Heterochrony in Two Sculpins of the GenusPsychrolutes: Growth Outpaces Skeletal Development in an Apex Predator among Ichthyoplankton

Abstract

In fishes, development is a plastic process, even among closely related, sympatric taxa. Selective pressure manifests itself through morphological divergences in early life. Of particular interest in the present study is heterochrony: alterations in developmental rates of change. Examinations of skeletal development in the Soft Sculpin, Psychrolutes sigalutes, and Tadpole Sculpin, Psychrolutes paradoxus, revealed marked developmental differences between species. While P. paradoxus quickly develops an adult skeleton and settles in adult habitat, P. sigalutes undergoes a remarkably protracted transformation (the transition from larval to juvenile characters) over a period of three to four months. It reaches sizes in excess of 40 mm (75% of adult size) before settling. While the earliest phases of life focus on the development of feeding elements and a transition from larval/anguilliform locomotion to caudal/subcarangiform propulsion, the two species diverge quickly in postflexion development. With the excep...