Thanks to the fine work of Cambridge’s Prof. Rebecca Kilner and her colleagues, in addition to her giving me access to her lab next year to photograph her beetles, today I have a photograph appearing in The Economist! The Kilner group have a new paper in the journal eLife that demonstrates how different levels of parental care have strong effects on offspring once they themselves have reached adulthood. I made the photograph above available via Creative Commons Attribution Licence so that it could be used in eLife, but The Economist wanted to use a different one, which they paid a licensing fee for (see below):
A popular science article getting a lot of attention right now is journalist David Dobbs’ latest offering, ‘Die, Selfish Gene, Die‘. There are a few things that don’t sit quite right with me, but I don’t feel qualified enough (or with the requisite time to read up enough on it) to comment in detail (although comments from people I know and whose opinion I respect include ‘wrong’ and ‘thoroughly terrible‘). One general problem with this type of article is that there have to be some ‘controversial’ statements to pique the reader’s interest; here, even the sub-heading claims that the content will overturn the central idea of Richard Dawkins’ famous book:
The selfish gene is one of the most successful science metaphors ever invented. Unfortunately, it’s wrong.
Dawkins has responded to this ‘adversarial journalism’ on his own blog; meanwhile, Jerry Coyne at ‘Why Evolution is True’ has written two lengthy pieces which go into rather more detail on the science:
It’s worth reading all these to get a feel for the different ideas flying around, although reading ‘The Selfish Gene’ itself (or Dawkins’ later book, ‘The Extended Phenotype’) should be on your xmas list if you don’t own them already.
I also tried to follow a twitter conversation between the likes of Richard Lenski, Razib Khan, Josh Witten, Karen James, Emily Willingham, Joel McGlothlin, Aylwyn Scally… among others… but it all got a bit too intense for me! Hopefully someone will gather those tweets together under one internet roof, but that someone certainly isn’t going to be me.
I’m pretty sure we haven’t heard the last of this, so I’ll try to keep adding links as I find them…
ps yes, ‘light reading’ is supposed to be sarcastic.
It wouldn’t be a scientific debate on Twitter without a blaze of capslock hulkspeak. SMASH LINK TO READ
‘Die, Selfish Gene, Die’ has evolved: David Dobbs has, rather wonderfully, published a revised version of his article. While I’m sure many will still take issue with the ideas contained within it, it’s fantastic that he has taken all of the criticism and comments onboard and updated his article. The original version still exists online, and I’ve changed the link at the top of this post so that it is linked there. There is also another (!) version of the revised article with links inserted by Dobbs to show his sources.
Finally (for today, at least), I just saw a great post by Sergio Graziosi on the whole affair, discussing both the public understanding of evolution and the technical points of Dobbs’ article. It’s well worth a read.
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 horn is 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. Sexual selection is all about the struggle to reproduce, and so traits are ‘sexually selected’ if their expression confers some benefit to the holder in terms of reproduction. In this case, large males with large horns are more likely to win battles with rivals, enabling them greater access to females, 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, these horns are likely expensive in terms of resources, and any energy ploughed into growing horns is not available for investing in other traits – indeed, horns 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 (i.e., the more likely that your little swimmers are going to be racing against some other dude’s, the more investment you should be making in ensuring your ejaculate is the biggest and best it can be).
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 (yes, this is another Doug Emlen-related post) 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. When compared to a control group comprising beetles allowed to develop normally, the cauterised individuals not only grew larger in size, but also developed disproportionately large testes. These results revealed the metabolic trade-off between horn development and both body size and testis size, in line with predictions from evolutionary models of ejaculate expenditure.
But what does this mean for the two beetles at the top of the page? Well, there’s a general tip here: 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 during googling I accidentally clicked on ‘images’ and.. yeah. I need to keep safe-search on in future.
This post is a slightly modified version of an earlier entry on my ‘Nature!Sex!TopTips!‘ website.
Research blogging reference:
Simmons, L., & Emlen, D. (2006). From the Cover: Evolutionary trade-off between weapons and testes Proceedings of the National Academy of Sciences, 103 (44), 16346-16351 DOI: 10.1073/pnas.0603474103
Blatant plug: I am really interested in the intersection between sexual selection and life-history allocation – the way that individuals invest their resources – and (along with my long-suffering supervisor) have written an article on this topic for Wiley-Blackwell’s Encyclopedia of Life Sciences online journal. You can find it at the following link, or drop me a line if you would like a copy:
Recently, I have joined with some colleagues from around the world in a new venture which combines several things that I feel rather passionately about: science communication, trying to get over my crippling self-confidence / public speaking issues, and generally chatting shit about insect humping. That’s right, there’s a new podcast in town! It’s called Breaking Bio, and it all stemmed from the mind of Steven Hamblin, the guy who shot to fame after taking various reporters and commentators to task in the ‘dolphin rape edition‘ of his blog. Here he is in all of his glory:
I should probably mention that the blog post in question was actually a rather sober discussion of science journalism and sensationalism in the mainstream media, but hopefully the previous paragraph and accompanying picture will have done the desired damage to Steven’s reputation.
