Figure 1.
(A) Sample thermograph from Experiment 1, showing 2 male (top and left) and 2 female (bottom and right) pups during cold challenge. (B–C) Sample thermographs of litters during cold challenge in Experiment 2. In (C) the zones used for measuring interscapular (D) and rump (E) temperatures (TIS and Trump, respectively) are shown for a pup that has separated from its huddle.
Figure 2.
Thermal measurements for Experiment 1.
Average temperatures for interscapular (TIS) and rump (Trump) regions ± SEM for male (blue lines) and female (red/pink lines) PND8 mouse pups.
Table 1.
Thermal Measures in Experiment 1 by Sex.
Figure 3.
A depiction of the system used for scoring contact behavior, adapted from that employed by Sokoloff and Blumberg [28]. Each pup in the litter was scored each minute for how many males (blue pups) and females (pink pups) they were in contact with, excluding contacts via tails and outstretched paws. Each combination of contacts was assigned a unique identifier or “contactogon”. For example, 0 M 2 F designates contact with zero males and two females. Contactogons possible for only a single sex (e.g., 3 M 0 F) are not shown, and were collapsed into a single category for the purposes of statistical analysis.
Figure 4.
Thermal measurements for Experiment 2.
Average temperatures for interscapular (TIS) and rump (Trump) regions ± SEM for male (blue lines) and female (red/pink lines) PND8 mouse pups.
Table 2.
Consistency of Sex Differences in Thermal and Contact Measures in Experiment 2.
Figure 5.
Contactogon distributions for warm and cool phases.
Distribution of contactogons (contact types) during the warm and cool phases of Experiment 2 (upper and lower panels, respectively). Values on the y-axis indicate total number of occurrences of each contactogon observed and expected by chance for males and females during the 50 minute trial. As can be seen, the distribution is skewed leftward, to more dispersed contactogons during the warm phase (which did not differ significantly from the chance distribution; G = 6.3, p = .705), and rightward, toward greater amounts of contact during the cool phase (which differed significantly from the distribution expected by chance; G = 39.7, p<.00001). Asterisks indicate significant deviation from chance responding in specific contactogons using Fisher’s exact tests (p<.005).
Figure 6.
Contact time series for warm and cool phases.
Average number of contacts over time ± SEM, by (A) sex, (B) type (opposite- vs. same-sex), and (C) sub-type (male-male vs. female-female). Values in (B) are corrected for the fact that opposite-sex are always slightly more likely than same-sex contacts in a 2∶3 ratio (opposite-sex contacts x.4; same-sex contacts x.6). Asterisks indicate a systematic difference (i.e. a non-random distribution of differences) between the two series using a Sign test (p<.005).
Figure 7.
Correlation between relative TIS and contact.
Linear regressions, coefficients of determination (R2), and p-values for Pearson product moment correlations on TIS relative to huddlemates (TISrel) and (a) total contacts, (b) contacts with females, and (c) contacts with males, during the warm and cool phases of Experiment 2 (left and right, respectively). Asterisks indicate significant correlation, using a criterion of α = .05/6 = 0083. As can be seen, there was no relationship between TISrel and contact during the warm phase, and a significant correlation between TISrel and both total contacts and contacts with females, but not contacts with males, during the cool phase.
Figure 8.
Granger (causal) analyses of relative TIS and contact during cold challenge.
The results of Granger analyses on relative TIS (TISrel) and contact with males and females. Asterisks indicate significant Granger causality, evaluated at α = .05/6 = .0083. Non-significant results (p<.05) are also shown to depict trends in the data. Arrows indicate that a change in one variable at time tn predicts a change in another variable at tn+lag. For example, in all but the Female Lag 0 models, TISrel is a stronger predictor of contacts with females than the reverse. Arrows in both directions indicate a feedback relationship between the two variables [65]; for example, our results indicate negative feedback between female TISrel and female contacts with males and positive feedback between the male TISrel and male contacts with females. The coloration of arrows indicates significant lagged Pearson product moment correlations between the two variables (p<.001), with positive and negative correlations indicated by green and red, respectively. Tests between TISrel and total contacts were run, but are not shown given that none were statistically significant. Models for Lag 3 were constructed but are not shown. For females, the model was null (no significant Granger causality detected), whereas for males the only significant effect was that male TISrel Granger caused male contacts with males (F = 4.94, p<.003).
Figure 9.
Granger (causal) analyses of relative TIS and contact during the warm phase.
The results of Granger analyses on relative TIS (TISrel) and contact with males and females. Asterisks indicate significant Granger causality, evaluated at α = .05/6 = .0083. Non-significant results (p<.05) are also shown to depict trends in the data. The coloration of arrows indicates significant lagged Pearson product moment correlations between the two variables (p<.05), with positive and negative correlations indicated by green and red, respectively. Tests between TISrel and total contacts were run, but are not shown.