First record of the tropical house gecko Hemidactylus mabouia (Moreau de Jonnès, 1818) in Texas

Invasions of the tropical house gecko Hemidactylus mabouia (Moreau de Jonnes, 1818) in the tropical Americas are well documented. While this gecko has been reported as well established and expanding its range in Florida, here we document the first record in the United States outside of this state. We detected a small reproducing population in Cameron County, Brownsville, Texas. We expect a rapid colonization of buildings by this species in southern Texas. We consider that this potential invasion poses novel obstacles to the continued presence of the earlier invasive Mediterranean gecko Hemidactylus turcicus (Linnaeus, 1758) across Texas.


Introduction
Among reptilians, geckos from the genus Hemidactylus have the most extensive longdistance dispersal. Although phylogenetic studies suggest a long history of natural colonizations in this group, the majority of large range extensions are likely anthropogenic (Carranza and Arnold 2006). One of the most successful colonizers of this genus is Hemidactylus mabouia (Moreau de Jones, 1818), commonly known as tropical house gecko (Rocha et al. 2011;Short and Petren 2011). Native to sub-Saharan Africa, Madagascar and the Mozambique Channel Islands, it is now naturalized thorough the Caribbean and most tropical South America, and is well established in the southern Gulf of Mexico coastal region (Powell et al. 1998;Rödder et al. 2008). In the United States, it has been recorded for more than two decades, only in peninsular Florida and the Keys (Short and Petren 2011).
Hemidactylus mabouia is a nocturnal buildingdwelling gecko, usually found in anthropic environments (Howard et al. 2001) (Meshaka 2000;Rödder et al. 2008). Here, we present the first record of the tropical house gecko in Texas and briefly discuss the potential impact of this invasion on H. turcicus, another invasive gecko.

Methods
Several geckos were found on walls of various buildings in an urban area of Brownsville, Texas (Figure 1), within a 100 m radius of exact location specified in Table 1. Specimens were spotlighted and captured by hand during early evening hours; four were documented and preserved (Table 1). We surveyed about 10 evenings in October 2013 when weather was relatively fair and warm. Captured specimens were identified using the key to geckos from Krysko and Daniels (2005). Specific characters observed include vertical pupil,   First record of Hemidactylus mabouia in Texas 311 digits with widened subdigital lamellae, subdigital lamellae of digit IV do not extend to base of digit (Figure 2A), and darker chevron markings ( Figure  2B). Total length, snout-to-vent (SVL) length and gender were recorded. The specimens were euthanized by deep hypothermia, fixed with 95% ethyl alcohol and stored in 70% ethyl alcohol for at least 7 days prior to shipping to the Texas Natural History Collections at the University of Texas at Austin, where they were deposited and given a catalogue number (Table 1).

Results and discussion
We H. mabouia, and many gecko species, have a series of traits that represent advantages for long-distance and overseas dispersal, including eggs which are resistant to desiccation, relatively long incubation periods (1-2 months), and effective digital adhesive structures (Gamble et al. 2010;Anjos and Rocha 2008). We found evidence that individuals are surviving and reproducing (juveniles, egg clutches) near the possible site of introduction. Therefore, according to the unified framework for biological invasions (Blackburn et al. 2011), H. mabouia has already overcome the first three barriers in the process of invasion in Texas (geography, survival and reproduction), and is on the verge of entering the stage of spread. According to a climate envelope model, Brownsville Texas is at the northern margin of the potential distribution for this species (Rödder et al. 2008).
In Texas, two other Hemidactylus geckos have been reported. The Mediterranean gecko (H. turcicus) was first detected in downtown Brownsville, Texas as early as 1950, and dispersed quickly through south and south-central Texas (Davis 1974). More recently, H. turcicus has also been found to be abundant in northeastern Texas (Jadin and Coleman 2007). The common house gecko (H. frenatus), has been reported around Dallas Zoo since the early 1990's (McAllister et al. 1990) and recently in Corpus Christi (LaDuc, personal communication). Cyrtopodion scabrum Heyden, 1827, another building-dwelling exotic gecko, is well established in the Galveston Texas area (Bloom at al. 1986).
When H. mabouia colonizes a region already invaded by another Hemidactylus gecko, it tends to displace it, apparently due to competitive exclusion (Meshaka 2000). In peninsular Florida and the Keys, the once abundant H. turcicus, followed by H. garnotii, are being replaced by H. mabouia (Townsend and Krysko 2003). In central and western Cuba, H. mabouia is apparently displacing H. angulatus, another closely related invasive gecko (Iturriaga and Marrero 2013). It is then likely that in the Rio Grande Valley of Texas and the southern Texas Gulf Coast, the ubiquitous H. turcicus will be displaced by the newcomer H. mabouia. There is evidence that H. mabouia can also colonize natural environments far from buildings and other human made structures (Rocha et al. 2011). However, this exotic by exotic replacement may well be the only significant impact of this invasion. No native buildingdwelling geckos are known from the lower Rio Grande Valley of Texas.