Meeting Abstract
According to Dollo’s Law the evolutionary loss of a complex feature is irreversible, such that organisms can never completely regain or return to an ancestral state. Among fishes, loss and subdivision of fins is far more common than regaining lost fins, supporting Dollo’s Law. For example, Gymnotiformes (knifefishes and electric eels) are an order of weakly-electric freshwater fish that produce thrust through undulation of an elongate anal fin (gymnotiform swimming), and all species completely lack a dorsal fin. This dorsal fin loss is seen in convergent Osteoglossiformes and Siluriformes, which also swim with anal fin undulation, suggesting the lack of a dorsal fin may play a role in the performance of gymnotiform swimmers. However, a mutant form of the gymnotiform black ghost knifefish (Apteronotus albifrons) that possesses an elongate dorsal fin has been found among captive bred populations. The presence of this mutant fish challenges Dollo’s law by suggesting that fin loss is reversible and these mutants provide an opportunity to examine the effects of dorsal fin presence on gymnotiform swimming performance. The goals of this study were to 1) describe the morphology of this mutant knifefish and 2) compare aerobic and anaerobic swimming performance among mutant and wild type knifefish. We used µCT scans to describe dorsal fin morphology, respirometry to measure swimming energetics, and sprint speed for anaerobic performance. Preliminary results show that mutant knifefish have regained both fin rays and fin ray supports (pterygiophores), although the fin is not moved during swimming. We found no difference in swimming energetics and a reduction in sprint swimming performance. We discuss these results in the context of Dollo’s law and major evolutionary transitions of fins among fish.
