14
David B. Dusenbery
4.4 Advantage of Male and Female Mating Types
The size limit on effective pheromone use suggests a possible explanation for why
male and female mating types, producing sperm and eggs, have been so successful
that almost all familiar organisms have males and females, although they are not
necessary for sexual reproduction. Employing an analysis similar to the above
(Dusenbery 2000), it has been demonstrated that at low population densities of
broadcast spawners, fertilization is more probable if one sex produces a few large
gametes (eggs) that release pheromone, while the other sex produces many small
motile gametes (sperm), (see Fig. 5).
4
3
- (/) 2
-(")
E
~
Q)
- ~ 0
'..c
u '- -1
~
Q)
U)
0> -2
0
-3
-4
0
0.1
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Organism radius (mm)
1
Fig. 4. Search rate dependence on size and target behavior. The target organism can remain
passive or devote energy to random locomotion or to pheromone release. Calculations
assumed spherical organisms of the indicated radius; power applied to mate location =
6000 ergs· 1 cm· 3 of organism; conversion efficiency for pheromone release = l x 10' 14
mole/erg; threshold sensitivity to pheromone = l x 10' 7 molar; efficiency of propulsion =
0.1 %, which gives a swimming speed of about l 0 diameters per second. The critical size
with these values is 215 f..Lm diameter. (Data from Dusenbery and Snell 1995)
Thus, lineages with male and female mating types can better survive population
crashes and persist longer than lineages with other types of sexual reproduction.
This allows more time to evolve other features such as multicellular individuals.
Here we have a possible explanation for why male and female mating types are so
common among the largest and most complex plants and animals.
David B. Dusenbery
4.4 Advantage of Male and Female Mating Types
The size limit on effective pheromone use suggests a possible explanation for why
male and female mating types, producing sperm and eggs, have been so successful
that almost all familiar organisms have males and females, although they are not
necessary for sexual reproduction. Employing an analysis similar to the above
(Dusenbery 2000), it has been demonstrated that at low population densities of
broadcast spawners, fertilization is more probable if one sex produces a few large
gametes (eggs) that release pheromone, while the other sex produces many small
motile gametes (sperm), (see Fig. 5).
4
3
- (/) 2
-(")
E
~
Q)
- ~ 0
'..c
u '- -1
~
Q)
U)
0> -2
0
-3
-4
0
0.1
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Organism radius (mm)
1
Fig. 4. Search rate dependence on size and target behavior. The target organism can remain
passive or devote energy to random locomotion or to pheromone release. Calculations
assumed spherical organisms of the indicated radius; power applied to mate location =
6000 ergs· 1 cm· 3 of organism; conversion efficiency for pheromone release = l x 10' 14
mole/erg; threshold sensitivity to pheromone = l x 10' 7 molar; efficiency of propulsion =
0.1 %, which gives a swimming speed of about l 0 diameters per second. The critical size
with these values is 215 f..Lm diameter. (Data from Dusenbery and Snell 1995)
Thus, lineages with male and female mating types can better survive population
crashes and persist longer than lineages with other types of sexual reproduction.
This allows more time to evolve other features such as multicellular individuals.
Here we have a possible explanation for why male and female mating types are so
common among the largest and most complex plants and animals.