Biometric comparison of two parthenogenetic populations of Artemia Leach, 1819 from the Urmia Lake basin, Iran

Abstract

So far, 18 Artemia sites were reported from Iran of which 16 belong to the parthenogenetic populations. The Urmia Lake basin includes three populations: a bisexual species, Artemia urmiana Gunther, which is endemic to the Urmia Lake, and two parthenogenetic Artemia populations, one from the lake and the other from its lagoons (see ABATZOPOULOS et al. 2006, VAN STAPPEN 2002). Here we compare the two parthenogenetic populations from a morphological point of view. One of them was the population occurring in the Urmia Lake, the other from the lagoon in the Rashakan region in the south-west of the lake. The lagoon is entirely separated from the lake but it is temporarily and seasonal. Biometrical parameters such as diameters of untreated and decapsulated cysts, chorion thickness and length of newly hatched nauplii of the two parthenogenetic Artemia were studied. Cysts were collected in the Rashekan region with the help of a net, and cysts from the parthenogenetic population living in Urmia Lake were taken from AAARI cyst bank (Artemia and Aquatic Animals Research Institute). These two samples were hatched at standard laboratory conditions (LAVENS & SORGELOOS 1996). Nauplii were cultured in 80 ppt salinity. The cysts of adult females were collected and the diameter of untreated and decapsulated cysts and the length of nauplii hatched from these cysts were measured. T-Test was used for analyzing the data. 30 adult females were randomly selected from each population because parthenogenetic populations of Artemia rarely produce male sex (MACDONALD & BROWNE 1986). They were then fixed by using %1 lugol solution. 13 morphometrical characters were measured and the number of setae per furca was counted. There is no significant difference in diameter of decapsulated cyst and the nauplii length between the two samples (p>0.05) but untreated cysts of the parthenogenetic Artemia from inside Urmia Lake are larger in size than the other population (p<0.05) (Table 1). The cyst chorion of the population from inside Urmia Lake (8.31 μm) is also thicker than in specimens from the lagoon (5.53 μm). Ten characters (TL, AL, ED-R, ED-L, LF-R, LF-L, OW, LT, S-R and S-L) show significant differences between the two populations (T-test, p<0.05) (Table 2). According to this analysis, the parthenogenetic population within Urmia Lake is larger in size in comparison eith the parthenogenetic Artemia in the lagoon. On the other hand, the size of furca and number of setae is higher than in the lake parthenogenetic population. In addition, the diameter of decapsulated cyst (embryo) and the nauplii size show no statistical variation between the two parthenogenetic samples, but adult parthenogenetic Artemia from in the lake are larger than those frome the lagoon. This can be ascribed to difference growth rates. Study of Table 2 shows that the mean of ED-R shows statistical variation between the two populations, but ED-L does not show any difference. There are significant differences between the length of right/left branches of furca in specimens from the lagoon and also length of right/left antenna in Artemia originating from Urmia Lake (pair sample T-test, p<0.05). According to these results, there are differences between pair morphometrical characters in Artemia but usually only one of these pair characters is used for morphometrical studies. Here, we suggest using of both pair traits such as length of right/left antenna, diameter of left/right eye, length of left/right branch of furca, and