ORIGINAL CONTRIBUTION Living in a jar: genetic variation and differentiation among laboratory strains of the red flour beetle M. Lagisz 1,2 , G. Port 1 & K. Wolff 1 1 School of Biology, Newcastle University, Newcastle upon Tyne, UK 2 Zoology Department, University of Otago, Dunedin, New Zealand Introduction The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae), is an important pest of stored grain products that is easy to breed in the lab- oratory. Its biology is well studied and its assembled genomic sequence was recently published (Tribolium Genome Sequencing Consortium 2008). Therefore, it is not surprising that T. castaneum is increasingly used as a model species in genetic, ecological, evolution- ary, developmental and ecotoxicological research (Denell 2008). Although some researchers work on beetles recently derived from natural populations, most studies rely on established laboratory stocks. Natural populations of T. castaneum are diverse both phenotypically and genotypically. Significant phenotypic variation among field-collected strains has been found for many traits, including behaviour (Prohammer and Wade 1981), resource use (Via 1991) and resistance to different insecticides (Rah- man et al. 2007). Also, genetic differentiation between wild populations was demonstrated. For example, studies showed differences in the distribu- tion of selfish genetic elements (Beeman et al. 1996; Beeman 2003) and in the alleles conferring resis- tance to cyclodiene (Andreev et al. 1999). A recent study using microsatellite markers showed high lev- els of genetic divergence among wild-collected popu- lations (Drury et al. 2009). Over the long history of research on T. castaneum many laboratory stocks were established from wild populations collected from various locations around Keywords genetic variation, insecticide resistance, laboratory populations, multiple co-inertia analysis, strain divergence Correspondence M. Lagisz (corresponding author), School of Biology, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. E-mail: losialagisz@yahoo.com Received: June 28, 2010; accepted: October 4, 2010. doi: 10.1111/j.1439-0418.2010.01593.x Abstract The red flour beetle, Tribolium castaneum, is a common pest, which has become an important model study organism, especially in genetic, eco- logical and evolutionary research. Although almost all studies on this species have been conducted using established laboratory strains, very little is known about the loss of genetic diversity within the strains and genetic divergence between different laboratory stocks. In this study, five long-term laboratory strains and one wild strain were examined for genetic variation at 12 microsatellite loci, which were designed using publicly available sequences. One of the laboratory strains is resistant to phosphine and one to organophosphorous insecticides. All strains had significant amounts of molecular variation, but genetic diversity in the laboratory strains was lower than in the wild-derived strain used as con- trol. We observed significant molecular divergence among the strains, however, the relationship between them reflected resistance status rather than geographic origins. We found no evidence for recent bottle- necks, but the wild-derived population showed signs of demographic expansion. A novel multivariate method, multiple co-inertia analysis, revealed that the two loci contributing most to the divergence between the resistant strains were located on the eighth chromosome, near genes associated with insecticide resistance. J. Appl. Entomol. 682 J. Appl. Entomol. 135 (2011) 682–692 ª 2010 Blackwell Verlag, GmbH