Study sites were selected based on known occurrences of C. psychedelica on Hon Khoai and on Hon Tuong islands, Ca Mau Province, southern Vietnam, according to previous surveys (Grismer et al. 2010, Ziegler et al. 2016). The region is characterised by a monsoon sub-equatorial climate with constant annual temperatures, but with distinct climatic difference between a dry and a wet period with heavy rains (Fig. 1) (General Statistics Office of Vietnam 2016).

Figure 1.

Mean annual air temperatures (°C) and monthly precipitation (mm) in 2015 and 2016 in Ca Mau Province, Vietnam (source: https://www.gso.gov.vn/default.aspx?tabid=713, accessed on 05 July 2018).

Field surveys were carried out during the wet season in November 2015 as well as during the beginning of the dry season in January 2016. Another short survey on Hon Khoai Island took place in January 2017. We mainly conducted night excursions after sunset between 19:00 h and 24:00 h. In order to determine the sex of the geckos and for taking measurements, individuals were captured by hand and subsequently released at the same spot in the morning or afternoon of the next day between 10:00 h and 17:00 h. While releasing geckos, further sighted individuals were also recorded, measured and released. Each gecko was measured with a digital slide-caliper to the nearest 0.1 mm. Abbreviations are as follows: snout-vent length (SVL), measured from tip of snout to anterior margin of cloaca; tail length (TL), measured from posterior of cloaca to tip of tail in geckos (Grismer et al. 2010).

In order to investigate the biodiversity of Hon Khoai Island, we carried out respective field surveys in January 2016. During these surveys, a few amphibians and reptiles were also collected and subsequently deposited in the collection of the Institute of Ecology and Biological Resource (IEBR), Hanoi, Vietnam. Stomach contents of collected snakes were analysed after dissection in order to identify whether they might represent natural predators of C. psychedelica.

Microhabitat parameters were recorded for each sighted individual, including substrate type (classified as cliff, rock, branch, leaves, forest floor), perch height [in m] (vertical distance between captured animal and ground), percentage of vegetation or rock coverage above animal, position (resting outside, under a rock or within a crevice), substrate surface condition (dry or wet), activity (resting, feeding, foraging), air temperature [°C], substrate temperature [°C], animal’s body surface temperature [°C] and relative air humidity [%]. Air temperature and relative air humidity were measured with a digital thermo-hygrometer at a vertical height from the ground up to 2m height at each microsite (TFA Dostmann/Wertheim Kat.Nr.30.5015), while substrate and body surface temperatures of animals were determined with an infrared thermometer (Measupro IRT20).

To identify intraspecific differences in microhabitat selection of C. psychedelica, individuals were classified into different age classes according to Ngo et al. (2016) based on snout-vent lengths (SVL): SVL < 58 mm = juvenile and SVL ≥ 58 mm = adult.

Chi-square tests and t-tests with P ≤ 0.05 were performed to determine significant differences in selected microhabitat parameters with categorical and continuous variables, respectively, between wet and dry season and amongst age classes. Statistical analyses were applied with the programme SPSS Version 16.0 (SPSS Inc., Chicago).

To obtain an overview on the availability of and evidence for trade in Cnemaspis psychedelica in Vietnam, we visited several local pet markets (one in Ca Mau Province where the species occurs, one in Dong Nai Province, one in Ho Chi Minh City and one in Ha Noi City) and further investigated different internet platforms, reptile Facebook pages and Forums. We also interviewed three local dealers offering the lizard online and two local keepers in March 2018, in order to obtain information on origins, commercial prices and networks of illegal trade in this species. Additionally, we conducted field surveys at previous survey sites located on Hon Khoai Island, Ca Mau Province in January 2017 to evaluate anthropogenic threats. Nearly 10 road workers on Hon Khoai Island were interviewed to determine the local use of the species. Names of interviewees were kept anonymous to ensure data privacy rights and internet links were not disclosed to prevent misuse.

A total of 569 sightings took place (156 during the wet season and 413 during the dry season) including both subpopulations from Hon Khoai and Hon Tuong islands, respectively. Cnemaspis psychedelica was found to be active in the surroundings of granite basements within thick forest coverage, dominated by semi-deciduous forest vegetation. Mean air temperatures were with 29.1 ± 0.75 °C (26.0–31.5 °C, n = 569) slightly higher than average substrate temperatures of 26.6 ± 1.07 °C (20.0–31.7 °C, n = 567). Regarding seasons, substrate temperatures were with 26.9 ± 0.77 °C (25.2–31.7 °C, n = 411) slightly higher during the dry season than temperatures during the wet season (26.1 ± 1.48 °C, 20.0–29.6 °C, n = 156) (t-Test, t = 6.23, df = 187.8, P < 0.001) (see Fig. 2C, Table 1). Generally, temperatures remained relatively constant throughout the year without high fluctuations (Fig. 1). In contrast, relative humidity at microsites was with 86.2 ± 6.1% (71–100%, n = 156), distinctly higher during the wet season compared to 73.3 ± 2.56% (65–80%, n = 413) during the dry season (t-Test, t = 25.4, df = 175.9, P < 0.001) (see Table 1).

