@article{THESIS,
      recid = {3060},
      author = {Witte, Matthew},
      title = {Trait Asymmetry and Development in the Middle Devonian  Trilobite Genus <i>Eldredgeops</i> Struve 1992},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2021-06},
      number = {THESIS},
      pages = {175},
      abstract = {Developmental systems regulate the expression of  phenotypic variation (Laland et al., 2015) through various  types of morphological homeostasis or canalization (per  Canon, 1932; Waddington, 1957). This variation is one of  the main drivers of evolution by means of natural selection  (Darwin, 1859). The processes of environmental and/or  genetic canalization—which control the expression of  symmetric phenotypic variation among individuals in a  population—are known to serve as a constraint on evolution  (see reviews by see reviews by Møller and Swaddle, 1997;  Polak, 2003; Graham et al., 2010; Klingenberg, 2015;  Webster, 2019 and references therein), whether and how  homeorhesis—the process regulating within individual  left-ride symmetry of individual traits—relates to  phenotypic evolution is not well known; nor is the degree  to which genetic and environmental canalization relate to  homeorhesis. Empirical studies of homeorhesis have almost  exclusively been conducted by neontologists. However, to  understand the macroevolutionary consequences of  morphological homeostasis, and to determine the timescale  over which morphological homeostasis limits the expression  of phenotypic variation—both within a species and across  clades—it is necessary to study homeostasis within the  fossil record (see discussion by Webster, 2019).

The  following studies build upon the central idea of  understanding the components of variation within the Middle  Devonian trilobite genus Eldredgeops. Chapter 1 presents a  phylogenetic framework for the clade of interest, focusing  on the taxonomic relationships of Eldredgeops within the  larger context of the family Phacopidae. Using Bayesian  inference and parsimony-based methods, trees were recovered  that largely converged on similar topologies suggesting a  greater degree of phylogenetic signal than previous  phylogenetic studies examining the Phacopidae. Chapter 2  explores the relationship between the components of  variation in related to eye-lens distributions in the eyes  of two species of Eldredgeops. This study is the first to  use a maximum likelihood method proposed by Young (2007) to  estimate the symmetric and asymmetric components of  variation. The final chapter, Chapter 3, further explores  developmental asymmetries in the eye, as well as the  relative addition of eye-lenses through ontogeny, to  propose a model of eye development that can be applied to  all trilobites. 

These studies represent the first steps  in testing developmental hypotheses in deep time ultimately  aimed at understanding what role developmental asymmetries  may have on the evolutionary trajectory of traits.},
      url = {http://knowledge.uchicago.edu/record/3060},
      doi = {https://doi.org/10.6082/uchicago.3060},
}