Patterning the posterior lateral line in teleosts: Evolution of development

Abstract

The lateral line system of teleost fishes presents large variations of patterns and forms, usually thought of as adaptive. This raises the question of how divergent adult patterns are achieved, and how selective pressures have contributed to this divergence. Our understanding of the development of this sensory system has much improved over the past 10 years, mostly through work on the zebrafish. Because this progress is restricted to a single species, we cannot yet answer questions about the determinism of lateral line evolution, but we can at least propose plausible and testable hypotheses. Here we review the mechanisms that mediate the transition from embryonic to adult pattern in the zebrafish posterior lateral line system (PLL), and we show that the adult pattern is largely determined by developmental events that take place during early larval life. We also show that simple variations in the use of the same mechanisms account for the very different patterns observed in juvenile zebrafish and blue-fin tuna, and could potentially account for many or all of the patterns observed in other adult teleosts. We conclude that, in the case of the lateral line at least, large variations in pattern depend on minor changes in the deployment of conserved developmental programs, with uncertain adaptive value. We propose that organisms neurally adapt to whatever tools they are provided with by their own development, and use them as best as they can, thereby giving the impression that such tools were actually selected for.