2 new scorpion papers

Article 1

Graham, M.R., R.W. Bryson & B.R. Riddle. 2014. Late Pleistocene to Holocene distributional stasis in scorpions along the Baja California Peninsula. Biological Journal of the Linnean Society. Early View (LINK)

ABSTRACT: The biota of the Baja California peninsula (BCP) assembled in response to a complex history of Neogene tectonics and Quaternary climates. We constructed species distribution models (SDMs) for 13 scorpion species from the BCP to compare current suitable habitat with that at the latest glacial maximum about 21 000 years ago. Using these SDMs, we modelled climatic suitability in relation to latitude along the BCP. Our SDMs suggested that most BCP scorpion distributions have remained remarkably conserved across the latest glacial to interglacial climatic transformation. Three areas of climatic suitability coincide remarkably well with genetic discontinuities in other co-distributed taxa along the BCP, indicating that long-term persistence of zones of abrupt climatic transition offer a viable alternative, or synergistic enhancement, to hypotheses of trans-peninsular seaways as drivers of peninsular divergences.

Article 2

Webber, M.M. & M.R. Graham. 2013. An Arizona bark scorpion (Centruroides sculpturatus) found consuming a venomous prey item nearly twice its length. Western North American Naturalist, 73:530–532. LINK

ABSTRACT: Arizona bark scorpions (Centruroides sculpturatus Ewing) are commonly found throughout the Sonoran Desert in southwestern North America, and they are well known for being the most venomous scorpion in the United States. Despite their medical significance, C. sculpturatus remains ecologically understudied, and little is known regarding its natural foraging and feeding behaviors. Here, we present the first documented case of C. sculpturatus feeding on the Sonoran Desert centipede (Scolopendra polymorpha Wood) in the wild.

Dag Nummit! – NUMTs in scorpions

It has finally happened.  After sequencing mitochondrial genes of hundreds of scorpions over the years, I have finally sequenced of couple dreaded pseudogenes, also known as NUMTs, short for nuclear mitochondrial DNA (pronounced “new mights” or “nummits”).  Uggg!

Commonly encountered in many other organisms, including the human genome, NUMTs are fragments of the mitochondrial genome that have transferred to the nucleus via one of several postulated pathways (see figure) and have been incorporated into the nuclear genome. Gone undetected, NUMT sequences can seriously mislead phylogenetic interpretations and are often responsible for artificially inflating genetic diversity in phylogenetic research and species diversity in DNA barcoding efforts. Fortunately, these potential sources of error are usually easy to detect.

Potential NUMT pathways

Once in the nucleus, NUMTs are not thought to be transcribed, instead behaving as non-coding ‘junk’ DNA. They can then accumulate random mutations as well as indels (insertions and deletions) at any codon position without consequence. Thus, NUMts can be detected by more mutations at the 1^st and 2^nd codon positions than expected for coding genes, by stop codons or indels within a reading frame, and by heterogeneous positions (double peaks) in chromatograms.

Yesterday I realized that I had clearly sequenced NUMTs when several sequences from Giant Hairy Scorpions, which were clean, contained a several hundred bp deletion replaced by a 30 bp insertion. As frustrating this was, especially in one of the very last populations left to sequence for my biggest research project, I was also somewhat fascinated.  Interestingly, it appears that I may have sequenced two separate NUMTs that may have incorporated themselves into the nuclear genome of common ancestors at different times in the deep history of these scorpions…. the oldest NUMT might even have been transferred in the common ancestor of all Giant Hairy Scorpions before the group had diversified into the species found today!

Once in the nuclear genome, NUMTs still acquire mutations, but are expected do so much more slowly than their mitochondrial counterparts due to the larger effective population size of the nuclear genome.  This means that NUMTs should be more similar to the original gene sequence of the common ancestor, making them a sort of window into the past, very similar to sequencing ancient DNA!  In theory, NUMTs should therefore be useful in rooting or polarizing phylogenetic trees.

Although I don’t think that I will use these NUMTs in my own research, please contact me if you have an interest in investigating these bizarre sequences of DNA. As far as I am aware, this is the first time that pseudogenes have been discovered in scorpions.

Image reference: Hazkani-Covo E., R.M. Zeller, W. Martin. 2010. Molecular poltergeists: mitochondrial DNA copies (numts) in sequenced nuclear genomes. PLoS Genetics 2010, 6:e1000834

a rattling close call

Although I am always rather careful about rattlesnakes while out at night collecting scorpions, I continue to have run-ins with snakes that convince me that I am still not being careful enough. Just this last week I had two such experiences, one where I almost stepped on a very large and angry Mojave Rattlesnake, and another where I almost put my hand right on top of a juvenile Sidewinder. The encounter with the Sidewinder was especially close.

My friend Ryan and I were looking for Giant Hairy Scorpions in a wash just outside of Anza Borrego Desert State Park the other night when I saw a small scorpion crawling into a hole in a shallow depression in the sand. When I reached down with tweezers to grab the scorp, luckily, and for some reason, I noticed that the sand that I was about to brace my hand on was actually a coiled up baby Sidewinder (Crotalus cerastes) laying camouflaged in the sand! My hand was literally 1 inch in front of the snake’s head before I noticed it, and for some reason it decided not to bite me. Although I was ‘rattled’, Ryan and I managed to snap a picture of the snake’s tail just before it disappeared back into its burrow (below).

Now of all the rattlesnakes to get bitten by, a juvenile sidewinder really wouldn’t be that bad, but the experience was an eye-opener.  I always wear sturdy boots and snake chaps while out collecting, but I never thought I’d have to worry about a snake bite to the hand. So to my fellow scorpion collectors out there, wear your snake chaps and pay close attention to what is around you when you squat down to grab a scorpion…  maybe it is even time for some gloves?

Nah.

juvenile Sidewinder escaping into a burrow

Dissertation sampling completed!

Matt, Jessica, Bruneau & Vegas in "the trailer"

George & Penny Graham

After four grueling field seasons I have finally completed the sampling needed to finish my dissertation research. There have been numerous road blocks along the way, and it was definitely never easy, but with the help with family and friends I have finally done it. I now have excellent genetic sampling of Hadrurus, Anuroctonus, and Paruroctonus becki (the focal taxa of my dissertation), as well as numerous other scorpions throughout the American West. Now I just need to get back in the lab to finish with sequencing, analyses, and writing!

I want to give a special thanks to my wife Jessica, and my parents George and Penny. They have made huge sacrifices to support an effort that they knew was important to me… I will be forever indebted and couldn’t ask for a better family.  Oh, and thanks to Bruneau and Vegas for all of the licks along the way!!