Collective exodigestion favours blow fly colonization and development on fresh carcasses

Abstract

26Necrophagous flies breeding on carcasses face high selection pressures and therefore 27 provide interesting opportunities to study social adaptations. We postulated that blowfly 28 necrophagous larvae gregariousness is an adaptive response to the environmental 29 constraints of fresh carcasses. Cooperation is indeed believed to be a key to the global 30 success of social species. To test this idea, the development of Lucilia sericata 31 (Diptera: Calliphoridae) larvae growing on low-or high-digestibility food substrate 32 (control or trypsin-added ground beef muscle, respectively) at different larval densities 33 was monitored. Results showed that larvae developed faster and had decreased 34 mortality at high larval density compared with low larval density. Furthermore, 35aggregation had no deleterious effect on the morphological characteristics (e.g., size) 36of post-feeding larvae and flies. We concluded that increased density positively 37 affected population fitness, which is a conclusion consistent with the predictions of the 38 Allee effect. Compared with regular food, larvae fed on high-digestibility food had 39 reduced mortality and faster development on average. According to these results, we 40 postulated that collective exodigestion might be an adaptive response allowing 41 blowflies to colonise fresh carcasses before the arrival of other insects and the 42 multiplication of microbes. This hypothesis is consistent with the idea that cooperation 43 may enable species to expand their niches. 44 45

Cooperative foraging during larval stage affects fitness in Drosophila

“…Clustering was shown to speed up the process of media liquefaction in vials (Dombrovski et al 2017 ) that could in turn facilitate and speed up food ingestion. A more complex explanation features a phenomenon of communal exodigestion that is mostly observed among various fly larvae feeding on flesh and other high-protein substrates (Scanvion et al 2018 ) but was also documented in Drosophila (Gregg et al 1990 ). Larvae are able to secrete a variety of enzymes that digest external polymers (amylose, cellulose and even chitin), therefore reducing energy expenditure per individual animal required to process and ingest a food source.…”

“…Indeed, highly efficient foraging aggregations that enhance survival rates compared to solitary foragers are documented in sawfly larvae (Ghent 1960), various species of caterpillars (Clark and Faeth 1997), where animals reared in larger groups displayed higher developmental rates and increased survival. This is also true for corpse-devouring necrophagous flies (Scanvion et al 2018;Aubernon et al 2019). Importantly, factors that provide trophic benefits can serve as tradeoffs in case of severe overcrowding (e.g., overly elevated temperature and proteotoxic stress caused by excessive tissue digestion, exemplified by Rivers et al 2011), implying a complex nonlinear pattern of relationship between group size (Cash et al 1993) and composition (Trowbridge 1991), food availability and distribution (Monaghan and Metcalfe 1985), presence or absence of predators (Turchin and Kareiva 1989) and individuals' investment into cooperative efforts (Valone 1989;Courchamp 1999;Giraldeau and Caraco 2018;Lindstedt et al 2018).…”

Quickie well done: no evidence of physiological costs in the development race ofLucilia sericatanecrophagous larvae

“…Neither adult body size, nor female fertility were measured in these experiments. First, because previous development studies in our laboratory showed that the body size of flies did not differ significantly (Scanvion et al ., ), and, second, because the determination of the fertility of each fly would have raise several technical problems and exceeded the time frame of the present study.…”

“…In previous experiments (Scanvion et al ., ), differences in development rates and final sizes between individuals are reported. This plasticity exists not only between different developmental conditions, but also under constant biotic and abiotic parameters (i.e.…”

“…() and Scanvion et al . (). For each experiment, the bottom of a large plastic box (180 × 135 × 195 mm) was covered with sand and a smaller breeding container (100 × 75 × 63 mm) containing 50 g of beef burger (100% muscle with 15% fat content; Cora®; Superstore Cora, Groupe Louis Delhaize, France) mixed with 15 mL of 0.9% NaCl solution was placed inside.…”