31 July 2018

The Great Lakes least wanted

The Michigan Sea Grant has spearheaded a “#CrayWeek” campaign for the second year in a row! Of course I’m participating.

One of the piece of information that Michigan Sea Grant tweeted out was that Marmorkrebs have found themselves on another invasive species watch list, this one for the Canadian / American Great Lakes and Saint Lawrence River.

On May 4, 2018, the Great Lakes St. Lawrence Governors & Premiers announced five additions to the list of “least wanted” aquatic invasive species. In 2013, the Governors and Premiers released the first list of 16 “least wanted” aquatic invasive species (AIS) that present a serious threat to the Great Lakes St. Lawrence Basin. Since then, the region’s eight states and two provinces have taken more than 40 actions to prohibit or restrict these high-risk species, including the Asian carp. The new “least wanted” AIS include:
  • Tench Tinca tinca
  • Marmorkreb (sic) (marbled crayfish) Procambarus fallax forma virginalis
  • New Zealand mud snail Potamopyrgus antipodarum
  • European frogbit Hydrocharis morsus-ranae
  • Yellow floating heart Nymphoides peltata
State and provincial AIS and fisheries experts, in conjunction with leading regional researchers, identified these five AIS as posing a high risk of invasion or spread within the region. The Governors and Premiers will take aggressive action and work with regional partners to prevent the spread of these aquatic invaders.

What’s not clear to me from this statment is what action has been, or might be, taken to try to curb the spread of any of these species. A recent paper I co-authored pointed out (Patoka et al. 2018), the track record of legislation on curbing the movement of aquarium pets is... not great.

External links

Great Lakes St. Lawrence Governors & Premiers Add Five “Least Wanted” AIS


Patoka J, Magalhães ALB, Kouba A, Faulkes Z, Jerikho R, Vitule JRS. 2018. Invasive aquatic pets: Failed policies increase risks of harmful invasions. Biodiversity and Conservation 27(11): 3037-3046. https://doi.org/10.1007/s10531-018-1581-3

26 July 2018

Le Page, 2018

Le Page M. 2018. Crayfish clone army on the loose. New Scientist 239(3185): 16. https://doi.org/10.1016/S0262-4079(18)31193-X


Without abstract. First paragraph:

Sometime before 1995, a container of freshwater crayfish from Florida got too hot or too cold en route to a pet shop in Germany. The shock disrupted the development of an egg being carried by one of the females, creating an army of clones that are invading rivers and lakes in continental Europe, Madagascar and Japan.

Keywords: None provided.

Notes: If you click to enlarge the cover of this issue, the cover includes “Clone crayfish” in the bottom left. This article was published online with the title, “Freak accident created a massive army of super-fertile clones.”

14 July 2018

Nischik and Krieger, 2018

Nischik ES, Krieger J. 2018. Evaluation of standard imaging techniques and volumetric preservation of nervous tissue in genetically identical offspring of the crayfish Procambarus fallax cf. virginalis (Marmorkrebs). PeerJ 6: e5181. https://doi.org/10.7717/peerj.5181


In the field of comparative neuroanatomy, a meaningful interspecific comparison demands quantitative data referring to method-specific artifacts. For evaluating the potential of state-of-the-art imaging techniques in arthropod neuroanatomy, micro-computed X-ray microscopy (μCT) and two different approaches using confocal laser-scanning microscopy (cLSM) were applied to obtain volumetric data of the brain and selected neuropils in Procambarus fallax forma virginalis (Crustacea, Malacostraca, Decapoda). The marbled crayfish P. fallax cf. virginalis features a parthogenetic reproduction generating genetically identical offspring from unfertilized eggs. Therefore, the studied organism provides ideal conditions for the comparative analysis of neuroanatomical imaging techniques and the effect of preceding sample preparations of nervous tissue. We found that wet scanning of whole animals conducted with μCT turned out to be the least disruptive method. However, in an additional experiment it was discovered that fixation in Bouin’s solution, required for μCT scans, resulted in an average tissue shrinkage of 24% compared to freshly dissected and unfixed brains. The complete sample preparation using fixation in half-strength Karnovsky’s solution of dissected brains led to an additional volume decrease of 12.5%, whereas the preparation using zinc-formaldehyde as fixative resulted in a shrinkage of 5% in comparison to the volumes obtained by μCT. By minimizing individual variability, at least for aquatic arthropods, this pioneer study aims for the inference of method-based conversion factors in the future, providing a valuable tool for reducing quantitative neuroanatomical data already published to a common denominator. However, volumetric deviations could be shown for all experimental protocols due to methodological noise and/or phenotypic plasticity among genetically identical individuals. MicroCT using undried tissue is an appropriate non-disruptive technique for allometry of arthropod brains since spatial organ relationships are conserved and tissue shrinkage is minimized. Collecting tissue-based shrinkage factors according to specific sample preparations might allow a better comparability of volumetric data from the literature, even if another technique was applied.

