Posted by: salamandercandy | June 3, 2006

You Can’t Spell “Salamander” Without S&M

Although SC is not just about salamanders, our stat counter suggests that many folks are searching for info about them when they stumble upon our site. I am appalled by the idea of curious people remaining ignorant of amphibian biology for even a few seconds, so I thought I’d share some more amazing stories about salamanders.

My own personal experiences with salamanders began when I was an undergraduate at Cornell University in upstate New York, and I worked in the coolest lab on campus. Our research focused on a local population of spotted salamanders (Ambystoma maculatum). These amphibians spend most of their time in the woods underground, but for a short period in the Spring, they all migrate to temporary ponds to mate and lay their eggs. Thanks to their crazy reproductive biology, they have internal fertilization but do not copulate. Try to imagine what that entails before you keep reading. Basically, the males deposit little white packets of sperm called spermatophores on twigs and leaf litter at the bottom of the pond. A female will squat on these spermatophores and take up the sperm, where it fertilizes the eggs inside her body. Very soon afterwards, the eggs are laid in a big clump attached to a stick or something else in the water. The adults then abandon the pond full of eggs, and the young must hatch, swim around the pond while growing, and metamorphose into tiny salamanders before the pond dries up at the end of the summer.


We built a foot-high fence around the pond, and stuck buckets in the ground all along the fence. When lusty salamanders approached the pond, they’d hit the fence, then walk along it trying to get to the water and inevitably fall into a bucket. In this way, we could record every individual entering and leaving the pond (after obtaining our data, we’d put the salamanders on the other side of the fence so they could continue their business). The salamanders were mostly active at night, so we’d tromp into the woods in the dark, often through snow, to do our field work. Although salamanders are pretty quiet, the constant sound of the spring peepers (tree frogs, Pseudacris crucifer), punctuated by the lower croaks of wood frogs (Rana sylavatica) was nearly deafening. Our buckets would be mostly full of red-spotted newts (Notophthalmus viridescens), along with a few Jefferson salamanders (Ambystoma jeffersonianum), and our target species, the spotteds. Occasionally we would find shrews (Sorex sp?), which sometimes starved to death in the buckets even after killing and devouring the less toxic parts of a salamander or two (small warm-blooded animals are little calorie-burning factories that must always be eating, unlike the chillin’ amphibians).

My own research involved mating chambers I had built and set up in the pond. I’d add a female and a male to the “love shack,” and then later I’d add a second male to complete the ménage à trois. We were testing whether the females tended to mate with the first male they encountered. The set-up was just to keep the salamanders of interest isolated from other potential mates, not to indulge the salamanders in their own fantasies of bondage, but then, who wouldn’t want to be trapped in a cage with a hot and horny member of the opposite sex? To determine parentage, we eschewed more traditional methods and used genetic markers. Our results showed that the first male does tend to sire most of the offspring, but females do pick up spermatophores from more than one male, so the second male has some success, too. Also, many larvae were not fathered by either male in the chamber, suggesting that females approach the pond carrying stored sperm from previous matings.

Why did we do all of this? First of all, salamanders just have neat reproductive biology, and it’s nice to know more about it. In the bigger picture, sexual selection is a major evolutionary force, and we need to understand it if we want to get a handle on how the world came to be this way, how populations of organisms are behaving right now, and where evolution might take us in the future. That means learning what determines reproductive success or failure in lots of different kinds of species, from apple trees to salamanders to humans.

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Responses

  1. Keep up the great work on your blog. Best wishes WaltDe


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