The phylogenetic tree on the left shows the evolutionary relationships among three types of fish: non-electric fish (I. punctatus), electric fish with electric organs derived from muscle tissue (E. electricus, E. virescens), and electric fish with electric organs derived from spinal neurons (P. hasemani, A. leptorhynchus, A. albifrons). The graphs on the right show each species’ expression of different voltage-gated sodium channel genes. Gene expression was measured in both muscle tissue and the spinal cord; error bars represent one standard deviation from the mean (n = 3). The genes represented by black bars are scn12ab, scn1lab, scn8aa, and scn8ab. The genes represented by colored bars, which are all derived from a gene called scn4a, are scn4aa (yellow), scn4ab (purple), scn4ab1 (red), and scn4ab2 (blue).

Project or distribute the image to engage students. The downloadable Educator Materials PDF includes background information, graph interpretation and discussion questions, and the Student Handout includes the image and background information.

Figure 1 from:

Thompson, Ammon, Daniel T. Infield, Adam R. Smith, G. Troy Smith, Christopher A. Ahern, and Harold H. Zakon. “Rapid evolution of a voltage-gated sodium channel gene in a lineage of electric fish leads to a persistent sodium current.” PLoS Biol 16, 3 (2018): e2004892.

View article: https://doi.org/10.1371/journal.pbio.2004892