Species Description: The green iguana, Iguana iguana is a popular pet trade species not native to Florida, but increasingly encountered as an escaped exotic in the southern half of the state.
I. iguana is variable in color, young animals being bright green and then becoming more uniform grayish green in color with age. Green iguanas also have a limited ability to alter color based on mood or social interaction or in response to environmental conditions, with males exhibiting more color variation than females (Frye 1995).
A prominent hanging dewlap under the throat, a dorsal crest of robust dermal spines running from neck to tail, a set of large scales on each side of the head, a membrane-covered tympanum, and a long, tapering, variably ringed tail are distinguishing features of the species (Oldham and Smith 1975, De Vosjoli 1992; Frye 1995, Gingell and Harding 2005). The eyes are laterally positioned and are protected by an immovable upperlid and a movable lower eyelid. A light-sensing organ—the parietal "eye"—is present on top of the head and is important in cueing diel coordination and gonadal maturation. The parietal eye exhibits rudimentary visual sensory abilities, namely the ability to perceive shadows from above the animal (Frye 1995).
Potentially Misidentified Species: Although a growing assortment of exotic iguanids, polychrotids (anoles), geckonids (geckos), and other non-native lizards are now encountered in Florida, relatively few of these could be easily misidentified as I. iguana. Black spinytail iguanas (Ctenosaura similis) and Mexican spinytail iguanas (C. pectinata) are potential exceptions, but looking for the diagnostic features described above should allow Iguana iguana to be differentiated from these animals.
Regional Occurrence: The green iguana is native to Latin America, including parts of Mexico, mainland and island regions of Central and South America, and the Lesser Antilles. It has been introduced into Florida, Hawaii and Puerto Rico where it is considered a serious pest (McKeown 1996, Engeman Smith and Constantin 2005, ISSG).
IRL Distribution: Iguana iguana has been reported from south Florida (Dade County) since 1966, and has probably been established and breeding there since 1980 (King and Krakauer 1966, Butterfield et al. 1997). More recently (2003), a presumed new breeding population has been identified from Palm Beach County, while an increasing number of animals (not reported breeding) are being encountered in Martin and St. Lucie counties (Krysko et al. 2005).
The apparent northward expansion of I. iguana into the central IRL watershed is of potential concern. Animal Control offices in both Martin and St. Lucie Counties have reported an increase in the number of green iguana sightings throughout the Treasure Coast area (Indian River Press Journal 2007).
Age, Size, Lifespan: Hatchlings are typically 17-25 cm in length. Growth is relatively rapid, and a 12 g hatchling can grow to a 1 kg adult in 3 years. Mature animals can attain total lengths of 2 m and can weigh as much as 8 kg, although 4-6 kg is more typical (De Vosjoli 1992, Gingell and Harding 2005).
Captive-reared green iguanas can live for more than 20 years, while wild individuals are believed to have a lifespan of around 8 years (De Vosjoli 1992, Frye 1995).
Abundance: Data collated by the Florida Fish and Wildlife Conservation Commission suggests breeding populations of I. iguana are established in at least 5 Florida counties. The statewide trend appears to be expansion of the overall population and invasive range.
Reproduction: Reproduction is sexual, sexes are separate and fertilization is internal. Individuals generally become reproductive at 3-4 years of age, although some animals mature up to a year earlier or later. Females remain reproductive for several years (Frye 1995). Peak breeding occurs in the dry season, ensuring that most young hatch in the wet season when food resources are most abundant.
A polygynandrous mating system (both males and females pair with multiple mates) seems to be typical of the species, and a variety of male-male antagonistic displays (e.g., head bobbing, dewlap exhibiting) and male-female courtship displays (e.g., nuzzling, biting) are usually involved. Dominant males mark territories and mates with a pheromone-containing substance secreted from femoral pores (De Vosjoli 1992, Frye 1995, Meshaka et al. 2004).
Females can store sperm for several years after mating, using it to fertilize eggs at a later date (De Vosjoli 1992, Frye 1995).
Embryology: Clutch sizes are relatively large, averaging 20-70 eggs. Females deposit eggs approximately 65 days after mating, usually over the course of three days, into nests excavated to a depth of 0.45-1 m. If suitable nesting sites are limited, several females can share nests (De Vosjoli 1992, Frye 1995).
Incubation takes 90 to 120 days at a nest temperature of 30-32°C. Hatchlings break through egg shells with the aid of a caruncle (egg tooth) that is shed shortly after hatching. Young are precocial and independent from the time of hatching, but they derive most of their nourishment in the first few weeks of life from yolk that has already been absorbed (Gingell and Harding 2005).
Temperature: Green iguanas are exothermic and rely on environmental temperatures and behavioral thermoregulation (e.g., basking) to maintain optimal temperature. Active foraging typically occurs at daytime temperatures of 25-35°C; low temperature suppresses both apatite and digestion (Frye 1995).
Northern range expansion of Iguana iguana in Florida appears to be limited by winter low temperatures, althouh population numbers in the wake of a south Florida freeze in 2002-2003 were reduced only temporarily (Meshaka et al. 2004).
Trophic Mode: Iguana iguana is primarily herbivorous, consuming leafy plants and ripe fruits as preferred dietary items. A small percentage of invertebrate matter and carrion is also typically consumed (Gingell and Harding 2005).
Associated Species: Green iguanas are known carriers of several Salmonella spp. bacterial strains considered to be pathogenic. Salmonella colonize the intestines and is shed in feces. Tortora at al. (1998) note that the carriage rate in pet reptiles may be as high as 90%.
Invasion History: The pet trade has provided a steady source of introduction of Iguana iguana to Florida. Iguanas escaped from captivity were reported from south Florida as early as 1966, at Key Biscayne, Hialeah, Coral Gables, and near the Miami International Airport (King and Krakauer 1966). Populations have since become established at least as far north as Palm Beach County on the Atlantic coast and Lee County on the Gulf coast of the state, and an increasing number of animals (not yet reported breeding) are now reported from Martin and St. Lucie counties (Bartlett 1980, Bartlett and Bartlett 1999, Townsend et al. 2002, Krysko et al. 2005). The animals are frequently encountered in Everglades National Park, and have been reported in the Keys at least as far south as Stock Island (Meshaka et al. 2000).
In addition to Florida, I. iguana has been introduced to Hawaii where it is also a nuisance species (McKeown 1996).
Potential to Compete With Natives: I. iguana is the largest known lizard to occur in the U.S. (Conant and Collins 1998, Campbell 1998). McKie et al. (2005) reported concern over the potential for iguanas to disrupt native bird nests or destroy nestlings and eggs.
Possible Economic Consequences of Invasion: The potential economic consequences associated with expanding Florida green iguana populations are believed to be minor, mostly related to the destruction of tropical garden and landscape foliage caused by iguana foraging (Gingell and Harding 2005). Health-related issues arising from iguanas being carriers of Salmonella are anticipated to be very minimal.
In other parts of the world, green iguanas are an important source of food and leather, but they are unlikely to be utilized in this manner in Florida.
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