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This species measures 23-29 mm in SVL for adult males and 24-32 mm for adult females (Lampert 2001). Hyperolius have horizontally elliptical pupils and narrow heads with a blunt snout (Adler and Halliday 2002). The body shape is slender and half-cylindrical with long thin limbs (Kobelt and Linsenmair 1995). Skin folds are present, allowing frogs to hide their feet underneath while aestivating (Geise and Linsenmair 1986). Fingers and toes have circummarginal discs. Males have a median subgular vocal sac (Lampert 2001).
Adults exhibit metachrosis (change in color) with coloration varying throughout the day, in response to factors such as temperature, humidity, light intensity, and stress (Adler and Halliday 2002). At night, H. nitidulus are uniformly beige (Lampert 2001). During the day, the skin color varies between beige and bright colors like yellow and orange, with dark markings present on the flanks (Lampert 2001).
Juveniles are beige in ground color and display a dark lateral stripe along the body from snout to vent (Lampert 2001). During the dry season, juveniles become white when they aestivate and the skin on the inside of their limbs becomes red due to the underlying capillary network (Geise and Linsenmair 1986).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Benin, Cameroon, Cote d'Ivoire, Ghana, Guinea, Mali, Nigeria, Sierra Leone
Hyperolius nitidulus is found in the savannas of western Africa south of the Sahara (Lampert 2001), as well as in shrublands, grasslands, and wetlands (IUCN 2008). It occurs between 250-900 m in elevation (Lampert 2001).
Life History, Abundance, Activity, and Special Behaviors
Hyperolius nitidulus is primarily a nocturnal, arboreal species, commonly found on reeds in the African savanna (Adler and Halliday 2002). Adults are insectivores, consuming flies in the genera Drosophila, Musca, Phormia, Lucilia, and Calliphora (Geise and Linesenmair 1986).
Breeding occurs during the wet season, May to October (Lampert 2001), and is prolonged (Beltz 2005). Males migrate to temporary ponds during the breeding season, and may wander between ponds or remain stationary at one pond (Lampert 2001). Approximately two months after the first rains of the season, males begin calling at savanna ponds between dusk and midnight. They have two distinct calls, a advertisement (mating) call and a territorial call. The mating call is characterized by a short metallic click that lasts between 0.10-0.24 s and has a frequency of 2.04-3.43 kHz, depending on the size of the frog (Lampert 2001). The territorial call is a "croak" call, longer and deeper than a mating call, which lasts from 0.28-0.36 s and has a frequency of 0.98-2.6 kHz (Lampert 2001). Males tend to aggregate and defend small calling territories. Lampert (2001) characterized this as a lek, with mating occurring aquatically, since females have not been found to be selective when choosing a mate. Amplexus is axillary (Adler and Halliday 2002).
Hyperolius nitidulus is oviparous. The female deposits her eggs in the water and attaches them to underwater vegetation or to the bottom of the pond. Females lay from 94-800 eggs (Lampert 2001). The eggs are distinguished by a white color with a dark brown animal pole (Lampert 2001). This species exhibits no parental care (Lampert 2001). Within two to five days after the female lays her eggs the embryos hatch as free-swimming tadpoles (Adler and Halliday 2002). Development may take longer depending on water temperature (Lampert 2001). The free-living larvae live in dense vegetation on the edges of the pond where they feed off algae (Lampert 2001). Tadpole predators include dragonfly larvae, beetle larvae, turtles, and fish (Lama 1997). After six to eight weeks, tadpoles metamorphose into adult frogs, at which point they weigh 0.2 g and are 12-15 mm (Lampert 2001). Maturation typically takes place within two months (Lampert 2001).
Hyperolius nitidulus is known for its unique aestivation behavior (Schmuck et al. 1994). Unlike other amphibians, juvenile H. nitidulus do not seek shelter or hide during the dry season. Instead, they fully expose themselves to the sun by sitting on dry plants, with their legs held tightly to the body and feet hidden under skinfolds (Lampert 2001; Geise and Linsenmair 1986). Geise and Linsenmair (1986) have reported that juvenile frogs can withstand water loss up to 50% of their body weight. The young frogs cope with dehydration by sitting in a position that reduces rapid water loss, and can remain in this position for months without food or water (Geise and Linsenmair 1986). Extending their arms and legs exposes the inner vascular skin portions, which are responsible for quick water uptake (Lampert 2001). Uptake of water can occur very rapidly, approximately 69.3+/-19.4% of the body weight per hour (Geise and Linsenmair 1986).
