Terrestrial larval development and nitrogen excretion in the afro-tropical pig-nosed frog, Hemisus marmoratus

Autor: T. Ulmar Grafe, Stefan K. Kaminsky, K. Eduard Linsenmair
Rok vydání: 2005
Předmět:
Zdroj: Journal of Tropical Ecology. 21:219-222
ISSN: 1469-7831
0266-4674
DOI: 10.1017/s0266467404002172
Popis: In general, amphibian larvae dispose of nitrogenous wastes as ammonia and change to urea excretion during metamorphosis (Balinsky 1970). Ammonia excretion, however, poses a problem for tadpoles and embryos that live in a limited volume of fluid because it is toxic in higher concentrations. One solution is urea excretion or ureotelism. In amphibians it occurs in species with terrestrial modes of reproduction when larvae develop within the uterus as in the ovoviviparous Salamandra salamandra (Schindelmeiser & Greven 1981), when embryos develop in foam nests as in Leptodactylus bufonius (Shoemaker & McClanahan 1973), or when offspring develop in brood pouches as in Gastrotheca riobambae (Alcocer et al. 1992). Terrestrial reproduction occurs in the afro-tropical pignosed frog Hemisus marmoratus (Hemisotidae), a fossorial frog that inhabits seasonally dry savanna habitats (Kaminsky et al. 1999, Rbdel et al. 1995, Van Dijk 1997). Females construct underground nests, typically at the beginning of the rainy season before temporary ponds fill, in which they oviposit and attend eggs and tadpoles. Tadpoles remain confined in the nest until they are released by the female during the following rains (Kaminsky et al. 1999). Females guide tadpoles to open water by constructing slides if nests remain above the water level (Kaminsky et al. 1999). Extended periods of development within terrestrial nests, in which moisture can be provided only by attending females, suggest that pig-nosed frog tadpoles are ureotelic. In this study we examine the mode of nitrogen excretion in pig-nosed frog tadpoles. We hypothesized that urea excretion should be the dominant form of nitrogen output. We also monitored larval growth and development in the nest to assess whether larval development is arrested during prolonged tadpole tenure in the nest, as reported for Leptodactylus fuscus (Downie 1994), and whether females influence arrest. Research was carried out in the southern Guinea savanna region of the Comoe National Park in the Ivory Coast (8045'N, 3?49'W) in 1997 and 1998. Amplectant airs of frogs were collected at a large temporary pond used for breeding (Grafe et al. 2004, Kaminsky et al. 2004). Larval development and nitrogen excretion were examined in tadpoles collected from nests constructed by females in large open plastic tubs (50 x 39 x 27 cm) that were filled with damp soil collected from the same temporary pond from which amplectant pairs were collected (Kaminsky et al. 1999, 2004). Tubs were kept in the shade of the gallery forest under ambient conditions (22-3 8 ?C), the soil moistened periodically, and nests left undisturbed for 1 wk until tadpoles had hatched. The nest ceiling was then carefully removed and replaced by a Petri ish to facilitate taking samples repeatedly and the nest covered with several cm of soil to re-seal it. Larval growth and development was investigated in eight nests. Each week, up to 9 wk after hatching, we removed 8-10 tadpoles from each nest with forceps or plastic pipettes. Fresh mass of each tadpole was determined to the nearest 2 mg using a portable balance (CT-10, Ohaus). Tadpoles were examined under a dissecting microscope and the developmental stage was classified according to Gosner (19 60). We also determined the development of the oral discs. Body length of tadpoles was measured with the help of an ocular micrometer. Nest construction took place on different dates within the study season. Since our study season lasted 9 wk we were not able to monitor all nests over the same number of weeks. To determine dry body mass and lipid reserves, tadpoles 'Corresponding author. Email: grafe@biozentrum.uni-wuerzburg.de
Databáze: OpenAIRE
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