Tissue-specific expression profiles and positive selection analysis in the tree swallow (Tachycineta bicolor) using a...

Area of Science:

• * Avian biology
• * Genomics
• * Evolutionary biology

Background:

• * Tree swallows (Tachycineta bicolor) are a vital model organism in North American ecological and physiological research.
• * Limited transcriptomic resources have previously hindered in-depth molecular studies of this species.
• * Advancing genomic tools is crucial for understanding adaptation and endocrine function in wild populations.

Purpose of the Study:

• * To generate a comprehensive de novo transcriptome for the tree swallow from six distinct tissues.
• * To identify genes under positive selection and investigate tissue-specific expression of genes related to sex steroidogenesis.
• * To provide a valuable genomic resource for diverse biological disciplines studying tree swallows.

Main Methods:

• * RNA sequencing was performed on six tissues (brain, blood, ovary, spleen, liver, muscle) from breeding female tree swallows.
• * A de novo transcriptome assembly yielded 207,739 transcripts, aligned to 14,717 protein-coding genes.
• * Analyses included identifying single-copy orthologs under positive selection and characterizing tissue-specific gene expression patterns.

Main Results:

• * A high-confidence reference transcriptome for tree swallows was successfully generated.
• * 46 genes under positive selection were identified, suggesting adaptive evolution in the tree swallow lineage.
• * Tissue-specific expression analysis revealed ovary-limited steroid synthesis and widespread steroid-binding gene distribution.

Conclusions:

• * The generated tree swallow transcriptome is a significant resource for evolutionary and endocrinology research.
• * Identified genes under selection offer insights into species-specific adaptations.
• * Tissue-specific hormone processing highlights complex regulation of reproductive traits and phenotypic variation in female birds.