The nearest-living-relative method of paleoclimate reconstruction: Testing the assumptions with species of the rodent Marmota [La méthode du plus proche parent vivant de reconstruction paléoclimatique : examen des hypothèses avec les espèces de rongeurs Marmota].

Résumé

The nearest-living-relative method is often used in extracting paleoclimate information from fossil assemblages. One of its primary assumptions is that there is a phylogenetic control on the climatic tolerances of evolving lineages. This assumption is critical but rarely is tested. If it holds true, then correlations should exist between cladograms that reflect evolutionary history and multivariate data that reflect relationships between climate spaces of taxa under consideration. This study applies a phylogenetic approach to explore the relationship between climatic features (such as maximum and mminimum January and July temperatures, annual precipitation, and seasonality) and evolution of extant species within Marmota (the marmots and woodchucks). Species within this genus are potentially important paleoclimatic indicators because of their relatively restricted geographic distribution and habitat requirements and their abundance in certain fossil deposits. The association between a phylogenetic hypothesis based on molecular data and multivariate climatic parameters, both derived from published records, was tested using several methodologies, including Felsenstein's independent contrast method. The technique involved mapping the climatic tolerances of various species onto the hypothesized phylogenetic relationships and thereby determining if groups of species were delineated by identifiable climatic boundaries. In addition, the relative distances between taxon-defined multivariate climate space were compared to the evolutionary distances between taxa to determine if the amount of climatic difference between given taxa corresponded to their taxonomic distance. Preliminary results do not support a correlation between phylogeny and climatic tolerances for the analyzed Marmota species. Further work is needed in order to fine-tune these methods and better explore the relationship between climate and mammalian evolution.