Extended Data Figure 2-1
Hybrids exhibit reduced anxiety-like behavior, improved learning, and improved memory. A, HYB explore the open arms of an elevated plus maze more than C57 mice, particularly at an older age, indicating reduced anxiety-like behavior. Here and in subsequent panels, Top and center, Every box plot shows median and interquartile range (IQR), whiskers extend for 1.5 times the IQR in every direction, and a “+” sign indicates an outlier. Here and in Eb, Ec, P-values indicated by text are for a one-way Kruskal–Wallis test; lined *p < 0.05, **p < 0.01, ***p < 0.001, Kruskal–Wallis test, corrected for multiple comparisons; *p < 0.05, **p < 0.01, ***p < 0.001, Wilcoxon’s signed-rank test, comparing indices to chance level. Bottom, Aging index. Bars and errors show mean and SEM, respectively; ***p < 0.001, bootstrap test, compared to a no-change null (index of zero). B, Depressive-like behavior is not consistently different among HYB and C57 mice, and is reduced among older FVB mice. C, Open field exploration increases at an older age for all strains. Top, In the three-month-old age group, HYB were more active in the open field than FVB; **p < 0.01, Kruskal–Wallis test, corrected for multiple comparisons. Center, In the nine-month-old group, C57 were more active than FVB. Bottom, Mice of all three strains exhibited increased activity upon aging, evident as above-zero aging indices; **p < 0.01, ***p < 0.001, bootstrap test. D, Learning on the MWM task is improved for HYB compared to C57, and is maintained at older age. a, Mean (and SEM) latency to finding the platform (limited to 60 s). Here and in c, **/*** next to the text indicate p < 0.01/p < 0.001 in a two-way, strain by day, Kruskal–Wallis test; */**/*** at right indicate p < 0.05/p < 0.01/p < 0.001, one-way Kruskal–Wallis test, measuring the within-strain, across-day effect. In both age groups. only HYB showed consistent across-day learning. Bottom, Aging indices, averaged over all learning days. Learning performance of C57 deteriorates at an older age. b, Day-by-day “C57 indices” (Fig. 1D), measuring the change in latency to the platform between FVB (blue) or HYB (green) and C57 mice. Bands show mean and SEM; *p < 0.05, **p < 0.01, ***p < 0.001, bootstrap test. Insets, Mean (and SEM) C57 indices, averaged over all learning days; p-values, geometric mean over all learning days. c, C57 and HYB travel progressively shorter distances over training days, indicating learning. All conventions are the same as in a. E, On the probe day of the MWM task, HYB spend the longest time in and the shortest latency to the target quadrant. a, Time spent in every quadrant; *p < 0.05, **p < 0.01, ***p < 0.001, Wilcoxon’s signed-rank test, comparing time in each quadrant to chance level (0.25 of the total time). b, Time spent in the target quadrant, for three-month-old (top) and nine-month-old (center) mice. Here and in c, Horizontal dashed lines indicate chance level of 0.25, expected for random exploration; other conventions are the same as in A. Compared to C57 or FVB, nine-month-old HYB spend a larger fraction of time in the target quadrant. Bottom, Aging indices. Compared to younger HYB, older HYB spend more time in the target quadrant. c, In both age groups, the fraction of visits to the target quadrant is highest for HYB. d, Latency to the platform location, measured during the probe day, is the shortest for HYB. Download Figure 2-1, EPS file.