1. Data on experimental infections by A. woodiana parasitic larvae (glochidia.txt) Variables: fishID: unique code for individual fish musselindiv: unique code for individual parental mussel used for experimental infections musselsite: region of parental mussel origin (P: Baltic region (Lake Lichenskie,Poland), C: Danubian region (River Kyjovka, Czech Republic) fisharea: region of fish origin (P: Baltic region (Lake Lichenskie,Poland), C: Danubian region (River Kyjovka, Czech Republic) group: coding for particular host-parasite combinations (the first letter C or P is for the mussel (Baltic or Danubian; the second letter stands for fish population origin: L: Lake Lichenskie (=Baltic sympatric), W: Vistula River (=Baltic allopatric), K: River Kyjovka (=Danubian sympatric), M: River Morava (=Danubian allopatric) sympatric: categorical, host fish either sympatric (=yes) or allopatric(=no) to A. woodiana filtrjuv: the number of recovered juvenile mussels filtrgloch: the number of parastici larvae rejected by the host fish glochTot: sum of filtrgloch + filtrjuv transrate: proportion of successfully metamorphosed fish (filtrjuv/glochTot) group2: auxiliary variable for exploratory inspection of the data, unique coding for each 2. Data on R. amarus behavioural discrimination between A. woodiana and A. anatina mussels (preference.txt) Variables: fish: fish population code (K: River Kyjovka (=Danubian sympatric), M: River Morava (=Danubian allopatric, PL: Vistula River (=Baltic allopatric)) AW: A. woodiana population code (P: Baltic region (Lake Lichenskie,Poland), C: Danubian region (River Kyjovka, Czech Republic)) Duration: duration of behavioural observation in seconds (typically 600 s, but less if oviposition occurred, or more in three cases) aaTL: shell size of A. anatina mussel (in mm) awTL: shell size of A. woodiana mussel (in mm) mussDiff: difference between sheel size of the two mussels (A. anatina minus A. woodiana, in mm) fSL: body size of female fish mSL: body size of male fish pc1: PC1 score for behaviourala contrast between the two mussels AAlead: the number of male leads towards A. anatina mussel AAspe: the number of male sperm releases towards A. anatina mussel AAminsp: the number of male inspections of A. anatina mussel AAfinsp: the number of female inspections of A. anatina mussel AAskim: the number of female skims over A. anatina mussel AAspawn: the presence of oviposition into A. anatina mussel (scored as 1, no oviposition scored as 0) AWlead: the number of male leads towards A. woodiana mussel AWspe: the number of male sperm releases towards A. woodiana mussel AWminsp: the number of male inspections of A. woodiana mussel AWfinsp: the number of female inspections of A. woodiana mussel AWskim: the number of female skims over A. woodiana mussel AWspawn: the presence of oviposition into A. woodiana (scored as 1, no oviposition scored as 0) 3. Data on R. amarus behavioural discrimination between A. woodiana and A. anatina mussels (popconCZ.txt, popconPL.txt) Variables of popconCZ.txt: pool: unique ID of the experimental population fish: R. amarus population (k: River Kyjovka, Danubian sympatric; m: River Morava, Danubian allopatric mussel: mussel community treatment (a: 4 A. anatina; c: 2 Danubian A. woodiana + 2 A. anatina, p: 2 Baltic A. woodiana + 2 A. anatina) offspring: the number of embryos recovered by dissecting the mussels at the end of the experiment Variables of popconPL.txt: pool: unique ID of the experimental population fish: R. amarus population (l: Lake Lichenskie, Baltic sympatric; w: Wloclawski Reservoir, Baltic allopatric mussel: mussel community treatment (a: 4 A. anatina; c: 2 Danubian A. woodiana + 2 A. anatina, p: 2 Baltic A. woodiana + 2 A. anatina) emb: the number of embryos recovered by dissecting the mussels at the end of the experiment juv: the number of juvenile fish emerged from the mussel and collected at the end of the experiment in the pool offspring: the sum of emb and juv mortAA: the number of A. anatina mussels that died during the experiment