HAVE MANY MATING STRATEGIES
June 27, 2010
on an early summer evening, I watched a big salamander creep through a
swamp. The animal was a greater siren, one of the largest salamanders
in the world. The one I watched that night was more than two feet long.
I stood on the bank for several minutes, following its movements with
It may have
been looking for food, but my hope was that it would encounter another
greater siren of the opposite sex. Because despite the immense size of
this native salamander of the Southeast, few people see it in the wild,
and ecologists know next to nothing about its breeding habits. I was hoping
to be the first to see sirens mate.
of animal mating systems and social structure is an intriguing area of
ecological research. Mating among animals is not a random, haphazard process.
Within each species, mating strategies and patterns--often highly complex
and intricate--have been molded throughout the species' evolutionary history.
Each year our knowledge across the spectrum of species increases and patterns
begin to take shape.
like Canada geese, are relatively monogamous, often remaining with the
same mate for life. Male wild donkeys may keep a harem of females and
physically prevent younger males from mating with them. The timing of
mating also varies among species. Most frogs breed at night. Most birds
breed during the day. Zebras breed year round. Garter snakes mate in the
spring. Timber rattlers look for mates in the fall.
collect information about when, where and how mating occurs. These ecological
voyeurs try to determine the social structure of animal populations and
unravel the complexities and relationships among individuals. Each new
discovery can increase our understanding of the relationships between
the ecology, evolution and breeding pattern of the species.
frog found in Guyana, South America, provides evidence that an individual
animal's actions may be best for propagation of that individual's genes
but not best for producing the most offspring. The females, if given a
choice, will select male mating partners that are about 80 percent of
their own length. Experiments revealed that this female-to-male size ratio
produced the highest fertilization of a female's eggs. When the male was
larger than the female, it fertilized significantly fewer eggs because
it was not in proper position for the sperm to reach all the eggs. Males
smaller than the optimal size did not have an adequate sperm supply to
fertilize all the eggs. So to maximize egg fertilization and have the
highest reproductive success, a female needs a mate about 80 percent her
however, have their own agenda, and a larger male can physically displace
a smaller one chosen by the female. Thus, a larger one may end up mating
with her. These bullies of the frog world fertilize a lower percentage
of the female's eggs. But they produce some of their own offspring and
pass on their own genes, which would not have happened if they had not
practice a satellite mating strategy in which smaller but opportunistic
males sometimes successfully mate. When a male bullfrog gives a mating
call to attract the female, a smaller male may remain quiet but alert
as she approaches. When a female passes by on her way to check out the
calling male, a small, silent, satellite male may intercept her and mate.
Such competition between males can reduce the reproductive success of
some females while ensuring the propagation of a particular male's genes.
has a mating story. Yet in spite of our having discovered enough about
breeding systems to identify patterns and classify them into categories,
basic information about individual behaviors and strategies remains to
be discovered for most species. Perhaps mating patterns exist of which
we are still unaware. One day, when someone adds the siren breeding story
to the list, we may discover that one of our native wetland species has
a fascinating mating strategy of its own.
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