Quacking Frog - Reproduction and Development

Reproduction and Development

Crinia georgiana breeds mainly in the winter months, from July to October, usually near granite outcrops, in shallow murky pools. Breeding has also been known to occur in puddles and wheel ruts.

Amount of rainfall affects the timing of breeding, as this species usually breeds in temporary ponds that are only full after rain. Temperature can affect the rate of egg lying, which slows when ambient temperatures are very low. However, since water temperature is usually warmer than air temperature, it is unlikely that the water temperature will drop below 2 °C, the temperature necessary to significantly decrease breeding activity. Lunar phasing also affects mating, with higher rates occurring around the full moon. Although it is unclear why this is so, it can be inferred that the sexual activity of both males and females is synchronised by this variable.

Fertilisation occurs via amplexus, which lasts about 23 minutes. Amplexus is a form of copulation in which the male grasps the female with his front legs while she lays her eggs and he simultaneously releases fluid containing sperm.

Matings in this species are relatively unique in that quacking frogs are polyandrous; about half of all matings involve more than one male, and possibly up to nine, resulting in a brood of offspring with multiple paternities. Polyandrous mating is more likely among smaller males, as large males can monopolize and dominate the female during amplexus. This does not appear to be beneficial, as the efficiency of the sperm does not differ significantly in terms of sperm number, size, motility, and longevity between large and small males. Furthermore, when a single male mates with a female, there is a 90–95% chance that fertilization will be successful, while there is only a 64% chance of success when three to five males mate with one female. Often this drop is due to fights that arise when other males join in an existing act of copulation, reducing the likelihood of successful sperm transfer. Therefore, there is no benefit to polyandry in terms of offspring survival to offset the high cost of reduced fertilization success and occasional female mortality. It is thus unclear why polyandry is prevalent in this species, although it could possibly be due to males wanting to increase their chances of procreation with a limited number of females.

When there is a high density of males in an area, they will fight over access to the females, with the larger males usually succeeding and gaining access to the female. Calling also decreases when densities are high, with larger males calling much more frequently than smaller males. Smaller males may refrain from calling in order to conserve energy. Energy is limited due to their size and would only be wasted by trying to compete with larger males. Females are more likely to mate with a calling male, so in order to increase the likelihood of mating success, smaller, noncalling males will often engage in “satellite” behaviour, especially at low densities. This involves associating themselves with a calling male, and when the female approaches and she and the larger male begin to mate, the smaller male will join and thus force group spawning. Group spawning also occurs at high densities when a male that has secured a calling site mates with a female and others then join in after. The larger, calling male will secure the preferred dorsal amplexus position, while inferior males are forces to take on ventral or dorsolateral positions.

The mating, and thus the laying of eggs, occurs in seeps that are shallow and temporary and often dry up before tadpoles metamorphose (roughly 4–7 weeks). This results in unique adaptations, such as the development of Crinia Georgiana tadpoles in eggs that are very large relative to those of other species. This allows them to mature earlier and cope with unpredictable climates. Within the species, tadpoles with larger eggs are more likely to survive to the stage of metamorphosis. Females that lay smaller eggs also lay more of them; it is logical that since smaller eggs have a decreased chance of survival, a female would produce more to increase the chances of regenerating the species. Interestingly, egg size and number of eggs laid varies unpredictably from female to female, so it is unclear why some lay large eggs while others lay small ones, but more of them.

It has been determined that although tadpoles with limited foodstuff (i.e., a smaller egg) have a higher rate of mortality, those that do survive can still complete metamorphosis at the same rate as those that have plentiful food. In addition, if water levels drop, tadpoles can speed up development so as not to remain in such a fragile state while water, a critical resource, is limited. This indicates that the quacking frog has developed adaptations that allow for its survival in the dry climate of Western Australia.