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Presenting Author(s) Richard Hinchliffe
Abstract Title Making very long larval limbs: modulation of urodele skeletogenic processes in the floating larvae of the Southern Crested Newt, Triturus karelini.
Full author List Richard Hinchliffe (University of Wales, Aberystwyth, UK), Emilia Vorobyeva (Institute of Ecology & Evolution, Moscow, Russia) & Jacqueline Géraudie (Université Paris 7, France).
Text of abstract

Most species of urodele are small-bodied with larvae adapted to bottom living with relatively short developing limbs (the "standard" pattern), But a few others including the Southern Crested Newt (Triturus karelini; specimens collected in Georgia) have early larvae with a floating lifestyle and relatively very long forelimbs (approximately 50% of snout/vent length compared with the "standard" 25%). Post-metamorphosis their limbs attain a typical urodele definitive morphology and become weight bearing.

For T. karelini we examined larval skeletal development especially of radius/ulna and metacarpals/phalanges (digit 2), aiming to identify the modification of the standard developmental programmes involved. Initial prechondrogenic condensations appear only marginally longer than "standard", but the remarkable elongation of the thin cartilage "models" is achieved mainly by early and prolonged cartilage hypertrophy, accompanied by early diaphysis ossification. Thus long thin skeletal elements form. The most unusual of these is the terminal phalange which is very long and thin (its cartilage is only one to 3 cells thick): it is the last digit element to ossify (this begins proximally). The remarkable morphology of the terminal phalange of the larva with its increased surface area can be regarded as a larval adaptation for floating.

Overall this modification of the "standard" limb developmental programme appears to be adaptive and at least in some features to involve heterochronic Alberch-style* changes in the relative timing of developmental processes. Our analysis suggests in urodeles that despite the relatively uniform morphology of the definitive limb skeleton this is achieved by a rather plastic developmental programme.

*Blanco M J & Alberch P 1992 Evolution 46, 677-687.

Which session is your work most relevant to: Limb evolution