Reproductive Modes of Frogs - Recent Discoveries

A male Oreophryne guarding 
eggs glued to a leaf, a rarely 
observed behavior amongst 
microhylids. Photo credit: 
S. J. Richards.
Reproductive modes in amphibians encompasses a combination of morphological, physiological and behavioral traits that include where the anaimal lays its eggs,  egg size and number, development time, stage and size of hatchling, and the type of parental care, if it occurs at all. Most of us in North America are familar with frogs depositing their eggs in water, the tadpoles develop into froglets, and then into adults, but go to the tropics or other regions of the world and frog reproductive modes become remarably diverese. The number of papers reporting advances in knowledge on reproductive modes in frogs is ever increasing, and some species have evolved remarkably complex and diverse mechanisms for protecting their offspring. Here are just a few that have been reported in the last year.

Within the genus Hypsiboas (family Hylidae) two reproductive modes are known: some species deposit their eggs in stagnant water and others deposite eggs in natural or constructed basins, with subsequent flooding that releases tadpoles into ponds or streams. Apparently, individuals within a species can be somewhat flexible in their reproductive modes. Ribeiro de Moura and colleagues (2011) described Hypsiboas pardalis depositing its eggs in a terrestrial bromeliad. Bromeliads are relatively safe habitat for tadpoles and spawns compared to puddles and streams, where competitors and predators are more abundant. Similarly, Touchona and colleagues (2011) recently reported that the neotropical treefrog Dendropsophus ebraccatus (Hylidae) lays eggs both above water on leaves and directly in water, this exposes embryos to different abiotic conditions and predator communities and undoubtedly increases the chances of survival for some of the eggs.

 Rodriguesa and colleagues (2011)  report observations on the reproduction of three shoaling/maternal-caring leptodactylids  (Leptodactylus latrans, Leptodactylus podicipinus and Leptodactylus  leptodactyloides), that suggest female presence to tadpoles is important. Females of the three species connected water bodies by digging channels to their tadpoles so that the larvae would not be stranded in drying pools and could find additional food. Females of one species,  Leptodactylus latrans, drove off predatory snakes, as well as conspecific males that approached tadpoles to prey upon tadpoles. In water bodies containing predatory fish, tadpoles of L. latrans only reached metamorphosis despite the presence of guardian females.

Direct development in frogs is where the embryos bypass the aquatic tadpole stage and hatch from the egg as froglets - miniatures of the adults. It is perhaps the most extreme evolutionary modifications of amphibian life histories. The direct development strategy has evolved independently at least 10 times in frogs and resulted in many hundreds of direct-developing species that are mostly tropical. The family Microhylidae (sometimes called narrow-mouth frogs) has a global distribution in the tropics and subtropics with members of the family exhibiting  a diversity of reproductive strategies, however direct development has been documented in only one microhylid subfamily, the Australasian Asterophryinae. This subfamily reaches its greatest diversity in New Guinea, where it is represented by 23 genera. Anstis and colleagues (2011) examined embryonic development in some members of three genera Cophixalus,  Austrochaperina, and Oreophryne and found direct development during which the embryo develops to a minute froglet within the jelly capsule. They compared the development of these Australasian frogs with the neotrpical Eleutherodactylus and foun the New Guinea frogs have a different scenario for development - so not all direct developing frogs are the same.

Gramapurohit and colleagues (2011) studied another direct developing frog in India's Western Ghats, Nyctibatrachus humayuni (family Nyctibatrachidae). Nyctibatrachus frogs exhibit a unique reproductive behavior  completely lacking or having an abbreviated amplexus. They deposit terrestrial eggs and have male paternal care. The authors studied the courtship and spawning behaviour of Nyctibatrachus humayuni from Matheran in the northern region of the Western Ghats. The breeding season coincides with the onset of south-west monsoon; and adult males vocalize from wet rocks or dead logs that often contain egg clutches. Females approach the calling males, resulting in a loose cephalic amplexus that lasts less than 10 minutes. The male dismounts, sits on the side, while the female deposits the eggs and moves away from the spawning site. Once the female moves off the spawn, the male slowly moves on to the eggs and fertilizes them. The males appear to be territorial and attend the eggs only at night, and presumably reduces the risk of predation by nocturnal predators.

Anstis, M., F. Parker, T. Hawkes, I. Morris, and S. J. Richards. 2011.  Direct development in some Australopapuan microhylid frogs of the genera Aus­trochaperina, Cophixalus and Oreophryne (Anura: Microhylidae) from northern Australia and Papua New Guinea. Zootaxa 3052: 1–50.

Gramapurohit, N. P., M. S. Gosavi, and S. K. Phuge. 2011. Unique courtship and spawning behaviour in the wrinkled frog, Nyctibatrachus humayuni.  Amphibia-Reptilia, 32: 333-339

Ribeiro de Moura, M., A. P. Motta, and R. Neves Feio. 2011. An unusual reproductive mode in Hypsiboas (Anura: Hylidae).Zoologia (Curitiba, Impr.) 28(1)

 Rodriguesa, A. P., A A. Giarettab, D. R. da Silvab and K. G. Facureb. 2011.Reproductive features of three maternal-caring species of Leptodactylus (Anura: Leptodactylidae) with a report on alloparental care in frogs.Journal of Natural History 45 (33-34):2037-2047.

Touchona, J.C., J. Urbinac and K. M. Warkentina, 2011. Habitat-specific constraints on induced hatching in a treefrog with reproductive mode plasticity. Behavioral Ecology (2011) 22 (1): 169-175.


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