Monthly Archives: April 2018

Can you imagine, if the human skins could “see” a threat and respond accordingly, while our backs were turned (No seeing with eyes or touching involved)? Eye-independent, light-activated chromatophore expansion (LACE) and phototransduction genes in the skins of cephalopods make this possible. This mind blowing feature of Octopus bimaculoides and other cephalopods is what I would like to discuss on this final blog.

When the skin of O. bimaculoides is exposed to bright white light, the chromatophores present react by expanding, a behavior termed LACE.  LACE responses is evident that the skin of  O. bimaculoides can sense light, independent of eyes.

Ramirez and Oakley hypothesized that r-opsin, a protein responsible for detecting light found in the eyes of octopuses may also be present in their skin, thus activation of light-sensitive chromatophore in their skin was possible, without the input of the eyes (Ramirez et al., 2014).

11 adult Octopus bimaculoides and their hatchlings were obtained, killed and their funnels dissected. Ten dissected funnels were mounted in fresh seawater filled Petri dishes using insect pins. The mounts were set up at equal distance from a white light fiber optic source and the reaction of the chromatophores on the skins was observed and recorded using infrared CCD camera. The photon counts and absolute radiance were measured with spectrophotometer. Three trials for the set ups were performed to ensure accuracy.

There have been a lot of behavioral and physiology research in relations to light sensitivity of mollusks skins (Ramirez et al., 2011). This specific research paper is the best evidence till date for cephalopods’ light-sensitive skin and the role of LACE in controlling chromatophore for camouflage, alongside the main control of the central nervous system.

Further studies to determine on the specific functions of opsin-expressing cells in hatchling O. bimaculoides skin and the extent of importance of the role of opsin in their function/functions apart from photoreception. The evolutionary path to LACE in the skins of octopuses is worth  researching also.

REFERENCE

Ramirez, M. et al (2011). Understanding the dermal light sense in the context of integrative photoreceptor cell biology. Vis. Neurosci. 28, 265-279.

Ramirez M. D.& Oakley T. H. (2014) Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides. Journal of Experimental Biology 2015, 218: 1513-1520; doi: 10.1242/jeb.110908    http://jeb.biologists.org/content/jexbio/218/10/1513.full.pdf

KEYWORDS

 Chromatophore is a pigment-containing cell in the deeper layers of the skin of animals. The distribution of the chromatophores and the pigments determine the color patterns of an organism.

Mechanoreceptors are specialized neurons that transmit mechanical deformation information into electrical signals.

Phototransduction is the conversion of light into a change in the electrical potential across the cell membrane. This process involves the sequential activation of a series of signaling proteins, leading to the eventual opening or closing of ion channels in the photoreceptor cell membrane.

Visual phototransduction is the photochemical reaction that take place when light (photon) is converted to an electric signal in the retina. 

In my previous blog while comparing two cladograms of Octopoda, Octopus bimaculoides and Hapalochlaena muculosa were shown as sister taxa in both relationships. A sister taxon relationship based on shared trait of ink sac and two sucker rows.There is an African proverb that embodies the importance of this blog,it states that “show me your friend and I’ll show you your character”.

Fig 1-Blue-ringed octopus, Hapalochlaena muculosa Marcello Di Francesco/courtesy of University of Miami 

 It is befitting to feature Hapalochlaena muculosa as organism of todays’ blog.Commonly known as the Blue-ringed octopus, it has numerous blue eyespots on its mantle as compared to the California two-spot octopus with only one blue eye spots below each eye.(Fig 1) (Lydia M. et al (2012)

Hapalochlaena sp. is also a small sized octopus but normally found along the southern coastal regions of Australia unlike O. bimaculoides found on the southern coast of California Santa Barbara stretching to San Quintin, Mexico. (Tranter, D.J.et al ,1973)

 Hapalochlaena sp. is venomous and displays its numerous vibrant blue rings on mantle when disturbed. This creates an effective conspicuous warning display. The venom contains primarily tetradotoxin, is used to kill or paralyze its prey i.e. crabs and crayfish. (Sheumack et al,1978) Hapalochlaena muculosa was the first species with venom contain primarily tetrodotoxin unlike others that occurs as a poison in the skin, liver, muscle, eggs or ovaries. Tetradotoxin is a very potent neurotoxin that can paralyze and even kill humans.

