Either tropical niche divergence or tropical niche conservatism could drive the latitudinal diversity gradient. Greater niche divergence in the tropics could accelerate reproductive isolation leading to more rapid species formation. Alternatively, latitudinal asymmetry in niche conservatism, whereby tropical species are more conserved than high latitude species, could promote more dispersal in to than out of the tropics, leading to greater tropical richness. Here I test whether rates of climatic niche evolution vary across the latitudinal gradient for 164 closely related pairs of species. Using the evolutionary ages at which sister species diverge, and the niche divergence between them, I applied Brownian motion models to test whether rates of climatic niche evolution varied with latitude. My results indicate that climatic niche conservatism is strongest in the tropics. This suggests that the latitudinal diversity gradient is driven by the inability of tropical to adapt to temperate climates and colonize non-tropical latitudes.

Either tropical niche divergence or tropical niche conservatism could drive the latitudinal diversity gradient. Greater niche divergence in the tropics could accelerate reproductive isolation leading to more rapid species formation. Alternatively, latitudinal asymmetry in niche conservatism, whereby tropical species are more conserved than high latitude species, could promote more dispersal in to than out of the tropics, leading to greater tropical richness. Here I test whether rates of climatic niche evolution vary across the latitudinal gradient for 164 closely related pairs of species. Using the evolutionary ages at which sister species diverge, and the niche divergence between them, I applied Brownian motion models to test whether rates of climatic niche evolution varied with latitude. My results indicate that climatic niche conservatism is strongest in the tropics. This suggests that the latitudinal diversity gradient is driven by the inability of tropical to adapt to temperate climates and colonize non-tropical latitudes.

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Actualment, degut a la disponibilitat d’un gran nombre de genomes seqüenciats, el camp de la genòmica comparativa està experimentant grans avenços. Ara són possibles una àmplia gama d’estudis que fins fa poc eren inimaginables. En aquesta tesi hem volgut estudiar les innovacions evolutives en els genomes de mamífers. Hem escollit centrar l’estudi en mamífers degut a que els seus genomes tenen bona qualitat i hi ha més informació disponible, a més el fet d’incloure l’espècie humana afegeix interès. Ens hem centrat en tres qüestions interessants en el camp de l’evolució. Primer hem volgut determinar quina és la fracció de gens ortòlegs de mamífers que presenten desviacions específiques de llinatge en les tasses evolutives. Hem obtingut que al voltant del 25% dels gens tenen evidencies d’haver estat sotmesos a acceleracions i deceleracions específiques de branca. Hem trobat que sorprenentment, els gens accelerats normalment no solapen amb els gens amb evidencia de selecció positiva, demostrant que els tests emprats per detectar selecció positiva són massa conservadors. En segon lloc, hem aprofundit en quins són els determinants de l’evolució proteica, centrant-nos en l’edat d’origen i en les característiques estructurals. Per estudiar-ho hem utilitzat tant dominis com estructures proteiques i principalment hem trobat que l’edat d’origen és un dels determinants més importants. Finalment, hem investigat les característiques i els mecanismes d’origen d’un grup de gens molt joves: els gens específics de primats. Hem trobat que els gens específics de primats evolucionen ràpid, són curts i específics de teixit. Pel que fa al seu mecanisme d’origen, al voltant d’un 53% dels gens presenten evidencies d’haver-se originat a través de l’exaptació de transposons, 24% a partir de duplicacions parcials o totals i sorprenentment, 5.5% de novo a partir de regions no codificants de mamífers. / With the availability of a high number of sequenced genomes the comparative genomics field has experienced a great advance. A wide range of studies that some years ago were unconceivable are now possible. In this thesis we aimed to study evolutionary innovations in mammalian genomes. We chose to centre our studies in mammalian species because at that moment were the genomes with higher quality and also more additional information was available for them, and of course, the inclusion of human species added a point of interest. We wished to give insights into three exciting questions in the field of evolution. First we wanted to assess which is the fraction of mammalian orthologous genes that present lineage-specific deviations in the rate of evolution. We obtained that around 25% of the genes had evidence of accelerations and decelerations specific of a branch and, surprisingly, accelerated cases did not usually overlap with cases of genes experiencing positive selection, showing that tests to detect positive selection are excessively conservative. Secondly, we wanted to deepen into the determinants driving protein evolution, centering on age of origin and structural characteristics. We used protein domains and structures to study them and we mainly found that age of origin seems to be one of the most important determinants. And finally, we investigated the characteristics and mechanisms of origin of a group of very young genes: primate-specific genes. We report that primate-specific genes evolve fast, are short and highly tissue specific. Regarding their mechanism of origin, about 53% of them showed evidence of transposable elements exaptation, 24% of partial or total duplication and surprisingly 5.5% of de novo origination from mammalian noncoding regions.