Science Drinks #2: Information Transfer, Daddy Cool, Sex Hormones, Bright Blue Flies

Welcome back to Science Drinks! This is a fortnightly meeting of folk in Biological and Environmental Sciences (BES) at the University of Stirling which takes place (currently) at the Meadowpark pub. Science Drinks was established by Luc Bussière as a way of getting people together to chat about their weird data, new papers, or science news stories in a more relaxed environment than a lab meeting or journal club.

In attendance this week were Luc, Lilly Herridge, Frances Fraser-Reid, Nadine Royle, Frederick Hunter, myself and SOMEONE NOT FROM BES WHAAAAAT?!, Jessica Enright, a Lecturer in the Maths department at Stirling who has research interests in contagion networks, models of infectious disease, games on graphs, and graph theory. Luc’s new twitter account is already reaping rewards: Jess heard about Science Drinks through one of Luc’s tweets, so there’s just a chance he’ll persevere and tweet again!

WARNING: we seem to have got though a lot more than we did last week, so I hope this is the point of the day where you’ve committed to a cup of tea and are not planning to do any *actual* work…

Luc immediately put Frances, Nadine and Freddie on the spot and made them give ‘elevator pitches’ of their undergraduate research projects. This is a very useful skill to a researcher at any level, and is actually very difficult to do: the idea is to give a 30-second summary of who you are, what you do, and why it’s interesting/important in the time it takes for your trip in an elevator with someone you’ve just met. Great tips can be found here! We tried to think of the British equivalent (The Queueing Patiently Pitch? The Standing Awkwardly Close On A Crowded Train Pitch?), but we couldn’t.

We then got onto a couple of other ways of presenting information. Luc told us all about Edward Tufte’s thoughts on why presenting information using “slideware” (i.e. Powerpoint) sucks. Tufte thinks that too much information is lost, and that presentations should just involve giving the audience a table of information and then fielding questions. I can’t help feeling that most of the ‘story’ behind our science would sadly be lost this way.

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Without Powerpoint, this little chap would be replaced by reams of tables and parameter estimates. IS THAT WHAT YOU WANT?!

Lilly then brought up Tom Houslay’s recent blog post on applying the ‘story circle’ to academic writing. Tom suggests that if we want people to read our research, surely it’s better to make it a pleasurable experience, rather than a dreary slog through experimental procedure and results written in the passive voice. He introduces the ‘story circle’ of one of his favourite writers, Dan Harmon, which essentially describes a journey, beginning with a need to go somewhere and find something, followed by a journey of discovery and ending with CHANGING THE WORLD. Since this is essentially how we do science, Tom applies this to how we could write papers in a more dynamic and interesting way.

Story circle
Dan Harmon’s story circle, taken from the LA screenwriter

To some science then! Lilly spoke about her grapple with using allele frequencies to estimate the mating rates of dance flies, of which there are hundreds of species, some of which have ornamented females. The flies gather in large mating swarms and males collect nuptial food gifts, which females need since they can’t catch prey themselves. Females attract males and their gifts by looking fecund, and so they have very cool features including pennate spines and inflatable abdomens to make themselves look swollen with eggs. Lilly has dissected the spermatheca (sperm storage organs) from hundreds of females and is using microsatellite markers to determine how many males a female has mated with. Currently there are two methods for estimating mate number from genotyped stored sperm: first, using allele counts to give a conservative minimum estimate of mate number; and second, using population allele frequencies to estimate the most probable number of mates. Both methods rely on the one (the most) variable locus to obtain an estimate, but Lilly has been considering ways of using information from multiple loci to give her more precise estimates of mate number.  Jess suggested a  simulation approach, computing all possible combinations of allele frequencies, based on the frequencies of the alleles in the population, for a realistic range of mate number (e.g. 1-30 males), to give the likeliest number of males for a given combination of alleles.

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A view of a long-tailed dance fly (Rhamphomyia longicauda) female down the dissecting microscope. Photo by Lilly Herridge, used with permission.

