Complexity of trophic relationships between Gammarus aequicauda (Amphipoda) and Eucypris mareotica (Ostracoda) in a hypersaline lake.

In the hypersaline lakes of Crimea, only 5-7 species of animals are common including Gammarus aequicauda (Amphipoda) and Eucypris mareotica (Ostracoda). Two experiments were carried out to characterize the trophic interactions between these species. In one, G. aequicauda were used freshly caught from the lake, and in the other, after they were starved for 2.5 days in the laboratory. The experimental options were one male or female G. aequicauda and either 10, 20, or 30 ostracods. The gammarids actively fed on the ostracods, and significant differences were between females and males. The feeding intensity of males was higher than that of females. However, ostracods are not passive prey, they can actively attack their predator and are capable of causing them harm. Ostracods attacked a Gammarus only if it had captured one of the ostracods. Sex differences in G. aequicauda were also evident in the reaction to the group's aggressive behavior of ostracods. Interactions between Ostracoda and Gammarids cannot be considered unidirectional; they both may be prey or predators depending on the situation.

Feeding behavior of Gammarus aequicauda in the presence of two prey species of Artemia sp. and Baeotendipes noctivagus.

Gammarus aequicauda is the most abundant amphipod species in the Crimean hypersaline lakes, and is predatory upon other invertebrate species, suppressing their populations. The authors studied a time balance during the feeding of G. aequicauda in the presence of two prey species. The different variants of prey composition were: (1) two Artemia sp., (2) two chironomid larvae, and (3) one Artemia sp. and one chironomid larva. The duration of the experiments differed and continued until both prey were consumed. The experiments were carried out in vessels with and without bottom sediments. The result showed that in vessels with and without sediments in the case of both species of prey, the time to the capture of the first prey did not depend on whether Artemia sp. or chironomid larva was the first prey; the time differences are statistically insignificant. The duration of eating prey in all experimental variants depended on the kind of prey, and those differences were highly significant. The average hourly consumption rate was dependent on prey composition and order of prey capture and eating. The maximum consumption for two prey was when both were brine shrimp. In vessels without sediments and containing both Artemia sp. and chironomid larva the consumption rate was higher if the first caught prey was Artemia sp. rather than сhironomid larva. The order of prey eating did not influence a ration size in vessels with bottom sediments. When both prey were chironomid larvae, the total diet did not practically differ in vessels with or without sediments.

The behavior of Gammarus aequicauda (crustacea, amphipoda) during predation on chironomid larvae: Sex differences and changes in precopulatory mate-guarding state.

The foraging behavior determines the diet size influencing the growth and reproduction of a predator and its prey populations. Amphipods play a key role in various aquatic ecosystems. Gammarus aequicauda is an abundant widespread omnivorous species and the only known amphipod species of hypersaline waters. Its predation can suppress the populations of planktonic and benthic invertebrates. Males of G. aequicauda actively eat chironomid larvae but there is no data on predatory females. Experiments were conducted to study sex-related differences in feeding behavior including during precopulatory mate guarding (PCMG). There were significant sex differences in feeding characteristics. For females, calculations showed that maximum consumption could be 3-4 chironomid larvae per day and for males about 9-10 larvae per day. During PCMG, males did not feed and females fed as efficiently as single females. Males transported females and alone carrying the energetic costs of swimming during PCMG. Less expenditure of energy on swimming means more energy for reproduction for females. This allows more energy-efficient use of food resources and increases the reproductive success of the population. There are currently two alternative views on PCMG among crustaceans. 1. It is a sexual conflict between males and females serving as a male adaptive strategy to achieve a female during strong male competition, while females bear many costs during the long guarding period. 2. There is also the opposite view that pairs get energetic benefits from long PCMG. Obtained data suggest that PCMG is likely to be intersexual cooperation and not intersexual conflict.