Shape Matters

Being able to accurately identify species is crucial to understanding biodiversity in the deep sea, that is one of the reasons taxonomy is so important. But classifying deep-sea organisms accurately can be difficult because some species look very similar despite being genetically distinct. This is a big issue for a group of deep-sea isopods belonging to the family Macrostylidae, which exhibit striking morphological uniformity. So how do Isopodologists (people who study isopods) distinguish between different species? For this family of isopods, it involves taking a closer look at the isopod’s booty (okay, pleotelson to be scientifically accurate)!

Senckenberg PhD student, Anchita Casaubon, has been testing a method called geometric morphometrics to study the shapes of body parts in 41 specimens of five different Macrostylid species from Icelandic waters. Macrostylid isopods are especially interesting because they exhibit varying degrees of sexual dimorphism (the males and females look different), with it being so extreme in some, that the males and females have been classified as different species! Geometric morphometrics is an approach that combines statistics with two- and three-dimensional coordinates to identify subtle shape differences that are hard to see with the naked eye. Anchita focused on a specific body part called the pleotelson – the last segment on the isopod’s body – as the main feature to differentiate between species.

And what did Anchita find?

1. This method works!! – Geometric morphometrics successfully distinguished between species that looked very similar, showing clear differences in the shape of their pleotelsons.
2. Macrostylid Isopods have important shape differences – Even species previously thought to be the same (like M. spinifera and M. aff. spinifera) were shown to have distinct shapes, suggesting they might actually be different species.
3. This method could be used for other deep-sea animals – The method revealed patterns of shape variation that traditional techniques missed, making it a promising approach for identifying these deep-sea species.

This study is the first to use geometric morphometrics on deep-sea isopods. It shows that the technique can improve species identification in difficult cases and may help identify hidden species. Additional research using more specimens, more species, and more body parts is needed to uncover the true potential of this method to help classify these hard to distinguish deep-sea animals.

Better tools for identifying species can help us better understand biodiversity in the deep sea, an under-studied but crucial ecosystem. This approach could also aid conservation efforts by identifying species more accurately. Innovative taxonomic research, like Anchita’s, brings us closer to understanding what lives in our oceans and the value a tiny deep-sea isopod has in our global ecosystem.

Learn more about Anchita’s research in the recently published paper, Shape matters: investigating the utility of geometric morphometric techniques in the deep-sea isopod family Macrostylidae (Isopoda: Asellota).

Check out some images of Anchita’s research below: