Inseminated Female Mice Investigate Rather Than Avoid Novel Males That Disrupt Pregnancy, but Sires

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Inseminated Female Mice Investigate Rather Than
Avoid Novel Males That Disrupt Pregnancy, but
Sires Protect Pregnancy

• Denys deCantanzaro and Tasleem Murji
• McMaster University

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The Bruce Effect

• A form pregnancy disruption in mammals in which
  exposure of a female to an unknown male results
  in pre or postimplantation failure

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Question

• Are sires capable of protecting pregnancy when
  the sire is confined and not capable of
  intervening in females interactions with novel
  males ?

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Purpose

• To observe the behavior of inseminated female
  mice in the presence of male mice to determine
  whether there are indications that the females
  recognizes the sire and/or avoids novel males
  that could terminate pregnancy

They did this because previous report stated that
inseminated females avoid the urine of novel
males, but the behavior toward novel males had
not been fully studied
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Experiment 2
Choose to start with experiment 2 because
experiment 1 was performed just to simply
replicate and the Bruce effect

• Whether inseminated females recognize and
  affiliate with the sires of their pregnancies and
  avoid novel males that could jeopardize pregnancy

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Method
Females were housed alone with males in the CF1
strain. Checked 3x daily for the presence of a
copulatory plug. When plug was detected the
female was designated as a subject and separated
from the sire and housed individually until day 3
when testing began

• Females where given a choice between
• (1) The Sire CF1
• (2) A Similar CF1 Male
• (3) Novel Male from a Heterogeneous Strain

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• Four Arm Radial Maze

The maze consisted of a central octagon with four
symmetrically located openings. At the end of
each arm was a standard mouse cage. In the four
cages at the ends of the arm were no animal
(control), the sire, a novel male, and the novel
male from the heterogeneous strain. Females were
placed in the central area, given 5 minutes to
adapt . - NEXT SLIDE -
Novel Male from Heterogeneous Strain
CF1 Male
No Animal
Sire
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• Females where observed for one hour by a trained
  observer
• Assisted by computerized event recorder
• Press key on entrance and exit from each specific
  arm
• Additional keys were pressed if there was
  physical contact

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Findings

• Inseminated females do not avoid novel males that
  put their pregnancies in jeopardy
• Suggests that they actually investigate these
  males more than the sire and other similar males

Time in the Heterogeneous male containing arm
exceeded time in the arm leading to the
sire. There was no significant difference between
time spent in novel or sire arm
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Experiment 3
In experiment one typical 5 day exposures were
used to disrupt pregnancy

• Arguable that 1-hour opportunities to investigate
  males might not reflect ongoing behavior in
  longer samples.
• Study was designed to provide observations of
  inseminated females behavior when animals had
  three days of contact.

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Method

• Females were inseminated as described in previous
  experiments.
• Females remained housed with the inseminating
  male until day 2 of pregnancy

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Apparatus was divided into four upper and lower
compartments by a wire-mesh grid. The upper
compartment was divided into 4 equal compartments
by plexiglass to prevent all interactions among
males. All males were given continuous access to
food and water. The lower compartment housed the
female which was separated into quadrants that
corresponded to those above One quadrant allowed
continuous access to food and water which
corresponded to the upper compartment that housed
no male.
Double-Decker Housing Apparatus
Males
Plexiglass
Female
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Observations
Time in contact with the male was characterized
as Female pointing head upward toward the male,
reaching up to grab the grid, or actually
climbing up on the grid, hanging upside down

• Occurred on day 3-5 of pregnancy
• Observations involved 15-min interval samples at
  1, 5, and 9 hours after commencement.
• Trained observer used a stopwatch and metronome
  for timing the locations of the female.
• Observer recorded time in contact with the male
• Observer also recorded where the nest was built

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Findings

• Time spent in each lower quadrant by inseminated
  females did not show any significant difference

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Findings

• Time interval interacting with each male showed
  no significant difference

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Results

• Females nested under the sire than in any other
  locations

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Overall

• The experiment did not indicate any prevailing
  tendency for inseminated females to locate
  themselves near or affiliate with the sires as
  opposed to novel males in longer duration
  contacts than those observed in experiment 2

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Experiment 4

• Previously established that the presence of the
  sire with the inseminated female can diminish the
  Bruce effect.
• Present study was designed to replicate the
  effect and to determine the role of the
  inseminated females and sires behavior in this
  effect

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• Examined contacts between inseminated females and
  novel males when the sire was present or absent,
  and observed the behavior of the sire in this
  context.

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Conditions
Each female was housed in a double-decker
apparatus as previously described

• Control female housed alone in the lower
  compartment with no male above
• Sire Absent Female housed below 2 novel males
• Free-sire sire present with the female and free
  to move in the compartment
• Corralled-sire sire confined with mesh wire
  which allowed contact with the female but not the
  novel males

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Method

• During 15 min intervals on days 3-6 the number of
  times the female made contact with either of the
  novel males.
• Contact defined as raising head toward males,
  reaching up with forearms to grab the grid, or
  climbing and hanging upside down on the grid
• Observations of contacts between the free sires
  and the novel males were recorded

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Findings

• Contact between the inseminated female and novel
  males were fewer when the sire was present,
  regardless of whether the sire was free or
  corralled

Figure (7) shows the number of contacts made
between females and novel males in the
sire-absent, free-sire, and corralled sire
condition
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• Percentage of parturient females was reduced in
  the sire absent control relative to the control.
• The presence of the sire of the sire mitigated
  this effect to a large degree.. Even when the
  sire was corralled

Figure (8) shows pregnancy outcome for all
conditions
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Findings

• Unanticipated intense aggression was observed in
  all of the free-sire cases. Sires were observed
  making frequent contacts with and inflicting
  bites upon novel males
• Pregnancy outcome was identical in the female in
  the free-sire condition before and after the
  induction of the double mesh

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Findings
As previously mentioned, the Free sires are
aggressive toward the novel males Although such
behaviors by sires would serve to reduce
interactions between females and novel males, the
effects seen with the confined sires suggest that
the aggressive behavior is not necessary for
reduction of females interactions with novel
males and the mitigation of pregnancy disruption

• Inseminated females spend significantly less time
  interacting with novel males and show
  substantially reduced pregnancy disruption when
  the sire is immediately present.
• Effects occur when both the sire can move freely
  in the same compartment and when the sire is
  confined and less capable of intervening in
  females interactions with novel males

Answer to the Question
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Overall Findings
Which was clearly demonstrated in the 1hour
choice situation in experiment 2, in which
females actually approached novel male
significantly more And that interactions with
males and nesting sites under males were not
consistent and appeared random

• Inseminated females do not avoid novel makes that
  can terminate pregnancy
• Data are not entirely in accord with published
  reports that females show olfactory preferences
  during gestation, avoiding the urine of novel
  mice