Smilisca baudinii (Duméril and Bibron, 1841)
John H. Malone1
1. Historical versus Current Distribution. In the United States, Mexican treefrogs (Smilisca baudinii) are mainly found in Cameron and Hidalgo counties in the extreme southern tip of Texas (Dixon, 1987, 2000; Conant and Collins, 1998). A specimen exists from Bexar County (Murphy and Drewes, 1976), and Mexican treefrogs have been reported from Refugio County (Strecker, 1908b). Both these extraneous locales are widely separated from extreme southern Texas. These disparate records may be the result of accidental introductions due to human transport of potted plants from southern Texas (Dixon, 2000). However, Wright and Wright (1949) report that Mexican treefrogs have “been found by Mr. Marnock in the low country southwest of San Antonio, commencing with San Miguel Creek, a tributary of the Medina.” This report is confirmed by a specimen record (Murphy and Drewes, 1976). These reports differ from Raun and Gelbauch (1972) who state that both the Bexar (but see Murphy and Drewes, 1976) and Refugio records are erroneous. Garrett and Barker (1987) believe that the Bexar County population may no longer exist ,and no additional data exist for the Refugio County record. Texas represents the northern extreme of the Mexican treefrog distribution that extends south to Costa Rica. Mexican treefrogs inhabit lowlands and foothills below 2,000 m, but most localities are below 1,000 m (Duellman and Trueb, 1966; Duellman, 1968, 2001).
2. Historical versus Current Abundance. Mexican treefrogs are listed as Threatened in Texas but have no federal status. In Texas, Mexican treefrogs are thought to consist of small, patchy populations (G. Stolz, Santa Ana Wildlife Refuge, personal communication), but to date no formal census has been conducted to assess population status or viability. In the early 1990s, Kelly Irwin (Arkansas Game and Fish Commission, personal communication) performed an amphibian and reptile inventory of the Lower Rio Grande Valley and noted the presence of Mexican treefrogs at sites near Santa Ana National Wildlife Refuge and the Sabal Palm Grove Sanctuary. Following a 75 mm rain on 17 June 1991, Kelly Irwin (personal communication) found approximately ten males calling from a flooded ditch on the Santa Ana National Wildlife Refuge. Gadow (1908) estimated 45,000 Mexican treefrogs at a breeding site near Cordoba, Veracruz, Mexico. Lee (2000) calls Mexican treefrogs “the most abundant and ubiquitous amphibian in the Yucatán Peninsula.” Stuart (1934) found a Mexican treefrog chorus so large that the weight of individuals bent the branches. Duellman (2001) reports observing several hundred to thousands of individuals at breeding sites in Mexico, Guatemala, and Costa Rica. Campbell (1998) calls Mexican treefrogs the most common treefrog species in the Petén region of Guatemala. Based on these reports, it appears that Mexican treefrogs are more abundant in parts of Central America than they are in Texas.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Mexican treefrogs breed any time of the year following adequate rainfall (Webb, 1971; Duellman, 2001). In 1992, Kelly Irwin (personal communication) noted Mexican treefrogs calling at Santa Ana National Wildlife Refuge from June–August. Mexican treefrogs typically call in duets, and the initial calls of a duet cause other duets to respond (Duellman, 1967). Males will call during the day (Webb, 1971). Amplexus is axillary.
ii. Breeding habitat. Males will vocalize from nearly any body of water, but usual breeding sites are small, temporary pools (Duellman, 2001).
B. Eggs. Eggs have a diameter of 1.3 mm and a vitelline membrane of 1.5 mm (Duellman and Trueb, 1966).
i. Egg deposition sites. Eggs are initially deposited as clusters and then disperse into a surface film. Webb (1971; see also his fig. 1) describes breeding sites as shallow pools that may or may not have vegetation along the shoreline. In Yucatán, Mexico, Maslin (1963a,b) observed tadpoles in small (60 cm in diameter, 25 cm deep) limestone basins, where eggs must have been deposited.
ii. Clutch size. Estimates ranged from 480–560 (Webb, 1971). Duellman and Trueb (1966) removed and counted ovulated eggs from three female Mexican treefrogs. They reported 2,620; 2,940; and 3,320 eggs/female; these clutch sizes are considerably larger than those reported by Webb (1971). Webb (1971) did not observe the total number of eggs deposited by each female and thus his clutch size observations may be conservative.
