1. Post-maturation growth leading to indeterminate growth patterns is widespread in nature. However, its adaptive value is unclear. Life history theory suggests this allocation strategy may be favoured by temporal pulses in the intensity of mortality and/or the capacity to produce new tissues.

2. Addressing the origin of indeterminate growth and the variability of growth patterns, we studied the growth of duck mussels, Anodonta anatina, a pan-European unionid, in 18 Polish lakes. For each population the sex, size and age of collected mussels were measured to estimate Bertalanffy’s growth curve parameters. We integrated information on A. anatina mortality rates, lake trophy, biofouling by zebra mussels, Dreissena polymorpha, and the prevalence of parasitic trematode larvae to identify selective conditions in lakes.

3. We found two sources of mortality in A. anatina populations, pertaining to adverse effects of zebra mussel biofouling and trophy state on mussel survival. Additionally, populations with heavier biofouling presented a smaller abundance of parasites, indicative of a relationship between filtering intensity and contraction of water-borne trematode larvae by filtering A. anatina.

4. Consistently for each sex, populations with a greater trophy-related mortality were characterized in A. anatina by a smaller asymptotic size L_max, indicative of a life history response to mortality risk involving early maturation at a smaller body size. In all populations, females featured higher mortality and larger asymptotic size vs. males.

5. Our findings support a theoretical view that adaptive responses to selection involve adjustments in the lifetime resource allocation patterns. These adjustments should be considered drivers of the origin of indeterminate growth strategy in species taking parental care by offspring brooding in body cavities.

Duck mussels were sampled from 18 lakes in Poland (18 populations). For each populations, sex-specific values were calculated: Bertalanffy's growth curve parameters, overgrowth by zebra mussels, infestation by trematodes, mortality rates. For each lake also a trophy index was calculated. Deposited are two datasets. Dataset 1 shows quantitative measures of the intensity of overgrowth in the studied lakes. Dataset 2 shows population and sex specific values of all studied traits that were used for hypothesis testing in the paper linked to these datasets.