Passing genes to the next generation is tricky, and not as easy as you might think. Disease, predators, environmental barriers, or just plain loneliness can all get in the way. Every species on earth needs an adaptive solution to these challenges. Each adaptation adds up to what's called a “reproductive strategy.”
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Strategy
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Scroll down to see how one species of salamander solves the challenges of ensuring future generations of its kind.
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Amphibians, as one of the oldest classes of land animals, have evolved an amazing diversity of reproductive strategies over the many eons of looking for solutions to this very basic challenge. One highly successful solution for many species of frogs and salamanders is the “ANNUAL SPRING MIGRATION.”
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Spotted Salamanders (Ambystoma maculatum), a North American salamander that lives underground burrowing through soil, makes a muddy emergence on the surface for only a couple of weeks each year. On chilly, rainy nights in the early spring, its migration begins.
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From wherever they find themselves at the end of the winter, they travel far distances to crowd into a relatively small set of habitats and get down to the business at hand: performing fancy breeding dances, choosing a partner, and laying and fertilizing eggs.
In shallow collections of water called vernal pools, males swim in swirling clusters around females, hoping to get their attention and make a new generation possible.
The bottoms of these vernal pools become dotted with small fuzzy objects called spermataphores – tiny packets of DNA dropped by the males to be picked up and carried away by females ready to fertilize their eggs.
Females use these spermatophores to fertilize themselves, after which they will lay globular clusters of eggs attached to submerged vegetation in the vernal pool.
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Eggs drift and bob in an otherworldly existence of rapid development over days or weeks. The eggs are protected by thick walls of jelly that resists pathogens, predators, and physical damage. Nestled within the jelly, the salamander embryos' development can be observed from the outside.
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The eggs do suffer some risk. Opportunistic predators such as leeches and aquatic insect larvae stalk the vernal pools, search for ways to burrow into the protective eggs masses and consume the nutritious embryos within.
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Eggs that escape predation or sudden evaporation of water in unpredictably drier years, will develop into larval salamanders that hatch into gilled, tadpole-like swimmers. After weeks or months, these larval babies will metamorphose, changing their bodies into land-dwelling forms.
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All amphibian reproductive strategies are cyclical. Once a metamorphosed juvenile salamander leaves its watery home and moves onto land as an adult, it will eat small arthropods and invertebrates until it grows to near adult size. It will then head for upland forests and burrow back into the soil for the next 300+ days, until a new season of spring rains brings it back to the area's vernal pools to begin the cycle anew.
Images and text, © Dave Huth, davehuth.com