
Heterochronic shifts in gene expression timing and morph-specific gene expression contribute similarly to developmental differences between two larval morphs of the marine annelid Streblospio benedicti, with the regulatory architecture being predominantly trans-acting.


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New developmental programs can evolve through adaptive changes to gene expression. The annelid Streblospio benedicti has a developmental dimorphism, which provides a unique intraspecific framework for understanding the earliest genetic changes that take place during developmental divergence. Using comparative RNAseq through ontogeny, we find that only a small proportion of genes are differentially expressed at any time, despite major differences in larval development and life-history. These genes shift expression profiles across morphs by either turning off any expression in one morph or changing the timing or amount of gene expression. We directly connect the contributions of these mechanisms to differences in developmental processes. We examine F1 offspring— using reciprocal crosses— to determine maternal mRNA inheritance and the regulatory architecture of gene expression. These results highlight the importance of both novel gene expression and heterochronic shifts in developmental evolution, as well as the trans -acting regulatory factors in initiating divergence.

### Competing Interest Statement

The authors have declared no competing interest.

The role of heterochronic gene expression and regulatory architecture in early developmental divergence

comparative-transcriptomics-reveals-heterochronic-and-morph-specific-gene-expression-underlying-developmental-divergence-in-a-marine-annelid


Comparative Transcriptomics Reveals Heterochronic and Morph-Specific Gene Expression Underlying Developmental Divergence in a Marine Annelid
