Comparing perineuronal nets and parvalbumin development between blackbird species with differences in early developmental song exposure

Abstract

Brood parasitic songbirds are a natural system in which developing birds are isolated from species-typical song and therefore present a unique opportunity to compare neural plasticity in song learners raised with and without conspecific tutors. We compared perineuronal nets (PNN) and parvalbumin (PV) in song control nuclei in juveniles and adults of two closely related Icterid species (i.e. blackbirds): brown-headed cowbirds (Molothrus ater; brood parasite) and red-winged blackbirds (Agelaius phoeniceus; non-parasite). The number of PV cells per nucleus was significantly higher in adults compared to juveniles in HVC and RA, whereas no significant species difference appeared in any region of interest. The PNN per nuclei was significantly higher in adults compared to juveniles in HVC, RA and Area X but only RA exhibited a significant difference between species. PV cells surrounded by PNN (PV+PNN) also exhibited age-related differences in HVC, RA and Area X but RA was the only region in which PV+PNN exhibited significant species differences. Furthermore, a significant interaction existed in RA between age and species with respect to PNN and PV+PNN, revealing RA as a region displaying differing plasticity patterns across age and species. Additional comparisons of PNN and PV between adult male and female cowbirds revealed that males have greater numbers of all three measures in RA compared to females. Species-, sex- and age-related differences in RA suggest species differences in neural plasticity are related to differences in song production rather than sensitivity to song learning despite stark contrast in early exposure to conspecific male tutors.