Measurement of predatory behaviour in cow dung-colonising insect larvae, using compound-specific 13C-tracing of dietary fatty acids

Abstract

Studies of the trophic interactions between organisms in opaque environments where direct observation can be difficult, such as soil or leaf litter, often require the use of indirect inferential approaches. Here, the use of compound-specific 13 C-tracing of dietary biomarker fatty acids is evaluated as a method for studying predation by larvae of the dung-breeding fly, Mesembrina meridiana (Diptera: Muscidae); the technique was used to differentiate dung from high-enrichment 13 C-labelled prey in their gut contents. Potential prey, 13 C-labelled larvae of the dungbreeding fly, Neomyia cornicina (Diptera: Muscidae), were placed into unlabelled dung microcosms in the laboratory. A single 7-day-old M. meridiana larva was allowed to feed in each microcosm for 8 h. The magnitude of increases in the δ 13 C values of fatty acids (i14:0, 14:0, i15:0, a15:0, 15:0, 16:0 and 18:0) in the gut contents, relative to those of M. meridiana deprived of prey, demonstrated the predation of N. cornicina larvae which were estimated to have constituted at least 35% of the average dietary wet mass of these M. meridiana larvae. The tracing of specific labelled compounds increased confidence in dietary assessment and helped to avoid systematic errors associated with compound-dependent efficiency of assimilation in the gut. The results demonstrate the potential value of this method in helping to elucidate trophic interactions in predator-prey systems within opaque environments. The precision of the quantitative dietary estimation that arose from these isotopic data was superior to that generated using fatty acid distributional data, a widely used and evidentially independent line of evidence.

Temporal segregations in the surface community of an ephemeral habitat: Time separates the potential competitors of coprophilous Diptera

“…Regarding ecological guilds, only one ecological guild displayed compact successional optima. The omnivores were all early successional, attributably due to their larval habit of preying on larvae of other dipteran groups, predominantly the Calyptratae fly larvae (which are also early colonizers) (Skidmore ; Dickson et al ). The exception is Scatophaga stercoraria , whose adults are predatory and larvae coprophagous (Blanckenhorn et al ).…”

“…; Dickson et al . ); and (iii) predators, which are predatory in all stages of development (e.g. Dolichopodidae, Empididae) (Cumming & Cooper ; Hulcr et al .…”

“…Musca autumnalis De Geer) (Skidmore 1985;Haenni 1997;Pape 1998;Papp 1998;Papp & Wheeler 1998;Rognes 1998;Gregor et al 2002); (ii) omnivores, which are predatory in one stage of their development, or can not finish their development without consumption of living food, or are known to regularly prey on other species (e.g. Myospila meditabunda (Frabricius)) (Hammer 1941;Laurence 1954;Skidmore 1985;Blackenhorn et al 2010;Dickson et al 2012); and (iii) predators, which are predatory in all stages of development (e.g. Dolichopodidae, Empididae) (Cumming & Cooper 1993;Hulcr et al 2005).…”