The podcast itself is a light-hearted chat between a bunch of nerds about various topics: recent discoveries, big topics in the scientific community, conferences, weird insect genitalia… all of the things you’d expect, and maybe more (especially when Bug Girl is around!)
We are about 6 episodes in just now, so there’s plenty for you to catch up on – there’s also something of a rotating cast of characters to get acquainted with:
Steven Hamblin – yeah, the dolphin rape guy in the underpants. Not only does Steven have to try and figure out times for various people across the globe to chat for an hour or so once a week, he also has the job of keeping us on a vague topic, and the frankly horrendous task of editing it all into something coherent afterwards. Oh, and he’s a postdoc in Australia doing extremely hard maths about zombie caterpillars.
Morgan Jackson – entomology PhD student at Guelph, awesome photographer, and fly lover. But not like Steven is a dolphin lover. This is a purer love.
Rafael Maia – a PhD student at the University of Akron, Rafael does some unbelievably cool work on the evolution of bird feather colouration. He’s also, like, Mexican or something. I dunno.
Bug Girl – with a PhD in entomology and a reluctance to reveal her true name, Bug Girl is something of an enigma. She’s like a superhero, albeit one whose superpower is talking non-stop about insect genitalia and how Spiderman should really spooge web out of his butt and suchlike. Basically, she’s fucking brilliant.
Crystal Ernst – another entomology PhD student and awesome photographer, Crystal also blogs as ‘The Bug Geek’, no doubt invoking her own ire as she struggles to contain her geekiness solely to the order Hemiptera.
Michael Hawkes – unfortunately, Michael is doing a PhD in something which can be described as ‘applied’, seeing as it might be of practical use one day, so I’ll be damned if I’m going to lower myself to writing about it here. He’s at the University of Exeter. He also MAKES ME SICK.
We’re also hoping to extend this list to a few more characters, with hyper-enthusiastic science goblin Lauren Reid lined up to join us in future, the fabulous Bug Chicks stopping by, and PROPER GROWN-UP REAL SCIENTIST GUY Rob Brooks having been cajoled into making a guest appearance. Rob shall likely be discussing his book, ‘Sex, Genes, and Rock & Roll‘. Hopefully we can also get him to respond to what is probably my favourite ever online comment, left underneath his article on cats and toxoplasmosis:
…but perhaps his cameo appearance on the podcast will make him feel better? Either that, or we’ll send him spiralling further down into a pit of despair.
But where can I watch this awesome sounding podcast?, you may be wailing at this point, anguished by my inability to write a short blog post that gets to the point within a reasonable number of characters, why dost thou maketh me wait like some putrid syphilis-riddled chump, you cry, suddenly resorting to ye olde English like creationists do when you’ve argued them down and they’re trying to regain the upper hand through patronising misquotations of not-particularly-relevant bible verses.
Thankfully, a bunch of your favourite tweeters/tweeps/tweehavioural ecologists (delete as appropriate, especially the last one) are keeping the rest of us in the loop; you can follow the stories as they come by using the #ISBE2012 hashtag. This is a great way to keep up with current and emerging research, as well as just finding out about cool stuff! Here are some highlights:
I urge you all to go and check out the full stream of #ISBE2012 tweets coming from this dedicated bunch of very excited academics – I recommend you follow them all anyway! If you want to find out more about any of the talks, you can look up the speakers on the conference programme. It’s so fantastic and exciting that we have the technology that enables those of us who can’t make these events to keep up with what’s happening, and feel as though we are still a part of it…
I’m going to skip ahead in my review of the talks which I enjoyed at Evolution 2012 in Ottawa, as Doug Emlen‘s latest research has just been published in the latest issue of the prestigious journal Science. This gives me an excuse to write about his talk and the new paper, as well as to engage in gratuitous posting of beetle photos.
I have a real soft spot for research on beetle horns, as followers of Nature!Sex!TopTips! may be aware, so I was really excited to see Emlen’s talk – even more so after the taster that was Erin McCullough’s presentation earlier in the week (McCullough is a PhD student co-supervised by Emlen and Bret Tobalske at the University of Montana’s ‘Flight Lab’). Research into animal weaponry often goes hand-in-hand with studies of ornaments because there is direct sexual selection upon them; females use ornaments as a basis on which to select a mate, while weapons are used by males to defeat rivals (or to assess their condition and status) and so gain access to females. Together, these exaggerated, elaborate structures are some of the most incredible sights we see in nature.
