Photoperiod-dependent reproductive plasticity of the brine shrimp Artemia franciscana.

Abstract

Photoperiod is a robust seasonal stimulus for phenotypic plasticity in the regulation of reproduction and development. Artemia brine shrimps have a unique reproductive mechanism to alter their reproductive mode between ovoviviparity, with the release of free-swimming nauplii, and oviparity, with the production of diapause cysts, in response to differences in photoperiod. However, the existence of relationships between reproductive modes and other reproduction-related traits (e.g., growing period, number of spawns, and litter size) remains elusive. In this study, we show that long-day conditions increase the proportion of free-swimming nauplii and the number of eggs during a lifetime compared to short-day conditions. Histological analysis revealed structural differences in eggs between ovoviviparity and oviparity, providing insight into the alteration of energy allocation: long-day conditions can produce a large number of eggs because a thin egg shell is formed, whereas short-day conditions decreased the number of eggs, because a thick egg shell is formed. The present study provides new insight into the energy trade-off to develop a phenotypically plastic trait in Artemia.