Baby Boy or Girl? Mammals Can 'Choose'

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Mammals can skew the male-female ratio of their offspring in order to maximize their reproductive success, new research finds.

The study, published today (July 10) in the journal PLOS ONE, confirms a long-held theory that animals can influence the sex of their young in response to environmental conditions and other factors. The results come from about 90 years' worth of records for 40,000 mammals, ranging from primates to rhinoceroses, at the San Diego Zoo.

Females that produced the most males went on to have up to 2.7 times the number of grandchildren from those sons as those who had even numbers of male and female offspring. (The 10 Strangest Pregnancies in the Animal Kingdom)

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"When mothers produced predominantly male offspring, those male offspring outcompeted their peers," said study co-author Joseph Garner, an ethologist at Stanford University.

Parents that produced more females also tended to produce more offspring from those daughters than those with an even gender split, though the effect was less pronounced.

Still, that doesn't mean mammals are consciously choosing to have a male or a female. Instead, environmental and social cues may be subtly influencing their physiology so that they produce offspring with the best chances of passing on their genes.

The funny animal genre evolved

The funny animal genre evolved in the 1920s and 1930s, as blackface became less socially acceptable. Early black-and-white funny animals, including Oswald the Lucky Rabbit, Mickey Mouse (perhaps the most enduring of the kind), Foxy the Fox, Felix the Cat and Flip the Frog, maintained certain aspects of the blackface design, including (especially with the advent of sound film) heavy emphasis on song and dance routines. The increased use of Technicolor and other color film processes in the 1930s allowed for greater diversity in the ability to design new "funny animals," leading to a much wider array of funny animal shorts and the near-total demise (except for Mickey Mouse and a few other Disney characters of the era) of the blackface characters. Song and dance fell out of favor and were largely replaced by comedy and satire. The Looney Tunes and Merrie Melodies shorts by Warner Bros. Animation, for instance, introduced dozens of funny animals, many of whom have reached iconic status in American culture. Other notable funny animals from the color film era included Walter Lantz's Woody Woodpecker, MGM's Tom and Jerry (among many others), and Paul Terry's Heckle and Jeckle.
Television changed the dynamic of animation, in that although budgets were much smaller and schedules much tighter, this prompted a shift from the physical comedy that predominated film shorts to more dialogue-oriented jokes (including celebrity impressions and one-liner jokes). Hanna-Barbera Productions focused almost exclusively on these kinds funny animal TV series in the late 1950s and early 1960s, creating an extensive line of funny animal series (Yogi Bear being one of the most enduring franchises). Jay Ward Productions also produced The Rocky and Bullwinkle Show, a series representative of the genre (albeit with much stronger Cold War overtones than Hanna-Barbera).

Sharks Slap Fish to Death

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Thresher sharks slap fish to death, according to a new study that adds sharks to the list of ocean predators that can kill with just a slap.

For this latest study, published in PLoS ONE, Simon Oliver of the Thresher Shark Research and Conservation Project and his colleagues observed thresher sharks hunting schooling sardines. The action took place in the waters off of a small coral island in the Philippines.

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Using handheld video cameras, suggesting that they were very close to the sharks, Oliver and his team recorded 25 instances where the sharks slapped their tails on or very near fish. The slaps either killed the sardines outright or stunned the fish so that the shark could easily gulp them down.

Thresher sharks initiated the behavior by drawing their pectoral fins inward to lift their posteriors rapidly. The forceful tail slapping followed. Slaps were so hard that they dissolved gases that bubbled out of the water.

The sharks ate an average of 3.5 sardines after each successful hunting event.

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Clearly this method works, and it’s more efficient than hunting fish one by one. Sardines are on the small side, so a predator could quickly run out of steam trying to chase a single fish, and then another and another.

Most fish species are on the decline, due to overfishing, pollution and other human-caused problems, so the hunting method is increasingly important for sharks.

“This extraordinary story highlights the diversity of shark hunting strategies in an ocean where top predators are forced to adapt to the complex evasion behaviors of their ever declining prey,” said Oliver in a press release.

The tail slaps might also help sharks to communicate with each other, although that hasn’t been proven yet. Humpback and sperm whales slap their tails a lot, turning them into a sort of oceanic Morse code to communicate over long distances.

Crickets Act Differently When Others Are Watching

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Everybody loves an audience—even crickets.

A new study shows that the insects change their aggressive behavior when they know other crickets are watching, the first time this phenomenon has been observed in any invertebrate. Mammals, birds, and fish are all known to be influenced by others.

In recent experiments, male crickets fighting in an arena acted more violently—and upon winning, were more jubilant—when other male or female crickets were in the audience. (See National Geographic's bug videos.)

Found worldwide, crickets live in communities defined by conflicts between individuals, usually to gain access to territories, resources, and mates.

But most previous research has focused on the fighters themselves, without placing them in the social networks in which they live.
Now, the new study reveals that cricket behavior "is much more complex than we give them credit for," said study leader Lauren Fitzsimmons, a biologist at the University of Windsor in Ontario, Canada.

Robert Matthews, a professor emeritus of entomology at the University of Georgia who was not involved in the study, said, "It's an area that should have been looked at long ago.

"Contests don't occur in isolation," he said. "They always are in a social context."
Taking the Stage

For their experiments, Fitzsimmons and colleagues caught male and female crickets from local fields and reared their offspring in isolation in the laboratory. The team then put pairs of either wild-caught males or laboratory-raised males in a small arena at separate times, which always led to fights.

In a glass-separated viewing area adjacent to the arena, the scientists set up experiments with three audience situations: a male watching a fight, a female watching a fight, or no audience. The lab-raised male fighters had a lab-raised audience, and the wild crickets had a wild-caught audience. (See pictures of the world's deadliest animal battles.)

The researchers then videotaped each fight and played them back in slow motion, noting the aggression and overall behavior of the males in the three separate audience situations.