Recorded “bee alarm” calls send pachyderms packing

Elephants are terrified of bees

Forget about the mouse freaking out the elephant. What these land behemoths fear most may be bees. Researchers report in PLoS ONE that African elephants live in such terror of African bees that the pachyderms have a specific alarm call that means “Bees!” Recordings of the call could send herds stampeding, even with no bees in sight or earshot.

Birds do it, prairie dogs do it, and so do elephants

Vulnerable vertebrates living in social groups often have calls specific to danger. Prairie dogs throw up little arms and let out a whoop that means “Hawk!” or “Snake!”. Some primates and birds also have vocalizations specific to certain threats. But why do elephants, with lions as their only non-human predator, fear bees so much? A swarm of angry African bees can sting their soft parts around the eyes and mouth, and the hide of young elephants isn’t tough enough yet to withstand the stingers.

Rumble in the jungle, er, savannah

When a bee threat is detected, the elephants emit a particular rumble (listen here), just one of the many vocalizations these social animals use to communicate with each other. Subtle variations in this rumble, which elephants may produce by small adjustments in lip and tongue, can send a pachyderm pack running as though a hive of angry bees were on their trail. But another small adjustment can leave most of them standing there, staring. These subtle changes may even cue the herd to the nature of a specific danger, as is the case with other vertebrate groups that sound alarm calls.

Other differences may not be so subtle. While bees get a rumble from the elephants, lions get an unmistakable elephantine reception that includes threatening roaring and trumpeting.

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Can rain make buffalos have boys?

African buffalo shift sex ratios with rain

African buffalos (Syncerus caffer) have more males during the rainy season in Kruger National Park, and it’s not just a random accident of fate. Researchers have found that specific sequences on the Y chromosome are correlated with seasonal differences in birth sex ratios in the buffalo population.

X sperm vs. Y sperm

Does that mean that rain somehow makes buffalos have more boys? Not directly. Instead, it may come down to a DNA-level battle royale involving the Y chromosome. Sometimes, sperm carrying the Y win the race to the egg, while at other times, X-carrying sperm are the victors. These times correlate with higher frequencies of certain sequences, or haplotypes, of the Y chromosome occurring in the population, with one sequence being much more common during the rainy season, when more males are born.

Selfish genes gone rogue

The investigation suggested the existence of a suppressor of Y chromosome success acting during the dry season, when females birthed more females, and a distorter in favor of Y chromosome success in the rainy season, when more males are born. The distorter may shift meiosis in favor of the Y-carrying sperm or disrupt survival of X-carrying sperm. Interestingly, distorters are not considered to act for the benefit of the individual carrying them and are considered “selfish genes.” Suppressors…well…suppress the distorters. The authors refer to these apparent Y chromosome suppressor/distorter regions¬†as sex-ratio, or SR, ¬†genes.

Dry season not a good sperm season

They also noted that during the dry season, buffalo didn’t make as much sperm, and the sperm they did make weren’t as frequently normal looking or very good swimmers. They hypothesize that semen quality may interact with the decreased availability of food in the dry season, leading to drop in Y haplotypes associated with a male-biased sex ratio. The investigative team, whose lead author, Pim van Hooft, is based at Wageningen University in The Netherlands, also suggested that the SR genes may be present in other species, adding a new dimension to the increasingly complex mechanisms of sex ratios in mammals.

For your consideration

1. Sex determination in vertebrates happens in a number of different ways. Some mechanisms don’t involve sex chromosomes at all but instead rely on environmental cues. Find an example of a species that uses environmental cues to determine sex. How can an environmental trigger be similar to a chromosomal trigger as a sex determinant? How do they differ?

2. Many species have life history strategies that involve adjusting sex ratios. What are possible explanations can you find to explain how adjusting sex ratio might benefit a species? How might it be a potentially dangerous gamble?

3. Distorters in general appear to be doing their host individual no favors. Given that fact, what is one explanation for the existence and persistence of suppressors of distorters?

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