Is that a testes or an iridescent stripe? A female squid's male-like true colors

Sep 05, 2013

During his time in Daniel Morse's lab at the University of California Santa Barbara, USA, PhD student Daniel DeMartini has seen many Doryteuthis opalescens squid pass through the lab's doors. These squid provide DeMartini with a steady supply of the iridocyte cells that are responsible for the squid's shimmering opal-like markings. Iridocytes are found in many cephalopods, but what makes those of D. opalescens so special is their ability to adapt and produce a rainbow of different colours from the same cell. Most iridocytes are found in patches across the squid's body but DeMartini recalls: 'We started to notice that some squid had bright iridescent rainbow stripes underneath their fins. Sometimes most of the squid in a batch would have them, sometimes none. After a while we started to realise the rainbow stripes were only seen in the females.' So after a few years of observing this, DeMartini decided to investigate this female-only trait further, publishing his results in The Journal of Experimental Biology.

Upon the 's arrival in the lab, DeMartini noted that on average, only half the females displayed colourful stripes, yet all were capable of producing them, as an hour after death all females had these vibrant markings adorning their bodies. When DeMartini examined the underlying tissue under a he found it was full of iridocytes jam packed with layer upon layer of reflectins (the proteins responsible for reflecting the light as colour). The sheer number of iridocytes each packed with a high number of reflectin layers results in stripes that are six times brighter than other patches of iridocytes.

Sandwiched between the two colourful stripes, DeMartini also noticed a large bright white area whose appearance coincided with the emergence of the iridescent streaks. When he delved a little deeper he found the underlying tissue was made up of leucophore cells. Like iridocytes, leucophores contain reflectin proteins, but instead of being arranged into layers, these light-reflecting proteins are packaged into rounded compartments throughout the cell. This alternative arrangement scatters light of all wavelengths, instead of reflecting just a single wavelength as colour, making the skin look white.

While leucophores are widespread in , this is the first time switchable leucophores have been identified in D. opalescens squid. What's more, these leucophores are predominantly made up of reflectin subtypes that have only ever been found in adaptive iridocytes before. In iridocytes, these adaptive reflectins contract and change their refractive properties in response to the neurotransmitter acetylcholine, allowing them to fine-tune colour of the reflected light. But are they also adaptive in a leucophores? Sure enough, when DeMartini treated the female squid with acetylcholine the white region became brighter. 'This discovery reveals a fundamental relationship between the switchable leucophores and the tunable colour-producing iridocytes, suggesting they share a mechanism at the molecular level', says DeMartini.

So what is the purpose of these markings in females? In short, DeMartini doesn't know, but he points out that the white stripe looks remarkably similar to the white testes seen in male squid. He speculates that the iridescent stripes might give a 3D perspective to the white strip: 'You could orient the iridocyte's reflection at some specific angle so it'll look brighter from certain positions, instead of white scattering which is always going to be uniformly bright in all directions.' As male squid are notoriously aggressive towards females, DeMartini suspects that these adaptable iridocytes and leucophores could help females mimic males to escape unwanted attention.

Explore further: Study reveals mechanism behind squids' and octopuses' ability to change color

More information: DeMartini, D. G., Ghoshal, A., Pandolfi, E., Weaver, A. T., Baum, M. and Morse, D. E. (2013). Dynamic biophotonics: female squid exhibit sexually dimorphic tunable leucophores and iridocytes. J. Exp. Biol. 216, 3733 – 3741 jeb.biologists.org/content/216/19/3733.abstract

add to favorites email to friend print save as pdf

Related Stories

ROV video offers clues on how rare squid catches prey

Aug 28, 2013

(Phys.org) —Video captured by a camera aboard a Remotely Operated Vehicle (ROV) off the coast of southern California is offering scientists clues to help explain how the rare squid Grimalditeuthis bonplandi, manage ...

Sexual selection in the sea

Jun 04, 2013

Biologists have uncovered new insights into how the male sexual behaviour of the peculiar southern bottletail squid is primed to produce the greatest number of offspring.

Recommended for you

Male monkey filmed caring for dying mate (w/ Video)

Apr 18, 2014

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Orchid named after UC Riverside researcher

Apr 17, 2014

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

Apr 17, 2014

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

Apr 17, 2014

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 0

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.