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The inter and intrapopulation variations in two species of genus Brachionus (Rotifera), in Iran: An ecological review

Samaneh Ansari, Alireza Shayestehfar* and Seyed Mehdi Talebi

Department of Biology, Faculty of Sciences, Arak University, Arak, Iran

Corresponding Author:
Alireza Shayestehfar
Department of Biology, Faculty of Sciences
Arak University, Arak, Iran
 
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Abstract

Brachionus is an suitable live foods for fishes larve of Brachionidae family, in the present study inter and interapopulation variations of two species of family Brachionidae were investigated. For this purpose 90 individuals of geographical populations of these species were collected from different parts of Arak country and for each habitat five ecological factors were examined. Totally eleven quantitative morphological characters were examined from Lorica. The ANOVA test and also one–sample T-test showed significant difference for some morphological characters. In interpopulation section, 10 individuals were selected randomly for each population. Individuals were separated from each other in PCO, PCA, CA plots and UPGMA tree. Significant correlations negative/positive found between some of morphological characters with studied ecological factors of habitat. In addition, variations in morphological characters were seen between populations and they were separated in CA plot and also UPGMA tree. Ecological factors were different between habitat, Therefore habitats were separated in UPGMA tree and PCO, PCA, CA plots. This subject confirmed effect of different ecological factors on phenotypic plasticity of populations.

Keywords

Ecology, Brachionidae, Species, Populations

Introduction

Rotifers as heterotrophic, microscopic, multicellular and diverse are abundance organisms which presence in almost aquatic ecosystem, they play important role as the second link of water food chain [1]. Rotifers are also commonly found on mosses and lichens growing on tree trunks and rocks, also they may be found in rain gutters and puddles, in soil or leaf litter, on mushrooms growing near dead trees, in tanks of sewage treatment plants, and even on freshwater crustaceans as well as aquatic insect larvae [2]. The variation and density of Rotifers in aquatic ecosystems are useful in ecological aspects, water indicator and fishery economy [3]. Difference in the morphological traits which seen in different individuals of a same species is an epigenetic variation that response to various environmental condition and different ecological factors is an aspect of phenotype plasticity [4, 5]. The genus Brachionus belongs to Brachionidae family comprising of 20 species in Iran [6]. In present study, in order to compare the effect of different ecological factors on morphological features of these organisms, 90 individuals of nine geographical populations of two species, Brachionus uceolaris and Brachionus quadridentatus, were examined at inter and intra-population levels.

Materials and Methods

The rotifer collection was done with the help of a standard plankton net Hydrobios, Kiel; 55 μm mesh size through vertical and horizontal hauls at about 20 centimeters below the water surface level. Sampling was done from June 2012 to May 2013. The collected samples were preserved in small bottles including 7% glycol–alcohol then transferred to the biological laboratory of Arak University. The genus Brachionus were separated from other genus and were identified based on funesticaly study with the help of Olympus-BX51 microscope, based on valuable and available references such as Ward and Whipple [7] Sharma and Miche [8]. Five geographical populations of the species Brachionus uceolaris and four populations of the species Brachionus quadridentatus were randomly collected with 10 repetitions. Eleven quantitative morphological characters examined between and within populations. Five ecological features such as longitude (E°), latitude (N°), elevation (in meter), average of temperature (in C°) and pH were examined of each habitat. Longitude, latitude and elevation were calculated with Garmin GPS and averages of temperature for each population were extracted from of meteorology organization of Arak county.

The mean of morphological characters of each populations were standardizes (means=0, variance=1) and used for multivariate analysis including UPGMA (Unweighted Paired Group Using Average Method). Principal Coordinate Analysis (PCA).Analysis of variance (ANOVA) test was performed to assess significant difference in quantitative morphological characters among populations. Pearson's coefficient of correlation was determined between quantitative morphological characters with ecological features of the population's habitat per year to show their possible relationship between them.

Results

In this study, different populations of two species of the genus Brachionus namely B. uceolaris and B. quadridentatus were identified and collected from different environments. This study was done in two levels, among (intra) and between (inter) species. Inter species study carried out at inter and intra-populations levels. Totally five populations of B. uceolaris and four populations' B. quadridentatus with ninety individuals were examined.

Intrapopulations study of B. quadridentatus

Quantitative morphological feature varied between individuals and ANOVA test performed between these characters showed significant difference (p<0.05) for all examined features such as lorica length, lorica width, antero midian spin, distance-antero midian spin, antero lateral spin, distance–antero lateral spin, antero intermediate spin, distance-antero intermediate spin, foot length, toes length and occipital median spin. In addition, one- sample T-test showed significant difference for all examined characters (Table 2, 3).

