Introduction
A myriad of microorganisms can be found living in the gastrointestinal tract of all animals. These microorganisms have a significant impact on host biology and can influence a variety of processes that affect host fitness [1, 2]. While certain variations in the composition of gut microbial communities can cause disease [3, 4], gut microbiome may also increase resistance to pathogens, besides being important for xenobiotics metabolism, nutrient uptake and energy acquisition [e.g. 5, 6]. Moreover, gut microbiota may also contribute towards host adaptation to environmental changes by enabling a response to new challenges, such as exploitation of novel food sources [7, 8]. Ultimately, gut microbiome can have major impacts on host development, behaviour and fitness, with cascading effects to the dynamics of ecosystems [2]. In turn, it can also be modulated by several host traits, such as host taxonomy, sex and size, as well as the external environmental, such as habitat or prey availability [e.g. 9, 10). In addition, social interactions between hosts can also influence the gut microbiome in many animal species, although these mechanisms remain less studied [see review by 11].
Gut microbiome dynamics has been studied in many mammals [e.g., 2], birds [e.g., 12], fishes [e.g., 13] and amphibians [e.g., 14]. Comparatively, fewer studies have been performed in reptiles, and only a handful of these addressed lizards [15]. Nevertheless, host taxonomy and ecology were seen to be important drivers of gut microbiota diversity in reptiles. For example, feeding habits influence the gut microbiota of the Chinese crocodile lizard, Shinisaurus crocodilurus Ahl 1930, with potential effects on host health due to the influence of diet on the abundances of pathogenic or opportunistic gut bacteria [16]. Diet and habitat of the Australian water dragon,Intellagama lesueurii (Gray, 1831), also have an effect on its gut microbiome, with lizards living in urban areas presenting higher bacterial diversity than populations living in natural habitats [17]. Moreover, host taxonomy and habitat also influence the gut microbiota of venomous snakes [18].
Here, we analyzed and compared the diversity and composition of gut bacterial communities of five phylogenetic related lacertid species captured in Portugal: Podarcis siculus (Rafinesque-Schmaltz, 1810), Podarcis virescens Geniez, Sá-Sousa, Guillaume, Cluchier and Crochet, 2014, Podarcis bocagei  (Lopez-Seoane, 1885), Podarcis lusitanicus Geniez, Sá-Sousa, Guillaume, Cluchier and Crochet, 2014 and Teira dugesi (Milne-Edwards, 1829).Podarcis species are considered as model organisms to study ecotoxicology, immune/histochemical reactions, among other processes [e.g. 19,20]; however, microbiome studies are still largely lacking, with a single study on the Balearic Podarcis lilfordi  (Günther, 1874) showing that islet and time since islet separation from mainland are significant factors contributing to gut microbiome structure [21]. Our main objective was to determine whether locality (which also corresponded to different habitats) and host factors such as species, size and sex modulate the gut bacterial diversity of these five lizards. To achieve our goal, we swabbed individuals’ cloacal exudate, known to be a good proxy for lizard gut bacterial communities [22], which were then characterized through the high-throughput sequencing of the V4 region of the 16S rRNA gene.