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

Abstract

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.

Feeding behavior ofGammarus aequicaudain the presence of two prey species ofArtemiasp. andBaeotendipes noctivagus

“…The obtained data on the quantitative characteristics of the G. aequicauda feeding behavior in the presence of two kinds of prey are very close to those found earlier when studying the consumption of Artemia sp. (Shadrin, Yakovenko, & Anufriieva, 2020b) and chironomid larvae (Shadrin, Yakovenko, & Anufriieva, 2021a,b) separately. The time spent on eating and digesting this prey by G. aequicauda did not depend on the presence of other prey species in the experience.…”

“…in Lake Sasyk‐Sivash. Vessels with a radius of 3.5 cm and water volume of 0.5 L were used for the ethological observations and experiments as in the previous studies (Shadrin, Yakovenko, & Anufriieva, 2020b, 2021a,b). A ratio of light and dark periods of 16:8 was set for the experiments.…”

“…had an average wet mass of 4.3 and 2.6 mg, respectively, and G. aequicauda— 23.7 mg. Before the experiments, gammarids were in vessels with filtered lake water for 3 days with aeration because such starvation standardized predators' satiety levels as shown earlier (Shadrin, Yakovenko, & Anufriieva, 2020a, b). In every experiment, one G. aequicauda male was used to avoid body‐size and sex‐related effects (Glazier, 2022; Shadrin, Yakovenko, & Anufriieva, 2021b). Different variants of prey compositions in terms of species and a number of individuals per species were used in the experiments: (1) two Artemia sp., (2) two chironomid larvae, and (3) one Artemia sp.…”

“…The duration of experiments was different and continued up to full consumption of both preys. Following (Shadrin, Yakovenko, & Anufriieva, 2020b, 2021a,b), the feeding behavioral time balance was monitored visually with a stopwatch. The moments to time of the capture of prey by G. aequicauda , time spent to consume whole or partial prey, as well as a rest between consumption of prey to the capture of a second prey and time of its consumption, were recorded.…”

“…To study trophic relations, a combination of bioenergetic and ethological approaches can quantify food consumed and also help to understand determining factors (Ivlev, 1944; Mikheev & Pavlov, 2005; N. V. Shadrin & Anufriieva, 2018b; Shokri et al, 2021). This approach is based on a time balance described by a simple equation (Ivlev, 1960; Petipa, 1981; Shadrin, Yakovenko, & Anufriieva, 2020b, 2021a,b): $$$C={W}_{a}/T={W}_{a}/({T}_{1}+{T}_{2}+{T}_{3}),$$$ where C is ration (mg/h); W a , an average mass of prey (mg); T , total time spent of one prey (h); T 1 , T 2 , T 3 are time spent for search, capture, and digestion of one prey, respectively (h).…”