11 January 2013

Updated map of introductions

Just wanted to post that the map of Marmorkrebs introductions has just been given a big update. In particular, it now includes all the locations listed in Chucholl et al. (2012). The map is not identical to Table 1 in that paper, however. The table only includes locations where there were either pictures of crayfish or voucher specimens to confirm the identification; my map includes some without those.

I’ve also used different placemarkers to distinguish locations with populations (dot in the middle of the placemarker) and those where there are single specimens, or the status is unclear (no dot).

Reference

Chucholl C, Morawetz K, GroƟ H. 2012. The clones are coming – strong increase in Marmorkrebs [Procambarus fallax (Hagen, 1870) f. virginalis] records from Europe. Aquatic Invasions 7: 511-519.

10 January 2013

Vogt, 2013

Vogt G. 2013. Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda. Biological Reviews 88(1): 81-116. http://dx.doi.org/10.1111/j.1469-185X.2012.00241.x

Abstract

The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life-history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean-type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico-chemical factors and phytoplankton availability in freshwater habitats. These life-history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r- to K-strategy in freshwater decapods are traded-off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio-temporal alteration of their socio-ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.

Keywords: marine-freshwater transition • Crustacea • life-history • development • parental care • trade-off • speciation • social systems • extinction threat

08 January 2013

SICB 2013 special session on crayfish

The special session on crayfish biology at SICB may well have been one of the busiest days for Marmorkrebs news and announcements in a long while. There were at least three major pieces of new information about our favourite crustacean.

Polyploidy

Peer Martin provided evidence that Marmorkrebs are triploid. This is an important step forward in understanding the original of asexual reproduction in this species. This strongly suggests that this may have been a "one off" chance event, either through some sort of incomplete separation of chromosomes or duplication of chromosomes, or hybridization.

Crayfish plague

As part of Peer Martin's talk, he discussed whether Marmorkrebs are "the perfect invader" as they were so memorably called. He included a discussion about the importance of crayfish plague as an issue in the invasive potential for Marmorkrebs. In the questions, I asked whether anyone had actually tested whether Marmorkrebs carry the plague, or whether it was simply assumed they were resistance, because essentially all North American species are. There is apparently one doctoral thesis that reports a Marmorkrebs carrying crayfish plague. That said, many in the lab, and one wild-caught animal, have tested for the disease.

More introductions in the wild

Chris Chucholl reported that there are now six confirmed populations in Europe, five of which are in Germany. During my talk, I reported the "breaking news bulletin" that I'd blogged while waiting in line at Starbuck's for a croissant that Marmorkrebs had been found in Sweden. Tadashi Kawai mentioned that a population had been found in Sapporo, but that it apparently died out.

Other highlights

Marmorkrebs was not the only only game in town in this session, however.

Tonio Garza de YTa discussed his experiences over a decade in working with farmers to develop sustainable, productive, profitable aquaculture for red-clawed crayfish in Mexico. The lessons he had were to develop the market first. There is no point in producing food nobody will buy. Secondly, make sure your product does not give itself away. The red-clawed crayfish got away from their cultured ponds and successfully established populations, which could be harvested more cheaply than the aquacultured crayfish.

Francesca Gherhardi talked about the importance of understanding behaviour of potentially invasive species. To give just one example, she examined the interaction between temperature and fighting between different invasive crayfish species. Spinycheek crayfish (Orconectes limosus) become more less active and more likely to seek shelter as temperatures increase. Signal crayfish (Pacifastacus leniusculus) become less competitive as water warms. Red swamp crayfish (Procambarus clarkii) change their aggressive behaviour very little, meaning swamp crayfish are poised to be the winners as temperatures warm under climate change.

Incidentally, my sympathy goes to Francesca, who was having quite severe voice problems. She had to whisper her whole talk. This worked to her advantage, as it gave her presentation an urgent, conspiratorial tone

Keith Crandall talked somewhat about some new research he is co-authoring on crayfish relationships, but much of his talk was geared to discussing tree of life projects. In particular, I’m excited about opentreeoflife.org. Most taxonomic papers now are published as PDFs, which are great to look at, but hard to re-use any data in them.

The goals of the Open Tree of Life project are, in part, things near and dear to much of the online science community. They want to encourage refinement of the tree, annotation, and promote a culture of data sharing, not simply publication. Currently, people are as consistent about putting things into Treebase or Dryad as they are into GenBank.

Oh yes, and they want to assemble a complete tree of life in three years. Keith mentioned that the National Science Foundation has been supporting various tree of life related projects for about a decade now, and are getting quite eager to see a tree. This project will make it easier to identify holes in the existing tree.

A great session marred only by the fact that I had to run to catch my plane, and couldn’t stay and chat more with  the other speakers! Much thanks to Tadashi Kawai for organizing the session!

07 January 2013

First record of Marmorkrebs in Sweden

I am preparing for today's crayfish special session at SICB, but this is too imporatant not to share immediately: marbled crayfish found in the wild in Sweden.

I will try to discover more details soon.

Update, 8 January 2013:

I have found the original press release from 5 December 2012. It describes the find of Marmorkrebs in the river “a few weeks ago,” so about November. That there are “several sizes” is suggestive of a population, but does not confirm it.

The map of Marmorkrebs introductions has been updated accordingly.

01 January 2013

2012 was an average year for Marmorkrebs research

After the boom of 2010 and the bust of 2011, Marmorkrebs research publications are back on a more even keel this year...


That’s not including Chucholl, 2013, which, despite an official 2013 publication date, was published in December.

2013 shall start with a bang, with the crayfish symposium at the Society for Integrative and Comparative Biology in San Francisco in mere days!