Teaching old beetles new tricks: applying novel genetic techniques to re-establish a classic ecological model system, Tribolium

The ‘red’ and ‘confused’ flour beetles (Tribolium castaneum and Tribolium confusum, respectively) have a long and distinguished history as a laboratory model system for studying population dynamics, interspecific competition, and invertebrate chemical ecology. Both species are pests of stored grain and can be reared easily in the laboratory. Park studied the effects that parasites (Park, 1948), temperature and humidity (Park, 1954), and initial starting densities (Park, 1957) had on competitive outcomes in what have become classical experiments. Park also provided an understanding of the mechanisms underpinning that variability by describing variation between the species in important life-history traits, including reproductive parameters (Park & Marian Burton, 1948) and intraspecific cannibalism (Park et al., 1965). A large body of evidence also suggests that a complex chemical ecology underpins Tribolium behaviour and evolution. Tribolium species possess two pairs of stink glands that store and release toxic compounds (benzoquinones). These compounds likely form the chemical cue that attracts/repels the beetle species to used flour. They probably also constitute ‘biological weapons’ used in intraspecific competition (they cause developmental mutations in the eggs/larvae of younger cohorts), as well as interspecific competition with both other invertebrate competitors and microbial competitors that populate flour – bacteria and fungi have been shown to flourish in populations of Tribolium mutants that have lost the ability to produce and secrete benzoquinone compounds. In addition, male Tribolium beetles produce a potent aggregation pheromone.

In the last few decades, Tribolium castaneum has been developed into a powerful genetic model for studying the evolution of arthropod developmental mechanisms (‘EvoDevo’ studies), and with a view to identifying genetic strategies to combat Tribolium as a pest of stored grain products. The Tribolium castaneum genome has been sequenced (Tribolium Genome Sequencing Consortium, 2008), gene expression can be knocked down efficiently in individuals and their offspring using parental RNA interference (RNAi) and many transgenic techniques and resources have been established. Importantly, many T. castaneum strains and transgenic lines are available that allow easy identification of individuals from the same Tribolium species in competition experiments. T. confusum has not seen the same level of investment, but the first draft genome sequence has recently become available. Interestingly, the T. castaneum genome sequence reveals an evolutionary expansion in the number of odorant receptors relative to other insect classes. A high number of pseudogenes suggests rapid evolutionary turnover in these sensory receptors during the evolution of this, and potentially related, beetle species. The ecological significance of this large repertoire, and evolutionary turnover, of sensory receptors remains to be determined.

Research programme

The interested applicant will be free to pursue a number of different avenues of investigation, some of which are summarized below. All involve modulating intrinsic variables (lowering gene expression using parental RNAi) and/or extrinsic variables (altering environmental conditions) and determining their effect on Tribolium population dynamics at both the intraspecific and interspecific level:

Foraging and migration – A few arthropod genes that encode receptors or enzymes exhibiting highly conserved roles in the control of foraging and/or migratory behaviour are known. Expression of these genes will be targeted by RNAi in an attempt to modify foraging and/or migratory behavior in T. castaneum and/or T. confusum populations, and monitor the effects on population ecology. Beetles will be assayed both individually and in the context of experimental metapopulations that vary in complexity and connectivity.

Benzoquinone production – The iBeetle whole genome RNAi screen has identified 65 genes that when knockdown lead to stink gland abnormalities consistent with a failure to produce benzoquinones. The results of this screen will be published shortly, allowing the production of laboratory T. castaneum and/or T. confusum populations with a reduced ability to produce and secrete these chemical cues. These experiments could be carried out in combination with those described below in (3).

Odor perception – It has been shown that Tribolium castaneum beetles loose the ability to respond to the Tribolium aggregation pheromone when a central part of odor reception (Tc-odr1) is knocked down. Targeting Tc-odr1 will allow the production of laboratory T. castaneum and/or T. confusum populations with a reduced ability to perceive chemical cues (probably including benzoquinones, although this needs to be tested) which can then be tested to evaluate the consequences for habitat preference, dispersal, and aggregation in both species.