Insight Into the Evolutionary History and Phylogenetic Relationships of Deep Sea Asteroidea Using Mitogenomics

 

        Mitogenomics is the the the sequencing and analysis of mitochondrial DNA. The majority of mitochondrial DNA comes from maternal descent, is relatively small, and has a high nucleotide substitution mutation rate. allowing researchers to better understand the evolutionary history and phylogenetic relationships of a particular organism.
        Sun et al. use this technique to study the geographic origin and relationships between shallow water and deep-sea Asteroidea. For their experiment, they selected five deep-sea genomes. It showed that deep-sea Asteroidea had a much higher A+T nucleotide content compared to those in shallow water, providing insight into the divergence of base composition. Studying the genome also allowed researchers to identify the sequences responsible for the deep-sea adaptations against cold temperatures and hydrostatic pressure.
        By comparing sequences of different Asteroidea with each other and seeing when new mutations arose and for how long they were passed on, the origin of each mutation could be speculated. The more matches in DNA, the closer the relationship. Using this information, it was speculated that during the Triassic-Jurassic transition marked by a mass extinction event, the rapid divergence between the deep and shallow water varieties occurred to fill in the newly opened niches. Although it was inconclusive, the results also pointed towards a deep-sea ancestral origin.
        It is important to understand the evolutionary history and evolutionary mechanisms of organisms since it helps us understand why a species may exist in a certain environment and how the world as we know it today came to be. It is also important to compare the survival mechanisms of different organisms because it can help with cultivation for commercial purposes or conservation efforts.


What to read next: Global Diversity and Phylogeny of the Asteroidea (Echinodermata)

Pesticide Runoff is affecting Aquatic Mammals due to Lost Genes

Today’s Marine mammals have all evolved from terrestrial mammals that trekked back into aquatic environments and created adaptations to thrive in these new environments. One of the genes they lost in adapting to aquatic life was an enzyme that would aid in defending against pesticides. With this discovery of a missing gene in marine mammals make the issues of pesticide runoff in oceans an even more important issue in our environment. The gene responsible for this defense was labeled as PON1 which was identified to defend against organophosphates, the pesticides used in agriculture. Most marine mammals have pieced together similar enzymes to replicate the results of the PON1 gene with some exceptions being walruses, fur seals, and spotted seals, all of which would be the most vulnerable to organophosphates. Now why did these marine mammals adapt to lose this gene that their terrestrial ancestors once had? The leading theory is that due to the fact that marine mammals take in large amounts of oxygen for deep dives, they evolved to remove oxygen carrying molecules. Molecules such as PON1, that otherwise would be harmful under the pressure of deep dives. (Zimmer, 2018)

These pesticide runoffs have also started to affect coastal avian species as well as the marine mammals. There have been a rise of unidentified diseases and conditions related to issues with the organisms endocrine systems. With an organisms endocrine system being exposed to its surroundings, many believe that these pesticide runoffs are to blame for the unusual mutations and reactions of these organisms. (Tanabe, 2009)

Even though there isn't evidence that directly links the runoff to these mutations and diseases in coastal organisms such as mammals and avians, the consensus of these researchers are that the pesticides have a part to play in this ecological issue. It is impossible to know exactly where runoff from agriculture will wind up but it is a guarantee that it will reach the oceans at once point. This means that we have to be conscious of the volume of pesticides we use on our plants as well as the possible reactions that organisms in the oceans and waterways will have to these chemicals. Although there aren’t direct links to the issues marine mammals are facing, i suspect that in the coming years more information will be discovered on the effects of such pesticides on marine mammals and other ocean going species.

References

Tanabe, S. (2002, 09). Contamination and toxic effects of persistent endocrine disruptors in marine mammals and birds. Marine Pollution Bulletin, 45(1-12), 69-77. doi:10.1016/s0025-326x(02)00175-3

Zimmer, C. (2018, August 09). Marine Mammals Have Lost a Gene That Now They May Desperately Need. Retrieved from https://www.nytimes.com/2018/08/09/science/marine-mammals-pesticides.html

All-female hybrid fish species that 'uses' males for better genetics

A naturally occurring hybrid fish species, Hexagramos octogrammus/H. grampus (Hoc/Hag), composed of all-female members, is thought to have developed a unique method of evolutionary survival by switching matings between two different male species of the same genus.  The (Hoc/Hag) hybrid females are thought to have a competitive advantage because 100% of their species is capable of producing offspring, thus allowing them to quickly replicate and outnumber other species that produce both male and female offspring.  Replication without variation is an evolutionary disadvantage though, and this can be detrimental to the long term survival of the all-female species due to also developing a decreased ability to genetically adapt to environmental pressures.

Researchers from Hokkaido University in Japan have compared the genes of three species: Hexagramos octogrammus/H. agrammus (Hoc/Hag), H. octogrammus/H. otakii (Hoc/Hot), as well as their maternal pure line, H. octogrammus (Hoc).  Their study, published in Ecology and Evolution, found that the hybrid females, (Hoc/Hag), mate with their choice of two hybrid male species: (Hoc/Hot) or (Hoc/Hag).  The result of either mating always produces 100% all-female hybrid offspring in which both maternal and paternal genes influence their development.  The subsequent generation only inherits the maternal genome though, and excludes the paternal genome from gamete formation when they're able to form their own eggs.  In addition, the all female offspring can only mate with (Hoc) males whose sperm activate their eggs to start development.  The resulting (Hoc) offspring undergo normal germ cell development in which genetic recombination can occur between maternal and paternal genomes, resulting in a more diversified genome for their male/female offspring.

“When a female descendant of one of these backcrossed Hocs mates with a Hag male, a new all-female Hoc/Hag hybrid lineage arises. This could be another factor that increases the diversity of Hoc/Hac hybrids, increasing their survivability,” says the paper’s lead author, Hiroyuki Munehara.

The researchers constructed a mtDNA genealogical tree that showed that the (Hot) and (Hag) species diverged from their common ancestor around 1.5 million years ago.  Furthermore, their analysis also revealed that (Hoc/Hot) hybrids originated from hybrid (Hoc/Hag) females switching choice of host; instead of breeding with (Hag) males, they bred with larger (Hot) males that would better protect their eggs.