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<\/div>The northern sea robin uses its legs to find food in the seabed<\/p>\n
Anik Grearson<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
A striking fish that lives at the bottom of the Atlantic Ocean has evolved legs \u2013 but not just for walking. These appendages are a novel sensory organ like a tongue, which they use to find prey buried in the seabed.<\/p>\n
Northern sea robins (Prionotus carolinus<\/em>) have three legs on each side of their body, protruding from the base of their pectoral fins. The legs are derived from structures within the pectoral fins, called fin rays.<\/p>\n On a research trip to Woods Hole, Massachusetts, Nicholas Bellono<\/a> at Harvard University and his colleagues heard stories of the hunting prowess of the sea robins\u00a0and decided to bring several live specimens back to their lab.<\/p>\n The team wanted to find out if the fish were as good at finding prey as their reputation suggested. \u201cTo our surprise, they were very, very good at it and could even uncover capsules filled with ground-up and filtered mussel extract, and single amino acids,\u201d says Bellono.<\/p>\n The researchers then collected more of the fish, only to discover that the second batch were good at walking but not at sensing prey buried in the sand.<\/p>\n <\/p>\n \u201cThis time the new sea robins didn\u2019t find anything, despite readily eating prey on the surface,\u201d says Bellono. \u201cWe thought we were maybe doing something wrong, but it turned out that we accidentally got a different species.\u201d<\/p>\n The team had inadvertently collected the striped sea robin (Prionotus evolans), <\/em>which walks but specialises in hunting unburied prey.<\/p>\n \u201cWhen we looked at the digging versus non-digging animals, the legs were so obviously different and the sensory papillae on the digging legs were even clear by eye,\u201d says Bellono.<\/p>\n These papillae are bumps containing taste receptors and touch-sensitive neurons, similar to the papillae made up of taste buds on the human tongue.<\/p>\n Various other fish have evolved modified pectoral and pelvic fins that allow them to walk or perch, says team member Amy Herbert<\/a> at Stanford University, California. \u201cHowever, a unique feature about the sea robin is that while other fish typically use the entire pectoral or pelvic fin for this purpose, the legs of the sea robin can move independently \u2013 and quite quickly \u2013 making them particularly adept at both walking and digging,\u201d she says.<\/p>\n The team also looked into the genes that drove the evolution of the sea robin\u2019s unique legs, and found that their development is controlled by an ancient regulatory gene called tbx3a<\/em>.<\/p>\n \u201cIt\u2019s normally expressed in a particular local domain of fin and limb buds in a whole range of animals from fish to mammals,\u201d says team member David Kingsley<\/a>, also at Stanford University. \u201cThis is an excellent example of making new body parts by modifying old, shared tools.\u201d<\/p>\n Topics:<\/p>\n<\/section><\/div>\n