Evolution of Gnathostome Lateral Line Ontogenies

Abstract

An outgroup analysis of multiple ontogenies provides the most robust approach to understanding phylogeny. Such an analysis of the lateral line system among extinct and extant gnathostomes reveals that lateral line placodes constitute the basic ontogenetic unit responsible for the development of this system. Six pairs of lateral line placodes appear to have existed in the earliest gnathostomes, and eight stages (stages A–H) can be recognized in their differentiation. Terminal truncation (heterochronic changes) in the primitive sequence of placodal development has occurred in one or more placodes in each gnathostome radiation, with the most extensive truncations occurring in arthrodire placoderms, lepidosirenid lungfishes and extant amphibians. The most extensive nonterminal changes in the primitive sequence of placodal development involve the failure of electroreceptors to form within the lateral zones of the elongatiang sensory ridges of the placodes. This nonterminal change appears to have occurred independently in ancestral neopterygian bony fishes, in many amphibians and, possibly, in the extinct acanthodians. At least two teleost radiations, osteoglossomorphs and ostariophysines, have re-evolved electroreceptors which may represent additional nonterminal changes in placodal patterning or, possibly, a change in the embryonic source of these receptors.

The lateral line microcosmos

“…On the trunk and tail, typically one canal is integrated into a row of specialized scales that are detectable with the naked eye, and form a "lateral line," thus giving the system its name. The pattern of canals is of important taxonomic value and has been extensively described in the past (Webb 1989;Northcutt 1997).…”

The development of the hindbrain afferent projections in the axolotl: Evidence for timing as a specific mechanism of afferent fiber sorting

“…1) have the full complement of octavo-lateral organs (inner ear, mechanosensory lateral line, ampullary electroreceptors; Fritzsch, 1981;Fritzsch and Wahnschaffe, 1983). Such organs are also found in other aquatic vertebrates such as lampreys, elasmobranchs and other non-teleosts (Bullock and Heiligenberg, 1986;Northcutt, 1997). In contrast, frogs ( Fig.…”

Evolution of electrosensory ampullary organs: conservation of Eya4 expression during lateral line development in jawed vertebrates

“…Fields of electrosensory ampullary organs flank the neuromast lines. Ampullary organs, which also contain modified hair cells (electroreceptors) and support cells, are found recessed at the base of pores of varying length (depending on the species) filled with a jelly-like substance of low electrical resistance (Northcutt 1997;Jørgensen and Pickles 2002;Schlosser 2002b;Bodznick and Montgomery 2005;Jørgensen, 2005).…”

“…While the mechanosensory system is found in all fishes and larval and adult aquatic amphibians, the electrosensory division has been independently lost several times (Bullock et al 1983;New 1997;Northcutt 1997;Schlosser 2002a) (Fig. 1A) suggesting that the development of these two sensory systems is, to some extent, independent.…”