Science Drinks April 8, 2014
Lilly started this week’s proceedings by pointing out new work by Tom Price and colleagues, recently published in Proceedings B. Tom and his colleagues studied a latitudinal cline in rates of polyandry in North America that covaries with the prevalence of sex ratio (SR), a meiotic-driving X chromosome. A selfish genetic element on the driving X causes sperm that carry Y chromosomes to die during development, which has two consequences for fathers carrying SR:
- All offspring sired by SR males carry the driving X (which is great for the selfish genetic element);
- Fathers only produce half as many sperm (which is terrible for dads who have to compete for fertilizations within females who mate more than once). This is why SR is a “selfish” genetic element — it improves its own fitness at a cost to its bearer).
Given that SR carrying males produce fewer sperm, females who mate more than once incite sperm competition that favours males who do not carry SR. This is a winning outcome for males who do not carry SR, as they are more likely to win in sperm competition by producing twice as many sperm. It also is a boon for polyandrous females, who are more likely to produce sons, which are rare when SR is prevalent and therefore have relatively high fitness. Price and his colleagues show that the elevated polyandry observed in regions of high SR prevalence is heritable, and argue that polyandry may frequently evolve to help reduce the intragenomic conflict imposed by selfish genetic elements.
Andy Dobson introduced himself to Science Drinks by explaining his research interest in parasite-host dynamics and his recent and ongoing modelling work with Stu Auld on virulence evolution, which has been constrained by processing power of late. Tim P. suggested that implementing subroutines in platforms other than R might accelerate things, and used the word “vectorized” to describe this, which I somehow found amusing. The discussion soon degenerated into some speculation of who has the most computer power and who has the most data, to slow down even the biggest and baddest of PCs. Think Robot Wars for stats nerds (I retain the copyright for this idea but am open to negotiating TV rights).
Adam then brought in a few figures to illustrate his ideas for upcoming grant applications. These are naturally Top Secret! We wouldn’t want anyone to steal his ingenious plan to secure a big research council grant.
Tim then mentioned an inspiring astro-physical story that was recently published in Science on one of Saturn’s moons, Enceladus. Summarizing this kind of work is dangerous for an entomologist, but your bloggy servant will have a go anyway: Luciano Iess and colleagues used telemetric data and Doppler radar antennae during flybys of Enceladus by the Cassini spacecraft to map the gravity field of Enceladus. Their findings indicate a magnetic anomaly near the south pole of Enceladus that is consistent with a large subsurface ocean 30-40 km deep(!). Wow! Amazing how some advanced number crunching can illuminate us about the state of one of Saturn’s moons from so far away, using tracking and careful measurements of the time taken to bounce radar signals off objects….
Each of the undergrads in attendance then took a turn presenting the latest discoveries: Gregor showed us some of his most recent findings on the phenologies of dance flies; Claudia showed us some intriguing and contrasting effects of body size and mass on the accumulation of resources by crickets, and Toby showed us data indicating that the relationship between compound eye facet size (which prevails in unspecialized eyes) and interommatidial angle may be disrupted among flies with derived “bright zones”. Watch this space for more in the coming weeks.
Andy then asked a provocative question: how does brood parasitism in birds (such as is seen in cuckoos) evolve in the face of imprinting, which is the phenomenon that leads many birds to identify with whatever rears them? We engaged in quite a lot of speculation without finding convincing answers. I did since find a handy webpage containing an expert answer from Naomi Langmore from ANU.
We wrapped up Science Drinks with a meaty paper by Mathieu Delcourt and colleagues in PNAS (not so hot off the press, but only recently read by me). Delcourt and his colleagues note that most populations tend to remain phenotypically stable over time in spite of strong directional selection (for example strong sexual selection for the increased expression of some sexual traits) and substantial genetic variance for the traits in question. Most of the time we assume that selection must be balancing on the character in spite of strong selection in one context (for example because overinvestment in a trait starves other important life history traits of resources). By measuring the genetic covariance between traits under sexual selection and total fitness, the authors here were able to use the multivariate Robertson-Price identity (also called the “secondary theorem of natural selection”, this equation is an alternative to the Breeder’s equation which Michael Morrissey and his colleagues note makes fewer assumptions) to demonstrate that in spite of substantial directional selection on male cuticular hydrocarbons (CHCs), there was little multivariate genetic covariation between these traits and fitness. Instead, their analysis of trait deviations revealed stabilizing selection on some aspects of genetic variance in CHCs. This work clarifies new methods for studying evolutionary responses (or the lack of them) in wild systems.