Introduction

Methods

Results

The effect of litter size on the anatomy of the female mammalian reproductive system

Erin Nicola

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.

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.

Works Cited

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.

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.

Gordon, I.J. 1989. The interspecific allometry of reproduction: Do larger species invest relatively less in their offspring? Fuctional Ecology (3):285-288.

Sawyer, S. et al. 1985. Homing and ecology of the southern flying squirrel Glaucomys volanism southeastern virginia. American Midland Naturalist 113: 238-244.

Tuomi, J. 1980. Mammalian reproductive strategies: A generalized relation of litter size to body size. Oecologia (45): 39-44.

Mammal 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

Figure 1. Total Body Weight versus Uterine Horn Weight.

Figure 2. Total body weight versus uterus weight.

Figure 3. Total body weight versus fallopian tube weight.

Figure 4. Total body weight versus ovary weight.Figure 8. Total body weight versus ovary length.

Figure 7. Total body weight versus fallopian tube length.

Figure 6. Total body weight versus uterus length.

Figure 5. Total body weight versus uterine horn length.

Figure 9. Litter size versus uterine horn weight.

Figure 13. Litter size versus uterine horn length.

Figure 10. Litter size versus uterus weight. Figure 14. Litter size versus uterus length.

Figure 15. Litter size versus fallopian tube length.

Figure 12. Litter size versus ovary weight. Figure 16. Litter size versus ovary length.

Figure 11. Litter size versus fallopian tube weight.

Advisor: Dr. Hancock

White-tailed Deer

Domestic Pig

Acknowledgements

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.