Friday, July 08, 2016

Sorry, tiger dudes: your ladies are faking it

India’s tigresses may be feigning interest in sex as the result of shrinking habitat and overlapping territories

By Jason Overdorf
July 8, 2016

When Maya, a much-adored tigress in India’s Tadoba Andhari Tiger Reserve, abandoned her equally adored young cubs this June, park officials feared the worst. Soon after, Maya was spotted mating with some roving males, seemingly unconcerned about her one-year-old litter. But now local naturalists think Maya’s behavior is actually evidence of a crafty new strategy to help ensure her cubs’ survival: “false mating.”

Like many mammals—including bears, lions and bottlenose dolphins—male tigers will kill the cubs of their rivals whenever they can, so as to precipitate a new estrus cycle and impregnate the tigress with their own offspring. Tiger moms typically seek to protect their cubs from such a fate for 18 to 24 months, before pushing them out to establish their own territories. (Tiger fathers have no role in raising the young, so no help there.)

But the crowded conditions in Tadoba and other Indian national parks are making that increasingly difficult. The ranges of several roving rivals frequently overlap with the dominant male’s, bringing danger precariously close to vulnerable cubs, says Bilal Habib, a carnivore researcher at the Wildlife Institute of India.

“In high-density areas, where there are more males, the best strategy for a female is to try to leave the cubs early, go with the males, and then go back and look for her litter again,” Habib explains. “If she tries to fight with the males, that may be fatal for her and fatal for the cubs.”

The name “false mating”—which occurs among lions and other species—is a little misleading. It refers to actual sex, just not at the time when a female is able to conceive. (Typically, tigresses go into estrus once every three to nine weeks, and are most likely to conceive during three to six days within that period.) Habib’s theory is that Maya is using sex not to conceive, but to placate roving male tigers and perhaps make them think they have successfully impregnated her.

Afterwards, she returns back to her cubs, leaving the appeased male none the wiser.

Nobody will know if he is right for at least another six weeks. “We don’t know as of now if it’s real mating or false mating. She’s probably not conceiving, but it’s not clear yet,” Habib says. “If it was real mating, we will expect to see cubs in 90 to 120 days.”

Other tiger researchers say Maya’s seemingly strange mating habits are just the tip of the iceberg. Overlapping territories have bred all sorts of unusual tiger behaviors, including more frequent fighting and dominant males apparently tolerating rivals. In some crowded ranges, serial mating with different males suggests the possibility that tiger litters—like those of domestic cats—may even have multiple fathers.

Though scientists have a wealth of data from captive breeding programs, surprisingly little is known about the finer points of tiger reproduction in the wild because there have been very few long-term breeding studies, says Raghunandan Singh Chundawat, a conservation biologist in India who has published papers on tiger mating behavior.

For instance, in some cases, tigresses have failed to conceive after as many as 30 couplings and then inexplicably become pregnant. It's known that friction from the sharp spines of the male's penis are required to induce ovulation. But the variance in how many matings are required for conception has led to the speculation that tigresses, like several other mammals, may be able to control whether or not they ovulate.

“We know very little about the biology,” Chundawat says.

That’s daunting, considering the stakes. According to the latest population survey, India boasts around 2,226 tigers, or about 70 percent of the world’s total—nearly a third more than believed at the time of the last count (which used a less accurate method). That’s great, but it also means that India’s 13 tiger reserves are more crowded than we thought, even as highways, factories and towns eat away at the rest of the country’s forests.

Many of the tiger reserves are too small for the tigers they contain, so animals end up overlapping territories and coming into conflict with each other and with people. In a ten-year study that tracked tigers in the Panna Tiger Reserve of central India using radio collars, Chundawat and his colleagues found that roving males “floated” in and out of the territories of dominant males, often managing to mate with females on the sly.

The researchers found that radio-collared females mated with the territorial males on 14 occasions, and mating with the floater males on six occasions. Meanwhile, three out of four radio-collared females mated with more than one male during the same estrus cycle. "Because in dry forests the ranges are very large, the dominant male cannot keep all the other males out," Chundawat says. "He will tolerate them, as long as he has first access to the females."

While that shared access might result in greater genetic diversity and prevent rival males from killing strange cubs, it could also prove problematic. High-density areas see more frequent infighting between rival males and territorial females alike, Habib says. And the imperative for mothers like Maya to leave their cubs early could itself have dire implications.

“What we suspect is if tiger cubs in high-density areas are forced to disperse early—at 12, 14 months—that makes their chances for survival very low,” he says. Danger, it seems, comes in many stripes.