27 May 2019

Concealed crayfish and The Hidden Half

Marmorkrebs rarely make appearances in pop culture. Based on this summary from the Financial Times, I want to read this.

Michael Blastland’s recent book, The Hidden Half, argues that much of the variation we see in the world around us is essentially mysterious. Mr Blastland’s opening example is the marmorkrebs, a kind of crayfish that reproduces parthenogenetically — that is, marmorkrebs lay eggs without mating and those eggs develop into clones of their mothers.

Place two clones into two identical fish tanks and feed them identical food. These genetically identical creatures raised in apparently identical environments produce genetically identical offspring who nevertheless vary dramatically in their size, form, lifespan, fecundity, and behaviour. Sometimes things turn out very differently for no reason that we can discern. We might as well call that reason “luck” as anything else.

There’s a preview on Good Reads of the first chapter, which includes most of the stuff on Marmorkrebs. I’d like to point out that this is similar in some ways to an older post here on the blog about similarity and variation.

Related posts

How Marmorkrebs can make the world a better place

External links

The Hidden Half (publisher’s site)

Neil Woodford shows it can be hard to tell luck from judgment

25 May 2019

Gatzmann, 2019

Gatzmann F. 2019. DNA methylation in the marbled crayfish Procambarus virginalis. Doctoral dissertation, The Faculty of Bio Sciences, Heidelburg University. https://doi.org/10.11588/heidok.00026426


The all-female marbled crayfish Procambarus virginalis is a freshwater crayfish which is the only known obligatory parthenogen among the decapod crustaceans. Marbled crayfish are recent descendants of the sexually reproducing slough crayfish Procambarus fallax and have most likely emerged through a recent evolutionary macromutation event in P. fallax. Marbled crayfish reproduce by apomictic parthenogenesis, where oocytes do not undergo meiosis and all offspring are genetically identical clones of the mother. Nevertheless, marbled crayfish show a high degree of phenotypic variation and are a highly invasive species, where (through parthenogenesis) a single animal can establish a whole population. Moreover, they have been distributed via the pet trade and anthropogenic releases, and have formed stable populations in a variety of ecological habitats. Earlier this year, our group performed whole-genome sequencing for 11 marbled crayfish animals from different populations and countries, and found only four non-synonymous single nucleotide variances in coding regions. Since the marbled crayfish’s remarkable adaptability is not due to genetic variability, it is crucial to investigate epigenetic programming in this organism. I present here a comprehensive analysis of DNA methylation in marbled crayfish. Whole-genome bisulfite sequencing data was used to directly compare methylation patterns from multiple replicates in different tissues and from different marbled crayfish and Procambarus fallax animals. These methylation maps were integrated with RNA-seq and ATAC-seq data to comprehensively analyse the interplay between DNA methylation, chromatin accessibility, and gene expression. I found 18% of CpGs in marbled crayfish to be methylated. Repeats showed overall low methylation levels, with the exception of a single class of DNA transposons, which was ubiquitously methylated. DNA methylation was mainly targeted to the coding regions of housekeeping genes in marbled crayfish. In contrast to paradigmatic mammalian methylomes, I only observed very moderate methylation differences between tissues for both gene bodies and promoters. I did, however, identify a set of approximately 700 genes that showed a high variance in their methylation across tissues and animals. Gene body methylation was significantly inversely correlated with gene expression variability. Interestingly, the marbled crayfish shows overall lower methylation levels and higher gene expression variability than its parent species P. fallax. Since plasticity in gene expression can be a beneficial trait for adapting to new environments, this trait might contribute to the marbled crayfish’s adaptive and invasive success. The integrative analysis of DNA methylation, chromatin accessibility, and gene expression revealed that genes with highly methylated gene bodies were located in regions of poorly accessible chromatin and showed stable expression patterns. In contrast, lowly methylated genes were found in more accessible chromatin when stably expressed, and in more condensed chromatin when variably expressed. In this context, gene body methylation might function to stabilise gene expression in regions of limited chromatin accessibility. These findings broaden our knowledge of evolutionary conservation of DNA methylation patterns in invertebrates and provide novel insights on the interplay between gene body methylation, chromatin accessibility, and gene expression.

Note: Access restricted until 17 January 2020.

21 May 2019

“Step away from the aquarium...”

On this blog, I am frequently reporting new reports of Marmorkrebs as invaders, so it’s nice when Marmorkrebs are not bad news.

A news article in Ireland reports that a pet owner voluntary gave up Marmorkrebs kept in tanks to parks officials. In looking at the pet crayfish trade, one of my biggest concerns is the level of enforcement. It’s important for people not only to know that laws about the pet trade exist, but that they are people who genuinely do enforce those laws.

Unfortunately, this good piece of news is outweighed by two pieces of bad news. First is another outbreak of crayfish plague in Ireland.

The second is that there is a non-native crayfish population of Australian yabbies (Cherax destructor) in Ireland, the first time any non-native crayfish has gotten a toehold in the island. In a previous paper, I didn’t find anyone selling C. destructor as pets (Faulkes 2017). Several unidentified species sold as pets were described as “blue,” which fits C. destructor well. So it’s possible they were someone’s pets.


Faulkes Z. 2017. Slipping past the barricades: the illegal trade of pet crayfish in Ireland. Biology and Environment: Proceedings of the Royal Irish Academy 117(1): 15-23. https://doi.org/10.3318/BIOE.2017.02

External links

Warning issued over 'severe and increasing' threat to native crayfish species
Invasive species and diseases threat to native crayfish

17 May 2019

First Marmorkrebs on Twitter!

Set the wayback machine to a decade ago. Ten years ago, Marmorkrebs debuted on Twitter. The First to Tweet account says:

The first to tweet ‘Marmorkrebs’ was @DoctorZen in 2009!

It is a bit of a cheat, though, since the tweet was about this blog more than Marmorkrebs.

Enjoying that Marmorkrebs.blogspot.com was a finalist for Open Laboratory 2008.

16 May 2019

Marmorkrebs in the Middle East

I heard from astacologist Chris Lukhaup today that marbled crayfish are now in the rivers and ponds on Israel. Yes, plural.

This represents another signifcant expansion of Marmorkrebs across the globe, as it is the first report in western Asia. 

I don’t have more details at this time as to location and such, but am sure it will be forthcoming. I have updated the map of Marmorkrebs introductions with a generic pin for all of Israel at this time.

Thanks to Chris for giving me permission to share this.