The widespread Indo-Pacific Slender Gecko Hemiphyllodactylus typus: a single species across the Oceans ?

Abstract

The Indo-Pacific Slender Gecko Hemiphyllodactylus typus is distributed across the Indian and Pacific Oceans. Its ecological flexibility and vast distribution may raise concerns of a potential invasion in tropical and subtropical islands worldwide, but evidence of a recent spread is lacking. The identity of the species has also been questioned across its distribution range. In this note we synthesise information obtained from the literature on the distribution and the habitat use of the species. We stress the need to develop new sampling techniques to improve its detection, and perform phylogenetic analyses to formally identify the species across the different regions and determine its colonisation history.

Full text

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Bulletin Phaethon- Volume 51 (2020)
Bulletin Phaethon, 2020, 51 : 38-41.
The widespread Indo-Pacific Slender Gecko Hemiphyllodactylus typus:
a single species across the Oceans ?
Grégory Deso1, 2*, Jean-Michel Probst2, Nicolas Dubos2, 3
1 Ahpam (Association herpétologique de Provence Alpes Méditerranée), 384 route de Caderousse, 84100 Orange, France.
2 Association Nature & Patrimoine. Île de La Réunion, France.
3 Centre d'Ecologie et des Sciences de la Conservation (CESCO UMR 7204), Sorbonne Universités, MNHN, CNRS, Paris, France.
*Corresponding author: ahpam.contact@gmail.com
Abstract: The Indo-Pacific Slender Gecko Hemiphyllodactylus typus is distributed across the Indian and Pacific Oceans. Its ecological flexibility and
vast distribution may raise concerns of a potential invasion in tropical and subtropical islands worldwide, but evidence of a recent spread is lacking.
The identity of the species has also been questioned across its distribution range. In this note we synthesise information obtained from the literature on
the distribution and the habitat use of the species. We stress the need to develop new sampling techniques to improve its detection, and perform
phylogenetic analyses to formally identify the species across the different regions and determine its colonisation history.
Keywords: Hemiphyllodactylus typus, Distribution, Invasive alien species, parthenogenesis, insularity, habitat generalist
Résumé : Le Gecko arboricole indopacifique Hemiphyllodactylus typus est réparti dans toute l'Asie du Sud-Est et dans l’océan Indien et Pacifique. Sa
flexibilité écologique et sa vaste répartition suscitent matière à réflexion quant à une éventuelle invasion, mais les preuves d'une extension récente de
sa répartition font défaut. De même, l’identité de l’espèce a été remise en question de part et d’autre son aire de répartition. Cette note synthétise les
informations au travers de la littérature concernant la répartition et l’utilisation des différents habitats par l’espèce. Nous soulignons la nécessité de
développer de nouvelles techniques d’échantillonnage afin d’augmenter sa détectabilité et d’effectuer des analyses phylogénétiques pour identifier
formellement l'espèce et déterminer l’historique de sa colonisation.
Mots clés : Hemiphyllodactylus typus, Répartition, espèces invasives, parthénogenèse, insularité, généraliste à l’habitat
Citation : DESO, G., PROBST, J.M., DUBOS, N. 2020. The widespread Indo-Pacific Slender Gecko Hemiphyllodactylus typus: a single species
across the Oceans ? Bulletin Phaethon, 51 : 38-41.
Fig. 1. Lateral (left) and dorsal view (right) of Hemiphyllodactylus typus Bleeker, 1860 in indigenous shore patches of Scaevola (Anse des Cascades,
Reunion Island)
Fig. 1. Vue latérale (gauche) et dorsale (droite) de Hemiphyllodactylus typus Bleeker, 1860 dans les formations végétales indigénes à Scaevola du
littoral (Anse des Cascades, Île de La Réunion). (© Pictures J.M. Probst)