Figure 2.

Microhabitat selection of Cnemaspis psychedelica A Substrate selection B Microsite selection C Box plots of substrate temperature D Box plots of canopy coverage E Box plots of perch height.

The Psychedelic Rock Gecko was found active during both the wet and dry seasons. Regarding daily activity pattern, C. psychedelica was observed active during any sighting between 10:00 h to 24:00 h. The vast majority of lizards were found in the shade, even if a patch of direct sunlight was in close proximity.

During the wet season, C. psychedelica was mainly found on loose granite rocks, followed by cliff and leaves on trees (61%, 38%, 1%, n = 413, respectively, see Fig. 2A), but never on branches or on the forest floor. During the dry season, the main selected substrate types were cliffs, followed by loose granite rocks, leaves on trees and branches (65%, 19%, 14%, 2%, n = 156, respectively, Chi² = 36.4, df = 3; P < 0.001, see Fig. 3A–D). We mainly encountered lizards resting under rock formations during the wet season, while animals frequently resided outside of caves or rock shelters during the dry season (outside of caves: 38.5% during the wet season vs. 56.7% during the dry season, respectively, see Fig. 2B, Chi² = 19.1, df = 2, P < 0.001). We further observed C. psychedelica at mean heights of 0.71 ± 0.6 m (0.01–3 m, n = 569) (see Table 1). There was no difference in the height selections of lizards between wet and dry season (t-Test, t = 0.86, df = 567, P > 0.05) (see Fig. 2E). While animals tended to reside under a mean canopy coverage of 79.6 ± 30.5% (n = 156) during the wet season, a higher percentage of canopy cover of 91.2 ± 20.1% (n = 413) above the animals was recorded during the dry season (t-Test, t = 4.4, df = 208, P < 0.001) (see Fig. 2D, Table 1). We observed that the majority (about 75.9%, n = 432) of lizards were resting during surveys, whereas only about one quarter of individuals (n = 137) were found actively foraging.

Figure 3.

A–D Selected substrates of Cnemaspis psychedelica on Hon Khoai Island.

We found adult specimens at mean heights of 0.76 m (n = 419), while juveniles commonly resided at lower heights of 0.61 m (n = 149) (t = 2.9, df = 296.4, P = 0.004). Both age classes preferred to occupy granite rock formations (60.8%, 74.2%, respectively), while another high percentage of adults resided on cliffs (29% vs. 9%, respectively) and a lower percentage of adults occupied branches (7.8%, 16.8%, respectively).

Egg depositions of Cnemaspis psychedelica happened on flat surfaces of cliff walls, without direct sunlight. Egg deposition sites were located under high vegetation coverage during both seasons (see Fig. 4A). We did not find any eggs attached to branches or leaves. Newly laid eggs were bright and clear white in colouration, then changed to pinkish (early development of embryos) and then to a slightly grey colour (with developed embryos). Eggs were almost round in shape, except for the flattened side attached to the substrate. Clutches of C. psychedelica consistently comprised two eggs. Clutches of different individuals of C. psychedelica were commonly deposited in close proximity to each other, forming clusters. Furthermore, new clutches were frequently found to be deposited on top of remains of eggshells from previous clutches. We measured the minimum distance amongst different clusters as about 25 cm. Furthermore, the maximum observed number of unhatched eggs within a cluster was 10 eggs/5 pairs (see Fig. 4A, B). The clusters were generally deposited at heights ranging from 0.3 to 3.5 m above the ground. We frequently found several adult individuals in close proximity to the aggregation of clusters. Solitary clusters comprising only two eggs were usually observed higher than 2.5 m above the ground and were scarcely attended by adult individuals.

Figure 4.

A Communal nesting in Cnemaspis psychedelica B Clumped distribution of clutches.

An ingested adult female of C. psychedelica (IEBR. 4141: SVL = 68.64 mm, TL = 74.8 mm) has been found within a preserved and subsequently dissected Common Wolf Snake (Lycodon capucinus, IEBR. 4211: SVL = 471.4 mm, TL = 95.11 mm) (Fig. 5A). The gecko was ingested with the head first and accounted for 30.4% of the snake’s SVL.

