19 November 2014

Patoka and colleagues, 2014

Patoka J, Kalous L, Kopecký O. 2014. Risk assessment of the crayfish pet trade based on data from the Czech Republic. Biological Invasions 16(12): 2489-2494. http://dx.doi.org/10.1007/s10530-014-0682-5


The pet trade in freshwater crustaceans, including crayfish, has grown rapidly in recent decades and become an important pathway for introducing new non-indigenous species into Europe. This paper provides the first overview of non-indigenous crayfish species (NICS) traded as ornamental and their potential impact in the Czech Republic, which is the second leading importer into Europe. The paper presents a full list of traded crayfish species, their market availability, and trade names or misnomers used in the country. In total, 27 crayfish species from all three families are advertised and marketed, of which Astacus astacus is the only indigenous species. Only three NICS were recognized as very common on the market. The invasiveness and risk associated with ornamental crayfish trade were assessed using the Freshwater Invertebrate Invasiveness Scoring Kit. Five NICS were classified into the high-risk category, the highest score being for Procambarus fallax f. virginalis. The invasiveness of crayfish indigenous to North America is significantly greater than that of crayfish from the rest of the world, and therefore regulation in this regard is recommended.

Keywords: Ornamental animal • Invasiveness • FI-ISK • Aquarium • Trade names

Chucholl, 2014

Chucholl C. 2014. Predicting the risk of introduction and establishment of an exotic aquarium animal in Europe: insights from one decade of Marmorkrebs (Crustacea, Astacida, Cambaridae) releases. Management of Biological Invasions 5(4): 309-318. http://dx.doi.org/10.3391/mbi.2014.5.4.01


The presence of the North American Marmorkrebs (Procambarus fallax f. virginalis) in European inland waters is entirely driven by ongoing propagule pressure from the ornamental trade. Since 2003 at least 25 independent introduction events have been confirmed, of which some have eventually resulted in established populations. This study links a maximum-entropy model that forecasts the probability of Marmorkrebs introduction based on socio-economic predictors to an updated species distribution model based on environmental predictors in order to explore the risk of further Marmorkrebs establishment in Europe. In line with related research, the probability of Marmorkrebs release was largely affected by gross domestic product and human population density, i.e. predictors very likely related to the density of Marmorkrebs owners, whereas environmental suitability was mostly influenced by minimum temperature and the availability of lentic habitats, which was indirectly assessed by terrain slope. While considerable parts of Europe were predicted as potentially suitable for establishment, high probabilities of introduction were forecasted in much smaller geographic areas. The consensus map of the model predictions suggests that introduction and subsequent establishment of Marmorkrebs is likely to occur in much of Germany, the Benelux countries, England, Italy, and areas of high human population density throughout France and Spain, as well as parts of southernmost Scandinavia and Southeastern Europe. Monitoring trades of Marmorkrebs in these high-risk regions is recommended and implications for proactive measures are discussed, including the need for consistent trade regulations at the EU level.

Keywords: marbled crayfish • propagule pressure • risk assessment • ornamental trade • introduction pathway

Celebrate diversity: Winning evolution without sex

Quanta magazine has a nice feature article on rotifers, which are apparently some of the longest running asexual lineages that we know about. Or maybe they’re not asexual... maybe it’s sex, Jim, but not as we know it:

The new work has shown bdelloids to be so good at generating genetic diversity that some researchers now question the very definition of sex, with some arguing for a more expansive one that doesn’t require the orchestrated swapping of genetic material. Others think that even if the traditional definition of sex remains intact, the unique genetic strategies of the bdelloid rotifer will illuminate the mechanisms that make sex such a successful evolutionary strategy.

11 November 2014

Vojkovská and colleagues, 2014

Vojkovská R, Horká I, Tricarico E, Duriš Z. 2014. New record of the parthenogenetic marbled crayfish Procambarus fallax f. virginalis from Italy. Crustaceana 87(11-12): 1386-1392. http://dx.doi.org/10.1163/15685403-00003365


To date, the ‘marbled crayfish’, Procambarus fallax (Hagen, 1870) f. virginalis, in Italy has been reported only from Tuscany (central Italy). Recently, specimens of this alien American crayfish were found in the Po di Maistra Channel, Porto Tolle, south of Venice (northern Italy). The identification of this species was confirmed by its external morphology and colour pattern, as well as by molecular analysis. The present report provides the second record for the marbled crayfish in Italy.

Keywords: None provided.

28 October 2014

Celebrate diversity: Big babies

The latest additions to “creatures we thought reproduced sexually but turn out to be able to reproduce asexually” is a pretty spectacular one, because one of the two species is one of the biggest snakes in the world.

A paper published back in June by Booth and colleagues is suddenly making the rounds on news and social media. It describes research on two python species, the reticulated python (pictured, record holder for longest snake), and the royal python. While the news is focusing on “snake gives virgin birth!” angle, this paper is far more interesting.

The major question in this paper is: how do animals switch, genetically, from sexual to asexual reproduction? In most vertebrates - including the two in this paper - the answer is “terminal fusion automixis.”

