Decoded Science Interview with Heather King Continued
Decoded Science: How long did you spend analyzing video for this research?
King: The video analysis for this study took approximately six to nine months.
Decoded Science: What was the most difficult aspect of creating this experiment and analyzing the data?
King: It was challenging to work with live animals with minds of their own – to collect the video data, I allowed the fish to move in a large tank while I filmed. To get a good understanding of the behaviors they typically used, I let the fish do what they wanted without much interference from me. Even after I had a better idea of what they were doing and tried to elicit particular behaviors from the fish, they didn’t always want to cooperate with me!
Decoded Science: What do you think is the most significant aspect of this research?
King: One way we can understand the vertebrate water-to-land transition is to determine the order in which important traits were acquired in lobe-finned fishes, the large group to which lungfish and tetrapods belong. These traits include the evolution of digits (fingers and toes), the use of hindlimbs for propulsion, terrestriality, and substrate dependency during locomotion (ie walking on the bottom). This study gives us another line of evidence we can use to order these traits in the evolution of tetrapods and their relatives (including lungfish).
We knew from another lobe-finned fish, the coelacanth, that using pelvic (hind) fins for propulsion evolved in lobe-finned fishes prior to tetrapods. We also know from Acanthostega, a fossil tetrapod from the Devonian, that digits evolved before terrestriality. Since the lungfish does not have digits and does not walk on land, but we now know that it does use both substrate-based locomotion and hindlimbs for propulsion, this suggests that the ordering of these traits could be this: 1. hindlimb propulsion, 2. substrate-dependent locomotion, 3. digits, 4. terrestriality.
Personally, I find it exciting and surprising that even with such small fins, this lungfish is able to not only propel itself (with just one pair of fins), but lift its body clear of the bottom as well. If you were to look at just the skeleton of the lungfish, you might never guess that it was capable of this behavior, especially since they don’t have feet! It’s also important to note that lungfish, like other non-tetrapods, lack a sacrum, which is the part of the skeleton that connects the pelvis to the spine. In tetrapods, the sacrum is thought to provide support to the limbs and allow them to lift the body. Lungfish can lift their bodies clear of the bottom despite lacking this feature.
Lungfish Research Advances
Observations of this fish in motion, from all angles, helped scientists better understand how the tiny appendages actually work. Even though the lungfish’s limbs appear to be useful solely for swimming, we now know that the African lungfish is actually able to use its spiny limbs to propel itself forward with walking motions. Many thanks to Heather King for consenting to this interview!
King, H. et al. Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes. Edition of Proceedings of National Academy of Sciences. December 12, 2011. Accessed December 12, 2011.