Striking variation in the sex ratio of pups born to mice according to whether maternal diet is high

1
Striking variation in the sex ratio of pups born
to mice according to whether maternal diet is
high in fat or carbohydrate.

Background In Female mammals, if you vary the
diet, does that affect the gender distribution of
the offspring? There has often been little known
about gender distribution in animals, just
recently in the late ninety's it was discovered
in some birds and other insects that in a
laboratory situation, if the type of diet and
amount of food available is monitored and limited
that the gender of the offspring can be
pre-determined. This was successfully done on
birds and insects in the lab and is easily
repeatable with the correct species, however, it
is unknown whether this holds true for mammals.
In mammals we have commonly learned that Sex is
determined chromosomally with the XY system, in
the animals being studied it is determined by
environmental factors if the mother is able to
receive high amounts of nutrients prior and
during her maternity.
Hypothesis That by controlling the diet of
mammals (specifically mice) that you can increase
the chance of a male or female dominated litter.
Results The two test groups varied in only one
main respect, that of the diet, the VHF group was
given carbohydrates and triglyceride in
respective amounts, where the LH group was
deprived of these and was given lard as a
supplement of the carbohydrate. The VHF group
was significantly heavier. However over the 4
rounds of breeding the VHF group produced
predominantly male pups where the LH group
produced predominantly female pups (Plt0.0001).
The control group (Purina) had litters of close
to equal numbers of males and females. The
question that is left is that of was it the diet
change or the increased weight that skewed the
litter gender. This was approached by comparing
comparable body masses of two pregnant female
mice of each group and testing the ratio of their
litters. It showed that body mass is not the
variable and it is indeed the nutrient
variability in the diet that controls sex ratio.
Fig. 1.   Changes in mean body weight of female
mice on the VHF and LF diets. The information is
from one of the two studies from which the data
in Table 2 were obtained. Two groups of eight
mice were initially introduced to the diets when
they were 30 days of age and maintained on the
VHF (upper line) and LF (lower line) diets for
40 wk, during which time the mice delivered four
sets of pups a, male introduced b, mean day of
delivery , first parity 1 , second parity
, third parity , fourth parity. The graph
illustrates the rapid increase in body mass
accompanying pregnancy, as well as the fall in
weight after delivery.. The results from the
duplicate study were essentially
indistinguishable from the one Described here.
(Science, Rosenfeld)
Fig. 2.   Frequency distribution of sex ratio
(fraction males) within litters at parity
2, 3, and 4 for the VHF and LF dietary groups.
Each of the bars on that graph represents the
number of litters with a sex ratio within the
range 0.05 of the number on the x axis i.e., a
value of 0.1 means there were no VHF litters with
sex ratio between 0.05 and 0.15, whereas for LF
there were two. Similarly, there were eight
litters with a ratio between 0.75 and 0.85 on the
VHF diet and one on the LF diet. Two VHF litters
were entirely male and one LF litter was entirely
female. (Science, Rosenfeld)
Discussion These results clearly show that diet
and nutrient composition clearly play a role, if
not a large role in determination of sex in lower
mammals. These findings also help confirm what
had previously been found in Birds and insects,
however it has only been shown in lower mammals.
Further research should be done to find impacts
on higher mammals and possibly some K type
strategists as opposed to R type, and eventually
into primates.
Picture of NIH Swiss Mouse
Methods In this experiment to determine sex
ratio in mice due to diet difference, 32 mice
were used, then divided up randomly into two
groups, each with a sample size of 16. There was
also a control group with a sample size of 8.
The mice that were used were NIH Swiss mice (as
pictured above). Each group was selected at
random, and then fed either the VHF or LF diet
until the end of the study the control group was
fed Purina food mix. The females were housed in
pairs and introduced to the stud male at 10, 20,
28, and 40 weeks of age. After there second week
of pregnancy the females were then housed alone
until birth. Three weeks after delivery the pups
were removed from their homes. Each mouse was
weighted every other day through the course of
the study. Each pup was gender assessed the
second day after birth by measuring androgenital
distance (Rugh, 1994), no errors were noted when
anatomical gender was assessed. The data was used
to determine if the content of the diet had a
profound affect on the gender makeup of the
litter.
Lit. Cited 2001 Rosenfeld, C.S. Striking
Variation in sex ratio in pups born to mice.
April 15 Science. 1994 Rugh,
R. The Mouse Its Reproduction and Development
(Oxford Univ. Press, New York).
Cheryl S. Rosenfeld, Kristie M. Grimm. Presented
by Thomas Welter