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Table 1. Habitat Characteristics of studied populations

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Table 2. One-SampleT-test of quantitative morpholiogical of B.quadridentatus

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Table 3. ANOVA test of quantitative morphological characters of B. quadridentatus

Significant correlations positive or negative occurred between morphological features of individuals with ecological factors of habitat for example a positive significant correlations (p<0.01, r=0.56) found between lorica length with north distribution, lorica length had significant negative correlations (p<0.05, r=-0.35) with east distribution and positive significant correlations (p<0.01, r=0.73) occurred between lorica length with temperature and also positive significant (p<0.01, r=0.56) width lorica with north distribution width lorica had significant negative with east distribution, positive significant width lorica with temperature (p<0.01, r=0.74), negative significant antero midian spin with east distribution (p<0.01, r=-0.52), pH (p<0.05, r=-0.30). A positive significant correlations found between distance-antero midian spin with north distribution (p<0.01, r=0.56), temperature (p<0.01, r=0.74), and also distance-antero midian spin had significant negative with east distribution (p<0.05, r=-0.34), A positive significant correlations found between antero intermediate spin with north distributions (p<0.01, r=0.47), temperature (p<0.01, r=0.64), antero midian spin had negative significant correlation (p<0.01, r=-0.40) with east distribution, A negative significant correlation (p<0.01, r=-0.53) found between distance-antero intermediate spin with east distribution and also positive significant(p<0.01, r=0.53) antero lateral spin with east distribution, distance-antero lateral spin had significant positive correlations with north distribution (p<0.01, r=0.51), habitat elevation (p<0.01, r=0.3), temperature (p<0.01, r=0.74) , also negative significant correlation(p<0.01, r=-0.42) distance-antero lateral spin with east distribution. A positive significant correlation found between foot length with north distribution (p<0.01, r=0.53) and temperature (p<0.01, r=0.72) also had positive significant correlations toes length with temperature (p<0.05, r=0.36), pH (p<0.01, r=0.44), A positive significant correlation occurred between occipital median spin with north distribution (p<0.01, r=0.55) and temperature (p<0.01, r=0.72). also negative significant with east distribution (p<0.05, r=-0.36). Studied individuals were separated from each others in UPGMA tree of morphological features (Figure 1). also PCO plat showed high difference between individuals of populations especially in Karahrod Fountain population (Figure 2).

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Figure 1: Plasma Na concentration (mmol/L).

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Figure 2: Plasma Na concentration (mmol/L).

Interpopulation study B. quadridentatu

In this section average amounts of each morphological character used for examination of variations between populations. Significant correlations positive or negative occurred between average amounts of morphological features with ecological factors of habitat for example a positive significant correlation (p<0.01, r=- 0.99) found between foot length with temperature. Studied populations were different in morphological characters and separated from each other in UPGMA tree as well as CA plot (Figure 3, 4).

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Figure 3: Plasma Na concentration (mmol/L).

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Figure 4: Plasma Na concentration (mmol/L).

Intrapopulations study of B. uceolaris

were studied quantitative morphological feature varied between individuals and performed ANOVA test showed significant difference (p<0.05) for all feature such as lorica length, lorica width, antero midian spin, distance-antero midian spin, antro lateral spin, distance–antero lateral spin, antero intermediate spin, distance-antero intermediate spin, foot length, toes length and occipital median spin. But one- sample T-test showed significant difference for all examined characters (Table 4, 5).

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Table 4. One-SampleT-test of quantitative morpholiogical of B. uceolaris

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Table 5. ANOVA test of quantitative morpholiogical characters of B. uceolaris

Significant correlations positive or negative occurred between morphological features of individuals with ecological factors of habitat for example a negative significant correlation (p<0.01, r=-0.39) found between lorica length with north distribution, lorica width had significant negative correlations (p<0.01, r=-0.47) with north distribution and negative significant correlation (p<0.01, r=-0.46) occurred between antero midian spin with north distribution .A negative significant correlation (p<0.01, r=-0.47) found between distance-antero midian spin with north distribution and also positive significant antero intermediate spin with north distribution (p<0.05, r=0.32), also distance-antero intermediate spin had positive significant (p<0.01, r=0.95) with north distribution, A positive significant correlation (p<0.05, r=0.36) was found between antero lateral spin with temperature and pH (p<0.05, r=0.32), foot length had negative significant correlation (p<0.01, r=-0.41) with temperature , also positive significant correlation with pH (p<0.05, r=0.27), A positive significant correlation was found between toes length with north distribution (p<0.05, r=0.38) and pH (p<0.05, r=0.29) also negative significant with habitat elevation (p<0.05, r=-0.29),temperature (p<0.01, r=-0.54), and occipital median spin had significant negative correlations (p<0.05, r=-0.5) with north distribution. PCO plot showed high difference between individuals of populations especially in Kellaleh Sinkholes population (Figure 5). Individuals of all populations were placed far from other in the mention diagram. this subject confirmed high variations in individuals morphological characters.

