The Tender Side of Alligators

Oct. 14, 2009— -- You probably thought an alligator had a face only a mother could love, but guess what? Scientists have made the surprising discovery that some female alligators mate repeatedly with the same male, so there seems to be a little pair-bonding going on in the bizarre world of crocodilians.

It's not exactly a storybook romance, since most gators play the field, whether male or female, but researchers found that in one wildlife refuge, up to 70 percent of the females stood by their man, year after year.

It appears the gators are acting like some famous species of birds that mate for life. Sort of. Some of the time.

A 10-year study published in the current issue of the journal Molecular Ecology reveals what the scientists call the first evidence of "partial marital fidelity in any crocodilian species," based on observations in Louisiana's sprawling haven for gators, the Rockefeller Wildlife Refuge, that extends for 26 miles along the Gulf Coast.

The refuge is home to so many alligators that researchers have found one nest per 10 acres in the 76,000-acre reserve, which is a lot for alligators. (The refuge encompassed 86,000 acres when the Rockefeller Foundation donated it to the state, but about 10,000 acres have been lost to coastal erosion.)

Years ago, scientists found that it wasn't too difficult, although a bit tricky, to recapture female gators over a long period of time. That opened the door to researching the mating habits of alligators -- which have been around since dinosaurs ruled Earth.

Together Forever. Almost

The scientists say they were astonished to find that in many cases, females returned to an earlier love.

"I don't think any of us expected that the same pair of alligators that bred together in 1997 would still be breeding together in 2005, and may still be producing nests together to this day," Stacey Lance of the University of Georgia's Savannah River Ecology Laboratory said in releasing the study.

The researchers found that one male was responsible for all the offspring produced by one female in 2000, 2002, and 2004. That's surprising, they say, because, unlike nearly all reptiles, female crocodilians exhibit extensive parental care, partly to keep their offspring from getting eaten by adult gators. But males are thought to remain pretty much out of the loop.

Alligator Love

This research suggests there may be more to the relationship than had been thought. But why should anyone care?

Because, researchers say, it's important to understand the mating habits of alligators if we want to understand how such things as low-level radiation can affect reproduction, even among humans.

Travis Glenn, a member of the research team, said in a telephone interview that his involvement dates back to early research into radioactive contamination in the Savannah River area of South Carolina.

"It's one of the places where they made nuclear materials for weapons," Glenn said. Reactors built there in the 1950s and 1960s had some "oopses," he said, and released some radiation into the environment. A large section of land was contaminated, and mountains of material had to be removed.

But at what point would the contamination become low enough to be safe for human contact? Perhaps alligators could help answer that lingering question.

Radiation is known to cause mutations, and scientists wanted to know if there was a significant change in the mutation rate among alligators that lived out their lives in the radiated muck. But to answer that, they had to learn a lot more about parenting. Could any change in the mutation rate have been caused by the radiation, or could it simply be multiple partners, thus bringing many other genes into play?

You can't answer that question unless you know the identity of the daddy.

Mutation Rate

It now turns out that there may be some continuity in paternity among many of the gators there, so a change in the mutation rate could be a result more of radiation than multiple partners. That question will take a considerable time to answer, since females don't reproduce every year, but in time it may help scientists determine "if there is any safe level," Glenn said. "We are looking for a direct assessment of mutations between parents and offspring."

Glenn is a specialist in DNA analysis, and he and his colleagues will continue to capture alligators in several locations. It looks a bit primitive, but the researchers literally lasso the gators, pull them ashore, then hold them down so a needle can be inserted and DNA material extracted.

Alligators Stand by Their Man

The female lays her eggs, usually around 30, in a nest. After the eggs hatch, the researchers extract DNA from the hatchlings and search for the signature of the male. Usually one, two, and rarely three males are responsible for the eggs.

The gender of the offspring, by the way, is determined by the temperature of the nest. Temperatures of 86 degrees produce females, and temperatures of 93 or higher produce males.

It's not entirely clear at this stage why the females in the Louisiana refuge tend to pick the same male from year to year. It's possible they just like the nest where they were successful the last time, so they return to the same site and find that the big guy is still hanging around.

Live Long and Prosper

This can go on for a long time, since the average longevity of an American alligator is 50 years. Some have lived beyond 70.

Alligators are found throughout much of the southeastern United States, and a few crocodiles live in the southern area of Florida. Gators tend to be shy, and usually retreat when a human approaches, but crocodiles can be very different.

"The principal differences between alligators and crocodiles are behavioral," Glenn said. "Crocodiles are like alligators on crack. They are hopped up, aggressive animals."

But all of these ancient reptiles can be dangerous. If they bite into an animal that is too strong to be pulled into the water and drowned, they may roll over quickly, pulling the arm or leg or whatever off the body of its prey, in a horrific maneuver called the "death roll."

But at least now we know they may also have a tender side. At least some of them. Some of the time.