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Permanent URL to this publication: http://dx.doi.org/10.5167/uzh-39846

Wilson, L A B. The evolution of morphological diversity in rodents : patterns of cranial ontogeny. 2010, University of Zurich, Faculty of Science.

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Abstract

The role of ontogeny in the generation of adult orphological diversity is poorly understood. The aims of this study are to investigate the developmental bases for the extraordinary level of anatomical and ecological diversity and differing life strategy displayed by hystricognath rodents (e.g. guinea pigs, porcupines, capybaras) compared with muroids (mice and rats). The complementary methodological frameworks of heterochrony and allometry are used as a base to explore patterns of cranial growth at different points in developmental time. Developmental series of 58 rodent species were examined for this work, including prenatal and postnatal specimens.
In one part of this thesis I examine the importance of equence heterochrony in morphological evolution. Two time windows are investigated: the onset of skeletal formation, beginning prenatally, and the point of suture closure, occurring during the latter part of postnatal growth. equence heterochrony was analysed using the Parsimov ethod. In the first comprehensive assay of heterochronies in cranial suture growth for a mammalian clade, we find that numerous heterochonies in suture closure have occurred in the evolutionary history of hystricognaths. Sutures are of particular interest because they serve as major sites of bone expansion during postnatal craniofacial growth in the vertebrate skull, and we show that their sequence of closure represents an aspect of ontogeny with functional and phylogenetic correlates. In complement, we present the most comprehensive sampling of rodent ossification sequences to date, including data for non‐model organisms nd several representatives from both muroid and hystricognath clades. This study contributes considerably to improving the amount of data that presently exist on skeletal development across mammalian clades. We find, in ontrast to the results for suture closure patterns, that heterochrony is not a common mode of evolutionary change during skeletal formation. We additionally present data on intraspecific variation in cranial, postcranial, and autopodial ossification sequences for Rhabdomys pumilio, to further expand the extremely limited literature regarding this topic.
It has been hypothesized that most morphological evolution occurs by allometric differentiation. Hence the second part of this thesis focuses upon the evolution and patterning of ontogenetic allometry in rodents. The evolution of postnatal growth trajectories is examined across major clades; prenatal skull growth is comprehensively recorded morphometrically for the first time for the muroid rodent, R. pumilio. Studies directed towards examining the evolution of allometry are few and of small scope. We investigated the influence of phylogenetic relations and ecological factors on the results of the first quantification of allometric disparity among rodents by exploring allometric space, a multivariate morphospace that, in this study, was derived from the ontogenetic trajectories of 17 muroids and 17 hystricognaths. Disparity was quantified using angles between ontogenetic trajectories. We found an overlapping occupation of allometric space for muroids and hystricognaths, indicating similar abilities to evolve in different directions of phenotypic space. We show changes to covariance structure were common during rodent evolution and anatomic diversity was not found to constrain the labile nature of allometric patterning. Grouping of taxa in allometric space was found to be related to dietary habit; rodents sharing morphological features considered to be associated with the processing of particular dietary materials were found to group most closely with one another, showing the evolution of allometry in rodents has an adaptive basis. Whilst postnatal ontogenetic allometry has been documented for many species, there are very few studies that compare the dynamics of prenatal and postnatal growth. From this standpoint, trends regarding the linearity of prenatal allometry and its association to postnatal growth patterns are relatively unknown. Using a reflex microscope to measure cleared and stained specimens of R. pumilio, I performed the first study of prenatal ontogenetic allometry in a rodent, providing a crucial base for future comparative studies. Bivariate and multivariate estimates of allometry were coupled with matrix comparison methods to assess growth trends. The results indicate that prenatal growth is characterized by rapid lengthening of cranial elements. Ontogenetic allometric trends are found to shift between the prenatal and postnatal period, and localized variation in growth relationships occurs among cranial elements.

Item Type:Dissertation
Referees:Sánchez-Villagra M R, Brinkmann W, Bucher H, Goswami A
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
DDC:560 Fossils & prehistoric life
Language:English
Date:2010
Deposited On:03 Jan 2011 18:21
Last Modified:19 Oct 2012 01:52
Number of Pages:239
ISBN:978-3-905923-06-3
Additional Information:The evolution of morphological diversity in rodents : patterns of cranial ontogeny / vorgelegt von Laura A.B. Wilson. - Zürich, 2010
Related URLs:http://opac.nebis.ch/F/?local_base=NEBIS&con_lng=GER&func=find-b&find_code=SYS&request=006250147 (Publisher)

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