The effects of ploidy level on the thermal distributions of brine shrimp artemia parthenogenetica and its ecological implications

The responses to temperature change of sympatric diploid and pentaploid brine shrimp Artemia parthenogenetica were studied. Pentaploids survive better at extremes of both cold (0°C) and heat (37.5°C). When placed in a thermal gradient ranging from 12.5 to 35.1°C, diploids generally located at temperatures above 19°C while pentaploids were more evently distributed along the gradient. These results suggest that pentaploids may be better suited to temperature extremes than sympatric diploids. Our study provides the first experimental evidence in animals of differential temperature use by conspecific sympatric diploid and polyploid organisms. Our literature review indicates that polyploid Artemia are found with greater frequency in low and high latitudes (i.e. <25°N and >40°N) than in temperate regions (latitudes 35-40°N). The ecological implications of the physiological and behavioural differences between diploids and pentaploids are discussed as they relate to the latitudinal distributions of sexual and partheno- genetic Artemia in the Old World.