I’ve just about recovered from an excellent time at the 16th congress of the International Society for Behavioral Ecology (ISBE), where I saw a ton of cool science, caught up with loads of friends, and learned (and drank, and ate) a lot! I also gave my first talk on the work I’ve been doing in my postdoc with Alastair Wilson – hopefully I can figure out how to share my slides on here at some point – which seemed to go over reasonably well.
At the end of the conference there were various symposia, and I went to one on ‘The Causes and Consequences of Behavioural Plasticity‘ (organised by Suzanne Alonzo and Nick Royle). I had some code I’d made for a previous workshop in our department, so gave a quick tutorial on how to model plasticity (in particular, among-individual differences in plasticity) in R. Unfortunately the licence servers for ASreml had gone down until an hour before lunch, so I didn’t end up showing the multivariate modelling (also turns out I’d forgotten how hard it is to present something in any kind of charismatic fashion when you are scrolling through code and haven’t really had any sleep)… but I have gathered together the code for modelling individual differences in plasticity in both a ‘reaction norm’ (random regression) and ‘character state’ (multivariate modelling) framework at the link:
Any comments / suggestions very welcome – just fire me an email, or contact me on twitter! I’m currently working on the manuscript for the work I showed at ISBE, which involved using multivariate models, matrix comparisons etc to figure out the plasticity of personality structure over different contexts – the code (and data) will be made available when the paper is out…
A quick, very unsubtle plug: bookings are now being taken for the next Advancing in R workshop run by PR Statistics (taught by Luc Bussière, with me as glamorous assistant), where we cover data wrangling, visualisation, and regression models from simple linear regression up to random regression. We will also teach the ‘ADF method’ for your statistical modelling workflow – hopefully also to be immortalised in a paper at some point!
I have been reminded to stress a very important point…
One of the comments I received on this was from Luis Apiolaza, he of quantitative genetics, forestry, and many excellent ASreml-r blog posts. He noted that – had he been writing such a tutorial – he would typically have started from the multivariate approach, and extended to random regression from there (citing a recent study in which they had 80+ sites/traits). I think this is a good point to make, in particular the realisation that it’s very easy to just think about our own studies (as I was doing).
My work is usually in the laboratory, so I’m likely to have a small number of traits / controlled environments that I’ve observed. In these cases, while reaction norms are easy to draw and to think about, modelling the data as character states actually provides me with more useful information. I am also aware that – in ecology and evolution – random regression models have been pushed quite hard, to the extent that it’s seen almost as a ‘one size fits all’ solution, and people are often unaware of the relative advantages of character state models. However, they are not always suitable for the data: it may be that there are too many traits/environments to estimate all the variances and covariances, or – as in another study I’m involved with – the repeated measurements of an individual are taken on an environmental gradient, but it is not possible to control the exact points on that gradient. In that case, of course, we can use random regression to estimate differences in plasticity using all of our data, and convert the intercept-slope covariance matrix to character state for specific values of our environmental predictor if we want to look at relative variation.
I’m not convinced there’s truly a ‘right answer’, rather that it’s nice to have the option of both types of models, and to know the relative advantages / disadvantages of each…
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):
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.
(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.
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.
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.
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.
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.
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’.
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.