RNA-Seq reveals divergent gene expression between larvae with contrasting trophic modes in the poecilogonous polychaete Boccardia wellingtonensis

Álvaro Figueroa,Antonio Brante,Leyla Cárdenas

doi:10.1038/s41598-021-94646-y

Abstract

The polychaete Boccardia wellingtonensis is a poecilogonous species that produces different larval types. Females may lay Type I capsules, in which only planktotrophic larvae are present, or Type III capsules that contain planktotrophic and adelphophagic larvae as well as nurse eggs. While planktotrophic larvae do not feed during encapsulation, adelphophagic larvae develop by feeding on nurse eggs and on other larvae inside the capsules and hatch at the juvenile stage. Previous works have not found differences in the morphology between the two larval types; thus, the factors explaining contrasting feeding abilities in larvae of this species are still unknown. In this paper, we use a transcriptomic approach to study the cellular and genetic mechanisms underlying the different larval trophic modes of B. wellingtonensis. By using approximately 624 million high-quality reads, we assemble the de novo transcriptome with 133,314 contigs, coding 32,390 putative proteins. We identify 5221 genes that are up-regulated in larval stages compared to their expression in adult individuals. The genetic expression profile differed between larval trophic modes, with genes involved in lipid metabolism and chaetogenesis over expressed in planktotrophic larvae. In contrast, up-regulated genes in adelphophagic larvae were associated with DNA replication and mRNA synthesis.

Highlights

Marine invertebrates exhibit contrasting developmental modes that may affect the speciation, extinction, and connectivity of species[1]
The raw reads were subjected to a quality trim (Phred = 0.001), and adapters were removed, resulting in a total of 624,918,240 PE post-trim reads with an average of 85.04 bp (Supplementary File S1)
We assembled the first de novo transcriptome of the species B. wellingtonensis, a poecilogonous species, to characterize its genes and their expression profiles focused in the differentially expressed genes (DEGs) related to the different larval trophic modes

Summary

Introduction

Marine invertebrates exhibit contrasting developmental modes that may affect the speciation, extinction, and connectivity of species[1]. In species that encapsulate their offspring, the indirect developmental mode is characterized by embryos that develop partially inside capsules and hatch as planktotrophic larvae This type of larvae shows a set of morphological traits that allows them to swim and feed on plankton. In the poecilogonous polychaetes Boccardia wellingtonensis and Boccardia proboscidea, females lay both planktotrophic and adelphophagic larvae in the same clutch or capsule These larvae are morphologically similar but differ in their feeding capacities; while both larval types can swim and feed on plankton if they are released into the water, only adelphophagic larvae may feed on nurse eggs and other larvae inside the c apsules[10,11]. Exploration of these potential underlying mechanisms in B. wellingtonensis would improve the existing understanding of evolution and the diversity of developmental modes in marine invertebrates

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Results

Conclusion