Gut microbes limit growth in house sparrow nestlings (Passer domesticus) but not through limitations in digestive capacity.

Recent research often lauds the services and beneficial effects of host-associated microbes on animals. However, hosting these microbes may come at a cost. For example, germ-free and antibiotic-treated birds generally grow faster than their conventional counterparts. In the wild, juvenile body size is correlated with survival, so hosting a microbiota may incur a fitness cost. Avian altricial nestlings represent an interesting study system in which to investigate these interactions, given that they exhibit the fastest growth rates among vertebrates, and growth is limited by their digestive capacity. We investigated whether reduction and restructuring of the microbiota by antibiotic treatment would: (i) increase growth and food conversion efficiency in nestling house sparrows (Passer domesticus); (ii) alter aspects of gut anatomy or function (particularly activities of digestive carbohydrases and their regulation in response to dietary change); and (iii) whether there were correlations between relative abundances of microbial taxa, digestive function and nestling growth. Antibiotic treatment significantly increased growth and food conversion efficiency in nestlings. Antibiotics did not alter aspects of gut anatomy that we considered but depressed intestinal maltase activity. There were no significant correlations between abundances of microbial taxa and aspects of host physiology. Overall, we conclude that microbial-induced growth limitation in developing birds is not driven by interactions with digestive capacity. Rather, decreased energetic and material costs of immune function or beneficial effects from microbes enriched under antibiotic treatment may underlie these effects. Understanding the costs and tradeoffs of hosting gut microbial communities represents an avenue of future research.

Cite this article as:

Kohl KD, Brun A, Bordenstein SR, Caviedes–Vidal E, Karasov WH (2018). Gut microbes limit growth in house sparrow nestlings (Passer domesticus) but not through limitations in digestive capacity. Integrative Zoology 13, 139–51.

Figure S1 Mass gain of nestlings subjected to different diet and antibiotic treatments. HC, high carbohydrate; HP, high protein. Mass gain over the course of the experiment was determined by subtracting mass at the beginning mass (measured at 13:30 hours at 3 days old) from the mass at a given time. Nestlings were dissected in the morning of day 7 post‐hatch. Bars represent means ±SEM.

Figure S2 Faith's phylogenetic diversity of the mucosal microbial communities from nestling House Sparrows subjected to various diets and antibiotic treatments. Bars represent means ± SEM.

Supporting Information

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Supporting Information

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