Friday, May 28, 2010

Sneaky Males

The boy-meets-girl scenario is not always so simple in nature. Often it is the boy-must-convince-girl and/or boy-must-keep-girl scenario. Many males pick flashy coloration, elaborate dancing, amazing architecture, gift-giving, feats of courage, and cautious mate guarding. This particular story is one of deception, antelope deception that is.

Many antelope mating systems are set up so that a male maintains a territory and females who like a territory will stay there to feed and likely mate with the male of that territory. And so, the higher quality the territory the more likely that a female, or many females, will mate with that particular male. That's the plan anyway.

In the case of the topi antelope, males have found a loophole in the system. Topi antelope females are only in heat for one day per year, and they generally visit multiple territories, mating with resident males during that time. So if you are a male topi antelope you want to keep females in your territory as long as possible to increase the likelihood that you are the father of the most antelope babies. How do you accomplish this? When a female is appearing to leave his territory the male runs in front of her, freezes, stares in the directions she is going, and starts snorting loudly. This is typically a behavior exhibited by animals who detect a predator (a cheetah, lion, leopard, or whatever) -- an alarm snort, if you will. The female then retreats back into the territory. In this case its all a big show, further evidenced by the fact that the male attempts to mate with the female right after the curtain falls. The male is pretending to sense a predator so that the female will stay in his territory. This study, published online in The American Naturalist, is the first case to find males duping females in this way. This is a pretty ingenious and relatively rare behavior, considering it is energetically efficient, safe for the male, and it works because ignoring a predator-alert signal could potentially be fatal.

Bro‐Jørgensen and Pangle, the authors of the paper, tracked 74 female topis in estrus through the years 2005-2009. They observed the females as they visited the territories of various males. They also observed the males in the absence of females. They observed this fake-alarm-sound behavior and found that the females almost always fell for it.

They also recorded the sounds made by males and found that they could be classified into three categories: a real alarm sound, a false alarm sound, and a regular grunt or snort. When they played these recorded sounds to 60 different females they observed that the females ignored the regular grunts but froze in place at the real and fake snorts. This suggests that the sound itself (excluding the visual, body language signals) is close enough that real and fake are indistinguishable to the females.

Smooth, very smooth.

Jakob Bro‐Jørgensen and Wiline M. Pangle. (2010) Male Topi Antelopes Alarm Snort Deceptively to Retain Females for Mating. The American Naturalist: 176, published online. (DOI: 10.1086/653078)

Here are a couple of write-ups about the article:
http://www.nytimes.com/2010/05/25/science/25obantelope.html?ref=science#
and
http://www.time.com/time/health/article/0,8599,1991425,00.html

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