Summary of :
Eadie, J. M., McEachern, M.B., McElreath, R. L., Van Vuren, D. H. (2009). Another genetically promiscuous ‘polygynous’ mammal: Mating system variation in Neotoma fuscipes. Animal
Behaviour 77, 449-455.
Summary by:
Cassandra Gergis, Nicole Ghafourian, and Simon Stewart
For Dr. Mills’ Psyc 310 class, Spring, 2014
Variation in mating systems plays a crucial role in understanding the evolutionary process of species. Mating is defined as the production of offspring between mated pairs (Eadie,
McEachern, McElreath & Van Vuren, 2009, 450). Within the realm of reproduction lie several different mating systems: polygyny, males that mate with multiple females, polyandry, females that mate with multiple males, monogamy, a male and female mating exclusively, and finally promiscuity, where both sexes mate nonexclusively. Although these different mating systems have been found in both males and females, earlier studies focused more on males alone.
However, recent evidence has revealed that mating systems such as promiscuity occur within both sexes.
In order to learn more about the mating system variation (MSV), an experiment was conducted which studied the behavior of dusky-footed woodrats, formally known as Neotoma fuscipes . The woodrats were observed in three different habitats (coniferous, juniper, and oak forests), and data was collected regarding spatial distributions, densities, and sex ratios. “Spatial and demographic data were used to calculate population density, defined as the number of woodrats per hectare, and the operational sex ratio (OSR), expressed as the proportion of adult males in the adult population in a given year and habitat.” (Eadie, McEachern, McElreath & Van
Vuren, 2009, 451). Population density was highest in the oak woodland, followed by the juniper woodlands, and the lowest population density was found in the coniferous forest. Woodrats were placed in homes where potential mother and father candidates were examined. One of the goals of the experiment was to determine whether or not a successful mating would occur, and, if so, how many offspring would be produced. By testing the woodrats, scientists hoped to figure out whether mating is random, or influenced by things such as the sex ratio, density, and/or distance.
The ultimate goal of the experiment was to determine whether the woodrats were mating polygynously, as had been previously assumed, however the results of the experiment showed little evidence, and in fact, indicated that there was more promiscuous and monogamous behaviors. The researchers found that the habitat had an effect on which mating system the rats chose. The highest proportion of polygamous females was found in the low-density coniferous forest (43%), while the highest proportion of monogamous females was found in the denser juniper woodland (58%). It is important to note that there was a sex difference noted in the mating system trends, though. The highest proportions of polygamous males were found in the higher-density oak and juniper woodlands (36% and 33%, respectively), and an outstanding 75% of the males in the low-density coniferous forest were found to be monogamous. Combining data from all habitats and years of data, it was found that in the overall sample “54% of adult females were monogamous, 15% were polygamous, and 31% failed to produce detectable offspring,” and
“43% of males were monogamous, 30% were polygamous, and 26% failed to produce detectable offspring” (Eadie, McEachern, McElreath & Van Vuren, 2009, 453). The study showed that sex

ratio, and density did influence the mating system variation (MSV), although it did not necessarily increase the mated pairs in a population. The experiment also concluded that the
MSV is not random, and that the distance to the nearest partner did have a small effect as well.
Furthermore, the study showed that to understand the mating system variation in different species, it is important to acknowledge the variables that influence the system.
Outline
I. Introduction
A. Mating
1. Defined as mated pairs producing offspring
B. Mating Systems (during breeding seasons)
1. Polygyny: one male + two or more females
2. Polyandry: one female + two or more males
3. Promiscuity: both sexes mate nonexclusively with multiple partners
4. Monogamy: one male + one female mate exclusively
C. Mating System Variation (MSV)
1. Variables that may or may not influence mating between females and males
D. Dusky-footed Woodrat
1. Scientific name, Neotoma fuscipes
2. Previously considered of being (mostly) polygynous
E. Experiment/Hypotheses
1. Mating is random
2. Mating is influenced by population density
3. Mating is influenced by operational sex ratio (OSR)
4. Mating is influenced by pairwise distance
5. Mating is influenced by male body mass
II. Methods
A. The researchers began by trapping woodrats and relocating them into houses
B. They then assigned candidates that were most likely-parents to offspring based off allele frequencies to a pool
C. Calculations
1. Calculated population density, number of woodrats per hectare
2. Calculate operational sex ratio (OSR), proportion of adult males in adult population
D. Narrow the results with two outcomes: successful mating or no successful mating.
III. Results
A. Overall population
1. Adult Female
a. 54% were monogamous
b. 15% were polygamous
c. 31% failed to produce offspring
d. Polyandry not detected

2. Adult Male
a. 43% were monogamous
b. 30% were polygamous
c. 26% failed to produce offspring
d. 4/14 classified as polygynous
B. Mating system by habitat
1. Coniferous forest (low-density)
a. Highest proportion of polygamous females (43%)
b. Highest proportion of monogamous males (75%)
2. Juniper woodland (low-to-mid density)
a. Highest proportion of monogamous females (58%)
b. Middle proportion of polygamous males (33%)
3. Oak woodland (high density)
a. Middle proportion of monogamous females (50%)
b. Highest proportion of polygamous males (26%)
C. Mating is not random,
D. Sex ratio, density, and distance do influence mating
E. Variances in number of mates continues to be higher in males than in females
F. There are more indications of promiscuous behavior than any other mating system
IV. Critical Review
A. Population density
1. Low population density resulted in highest proportion of polygamous females
2. High population density resulted in highest proportion of polygamous males
3. Males were found to be more polygamous in habitats that gave them more choice
B. Their characterization of the mating system does not include unsuccessful mating attempts
1. It is possible that some offspring were undetected, confounding the data
2. Lack of offspring data underestimates the social mating partners in both sexes
C. Researchers are unclear in results section regarding the individual significance of variables/hypotheses in mating system selection.
Test Questions
#1. Which of the following is NOT a mating system?
a) Polygamy b) Monogamy c) Promiscuity d) None of the above

#2. Which of the following was NOT mentioned in the Dusky-footed Woodrat experiment as a factor in influencing the mating results?
a) Distance b) Operational Sex Ratio c) Fur Color d) Density
#3. What species is a Neotoma fuscipes?
a) Parasite b) Bird c) Spider d) Rat
True or False
#4. Polyandry is when a male mates with two or more females
#5. The operational sex ratio (OSR) is expressed as the proportion of adult males in the adult population in a given year and habitat.
#6. Distance only had a small effect on the woodrats mating.
Answer Key
1. D. None of the above
2. C. Fur Color
3. D. Rat
4. False
5. True
6. True