Mesocosm experiments reveal the loss of migratory tendencies in a recently isolated population of three-spined sticklebacks A. Ramesh1*Ж, J. Gismann1 Ж, T.G.G. Groothuis1, F.J. Weissing1 and M. Nicolaus1 1.     Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands *Corresponding author. E-mail: a.ramesh@rug.nl Ж Shared first authorship ORCID: A. Ramesh: 0000-0002-7200-1366, J. Gismann: 0000-0002-2570-590X, T.G.G. Groothuis: 0000-0003-0741-2174, F.J. Weissing: 0000-0003-3281-663X, M. Nicolaus: 0000-0003-1808-1526 Data collection: Data were collected from automated Radio-frequence identification (RFID) transponsers. Additionally, dataon temperature, turbidity, other remarks were noted in a lab journal on the day of testing File formats to record data: csv files and excel sheets Software used for obtaining secondary data from raw data of RFID system We used R software to write codes to obtain crosses from the raw data. Statistical analysis done on data: All statistical analyses were carried out in R and is describes in the main text and supplementary information Description of columns of dataset: X: Serial number tag_ID: Unique identification code of the PIT tag of fish test_id: Test done on the same day status: Origin of the fish - resident / migrant group_id: Test group containing ~10 fish bottom_crosses: Exp-1 Number of crosses an individual made between bottom antennas within ponds surface_crosses: Exp-1 Number of crosses an individual made between top antennas within ponds pond_crosses: Exp-1 Number of crosses an individual made between ponds flow1_pond_crosses: Exp-2 Day 1 of flow treatment: Number of crosses an individual made between ponds flow2_pond_crosses: Exp-2 Day 2 of flow treatment: Number of crosses an individual made between ponds noflow1_pond_crosses: Exp-2 Day 1 of no-flow treatment: Number of crosses an individual made between ponds noflow2_pond_crosses: Exp-2 Day 2 of no-flow treatment: Number of crosses an individual made between ponds temp: Temperature of water - only for Exp-1 turbidity: Turbidity of water - only for Exp-1 number_fish: Number of fish in a group - only for Exp-1