Title
Using the geometric probability to compare the random and actual mating success of the Sponge,
Phyla Calcarea/Silicea.
Author
Allie Horton
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Abstract
Sea sponges belong to the Phyla Calcarea or Phyla Silicea. Sponges are a sessile animal that will
stay in one place for their entire life unless they break off into pieces. The fact that they are
sessile makes it seem as though reproduction would be extremely difficult. However, I have
found that it is actually pretty easy for sponges to reproduce because they coordinate when they
are all going to release sperm and produce eggs, and sperm is easily absorbed through any part of
the sponge. Also, sponges can reproduce asexually, meaning they can release sperm and then
absorb it right back up to produce fertilized eggs.
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Introduction
Sponges are some of the oldest known animals on earth with fossil records dating older
than 580 million years ago. Throughout all that time they have been filter feeders, consuming
over thousands of liters of water per day. Sponges reproduce sexually and asexually. While
sponges can transfer sperm to another sponge for fertilization, they produce both eggs and sperm,
allowing them to act as hermaphrodites and fertilize themselves when appropriate. When
sponges ejaculate, on certain times of the year, they will release sperm for three hours at a
volume reaching two to three meters high.
Method
The large rectangle represents the surface area of the sponge. The circle represents the
sponges’ opening where sperm is released and can also be absorbed. A sponges’ sperm can be
absorbed by any part of the sponge, not just the small opening. Random mating success was
calculated as the sponges surface area divided by the sponges target area.
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Figure 1
Image obtained from http://news.discovery.com/animals/are-sponges-the-worlds-mostsuccessful-animals.htm
Results
Female target: 2 x 3.14 x 2.65 x (16+2.65) = 310.4cm²
Bull’s-eye (insemination location):
2 x 3.14 x 2.65 x (16+2.65) = 310.4cm²
The random probability of mating success according to my geometric calculations: 310.4/310.4 =
1 x 100 = 100%. Therefore, there are 100 chances out of 100 that random mating will be
successful.
Discussion
The sea sponge, Phyla Calcarea or Silicea, can release sperm and reabsorb it right away,
allowing for asexual reproduction. The random probability of mating success, estimated at
100%, was on average far greater than that of mammals (< 5%). The reason for the greater
random success is that a sponge can release sperm into the water and have it absorbed by any
part of any sponge. Since sponges filter thousands of liters of water every day it is highly likely
that during their reproduction periods that a sponge will absorb some sperm to fertilize its eggs.
Sponges are able to absorb so much water because their skeleton is composed of protein fibers
with a lot of empty space that work like a canal allowing for maximum water flow in and out of
the sponge.
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References
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