It’s no surprise that a lot of research investigates these amazing traits, but there are still some big questions to grapple with. For example, they seem to be very reliable indicators of male quality – why should this be so? Can’t some males ‘cheat’ by somehow investing more into ornament or weapon growth than other things? Also, if females select upon a particular heritable trait, then shouldn’t we see very little variation by now, with all males having pretty much the same size of trait? Consider the range of deer antler size in comparison to, say, the range of deer leg length. Antlers are much, much more variable – but why?
I’ve written about the maintenance of genetic variation in such traits before, both here and over at the Nothing in Biology Makes Sense blog, using the ‘genic capture’ model proposed by Rowe and Houle. This model posits that the continued evolution of sexually selected ornaments and weapons is enabled by these traits ‘capturing’ the underlying condition of the animals. An individual’s condition is affected by its general health, nutrition, parasite resistance, competitive ability, etc… essentially, the genetic variation among males in terms of all these factors underlies the variation in these amazing traits. It’s this ‘condition-dependence’ of traits, a close association with the individual’s condition, which means that the expression level should be ‘unfakeable’ and thus a reliable indicator of male quality. Not only this, but it also allows the evolution of ever-more exaggerated ornaments and armaments. So, these traits have some particular characteristics which have triggered huge interest from an evolutionary point of view: extreme size, heightened sensitivity to condition, and much more variability than we see in other morphological traits. We often think of condition-dependence as a kind of ‘black box’ – environmental and genetic factors go in, and traits come out. Emlen’s current research asks the question of, well, what mechanism enables this to happen? What’s inside the black box that creates these incredible, extreme biological structures?
Emlen proposes that there is a developmental explanation for this, and it lies within the insulin / insulin-like growth factor (IGF) pathway. This pathway has emerged as the central mechanism in animals for integrating physiological condition with growth; insulin and IGFs not only regulate tissue growth and body size, but they are also sensitive to factors such as nutrition, stress and infection. The levels of insulin / IGF circulating in an individual would cause a graded response via this particular pathway, with growth speeding up or slowing down in response to changes in nutritional or physiological state – i.e., the same kind of factors which affect what we term ‘condition’. So far, so straightforward, you might think: there’s a pathway which controls tissue growth that depends on how healthy and well-nourished you are. But how might this lead to the evolution of highly exaggerated weapons and ornaments?
Well, here comes the even cooler bit: traits differ in how they respond to these signals. This can have a truly profound effect on the amount and nature of their growth. Some traits, like Drosophila genitalia size, are not particularly sensitive to insulin / IGF signalling, meaning that they tend to be around the same size in all individuals, no matter their nutritional state. Wings, meanwhile, are more sensitive to these signals. Within a variable population of fruit flies, with a normal range of body sizes, we would see variation in wing size approximately equal to variation in body size, while genitalia size would hardly vary at all. So, just as wings are more sensitive to insulin signalling in Drosophila than are genitals, Emlen predicted that exaggerated weapons or ornaments are even more sensitive than that. Such heightened sensitivity to insulin / IGF levels would explain how such traits grow to extreme sizes, why there is such huge variation within populations, and why such traits seem to be reliable indicators of underlying quality.
Emlen and his colleagues tested this hypothesis in male rhinoceros beetles (Trypoxylus dichotomus), which have a large forked horn on the top of their head. They used RNA interference (RNAi) to perturb transcription of the insulin receptor (InR) – that is, they simply stopped this particular signalling pathway from working properly. They did this at the beginning of metamorphosis, a point when body size is no longer growing, but adult structures – such as genitalia, wings, and the huge sexually-selected horn – are. If increased cellular sensitivity to insulin / IGF signalling is at least partly responsible for the evolution of this exaggerated horn in these beetles, then horns should be more sensitive than wings to the experimental manipulation of the pathway activity via RNAi. Furthermore, Emlen and his team predicted that – just as with fruit flies – genitalia should be relatively insensitive to this disruption of insulin / IGF signalling.
Results showed that the genitalia of males whose InR pathway activity was disrupted did not show a significant reduction in size when compared to control males (which did not undergo the RNA interference treatment). Meanwhile, the wings of RNAi treatment males showed a significant reduction in size that measured around 2% in comparison to control males. This is typical of the majority of ‘metric’ traits, such as eyes, legs, etc. Horns, however, predicted to be the most sensitive to nutritional state, suffered a significant reduction of around 16% in RNAi treated males relative to control animals. This eight-fold increase in sensitivity of horns in comparison to wings is highly consistent with Emlen’s model of the evolution of exaggerated trait size from heightened sensitivity to this particular pathway – giving us a real insight into the black box of condition-dependence, and how such incredible traits evolved.
Note: I highly recommend reading the paper itself, not only because it’s very well-written, but also because Emlen does a great job of summarising models of sexual selection and condition-dependent traits, and the impact of this latest research on those models. Plus there’s some nice beetle pictures in there, and you love nice beetle pictures. DON’T YOU?