Microbes dominated the earth for at least 2.5 billion years before multicellular life appeared in the biosphere (Hooper and Gordon 2001; Ley et al. 2008). In fact, animals have been living and evolving in a microbial world (Margaret et al. 2013). Microbes inevitably colonized animals and coevolved through the process of interactions with their hosts (Clayton et al. 2018). Microorganisms can inhabit multiple parts of a host's body, such as the skin, oral cavity, sex organs, and the gastrointestinal (GI) tract. They are usually recognized as the microbiome of a particular host. As an essential part of the host's body, the microbiome plays an important role in host physiology by influencing nutritional intake, metabolic activity, and immune homeostasis (Turnbaugh et al. 2006; Greenblum et al. 2012; Hooper et al. 2012). Thus, the complex relationship between hosts and their microbiomes provides a unique opportunity for understanding mammalian adaptation and evolution (Hird 2017). As the most complex and diverse ecological system of the mammalian body, the GI tract is colonized by bacteria, archaea, fungi, and viruses (Underhill and Iliev 2014). Previous studies have revealed that the gut microbiota play an important role in immune regulation, vitamin synthesis, energy acquisition, and disease risk