The effect of litter size on the anatomy of the
female mammalian reproductive system
Erin Nicola
Introduction
Advisor: Dr. Hancock
Results
Discussion
R- and K- selection are two types of natural selection
(Tuomi, 1980, 39). R-selected species characteristics include
early maturity, large litter size, short life span, and small body
size. R-selected species depend on high resource availability
and the young of these species only require minimal parental
care (Tuomi, 1980, 39). A mouse would be an example of a
mammal that is a r-selected species.
K-selected species characteristics include late maturity,
small litter size, long-life span, and large body size (Tuomi,
1980, 39). These species tend to need a large amount of
parental care over a long period of time. They are highly
dependant on density, but do not require high resource
availability. K-selected species also tend to live in stable
environments (Tuomi, 1980, 39). An example of a K-selected
species would be deer.
The objective of the first part of this study was to
determine the ratio of reproductive organ size to total body
weight in different species of mammals. It is expected that
the weight of the organs would scale with total body weight at
a ratio of 2:3 and the length of the organs would scale to the
cubed root of total body weight at a ratio of 1:3 . The
objective of the second part of the experiment was to compare
litter size to total body weight and reproductive organ weight
and length. It is hypothesized that litter size will be
negatively correlated with total body mass of the mammal,
and that the size of the reproductive organs will depend on an
average size of the litter for the species.
Methods
Figure 1. Total Body Weight versus
Uterine Horn Weight.
Figure 2. Total body weight versus uterus
weight.
Figure 5. Total body weight versus uterine
horn length.
Figure 6. Total body weight versus uterus
length.
Figure 9. Litter size versus uterine horn
weight.
Figure 10. Litter size versus uterus weight.
Figure 13. Litter size versus uterine
horn length.
Figure 14. Litter size versus uterus length.
Eight different mammalian species were dissected. The
uterine horn, uterus, fallopian tube, and ovary lengths and weights
were recorded. The size of each reproductive organ was compared
to the total body weight and then to the median litter size of each
mammal. Also, total body weight of each mammal was compared to
the median litter size. The log was taken from the size of each
reproductive organ and graphed against the log of the total body
weight or the cube root of the total body weight of each mammal to
determine a linear regression line. Furthermore, the each log was
also compared to the mean of the mammals litter.
The results from this study do
not support the hypothesis that the
weight of female mammalian
reproductive organs will correspond
with total body weight at a 2:3 ratio or
that the length of the reproductive
organs will scale at a 1:3 ratio.
However, the results do show a trend
of organ size increasing with body
weight. More specifically, the weight
of the uterine horn scaled to the total
body weight at a ratio of 4:5; the
weight of uterus scaled at a ratio of
9:10; the weight of the fallopian tube
scaled at a ratio of 1:2; and the weight
of the ovary scaled at a ratio of 3:5.
The length of the uterine horn scaled
at a ratio of 3:5 to the cubed root of
total body weight; uterus length scaled
at a ratio of 7:10, fallopian tube length
scaled at a ratio of 1:2; and the ovary
length scaled at a ratio of 3:5.
There was a no clear
relationship between total body weight
and median litter size. There also was
no clear relationship between litter size
and size of the reproductive organs.
Overall, the scaling relationships
between total body weight and
reproductive organ size differed
between the different organs. As a
result no general conclusion can be
made for all reproductive organs.
Additionally, no there was no
conclusive evidence for a relationship
between litter size and body size or
reproductive organ size.
Works Cited
Deanesly, D. 1934. The reproductive process of
certain mammals, part VI. The reproductive cycle
of female hedgehog. Philosophical transactions of
the royal society of London 223: 239-276.
Figure 3. Total body weight versus
fallopian tube weight.
White-tailed Deer
Mammal
Figure 7. Total body weight versus fallopian
tube length.
Figure 11. Litter size versus fallopian tube
weight.
Figure 15. Litter size versus fallopian
tube length.
Sawyer, S. et al. 1985. Homing and ecology of the
southern flying squirrel Glaucomys volanism
southeastern virginia. American Midland Naturalist
113: 238-244.
Domestic Pig
Range of
Litter Size
Median
Litter Size
Total Body
Weight
Hedgehog (Aterelix albiventris)
2-9
5
436.6g
Chinchilla (Chinchilla laniger)
1-5
2
383.95g
Deer Mouse (Peromyscus maniculatus)
4-6
5
34.67g
Opossum (Monodelphis domestica)
4-14
8
70.44g
White-tailed Deer (Odocoileus virginianus)
1-3
2
45.4kg
Flying Squirrel (Glaucomys volans)
2-4
3
53.11g
Domestic Pig (Sus domesticus)
8-12
10
113.33kg
Black Angus Heifer (Bos taurus)
1
1
419kg
Gordon, I.J. 1989. The interspecific allometry of
reproduction: Do larger species invest relatively
less in their offspring? Fuctional Ecology (3):285288.
Tuomi, J. 1980. Mammalian reproductive
strategies: A generalized relation of litter size to
body size. Oecologia (45): 39-44.
Acknowledgements
Figure 4. Total body weight versus ovary weight.
Figure 8. Total body weight versus ovary
length.
Figure 12. Litter size versus ovary weight.
Figure 16. Litter size versus ovary length.
I would like to thank Dr. Hancock for being so
supportive and helpful throughout my senior capstone
project. Also, I would like to thank the faculty and staff
in the Life and Science department at Ohio University
and Jason Smith with Hickory Hill Meats for donating
mammals to my capstone project.