What makes the difference between the siberian sturgeon and the ponto-caspian sturgeon species?

Abstract

Adaptive features of the Siberian sturgeon connected with species structure (adaptive radiation), population structure, ecology, physiology, reproduction and development in comparison with phylogenetically closely Ponto-Caspian sturgeon related species were analyzed. The adaptive radiation of freshwater Siberian sturgeon unlike anadromous Ponto-Caspian sturgeon was directed to formation of continuous rows of populations (so called "population continuums") over wide ranges in a single river basin allowing separate populations inhabiting different sections of the river to reproduce in the optimal time without performing energetically expensive migrations under conditions of the limited food supply. Unlike most of sturgeon species sex ratio in Siberian sturgeon is close to 1:1. In populations living under worse foraging conditions the life span of males is almost twice less than that of females. The Siberian sturgeon have to feed at the main part of the range through the winter at the water temperature close to 0 °C and in populations living in the most severe conditions (Lena and Indigirka rivers) it feeds through the spawning period. In these populations were found (1) significant increase in generative tissue synthesis level, (2) decrease of somatic growth efficiency, (3) maturation at earlier age and smaller size, (4) increase of relative fecundity and relative gonad weight of females, (5) increased duration of interspawning intervals of females. The efficiency of yolk utilization in the Siberian sturgeon is higher than in Russian sturgeon. Despite the smaller size of the eggs, this results in larger size of hatchling prelarva in Siberian sturgeon than in Russian sturgeon.