Meeting Abstract
57.2 Tuesday, Jan. 5 The development of widened lateral line canals in a Lake Malawi cichlid: Insights into lateral line evolution DICKSON, JM*; WEBB, JF; University of Rhode Island; University of Rhode Island jdickson@mail.uri.edu
The mechanosensory lateral line system of bony fishes is composed of an array of neuromast receptor organs located in lateral line canals and on the skin of the head and body. The lateral line canals are an important component of the dermal cranial skeleton. Among teleosts there are four types of canal systems – one of these, widened canals, has evolved convergently in only ~12 families. Its taxonomic distribution suggests that it is an adaptation for prey detection and that widened canals evolved from narrow canals. But, what sorts of developmental changes can explain how they evolved? To answer this question the development of widened and narrow canals must be compared quantitatively among related taxa. Species with widened canals that are available for laboratory study are rare, but the Lake Malawi cichlid genus Aulonocara provides a unique opportunity for such a study. We carried out the first detailed histological analysis of the pattern and timing of the development of widened canals and canal neuromasts in the cichlid, Aulonocara baenschi (5-53 days post fertilization [dpf], <5mm–23 mm SL). Preliminary data show that the mandibular canal is partially formed at 15 dpf (9 mm SL) and canal enclosure is complete more than a month later at 47 dpf (22 mm SL). Simultaneously, canal diameter increases, maximum canal neuromast length triples (from 64 to 224 µm) and neuromast width appears to increase indicating a change in neuromast shape. Ontogenetic changes in canal diameter and neuromast size in A. baenschi will be compared to those in several other species of cichlids that have narrow canals in order to assess how the timing of developmental patterns can explain evolutionary change in the mechanosensory lateral line system of teleost fishes. Supported by NSF grant 0843307 to JFW.
