Posted 1 year ago

SHUTDOWN

Just a quick note to say that I will no longer be posting new content here, but don’t worry, I shall try to keep posting weird insect sex stuff over at my blog! And if you want to see/hear me talking about insect sex and a whole lot more, be sure to check out the podcast that I co-host with a bunch of other biologists, Breaking Bio.

Posted 2 years ago

I know, I know. Despite the nature of this tumblr, I am always cautioning against anthropomorphising. But some male water striders really can be total dicks.

In many species of animals, males court females with visual or acoustic displays that may also attract predators - the cost to fitness of potential predation is balanced against the fitness benefits of having more sex. After all, there’s no point living if you’re never going to have sex (that’s another life lesson for you all right there).

However, in this particular species of water strider, Gerris gracilicornis, males actually attract underwater predators by tapping the water. Why the hell would they do this? Well, males want to mate with as many females as possible - this means they have the greatest chance of fertilising lots of eggs and having lots of offspring, and so ensuring that their genes get to the next generation. For females, however, one mating is enough - anything more than that is unnecessary, and can actually be damaging. This discrepancy in the ideal mating rate for males and females is just one example of what is called ‘sexual conflict’.

Sexual conflict can create evolutionary ‘arms races’ between males and females, and this species is no exception. The females have evolved a ‘shield’ over what we shall demurely refer to as their ‘opening’; males which mount them cannot actually start the mating process until the female exposes her genitalia. Oh, ladies. It was almost so foolproof. Unfortunately, predatory aquatic insects and fish are attracted to vibrations on the surface…  giving the mounting male a route for some rather serious intimidation.

A female can, of course, attempt to throw the male off her back, but this will also cause vibrations. A failure to dislodge him quickly means that death from below may not be far away. So, again, there’s a trade-off: accept the costs of unwanted excess mating, or dice with death…

Read the full paper here:

Han & Jablonski (2010) Male water striders attract predators to intimidate females into copulation. Nature communications 1(52).

Not sick of water striders? Head over to my blog to read more!

Sexual conflict driving the elaboration of a sexually dimorphic trait.

Original image copyright Chang S. Han.

Posted 2 years ago

That’s correct, friends – the two beetles you see in this image are both adult males of the same species of dung beetle, Onthophagus nigriventis. The chap on the right is clearly larger, and has a rather ostentatious horn extending from his thorax. This is, of course, a sexually-selected trait – horned males can use their armaments in battles over females, driving rivals away from mating sites, and even prying other males off a female whilst in flagrante. Large males with large horns are more likely to win battles, so there is a clear advantage to investing resources into weapons development.

Given that big, horned males fight rivals and guard their female partners (they may engage in the rather ungentlemanly pursuit of trapping lady beetles in mating burrows in order to have their way with them), then what the crap is going on with the guy on the left? Well, horns are expensive, and are known to trade off against morphological structures including eyes, antennae, and wings. Species of Onthophagus are well known for the size and diversity of their horns, but often these are only expressed by the largest ‘major’ males. What happens, then, if you’re a down-on-your-luck, resource-starved ‘minor’ male? Is there really any point in cashing in your precious metabolic chips for a gamble on a crappy little horn that’s never going to help you win any contests anyway? Surely there’s another strategy to be taken?

Indeed there is, and it’s called being a ‘sneaky fucker’*. While some males guard their mates, others will try to ‘sneak’ copulations with females. We now enter the realm of sperm competition: females may mate with multiple partners, so there is a battle amongst the sperm within her reproductive tract to fertilise eggs. If ejaculates are costly, males have to trade off resource investment on gaining fertilisation with investment on gaining additional matings. The more sperm ejaculated in a mating, the more eggs are likely to be fertilised - but, again, this requires resource investment. Furthermore, an increased risk of sperm competition should favour the evolution of increased expenditure on the ejaculate.

In plain English (or, at least, an approximation thereof): if you’re a big horned dude protecting a little beetle harem, then you shouldn’t be all that worried about the fertilisation aspect – after all, you should be the only one for your ladies. You want to invest in lots of mating, not lots of ejaculate. Meanwhile, as a sneak, you’ve got to make those precious moments count, and ploughing your resources into the ejaculation makes sense – it’s in the female’s interests to have a few flings behind the dung-balls, so the greater the ejaculate, the better your chances of gaining fertilisations. Of course, the best way to produce larger amounts of ejaculate is to invest more resources into testis development.

