Temperature drives reproductive activity in a rare trioecy population of Corbicula clams

Trioecy systems are generally considered to be less stable and less widely distributed. Recently, a rare and mostly hermaphrodite (> 50%) trioecy system was detected in a single indigenous population of Corbicula fluminea. While hermaphrodite specimens are common in the invaded range, dioecy systems dominate C. fluminea populations in native regions, with trioecy populations being rare and transient in both ranges. To date, the stability of this trioecy system, as well as how environmental conditions effect sex allocation and reproductive activities remains unknown. To address this, the population sex ratio and brooding characteristics were analyzed through morphological and histological examination of C. fluminea specimens. Trioecy was sustained over the assessment period, with an approximate sex ratio of 1:1:6 (male:female:hermaphrodite). Greater water temperature significantly increased the population ratio in favor of males, while lower water temperatures were significantly associated shift toward females. Gametogenesis and brooding occurred throughout the year, but asynchronously. The incubation rate substantially increased between June and December, and had a significant and positive correlation with water temperature. Overall, these data suggest that a C. fluminea trioecy sexual system can be a stable phenomenon, and water temperature is both a driver of population sex ratio and reproductive activities.