A Comparative Morphometric Study on Odontobuthus bidentatus and Odontobuthus doriae (Scorpionida: Buthidae) in Iran

Document Type : Original Articles

Authors

1 Department of Medical Entomology and Vector Control, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

2 Department of Medical Entomology and Vector Control, School of Public Health, Urmia University of Medical Sciences, Urmia, Iran

3 National Reference Laboratory for Plague, Tularemia and Q Fever, Research Centre for Emerging and Reemerging Infection Diseases, Pasteur Institute of Iran, Akanlu, Kabudar Ahang, Hamadan, Iran

4 Razi Reference Laboratory of Scorpion Research, Department of Venomous Animals and Toxins, Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran

Abstract

Scorpions are one of the most venomous animals which cause serious public health problems. The sting of scorpions can sometimes be fatal depending on the scorpion species involved. So far, sixty-six (66) scorpion species have been identified in Iran. Annually, about 40-50000 cases of scorpionism are reported in Iran. Odontobuthus doriae and O. bidentatus are among the most medically important scorpion species in Iran, and they are very similar to each other in coloration, carination, and trichobotrial patterns. This morphometric study aimed to compare some of the important morphological characteristics in order to identify the key differences between these two species. A total of 45 morphological characters were measured using calipers and stereomicroscope, and 55 morphological characters and ratios (relative of length to width ratio of morphological characters of scorpions) were analyzed. The independent sample t-test in SPSS software (version 24) was used for the statistical analyses in this study. The mean total length, carapace width, length of fixed and moveable fingers, and chelicerae length of O. doriae were greater than those of O. bidentatus in our study area. The morphological measurements displayed a clear distinction between O. doriae and O. bidentatus in our study area; therefore, they can be used as morphological identification keys for distinguishing between these two species.

Keywords

Main Subjects


1. Introduction

Till now, 66 species of scorpions belonging to three scorpion families of Buthidae, Hemiscorpiidae, and Scorpionidae have been identified in different localities of Iran. Scorpionism is a major public health concern and can sometimes be fatal. Annually, about 40-50000 cases of scorpionism are reported in Iran. Among the Iranian scorpion fauna, the most medically important species include Mesobuthus eupeus, Mesobuthus phillipsii, Androctonus crassicauda, O. doriae, Hottentotta saulcyi, Hottentotta zagrosensis, Compsobuthus matthiesseni, and Hemiscorpius lepturus ( 1 - 15 ).

The Odontobuthus spp. are among the burrowing scorpion species in Iran, and they mostly burrow to find shelter and protection against predators. The genus Odontobuthus (Family Buthidae) is comprised of four species in Iran, namely Odontobuthus bidentatus, Odontobuthus brevidigitus, Odontobuthus tirgari, and Odontobuthus tavighiae. Odontobuthus doriae has a wider distribution range from the west to central parts of Iran at higher altitudes. Odontobuthus brevidigitus is commonly distributed in the Zagros mountain ranges in the West, whereas O. tavighiae has only been reported in the southern region of Iran (Hormozagan Province). Odontobuthus tirgari is mostly observed in the eastern region of Iran. Epidemiologically, O. doriae is considered among the scorpions of medical importance in Iran, and morphologically, it is similar to O. bidentatus ( 16 - 18 ). There are no morphometric data on the comparison between these two species; therefore, comparing morphometric measurements between these species can be of great help in accurate identification of these scorpion species, providing the basis for the production of appropriate regional antivenom. In light of the aforementioned issues, the present study aimed to analyze and compare basic morphometric measurements of O. doriae and O. bidentatus.

2. 2. Materials and Methods

2.1 Study Area and Specimens Collection

The scorpion specimens were captured from Tehran, Markazi, Khuzestan, and Kerman Provinces between 2014-2015 using the digging and ultraviolet methods (Figure 1). The specimens were kept in plastic bottles containing 75% ethylic alcohol and transported to the Medical Entomology lab of the School of Public Health, Tehran University of Medical Sciences. Valid Iranian scorpion identification key (Farzanpay 1987) was used to identify the scorpion species ( 19 ). Following scorpion identification and sex determination, two species (O. doriae and O. bidentatus) (Figure 2) were selected for further morphometric studies. Only females were included in this study, and 55 morphological characters and ratios were examined according to recommended nomenclature by Stahnke ( 20 ).

