Impact of the terrestrial-aquatic transition on disparity and rates of evolution in the carnivoran skull

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• 作者：Katrina E Jones (1) (5)
  Jeroen B Smaers (2)
  Anjali Goswami (3) (4)
  
  1. Center for Functional Anatomy and Evolution ; Johns Hopkins University ; Baltimore ; MD ; USA
  5. Department of Organismic and Evolutionary Biology ; Museum of Comparative Zoology ; Harvard University ; 26 Oxford Street ; Cambridge ; MA ; 02138 ; USA
  2. Department of Anthropology ; Stony Brook University ; Stony Brook ; New York ; NY ; 11794-4364 ; USA
  3. Department of Genetics ; Evolution & Environment ; University College London ; Gower Street ; London ; WC1E 6BT ; UK
  4. Department of Earth Sciences ; University College London ; Gower Street ; London ; WC1E 6BT ; UK
  
• 关键词：Disparity ; Carnivora ; Fissiped ; Pinniped ; Cranial morphology ; Radiation ; Ecological transition ; Aquatic mammal
• 刊名：BMC Evolutionary Biology
• 出版年：2015
• 出版时间：December 2015
• 年：2015
• 卷：15
• 期：1
• 全文大小：2,881 KB
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• 刊物主题：Evolutionary Biology; Animal Systematics/Taxonomy/Biogeography; Entomology; Genetics and Population Dynamics; Life Sciences, general;
• 出版者：BioMed Central
• ISSN：1471-2148

文摘

Background Which factors influence the distribution patterns of morphological diversity among clades? The adaptive radiation model predicts that a clade entering new ecological niche will experience high rates of evolution early in its history, followed by a gradual slowing. Here we measure disparity and rates of evolution in Carnivora, specifically focusing on the terrestrial-aquatic transition in Pinnipedia. We analyze fissiped (mostly terrestrial, arboreal, and semi-arboreal, but also including the semi-aquatic otter) and pinniped (secondarily aquatic) carnivorans as a case study of an extreme ecological transition. We used 3D geometric morphometrics to quantify cranial shape in 151 carnivoran specimens (64 fissiped, 87 pinniped) and five exceptionally-preserved fossil pinnipeds, including the stem-pinniped Enaliarctos emlongi. Range-based and variance-based disparity measures were compared between pinnipeds and fissipeds. To distinguish between evolutionary modes, a Brownian motion model was compared to selective regime shifts associated with the terrestrial-aquatic transition and at the base of Pinnipedia. Further, evolutionary patterns were estimated on individual branches using both Ornstein-Uhlenbeck and Independent Evolution models, to examine the origin of pinniped diversity. Results Pinnipeds exhibit greater cranial disparity than fissipeds, even though they are less taxonomically diverse and, as a clade nested within fissipeds, phylogenetically younger. Despite this, there is no increase in the rate of morphological evolution at the base of Pinnipedia, as would be predicted by an adaptive radiation model, and a Brownian motion model of evolution is supported. Instead basal pinnipeds populated new areas of morphospace via low to moderate rates of evolution in new directions, followed by later bursts within the crown-group, potentially associated with ecological diversification within the marine realm. Conclusion The transition to an aquatic habitat in carnivorans resulted in a shift in cranial morphology without an increase in rate in the stem lineage, contra to the adaptive radiation model. Instead these data suggest a release from evolutionary constraint model, followed by aquatic diversifications within crown families.