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Parental care is critical for offspring survival in many species. However, parental behaviors have been lost in roughly 1% of avian species known as the obligate brood parasites. To shed light on molecular and neurobiological mechanisms mediating brood parasitic behavior, we compared brain gene expression patterns between two brood parasitic species and one closely related non-parasitic Icterid (blackbird) species. Our analyses focused on gene expression changes specifically in the preoptic area (POA), a brain region known to play a critical role in parental behavior across vertebrates. Using comparative transcriptomic approaches, we identified gene expression patterns associated with brood parasitism. We evaluated three non-mutually exclusive alternatives for the evolution of brood parasitism: (1) retention of juvenile-like (neotenic) gene expression, (2) reduced expression of maternal care-related genes in the POA, and/or (3) increased expression of genes inhibiting maternal care. We find evidence for neotenic expression patterns in both species of parasitic cowbirds as compared to maternal, non-parasites. In addition, we observed differential expression in a number of genes with previously established roles in mediating maternal care. Together, these results provide the first insight into transcriptomic and genetic mechanisms underlying the loss of maternal behavior in avian brood parasites., (Copyright © 2019 Lynch et al.)

Over the last decade, tremendous progress has been made toward a comparative understanding of gene regulatory evolution. However, we know little about how gene regulation evolves in birds, and how divergent genomes interact in their hybrids. Because of the unique features of birds - female heterogamety, a highly conserved karyotype, and the slow evolution of reproductive incompatibilities - an understanding of regulatory evolution in birds is critical to a comprehensive understanding of regulatory evolution and its implications for speciation. Using a novel complement of analyses of replicated RNA-seq libraries, we demonstrate abundant divergence in brain gene expression between zebra finch (Taeniopygia guttata) subspecies. By comparing parental populations and their F1 hybrids, we also show that gene misexpression is relatively rare among brain-expressed transcripts in male birds. If this pattern is consistent across tissues and sexes, it may partially explain the slow buildup of postzygotic reproductive isolation observed in birds relative to other taxa. Although we expected that the action of genetic drift on the island-dwelling zebra finch subspecies would be manifested in a higher rate of trans regulatory divergence, we found that most divergence was in cis regulation, following a pattern commonly observed in other taxa. Thus, our study highlights both unique and shared features of avian regulatory evolution., (Copyright © 2016 Davidson and Balakrishnan.)