Genome Size Dynamics in Marine Ribbon Worms (Nemertea, Spiralia)

Abstract

Nemertea is a phylum consisting of 1300 mostly marine species. Nemertea is distinguished by an eversible muscular proboscis, and most of the species are venomous. Genomic resources for this phylum are scarce despite their value in understanding biodiversity. Here, we present genome size estimates of Nemertea based on flow cytometry and their relationship to different morphological and developmental traits. Ancestral genome size estimations were done across the nemertean phylogeny. The results increase the available genome size estimates for Nemertea three-fold. Our analyses show that Nemertea has a narrow genome size range (0.43–3.89 pg) compared to other phyla in Lophotrochozoa. A relationship between genome size and evolutionary rate, developmental modes, and habitat was found. Trait analyses show that the highest evolutionary rate of genome size is found in upper intertidal, viviparous species with direct development. Despite previous findings, body size in nemerteans was not correlated with genome size. A relatively small genome (1.18 pg) is assumed for the most recent common ancestor of all extant nemerteans. The results provide an important basis for future studies in nemertean genomics, which will be instrumental to understanding the evolution of this enigmatic and often neglected phylum.

First Chromosome-Level Genome Assembly of a Ribbon Worm from the Hoplonemertea Clade, Emplectonema gracile, and Its Structural Annotation

“…With a genome size estimate ranging from 153.7 to 161.8 Mb, the E. gracile genome is shorter than the size of 210 ± 5 Mb previously estimated based on flow cytometry ( Paule et al 2021 ). Moreover, the E. gracile genome is substantially smaller than those of the species previously sequenced: L. longissimus (391.2 Mb in 19 putative chromosomes; Kwiatkowski et al 2021 ), C. simula (427.7 Mb in 262,498 scaffolds), C. spiralis (650.6 Mb in 427,796 scaffolds), N. geniculatus (558.6 Mb in 11,108 scaffolds; Luo et al 2018 ), T. punctatus (367.7 Mb in 230,562 scaffolds), and T. ruber (312.5 Mb in 205,164 scaffolds).…”

First chromosome-level genome assembly of a ribbon worm from the Hoplonemertea clade,Emplectonema gracile, and its structural annotation

“…With values ranging between 157.9 and 161.8 Mbp, the Emplectonema gracile genome is shorter than the haploid size of 210 ± 5 Mbp previously estimated based on flow cytometry (Paule et al 2021). Moreover, the E. gracile genome is substantially smaller than those of the two pilidiophoran species previously sequenced: Lineus longissimus (391 Mbp in 15 putative chromosomes distributed over 109 contigs) (Kwiatkowski et al 2021), and Notospermus geniculatus (859 Mbp distributed over 60,228 contigs) (Luo et al 2018).…”

Ribbon worms (phylum Nemertea) from Bodega Bay, California: A largely undescribed diversity

“…Distribution. Bodega Bay, CA, USA (this study); Coquimbo, Chile ( Sundberg et al 2016 ); Camarones Bay, Argentina; Vilan Cape, Spain (Fernández-Álvarez et al, unpublished); Roscoff, France ( Sagorny et al 2019 ; Paule et al 2021 ).…”