To invest or not to invest, that is the question: Male presence and genetic relatedness as modulators of female reproductive effort in a shrimp

The present work was aimed at evaluating whether females of a freshwater shrimp, Neocaridina davidi (Bouvier, 1904), allocate differentially to reproduction when reared in the presence of males and in the presence of brothers/non-brothers. Ovarian growth was evaluated in three consecutive maturation cycles. The composition of biochemical reserves was determined in the eggs (i.e., embryos) laid at the end of the first cycle, in 20-day-old juveniles produced at the end of the second cycle, and in the mature ovary of females at the end of the third cycle. When reared in the absence of males, females took longer to mature the ovaries and stored less proteins, triglycerides and cholesterol in the mature ovary. Females reared with brothers took longer to mature the ovaries than females reared with non-brothers, with no differences in the biochemical composition of their mature ovaries. The eggs produced by females mated to brothers showed a lower carotenoid content, higher cholesterol content and a tendency towards lower energy content than those produced by females mated to non-brothers. These results suggest that females are capable of recognizing kin and modulate primary reproductive effort, in terms of ovarian and egg biochemical composition, according to male presence and genetic relatedness.