Nesting strategies and disease risk in necrophagous beetles

• Published in: Ecology and evolution 2018-03, Vol.8 (6), p.3296-3310
• Main Authors: Fialho, Verônica Saraiva, Rodrigues, Vinícius Barros, Elliot, Simon Luke
• Format: Article
• Language: English
• Subjects: Adaptation; Beetles; behavioral immunity; Carcasses; Carrion; carrion ecology; Coleoptera; Coprophanaeus bellicosus; Decomposition; Density; Dung; dung beetles; Feeders; Fungi; Health risks; Hypocreales; Insects; Life history; Microorganisms; Nesting; Nesting behavior; Opportunist infection; Original Research; Silphidae; Soil bacteria; Soil microorganisms; Soils; Survival
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3919

While the effects of carcass decomposition on microorganisms have been demonstrated in recent years, little is known of how this impacts necrophagous insects. A common assumption is that insects that exploit carcasses are exposed to a high density of potentially harmful microorganisms, but no field data have so far validated this. Necrophagous beetles such as the Scarabaeinae have complex nesting behaviors with elaborate parental care. So here, we begin to explore whether this conjunction of life history and nesting behavior represents an adaptive response to the threat posed by microbes in these environments, mainly by entomopathogens. We evaluated the density and distribution of fungi and bacteria from soil near the carcasses, and their ability to infect and kill insects that are in contact with this soil during the decomposition process. Our data showed an increase in the density and activity of opportunistic or facultative pathogens during the apex of decomposition, when there is a predominance of necrophagous insects. Meanwhile, the survivorship of bait insects decreased when in contact with soil from this period of decomposition, indicating a potential risk of infection. However, the density and activity of these microorganisms decreased with distance from the carcass, mainly with depth, which would benefit tunneller beetles in particular. We have thus provided the first field data to show that necrophagous insects are indeed exposed to high densities of potentially harmful microorganisms. Furthermore, we propose that some parental care strategies may have arisen not only as a response to competition, but also as adaptations that reduce the risks of disease. Although we have focused on carrion feeders, we suggest that the same occurs with coprophagous beetles, as both carrion and dung are nutrient‐rich resources. Carcasses are rich, unpredictable, and ephemeral sources of nutrients for which organisms compete, but we show for the first time that their decomposition also increases local densities of potentially harmful microorganisms, including insect pathogens. We propose that the diversity of nesting strategies among necrophagous insects is largely the result of natural selection to deal with threats from these microorganisms, rather than competition as previously understood.