Female-embryo relationships in Ostrea chilensis: brooding, embryo recognition, and larval hatching

Flat oysters brood their embryos and larvae in the female pallial cavity, and the previous work has examined their relationship to the gill/mouth complex. However, the details of this relationship are unclear. By transplanting embryos and using endoscopy, the capacity for embryonic recognition in brooding oysters, Ostrea chilensis, and the ability to clear the pallial cavity of dead embryos were studied. The oysters were collected in 2016 and 2017 in the Quempillen estuary in southern Chile (41 degrees 52S, 73 degrees 46W). Non-brooding and smaller oysters (males) did not retain transplanted embryos in their pallial cavities. Brooding oysters retained transplanted foreign embryos and larvae, which developed along with a female's own larvae. Dead larvae were detected by brooding oysters and ejected from the pallial cavity in pseudofeces. This was effective but not efficient; females frequently rejected some of their own veligers together with the dead larvae. Brooding females likely recognized dead larvae by their inactivity. At hatching, brooded larvae were released in several short pulses by maternal pumping, which ejected larvae at mean speeds of 178.6 +/- 56.6mm s(-1), considerably greater than larval swimming speeds (0.32 +/- 0.24mm s(-1)) or female counter-currents (0.67 +/- 0.42mm s(-1)). It remains unknown whether the presence of embryos and larvae in the pallial cavity over the extended brooding period of8weeks in O. chilensis contributes to the hatching process in some way.