C. Larvae/Metamorphosis. Series of tadpoles were described by Duellman and Trueb (1966). Mexican treefrogs have a generalized hylid type tadpole. They are exotrophic with an anteroventral oral apparatus and a dextral anus. The color is a uniform brown with a pale dorsolateral stripe on the body and light banding on the dorsal tail musculature (Altig and McDiarmid, 1999).
i. Length of larval stage. Larval stage duration is apparently unknown, but probably is rapid. On 4 July 1959, Maslin (1963a,b) collected a series of 12 specimens in Gosner (1960) stages 29–36 ranging in size from 19–32 mm TL. Duellman and Trueb (1966) showed that Mexican treefrog tadpoles increase from 5–35 mm TL (from Gosner stages 21–38, respectively). As metamorphosis began and tails resorbed, total length decreased to 13 mm at Gosner stage 46.
ii. Larval requirements.
a. Food. Larvae use suspension feeding to ingest small organic and inorganic particles.
b. Cover. Larval habitat characteristics are unknown. Maslin (1963a,b) observed clouds of tadpoles in the small limestone basins he studied.
iii. Larval polymorphisms. Polymorphisms have not been reported, although Maslin (1963a,b) noted morphological differences between the tadpoles he studied and those studied by Stuart (1948). Duellman and Trueb (1966) noted that degree of pigmentation is variable and likely correlated with light levels. Additionally, length and depth of the tail are variable (Duellman and Trueb, 1966).
iv. Features of metamorphosis. Tadpoles metamorphose when total length (newly metamorphosed animals) is 13 mm (Duellman, 2001).
v. Post-metamorphic migrations. Migrations are probably from shallow, drying breeding wetlands to upland cover sites; however, data do not exist for juvenile dispersal.
D. Juvenile Habitat. Unknown.
E. Adult Habitat. Mexican treefrogs are nocturnal and most active following rains. In the arid and semiarid places where they are found, Mexican treefrogs inhabit forested and brushy areas around streams, resacas, and roadside ditches. Mexican treefrogs have been observed living in the tops of palm trees. Individuals seek shelter from heat and dry conditions under loose tree bark, in tree holes, in damp soil, and in the leaves of banana plants, bromeliads, and heliconias (Meyer and Wilson, 1971; Duellman, 2001).
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Mexican treefrogs and lowland burrowing treefrogs (Pternohyla fodiens) are the only frogs found in the United States known to form cocoons (Ruibal and Hillman, 1981; McDiarmid and Foster, 1987).
I. Seasonal Migrations. Following rains, Mexican treefrogs move to and from wetlands to breed. These migrations can occur at any time of the year.
J. Torpor (Hibernation). Does not occur.
K. Interspecific Associations/Exclusions. Unknown.
L. Age/Size at Reproductive Maturity. Body size dimorphism exists between males (51–76 mm SVL) and females (≤ 90 mm; Duellman, 1968; Conant and Collins, 1998).
M. Longevity. Unknown.
N. Feeding Behavior. Mexican treefrogs feed on invertebrates, especially insects and spiders (Lee, 2000).
O. Predators. In Mexico, Duellman and Trueb (1966) observed the xenodontin snake Leptodeira maculata engulfing a male Mexican treefrog. Frog-eating snakes are likely to be important predators on both adults and juveniles. Webb (1971) suggested that predaceous aquatic insects feed on tadpoles, but he did not observe this.
P. Anti-Predator Mechanisms. Both males and females emit a distress vocalization that may serve to attract secondary predators (Duellman, 2001).
Q. Diseases. Unknown.
R. Parasites. The trematodes Mesocoellum monas and Metacercariae gen. sp. were found in the intestines of Mexican treefrogs from Los Tuxtlas, Veracruz, Mexico (Guillén-Hernández et al., 2000; Pérez-Ponce de Leon et al., 2000). Goldberg and Bursey (2002) examined 19 specimens (5 females and 14 males) of Mexican treefrogs from southern Sonora, Mexico, for helminth parasites. Small and large intestines of Mexican treefrogs were infected with the nematodes Aplectara incenta and A. itzocanensis (Goldberg and Bursey, 2002). The nematode Rhabdias americanus was found in the lungs, and cysts of Physaloptera sp. were found in the stomach (Goldberg and Bursey, 2002). The presence of Physaloptera sp. suggests that Mexican treefrogs may serve as a paratenic host for Pysaloptera sp. (Goldberg and Bursey, 2002). Four individuals of Mexican treefrogs from the Guanacaste Conservation Area, Costa Rica were examined for blood parasites but none were found (Dresser, 2001).
4. Conservation. Mexican treefrogs are a widely distributed species in Central America and are considered a common species. In the United States, Mexican treefrogs are at the most northern limit of their distribution; specifically, they occur in three counties in southern Texas, but populations in Texas are considered to be small and patchy. Mexican treefrogs are listed as Threatened by the State of Texas (Levell, 1997) but no federal protection exists or has been proposed. Due to the paucity of data for U.S. populations of Mexican treefrogs, efforts should be made to identify remaining populations and remaining habitats.
Acknowledgments. Thanks to David Bradford and Janalee Caldwell, who commented on this manuscript.
1John H. Malone
Department of Zoology
University of Oklahoma
730 Van Vleet Oval
Norman, Oklahoma 73019
Department of Biology
University of Texas-Arlington
Arlington, Texas 76019-0498
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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