Here in the UK the breeding season for our native species of newts is well under way, and members of our team from The Vivarium will be undertaking surveys in the Greater Manchester area over the next two months to see how our local amphibian populations are getting on. Female newts begin laying their eggs around this time of year, and instead of laying strings of eggs like our toads, or large clumps of spawn like frogs, newts carefully wrap individual eggs in vegetation; disguising them from predators. Over two months or so, female newts may lay hundreds of individual eggs. All three of our newt species share this method of reproduction; the lack of competition from other species has perhaps eliminated the need for more elaborate breeding strategies. Although this is not the case in other parts of the world where more species occur together, which causes more competition for the best place and time to reproduce.
The US and Canada contains one of the most salamander rich ecosystems on earth, with a diverse array of incredible species. In fact, in some areas in the US salamanders account for more of the biomass than any other species of vertebrate in the ecosystem. Due to this diversity of species some have developed unusual ways of breeding to ensure their young have the best chance possible against all of the competition. Some species such as the Eastern Newt (Notophthalmus viridescens) enter ponds after living terrestrially and breed much like our native species, laying individual eggs in vegetation. Some salamanders, such as the Slimy Salamander, Plethodon glutinosus, have a breeding strategy that eliminates the need for a pond all together, they lay eggs terrestrially which then undergo direct development; females guard their clutch until fully formed salamanders hatch from the egg.
The Marbled Salamander (Ambystoma opacum) arrives so early that the pond that their larvae will depend on is not yet there, their ponds dry out over summer and fill up again with the winter rains. Using ponds such as this is a very clever way of avoiding predation by fish, as their won’t usually be fish in a pond that is not full of water year round. Female Marbled salamanders lay their eggs in depressions that they somehow know will flood to form a pond when the rain arrives; they guard their eggs during their development and as they are submerged by the rains the female abandons them. In reaction to the water the eggs then hatch into swimming larvae within the newly filled pond. This gives them a head start against all other amphibian species that will begin to use the pond later in the year. Amazing!
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