Abstract
ABSTRACTCover illustration. The canals of the mechanosensory lateral line system of bony fishes vary in morphology among species, but are contained within a conserved subset of dermatocranial bones. In this issue of the Journal of Morphology, Webb et al. (pp. 678–692 10.1002/jmor.20247) investigate the role of heterochrony in the evolution of widened cranial lateral line canals from narrow canals using a comparative developmental morphological analysis of the lateral line canals in three Lake Malawi cichlids, Labeotropheus fuelleborni and Metriaclima zebra (narrow canals) and Aulonocara baenschi (widened canals). The cover image shows a 3‐D reconstruction (volume rendering) of μCT data from Aulonocara baenschi, revealing the large bony pores of the widened canals in the dentary, anguloarticular and preopercular bones.
Highlights
The mechanosensory lateral line system of fishes detects unidirectional and low frequency oscillatory water flows and plays critical roles in prey detection and other behaviors
Narrow and widened cranial lateral line canals have been shown to be functionally distinct (Webb, et al, 2008; Denton and Gray, 1988, 1989) and it has been suggested that the evolution of canal morphology among teleosts is the result of heterochrony, or evolutionary changes in developmental timing (Webb 1989a)
It has shown that: 1) canal neuromast number and the pattern of canal morphogenesis are conserved, regardless of adult canal morphology, 2) the evolution of widened canals from narrow canals can occur via dissociated heterochrony and regional heterochrony in canal diameter and neuromast size between canals accounts for variation among canals within a species, and 3) the morphology of the lateral line canals and the dermal bones in which they are found can evolve independently of each other
Summary
The mechanosensory lateral line system of fishes detects unidirectional and low frequency oscillatory water flows and plays critical roles in prey detection and other behaviors (reviewed inWebb, et al, 2008). The cranial lateral line canals, which are integrated into a conserved subset of the dermatocranial elements of bony fishes, demonstrate well-defined morphological variation among bony fishes and among teleosts in particular (narrow, widened, reduced and branched canals; Webb, 1989b). The most common of the four canal morphologies, are well-ossified with small pores that connect the fluid within the canal with the outside environment. The canal roof is weakly ossified and dominated by large bony canal pores, which are covered by an epithelium that is pierced by very small “epithelial pores” that provide the connection between the fluid within the canal and the external environment. The study of closely related species with narrow and widened canals provide an interesting context for the integrative study of the adaptive evolution of the lateral line system, but it requires detailed analyses of lateral line development
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