Male hairy ‘Hoff crab’ has oversized claws to compete for females

New research has revealed that a hairy crustacean – dubbed “The Hoff Crab” when it was discovered in 2010 – is the first species in its family to show different claw characteristics between sexes.

The creature, whose official name is Kiwa tyleri, is a type of deep-sea crustacean which lives in vast communities around hot vents on the seafloor in Antarctica. Its many hairs host bacteria that the animal harvests to sustain itself. 

The Hoff Crab is part of the Kiwaidae family, first discovered in 2005, which is made up of animals commonly referred to as “yeti crabs”, after the legendary yeti because of their bristly appearance. 

Scientists from the University of Portsmouth and University of Southampton have discovered a characteristic of Hoff crabs that is a first for the yeti family. 135 specimens from the East Scotia Ridge in the Scotia Sea were examined, and the team found the male Hoff crabs have oversized claws compared to females of similar size – indicative of faster claw growth rates throughout their lives. 

The study, published in PLOS One, says this marked difference likely suggests the larger claws are used for males to compete with each other for access to a mate, but it may also reflect females focusing energy resources on reproduction.

Lead author Dr Nicolai Roterman, a deep-sea ecologist from the University of Portsmouth’s School of the Environment and Life Sciences, said: “This is the first study to show claw sexual dimorphism in yeti crabs  – which live exclusively in harsh deep-sea environments like hydrothermal vents and methane seeps.

“Knowing that there’s a difference in size between the male and female claws helps us understand the behaviour and ecology of the yeti crab family – which we know little about because they are a fairly recent discovery, and their home is very difficult to reach.

“Physical differences between males and females is a common feature of decapod crustaceans which live in shallow water, and usually it’s because the male is forced to guard the mate, or females have to divert their growth energy for reproduction.”

The team also compared the Hoff crab with another yeti crab found in 2009 off Costa Rica, called Kiwa puravida. Unlike the Hoff crab, the Costa Rica yeti crab doesn’t show different claw characteristics depending on sex – known as sexual dimorphism – which suggests something interesting is going on. 

Dr Roterman added: “This could be because the Costa Rica yeti crabs may be using their claws – which are longer and hairier than those of the Hoff crab – primarily for food production rather than fighting, or perhaps there is some other factor at play that we have yet to discover. 

“We don’t yet know if these claw sex differences are the norm for the yeti crab family, or an exception. But the discovery provides a starting point for future research.”

The Hoff crab’s nickname – coined by Dr Roterman when it was first discovered – references the often bare-chested US actor David Hasselhoff because of its perfusion of hair-like structures, called setae, on their ‘chests’. Scientists’ interest in the species goes beyond its unusual appearance though. 

“Water temperatures around the Antarctic are normally around, or below zero Celsius, making living incredibly difficult for crab-like animals”, said Dr Roterman.  

“But the Hoff crab is able to survive by crowding around the hot hydrothermal vents and evolving in ways we’re only just beginning to understand.”

The vents are made up of volcanic rock systems that draw water through cracks in the seafloor, super-heat it, load it with dissolved metals and other chemicals, and then eject it back into the ocean.

The crab feeds by “farming” bacteria – known as chemosynthetic microbes – that are sustained by chemicals in the 380 degree water coming out of the hydrothermal vent chimneys. 

By climbing the sides of the chimney-like structures, the crabs are able to maximise bacteria growth, but risk cooking themselves or suffocating if they get too close to the super heated, de-oxygenated water coming out of the chimney.

Dr Roterman explained the importance in studying these deep sea creatures: “Understanding the physiology, behaviour, ecology and evolution of animals adapted to the most extreme conditions give us insights into what evolution is capable of, and therefore how life is likely to adapt to a warming planet and other natural and human-induced ecological stressors.”

ENDS

Notes to Editors

The paper, ‘Yeti Claws: Cheliped Sexual Dimorphism and Symmetry in 2 Deep-Sea Yeti Crabs (Kiwaidae)’, is available to view online here: www.journals.plos.org/plosone/article?id=10.1371/journal.pone.0314320

DOI: 10.1371/journal.pone.0314320

Photos and videos of the “Hoff Crab” can be downloaded here.

Full paper attached here.

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Robyn Montague, PR and Media Manager, tel: 07980419979 email: [email protected]

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