Tracing the origin of the panda's thumb

© 2015, Springer-Verlag Berlin Heidelberg. We investigate the relative development of the carnivoran radial sesamoids to untangle the evolution of this iconic structure. In the pandas (both giant and red), this `false thumb¿ is known to perform a grasping role during bamboo feeding in both the red and giant pandas. An original locomotor role has been inferred for ailurids, but this remains to be ascertained for ursids. A large sample of radial sesamoids of Indarctos arctoides from the Miocene of Batallones-3 (Spain) indicates that this early ailuropodine bear displayed a relatively hypertrophied radial sesamoid, with a configuration more similar to that of the red panda and other carnivorans than to that of giant pandas. This false thumb is the first evidence of this feature in the Ursidae, which can be linked to a more herbivorous diet. Moreover, in the two extant pandas, the false thumb should not be interpreted as an anatomical convergence, but as an exaptive convergence regarding its use during the bamboo feeding, which changes the evolutionary view of this singular structure.This study was supported by the Spanish Ministerio de Economía y Competitividad (CGL2011-25754, CGL2011-28681 and RYC–2009–04533 to D.M.A.). A.V. is a researcher in formation in the CSIC program JAE-PRE_CP2011 (CSIC program‘ Junta para la ampliación de estudios’), co-funded by the European Social Fund and has received funding from the European Union’s Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 226506 (SYNTHESYS; SE-TAF-3637),Peer Reviewe

The evolution and diversity of the Anolis dewlap

The neotropical lizard genus Anolis is an important model system for studies of the ecology and evolution of animal diversity. One of the most striking elements of Anolis diversity is found in the morphology of the dewlap, an extensible flap of colored skin on the throat that anoles use to communicate during social interactions. The evolutionary forces that have promoted the evolution of dewlap diversity are poorly understood. A study of reproductive success in A. carolinensis showed for the first time that dewlap color is currently under selection in an anole (Chapter 1). However, this is unlikely to be a result of intrasexual competition because neither dewlap morphology nor reproductive success are related to male territory size or quality. Instead the dewlap may be under intersexual selection from female mate choice. In addition to sexual selection, the dewlap may evolve in response to a variety of other processes such as species recognition, predation, sensory drive, or a combination of these. A study of variation among populations of a single species, A. sagrei, revealed that the dewlap may be undergoing rapid adaptive diversification driven by several of these processes simultaneously (Chapter 2), while a study of variation among species in dewlap size showed that similar processes are likely shaping the evolution of the dewlap in female anoles (Chapter 3). In a case study of male-female pair formation in the Costa Rican anole A. limifrons, dewlap size or color were not good predictors of which males would form pairs and which would not, though males and females that were similar in size were found to form pairs more often than animals that were dissimilar in size (Chapter 4). Finally, a study of the correlated evolution of traits related to locomotion in anoles found that morphology, behavior, and habitat use evolve in tandem among 31 species of anoles from the Greater Antilles (Chapter 5). Together, these studies suggest that the evolutionary ecology of anoles is more complex than previously thought, and that future studies of the dewlap may provide more general insight into the evolution of diversity of animal ornaments

Patterns of tooth replacement in osteichthyans: variations on a theme

Nonmammalian tooth-bearing vertebrates usually replace their teeth throughout life. Much about how a replacement pattern is generated has been learned from zebrafish. However, to understand general mechanisms of tooth replacement, advantage can be taken from studying other, “nonmodel” species. We have mapped the patterns of tooth replacement in widely divergent aquatic osteichthyans using 2D charts, in which one axis is time, the other linear spacing along the tooth row. New teeth that are generated simultaneously are considered part of the same odontogenic wave. Using this approach, it appears that a similar, general pattern underlies very distinctive dentitions in distantly related species. A simple shift in spacing of odontogenic waves, or in distance between subsequent tooth positions along a row (or both), can produce dramatically different dentitions between life stages within a species, or between closely related species. Examples will be presented from salmonids, cyprinids, and cichlids. Our observations suggest that lines linking subsequent positions may have more biological significance than replacement waves (usually linking alternate positions), often used to explain the generation of patterns. The presence of a general pattern raises questions about common control mechanisms. There is now increasing evidence, at least for the zebrafish, to support a role for stem cells in continuous tooth renewal and control of replacement patterns

The role of visual adaptation in cichlid fish speciation

D. Shane Wright (1) , Ole Seehausen (2), Ton G.G. Groothuis (1), Martine E. Maan (1) (1) University of Groningen; GELIFES; EGDB(2) Department of Fish Ecology & Evolution, EAWAG Centre for Ecology, Evolution and Biogeochemistry, Kastanienbaum AND Institute of Ecology and Evolution, Aquatic Ecology, University of Bern.In less than 15,000 years, Lake Victoria cichlid fishes have radiated into as many as 500 different species. Ecological and sexual sel ection are thought to contribute to this ongoing speciation process, but genetic differentiation remains low. However, recent work in visual pigment genes, opsins, has shown more diversity. Unlike neighboring Lakes Malawi and Tanganyika, Lake Victoria is highly turbid, resulting in a long wavelength shift in the light spectrum with increasing depth, providing an environmental gradient for exploring divergent coevolution in sensory systems and colour signals via sensory drive. Pundamilia pundamila and Pundamilia nyererei are two sympatric species found at rocky islands across southern portions of Lake Victoria, differing in male colouration and the depth they reside. Previous work has shown species differentiation in colour discrimination, corresponding to divergent female preferences for conspecific male colouration. A mechanistic link between colour vision and preference would provide a rapid route to reproductive isolation between divergently adapting populations. This link is tested by experimental manip ulation of colour vision - raising both species and their hybrids under light conditions mimicking shallow and deep habitats. We quantify the expression of retinal opsins and test behaviours important for speciation: mate choice, habitat preference, and fo raging performance