Twitting about bioinformatics: who retweets whom?

Continuing with this short series of twitter analysis, today I decided to harvest 500 tweets talking about bioinformatics in order to investigate the retweets connections. My question was very simple: who retweets whom? To answer it we can use a network to visualize who is retweeting whom (here is the code in R). The direction of the arrows (eg @user2 -> @user1) indicates that @user2 retweets @user1. This is the result:

162 out of the 500 collected tweets contained a retweet entity. Doing a quick frequency analysis, the top eight more retweeted users were:

1. genetics_blog = 26 (16%)
2. bffo = 14 (8.6%)
3. phylogenetics = 8 (5%)
4. dullhunk =  8 (5%)
5. JChrisPires = 8 (5%)
6. brent_p = 7 (4.3%)
7. michaelbarton = 7 (4.3%)
8. pablopareja = 6 (3.7 %)

You can identify these users in the graph because they are located in the center of those groups with a star-like shape.