18S

18S is a commonly used ribosomal gene for studies of higher-level (ordinal level) relationships in insects (Caterino et al 2000). Chalwatzis et al (1996), for example, were able to use 18S to help determine the relationships between all the major groups of the Holometabola, though they noted that 18S could be problematic for phylogenetic analysis because of variable G+C content in different regions of the gene. Nonetheless, Caterino et al. (2000) asserted that "given satisfactory results from the 18S data and a substantial existing database, it seems advisable to concentrate future efforts in this region". 18S has been widely used in recent insect ordinal-level studies (Whiting et al. 1997, Wheeler et al. 2001, Whiting 2002, Kjer 2004).

The only previous study using 18S in bee phylogeny is that of Sheppard & McPheron (1991). In this study 18S was used to resolve relationships within the corbiculate Apidae. However, their alignment included just 237 nucleotide sites, seven of which were variable. We have chosen to use 18S for our studies of bee family level phylogeny because the gene is easy to amplify and may help provide resolution at the base of the tree. We are still in the process of assessing the utility of this gene for higher-level studies in bees.

Below is a figure, scanned from Caterino et al. 2000, which shows a map of ribosomal DNA and datasets including 18S sequences that were published prior to March 15, 1999.

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Gene Information:

18S primer information (.pdf file)

Related Papers:
Kjer, K.M. (2004). Aligned 18S and insect phylogeny. Syst. Biol. 53(3)506-514. (.pdf file)