Figure 1. Provinces of scorpion collection sites (Odontobuthus doriae was collected from Tehran and Markazi Provinces, Odontobuthus bidentatus was collected from Khuzestan and Kerman Provinces)

Figure 2.AOdontobuthus bidentatus, B:Odontobuthus doriae2.2 Morphological Characters

The 55 morphological characters and ratios examined in the current study were as the following: the length of body, Chelicerae length, width, and height, length and width of chelicerae, distance between median eyes, distance between median and lateral eyes, distance between median eyes and the anterior margin of the carapace, length of carapace, anterior and posterior width of carapace, height of carapace, length, width, and height of trochanter, length and width of the trochanter, length, width, and height of femur, length of femur/width of the femur, length, width, and height of patella, length of patella/ width of the patella, length of manus, length, width, and height of chela, length of chela/width of chela, length of I, II, III, IV, and V, length of metasomal segment I, II, III, IV, and V/ width of the metasomal segment I, II, III, IV, and V, length, width, and height of telson, length of pectines moveable finger, length of the fixed finger, length, width, and height of metasomal segments ( 15 ).

2.3 Data Analysis

These measurements were carried out using calipers and a stereomicroscope equipped with a caliper (accuracy to one-hundredth of a millimeter), and the data were transferred into an excel sheet for each species. Independent samples T-test was performed in SPSS software (version 24) to compare the studied characters between these two species (Table 1).

