Xavier Jordana

Publications (4)45.13 Total impact

• Article: Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology.

  Meike Köhler, Nekane Marín-Moratalla, Xavier Jordana, Ronny Aanes
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  ABSTRACT: Cyclical growth leaves marks in bone tissue that are in the forefront of discussions about physiologies of extinct vertebrates. Ectotherms show pronounced annual cycles of growth arrest that correlate with a decrease in body temperature and metabolic rate; endotherms are assumed to grow continuously until they attain maturity because of their constant high body temperature and sustained metabolic rate. This apparent dichotomy has driven the argument that zonal bone denotes ectotherm-like physiologies, thus fuelling the controversy on dinosaur thermophysiology and the evolution of endothermy in birds and mammal-like reptiles. Here we show, from a comprehensive global study of wild ruminants from tropical to polar environments, that cyclical growth is a universal trait of homoeothermic endotherms. Growth is arrested during the unfavourable season concurrently with decreases in body temperature, metabolic rate and bone-growth-mediating plasma insulin-like growth factor-1 levels, forming part of a plesiomorphic thermometabolic strategy for energy conservation. Conversely, bouts of intense tissue growth coincide with peak metabolic rates and correlated hormonal changes at the beginning of the favourable season, indicating an increased efficiency in acquiring and using seasonal resources. Our study supplies the strongest evidence so far that homeothermic endotherms arrest growth seasonally, which precludes the use of lines of arrested growth as an argument in support of ectothermy. However, high growth rates are a distinctive trait of mammals, suggesting the capacity for endogenous heat generation. The ruminant annual cycle provides an extant model on which to base inferences regarding the thermophysiology of dinosaurs and other extinct taxa.
  Nature 06/2012; 487(7407):358-61. · 36.28 Impact Factor
• Article: Evidence of correlated evolution of hypsodonty and exceptional longevity in endemic insular mammals.

  Xavier Jordana, Nekane Marín-Moratalla, Daniel DeMiguel, Thomas M Kaiser, Meike Köhler
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  ABSTRACT: Here, we test whether the increase in tooth height in insular endemics results from the expansion of the dietary niche under resource limitation, as widely considered, or whether it represents an investment in dental durability in response to the selection for extended longevity under low levels of extrinsic mortality. We tested these hypotheses in the extremely hypsodont fossil bovid Myotragus balearicus from the Balearic Islands, an ideal model to study the evolutionary trends on islands. Dental abrasion was significantly lower in the insular bovid than in highly hypsodont continental artiodactyls, suggesting that feeding habits are not the sole driving force behind increased crown height. However, the estimated longevity for M. balearicus based on dental durability was two times that predicted from body mass. Survivorship curves confirm that an extraordinarily large number of individuals approached the longevity of the species. Our results, hence, provide evidence that hypsodonty in insular endemics is the outcome of selection for increased durability of the permanent dentition in association with an extended lifespan. In the context of insularity, our results lend additional support to the disposable soma theory of ageing confirming the dependency of somatic maintenance and repair on lifespan, and its control by resource availability and extrinsic mortality.
  Proceedings of the Royal Society B: Biological Sciences 04/2012; 279(1741):3339-46. · 5.41 Impact Factor
• Article: The ontogeny of bone growth in two species of dormice: Reconstructing life history traits

  Rubén García-Martínez, Nekane Marín-Moratalla, Xavier Jordana, Meike Köhler
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  ABSTRACT: Abstract Though bone histology has become a powerful tool to reconstruct life history strategies and physiology in living and extinct reptiles and amphibians, it is of limited use in mammals. Dormice (Myoxidae) are good candidates for assessing the relation between bone microstructure and life history due to their long life span, marked physiological cycles and negligible bone remodelling. We carried out the most comprehensive study so far analyzing 16 wild individuals of unknown age belonging to two different species of dormice, Glis glis and Eliomys quercinus. Our study shows a high degree of consistency in the number of resting lines present in bones of the same individual, with femora providing the most accurate age estimations. Moreover, the presence of a single LAG in some juveniles allows discerning between offspring from different reproductive events (early or late litters). Résumé Bien que lhistologie des os soit devenue un outil précieux pour la reconstitution des stratégies de lhistoire de la vie et de la physiologie chez les reptiles et amphibiens vivants et éteints, elle est dune utilité limitée chez les mammifères. Les Dormice (Myoxidae) sont de bons candidats pour évaluer la relation entre microstructure de los et histoire de la vie, en raison de leur longue durée de vie, de leurs cycles physiologiques marqués et des modifications négligeables de leurs os. Nous avons réalisé létude jusquà présent la plus complète, en analysant 16 individus sauvages dâge inconnu, appartenant à deux différentes espèces de dormice, Glis glis et Eliomys quercinus. Notre étude montre un degré élevé de cohérence dans le nombre de lignes de repos présentes dans les os du même individu, avec les fémurs fournissant les estimations dâge les plus précises. En outre, la présence dun unique LAG chez certains juvéniles permet de faire la distinction entre progénitures, à partir de différents évènements de la reproduction (portées récentes ou anciennes).
  Comptes Rendus Palevol 01/2011; In Press,. · 1.04 Impact Factor
• Article: Enamel microstructure in the fossil bovid Myotragus balearicus (Majorca, Spain): Implications for life-history evolution of dwarf mammals in insular ecosystems

  Xavier Jordana, Meike Köhler
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  ABSTRACT: The causes underlying the evolution of insular dwarfs and giants are a matter of ongoing debate. Because body size is among the principle life history traits, recent works aim to understand the evolution of insular dwarfs in the framework of life history theory. However, the hypotheses put forward so far are conflicting. Early studies, suggested that dwarfing is a consequence of selection for an increased reproduction associated to an accelerated life history (formerly r-selection). Recent work, however, based on the analysis of bone histology of the fossil insular dwarf bovid Myotragus balearicus (Balearic Islands, Spain), concluded that dwarfing on islands results from a decrease in growth rate associated to a slow life history (formerly K-selection) in response to selective forces peculiar to insular conditions. In the present work, we reconstruct the schedule of certain life history traits by estimating the rate of dental development and eruption times in M. balearicus and, for comparisons, in an extant caprine (Ovis aries). We used histological techniques to calculate crown formation time, daily secretion rate and crown extension rate, in the lower molars. Eruption pattern in M. balearicus was analysed through the radiological images of an ontogenetic series of mandibles. Our results show that dental crowns grew at slower rates and the period of crown formation was more extended in the dwarfed fossil bovid than in other extant caprines, resulting in dental development and eruption time that doubles that of extant bovids of similar body size. This suggests an important delay in life history schedules. Concordant with the delayed dental development, the striking hypsodonty of Myotragus is indicative of an extended lifespan. These results, together with previous findings from long bone histology, provide empirical evidence for a shift towards a slow life history in this insular dwarfed mammal. Density-dependent resource limitation is hypothesized as the main trigger of the life history and body size evolution of Myotragus.Research Highlights► We estimate the rate of dental development in an extinct insular dwarf bovid. ► Results show that dental development was delayed twofold the time of other bovids. ► This provides empirical evidence to the slow life history hypothesis. Insular mammals evolve towards slow growth, delayed maturity and extended lifespan. ► Density-dependent resource limitation is hypothesized as the main trigger.
  Palaeogeography Palaeoclimatology Palaeoecology 300:59-66. · 2.39 Impact Factor