by Whit Gibbons

December 1, 2013

The season between Thanksgiving and Christmas brings to the forefront the importance of families. It also calls to mind the interactions - good, bad, and indifferent - that occur between family members, whether sitting around the groaning board, playing Frisbee, or watching a favorite football team on TV. And most families have behaviors that may seem peculiar to outsiders. Consider the behavior of some tiger salamanders and pilot whales.

Tiger salamanders are native to most states, including all southeastern ones. Having a typical amphibian life cycle, the adults live on land and migrate to wetlands to breed. The young, called larvae, have gills and live in the water, eating small aquatic animals. The juveniles metamorphose and leave the water to take up permanent residence on land.

One fascinating aspect of ecology is the variability that exists within species. In some populations of tiger salamanders, the larvae become cannibalistic, feeding on other tiger salamanders. The cannibal salamanders are larger than noncannibalistic ones and have specialized structures in the mouth that aid in eating other salamanders. Cannibalism occurs most frequently when larvae develop under crowded conditions.

As if such a lifestyle were not intriguing enough, research has unveiled another facet of tiger salamander biology. Salamanders reared in genetically unrelated groups are more likely to develop into cannibals than are groups of siblings. That is, tiger salamanders that are brothers and sisters are less likely to eat each other. How do they know who their siblings are?

The salamander experiments involved placing larvae in various groups. Some groups included siblings whereas others were unrelated. After analyzing the results of who had eaten whom, the investigators hypothesized that larval salamanders release chemical cues that can be used to distinguish close kin from others. Presumably, genetically similar salamanders have a similar "smell."

An explanation of the ability of larval salamanders to detect - and not eat - their siblings resides in evolutionary theory. Briefly, this predicts that organisms can increase their own genetic success by helping their relatives. Obviously, eating your brother, who shares many of the same genes, would not help achieve this goal.

Although different from salamander cannibalism, a particular whale behavior has also proved to be a challenge to explain. The research focused on the biology of long-finned pilot whales in the Faeroe Islands, located between Iceland and the British Isles. Pilot whales do not cannibalize each other, but some males exhibit a behavior that is different from what is considered normal.

Pilot whales form large social groups called pods. The investigators used molecular techniques to establish that pod members were closely related, forming an extended family. A pod normally has more adult females than males. In most mammal species in which females live in groups, males disperse from their homesite before they become breeding adults, thus avoiding genetic inbreeding. The departure of young males also reduces the competition that they would face from larger and more experienced males.

Among pilot whales, however, many of the males do not leave their family pod, which may number more than a hundred. Instead they remain with it. But genetic studies revealed that males in a pod rarely or never breed with any female of the same pod, who might be their mother or sister. Mating is presumably carried out when different pods encounter each other in the ocean. Scientists do not know exactly how the nonbreeding males "help" their relatives in a pod, but defense from marine predators and assistance in a communal feeding effort have been suggested. One of the exciting features of ecological research is attempting to explain such mysteries.

Many other unusual family relationships have already been discovered and many more remain to be uncovered as ecologists take a careful look at various wildlife species. As we visit with our own family members during the upcoming holiday season, let's be grateful for the vast array of plants and animals that make up this world we call Earth. Happy Thanksgiving!

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