All of which leads us nicely to what I think is one of the most ingenious (albeit slightly harrowing, once you really think about it) experiments I’ve read about while studying up for my PhD. Leigh Simmons and Doug Emlen cauterised those cells on beetle larvae which produce the thoracic horns in O. nigriventis, manipulating investment by ensuring that they could not grow these weapons. The results revealed the metabolic trade-off between horn development and both body size and testis size, in line with predictions. When compared to a control group of beetles allowed to develop normally, the cauterised individuals not only grew larger in size, but also developed disproportionately large testes.

To clarify: if you’re going to sneak around, you’d better have gigantic balls.

*I’ve been told that Geoff Parker coined this phrase, but have been unable to find a reference for this, and then I ‘accidentally’ clicked on ‘images’ and.. yeah. I need to keep safe-search on in future.

References and further reading:

Simmons LW and Emlen DJ (2006) Evolutionary trade-off between weapons and testes. Proceedings of the National Academy of Sciences of the United States of America 103(44): 16346–16351.

Simmons LW, Emlen DJ and Tomkins JL (2007) Sperm competition games between sneaks and guards: a comparative analysis using dimorphic male beetles. Evolution 61(11): 2684– 2692.

Emlen DJ (2008) The evolution of animal weapons. Annual Review of Ecology Evolution and Systematics 39: 387–413.

Parker GA (1990) Sperm competition games – sneaks and extra-pair copulations. Proceedings of the Royal Society of London Series B – Biological Sciences 242(1304): 127–133.

Blatant plug: I have recently had an article published in Wiley-Blackwell’s Encyclopedia of Life Sciences online journal, which discusses life-history allocation in the context of sexual selection. You can find it at the following link, or drop me a line if you would like a copy:

Houslay TM, Bussiere LF. 2012. Sexual Selection and Life History Allocation. In: eLS 2012, John Wiley & Sons, Ltd: Chichester.

The original image is the copyright of Alexander Wild, an entomologist, photographer, and all-round great guy. You can find the original, and more of Alex’s work, at the links below:

http://www.alexanderwild.com/

http://myrmecos.net/

http://blogs.scientificamerican.com/compound-eye/

https://twitter.com/#!/myrmecos

Posted 2 years ago

Ah, the humble flower. Often surrounded by kin, potential friends and partners, yet always somehow alone. Sometimes straining in the wind for just a gentle touch, the slightest caress, yet all around surge away as one. But what happens when every time you reach out, all others move aside? What can you do when you feel there is another flower out there, one just like you, one with which to share your thoughts and dreams and aspirations and poems you wrote at high school and, most importantly, your gametes?

Just as a shy teenager, crippled with insecurities, might ask a friend to pass a message on to a girl in class, so plants may harness the power of proxy. Insect pollinators, buzzing from flower to flower with a gametic note attached, are often bribed with food rewards of nectar or pollen as part of this sexy bargain. However, in another parallel with sullen human teens, orchids despise such brazen capitalist tendencies. 

Instead, they lure these pollinators, their little sex proxies, with sweetly perfumed and brightly coloured promises of food, promises they will never come good on. But this is not deception enough for some orchids, no. In a cruel twist, they can actually mimic the sex pheromones of the female of a particular insect species, driving the males wild with lust. The orchid’s labellum even imitates the look of the seductive female, tempting the male over to attempt copulation. And as he does so, grinding away in an ultimately fruitless pseudocopulatory frenzy, the orchid gently attaches some pollen to him, to be passed on to the next player in this nefarious reproductive game.

The image above shows the wasp Neozeleboria cryptoides attempting copulation with the “bird orchid”, Chiloglottis valida. The flower mimics the sex pheromone of a female wasp so precisely that the male cannot distinguish between the mimic and the real deal. In one genus of Australian orchids (Cryptostylis), the wasp can even be provoked into ejaculating with the orchid.

You may say to yourself, why sully yourself in such a manner? Why not just pay for this service? And isn’t allowing a wasp to engage in intercourse with you to the point of ejaculation akin to a warped form of bestiality?

To which the orchid would sigh, close its black moleskine notebook, and gaze up at the Che Guevara poster on its wall. Don’t push your human morality on me, man, it says. You just wouldn’t understand.

More information on orchid pollination can be found here:

http://www.anu.edu.au/BoZo/orchid_pollination/

The original image was provided by and is the copyright of Mike Whitehead, who studies this system in Australia, and from whom I first learned all about this weird shit when we met at ESEB 2011. Check out some more of his excellent photographs of this particular species in action:

http://www.flickr.com/photos/mwhitehead/4069584187/

http://www.flickr.com/photos/mwhitehead/4069582223/

http://www.flickr.com/photos/mwhitehead/6352712129/ 

You can see more of his photography and find out about his research at his personal website:

http://michaelwhitehead.weebly.com/index.html

..or just follow him on twitter:

https://twitter.com/#!/DrSway

Posted 2 years ago

Oh, little spidey pal. We’ve all been there. Kind of.