Fun fact

Copulation in  Hapalochlaena sp. is more vigorous than seen in other octopus and it lasts for about an hour. The male mounts and grasps the female securely and after a brief struggle the female subdues. Finally, the male deposits its sperm in the female’s oviduct using his hectocotylus.(Tranter, D.J.et al ,1973)

Joke of the day

I hope I’m not poisonous, says the first blue-ringed octopus

“Why?” asks the second blue-ringed octopus

“Because I just bit my lip.” said the first.

Reference

1.Lydia M. et al (2012) How does the blue-ringed octopus (Hapalochlaena lunulata) flash its blue rings? Journal of Experimental Biology 2012, 215: 3752-3757; doi: 10.1242/jeb.076869. Accessed on 4/10/2018 at http://jeb.biologists.org/content/215/21/3752.figures-only

2.Sheumack, D. D et al (1978). Maculotoxin: a neurotoxin from the venom glands of the octopus Hapalochlaena maculosa identified as tetrodotoxin. Science 199, 188-189. Accessed on 4/10/2018 at http://science.sciencemag.org/content/199/4325/188/tab-pdf

3.Tranter, D.J. & Augustine, O. (1973) Observations on the life history of the blue-ringed octopus Hapalochlaena maculosa. Marine Biology January 1973, Volume 18, issue 2 pp 115–128. Accessed on 4/10/2018 at https://doi.org/10.1007/BF00348686

FIG. 1. Maximum-parsimony tree obtained from analysis of the unweighted COI data Constraint of monophyly of the Octopodidae resulted in a significantly longer tree, whereas enforcement of monophyly of the Cirrata did not yield a significantly longer tree. Source-(Carlin D.A et al, 2001)

FIG. 2. Maximum-likelihood tree derived from a heuristic search of the COI data under the assumption of a general time-reversible model of substitution with site-specific rates (GTR ) estimated according to the gamma distribution. Branch lengths are drawn proportional to the probabilities of change occurring along each branch under the GTR model.

In today’s blog, let us explore phylogenetic relationships of the Octopoda comparing results from molecular data analyses with classification based on morphological features.

The Octopod phylogeny is complex and full of controversies. Research utilizing Molecular data did not support the Octopodidae as a monophyletic group (based on morphological features).(Carlin D.A et al, 2001)

 Notable disparities were seen at the order of branching.(Fig.1 and 2) At the base, Argonauta branched off first in the MP tree. Argonauta grouped based on smaller mature male compared to mature female, hectocotylus remain coiled inside a pocket until use, and hectocotylus break off during mating. (Nesis, 1987), Whereas in the ML tree, a clade consisting of Argonauta and three members of subfamily octopodinae (O. tetricus, O. bimaculoides, and Hapalochlaena sp.) initially branched off from the others.Based on the various positioning of  O. bimaculoides ,it’s evolutionary history is unconfirmed.

O. tetricus ;O. bimaculoides and Hapalochlaena were shown as sister taxa, in clade subfamily octopodinae .A sister taxon relationship based on shared trait of ink sac and two sucker rows. This was also supported by data from ML and MP trees.

In both tree,O. californicus was closely related to Benthoctopus sp. than O. bimaculoides, although O. californicus shared possession of ink sac and double  sucker rows with O. bimaculoides. Benthoctopus sp. on the other hand possess double sucker row with no  ink sac .(O’Shea S.1999)

MP tree was a  significantly longer tree compared to the ML tree especially since branch lengths were constructed proportionally to the number of parsimony steps between nodes.(Carlin D.A et al, 2001)

REFERENCE

Carlin D.A et al (2001) A molecular phylogeny of the Octopoda (Mollusca: Cephalopoda) evaluated in light of morphological evidence. Molecular phylogenetics and evolution, ISSN: 1055-7903, Vol: 21, Issue: 3, Page: 388-97 .

Nesis, K. N. (1987). “Cephalopods of the World: Squids, Cuttlefishes, Octopuses, and Allies,” Tropical Fish Hobbyist Publ. Inc., Neptune City, NJ.