In addition to the nutritional and chemical differences between the D. mojavensis cactus hosts, the shape and structure of the plants are markedly different (Fig. 1), especially between prickly pear and the other three cacti (Turner et al., 2005). As determined by my previous graduate student Alexandra Jost, across the four populations there are significant differences in the pupation behavior of larvae, where larvae from Catalina overwhelmingly prefer to pupate in the substrate while individuals from other populations migrate higher up the vial to pupate (Jost, Matzkin, in prep).
One trait influencing both pupation behavior and more importantly the acquisition of resources is larval activity (Godoy-Herrera et al., 1984; Sokolowski, 1985; Sokolowski et al., 1997). Associated with the difference in host and pupation behavior, D. mojavensis larvae from different populations have distinct patterns of locomotion. This is especially true between Catalina and Sonoran populations. My current graduate student Joshua Coleman has examined different aspects of locomotion of D. mojavensis third instar larvae including speed (mean, maximum and minimum) and total displacement. Larvae from the Sonoran population have significantly greater speed than Catalina in both banana and necrotic organpipe cactus (the natural host in Sonora). This suggests that although rearing media (environment) can have an effect on activity, genetic differences in locomotion genes are present between the ecologically distinct populations. We have a recently have been awarded an NSF IOS grant which will examine the physiology and life history consequences of these distinct larval behaviors and link it to the transcriptional and genomic changes between the distinct cactus host populations of D. mojavensis. Specifically, a quantitative trait loci analysis will examine the genetic underpinnings of larval behavior. CRISPR-Cas9 knockouts and transgenics will be generated to quantify the functional role of the candidate behavior QTLs in an ecological context and examine the life history consequences of variation at these loci.