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Figure 5: Plasma Na concentration (mmol/L).

Interpopulation study B. uceolaris

In this section average amounts of each morphological character were used for examination of variations between populations. Totally eleven qualitative morphological characters were investigated. For example, Amirkabir pool population had shortest lorica length, lorica width, antero midian spin, distance-antero midian spin, distance–antero lateral spin, distance-antero intermediate spin and occipital median spin. No significant differences between average amounts of morphological features with ecological factors of habitat. Studied populations were different in morphological characters and separated from each other in UPGMA tree as well as CA plot (Figure 6 and 7).

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Figure 6: Plasma Na concentration (mmol/L).

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Figure 7: Plasma Na concentration (mmol/L).

In addition, in the study, PCO plat as well as CA plot showed high difference between individuals of populations especially in Karahrod Fountain population (Figures 9, 10). Individuals of all populations were far from other in the mention diagram this subject confirmed high variations in individuals morphological characters. Variations showed in PCA plot and UPGMA tree between individuals of species B. quadridentatus in Karahrod Fountain populations (Figures 8,9). Also in CA Plot were found Variations between individuals of two species B. uceolaris and B. quadridentatus over an extended about of interactions inter species (Figure 10).

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Figure 8: Plasma Na concentration (mmol/L).

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Figure 9: Plasma Na concentration (mmol/L).

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Figure 10: Plasma Na concentration (mmol/L).

Ecological study

Five environmental factors were examined for each habitat including average temperature, elevation of habitat and their longitude, altitude and pH. The mentioned ecological factors differed between stations and habitat were separated in ecological PCA plot (Figure 12) and also UPGMA tree of ecological factors (Figure 11). In the mention diagram populations of B. uceolaris in Kellaleh Sinkholes habitat and B. quadridentatus in Karahrod Fountain habitant were far from each others. This subject confirmed difference and variation in ecological condition of habitats.

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Figure 11: Plasma Na concentration (mmol/L).

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Figure 12: Plasma Na concentration (mmol/L).

Discussion

Quantitative morphological characters had a significant variation between individuals and populations, the ANOVA test and also T-test confirmed these variations. In addition, significant correlations positive or negative occurred between some morphological features of inter and intra-population with ecological factors of habitat, which this phenomenon confirmed the effect of different ecological characters on populations phenotype about this two species. For example significant different were found in length and width lorica which was important for determination of lorica shape. Amictic females are the life history stage of rotifers that is exposed to natural selective most of time9, therefore directional natural selection is predicted to have various effects, If natural selection in give population favors individuals with higher values of particular trait, then the population mean value of that trait is predicted to increase from generation to generations [10]. Some fairly obvious but others less so that ought to affect plasticity and Compare species (or population) that vary with respect to ecological factors that might cause variation in how selection views plasticity [11]. Variation were occurred in morphological traits of population's individuals, therefore samples of populations were separated from others and placed separately. For intra-population investigation eleven quantitative morphological characters of ten individuals of four populations of B. quadridentatus were studied. Quantitative morphological feature varied between individuals in population Karahrod Fountain. Furthermore inter-populations study of B. quadridentatus showed similarity between populations Karahrod Fountain and Baghvahsh Pool. for intra-population investigation quantitative morphological characters of ten individuals of five populations B. uceolaris were studied. Morphological traits varied between individuals of populations Kellaleh sinkholes, in the study inter populations of B. uceolaris showed similar to between populations Serah khomein, Kellaleh dam, Kellaleh sinkholes and Baghvahsh Pool. In some case, the arrangements of populations in morphological and ecological plots and trees were similar. For example in UPGMA trees of morphological character and ecological factor, populations Kellaleh Sinkholes and Karahrod Fountain were separated from others populations. The phenotypic plasticity is typically induced by environmental heterogeneity or environmental stress [12]. The arrangements of some populations were alike in PCA plot of ecological factors with morphological characters. For example, Kellaleh and Sinkholes populations. Phenotypic plasticity is the ability of an organism to express different phenotypes depending on the biotic (e.g. predation, competition and social interactions) or abiotic (e.g. temperature) environmental in a variety of way and in a wide range of taxa. Single genotypes can change their chemistry, physiology, development, morphology, or behavior or in response to ecological cues [13]. The interpopulation variations may be related to habitat of populations. Therefore, phenotypic variation is due in part to variation in genotype, but it is also due in part to environment and morphological characters enables individuals of populations to establish different habitat and these types of variations provide material for evaluation of new taxa. Plasticity has also been suggested as a potentially important mechanism facilitating macroevolution [5, 14]. High variations were observed between individuals of two species B. uceolaris and B. quadridentatus, which this subject signature of reciprocal phenotypic change is the escalation of phenotypes between individuals of two species over an extended about of interactions [15].

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