FRAGILE X MICE SHOW CONTEXT-DEPENDENT DEFICITS IN VOCAL BEHAVIOUR DURING OPPOSITE SEX INTERACTION

Fragile X syndrome (FXS), the most common genetic cause of intellectual disability and autism spectrum disorder, is associated with auditory hypersensitivity and communication deficits. Vocal behavior in Fmr1 knockout (KO) mice, a widely used model of FXS, has been extensively studied. Previous work has reported only small and often inconsistent differences in vocalizations during same-sex or opposite-sex interactions.
Here, we investigated whether a more complex interaction context would better reveal vocalization deficits relevant to FXS. We recorded ultrasonic vocalizations (USVs) from male–female pairs of Fmr1 KO mice (FVB.129P2-Pde6b+Tyrc-ch Fmr1tm1Cgr/J) and wildtype (WT) littermates under two conditions: free interaction and separation by a translucent wall. The wall contained holes allowing limited snout contact but likely preventing whisker interactions. Vocalizations were semi-automatically detected and analyzed using DeepSqueak.
Wall-separated WT and Fmr1 KO pairs, most likely driven by males, produced a large number of traditional USVs, comparable to freely interacting pairs. In contrast, wall-separated Fmr1 KO mice produced very few traditional USVs, whereas WT pairs produced USVs similar to those observed during free interaction. Separated Fmr1 KO mice predominantly emitted lower-frequency vocalizations (10–40 kHz), similar to those reported in wall-separated same-sex interactions (Breslav et al., 2026). These vocalizations were shorter in duration and had narrower bandwidths. Wall-separated pairs also displayed greater genotype-dependent differences in call repertoire and bout structure than freely interacting mice.
This highlights the importance of behavioral context when studying communication disorders and suggests that more complex interaction paradigms may better capture clinically relevant deficits in FXS.