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The widespread Indo-Pacific Slender Gecko Hemiphyllodactylus typus: a single species across the Oceans ?
Deso, G., Probst, J.M. et Dubos, N.
Fig. 2. World distribution of Hemiphyllodactylus typus. Locality records were compiled from verified observations derived from Biswas and Sanyal
(1980), Ineich (1992a), Pauwels and Bauer (2001), Pauwels and Sumontha (2007), Deso et al. (2008), Zug (2010), Chandramouli et al. (2012) and
Fisher et al. (2013).
Fig. 2. Répartition mondiale de Hemiphyllodactylus typus. Les données d'occurrence proviennent d'observations vérifiées, extraites de Biswas and
Sanyal (1980), Ineich (1992a), Pauwels and Bauer (2001), Pauwels and Sumontha (2007), Deso et al. (2008), Zug (2010), Chandramouli et al. (2012)
and Fisher et al. (2013).
The Indo-Pacific Slender Gecko Hemiphyllodactylus typus Bleeker, 1860 (Fig. 1) is observed in many islands of the
Indian and the Pacific Ocean. Originally described from a specimen captured in Goenong Parong, Java, Indonesia
(Bleeker, 1860), its presence has been recorded through Malaysia, Japan (Ryukyu and Iriomotejima), Taiwan,
Indonesia, Philippines, Sri-Lanka, India (only Andaman and Nicobar Islands), the Mascarenes (Reunion Island,
Mauritius and Rodrigues) and in Oceania (Papua New Guinea, Solomon Islands, New Caledonia, Fiji, Polynesia as far
east as Pitcairn Islands and Hawaii; Vinson & Vinson, 1969; Biswas & Sanyal, 1980; Cheke, 1987; Ota, 1990; Ota &
Ross, 1990; Ineich, 1992a; Probst & Florens, 1992; Bauer & Sadlier, 2000; McKeown, 1996; Batuwita & Alagiyawadu,
2004; Schröder & Röll, 2004; Deso et al., 2008; Zug, 2010; Chandramouli et al., 2012; Fisher et al., 2013; Holden et al.,
2014; Ineich, 2016; Jayaneththi & Jablonski, 2016). The presence of the species is also highly suspected in Vanuatu
(Ineich, 2011). Its presence in continental Asia has only been reported in Thailand (Pauwels & Bauer, 2001; Pauwels &
Sumontha, 2007). However, given the newly described set of species discovered in the region, some preserved
specimen are currently being analysed in order to clarify the status of Thai populations (pers. com., O. Pauwels).
Its distribution has been recently clarified, as individual records in continental India, Vietnam, Palau and Enewetak
Atoll turned out to be erroneous, since specimens have subsequently been identified as H. aurantiacus, H. yunnanensis,
H. ganaklonis H. nilgiriensis, H. peninsularis and Lepidodactylus moestus (Zug, 2010; Fisher et al., 2013; Agarwal et
al., 2020; Uetz, 2020). A majority of authors hypothesised that the wide distribution of the species is the result of recent
colonisation through human-mediated transport. Findings of specimens in islands of both the Pacific and Indian Oceans
(Vinson & Vinson, 1969; Probst & Florens, 1990; Probst, 1995; Deso et al., 2008; Zug, 2010) are consistent with
heavily utilised shipping networks (Zug, 2010; Jayaneththi & Jablonski, 2016), which suggest a potential for a global
spread in tropical and subtropical regions (Fig. 2). However, the non-native status of H. typus in these islands has been
questioned (Ineich, 1992b) as indeed, the species appears as a poor colonisator in anthropogenic environments
compared to the invasive house gecko Hemidactylus frenatus or the typhlopid snake Indotyphlops braminus. No
dedicated phylogeographic study of H. typus has been performed so far and its geographical origin is still unknown
(Abhaya et al., 1997; Deso et al., 2008).
Hemiphyllodactylus typus is usually found in indigenous habitats in Oceania, away from anthropogenic activity (only a
few observation were made on house walls and gardens; I. Ineich, pers. com.). However, the species is still encountered
in anthropogenic habitats in the Indian Ocean (Deso et al., 2008; Jayaneththi & Jablonski, 2016). In the Mascarene
Islands and Sri Lanka, individuals were also observed in native remnant forests (Probst, 1995; Jayaneththi & Jablonski,
2016; Vincent Florens, pers. com.), where other invasive nocturnal geckos are generally absent. Of particular note, the
smaller, more slender and flattened habitus of H. typus may allow this species to take advantage of microhabitat
features inaccessible to native or other introduced geckos. For example, slender geckos have already been observed
using the compressed leaves of a myrmecophilous plant (Dischidia rafflesiana) as an oviposition site (Janzen, 1974).