Keywords: μCT • confocal laser scanning microscopy • nervous system • volumetry • Marmorkrebs • phenotypic plasticity

10 July 2018

Conference hashtag #IAA22

I was unable to go to the International Association of Astacology meeting this year, but have been following along on Twitter, using the #IAA22 hashtag. Those following from home have been fortunate to have Maggie Watson sketchnoting many of the presentations, and I can’t resist sharing her Marmorkrebs notes here and here)!

If you go to a conference, tweet about it. More people want to attend than can attend.

07 July 2018

Velisek and colleagues, 2018

Velisek J, Stara A, Zuskova E, Kubec J, Buric M, Kouba A. 2018. Chronic toxicity of metolachlor OA on growth, ontogenetic development, antioxidant biomarkers and histopathology of early life stages of marbled crayfish. Science of The Total Environment 643: 1456-1463. https://doi.org/10.1016/j.scitotenv.2018.06.309


The metolachlor OA is a metabolite of herbicide metolachlor and s-metolachlor. The objective of the present study was to assess the effect metolachlor OA on early life stages of marbled crayfish (Procambarus virginalis). The early life stages of marbled crayfish were exposed for 45 days to three concentrations of metolachlor OA: 4.2 μg/L (environmentally relevant concentration, E1), 42 μg/L (E2) and 420 μg/L (E3) under laboratory conditions. The effects were assessed on the basis of mortality, growth, ontogenetic development, behaviour, oxidative stress, antioxidant biomarkers and histopathology. Metolachlor OA caused significantly lower growth, superoxide dismutase, catalase and glutathione s-transferase activity in all tested concentrations. Metolachlor OA in higher concentrations (42 and 420 μg/L) resulted in significantly delayed ontogenetic development, lower reduced glutathione level and lipid peroxidation. Metolachlor OA has not significant effect on behaviour (activity, total distance moved and walking speed). Histological examination revealed alteration of hepatopancreas and gills in crayfish exposed to two higher tested concentrations. Hepatopancreas reflected histomorphological structural changes of individual cell types. Changes of gills included focal hemocytic infiltration together with enlargement of intralamellar space packed with granular substance. In conclusion, chronic metolachlor OA exposure affected growth, ontogenetic development, and the antioxidant system and caused pathological changes in hepatopancreas and gills of early life stages of marbled crayfish.

Keywords: herbicide • metabolite • crayfish • mortality • behaviour • oxidative stress

03 July 2018

Vogt and colleagues, 2018

Vogt G, Dorn NJ, Pfeiffer M, Lukhaup C, Williams BW, Schulz R, Schrimpf A. 2018. In-depth investigation of the species problem and taxonomic status of marbled crayfish, the first asexual decapod crustacean. BioRxiv: 26 June 2018. https://doi.org/10.1101/356170 [Unreviewed pre-print]


The marbled crayfish is the only obligately parthenogenetic decapod crustacean and a novel research model and invasive animal on three continents. It is regarded either as a parthenogenetic form of slough crayfish Procambarus fallax or as a separate species named Procambarus virginalis. In order to investigate the species question of this unusual crayfish in detail we have identified the similarities and differences in morphology, life history, genetics, behaviour, ecology and biogeography between marbled crayfish and P. fallax. We have investigated specimens from natural habitats, laboratory colonies and museum collections and performed a meta-analysis of our data and published data. Our COI based molecular tree with 27 Cambaridae confirms closest relationship of marbled crayfish with P. fallax. Marbled crayfish and P. fallax are similar with respect to morphological characters, coloration and body proportions, but differ considerably with respect to body size, fertility and longevity. The mitochondrial genes of both crayfish are similar, but some nuclear genomic features are markedly different. Both crayfish are eurytopic and have two major annual recruitment periods, but marbled crayfish show different population structure and higher invasiveness. Marbled crayfish occur in boreal to tropical habitats of Europe, Madagascar and Japan, but P. fallax is confined to the subtropics and tropics of the southeastern USA. Laboratory experiments suggest reproductive isolation of both crayfish. The application of the Evolutionary Genetic Species Concept for asexuals to all available data supports raising marbled crayfish from "forma" to species rank. A determination key is provided to discriminate Procambarus virginalis, the first asexual decapod species, from its most likely parent species P. fallax.

Keywords: None provided.