Russian scientists have explained the behavior of amphipods, in which males grab females with their paws and carry them until fertilization. Previously, it was believed that in this way they provide themselves with a pair for reproduction, keeping the females and at the same time preventing them from obtaining food. As it turned out, females in this position effectively feed and do not expend energy on movement, preserving it for reproductive function, which benefits the entire population.
The results of the study, supported by a grant from the Russian Science Foundation, are published in the journal J ournal of Experimental Zoology Part A: Ecological and Integrative Physiology. The process of reproduction and the preceding mating rituals are quite unusual not only in humans. For example, the birds of paradise Raggiana perform special mating dances, and fishing spiders give females a carcass of prey wrapped in cobwebs. But not all animals are strong in romance: for some, all preparation consists in grabbing a vending female and in one way or another escort her to the breeding site or wait for her to mature.
For example, frogs use it as a horse, and tiny omnivorous crustaceans Gammarus aequicauda honor the tradition of stealing brides and carry them with their paws on top. Males reach puberty earlier than females and, in order to achieve reproductive success, immediately capture an immature female. After capture, the male accompanies her until she is ready for fertilization.
“Previously, it was believed that the mating behavior of male crustaceans is a manifestation of intersexual conflict: the female will not go anywhere and at the same time will be deprived of the opportunity to choose the male she likes herself. However, our research has shown that everything is not as simple as it seems,”explains Elena Anufrieva, project manager for a grant from the Russian Science Foundation, Ph. D. in Biology and Head of the Laboratory of Extreme Ecosystems at the Institute of Biology of the Southern Seas named after A. O. Kovalevsky, Russian Academy of Sciences (Sevastopol).
Employees of FRC InBYUM collected crustaceans Gammarus aequicauda in the hypersaline (salt content is three to four times higher than the values for the Black Sea) Lake Moinaki in the Crimea - this species is the only one from the squadron of amphipods that can live in such conditions. The biologists' idea was to test how the breeding season affects the nutrition of these animals, namely, whether the accompanying males really force the females to eat worse. In this case, it is important to understand the mechanisms that ensure the stability and balance of an ecosystem with a low species diversity, because few people can live in hypersaline water.
The crustaceans were placed in vessels, providing them with conditions close to natural ones, and watching how they eat food. Several variants of experiments were carried out in parallel: separate female and male individuals, two pairs of individuals of the same sex and a heterosexual pair were placed in different vessels.
After three days, the larvae of belling mosquitoes, which amphipods usually feed on, began to be added to the vessels. Scientists estimated the time spent on various stages of feeding behavior: the time of catching the prey, eating it, resting after the hunt, and so on. The experiment also used seagrass ruppia - the authors measured the area of leaves that was eaten by crustaceans over a certain period.
Overall, solitary males caught nearly three times as many victims as females, who were more likely to consume sea grass. The reasons for this have also been revealed in the course of research: before the breeding season, males accumulate fat in the body. Only the most fattened males can capture a female for transportation and further copulation. In a state of precopulative (before fertilization) accompanying males, females consume as much food as they do alone, but do not expend energy on locomotion. Males do not eat at all during this period.
“Our observations refuted the assumption that this behavior is an inter-sex conflict. On the contrary, a long stay of individuals in this position is beneficial not so much for males as for females. In addition, this leads to an overall increase in the fertility of the population, as females can produce more eggs.
Therefore, the phenomenon can be called inter-sex cooperation or cooperation. Such behavioral features have been observed in many crustacean relatives of amphipods, for example, in some species of shrimp. Recent studies will not only help to understand the behavior of crustaceans, but also help them to be more successfully cultivated for feeding fish,”sums up the first co-author of the article Nikolai Shadrin, Ph. D.