Experimental clearance rates of Aurelia coerulea ephyrae and medusae,and the predation impact on zooplankton in Jiaozhou Bay

The population explosion of jellyfish Aurelia coerulea occurred in Jiaozhou Bay,China in 2009.The potential predation impact of A.coerulea on zooplankton was investigated.Population clearance potential and residence time(t 1/2)for copepods were calculated from laboratory clearance rates and measurements of jellyfish size and abundance from May to August 2009 in Jiaozhou Bay.Clearance rates varied widely with prey organisms,but they were not significantly different among various prey concentrations.Medusae captured rotifers,fish larvae and hydromedusae more efficiently than fish eggs,copepods and chaetognaths.Ephyrae captured rotifers and hydromedusae more efficiently than fish larvae and copepods.Clearance rate linearly increased with the cross sectional area of A.coerulea(size from 0.3 to 7.1 cm).Water temperature also had a marked effect on clearance rate and this was related to the increased beat frequency as water temperature increased.In early May 2009,A.coerulea potentially cleared the volume of water in the Bay less than 0.001 times a day,but this value was estimated to be more than 0.3 times a day in July.The t 1/2 for copepods was less than 6 d in June and July.Abundances of copepods,hydromedusae and chaetognaths were extremely low in 2009 compared to 2008 and 2010(jellyfish non-bloom years).Large predation pressure by the A.coerulea population occurred to control zooplankton communities in Jiaozhou Bay.A.coerulea,when present at a high population level,can be a keystone species in Jiaozhou Bay and control the trophic structure here.

Females prefer males producing a high-rate song with shorter timbal-stridulatory sound intervals in a cicada species

Uncovering mate choice and factors that lead to the choice are very important to understanding sexual selection in evolutionary change.Cicadas are known for their loud sounds produced by males using the timbals.However,males in certain cicada species emit 2 kinds of sounds using respectively timbals and stridulatory organs,and females may produce their own sounds to respond to males.What has never been considered is the mate choice in such cicada species.Here,we investigate the sexual selection and potential impact of predation pressure on mate choice in the cicada Subpsaltria yangi Chen.It possesses stridulatory sound-producing organs in both sexes in addition to the timbals in males.Results show that males producing calling songs with shorter timbal–stridulatory sound intervals and a higher call rate achieved greater mating success.No morphological traits were found to be correlated with mating success in both sexes,suggesting neither males nor females display mate preference for the opposite sex based on morphological traits.Males do not discriminate among responding females during mate searching,which may be due to the high energy costs associated with their unusual mate-seeking activity and the male-biased predation pressure.Females generally mate once but a minority of them re-mated after oviposition which,combined with the desirable acoustic traits of males,suggest females may maximize their reproductive success by choosing a high-quality male in the first place.This study contributes to our understanding mechanisms of sexual selection in cicadas and other insects suffering selective pressure from predators.