Parameters Odontobuthus bidentatus Odontobuthus doriae
No. X ±SE No. X ±SE
Length of body* 16 59.60 2.07 16 71.57 1.20
length of chelicerae* 16 2.67 0.32 16 3.46 0.59
Width of chelicerae* 16 2.35 0.37 16 2.75 0.21
length of chelicerae/ Width of chelicerae 16 1.21 0.05 16 1.26 0.05
Height of chelicerae 16 1.68 0.07 16 1.88 0.07
Distance between median eyes 16 1.33 0.47 16 1.40 0.05
Distance between median and lateral eyes 16 2.69 0.14 16 3.12 0.08
Distance between median eyes and the Anterior margin of the carapace* 16 3.20 0.09 16 3.51 0.08
Length of carapace* 16 7.00 0.28 16 8.91 0.23
Anterior width of carapace* 16 4.45 0.16 16 5.29 0.10
Posterior width of carapace* 16 8.59 0.30 16 9.76 0.21
Height of carapace 16 5.02 0.26 16 5.87 0.34
Length of trochanter 16 2.66 0.17 16 2.81 0.88
Width of trochanter* 16 2.35 0.07 16 2.66 0.04
Length of trochanter/ Width of trochanter 16 0.13 0.05 16 0.05 0.03
Height of trochanter 16 2.32 0.88 16 2.41 0.10
Length of femur* 16 6.27 0.25 16 7.16 0.16
Width of femur* 16 1.92 0.07 16 2.11 0.05
Length of femur/ Width of femur 16 0.13 3.25 16 3.40 0.09
Height of femur 16 1.60 0.06 16 1.58 0.06
Length of patella* 16 7.13 0.23 16 8.16 0.12
Width of patella 16 2.49 0.12 16 2.69 0.09
Height of patella 16 2.19 0.09 16 1.99 0.08
Length of patella/ Width of patella 16 1.03 0.03 16 1.11 0.04
Length of chela* 16 13.28 0.47 16 14.52 0.27
Width of chela* 16 2.87 0.13 16 3.39 0.01
Height of chela 16 2.65 0.96 16 2.58 0.13
Length of chela/ Width of chela 16 4.49 0.10 16 4.29 0.06
Length of fixed finger* 16 8.25 0.27 16 9.51 0.25
Length of moveable finger* 16 9.31 0.34 16 10.37 0.25
Length of metasomal segment I 16 4.53 0.22 16 4.26 0.12
Width of metasomal segment I 16 4.56 0.16 16 5.34 0.20
Length of metasomal segment I/ Width of metasomal segment I 16 0.99 0.03 16 0.82 0.06
Height of metasomal segment I 16 3.42 0.22 16 3.88 0.20
Length of metasomal segment II 16 4.72 0.23 16 4.98 0.13
Width of metasomal segment II* 16 4.01 1.48 16 4.83 1.36
Length of metasomal segment II/ Length of metasomal segment II 16 1.16 0.04 16 1.04 0.05
Height of metasomal segment II 16 3.62 0.18 16 3.82 0.20
Length of metasomal segment III 16 4.92 0.34 16 5.37 0.12
Width of metasomal segment III* 16 3.71 0.09 16 4.47 0.13
Length of metasomal segment III/ Length of metasomal segment III 16 1.28 0.07 16 1.22 0.06
Height of metasomal segment III* 16 3.55 0.10 16 3.87 0.18
Length of metasomal segment IV* 16 5.64 0.24 0.24 6.55 0.17
Width of metasomal segment IV * 16 3.63 0.13 0.13 4.22 0.14
Length of metasomal segment IV / Length of metasomal segment IV 16 0.43 0.04 0.04 0.44 0.05
Height of metasomal segment IV 16 3.08 0.12 0.12 3.34 0.17
Length of metasomal segment V 16 7.00 0.42 0.42 7.90 0.041
Width of metasomal segment V 16 3.25 0.09 0.09 3.65 0.18
Length of metasomal segment V/ Width of metasomal segment V 16 2.28 0.66 0.66 2.23 0.81
Height of metasomal segment V 16 2.55 0.08 0.08 2.65 0.11
Length of telson* 16 6.35 0.19 0.19 8.33 0.17
Width of telson* 16 3.28 0.10 0.10 3.80 0.05
Length of telson/ Width of telson* 16 1.97 0.33 0.33 2.19 0.14
Height of telson 16 3.18 0.10 0.10 3.08 0.14
Length of pectin* 16 6.55 0.17 0.17 7.32 0.19
*significant values
Table 1.Morphometric parameters of studied females of Odontobuthus doriae and Odontobuthus bidentatus in Iran from 2014-2015

3. Results

A total of 32 scorpion specimens, including 16 specimens of O. doriae and 16 specimens of O. bidentatus, collected from the aforementioned provinces were examined. The following morphological measurements from the two scorpion species were significantly different (P<0.05): body length, length and width of chelicerae, the distance between median eyes and the anterior margin of the carapace, carapace length, anterior and posterior width of carapace, trochanter width, length and width of the femur, patella length, length and width of chela, the width of metasomal segment II, III, length and width of metasomal segment IIII, length and width of telson, length of telson/width of telson*, and pectin length.

In almost all cases, the mean value of each measurement from the morphological characters was greater in O. doriae, as compared to that in O. bidentatus. These two burrowing scorpions are very similar to each other, except for one morphological character: the number of lateral lobes on the anal arch. Odontobuthus doriae has two lateral lobes on the anal arch, whereas O. bidentatus has three lateral lobes on the anal arch. The results of the present study pointed out that O. doriae has a larger body size than O. bidentatus: mean body lengths were 71.57 and 59.60 mm for O. doriae and O. bidentatus, respectively.

In the study area, the prosoma of O. doriae was wider than that of O. bidentatus: The mean values of anterior width of the carapace were reported as 4.45 and 5.25 mm for O. bidentatus and O. doriae, respectively, and the mean values of posterior width of the carapace were 8.59 and 9.76 mm for O. bidentatus and O. doriae, respectively. In the present study, O. doriae had a wider metasoma in some segments, compared to O. bidentatus, and the telson of O. doriae (mean telson length and width: 8.33 and 3.80 mm, respectively) was bigger than that of O. bidentatus (mean telson length and width: 6.35 and 3.28 mm, respectively).

