Advances in systematics of bats: towards a consensus on species delimitation and classifications through integrative taxonomy

The order Chiroptera comprises all bat species and is the second-most diverse order of mammals. Organization of this diversity into well-delimited taxa embodying their evolutionary affinities remains challenging, particularly because the relationships among various groups at most taxonomic levels are not yet fully resolved. Historically, systematic questions were approached independently using tools and methodologies within researchers' individual expertise. With technological advances, this trend has shifted to more comprehensive analyses, merging independent datasets from various lines of research. Nevertheless, disagreements among phylogenetic relationships inferred from independent datasets, and derived from the complexity of modes of diversification and speciation, still preclude the achievement of a single, comprehensive, and stable classification framework for bats. In this context, integrative taxonomy uses complementarity among various disciplines to improve the outcome of hypothesis testing, which can be achieved by congruence or cumulation of datasets. Here, we provide a review of bat systematics, with emphasis on the instances where integrative taxonomy has proven to be crucial in delimitation of taxa. We focus on examples of true integration or integration using discrete data to support delimitation at different taxonomic levels. In addition, we discuss the difficulties associated with the integration of incongruent phylogenies, as well as how to incorporate information crucial to phylogenetic decisions from data not easily comparable to most common datasets. Our goal is to provide exemplar guidelines that can be useful to taxonomists for the creation of stable classifications without subjectivity and limitations of single datasets. Accordingly, we present a review of recent issues in chiropteran systematics, including comments on how the use of integrative taxonomy helped to solve them.