Meeting Abstract
51.4 Sunday, Jan. 5 11:00 Modularity and Heterochrony in the Adaptive Evolution of the Lateral Line System of Fishes BIRD, NC*; WEBB, JF; University of Rhode Island; University of Rhode Island nathan_bird@mail.uri.edu
The ability of different modules to evolve independently is a fundamental concept in organismal evolution. Module independence is critical for local evolutionary changes in developmental rate or timing, i.e., heterochrony. This study examined the role of heterochrony in the evolution of the cranial lateral line (LL) canals and how it reveals modularity. Among the four LL canal phenotypes found in teleosts, simple heterochronic shifts may explain the evolution of branched and reduced canals from a narrow canal phenotype, but widened canals cannot be explained as simply. Rather, it was hypothesized that dissociated heterochrony, or a mix of paedomorphic and peramorphic changes, may explain the evolution of widened canals. This hypothesis was tested by comparing ontogenetic trends in canal and neuromast growth in two closely related Lake Malawi cichlids with divergent adult LL canal morphologies, Tramitichromis sp. (narrow canals) and Aulonocara stuartgranti (widened canals). Neuromast patterning and the pattern of canal morphogenesis was the same, but Aulonocara tended to show delayed canal enclosure and ossification, indicating a paedomorphic shift. ANCOVA revealed that the increase in LL canal diameter was 1.8-3.6X faster and neuromast growth (width) was 1.6-2.1X faster in Aulonocara than in Tramitichromis. Johnson-Neyman tests showed that canals are already wider and neuromasts are already larger in Aulonocara larvae and juveniles of 7.8-12.2 mm SL, indicating a developmental acceleration. Such peramorphic shifts in both canals and neuromasts suggest tight integration among these genetic modules. The mix of paedomorphic and peramorphic trends in the lateral line system supports the hypothesis of evolution by dissociated heterochrony. Supported by NSF grant IOS-0843307 to JFW.
