The mechanism of transformation of life history parameters in Artemia (Anostraca, Branchiopoda, Crustacea) as a factor of adaptation to environment

Abstract

Anostracan crustaceans of the genus Artemia are almost the only invertebrates to inhabit ultrahaline waters, mainly in arid regions. Changes in climatic factors (temperature, precipitation, and their distribution between seasons of the year) with season and during periods of many years determine wide variations of the water level and salinity in these water bodies. This results in irregular, unpredictable changes in the duration of the vegetation season of Artemia (the season where the water salinity is within the range 25‐180‰ and the temperature is above 7–8°e ) from year to year [1]. Many populations of Artemia are characterized by considerable lability of individual life history (LH) parameters and alternative modes of reproduction (parthenogenesis and bisexual reproduction), which is considered to be one of the main population adaptations to extreme environmental conditions [2, 3]. However, many important aspects of this process remain poorly understood. These are, e.g., the effect of the mode of reproduction on the variation of LH parameters, the strength of correlations between them, and LH heritability. We performed studies on this subject with the use of a laboratory culture of Artemia originating from the population inhabiting Lake Shtormovoe (the Crimean Peninsula, Ukraine). This population was characterized by alternation of reproduction modes, which was also observed in the laboratory culture. Experiments were performed on families (offspring hatched from the same clutch of eggs resulting from either parthenogenesis or bisexual reproduction). The methods for obtaining families of Artemia are described in [2]. Crustaceans from the families were grown individually in vials containing 50 ml of artificial aquatic medium with a salinity of 50‰ at 28°e throughout the life history. Food (a suspension of Chlorella sp. with a concentration of 10 6 cells/ml) was added in excess. The experiments were carried out on 132 females of parthenogenetic origin (six families) and 77 females originating from bisexual reproduction (five families). The following LH parameters were determined for each female: the durations of the juvenile period ( D j ) and the entire lifespan ( D ); body sizes upon laying the first clutch ( L 1 ) and at the end of the lifespan ( L d ); the numbers of generative products (nauplii or cysts) in the first clutch ( E 1 ); and summary reproduction parameters (for the entire lifespan), including the total number of clutches ( N ) and sexual products ( E ), numbers of clutches producing nauplii ( N 0 ) and cysts ( N n ), the numbers of nuplii ( E 0 ) and cysts ( E n ), and the ratio of the number of nauplii to the total number of sexual products ( g = E n / E ). For samples of the offsprings resulting from both reproduction modes, we estimated the mean values ( X ) of individual LH parameters, their standard deviations ( σ ) and coefficients of variation ( e V = ( X / σ ) × 100%). In pooled samples of the offsprings resulting from both reproduction modes, we calculated Spearman’s rank