Juveniles adhere to the plants by dried skin gland secretions (Geise and Linsenmair 1986). Having the skin secretions dry is important; when exposed to water, the mucus loses its adhesiveness and the frog accordingly loses its ability to prevent water loss and to aestivate (Geise and Linsenmair 1986). When aestivating, the juvenile frogs do not urinate or defecate (Kobelt and Linsenmair 1995). The nitrogenous wastes are stored as urea in body fluids and purines (Geise and Linsenmair 1986). During aestivation at temperatures above 39 degrees C, the frog's skin turns white, due to the presence of iridophores filled with purine crystals that reflect the sun's rays (Lampert 2001; Geise and Linsenmair 1986).
Juveniles born in the first 2/3 of the wet season are able to mature and reproduce the same season in which they were born (Lampert and Linsenmair 2001). These individuals invest in growth and reproduction instead of storing energy to carry them through aestivation (Kobelt and Linsenmair 1995). Therefore, they will not survive the dry season (Geise and Linsenmair 1986). Those born in the last third of the wet season do not reproduce, but allocate resources to energy storage in order to survive the dry season and reproduce the following year (Lampert and Linsenmair 2001). Adult H. nitidulus have little energy reserve after reproduction and are not able to reduce activity and metabolism as quickly or as effectively as juveniles; thus, adults generally do not survive the dry season (Geise and Linsenmair 1988; Lampert and Linsenmair 2001).
Trends and Threats
Hyperolius nitidulus is stable, abundant, and does not appear to be facing any major threats (IUCN 2008). Factors contributing to this stability include the wide distribution, tolerance of a large range of habitats, and large population size (IUCN 2008). The species is found in many protected areas, such as Comoe National Park (in north eastern Cote d'Ivoire) and Niokola-Koba National Park in Senegal (Joger and Lambert 2002).
Adler, K., and Halliday, T. (2002). Firefly Encyclopedia of Reptiles and Amphibians. Firefly Books Limited, Buffalo, New York.
Beltz, E. (2005). Frogs: Inside Their Remarkable World. Firefly Books, Buffalo, NY.
Geise, W. and Linsenmair, K. E. (1986). ''Adaptations of the Reed Frog Hyperolius viridiflavus (Amphibia: Anura: Hyperoliidae) to its arid environment, II. Some aspects of the water economy of Hyperolius viridiflavus nitidulus under wet and dry season conditions.'' Oecologia, 68, 542-548.
IUCN (2008). 2008 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 23 November 2008.
Joger, U. and Lambert, M.R.K. (2002). ''Inventory of amphibians and reptiles in SE Senegal, including the Niokola-Koba National Park, with observations on factors influencing diversity.'' Tropical Zoology, 15, 165-185.
Kobelt, F. and Linsenmair, K.E. (1995). ''Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment, VII. The heat budget of Hyperolius-viridiflavus-nitidulus and the evolution of an optimized body shape.'' Journal of Comparitive Physiology B- Biochemical Systemic and Environmental Physiology, 165(2), 110-124.
Lama, W. (1997). The World's Most Spectacular Reptiles and Amphibians. World Publications, Tampa, Florida.
Lampert, K. (2001). Alternative life history strategies in the West African reed frog, Hyperolius nitidulus. Unpublished dissertation, Universität Würzburg, Fakultät für Biologie, Germany.
Lampert, K. and Linsenmair, K.E. (2001). ''Alternative life cycle strategies in the West African reed frog Hyperolius nitidulus: the answer to an unpredictable environment?'' Oecologia, 130, 364-372.
Schmuck, R., Geise, W., and Linsenmair, K.E. (1994). ''Life cycle strategies and physiological adjustments of reedfrog tadpoles (Amphibia, Anura, Hyperoliidae) in relation to environmental conditions.'' Copeia, 1994(4), 996-1007.
Written by Christine Bubac (christib AT rap.midco.net), Black Hills State University
First submitted 2008-12-27
Edited by Kellie Whittaker (2009-02-09)
Species Account Citation: AmphibiaWeb 2009 Hyperolius nitidulus <http://amphibiaweb.org/species/6142> University of California, Berkeley, CA, USA. Accessed Oct 20, 2017.
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Citation: AmphibiaWeb. 2017. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 20 Oct 2017.
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