Freddie then spoke about a really nice paper about which he is writing a review of as part of his third-year undergraduate course. The paper studies how monarch butterflies protect their offspring from a protozoan parasite. The parasite lives on the abdomen of adults but is then transferred onto the surface of eggs and the milkweed plants onto which the butterflies lay their eggs. When the larvae hatch, they consume their own egg cases….and become infected with the sneaky parasite!  Larvae can (yay!) resist the parasite by consuming chemicals (cardenolides) present in medicinal milkweed species. The study tested whether parents could transfer protection to their offspring, by rearing butterflies on medicinal and non-medicinal milkweed species. They showed that offspring were more resistant to infection when their fathers were reared on medicinal milkweeds, and females produced eggs with higher levels of cardenolides if they mated with males from medicinal milkweed. Hence, dad seems to be able to transfer protection to his offspring, just by eating stuff and then transferring it, via sperm, to the female he mates with. We all tried hard not to think about a human analogy here because UGH. Anyway, the mechanism has yet to be determined, though it is possible that compounds could be transported with sperm, and then absorbed by the female. If you’re the sort of perverse individual who is somehow excited by that sickening thought, you should go find out more on the butterfly parasite work at Jaap de Roode’s lab. I definitely have.

Monarch_Butterfly_Danaus_plexippus_Vertical_Caterpillar_2000px
A monarch butterfly (Danaus plexippus) feeding on swamp milkweed (Asclepias incarnata), a species low in protective cardenolides. No idea which way round it is. Must be the lack of a face. Photo from wikimedia commons.

We then (OH WOW FINALLY!) got onto the meta-analysis which I was going to talk about last week, on the effects of sex hormones on immune function. This is a question at the heart of the hotly-debated ‘immunocompetence handicap hypothesis’ (ICHH). ICHH suggests that testosterone is linked to the development of the showy ornaments which males use to attract mates, but also suppresses immune responses. This means that only the very best males can afford such showy ornaments AND suppress their parasite loads. Hence, females should pick the males with the largest ornaments. For the ICHH to be true, testosterone should have a negative effect on immune function, but a meta-analysis of ten years ago showed that it did not. Also, since females tend to mount more effective immune responses than males, female sex hormones, such as oestrogen, should be linked to more effective immune responses. The new meta-analysis reviewed almost 500 effect sizes from 130 studies to work out the effects of testosterone and oestrogen on immune function in experiments, and correlations between hormones and immune function in correlational studies. They showed that manipulating testosterone has a negative effect on immune function, and that manipulating oestrogen seems to have a positive effect, though this depended on the immune measure used. Some bad news was that if you just go out and measure natural levels of hormones and immune function in a wild animal, there is unlikely to be a strong correlation. We did wonder about where stress hormones come into this, because they are also elevated during reproduction and have documented effects on immunity, which may be positive (if acute) or negative (if chronic). Perhaps a meta-analysis of the effects of glucocorticoids is in order?

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‘What do you mean, ‘no’?’ Is the peacock’s testosterone-fueled tail feather display a signal of his ability to cope with the effects of parasites? Caption from Punch, photo from wikimedia commons.

Finally (I hear you sigh…), Luc showed some data from an experiment he did with Lilly and Svenja Kroeger, his former undergraduate project student and now marmot-chasing PhD student in Aberdeen. They wanted to know how often males and females of different species visited dance fly mating swarms. Every day, they went out into the field, caught some flies and then dunked them in paint (or something). They then returned to the mating swarm the next day with another colour, and noted how many of the previous colour were present, and so on. He brought along a couple of graphs which showed….something exciting, but you’ll just have to wait for the paper, you highly persistent so-and-so. And now it really is time you got back to work, don’t you think?

bluefly
A dance fly (Hilara maura), either very cold, or recently dunked in dye. Photo by Lilly Herridge, used with permission.

 

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