Massive egg production by a salp symbiont, the poecilostomatoid copepod Sapphirina angusta Dana, 1849

Abstract

Egg-carrying pelagic copepods are characterized by low reproductive growth rates. It has been suggested that this is due to relatively high mortality rate in adult females, relative to broadcast spawning copepods. The poecilostomatoid copepod Sapphirina angusta, a ubiquitous member of pelagic zooplankton communities, seems to be an exception to this rule. We studied egg production of S. angusta on the Southern Brazilian Bight. In five separate experiments, egg clutch size was measured in 15 to 25 individual females followed for approximately 5 days in each experiment. The mean time to produce a clutch was ∼ 2 days. Egg hatching success was > 80% and independent of clutch size or egg production rate. Clutch size ranged from 9 to > 1000 eggs female − 1 during the study. The mean egg production rate was estimated from clutch size and the inter-spawning period. The mean and median egg production rate were essentially similar and ranged from 155 to 218 eggs female − 1 d − 1 among experiments, with a grand mean of 186 eggs female − 1 d − 1 . This is the highest observed egg production rate in an egg-carrying copepod. Based on female and egg body mass, the egg production rate represents a growth rate of ∼ 0.45 d − 1 , among the highest in all marine copepods. We hypothesize that two evolutionary factors that select for high fecundity are responsible for the extremely high egg production rate of S. angusta: 1) The symbiosis of Sapphirina and their host salps, which relaxes female mortality; 2) The parasitoid (both parasitic and predatory) behavior of Sapphirina leading to death of their salp host, which causes high mortality in Sapphirina juveniles while in between highly patchy hosts.