Figure 5.

A Adult female Psychedelic Rock Gecko found as a prey item in the stomach of a Common Wolf Snake (Lycodon capucinus) B Wild-caught individual of Cnemaspis psychedelica offered for sale in a pet shop in Dong Nai Province, Southern Vietnam C, D Preserved reptile species in alcohol, used for traditional medicine on Hon Khoai Island.

During the survey in January 2017, the optimal habitats of C. psychedelica on Hon Khoai Island were found to have experienced further degradation due to expanding road construction and the building of further artificial ponds (see Fig. 6A, B). In particular, destruction with dynamite has entirely removed the natural habitat of C. psychedelica at one survey site and further extended to other survey areas.

Figure 6.

A Forest degradation caused by building new roads B New artificial pond on Hon Khoai Island.

Trade in living C. psychedelica has been recorded by our team in local pet shops from northern Vietnam (Ha Noi City) and southern Vietnam (namely, Ca Mau Province where the species is distributed, further in Dong Nai Province and Ho Chi Minh City), as well as online in Vietnamese Reptile Forums, Zalo Online and Facebook. During our visit to two pet shops, one in Ca Mau Province and one in Dong Nai Province in March 2018, we observed 20 and only one remaining C. psychedelica, respectively, which were kept in small boxes (Fig. 5B). A large number of animals had already been previously exported. Local dealers confirmed that C. psychedelica have been caught from the wild for sale since 2015. According to interviews with local dealers, 15 to 70 specimens from Vietnam have been frequently offered for sale and export to Thailand and Indonesia (for USD 100–300 per individual) and afterwards smuggled to Russia and Europe for USD 700 per individual, while prices achieved in the local trade were comparably lower (USD 20–40 per animal). According to one private keeper in Ho Chi Minh City, C. psychedelica have been offered for USD 450 per pair from another local pet shop in Ho Chi Minh City since 2016. In March 2018, he had 15 breeding specimens for sale for USD 200 per individual and several eggshells were observed in his terrarium. Regarding international trade, at least 23 specimens of C. psychedelica were found being offered for sale online (such as on Facebook) in Europe between September 2017 and March 2018 (Altherr et al. pers. comm.).

During the survey in January 2017, we found some reptile species such as Cnemaspis psychedelica, Cyrtodactylus leegrismeri, Draco maculatus, Hemidactylus frenatus, Gehyra mutilata, Gekko gecko and Ahaetulla prasina soaked together in rice wine and used for traditional medicine by road workers on Hon Khoai Island (Figs 5C and D). According to interviews with road workers, C. psychedelica individuals have been kept as pets in their terrariums at home since 2015.

We found that selected microhabitat characteristics such as substrate type, temperature and canopy cover slightly differed between the wet and dry seasons. Our data showed that the species is more frequently found under granite rock formations during the wet season, probably to avoid heavy rains (10 of 11 survey days). During the dry season, geckos were observed in remarkable numbers outside of caves or rock formations. The species was found strongly associated with granitic rock formations and cliffs during all life stages. While C. psychedelica has never been found on the forest floor and only scarcely within the vegetation, clutches were also unexceptionally deposited on rock formations at heights of at least 0.3 m above the ground. We assume that vertical cliffs might provide shelter from ground-dwelling predators.

Furthermore, animals were found at spots which were more densely covered with canopy during the dry season than during the wet season, which could be their behaviour to avoid direct sun exposure. Accordingly, fewer animals were found along transects with only slight vegetation coverage during the wet than during the dry season. These findings suggest the dependence of C. psychedelica on the availability of shaded habitats. Egg depositions were also exclusively found on cliffs, which are facing away from the sun.

Our study revealed that the body surface temperature of C. psychedelica was positively correlated with the substrate temperature (r_s = 0.51, P < 0.001, n = 567). Thus, as in other ectotherms, basic physiological functions of C. psychedelica, such as locomotion, growth and reproduction are determined by the environmental temperature. Since tropical lizards are considered to have narrow temperature optima and only few options for behavioural and physiological compensation, they are assumed to be, in particular, vulnerable to extinction by climate warming (Deutsch et al. 2008; Doody and Moore 2010; Huey et al. 2009; Vié et al. 2009).

