Differences Among Antimicrobial Properties of Carrion Beetle Secretions Reflect Phylogeny and Ecology

Abstract

Carrion beetles (Coleoptera: Silphidae) consist of two subfamilies in North America. Members of the Silphinae arrive at carcasses during the mid-stage of decay and their larvae feed on developing maggots, while members of the Nicrophorinae bury and tend carcasses upon which their developing larvae feed. The Nicrophorinae maintain the condition of the carcass by applying oral and anal secretions that reduce carcass decay apparently through bacterial inhibition, although quantification has not been made. We hypothesized that enzymes in the oral and anal secretions of the subfamily Nicrophorinae would inhibit bacterial growth, while secretions from the subfamily Silphinae would not. The secretions were assayed for inhibitory effects with a Microtox Analyzer that monitors the decrease in bioluminescence from the bacterium Vibrio fischerii. We found a significant difference of bioluminescence in the control compared to secretions of 8 out of 10 tested Nicrophorinae (with oral secretions being most active), while only anal secretions from Necrodes surinimensis of the Siphinae significantly reduced bacterial survival. These data follow the known phylogenic relationship in which Necrodes is the closest genus to the Nicrophorinae. The two species of Nicrophorinae, which did not show significant reductions in bacterial growth, differ ecologically from the others. Thus, the presence of antimicrobial compounds in most Nicrophorinae secretions, but not in most other Silphinae, represents an adaptation to preserve the buried carcass.

Temperature and Food Availability Differentially Affect the Production of Antimicrobial Compounds in Oral Secretions Produced by Two Species of Burying Beetle

“…Carrion beetles (Coleoptera: Silphidae) also have an antimicrobial oral secretion (Hoback et al 2004). Silphid beetles respond to carrion that they externally digest by secreting extracellular enzymes produced in the salivary gland (Ratcliffe 1996;Rana et al 1997).…”

“…Members of the subfamily Nicrophorinae often are referred to as 'burying beetles' because they arrive at the carcass during the early stages of decomposition and then bury and tend the carcasses (Milne and Milne 1976;Ratcliffe 1996). After interment, burying beetles coat the carcass with secretions that contain antimicrobial activity that delays the decomposition of the carcass ensuring a reproductive source (Milne and Milne 1976;Ratcliffe 1996;Scott 1998;Hoback et al 2004).…”

“…In a study of 10 species of Nicrophorus beetles from Nebraska, antimicrobial activity was found in the oral secretions of all but 2 species (Hoback et al 2004). The results showed that the secretions of N. orbicollis, N. americanus, N. obscurus, N. tomentosis, and N. marginatus exhibited antimicrobial properties that significantly reduced the amount of bacteria by 20 to 40%.…”

Gut Microbiota Colonization and Transmission in the Burying Beetle Nicrophorus vespilloides throughout Development

“…vespilloides larvae may be exposed to a varied microbiota throughout development, and this will likely be influenced by the presence of parents and the stage of development (26)(27)(28)(29)33). First, parents may modify the carcass microbiota by coating it in antimicrobial secretions throughout the period of parental care (22,27,34). Notably, these secretions are not sterile and contain significant numbers of bacteria that can proliferate on the carcass (29).…”

Antimicrobial strategies in burying beetles breeding on carrion

“…Furthermore, parents prepare and clean the carcass by covering it with anal and oral secretions, which are assumed to provide behavioral and chemical defenses against microbial competitors (10)(11)(12)(13). Thus, for these beetles, parental care may represent a neglected strategy for dealing with intense microbial competition over carrion.…”