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Individuals were also witnessed occupying several thicknesses of sheathing and particularly compressed leaves of Musa
sp., palm tree spp. and rocky habitats (Deso et al., 2008). There is no doubt that this particular ecological plasticity is an
advantage for this species in its colonisation of different plant habitats. These records in primary and secondary forests,
along with plantations and manmade structures suggest a high flexibility in the habitat use of the species. Individuals
were sometimes found in highly isolated indigenous forest patches that host a unique endemic vegetation (e.g., in
Reunion Island: Mare Longue, littoral de Bois Blanc, Anse des cascades; in Mauritius: Moka, Pétrin; Rodrigues:
Grande Montagne; Vinson & Vinson, 1969; Probst & Florens, 1990; Probst, 1995). This suggest a strong ecological
plasticity and ability to colonise new environments, which may be strengthen by its capacity of parthenogenesis (Ineich,
1992b) and year-round continuous reproduction (Deso et al., 2008).
The possibility of a recent spread of H. typus and its apparent habitat generalism may raise concerns of invasion. Other
gecko species such as the house gecko Hemidactylus frenatus have been involved in the decline of endemic geckos and
other taxa in tropical islands (Cole & Harris, 2011). Where H. typus is supposedly non-native, it is possible that its
occurrence, sometimes found in high density in vegetation patches or cracked rocks (G. Deso & J.M. Probst, pers. obs.),
may drive the decline of sympatric native populations through competition for trophic resources (Cole, 2005; Cole &
Harris, 2011; Kusuminda et al., 2013), competition for egg laying sites (e.g., eggs of H. typus are found in fallen
branches and in anthropogenic structures, once found in sympatry with eggs of Phelsuma borbonica; Deso et al., 2008),
and disease/parasite transmission (Barnett et al., 2018). However, the risk of becoming invasive can be questioned
because of its overall scarcity and cryptic behaviour. It is also predated by a number of mammals, reptile and birds
species (including the endemic Saxicola tectes from Reunion Island; Deso et al. 2008), which moderates the risk of
invasion.
To date, there is no evidence that the spread of H. typus is recent. Given its cryptic, strictly nocturnal behaviour, it is
possible that the species has colonised islands of both Oceans before human arrival, by natural rafting, without being
detected until recently. In addition, it is not certain to date that populations from Indonesia, Pacific and Indian Oceans
belong to the same species. Interestingly, the case of H. typus is similar to that observed for Gehyra mutilata: the type-
locality of the species is also located towards the centre of its distribution area and populations are largely spread on
islands on either sides (Indian Ocean and Pacific Ocean). Recent genetic analysis have shown that Indian Ocean
Populations of G. mutilata correspond to a distinct species from Pacific Ocean populations (Gehyra insulensis; see
Rocha et al., 2009). Moreover, Gehyra mutilata is more often encountered in anthropogenic habitats in the Indian
Ocean populations, similarly to H. typus (I. Ineich, pers. com.). Hence, there is a need to perform population genetic
analyses to formally elucidate the identity of the different populations, determine the geographical origin of the species,
and provide evidence of its putative recent spread. We also recommend the study of internal and external parasite
prevalence patterns since parasites can provide material for characterising colonisation patterns, which are often taxon-
specific (e.g., Ineich, 1999). Since the species is difficult to observe, we encourage the development or application of
new sampling techniques to improve the detection of the species (e.g., by using specific flashlights). In addition, we
recommend the assessment of the climatic niche of the species, which would enable to predict its potential distribution,
and identify putative invasion or local extinction risks in regard to future climate scenarios. This relies on a
comprehensive synthesis of occurrence data with a careful species allocation confirmation and tissue samples at the
global scale, which can be achieved with the involvement of naturalist professionals and museological collections.
Acknowledgements
We sincerely thank Ivan Ineich for providing relevant material and helpful comments that greatly improved the
manuscript. We also thank Aaron Bauer and Olivier Pauwels for their constructive remarks and precisions.
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