Is the Ross Sea ruled by males?

As the days go by, our EBS samples keep piling up. Sorting them is so exciting – especially for me, since it means getting my hands on some Tanaids! Every now and then, we spot flashes of orange (or pink… or brown… honestly, the lab is in constant disagreement over what color this actually is). These little guys belong to the genus Nototanais, and what makes them particularly interesting is their sexual dimorphism!
 
Before we dive into that, let’s go over what a typical tanaid looks like (see picture below!). Their body consists of a cephalothorax, pereon, and pleon. Cephalothorax is covered by a calcified carapace. Like other crustaceans, tanaids have two pairs of antennae, mandibles, and two pairs of maxillae. The cephalothorax also has maxillipeds and a pair of large grasping appendages (chelipeds) that end in claw-like pincers (kind of like tiny boxing gloves).  
 
The pereon consists of six segments, called pereonites, each with a pair of legs (pereopods). The abdomen is made up of six pleonites, with the last one fused to the telson, forming the pleotelson. The abdominal appendages include five pairs of pleopods and a final pair of uropods. 
 
Now, back to that dimorphism… Female Nototanais have a slim, streamlined body with proportionally normal-sized chelipeds. Males, on the other hand, tend to be slightly larger, but their real characteristic feature is their massive chelipeds, which vary in shape depending on the species. Tanaidacea researchers believe these enlarged pincers help males hold onto multiple females, especially during the breeding season.  
 
What’s surprising is just how many males we’re finding in our samples. Very often, they outnumber the females in our samples. Which raises the question… is the Ross Sea ruled by males?
 
Kamila Głuchowska
University of Łódź