Jirikowski and colleagues, 2010

Jirikowski G, Kreissl S, Richter S, Wolff C. 2010. Muscle development in the marbled crayfish—insights from an emerging model organism (Crustacea, Malacostraca, Decapoda). Development Genes and Evolution 220(3-4): 89-105. http://dx.doi.org/10.1007/s00427-010-0331-7

Abstract

The development of the crustacean muscular system is still poorly understood. We present a structural analysis of muscle development in an emerging model organism, the marbled crayfish—a representative of the Cambaridae. The development and differentiation of muscle tissue and its relation to the mesoderm-forming cells are described using fluorescent and non-fluorescent imaging tools. We combined immunohistochemical staining for early isoforms of myosin heavy chain with phallotoxin staining of F-actin, which distinguishes early and more differentiated myocytes. We were thus able to identify single muscle precursor cells that serve as starting points for developing muscular units. Our investigations show a significant developmental advance in head appendage muscles and in the posterior end of the longitudinal trunk muscle strands compared to other forming muscle tissues. These findings are considered evolutionary relics of larval developmental features. Furthermore, we document the development of the muscular heart tissue from myogenic precursors and the formation and differentiation of visceral musculature.

Keywords: Marmorkrebs • development • muscle precursor • myogenesis • evolution

Crayfish + radio = craydio?

At the recent International Association for Astacology meeting, there were some student radio reporters from KBIA about, and some of them came by to chat about the conference and listen to a little about crayfish.

You can listen here; the RSS feed with mp3 files is here.

Going back to the end of July, ResearchBlogCast discussed asexual species concepts, which started by a post on this blog about a PLoS ONE paper. A little more discussion is here. The mp3 is here.

Photo by the third dream on Flickr; used under a Creative Commons license.

Hitting the wire: Orana vahiny

The German wire service Deutsche Presse-Agentur (or DPA) has released a story about the release of Marmorkrebs in Madagascar.

It started making the rounds last Wednesday. It has shown up, without modification, here:

• Earth Times: 18 August. I snagged the image at right from their story; it looks odd to me if it’s a Marmorkrebs.
• Sci-Tech Today: 20 August.
• Phantoms and Monsters, a blog of “close encounters, paranormal, UFOs, cryptids, conspiracies, extraterrestrial and alternative news.” 21 August.
• Fish and Aquatic News: 16 August.

I strongly suspect it will be showing up at other locations. I’ll be collecting links as I find them.

Meanwhile, some fact-checking:

It is not clear how or when the shrimp-like crustacean, which is believed to originate in North America, came to this vast island, which lies 400 kilometres off the coast of Mozambique.

“Shrimp-like”? Don’t most people know what crayfish look like? If you’re going to compare it to something more people will recognize, it’s more lobster-like than shrimp-like.

In 2003, German scientists proved that the marmorkrebs could clone itself. Although the crayfish also reproduced sexually, females were able to lay eggs which hatched without being fertilised.

There is no record that I know of, in the scientific literature or otherwise, indicating that Marmorkrebs ever reproduce sexually.

“We get diarrhoea after eating them,” one farmer said. “Even the pigs won’t eat them.”

There’s no reason I can think of for Marmorkrebs to be gastronomically worse than any other kind of crustacean to eat, either for humans or pigs. The quoted person may well have gotten sick after eating Marmorkrebs, but it probably had more to do with a bad batch than being generally unsuitable for eating.

I am pleased to learn that “orana vahiny” is the Malagasy name for Marmorkrebs.

Celebrate diversity: Old female salamanders

Imagine, if you will, a line of ancient females, who trick males into having sex with them, so that the females can continue living indefinitely.

I know, you’ve seen it before in a dozens of movies, books, and television episodes. Who hasn’t seen a vain sorceress stealing youth, particularly from young men?

Something like this goes on in some salamanders, except that no one salamander is living unusually long. The evolutionary line of salamanders, though, is showing surprisingly longevity.

Some salamanders are all female... but they are not, strictly speaking, asexual or parthenogenetic. These unisexual female lineages engage in a little sperm “theft” from several sexual salamanders species (Ambystoma laterale is pictured), a process known as kleptogenesis. Genetically, these unisexual females are all over the map. Some unisexuals have a paired set of chromosomes like the more typical sexual species (i.e., they are diploid); others have three, four, or five sets of chromosomes.

This unusual mode of reproduction is interesting, because it might allow a unisexual species to avoid genetic stasis. In theory, sexual species have the edge in a changing environment because more genetic variations are possible through sexual reproduction. Having every individual be genetically identical is great as long as the environment never changes.

But environments do change, so it’s generally though that parthenogenetic species tend to go extinct at much higher rates than sexual ones.

This new paper by Bi and Bogart tries to settle how old this odd lineage of female salamanders is. One previous study suggested millions of years; another estimated tens of thousands of years. Bi and Bogart come down on the side of millions of years; a little over 5 million years, to be precise.

The reason for the discrepancy comes down to an issue concerning the wrong bit of DNA being amplified and analyzed. Most animal cells have DNA in two places: the cell nucleus (where most people think of it being), and in the mitochondria (the cell’s power plant). In normal sexual species, nuclear DNA comes equally from both parents, while mitochondrial come from mom.

Because these all-female salamanders get nuclear DNA from the sperm they “steal,” you can really only try to trace relationships using mitochondrial DNA in these animals.

The problem is that nuclear DNA sometimes has some bits in it that are extremely similar to mitochondrial DNA. These sequences, called numts, are probably derived from the mitochondria. Bi and Bogart argue that the previous research that suggested that these female salamanders split from the sexual salamanders about 25,00 years ago probably sequenced a numt instead of a mitochondrial gene.

That DNA. It’s tricky.

Parthenogenesis in Marmorkrebs is blessedly simple in comparison.

Reference

Bi, K., & Bogart, J. (2010). Time and time again: Unisexual salamanders (genus Ambystoma) are the oldest unisexual vertebrates BMC Evolutionary Biology, 10 (1) DOI: 10.1186/1471-2148-10-238

Photo by whiteoakart on Flickr, used under a Creative Commons license.

Harmony

Marmorkrebs and red cherry shrimp, in peaceful coexistance in someone’s tank. Exemplified by the sweet soul music in the background.

Freshwater Crayfish

At the recent International Association of Astacology (IAA) meeting, there was a fair amount of discussion about one of the society’s publications, Freshwater Crayfish. Having examined a hardcopy at the meeting, I can say that they did a very nice job with the production of the last issue (pictured).

Since this is one forum that is a perfectly logical place to publish Marmorkrebs research, I’ll convey a few things I learned at the meeting.

First, Freshwater Crayfish is a journal. Because of its length time between issues, people often think that papers in it are proceedings from the IAA meeting. Nope – journal. It has an ISSN number and everything.

Second, you do not have to attend an IAA symposium, or be an IAA member to publish in Freshwater Crayfish. It is open to all. That said, the IAA could do more to facilitate outside submissions. For instance, the link to author’s instructions on the IAA website currently brings up a 2 page PDF document... that is completely blank. The author’s instructions were printed in the IAA conference booklet, so I’ll see what I can do about getting them online.

Currently, Freshwater Crayfish is indexed in Scopus, but not Thompson ISI Web of Science. There was some discussion about the future of the journal, which included a shorter time between publication, which would help it get into Web of Science. Still, “shorter delay” may be moving from every other year to every year.

North American crayfish diversity threatened

When I recently attended the International Association of Astacology meeting, it was ground into my face how bad things are for crayfish.

In Europe, crayfish are being beaten up by exotic North American species. If competition doesn’t get them, the crayfish plague that the exotics carry will.

In North America, the home to the greatest diversity of crayfish species in the world, non-indigenous species are playing a role in some regions, but habitat degradation is the bigger concern. At the Astacology meeting, we were treated to scenes like this:

Mountains are being flattened to remove coal.

Strangely, the same factors that lead to the wonderful high diversity of North American crayfish are the same factors that make them vulnerable, mainly geographic isolation. Because crayfish need to stay wet, and are not terribly mobile, they often don’t disperse very well on their own. Consequently, many species have a limited range, often falling within a few locations in a single American state.

Taylor and colleagues provide a summary of just how bad things are in North America. The take home message that every crayfish biologist and every crayfish pet owner should have burned into their brain is this:

Almost half of North American crayfish species are under threat.

I don’t use the phrase “under threat” in any sort of technical way, but just indicating some sort of conservation concern.

On a per species basis, crayfish are the second third most threatened kind of animal in North America, behind freshwater mussels and snails, which obviously have many of the same issues as crayfish: small geographic ranges, limited mobility (though crayfish are more mobile than snails and mussels), vulnerable to competition and habitat degradation.

Taylor and colleagues provide other useful information, including a list of all known species and a standard common name. The article is rather nicely illustrated with a few crayfish pictures, too (not for every species, however).

All of this makes the prospect of Marmorkrebs being introduced into North American waters a veritable nightmare scenario. Competition between Marmorkrebs and a local species could be enough to push a species into extinction.

Reference

Taylor, C., Schuster, G., Cooper, J., DiStefano, R., Eversole, A., Hamr, P., Hobbs, III, H., Robison, H., Skelton, C., & Thoma, R. (2007). A Reassessment of the Conservation Status of Crayfishes of the United States and Canada after 10+ Years of Increased Awareness Fisheries 32(8): 372-389. DOI: 10.1577/1548-8446(2007)32[372:AROTCS]2.0.CO;2

Photo by ddimick on Flickr. Used under a Creative Commons license.