Attraction and Oviposition of Lucilia eximia (Diptera: Calliphoridae) to Resources Colonized by the Invasive Competitor Chrysomya albiceps (Diptera: Calliphoridae)

Priority effects and density promote coexistence between the facultative predator Chrysomya rufifacies and its competitor Calliphora stygia

Highly competitive ephemeral resources like carrion tend to support much greater diversity relative to longer-lived resources. The coexistence of diverse communities on short-lived carrion is a delicate balance, maintained by several processes including competition. Despite this balance, few studies have investigated the effect of competition on carrion, limiting our understanding of how competition drives coexistence. We investigated how priority effects and larval density influence coexistence between two blowfly species, the facultative predator Chrysomya rufifacies and its competitor Calliphora stygia, which occupy broadly similar niches but differ in their ecological strategies for exploiting carrion. We examined how adult oviposition, larval survival, developmental duration, and adult fitness were affected by the presence of differently aged heterospecific larval masses, and how these measures varied under three larval densities. We found C. rufifacies larval survival was lowest in conspecific masses with low larval densities. In heterospecific masses, survival increased, particularly at high larval density, with priority effects having minimal effect, suggesting a dependency on collective exodigestion. For C. stygia, we found survival to be constant across larval densities in a conspecific mass. In heterospecific masses, survival decreased drastically when C. rufifacies arrived first, regardless of larval density, suggesting C. stygia is temporally constrained to avoid competition with C. rufifacies. Neither species appeared to completely outcompete the other, as they were either constrained by density requirements (C. rufifacies) or priority effects (C. stygia). Our results provide new mechanistic insights into the ecological processes allowing for coexistence on a competitively intense, ephemeral resource such as carrion.

Gene expression correlates of facultative predation in the blow fly Chrysomya rufifacies (Diptera: Calliphoridae)

Effects of intraguild predation (IGP) on omnivores and detritivores are relatively understudied when compared to work on predator guilds. Functional genetic work in IGP is even more limited, but its application can help answer a range of questions related to ultimate and proximate causes of this behavior. Here, we integrate behavioral assays and transcriptomic analysis of facultative predation in a blow fly (Diptera: Calliphoridae) to evaluate the prevalence, effect, and correlated gene expression of facultative predation by the invasive species Chrysomya rufifacies. Field work observing donated human cadavers indicated facultative predation by C. rufifacies on the native blow fly Cochliomyia macellaria was rare under undisturbed conditions, owing in part to spatial segregation between species. Laboratory assays under conditions of starvation showed predation had a direct fitness benefit (i.e., survival) to the predator. As a genome is not available for C. rufifacies, a de novo transcriptome was developed and annotated using sequence similarity to Drosophila melanogaster. Under a variety of assembly parameters, several genes were identified as being differentially expressed between predators and nonpredators of this species, including genes involved in cell-to-cell signaling, osmotic regulation, starvation responses, and dopamine regulation. Results of this work were integrated to develop a model of the processes and genetic regulation controlling facultative predation.