We frequently observed aggregated oviposition sites and the placement of fresh eggs on top of or close to previous oviposition sites. Communal nesting is defined as “non-incidental deposition of eggs at a shared nest cavity by two or more co-specifics” (Espinoza and Lobo 1996). Such communal oviposition has been described in numerous lizard species including other Cnemaspis species (e.g. Kalaimani 2015; Lima et al. 2011; Magnusson and Lima 1984; Vitt 1986; Soares de Oliveira et al. 2015; Somaweera 2009; Srinivasulu and Srinivasulu 2013a, b; Werner 2002) and is assumed to offer potential benefits such as protection, predator-satiation and metabolic heating (Gurgel de Sousa and Freire 2010, Sönmez 2018). Mateo and Cuadrado (2012) experimentally proved that hatching success was significantly higher in communal than in solitary clutches of the gecko Ptyodactylus oudrii and significantly decreased when adult lizards were excluded from the oviposition site. Accordingly, we also observed high densities of C. psychedelica specimens of different ages and sexes, accumulated in close vicinity to communal oviposition sites following the principle of clumped distribution. The maximum observed density was 23 individuals, including 18 adults (9 males), per 4 m². The clumped presence of individuals, independent of age and sex in close proximity to clutches, has also been observed by Mateo and Cuadrado (2012), assuming a high population density and restricted availability of suitable oviposition sites to trigger communal nesting.

With a closer look on the spatial distribution of C. psychedelica, we found age related differences in perch heights, namely juveniles occurring at significantly lower heights than adults. Similar habitat divergences between juveniles and adult individuals have also been reported for Cat Ba Tiger Geckos and Crocodile Lizards in Vietnam (Ngo et al. in press, van Schingen et al. 2015) and gekkonids from New Caledonia (Snyder et al. 2010). Van Schingen et al. (2015) suggested that climbing might be a trade-off in lizards between saving energy costs and the reduction of interactions with competitors and predators. However, this hypothesis needs to be tested in future studies. Furthermore, adult specimens were usually found at similar heights to the closest communal clusters, which might indicate some kind of parental care behaviour.

Reptiles, including lizards are commonly prey of other vertebrates, such as mammals and reptiles (Whiles and Grubaugh 1993). The first case of a snake as a predator of Cnemaspis psychedelica, as herein reported, is thus nothing extraordinary (e.g. Herman 2017, Nogueira et al. 2013, Vrcibradic and Eisfeld 2016, Whitaker and Captain 2004). However, Long-tailed Macaques (Macaca fascicularis) as predators, as reported by Grismer et al. (2010), is a worrying fact, as this species was introduced and thus does not belong to the normal ecosystem of Hon Khoai Island. The artificially enhanced predation probably impacts the population dynamics of C. psychedelica.

Lizards with limited geographic distributions, such as Cnemaspis psychedelica, may be extremely vulnerable to local habitat loss or alteration (Sodhi and Ehrlich 2010). The limited availability of habitats for the species, namely only two offshore islands in the Rach Gia Bay, Vietnam, makes the species particularly vulnerable to habitat destruction. The optimal microhabitats of C. psychedelica on Hon Khoai Island were found to have experienced ongoing degradation due to expanding infrastructure. If the present trend continues, not only C. psychedelica, but also other species and yet undescribed or just recently discovered diversity on the island (Nguyen et al. 2018), will become potentially threatened by extinction. Furthermore, these constructions will probably further facilitate hunters to illegally approach Hon Khoai Island. C. psychedelica has already been observed on international markets, but detailed information about illegal traffic networks has been lacking (Altherr 2014; Auliya et al. 2016, Ngo et al. 2016). New evidence from interviews with local reptile dealers indicates that they paid local fishermen and visited Hon Khoai Island as tourists to collect live specimens of C. psychedelica without any permits. Live specimens of C. psychedelica have been frequently offered for sale in southern and northern Vietnam and are mainly smuggled to Thailand as a middle country and then exported to be sold in Russia and Europe for relatively high prices. However, the number of smuggled animals has allegedly declined to fewer than a total of 20 individuals per deal which might be an effect of the improved control of trade in the species due to the recent inclusion in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) as well as promulgating strict decrees that have restricted harvest and reduced the stress from over-exploiting of a number of lizard species (Sodhi and Ehrlich 2010). However, traders still continue to harvest wild individuals and the species is still found to be offered in local and European markets probably due to high demands and commercial value. Our findings indicate that there are currently no legal commercial harvests and trade in the species in Vietnam, implying that wild specimens entering the international trade have been illegally harvested. We highly recommend that the Vietnamese authorities more strictly control the illegal collection of C. psychedelica in the natural habitat. Furthermore, wildlife law enforcement along key border regions should be highly improved to alleviate the illegal exploitation and trade, not only in wild C. psychedelica, but also in other taxa.