Abstract
The Caspian bent-toed gecko, Tenuidactylus caspius, is one of the most common nocturnal lizards of Iran with widespread distribution especially in the northern provinces. This research was done in order to study the diet and sexual dimorphism of this species in Sari County from 5 May to 20 October. During this research, 40 specimens of them including 20 males and 20 females were studied for diet and 140 specimens including 70 adult males and 70 adult females were studied for sexual dimorphism. Prey items identified were insects that belong to 15 species of 8 families and 6 orders. The most common prey items were Culex pipiens and Musca domestica. There is no significant difference between diets of males and females. Results show that the adult males in addition of having the apparent femoral and preanal pores are heavier than females and have larger body, head, and tail length.
1. Introduction
Sexual dimorphism in size, morphology, coloration, and aggression is widespread among lizard species and may result from three mechanisms: sexual selection, reproductive role mechanisms (e.g., fecundity selection), and intersexual food competition [1, 2].
Variation among male lizards in sizes of bodies, heads, and other structures in coloration and in courtship and aggression displays may be related to differences among males in reproductive success [3]. Larger male lizards win male-male aggressive encounters and gain greater access to females or they are chosen as mates either because of their size or characteristic that is correlated with large size [4]. However, sexual body size dimorphism may have causes other than sexual selection. The differential mortality between the sexes may cause an apparent size dimorphism because of unequal age of the sexes [5]. Males moving out in search of females must have a high rate of encounter with predators, so large body size of males would enhance their changes of evading some predators and of being too large for other. Two other possible reasons for males being larger than females are intersexual food resource partitioning [6] and forcible insemination of females [7].
The Caspian bent-toed gecko, Tenuidactylus caspius, is one of the most common lizards in northern Iran. This species is nocturnal and oviparous. Recently, some studies have been done on sexual dimorphism of lizards of Iran [8, 9]. Also, there is no work on the diet of this species.
This study was conducted to provide information on sexual dimorphism and food habits of T. caspius in northern Iran.
2. Material and Methods
2.1. Study Area
The study locality was Sari County (36°32 N, 54°7 E), in the Mazandaran province in northern Iran, located on the southern coast of the Caspian Sea. Sari is situated inland from the Caspian Sea in the semitropical coastal plain to the north of the Alborz Mountains. The rainy season lasts about seven months, with an annual precipitation of more than 1,110 mm, giving the countryside a green and lush appearance. The climate of this area is wet and temperate (during this study, the mean temperatures of the coldest and warmest seasons were 1.6°C and 22.5°C, resp.), with the most dominant plants being grassy species belonging to the families Asteraceae and Poaceae [10].
2.2. Sampling
Sampling took place periodically during the activity period of this species from 5 April to 20 October 2011. Sex determined on the basis of preanal and femoral pores which were present in males and absent in females. All specimens were collected by hand, with the aid of a torch, at midnight. Most of the specimens were collected from the walls of the old buildings and gardens. In total, 70 adult and mature females were captured (five specimens per sampling period). Our observations show that males and females reached to the sexual maturity when the body length (SVL) approached 42 and 45 mm, respectively, but we tried to capture specimens which had attained a larger SVL to be sure they were sexually mature adults. Some of specimens were kept in terrarium in order to study food habits.
2.3. Methods
The specimens were transferred alive to the zoology laboratory of Islamic Azad University, Damghan Branch. (weight), SVL (south-vent length), TL (tail length), and HL (head length) were measured by caliper 0.02. Body coloration and scales patterns were studied. Some of them were anaesthetized by chloroform and anatomized. Materials were extracted from their stomach. Insects were identified by valid keys [11]. Data were analyzed by SPSS 18 software, descriptive and -test ().
3. Results
The main food sources for T. caspius are insects (Figure 1). Also, cannibalism was observed sometimes between specimens, but if the ingested prey is too large, they will vomit it by the next day. Prey items identified and number of items found in the stomachs of males and females are shown in Table 2. The most common prey item in this species was Culex pipiens. Diet composition shows no differences between males and females. Individual lizards may only need two or three significant prey items throughout a month. The neonates of this species will take young/small insects.
Sexual dimorphism is distinguishable by larger weight, size of body (SVL), head (HL), and tail (TL) of males (Figure 2). There was no significant difference in body coloration or scales patterns. Results of histological studies on ovaries and testes of some specimens show that males reach to sexual maturity in smaller size than females. Statistics analyses of characters in males and females of T. caspius are shown in Table 1. Results show that there is a significant difference in measured characters in T. caspius ().
4. Discussion
Earlier, it has been reported that the ants are the most common prey item for most of insectivorous lizards of Iran such as T. caspius [12], but, in this research, we observed that the ants are not the favorite items for this species and they prefer other items.
Male biased sexual dimorphism in head size is common in lizards and is thought to evolve through not mutually exclusive, selection pressures [13]. In T. caspius of studied region sexual dimorphism of head size was observed. In other study on T. caspius in Mashhad County located in Khorasan-Razavi Province of Iran, there was no any significant sexual dimorphism [14]. This difference is probably because of different the localities or morphometrical differences between two populations of this species.
There is a little study on sexual dimorphism of gekkonids of Iran. In Tropiocolotes helenae, an endemic gecko of the western Iranian plateau, males are much smaller than females, but with relatively longer tails and more colour bars on the tail, together with more subtle shape differences [8].
Sexual dimorphism in head size was reported in a small gekkonid lizard, Hemidactylus turcicus that is native to the Middle East and Asia [15]. Males exhibited a mixture of isometric and positively allometric patterns of head size increase, whereas females exhibited isometric and negatively allometric patterns. There were no differences in average meal size or in any single dimension of prey size for similar sized males and females. In H. turcicus, sexual dimorphism in head size is not the result of diet partitioning but instead of differential growth patterns following sexual maturity in males and females [15]. In fact, females devote their energy to reproduction after maturation whereas males devote it to the continuing of the growth [15].
Butler and Losos investigated two hypotheses about why a relation between habitat use and extent of sexual dimorphism in shape might occur: (1) sexes adapt differently to the environment, and (2) intersexual niche partitioning occurs with sexes that are similarly adapted [16].
These correlations between sexual behavior and size dimorphism in terms of sexual selection theory were interpreted as follows: males are larger than females when large male size evolves as an adaptation to increase success in male combat, or to enable forcible insemination of females. In contrast, males are usually smaller than females where small size in males evolves to increase mobility (and hence the ability to locate females) or because selection for increased fecundity may result in increased female size [17].
Our results show that there are significant differences in weight, SVL, HL, and TL between males and females of T. caspius, which are not related to diet. Since, all specimens were collected from the same location; hence, the climate variations, altitude and latitude have no different effect on them. Therefore, larger size of males could be because of their advantage in sexual selection and mating.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
The authors wish to thank the Department of Environment of Mazandaran Province for permitting the collection of the specimens and Afshin Faghiri for his help with sampling.