Eleutherodactylus locustus Schmidt, 1920
Puerto Rican Small-eared Frog
© 2004 Luis J. Villanueva-Rivera (1 of 1)
Eleutherodactylus locustus, the Interior Robber Frog, is a small frog that typically has an average snout-vent length of 19 mm for both male and female. Its head is slightly narrower than its body, and is longer than it is broad. Its snout is rounded and slightly obtuse. Additionally, E. locustus has vomerine teeth and a large tongue (Schmidt 1920). The pupil of the eye is horizontally elliptical, with a thin, dark, vertical interorbital band (Lopez and Thomas 2007). They also have a rounded canthus rostrails. The tympanum is only just distinct, and is one-fourth the diameter of the eye. Male E. locustus have a large vocal sac. This frog has a rugose dorsum with rounded tubercles, a mid-dorsal ridge from snout-vent, and a smooth ventrum. When the elbows and knees are pressed toward the side of the body, they overlap. The heels overlap when they are placed vertically to the axis of the body. There are no tarsal folds. Finger and toe tips are rounded with well-defined discs, and E. locustus lacks any trace of webbing between digits (Schmidt 1920).
Eleutherodactylus locustus is closely related to, but differentiated from E. auriculatus mainly by its small size and smooth abdomen. It is even more closely related to E. gryllus, however their calls, and the wrinkled dorsum of the E. locustus set them apart (Schmidt 1920).
In life, this frog has a mottled grayish-brown dorsum and a light, uniform venter (Schmidt 1920). The pupil of the eye is horizontally elliptical, with a thin, dark, vertical interorbital band (Lopez and Thomas 2007).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Puerto Rico
Eleutherodactylus locustus occurs in the interior uplands of Puerto Rico with a lower elevation limit of 273 m and an upper limit of 1,050 m asl (Hedges and Rios-López 2008). The species’ distribution includes the Eastern Montane Forest above 370 m. Specifically, E. locustus can be found in the Carite Forest Reserve and the Luquillo National Forest Reserve (Hedges and Rios-López 2008). It is also present in the El Yunque National Forest (Burrowes et al. 2004). Its microhabitat includes the forest edge and mossy forest meadows above 700m (Drewry and Rand 1983). They can be found in open areas, under leaf litter, tree trunks, and roots (García et al. 2005). Their geographic range is 560.8 km2 (Lotters et al. 2010).
Life History, Abundance, Activity, and Special Behaviors
Eleutherodactylus locustus is a nocturnal species that has a call that is typically at a constant rate (Villanueva-Rivera 2006). Males have a very distinct call that begins with a shrill continuous note, nearly inaudible, followed by a succession of clicks and closely resembles that of a long-horned grasshopper (Schmidt 1920). The average maximum sound pressure is -50.7 dB. They frequently use low vegetation, such as ferns as their calling site, 0 to 1.5m above the ground (Drewry and Rand 1983).
Within their habitat, they are considered to be terrestrial and semi-arboreal (Heatwole and Newby 1972). They do not require an aquatic environment, as the female lays her eggs on the ground and reproduces by direct development (Hedges and Rios-López 2008). While little is known about the reproduction of E. locustus, a closely related species, E. portoricensis, was found to use axillary amplexus, produce on average 16 - 20 eggs per clutch, have a mean development period of 27.9 days +/- 5.6 days, and have eggs 5.1 mm in diameter on average. Eleutherodactylus portoricensis also shows male parental care (Lopez et al. 1927).
Predation of E. locustus by owls has been reported. The owls sometimes use the call of the male frogs to hunt them (Villanueva-Rivera 2006).
Trends and Threats
Eleutherodactylus locustus was listed as “Critically Endangered” by the IUCN Red List in 2004 and was reevaluated in 2008, receiving the same designation. This listing is justified because E. locustus has experienced a projected and observed 80% population decline over a ten-year period (Hedges and Rios-López 2008). This decline has been present in some of the most protected areas of Puerto Rico, such as the El Yunque National Forest (Burrowes et al. 2004). Although this decline is currently unexplained, likely causes include deforestation and chytridiomycosis. Historically, there has been extensive deforestation on Puerto Rico for lumber harvest and conversion to agriculture. Currently, tourisms-fueled development as well as construction of radio-communication infrastructure continue to disturb this species native range. Because E. locustus is a high elevation species, it may be especially susceptible to climate change and chytridiomycosis (Hedges and Rios-López 2008). Climate change is not likely a direct cause of the decline in this species, although it has increased the impact of chytridiomycosis on other Eleutherodactylus frogs in Puerto Rico. Similarly, extended periods of drought are believed to have increased the occurrence of chytridiomycosis on Puerto Rico Eleutherodactylus frogs (Burrowes et al. 2004). Introduced rats and mongooses have also been implicated in the decline of this species, however there is no consensus on the effects of these introduced predators on Eleutherodactylus frogs (Reagan and Waide 1996, Hedges 1993).
The species is being monitoring in their natural habitat to protect the species from further decline. There was also a captive breeding program with the Central Florida Zoo was started to generate management strategies for wild populations (Burrowes and Joglar 2011).
Relation to Humans
There is a captive breeding program at Central Florida Zoo to help booster this species survival (Burrowes and Joglar 2011).
Possible reasons for amphibian decline
General habitat alteration and loss
Eleutherodactylus locustus was found to be most closely related to Eleutherodactylus gryllus (Schmidt 1920). However, E. gryllus is now thought to be extinct. Smith et al. (1981) compared allelic frequencies using gel electrophoresis analysis of the proteins Albumin, Glutamate oxalate transaminase, general protein-2, isocitrate dehydrogenase, malate dehydrogenase, phosphoglucose isomerase, and phosphoglucomutase. Eleutherodactylus locustus and E. eneidae were found to be most similar both morphologically and genetically (Smith et al. 1981).
The genus, "Eleutherodactylus" is from the greek "eleutheros" meaning “free” and the greek "daktulos" meaning “finger.” The species epithet, "locustus" is derived from the latin "locusta" meaning “crustacean” or “locust.”
Burrowes, P. A. and Joglar, R. L. (2011). ''Puerto Rico: An island rich in amphibians subject to many threats.'' FrogLog, (96), 16-17.
Burrowes, P. A., Joglar, R. L., and Green, D. E. (2004). ''Potential causes for amphibian declines in Puerto Rico.'' Herpetologica, 60, 141-154.
Drewry, G. E., Rand, A. S. (1983). ''Characteristics of an Acoustic Community: Puerto Rican Frogs of the Genus Eleutherodactylus.'' Copeia, 1983(4), 941-953.
García, M., Cruz-Burgos, J., Ventosa-Febles, E. & Ricardo, L.-O (2005). ''Puerto Rico Comprehensive Wildlife Conservation Strategy.'' DRNA, 121.
Schmidt, K. (1920). ''Contributions to the herpetology of Porto Rico.'' Annals of the New York Academy of Sciences, 28, 167-200.
Smith, M. H., Straney, D. O. & Drewry, G. E. (1981). ''Biochemical Similarities among Puerto Rican Eleutherodactylus.'' Copeia,
Originally submitted by: Daniel Ellison, Alyssa Higham, and Laurasia Holzman Smith (first posted 2017-10-05)
Edited by: Maxine Weber (2017-10-05)
Species Account Citation: AmphibiaWeb 2017 Eleutherodactylus locustus: Puerto Rican Small-eared Frog <https://amphibiaweb.org/species/3026> University of California, Berkeley, CA, USA. Accessed Mar 28, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 28 Mar 2023.
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