First evidence of heritable latitudinal differences in reproductive diapause amongst stocks of northern river shrimp, Cryphiops caementarius, in Chile

Local adaptations are a key evolutionary mechanism that ensures species persistence across different environmental conditions. In exothermic organisms from mid and high latitudes, temperature and day length variation play a major role in the reproductive cycle and growth rate and can cause local adaptations. The northern river prawn (Cryphiops caementarius) is an amphidromous species widely distributed in rivers along the western slope of the Andes Mountains from Peru to northern Chile. Stocks of northern river prawns from three rivers in northern Chile were studied under common garden conditions to test for heritable differences in reproductive season and growth rate. Progeny of gravid females, collected from the Limarí, Choapa, and Huasco rivers, were cultured in the laboratory under the same environmental conditions. The sex ratio, reproductive period, and body size were observed throughout the culture period. No differences in growth rates were observed among the juvenile or adult stages, but larvae from the Limarí River had a faster developmental rate than the other two breeds. The reproductive season began later in the laboratory than in nature, with no differences between strains. However, the southernmost strain (Choapa) had a longer reproductive period than the other two strains. Since temperature was controlled, the data suggested a significant effect of photoperiod on controlling the onset and termination of the reproductive period in C. caementarius. These results imply that local adaptations allow different populations to adjust their reproductive periods in response to variations in day length at different latitudes throughout the year.