Evolutionary Aspects of Reproductive Strategies in Shrimps
The formation of reproductive adaptations in females of the suborders Dendrobranchiata and Pleocyemata (the first one is a more primitively organized group from the evolutionary perspective, while the second one is a younger and higher organized group) has been studied to distinguish the evolutionary aspects of their reproductive strategies. The structure of ovaries and the process of their maturation have been compared in different shrimp species. The type of oogenesis has been described. The size of mature oocytes and the values of absolute single fecundity have been evaluated. The evolutionary pathways of the morphology and anatomy of ovaries, vitellogenesis in species with large eggs, and the variability of gonadosomatic index have been shown. The results of evolution realized in reproductive adaptations are best seen at the macrotaxonomic level. Thus, two types of reproductive strategies (in each of four classes) have been distinguished and described. In Dendrobranchiata with poorly developed care for offspring, the following 4 classes of strategies have been revealed: well-expressed r -strategies (Aristeidae); medium-expressed r -strategists (some species of Penaeidae, Solenoceridae, Sicyoniidae); r -strategies with important components of K -strategy (some species of Solenoceridae, Benthesicymidae, Sergestidae); change of r-K strategy to the K -strategy (“incubation of embryos on pleopods”) (Luciferidae). Caring for offspring is well developed in Pleocyemata shrimps with the following 4 classes of strategies: K -strategies with important components of r -strategy (Nematocarcinidae, Acanthephyridae, some species of Pandalidae); medium-expressed K -strategies (Procarididae, Stenopodidae, Palaemonidae, some species of Crangonidae); well-expressed K -strategies (Pasiphaeidae, Oplophoridae, some species of Crangonidae); change of K-r strategy to r -strategy (refusal of caring for the offspring) (hydrothermal Alvinocarididae).