Evolution of body size of extinct endemic small mammals from mediterranean islands
- Autores: Blanca Moncunill-Solé
- Directores de la Tesis: Salvador Moyà Solà (dir. tes.), Meike Köhler (dir. tes.), Xavier Jordana Comín (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2016
- Idioma: español
- Tribunal Calificador de la Tesis: Josep Antoni Alcover (presid.), Marc Furió Bruno (secret.), María Rita Palombo (voc.)
- Programa de doctorado: Programa Oficial de Doctorado en Biodiversidad
- Materias:
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- Resumen
Body size (or its proxy: body mass) has a central position in the colossal web of interdependent biological variables of an organism. It shows correlation with lots of physiological, morphological, behavioral, ecological and life history features, and, thus, it affects the fitness of individuals and, ultimately, the biology and evolution of species. The shifts in size (or mass) from an evolutionary point of view are indicative of adaptations to ecosystems through natural selection. One of the most attractive and awesome ecogeographical trends in variation of body size is the well-known Island Rule. It is described that in island ecosystems small mammals evolve towards giants (relative to their mainland ancestors), while large mammals towards dwarf morphotypes. Associated with these size shifts, the insular biotas also show characteristic morphological, demographic, behavioral, and life history adaptations consequence of the different selective regimens of island (Island Syndrome). The possible causes of Island Rule have always been studied in extant biotas, which lack true endemic native species and have been highly modified by the arrival of humans and invasive species. The extinct biotas are the only ones that can provide a true view and genuine answers for explaining this phenomenon. Community ecologists have proposed several hypotheses to explain how ecological pressures trigger gigantism operating directly on the size of individual (predation hypothesis, food availability hypothesis or social-sexual hypothesis). However, recently other authors have interpreted the gigantism as a consequence of changes in the life history of individuals to which the body size is sensitive. The main objective of the present PhD Thesis is to make inference on the selection pressures behind the Island Rule taking into account the body mass of the extinct species and the island ecosystem (Mediterranean Islands). Due to the large amount of mammalian orders, the PhD Thesis is centered in micromammals because the knowledge of gigantism remains widely neglected. For knowing the weight of fossil species, it has been measured teeth, skulls and postcranial bones of 1340 individuals (170 species) of current relatives (rodents, lagomorphs and soricids). With this data, several predictive models have been developed with satisfactory results. Assessing the reliability of these models, it has been observed that the measurements of stylopods (principally diameters of femora and humeri) are better proxies of BM than other skeletal elements. Using these new models, the body masses of 22 fossil species (2250 individuals), including insular species and their mainland ancestor or relatives, were estimated. The results obtained contrast with previous approximations, where the authors used not suitable teeth predictive models. When the BM of insular species was compare with their mainland ancestor or extinct and extant relatives, it is observed that the most of them show a giant morph (with the exception of shrews from Crete and Sicily). The results of this PhD Thesis evidence that in small mammals the absence of predators is a primary driver in the body size shift in insular regimes. Thus, in small and more isolated islands is where the most incredible gigantism cases are observed. The study also evidences than in a total absence of predators, the resource availability can regulate the size increase. The study of the life history of these species reveals that they lived more than expected from their size. Thus, they move towards a slow life history, implying a longer lifespan and delayed reproduction. The results of this PhD Thesis give support to the model proposed where the mass changes due to their sensitive with life history changes.
