Anal Paste: Twitter for Hyenas?

Photo courtesy of Flickr Creative Commons user Rohit Varma.
Photo courtesy of Flickr Creative Commons user Rohit Varma.

By: Sara Knight
BU News Service

To mark the boundaries of our yards, most people plant hedges or construct fences. Hyenas, on the other hand, use paste – an oily, waxy, yellowish substance secreted from their anal glands.

Last fall I spoke with evolutionary ecologist Kevin Theis about his fascination with hyenas and his time spent tracking their various cliques as they roamed about the Kenyan Masai Mara National Reserve. During his time there, Theis became particularly interested in the hyenas’ scent-marking behavior.

Many mammalian species take advantage of their odiferous excretions – usually glandular goop, urine, or feces – to stake a claim to their territory. This behavior is known to biologists as “scent marking.” Hyenas mark their clans’ territory by extruding their anal pouch and dragging it along the ground, leaving a pungent paste trail behind them. Theis also suspects they use paste to communicate more nuanced information like fertility or advertising social status.

To determine the true nature of paste messaging, Theis first needed to identify what paste is exactly.Through a chemical analysis of the anal paste of hyenas from four different clans, Theis found that each group had a distinct “perfume” – allowing individuals to rapidly recognize if they were in a friendly or rival clan’s territory.

He also found that the waste products of microbial communities living within the hyenas’ anal pouches are responsible for paste’s distinctive odors. Each clan’s signature scent results from the unique composition of microbial species shared among that social group, meaning hyenas rely heavily on their resident cooperative microbe species for social communication.

Theis is continuing his work from the department of microbiology and molecular genetics at Michigan State University, where he aims to “elucidate the mechanistic roles bacteria play in the scent marking systems, and thus social lives, of solitary and social hyena species.” Read his blog here.

Do Dolphins Commit Suicide?

Dolphin Suicides

By Matthew Hardcastle
BU News Service

This summer, hundreds of dolphins beached themselves along the coast of New England. The National Oceanic and Atmospheric Administration (NOAA) has tentatively pegged the cause of this particular dolphin die-off as a viral outbreak. Yet even in normal years, dozens of dolphins around the country become stranded in shallow water or beach themselves on shorelines. Are these often sickened or injured animals simply disoriented, or are they making a conscious decision to leave their tightly-knit social groups and die on the beaches? In other words, do dolphins commit suicide?

Quite possibly.

From what we know of dolphin intelligence, they certainly have the capability of choosing to die. According to Lori Marino, a researcher who studies the brains and behaviors of animals, we know that dolphin intelligence has a lot in common with human intelligence. By administering tests to captive dolphins using mirrors, props, and memorized tasks, researchers have proved that the marine mammals are self-aware, remember their past actions, and can even think about their own thoughts.

However, compared to humans a dolphin’s sense of self-identity is more tightly tied up to its social identity. In the wild, this dolphin groupthink can result in one sick leader beaching its entire pod. To swim away from the shore and defy the will of the group would go against their core instincts. If rescuers push healthy dolphins back to sea while their leader remains on shore, the dolphins will usually just re-strand themselves.

Dolphin neurology also differs significantly from humans. The sophisticated echolocation system that dolphins use to hunt also serves as a constant form of communication, transferring personal information at a greater rate than do our sluggish human voices. A dolphin’s limbic system, the part of the brain that controls emotions, is also highly developed. Marino describes dolphins as hyper emotional; when they are hunted by fisherman, simple panic can send dolphins into cardiac or neurological shock.

A dolphin’s mix of intelligence, strong social bonds, and hyper-emotionality can backfire in the form of destructive behavior. Dolphins in captivity, even those born into it, are deprived of social interaction with their own kind, resulting in high levels of stress. Captive dolphins may ram their heads into the sides of their tank or aggressively lash out at other dolphins.

When a stressed dolphin jumps out of its tank, is it making a decision to ends its life? When a sick dolphin beaches itself, is it a selfless act made for the good of its social group? It’s hard to say. A test has not yet been developed to show whether dolphins understand the permanence of death or their own actions.

However, Marino said, dolphins can and do lose the will to live. If two dolphins in captivity become close companions, the removal or death of one will cause the other to spiral into despondency. The abandoned animal will stop eating and spend more and more time floating lethargically at the surface. At that point, it is only a matter of time before the dolphin dies of a broken heart.