First record of tail bifurcations in the snake–eyed skink Ablepharus kitaibelii Bibron & Bory de Saint–Vincent, 1833 from Pastrina hill (northwestern Bulgaria)

First record of tail bifurcations in the snake–eyed skink Ablepharus kitaibelii Bibron & Bory de Saint–Vincent, 1833 from Pastrina hill (northwestern Bulgaria).— We report for the first time on the occurrence of tail bifurcations in the snake–eyed skink (A. kitaibelii). This morphological anomaly was identified during a four–year monitoring program conducted in a herpetological hot–spot at Pastrina hill (northwestern Bulgaria). From a total of 415 captured specimens, four animals (0.96%) showed symmetrical or asymmetrical lateral duplication of the tail. Only bifurcations of the distal–most caudal section were detected in contrast to some other lizards (e.g. Gekkonidae, Lacertidae, Teiidae) that are reported to survive with bifurcations at more proximal tail sections.

Recently, a tail bifurcation was reported for a lizard from the genus Ablepharus [A.deserti Strauch, 1868 (Jablonski, 2016)].The genus Ablepharus belongs to the Family Scincidae and includes ten species of relatively small lizards with weakly developed extremities (Uetz & Hošek, 2016).Data on the frequency of occurrence of specimens from this genus with tail bifurcation are lacking.In the present study, we provide the first report on the occurrence of tail bifurcations in a member of the genus Ablepharus (the snake-eyed skink A. kitaibelii Bibron & Bory de Saint-Vincent, 1833).

Material and methods
One of the ten species of genus Ablepharus (A. kitaibelii) inhabits Bulgaria.The species occurs sporadically and shows habitat preferences for dry meadows with bush vegetation and sparse oak forests (Stojanov et al., 2011).The studied area (see fig. 1) covers approximately 0.6 ha of the ecotone zone between an oak forest and a meadow, at an altitude of 280 m.It is located on Pastrina hill, near Montana town (northwestern Bulgaria).The coordinates of the studied area are N43.384828,E23.301825 (Datum: WGS84, GCS).The site was visited аt irregular intervals of approximately 10 days during the active period of the species (Stojanov et al., 2011) from 2012 to 2016.The geographic coordinates were recorded by hand-held Garmin GPSMAP 62s unit (Garmin International Inc., Kansas, USA).Photo-documentation was made by using a Sony Cyber-shot DSC-HX300.
This study was conducted in compliance with the national laws of Bulgaria (collection permits No. 411/14.07.2011 andNo. 520/23.04.2013) and the international requirements for ethical attitude towards animals No animals were collected or harmed.All lizards were measured and documented and released at the site of capture.

Results and discussion
During a four-year monitoring program of population characteristics of the snake-eyed skink in Bulgaria, we captured 415 specimens.In four of the lizards (0.96 % of the captured individuals), we identified a tail bifurcation (fig.2).The percentage in A. kitaibelii seems lower than the 1.7% and 1.2% reported by Vrcibradic & Niemeyer (2013) for populations of two skink species, belonging to the genera Mabuya and the Notomabuya (Hedges & Conn, 2012).
According to Stojanov et al. (2011) andMcKelvy &Stark (2012), the caudal bifurcation in lizards may be lateral, as well as dorso-ventral.In all of our specimens with this kind of deformation, the bifurcation was lateral, as found in A. deserti (Jablonski, 2016).
The tail bifurcation in lizards may be either symmetrical or asymmetrical (Dudek & Ekner-Grzyb, 2014).In two of our specimens the second tale was substantially shorter than the autochthon part and in the other two both sections developed similarly (fig.2).In all four   studied specimens, the bifurcation was at the distal-most section of the tail.In some lizard species, the bifurcation may be positioned rather proximally (closer to the pelvis) and both sections of the tail may be equally developed (Dudek & Ekner-Grzyb, 2014;De Andrade et al., 2015;Passos et al., 2016).According to Passos et al. (2016), such design may impact the locomotor performance of the affected individuals.The snake-eyed skink mainly inhabits the layer of fallen leaves in the oak forests (Stojanov et al., 2011) and avoids being eaten by sudden changes of direction in the 3-D surrounding.Changes in the geometry of the tail could potentially diminish its chances to avoid predation.
No reports concerning tail bifurcation in A. kitaibelii have been reported to date.Our results from a four-year population study of over 400 individuals suggest that specimens with terminal lateral bifurcations are rare.The tail splitting presumably has a random character, and we propose that it is caused by errors in regeneration after partial or full autotomy of the distal caudal sections.

Fig. 1 .
Fig. 1.Map of the site where the study was performed in Pastrina hill (Montana, northwestern Bulgaria).Fig. 1.Mapa de la zona donde se realizó el estudio en el monte Pastrina (Montana, noroeste de Bulgaria).

Fig. 1 .
Fig. 1.Map of the site where the study was performed in Pastrina hill (Montana, northwestern Bulgaria).Fig. 1.Mapa de la zona donde se realizó el estudio en el monte Pastrina (Montana, noroeste de Bulgaria).