Disentangling Species Boundaries and the Evolution of Habitat Specialization for the Ecologically Diverse Mite Family Acaridae

Abstract

Testing habitat specialization and diversification patterns in poorly known groups such as mites contributes to our understanding of fundamental evolutionary questions. Organisms with morphological and physiological adaptations to more specialized habitats and resources are expected to have evolved from more generalized ancestors, but the opposite (i.e., generalists evolving from specialists) is not expected to occur. However, there are indications that ancestors of the mite family Acaridae had specialized habitats and that generalists lineages evolved from these specialist ancestors. Here I aimed to determine how niche breadth evolved in Acaridae and specifically evaluate whether or not habitat generalists evolved from specialist ancestors. I accomplished this objective by estimating a molecular phylogeny, reconstructing ancestral character states and transition rates for habitat use in this family. I found evidence that generalists have in fact evolved from more specialized lineages. All analyses showed that specialized habitat use is ancestral for acarid mites and confirmed that generalists evolved from specialized lineages. Ancestral character state reconstructions also revealed that specialist lineages gave rise to other specialist as well as generalist lineages. Given the difficulties that exist in delimiting species of some genera of Acaridae such as Tyrophagus, I documented subtle but important morphological differences between two cosmoplolitan species, Tyrophagus curvipenis and Tyrophagus putrescentiae. I also utilized several molecular species delimitation methods based on analyses of mitochondrial and nuclear DNA to untangle the taxonomic uncertain within this genus. I first recovered much of the intra-specific molecular variation that exists within several populations of the cosmopolitan mite, T. putrescentiae, from different geographic regions. The results revealed a tremendous level of hidden diversity within this genus, suggesting the presence of 17 morphospecies. Moreover, there was no support for recognition of cryptic species within T. putrescentiae as suggested from analyses of mitochondrial DNA sequences. It also highlighted the importance of integrating several complementary methods in a taxonomic framework that incorporate different forms of evidence when delimiting species. The work presented here advances our knowledge of the evolutionary history of a poorly known group of organisms, i.e. acarid mites, and provides important evidence regarding the diversification of this family. Even though major advances were presented in this dissertation, it will still be necessary to investigate other factors related to the genetic differences and ecological diversity that allowed this group to diversify into many habitats and develop broad distributions. On the other hand, it is not only necessary to conduct more extensive efforts for sampling in understudied regions like the Neotropics but also to develop a more extensive taxonomic study of the genus Tyrophagus given that I also found several undescribed morphospecies.