In most female vertebrates, gametes divide unevenly in meiosis, with one large cell set to become the egg, and the other becoming a “polar body,” which normally dies. Some species are able to take the polar body and have it act like a sperm cell. The offspring that result are not genetically identical to their mother, because there is a a random element in meiosis.

There’s been one apparent exception: a Burmese python reproduced without sex, and the offspring were clones of the mother. If so, the offspring could not have been generated by terminal fusion automixis. This would be weird, given that this is out of step with an increasingly large number of cases.

Booth and colleagues, however, describe some unpublished data from another Burmese python laying eggs without sex. Here, the offspring are apparently not clones of the mother, which is in line with other species, but not the one previous account. Because of this, Booth and company suggest the previous paper be “viewed cautiously.”

This would be the normal translation from academese:

Booth and colleagues suggest that the first clone python report is not due to an error. Instead, they suggest that an individual, which had been created by parthenogentic reproduction, reproduced again by the same means. They write:

If this is indeed the case, this would represent the first documentation of such reproductive competence of (facultative parthenogensis) in vertebrates.

Only time (and a few more replications) will tell if there are indeed clone snakes. If there are, they seem to be rare.

Hat tip to Jason Goldman.


Booth W, Schuett GW, Ridgway A, Buxton DW, Castoe TA, Bastone G, Bennett C, McMahan W. 2014. New insights on facultative parthenogenesis in pythons. Biological Journal of the Linnean Society 112(3): 461–468. http://onlinelibrary.wiley.com/doi/10.1111/bij.12286/full

External links

Virgin Birth Discovered In The World's Largest Snake
Python babies the result of 'virgin birth,' zoo confirms

Photo by Ryan Somma on Flickr; used under a Creative Commons license. Graffiti picture from here.

12 August 2014

Mestre and colleagues, 2013

Mestre A, Aguilar-Alberola JA, Baldry D, Balkis H, Ellis A, Gil-Delgado JA, Grabow K, Klobučar G, Kouba A, Maguire I, Martens A, Mülayim A, Rueda J, Scharf B, Soes M, S. Monrós J, Mesquita-Joanes F. 2013. Invasion biology in non-free-living species: interactions between abiotic (climatic) and biotic (host availability) factors in geographical space in crayfish commensals (Ostracoda, Entocytheridae). Ecology and Evolution 3(16): 5237–5253. http://dx.doi.org/10.1002/ece3.897


In invasion processes, both abiotic and biotic factors are considered essential, but the latter are usually disregarded when modeling the potential spread of exotic species. In the framework of set theory, interactions between biotic (B), abiotic (A), and movement-related (M) factors in the geographical space can be hypothesized with BAM diagrams and tested using ecological niche models (ENMs) to estimate A and B areas. The main aim of our survey was to evaluate the interactions between abiotic (climatic) and biotic (host availability) factors in geographical space for exotic symbionts (i.e., non-free-living species), using ENM techniques combined with a BAM framework and using exotic Entocytheridae (Ostracoda) found in Europe as model organisms. We carried out an extensive survey to evaluate the distribution of entocytherids hosted by crayfish in Europe by checking 94 European localities and 12 crayfish species. Both exotic entocytherid species found, Ankylocythere sinuosa and Uncinocythere occidentalis, were widely distributed in W Europe living on the exotic crayfish species Procambarus clarkii and Pacifastacus leniusculus, respectively. No entocytherids were observed in the remaining crayfish species. The suitable area for A. sinuosa was mainly restricted by its own limitations to minimum temperatures in W and N Europe and precipitation seasonality in circum-Mediterranean areas. Uncinocythere occidentalis was mostly restricted by host availability in circum-Mediterranean regions due to limitations of P. leniusculus to higher precipitation seasonality and maximum temperatures. The combination of ENMs with set theory allows studying the invasive biology of symbionts and provides clues about biogeographic barriers due to abiotic or biotic factors limiting the expansion of the symbiont in different regions of the invasive range. The relative importance of abiotic and biotic factors on geographical space can then be assessed and applied in conservation plans. This approach can also be implemented in other systems where the target species is closely interacting with other taxa.

Keywords: biological invasions • BAM diagrams • ecological niche models • host availability

Note: Co-author Menno Soes confirmed that the “Procambarus fallax” studied in this paper is indeed P. fallax f. virginalis, or Marmorkrebs.

First look at Freshwater Crayfish: A Global Overview

A new book on crayfish is now up at the publisher’s website. Here is the publisher’s description, with my emphasis added:


  • Provides an up-to-date reference work on commercially important crustaceans
  • Covers conservation status and biology of all endangered species, taxonomy, and distribution of crayfishes worldwide
  • Introduces a new model aquatic organism—a parthenogenetic freshwater crayfish


For their great commercial importance as a human food delicacy, crayfish are now becoming of wider interest to molecular biologists, and also to conservationists due to the fact that in some countries many of the native crayfish species are under threat from human activity, disease, and competition from other introduced crayfish species. Helmed by three editors in Japan, Europe, and the US, this book invites contributions from experts around the globe, covering the conservation status and biology of all endangered species, taxonomy, and distribution of crayfishes worldwide

It is slated for publication 15 April 2015.