The Evolutionary and Developmental Basis of Parallel Reduction in Mammalian Zeugopod Elements

• Published in: The American naturalist 2007-01, Vol.169 (1), p.105-117
• Main Authors: Sears, Karen E., Behringer, Richard R., Rasweiler IV, John J., Niswander, Lee A.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal morphology; Animal, plant and microbial ecology; Animals; Bats; Biological and medical sciences; Biological Evolution; Cartilage; Chiroptera - anatomy & histology; Chiroptera - embryology; Diaphyses; Evolutionary biology; Extremities - anatomy & histology; Fibula; Forelimbs; Fundamental and applied biological sciences. Psychology; General aspects; Mammalia; Mammals; Mice - anatomy & histology; Mice - embryology; Parallel evolution; Rodents; Skeletal system; Tibia; Ulna; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0003-0147; 1537-5323
• DOI: 10.1086/510259

Understanding the mechanisms by which parallel evolution occurs has the potential to clarify the complex relationship between evolution and development. In this study, we examine the role of development in the repeated reduction of zeugopod elements during mammalian evolution, a functionally important phenomenon enabling locomotor specialization. By completing a morphometric study (incorporating both analyses of variation and phylogenetics) of mammalian limbs, we are able to demonstrate an evolutionary trend toward width reduction in posterior zeugopod elements of the forelimbs and hindlimbs, the ulna and fibula, respectively. We also examine the developmental basis of limb reduction in three test cases, the batCarollia perspicillataulna and fibula and the mouseMus musculusfibula. The most common pattern of reduction, that of reduced element width, was achieved via the same developmental process in both bat and mouse limbs (i.e., by a slower growth rate relative to other skeletal elements), suggesting that the parallel reduction of the posterior zeugopod element within mammals could have occurred primarily by the repeated evolution of the same developmental mechanism. However, our findings also suggest that the developmental mechanisms behind the parallel evolution of other, more taxon‐specific characteristics of limb reduction (i.e., element fusion) are not conserved.