Hello readers! As promised, I’m devoting this week’s blog post to describing my primary research project, identifying and phylogenetically categorizing cryptic ribbon worms from Panama. It’s been an incredible experience to study ribbon worms with renowned expert, Svetlana Maslakova, and I hope that this week’s blog post (and included videos) will inspire you to join me in my new-found fascination with these “pythons of the sea!”
So… what are ribbon worms? Ribbon worms (nemerteans) are a highly-diverse phylum of marine-dwelling, unsegmented worms characterized by their proboscis, an oral appendage used to capture and stun prey (check out this video of a ribbon worm with a branching probisis: https://youtu.be/_keb7YpmAls). Ribbon worms range in length from 2 millimeters (genus Carcinomertes) to over a 100 feet (Lineus longissimus), most have planktonic larval stages and some undergo “catastrophic metamorphosis,” where the juvenile emerges from and subsequently consumes its larval body (and you thought puberty was rough?!). Check out Svetlana’s video of this incredible process: https://youtu.be/0Kt9BRcNB5w.
Recent estimates suggest that the majority of species on Earth remain undescribed. The fraction of undescribed species is largest in understudied taxa, such as ribbon worms. Some 1300 species are described, but the true diversity is likely several times that number. Studies of ribbon worms are further complicated by the presence of cryptic species, which are are morphologically-indistinguishable but identifiable as separate species via DNA-barcoding (comparisons of select genes). Cryptic species pose a challenge to conservation efforts because while visually similar, cryptic species may have different ecological roles and thus require different management strategies. Cryptic species also pose a challenge to biodiversity studies, because a population count for an endangered species may in fact describe multiple cryptic species (meaning there are more endangered species, with lower population numbers). DNA barcoding has been indispensable for the discovery and characterization of cryptic species, and I will be utilizing such methods for my research.
The putative cryptic species complex I’m researching was discovered by Svetlana and her graduate student Nicole Moss during a 2016 expedition to Bocas del Toro, Panama. On site, ribbon worm specimens were observed, photographed, and had tissue removed for DNA extraction (check out Svetlana’s video on how ribbon worms are collected from their environment: https://youtu.be/CX-C-vdEK0Y); during this process, the researchers observed subtle color variation between individuals of what looked like a single species, indicating the potential for a cryptic species complex (see pictures below). Preliminary DNA-sequencing efforts confirmed that this species may comprise several cryptic closely related species.
My research seeks to determine whether or not these individuals belong to separate species (and how many), and my work begins with the extracted DNA. Currently, I am PCR-amplifying fragments of two mitochondrial genes: Cytochrome Oxidase Subunit I and 16S rDNA from the DNA samples extracted from six individuals. Next week I plan to send my purified PCR products to a sequencing company. Once I’ve received the nucleotide sequences, I will build phylogenetic trees and calculate sequence divergence between individuals. I feel as though I am methodically solving a mystery through my research here, and it is truly thrilling! Equally thrilling is the knowledge that my research has the potential to serve as a resource for future conservation or biodiversity studies in Bocas del Toro, Panama.
There are more fascinating aspects of ribbon worms than I can possibly cover in one blog post, but I hope I’ve inspired you to learn more about this underappreciated phylum. Please comment below if you have questions, and check out Svetlana’s website for further information http://pages.uoregon.edu/svetlana/iWeb/Home/Nemerteans.html.
“Instructions for living a life./ Pay attention./ Be astonished./ Tell about it.” (Mary Oliver)