2006). Crazy wasps: when parasites manipulate the Polistes phenotype. Annales Zoologici Fennici., 43(5-6), 564-574.

Cappa, F., Manfredini, F., Dallai, R., Gottardo, M., Beani, L. (2014). Parasitic castration by Xenos vesparum depends on host gender. Parasitology, 141(8), 10808-7.

All strepsiptera images modified from Beani et al., 2005.

Other images used under a creative commons licence.

Additional links

There is a flickr group for all things Strepsiptera; not many pics, but they are quite wonderful.

Gregory Paulson has a nice bunch of SEM images of strepsiptera here.

Immediately prior to my posting this (well, the first time around), Sam Evans asked on Twitter whether I was writing about bed bugs, and sent me this cartoon. It’s basically a ‘Simpsons did it!’ for anyone blogging about traumatic insemination. THANKS GUY.

Goodbye to #stabbycockdagger

Stabbycockdagger is BACK, but in a new location! Go here: https://tomhouslay.com/2014/12/30/twisted-wings-twisted-sex/

STABBYCOCKDAGGER

Due to reasons too numerous and boring to go into, I had deleted this post, but now I have decided that I don’t care about those reasons, so the post is back. But somewhere else. You should go and read it. But maybe you want to read something else instead? Or AS WELL? Why not try this post on beetle sex: ‘horny decisions, sneaky f**kers, and the importance of balls‘?

If you’re set on some other stabbycockdagger action, then head on over to the Breaking Bio website to find some of our podcasts…  Episode 10 features Nik Tatarnic talking about traumatic insemination in plant bugs, while Episode 11 is an interview with Prof Mike Siva-Jothy, whose research involves work on some very stabby bedbugs. You can also get the Breaking Bio podcasts on iTunes.

The Praying Mantis: an unfairly maligned sexual cannibal?

Recently, probably due to the incredible macro photography of Igor Siwanowicz that I linked to recently, I’ve become rather obsessed with mantises. Before then, I’d paid very little attention to these weird creatures, and will admit to having been mildly terrified of them in the past. This stemmed from an unfortunate incident many years ago, when I tried to brush one off the door handle of a holiday apartment, only to learn that they can fly – and can propel themselves rapidly towards a human face. The neighbours came rushing out because they had heard what they assumed to be the cleaning lady screaming. Anyway, possibly due to this, I thought that there was just a ‘praying mantis’, and had no idea that the order could range from this:

Mantis by Igor Siwanowicz

to this:

Mantises by Igor Siwanowicz

…and many more incredible shapes, sizes and colours. The displays that a mantis can produce when threatened are really quite incredible, and I have been told that they are great for use in undergraduate practical classes. Mantises are apparently relatively short-sighted, and so two can be placed on opposing ends of a mounted piece of string, and it will suddenly become very clear when they notice each other. Unfortunately, the ‘loser’ will signify defeat by flying off to a remote corner of the classroom, delaying the end of the lesson as the tutor (or, more likely, a hapless TA) climbs up to gingerly retrieve it. Here are two videos of different mantis displays, the first relying on sound and wing movement, the other on the large peacock-style eyes on its wings:

So, what wonders does the mantis have in store for the intrepid sex researcher? Rather distressingly, the answer is sexual cannibalism. Males are smaller than females, which have voracious appetites and can eat up to 16 crickets per day, and so put themselves in a rather precarious position both prior to and during copulation. There is a lot of evidence, including the video below (complete with rather breathless commentary), of females devouring their mates during intercourse, but a controversy remains over the function of this.

Does the male, as in the case of the redback spider, allow himself to be eaten in order that the bearer of his children has a large meal when times are scarce, therefore helping to furnish his offspring with added nutrition? Some other insects allow females to ‘nibble’ on them during sex, thus lengthening the duration of copulation and enabling more sperm to enter the female and fertilise the eggs – could it be that this is a poorly-judged version of this adaptation? The latter seems unlikely, as females generally remove the head first, and although the body continues its final mindless act, studies have shown that ejaculation tends to happen more rapidly after decapitation, if at all.

A 2010 study by Kate Barry, of Macquarie University in Sydney, Australia, investigated the state of female nutritional status on mating dynamics in a sexually cannibalistic praying mantid. Previous studies have shown that scramble competition is important in these mating systems, and thus males are selected for their ability to detect and locate females. Given that each copulation holds the risk of death for the male (and the inherent fitness costs of this occurring), and that condition has been shown to be positively correlated with fecundity in female mantises, then theory would predict the evolution of strong male choice for females in good condition. A female in good condition is not only likely to have more eggs, making her a good choice for a male wanting to ensure that he makes the most of the copulation should it be his last, but is less likely to be starved of food. Interestingly, Barry found that long-distance male attraction to females is somehow linked to female fecundity, with ‘low condition’ females still being attractive to males as long as they had a base level of fecundity. Nutritional status seemed to have no bearing on male choice, and so it would appear that females may produce a pheromone that indicates fecundity. Indeed, in a species of cockroach there exists a relationship between ovarian development and pheromone production, meaning an honest signal is produced to demonstrate a female’s egg-bearing capacity.

It would seem, then, that the unfortunate decapitated males may be those that were unable to secure copulation with high-fecundity females, and sacrificed themselves in a final desperate attempt to pass on their genes. Or perhaps, as can happen in many species, they simply read the signals wrongly.

Read KL Barry’s paper here: http://dx.doi.org/10.1016/j.anbehav.2010.05.024

Note: since becoming more interested in the mantis, I’ve even come so far around as to having decided to place an order with Ornamental Insects for a ghost mantis, after listening to their interview on John F Taylor’s Reptile Living Room radio show. However, you may be able to tell from the picture below that, perhaps, I haven’t quite conquered my fear outright…

Ghost mantis by Ornamental Insects