New distribution record, ecology and tail trifurcation of Cyrtodactylus mamanwa (Gekkonidae) on Dinagat Islands, Philippines

This study highlights the ecology, natural history, and a new distribution record by providing a unique habitat occurrence record in karst ecosystem and describes a tail anomaly of the endemic Mamanwa Bent-toed Gecko Cyrtodactylus mamanwa in the province of Dinagat. The detection of a new population on Unib Island in the southwestern Dinagat extends the previously known distribution of this gekkonid by approximately 100 km south from its known distribution.

The Mamanwa Bent-toed Gecko C. mamanwa is a recently described cryptic species of lizard endemic to the province of Dinagat, split from the C. agusanensis complex (Welton et al. 2010). A nocturnal, arboreal, and medium-sized lizard, it occurs in ultramafic habitats (e.g., large boulders, fallen logs on stream banks) from sea level up to 195 m elevation in northeastern Dinagat islands (Welton et al. 2010;Sanguila et al. 2016). Females (maximum snout to vent length, SVL = 92 mm) are larger than males (maximum SVL = 67.5 mm) (Welton et al. 2010). However, its ecology and distribution remain understudied since its discovery.
For most lizards including gekkonids, an intact tail plays a vital role in locomotion, e.g., balance, locomotor performance, ecological flexibility, foraging, predation avoidance, obstacle evasion (Ballinger 1973;Garland and Losos 1994;Iverson et al. 2004;Ofori et al. 2018), storage of nutrients (Daniels 1984), and intraspecific interaction, e.g., courtship, mating, social status, territory defense (Bateman and Fleming 2009;McElroy and Bergmann 2013;Jagnandan et al. 2014). However, their ability to shed the tail and regenerate it does not always function perfectly and may result in unusual tail malformation during regeneration.
In the Philippines, bifurcation was documented only for Gekkonidae [C. mamanwa (Welton et al. 2010)] and Scincidae [Eutropis indeprensa (Sy and Dalabajan 2018)] from Palawan Island. Herein we present additional knowledge on the ecology, natural history, the distribution, and tail trifurcation anomaly of C. mamanwa on Unib Island.
Previous distribution records of C. mamanwa were summarized (Welton et al. 2010;Sanguila et al. 2016). All captured individuals were measured using a digital caliper (e.g., SVL), weighed using an electronic weighing scale (± 0.1 g), were identified using published references by Taylor (1922), Welton et al. (2010), Sanguila et al. (2016), and we followed the taxonomic arrangements of The Reptile Database (Uetz et al. 2020). Captured C. mamanwa were humanely preserved (euthanized with aqueous chloretone, fixed in 10% buffered formalin and consequently transferred to 70% ethanol), following a standard preservation protocol (Heyer et al. 1994;Simmons 2002) and were deposited in Mindanao State University-Iligan Institute of Technology Natural Science Museum (MSU-IIT NSM).
This gekkonid displays a variable dorsal color pattern, from canary-yellow to dark-brown depending on the environment it inhabits. It had a distinct red lining with irregular patterns of branching streaks at the cornea and distinctive eyelashes with yellow coloration. The dorsum portrays moderate longitudinal dark bands projecting from the anterior to the posterior (Welton et al. 2010), with hindlimbs and forelimbs forming an asymmetrical stripe extending to its digits. We observed lizards actively foraging and feeding on cockroaches, termites, and small arthropods at night. We located them in limestone outcrops, rock crevices, and tree trunks in mixed agricultural areas and secondary growth forests over limestone karst habitat at night, and found them utilizing cave walls, tree branches, and underneath a decaying log for shelter and refuge during the day.
The individuals we collected were visibly in good physical condition except for one male (MSU-IIT NSM 4020; SVL = 89.1 mm; weight = 11.7 g, Fig. 1), which had an unusual tail trifurcation. The original regenerated tail measured 71 mm. It presented a pronounced asymmetrically forked tail split near the tip of the regenerated autotomized tail (59 mm, posterior to the base of the original regenerated tail), with a distinct pale-greyish color pattern and exhibited a terminated regenerated tail end. The supernumerary tails were of different lengths. The secondary tail axis (bifurcated tail) measured 13.5 mm, forming a 67° angle with the main tail axis while the under-developed offshoot and less noticeable tertiary branch (trifurcated tail extension) measured 2.3 mm and created a 10° angle from the tip of the main tail axis (Fig. 1). The re-grown tail after autotomy varied distinctively from the original tail based on its color pattern and replacement of the bone and cartilage (Fig. 2). This observation suggests complete autotomy with incomplete tail regeneration possibly due to tail development injuries that may have triggered unparalleled growth of secondary tail, and subsequently with the tertiary tail. More than half of the collected specimens had regenerated tails (n = 11, 57.9%). Caudal autotomy was mostly detected in collected males (n = 9, 81.8%) rather than females (n = 2, 25.0%). We used three voucher specimens to represent the whole population documented on Unib Island and present tail features, patterns of sexual dimorphism, and a tail trifurcation anomaly of C. mamanwa (MSU-IIT NSM; ## 3982, 4020 and 4021).     Table 1.

Discussion
Cyrtodactylus mamanwa is endemic to the province of Dinagat. Published reports on its distribution are concentrated on the northern part of Dinagat Island (Municipality of Loreto; Sanguila et al. 2016). The detection of a seemingly numerous and healthy population of C. mamanwa on the island of Unib, approximately 25 km east of the large Dinagat Island, extends its known distribution by approximately 100 km southwest. It occupies diverse macro-and micro-habitats (e.g., ultramafic forest, forest over limestone or karst).
The present work provides an additional distribution record of C. mamanwa from the Dinagat Islands. It is not surprising that the distribution of C. mamanwa extends to the southwestern part of Dinagat islands since previous records suggest that it might be present on the neighboring islands of Bucas Grande and Siargao (Welton et al. 2010;Sanguila et al. 2016). However, the population on which we report here illustrates unique habitat occurrence where they are found to inhabit limestone karst ecosystem.
Tropical gekkonids demonstrate a high rate of tail autotomy (Arnold 1984). It is an important defensive strategy of lizards in escaping predators (Gogoi et al. 2018). However, this limits locomotion performance, decreases social status, and reduces mating opportunities (Chapple and Swain 2002;Bateman and Fleming 2009). The individuals we collected that exhibited caudal autotomy might have survived predatory attacks (e.g., birds, snakes) represented by a trifurcated regenerated tail. However, tail malformation may hamper locomotory ability and fitness which attracts putative predatory encounters reducing the survival of the lizards and affects them negatively (Bateman and Fleming 2009;Camper and Camper 2017). We presume that C. mamanwa is a natural prey item of predators such as the snakes Chrysopelea paradisi variabilis, Stegonotus muelleri, Dendrelaphis marenae, the birds Cexy argentatus, Halcyon coromanda, Penelopides panini that are present on Unib Island. We have documented a Chrysopelea paradisi variabilis preying on Lepidodactylus herrei (Maglangit et al. 2021), a closely related gekkonid species to C. mamanwa. The higher occurrence of caudal autotomy in males than in females may suggest intraspecific aggression during mating and territorial fights (Iverson et al. 2004;) and male-male competition over food resources (Koleska 2018). Although the cause of autotomy of these gekkonids is unknown, this species may be a good model for predator-prey interaction studies.
To further understand the process of tail regeneration and the incidence of tail malformations, we encourage herpetologists and biologists to focus on areas of developmental biology (e.g., mechanisms of tail regeneration), histology (e.g., anatomical and histological cause of tail breakage), and physiology (e.g., signals that trigger tail autotomy, effects on fitness and locomotion).