Hans van Someren Gréve

Gender-specific feeding rates in planktonic copepods with different feeding behavior

Planktonic copepods have sexually dimorphic behaviors, which can cause differences in feeding efficiency between genders. Copepod feeding rates have been studied extensively but most studies have focused only on females. In this study, we experimentally quantified feeding rates of males and females in copepods with different feeding behavior: ambush feeding (Oithona nana), feeding-current feeding (Temora longicornis) and cruising feeding (Centropages hamatus). We hypothesize that carbon-specific maximum ingestion rates are similar between genders, but that maximum clearance rates are lower for male copepods, particularly in ambush feeders, where the males must sacrifice feeding for mate searching. We conducted gender-specific functional feeding response experiments using prey of different size and motility. In most cases, gender-specific maximum ingestion and clearance rates were largely explained by the difference in size between sexes, independent of the feeding strategy. However, maximum clearance rates of males were approximately two times higher than for females in the ambush feeding copepod O. nana feeding on an optimal motile prey (Oxyrrhis marina), as hypothesized. We conclude that the conflict between mate searching and feeding can cause significant difference in feeding efficiency between copepod genders in ambush feeders but not in feeding-current and cruising feeders.

Sex-specific starvation tolerance of copepods with different foraging strategies

Planktonic copepods have sexual dimorphism that can lead to differences in starvation tolerance between genders. Additionally, mating may be energetically costly and thus reduce starvation tolerance. We investigated the influence of sexual dimorphism and mating on starvation tolerance of copepods with different feeding behaviours: Oithona nana (ambusher), Temora longicornis (feeding-current feeder) and Centropages typicus (cruiser). Males of C. typicus and O. nana had a starvation tolerance lower than females, whereas T. longicornis had a similar starvation tolerance between genders. Only O. nana males and females had reduced starvation tolerance when both genders were incubated together, which suggests that mating activities in ambushers have an energetic cost higher than in active feeding copepods. C:N ratios showed a non-significant difference between genders, which indicates that gender differences in starvation tolerance are not due to dissimilarities in lipid reserves. Gender differences in starvation tolerance can be partially explained by body size differences between sexes. This indicates a minor influence of mate-seeking behaviour on male starvation tolerance, likely due to reduced mate-searching behaviour under prolonged starvation. Our results demonstrate that sexual dimorphism can result in different starvation tolerance between copepod genders and that a negative effect of mating on starvation tolerance depends on the foraging strategy.