Functional Ecology 2004 18, 952–954 © 2004 British Ecological Society 952 Blackwell Publishing, Ltd. Oxford, UK FEC Functional Ecology 0269-8463 British Ecological Society, 2004 12 2004 18 6 Technical Note Starvation resistance R. B. Huey et al. TECHNICAL REPORT Starvation resistance in Drosophila melanogaster: testing for a possible ‘cannibalism’ bias R. B. HUEY,*† J. SUESS,‡ H. HAMILTON* and G. W. GILCHRIST§ *Department of Biology (Box 351800), University of Washington, Seattle, WA 98195–1800, USA, ‡Vanson HaloSource, Inc., 14716 NE 87th Street, Redmond, WA 98052, USA, and § Department of Biology (Box 8795), College of William & Mary, Williamsburg, VA 23187–8795, USA Summary 1. Starvation resistance is often measured in physiological studies with Drosophila and other insects. One common method involves measuring time until death of groups of insects. This method assumes that survivors are not obtaining nutrition from their vial mates that die early. However, because some Drosophila larvae can scavenge carcasses, this group protocol might inadvertently lead to a ‘cannibalism’ bias. 2. We evaluated whether starvation resistance of Drosophila melanogaster was increased if fly carcasses were available from the beginning of the experiment. We used a mixed- model  to assess the direct and interactive effects of isofemale line, sex and immediate access to carcasses. 3. Males survived starvation longer than females, despite the smaller size of males. Isofemale lines differed significantly in resistance. Immediate access to fly carcasses had no impact on resistance. 4. These results suggest that starving adult flies do not gain measurable benefits from access to carcasses. Consequently, this experiment seemingly validates a widely used method of measuring starvation resistance. Key-words: Experimental methods, isofemale line Functional Ecology (2004) 18, 952–954 Introduction Starvation resistance is a commonly measured trait in studies with Drosophila. It is directly relevant to general issues of the evolution of stress resistance (Hoffmann & Parsons 1991) as well as to studies of direct and cor- related responses to artificial selection (Chippendale, Chu & Rose 1996), of geographical clines in stress resist- ance (Karan et al . 1998; Hoffmann & Harshman 1999; Robinson, Zwaan & Partridge 2000), and of its physio- logical (Harshman, Hoffmann & Clark 1999) and genetic (Harbison & Mackay 2002) bases. Starvation resistance is often assayed by placing groups of flies in a vial or bottle giving them access to water but not to food, and then monitoring times until death (Chippendale et al . 1996; Harshman et al . 1999). In our own experiments using this group protocol with Drosophila subobscura (R. B. Huey et al. , unpublished data), we noticed that the distributions of death times of individual flies within a vial were often suggestively left skewed; specifically, a few flies lived much longer than did other flies in about a third of all vials. Because D. melanogaster larvae can scavenge on dead fly carcasses (Gregg et al . 1990), we wondered whether such ‘last-to- die’ adult flies might be either cannibalizing their dead vial mates or perhaps feeding on microorganisms growing on carcasses. Were either the case, this group protocol would overestimate true starvation resistance. To evaluate whether a ‘cannibalism’ bias does occur, we tested whether the median starvation resistance of flies would be increased if fly carcasses were accessible to test flies from the very beginning of an experiment. Control flies would gain access to fly carcasses only after their cohorts began to die ( ∼ 24 h). Thus, although flies in both experimental and control treatments eventually had access to carcasses, only the experimentals had access from the initiation of starvation. To implement this design, we used an isofemale line approach, such that each line was represented in both experimental and control vials; and we separated males and females as well. We can thereby determine whether starvation resistance is influenced by sex, by the presence of car- casses, whether it has a genetic component in our stocks, and also whether isofemale lines (or sex) differ in their response to prolonged access to dead vial mates (i.e. a isofemale line – or sex – by ‘feeding’ interaction). †Author to whom correspondence should be addressed. E-mail: hueyrb@u.washington.edu