Spring Dance


March 19, 1993|By DON C. FORESTER

I am well aware that spring officially begins some time after dinner tomorrow. But this is a less than perfect world, and Mother Nature is a free spirit, unconstrained by celestial calendars or official human pronouncements. And so, when the temperatures finally rose above freezing and the snow began to melt on the last day of February, I knew all bets were off -- spring would be early.

Sure enough, by the middle of the second week in March, the vernal cycle had begun. A heavy downpour in late afternoon served as the final cue, setting into motion a reproductive ritual that had been primed the previous fall by the release hormones, induced by a shifting photoperiod.

At dusk, a vanguard of big-eyed heads began to poke from their subterranean burrows -- Ambystoma maculatum, the spotted salamander, was ready to dance. The males came first, an incredible procession of awkward, lumbering creatures -- their black bellies and long, muscular tails dragging on the ground as four stubby legs struggled to negotiate natural obstacles. Their destination was a shallow pond formed where rainwater had collected between a steep hillside and an abandoned railroad grade.

Once in the water, it was as if the salamanders had been transformed -- suddenly endowed with the agility and grace of a native book trout. Despite the fatigue of their overland journey, .. they went right to work. Small aggregations of males began homosexual courtships -- a prelude to heterosexual pairings that would commence upon arrival of the females over the next several evenings.

In the beam of my head lamp, the dancing salamanders took on a surrealistic quality. Their black bodies were invisible against the dark pond bottom, and the bold yellow spots that adorned their backs appeared to bob and flicker like fireflies on a mid-summer evening.

As I watched the males milling about the bottom of their nuptial arena, a female, her sides distended with eggs, entered their midst. Instantly their demeanor changed and within 30 seconds, half a dozen sex-crazed suitors were nudging and rubbing her torso -- each anxious to renounce the vow of celibacy he had taken almost a year earlier.

Competition for the female's favor was vigorous. Occasionally a participant would pause, quiver sporadically, and then proceed on -- leaving behind a small mushroom-shaped spermatophore glued to the leaf litter. The gelatinous cap of each spermatophore contained semen, and within 20 minutes a spermatophore field littered the pond bottom. Although each is capable of fertilizing hundreds of eggs, on this night most would go unused, for the female had made her choice. She followed the lucky dancer through the field and carefully inseminated herself with one of his detachable sperm caps. Immediately after, she darted into the darkness.

Upon close inspection, some of the spermatophores appeared to be significantly larger than the others. These resulted from a behavior known as spermatophore covering -- a unique type of sexual interference common among ambystomatid salamanders. As a male courts a female, he inadvertently comes in contact with the sperm packets of other males. When this occurs he deposits a fresh spermatophore directly on top of the old one. By doing so he decreases the reproductive potential of a rival while increasing the likelihood of his own success.

Frequently competition between males escalates well beyond the innate act of covering spermatophores. During a subsequent visit to the pond, two nights later, I was observing a large female that had just entered the water. As I followed her progress, a male appeared in the circle of light created by my lamp. He moved quickly toward the female and began to prod her flank with his snout -- a sort of urodele foreplay. Sexually aroused by this tactile stimulation, the female crept after her prospective mate.

Suddenly, a second male came swimming from the darkness and without hesitation, inserted himself between the courting pair. The first male stopped to deposit his spermatophore and feeling what he presumed was a responsive female pressing against his tail, he moved a measured distance forward to facilitate spermatophore retrieval. As he did so, the interloping male deposited his own sperm packet on top of the first.

Oblivious to the deceit, the female made a flawless pickup -- at this stage of the sequence she was on behavioral autopilot and the paternity of her offspring mattered little. As I watched in fascination, a smile crinkled the corners of my mouth, for it is a biological axiom that in the game of life there must always be winners and losers. On this night, however, even the vanquished felt the glow of victory.

Don C. Forester teaches animal behavior at Towson State University. The ''storm of the century'' caught him -- and the salamanders -- by surprise.

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