Recent studies of lemur species diversity have particularly focused on mouse lemurs (Cheirogaleidae: Microcebus) – small, nocturnal, and superficially monotypic creatures (Radespiel et al., 2012; Zimmermann and Radespiel, 2014). Microcebus are widespread across the diverse habitats of Madagascar, and are present in primary, secondary, and disturbed forest types where suitable area remains (Mittermeier et al., 2010). Until the end of the last century, it was assumed that diversity in mouse lemurs consisted only of two morphologically and geographically distinct species – a larger, grayish western morph, Microcebus murinus, and a smaller, reddish eastern species, M. rufus (Mittermeier et al., 1994). Each of these species was thought to have a broad distribution, encompassing a relatively diverse array of climates and habitats. In addition, mouse lemurs were believed to have largely allopatric distributions, with very little, if any, sympatry observed. However, the number of recognized mouse lemur species on Madagascar has vastly increased in recent years with an emphasis on methods to delineate cryptic species in the field (Mittermeier et al., 2010). There are currently 21 formally described species of mouse lemur, including some taxa that have sympatric distributions (Zimmermann and Radespiel, 2014).
Some controversy exists over the taxonomic validity over the newly named species, associated in large part with problems of sample size and geographic coverage, and difficulty in distinguishing clinal variation from distinct phylogenetic species (Tattersall, 2007; Markolf et al., 2011). Although cryptic species are often differentiated solely on the basis of genetics (Pastorini et al., 2001; Olivieri et al., 2007; Horvath et al., 2008; Groeneveld et al., 2009; Weisrock et al., 2012), integrative studies of primate taxonomy have recently used diet, social system, communication signals, sleeping site ecology, and reproductive behavior to delineate species boundaries (Kamilar, 2006; Radespiel et al., 2006; Zimmermann, 2013; Zimmermann and Radespiel, 2014). Such studies have demonstrated that sympatric species of Microcebus coexist in several regions of Madagascar (Yoder et al., 2005; Weisrock et al., 2010; Rasoloarison et al., 2013). Thus, mouse lemurs provide an excellent opportunity to investigate the evolutionary and ecological mechanisms that allow species to coexist.