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Title:The influence of vicariance and dispersal on the diversification and evolution of springtails (collembola)
Author(s):Katz, Aron D
Director of Research:Davis, Mark A; Taylor, Steven J
Doctoral Committee Chair(s):Davis, Mark A
Doctoral Committee Member(s):Suarez, Andrew V; Whitfield, James B
Department / Program:Entomology
Discipline:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Biospeleology
Cave Biology
Collembola
Ecological Specialization
Evolution
Intertidal Biology
Molecular rates
New Species
Phylogeography
Abstract:Vicariance and dispersal are major drivers of the evolution of biodiversity, yet the relative impact of these processes, and the factors that influence them, often remain elusive. Identifying and understanding evolutionary processes responsible for generating diversity is essential for understanding ecological patterns and for the development and implementation of management strategies intended to conserve biodiversity. My dissertation research is focused on the historical, ecological and evolutionary underpinnings driving the origin, diversification, and maintenance of biodiversity in springtails (Collembola). This class of tiny, wingless insect-like hexapods includes some of the most abundant (and perhaps, most diverse) arthropods on earth. They have colonized, diversified, and adapted to nearly every terrestrial habitat from marine intertidal zones and tropical rainforests to polar deserts and caves, yet the evolutionary mechanisms behind their ecological success are poorly understood. Ecological specialization is a central theme in my first two chapters. Species with obligate ecological associations offer simple systems to evaluate biogeographical hypotheses and also provide an ecological context to test the effects and consequences of specialization on patterns of diversity. In Chapter 1, I identify and compare spatial and temporal patterns of molecular diversity for two ecologically distinct and codistributed genera of cavernicolous springtails (cave-obligate vs. cave-facultative species) from a regional cave-bearing karst system spanning the Mississippi River in Illinois and Missouri. Phylogeographic analysis revealed that evolutionary processes of vicariance and dispersal were both major influences on patterns of cave springtail diversity, but the effects of these processes are also strongly influenced by intrinsic ecological factors, in this case, the degree of cave-dependence. Estimates of genetic structure and divergence times also implicated climatic and geological processes involved in the formation of the modern Mississippi River valley as major factors driving the isolation of cave-obligate species, but cave-facultative species have been able to maintain genetic connectivity across this barrier. In Chapter 2, I developed a molecular dataset for marine littoral-obligate springtails collected along the Pacific and Atlantic coasts of Panama to identify transisthmian sister taxa, determine processes driving and maintaining their isolation, and to evaluate their timing of origin. I was able to identify multiple geminate species pairs spanning the Isthmus and molecular analyses revealed examples of pre-Pliocene vicariance, post-closure dispersal, and cryptic diversification across the Isthmus of Panama. This study not only demonstrates that ecological specialization can (but not always) reduce genetic connectivity across geographic barriers, but also corroborates recent (and controversial) geological and biogeographical estimates of an early Miocene closure of the Panama Isthmus. These works demonstrate the utility of incorporating ecologically specialized springtails in evolutionary investigations. However, independent timing information is essential for assessing historical factors influencing contemporary patterns of diversity. Unfortunately, springtails (and most other small, soft-bodied organisms) lack a useful fossil record for this purpose. As a result, employing “universal” rates of molecular evolution to estimate divergence times is common, even though evolutionary rates can vary considerable across taxa. In Chapter 3, I assess the validity of the generalized arthropod rate assumption by conducting a Bayesian phylogenetic analysis to evaluate the relative rate of molecular evolution across all major hexapod groups. I found that substitution rates in Collembola are not significantly different from most other hexapod groups and suggest that the use of “universal” insect molecular clocks are appropriate for estimating collembolan evolutionary timescales. An additional yet fundamental challenge impacting all fields of biology is the fact that most biodiversity remains to be discovered or is poorly understood—including many species that are of potential conservation concern. This is exacerbated in collembolan taxonomy, due to the lack of variation in discrete morphological characters, and the general shortage of taxonomic expertise in North America, reflected in the limited number of taxonomic tools available to researchers (and the public) for identifying species in this region. To help address this challenge, I produced detailed morphological taxonomic descriptions for all New World species of the springtail genus Willowsia, including a new species that is endemic to Florida in Chapter 4. Most members in this genus are from Asia, but comparative morphological analysis revealed two unique character states shared only by endemic New World Willowsia and Americabrya, providing prima facie evidence of their independent evolution from a common New World ancestor.
Issue Date:2018-07-11
Type:Thesis
URI:http://hdl.handle.net/2142/101700
Rights Information:Copyright 2018 Aron Katz
Date Available in IDEALS:2018-09-27
Date Deposited:2018-08


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