4. Discussion

The present study was conducted to compare 55 morphological characters and ratios between O. doriae and O. bidentatus, both of which belong to the family Buthidae. Odontobuthus bidentatus, previously known as O. odonturus, is mainly distributed in southern Iran. Odontobuthus doriae has a wider distribution extending from the west to the central part of Iran at higher altitudes, such as mountainous areas ( 19 ). Numerous morphometric studies have previously been conducted on scorpion species identification ( 21 - 26 ). Nonetheless, there is no morphometric study comparing O. doriae and O. bidentatus in Tehran, Markazi, Khuzestan, and Kerman provinces in Iran.

In the current study, almost all the morphological measurements from O. doriae and O. bidentatus were significantly different (P<0.05). The mean measurements of the morphological characters of O. doriae were larger, as compared to those of O. bidentatus. Molecular and morphometric studies on the genus Odontobuthus performed in Iran by Mirshamsi demonstrated that Odontobuthus tirgari was morphologically different from O. doriae and O. bidentatus ( 16 ). On the other hand, unlike the results of the present study, Odontobuthus doriae scores were lower than the other species. This discrepancy can be ascribed to differences in collection sites. In the current study, O. doriae was collected from Tehran and Markazi provinces, whereas O. bidentatus was collected from Khuzestan and Kerman Provinces.

It is worth mentioning that the geographical populations of O. doriae and O. bidentatus that are distributed in different localities in Iran ( 10 , 13 , 17 - 19 , 27 - 33 ) are different in body size. In a morphometric study on O. bidentatus carried out by Ahmadi, Vazirianzadeh ( 34 )in Khuzestan province, the pectines in the males were longer and more, as compared to those in the females. In the abovementioned study, the mean total body length of O. bidentatus was 74 mm; nonetheless, in the present study, it was 71.57 mm. This small difference in mean total body length between the present study and that of the research by Ahmadi et al. can be attributed to measurement errors.

In another study which was also conducted in Khuzestan province, the mean total length of O. bidentatus was reported as 77 mm ( 35 ), which is by far larger than the measurement in the current research. Regarding this finding, it can be stated that minor changes in the habitats of scorpions can affect their body size. Therefore, we reiterate that the results of the present research are only reliable in our study area. In another study, the mean total length of O. tavighiae was 49.8 mm ( 34 ). Based on the results of the present study, it can be concluded that total body size can be used to distinguish O. tavighiae from O. bidentatus in our study area.

5. Conclusion

Odontobuthus doriae and O. bidentatus, both belonging to the family Buthidae, have triangle sternum and are morphologically very similar to each other. They are categorized as burrowing scorpions. They have similar coloration and carination, making it difficult to distinguish between them. The findings indicated that there are significant (P<0.05) distinguishing morphological characters between these two species, especially the mean total body length, as well as the length of carapace, chelicerae, metasoma, and telson. The mean measurements of all morphological characters in O. doriae were greater than those of O. bidentatus in our study area. The morphological measurements demonstrated a clear distinction between O. doriae and O. bidentatus in our study area; therefore, they can be used as morphological identification keys for distinguishing between these two species. It is recommended that morphometric studies be conducted on the specimens of these species in other parts of Iran to clarify the differences between them.

Authors' Contribution

M. F., A. M., and J. R. designed the study, M. M. B. did the morphometric analyses and prepared the manuscript, and S. N. contributed to writing the manuscript and specimen identification.

Ethics

All the procedures were approved by the ethics committee of the Research Deputy of Tehran University of Medical Sciences (TUMS) Iran.

Conflict of Interest

The authors declare that they have no conflict of interest.

Grant Support

This study was supported by the Research Deputy of Tehran University of Medical Sciences (TUMS) Iran (project no. 92-01-27-20619).

Acknowledgement

We gratefully acknowledge the personnel of Razi Vaccine and Serum Research Institute, Department of Venomous Animals and Toxins for their invaluable help.

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