Age ranged from 3–7 years. Age structure of examined individuals was characterised by a predominance of 4–5 year-old age group. The maximum and minimum SVL of examined species was 62.92 mm and 36.70 mm, respectively. The mean age and SVL of specimens were 4.91 ± 0.19 SD years and 51.10 ± 1.15 SD mm, respectively. Sexual maturity is attained at the age of three years. Age and SVL were positively correlated (Spearman’s correlation; r = 0.797, P = 0.000) (Fig. 3).
Discussion
Skeletochronology, based on phalanges, has been used to evaluate age and growth of parthenogenetic species, including Darevskia (Arakelyan and Danielyan 2000; Arakelyan 2001, 2002; Arakelyan et al. 2013). In the present study, for the first time the skeletochronology method has been applied to D. bendimahiensis from eastern Anatolia, Turkey.
The SVL was given as 63.5 mm in the holotype of D. bendimahiensis (Schmidtler et al. 1994). In literature, the range of the SVL is reported as 54 - 67 mm with a mean of 60.60 (İret 2004). In our study, the average SVL for the specimens was slightly lower than specimens previously measured by Schmidtler et al. (1994) and İret (2004). Amongst reptiles, body size (SVL) may widely vary for different populations of the same species (Guarino et al. 2010; Gül et al. 2014). The relatively small maximum size of specimens in the present study could be explained by the smaller mean age and the shorter longevity (Bülbül et al. 2018a). Many factors, including age at maturity and longevity, affect the adult body size (Özdemir et al. 2012; Eroğlu et al. 2017).
The maximum age estimated for D. bendimahiensis (7 years) in the present study is within the range for other Darevskia species (Arakelyan and Danielyan 2000; Arakelyan et al. 2013; Gül et. al. 2014, 2015a; Bülbül et al. 2016a, b; Kurnaz et al. 2017, 2018; Altunışık and Eksilmez 2018).
The mean age of the specimens (4.91 years) is similar to other parthenogenetic Darevskia species (Arakelyan et al. 2013) living in highlands like D. bendimahiensis. As a general rule, lizard specimens, inhabiting high elevation sites and northern latitudes, usually live longer than specimens inhabiting low-elevations sites and southern latitudes (Roitberg and Smirina 2006; Gül et al. 2015b; Altunışık et al. 2016). The longevity is related to active period, altitude, latitude, other climatic and environmental factors, food availability, predation and human-induced stress (Bülbül et al. 2016a, 2018b).
Stained cross-sections of phalangeal bones of D. bendimahiensis showed that endosteal resorption was present and caused the loss of one or two innermost LAGs. Endosteal bone resorption is affected by growth processes, environmental conditions and daily and annual activity pattern of animals (Smirina 1972; Augert 1992; Esteban et al. 1999). Endosteal resorption of one or two innermost LAGs is commonly reported in lizard species in lizard species in the genus Darevskia: e.g. D. unisexualis, D. uzzelli (Arakelyan et al. 2013), D. parvula (Bülbül et al. 2016a), D. derjugini (Kurnaz et al. 2018). In the present study, lower endosteal resorption was observed in comparison with congeneric species (D. sapphirina and D. rudis) (Arakelyan et al. 2013; Gül et al. 2014).
The relationship between age and body size is an important life-history parameter that is frequently used in demographic surveys (Kurnaz et al. 2018). Our findings show that the age of specimens was positively correlated with their body size (SVL) as in many rock lizards (D. clarkorum, Bülbül et al. 2016b; D. valentini, Kurnaz et al. 2017; D. dryada, Altunışık and Eksilmez 2018; D. derjugini, Kurnaz et al. 2018). Based on relationships between SVL and each age group, contrary to our findings, there was no significant correlation in females of D. rudis (Gül et al. 2014) and both sexes of D. bithynica (Gül et al. 2015a) and D. parvula (Bülbül et al. 2016a).
The age at sexual maturity is estimated as 3 years for D. bendimahiensis which is in accordance with the other parthenogenetic lizard species of the genus Darevskia e.g. D. uzzelliD. sapphirina, D. unisexualis and D. armeniaca that reached sexual maturity after their third hibernation (Arakelyan et al. 2013). Previous studies reported that age at maturity was greatly influenced by local conditions (especially variation in the length of the active season for ectothermic animals at different altitudes and latitudes) (Olgun et al. 2005; Patrielle et al. 2012; Bülbül et al. 2018a). In general, lizard specimens reach sexual maturity at a higher age in cold regions (Gül et al. 2017).
In conclusion, for the first time we provided data on body size, age at maturity and longevity of D. bendimahiensis from Çaldıran, Van, eastern Anatolia using the skeletochronology method. We believe that detailed research is needed on the variation in life-history traits of this species. This research can help in planning of conservation measures for this endangered species that faces a number of threats along its range, such as habitat loss from tourism, overgrazing and water extraction (Eken et al. 2006).