Morphological covariation and growth of the skull in the house mouse (Mus musculus): the role of Robertsonian translocations in a zone of chromosomal polymorphism /

• Autores: Jessica Martínez-Vargas
• Directores de la Tesis: Jacinto Ventura Queija (dir. tes.), Francesc Muñoz Muñoz (codir. tes.)
• Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2017
• Idioma: español
• Tribunal Calificador de la Tesis: Xavier Jordana Comín (presid.), Neus Martínez Abadias (secret.), Riccardo Castiglia (voc.)
• Programa de doctorado: Programa Oficial de Doctorado en Biodiversidad
• Materias:
  • Ciencias de la vida
    • Biología animal (zoología)
• Enlaces
  • Tesis en acceso abierto en:  DDD  TDX 
• Resumen

  • The western European house mouse (Mus musculus domesticus Schwarz and Schwarz 1943) shows a particularly strong predisposition towards the occurrence and fixation of Robertsonian translocations; a type of chromosomal reorganization that entails centromeric fusion of chromosomes and, therefore, a decrease in diploid number. As a result, this house mouse subspecies displays great karyotypic diversity. The accumulation of Robertsonian translocations has the potential to hinder gene flow. Consequently, these chromosomal rearrangements are considered potential triggering factors of chromosomal speciation. Furthermore, restricted genetic exchange among populations could ultimately lead to their morphological divergence.

    The present PhD thesis intends to delve into the role that Robertsonian translocations may have on covariation among morphological traits, phenotypic diversification of skeletal structures, as well as on the growth of these structures over early postnatal ontogeny, in natural populations of the western European house mouse. The study area comprises the Barcelona Robertsonian system of Mus musculus domesticus, which is characterized by seven different metacentric chromosomes with a clinal distribution and includes metacentric populations with diploid numbers ranging between 27 and 39 chromosomes, as well as surrounding populations consisting of specimens with the standard karyotype of 40 chromosomes. The present research specifically focuses on comparative analyses of morphological covariation and phenotypic variation of the mandible and the cranium in adult specimens, as well as the pattern of mandible growth in ontogenetic series of juvenile specimens ranging from the second to the eighth week of postnatal life. Additionally, mandible growth is assessed in an ontogenetic series of the classical inbred strain of the house mouse (Mus musculus) C57BL/6J, with the aim of contextualizing the potential differences in mandible growth between wild mice with the standard karyotype and with Robertsonian translocations. While the study of the adult specimens is conducted by applying geometric morphometric techniques, the study of the ontogenetic series of juvenile mice involves a multi-method approach, including histological analyses of bone cross-sections and bone surface, as well as geometric morphometrics.

    The major results of the present research are the following: i) allometry has an important integrating effect over morphological structures, whose relevance increases as more Robertsonian translocations accumulate; ii) the modular structure of the mandible into the alveolar region and ascending ramus is maintained regardless of the number of Robertsonian translocations; iii) morphological integration between the dorsal and ventral cranial regions is not altered by Robertsonian translocations; iv) the modular organization of the cranium into the basicranium and face in ventral view, and into the neurocranium and face in dorsal view, is usually confirmed in all chromosomal groups; v) karyotypic differentiation in adult specimens, due to the accumulation of metacentrics, is positively associated with morphological diversification of the dorsal and ventral regions of the cranium; vi) the structure of morphological covariation of the mandible and the phenotypic differentiation of the dorsal region of the cranium positively correlate with geographic distancing among chromosomal groups; vii) mandible growth patterns differ between wild mouse specimens with the standard karyotype and those with Robertsonian translocations, although differences are more notable between the standard wild mice and laboratory mice of the C57BL/6J strain; viii) between-group dissimilarities in mandible growth become more evident after weaning; ix) strength of morphological integration of the mandible decreases over early postnatal ontogeny in all mouse groups.

    In light of these results, Robertsonian translocations can modify the morphological covariation of skull traits and can have certain influence over the ontogeny of the mandible during early postnatal life. Accordingly, these chromosomal rearrangements would play an important role in divergent morphological evolution.