Tuesday, July 17, 2012

Sieve Sorting

I am sure that ever since you read about the the sieve sorter system mentioned in our paper "A cost of sexual attractiveness to high-fitness females" you have been wondering what you will need to make your own set of sieves? In addition to a set of electo-formed sieves (which we purchased from Precision Electroforming Inc.), and a sieve-shaker (we use a Global Gibson SS-III), you'll need to make some fly-friendly modifications. I have posted some pictures here.
Sieve column on sieve shaker

Practice Makes Perfect

The last couple of weeks I’ve been getting in some practice here and there, taking pictures of eggs laid by backup lab culture flies, trying to figure out how to get the best picture I possibly can for measuring egg size in ObjectJ.
The 'Old' Way
Yesterday I size sorted IV flies, and let them lay on juice cookies over night. After clearing the flies and putting the cookies in the fridge to control for any changes in egg size from development, I worked my way through taking pictures of eggs in each size group. The pictures were looking pretty good, except for the lack of contrast between the red background and the eggs (that pick up a sort of pink colour from the cookie).
The 'New' Way

 It wasn’t until the last cookie that I discovered something that would make the photos much better. Instead of using a white platform underneath the juice cookie as I had been doing previously, I tried  using a black one. This instantly increased the contrast between the eggs and the background. I believe that with this discovery, future picture taking and egg measurements will be much more effective.
Getting in this practice and working out all the little details now will be very helpful in the future when I start working on my thesis project.

Sunday, July 15, 2012

Repeatability of mate choice in female red jungle fowl

Johnson, T.S. and Zuk, M. 1995. Behavioural Ecology. 7:245-246

The authors investigated the repeatability of mate choice in female red jungle fowl by examining the heritability of female preference that is an assumption in models explaining the evolution of mate choice. Male morphology was characterized 2 weeks before mate choice trials. For the mate choice trials, males were chosen randomly with the only condition that females never saw a male more than once and males were not paired more than once during the experiment. Females were placed in a small cage in front of two males and left there for 30 min. The female's behaviour was then observed for 20 mins after being released from the small cage. Preference was scored if a female copulated with a male. The results showed that female preference differed with both male trait and the timing of the breeding season. The highest estimate of repeatability was found to be 0.19, which indicates that current heritability may be low. Yet there is still evidence that a heritable component exists in the female red jungle fowl. Females showed repeatability with respect to male combs, but not with respect to hackle feather colour. Male traits can thus evolve through female choice when female preference is genetically determined. and the male trait is heritable.

Positive genetic correlation between female preference and offspring fitness

Hine, E., Lachish, S., Higgie, M., Blows, M.W. 2002. Proc. R. Soc. Lond. 269:2215-2219

These authors showed that female Drosophila serrata prefer extreme male cuticular hydrocarbon (CHs) blends and that this preference affects offspring fitness. Mate choice experiments were preformed using virgin females individually placed with two virgin males. After observed copulation, the males were removed and killed and prepared for gas chromatography analysis of the CHs. From these results, the authors estimated the sexual selection fitness function and linear selection gradient for the more attractive male CH blend. It was then determined if female choice affected offspring fitness with a quantitative genetics experiment. This experiment encompassed female preference, male attractiveness, and offspring fitness all in one. The authors found that female preference is positively correlated with offspring fitness, and that choosing the more attractive male results in genetic benefits. In addition, males with the highest probability of mating conferred intermediate levels of offspring fitness, indicating that female choice in under stabilizing natural selection. Even though male cuticular hydrocarbons experience strong sexual selection, the genes underlying this conferred lower offspring fitness, suggesting a balance between sexual selection and natural selection may have occurred in this population.