Of course, the wolf spider Schizocosa ocreata doesn’t have to undergo the torturous embarrassment of doing the ‘wrong’ dance in a misguided attempt to court a mate, or even to win a tv show which probably isn’t fronted by Simon Cowell but I couldn’t be bothered looking that up because REALLY. Further to this, these wolf spiders employ tactics to ensure that they don’t miss an opportunity to impress females they may not have seen, but which are being courted by other males in the vicinity.

A new study published in this month’s issue of the journal ‘Biology Letters’ indicates that males of this species ‘eavesdrop’ on their rivals, as well as engaging in ‘signal matching’. If a wandering male notices that another male is performing a courtship dance, then he may well do the same; while he will incur costs due to the energetic nature of the display, this must be traded off with the potential fitness cost associated with missing a mating opportunity.

However, this isn’t even the coolest part of this study: these male wolf spiders show behavioural plasticity, where they can actually alter their courtship behaviour depending on the behaviour of others, including changing their ‘tapping’ rates based upon that of their rivals! They may be attempting to outcompete, or synchronise with those around them. To continue the tenuous link to ‘talent’ shows etc, it’s not vastly unlike those ‘flash mobs’ that were all the rage a year or two back.

Except far less shit, obviously.

Check out the research here - Clark et al (2005). Eavesdropping and signal matching in visual courtship displays of spiders. Biology Letters.

Original image stolen unceremoniously from Zen Faulkes’ blog, where you should read some cool stuff about females of this species being massive gluttons*.

*so, yeah, the spider in the picture might be a female. I don’t really know how to check spider sex. Spiders are gross anyway. HAH.

Posted 2 years ago

A chivalrous gentleman caller should always take a gift along when visiting a lady, and this often holds true in the animal kingdom. Such items are usually nutritional - perhaps wine, chocolates, a fly snatched from a spider’s web, a gelatinous substance synthesised internally beforehand - and often advertised by the male during the courtship phase. Females may then be able to assess the quality of these ‘nuptial gifts’, and shun those males who have been so rude as to turn up empty-handed.

In empidid flies, such as the dance fly Empis opaca pictured above, males usually fly in a swarm at a landmark site, holding captured prey beneath them. Females can compare the gifts available, select a male, then take the offering in order to assess it properly before deciding whether to accept him as a partner. Not only has the gift shown here secured this male a mating, but it also means that she has extra nutrition which can be used to furnish her eggs.

The world of nuptial gifts and courtship feeding in invertebrates is wide-ranging, species-specific, and often quite bizarre, so we shall be coming back to them again in future. How bizarre, you ask? Well, in the particular species pictured here, males often have success with females after having carefully prepared a balloon of willow-seed fluff, which they offer up instead of a dead fly. Perhaps this shows that they are sensitive, arty souls? More likely that they are taking advantage of a sensory bias with little adaptive value, but we all get fooled sometimes…

For further reading on this topic, I recommend Karim Vahed’s excellent 2007 Ethology review ‘All that glisters is not gold: sensory bias, sexual conflict and nuptial feeding in insects and spiders’.

Original photograph taken from http://www.wildaboutbritain.co.uk/archive/showphoto.php/photo/94766

Posted 2 years ago

Sometimes, preventing your partner from going off and pumping someone else can be a bit of a drag. It might even entail hanging out with them for a post-copulatory period (often known as ‘mate harassment’, although I kind of wish my girlfriend* would stop referring to it as that).

The males of a number of species - including the rather adorable buff-tailed bumble bee Bombus terrestris, above - have developed a handy little technique whereby they secrete a special fluid into a female’s genital tract at the end of copulation. This fluid hardens to form a ‘mating plug’. While females can expel them after a period of time, it just might be long enough that this first male’s sperm get a bit of a jump on the next guy to try his luck. It’s also thought that some of the chemicals in these mating plugs may make females less receptive to further matings for a little while!

All of which gives our plucky hero more time to go and do what he does best (e.g., watch ‘the game’, get more matings, or sting some nosy researchers in the face).

*I’m not telling her about this blog

Photograph used under a creative commons licence, and courtesy of Africa Gomez at http://abugblog.blogspot.com/