THE FAMILY TIME OF YEAR BUT NOT ALL FAMILIES ARE THE SAME
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
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.
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
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."
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.
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.
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.
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
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!
you have an environmental question or comment, email