On the other hand, by using the phylogenetic lesions generated by this evolutionary approach, we hope to obtain a perspective on a well-studied model system that is essentially unique. Ultimately, our goal is to establish not a new model species but a uniquely powerful model lineage with which to address questions of learning and memory as well as cellular signaling. The presence or absence of these two traits is mapped onto the cladogram of 6 species of sea slugs related to Aplysia . Solid lines depict proposed evolution of spike broadening. Striped lines depict evolution of increased excitability.
Bold lines indicate presence, lighter shading absence, of a trait.
This hypothesis proposes that increased excitability is an ancestral trait that was subsequently lost in the lineage leading to Dolabrifera dolabrifera. Spike broadening, on the other hand, appears to have been newly acquired in the aplysiid clade shortly after its split from the lineage leading to Akera . Spike broadening was then lost in the Dolabrifera lineage after its split with Bursatella leachii .