Interactive Lunar Mosaic

Are you ready for some interactive spacey goodness? Stupid question, I know.

NASA recently released their Lunar Reconnaissance Orbiter Camera (LROC) Northern Polar Mosaic (LNPM). Using two Narrow Angle Cameras aboard their Lunar Reconnaissance Orbitor (LRO) along with additional information about the moon's topography from LRO's Lunar Orbiter Laser Altimeter and gravity information from NASA's Gravity Recovery and Interior Laboratory (GRAIL), they were able to create the largest high resolution mosaic of our moon’s north polar region. This mosaic is comprised of 10,581 six-and-a-half feet (two-meters)-per-pixel images covering an area equal to more than one-quarter of the United States. Put together, the entire image measures 931,070 pixels square. Do the math? That's almost 867 billion pixaels total!

And here's the interactive part: web viewers (that's you) can zoom in and out, and pan around an area. There is enough detail in these images that you can see textures and subtle shading of the lunar terrain, and the consistent lighting throughout the images makes it easy for you to compare different areas.

LROC Northern Polar Mosaic (LNPM) Interactive Website

Also check out more information about LRO at NASA's LRO website

and look through the complete collection of LROC Images

and NASA's Press Release "NASA Releases First Interactive Mosaic of Lunar North Pole"



(image via NASA's press release)

Nerd Life

You livin' it.

The Physics of Cow Tipping

Because I know you wanted to know.

(via Science Dump)

The Charge of the Crazy Ant: Chemical Warfare Between Invading Species

LeBrun, Jones, and Gilbert (2014) Figure 1A

I’ll be the first to admit that I've been a little blog-negligent lately. Even when all of the ice and snow we've gotten here on the East Coast forced me to stay inside I just binge watched shows on Netflix instead. I’m not sure what brought me out of my procrastination funk and compelled me to do a little reading and writing. If you've been following the Facebook page then you've been getting a lot of yummy sciency tidbits, but it’s time for me to get back on the hard science wagon. I think I’ll start off with a great couple of papers about ant chemical warfare.

These papers focus on invasive ants, a big problem in many regions. To really grasp one of the underlying aspects of their warfare strategies, you must first understand the basics of an invasive species. Start by recognizing the difference between a native species and an exotic species. Put simply, a native species occurs naturally (or natively) to a habitat and an exotic species does not. Exotics can come in any biological form, but they are not necessarily a problem to their new habitat (think: earthworms). It’s when an exotic species becomes an invasive species that there is a problem because invasives cause environmental, economic, and/or human health harms. The reason for this is that they did not evolve together with the ecosystem in which they find themselves. There are no checks and balances in place to curb their population growth, things like predators, parasites, and competitors. Their unnaturally large population numbers then become harmful to the native species that suddenly have to deal with and compete against them, dramatically altering the community and habitat.

It is often the case that multiple species invade a region. Throughout the rest of this post I’ll be discussing new papers by Michael Kaspari and Michael Weiser and by LeBrun, Jones, and Gilbert (specifically at the latter) that take a look at just such a case in ants. The red imported fire ant (Solenopsis invicta) first came to the United States from South America around 1930. This species is far more aggressive than your typical American ant, not only in how they like the bite the hell out you (that’s a lot of personal experience talking) but also in their predatory abilities and landscape re-engineering. Now enter the tawny crazy ant (Nylanderia fulva). This new exotic invasive species was transported to the southeastern U.S. in the early 1980s and has begun to spread.. These two species have common source assemblages, their native ranges overlapping in northern Argentina, Paraguay, and southern Brazil. Until the introduction of crazy ants, the fire ant has enjoyed an uninterrupted domination of the native grassland ant assemblages. But now that the crazy ant has arrived on the scene they are displacing the fire ants. Why is this?

Since the fire and crazy ants have overlapping native habitats, they have evolved to compete directly for resources. The tawny crazy ant easily expels the fire ant from any food items it controls, up to 93 percent of the time. Also, tawny crazy ants have often been found living inside fire ant mounts, having usurped the mound and evicted the owners. Fire ants are strong and resilient and so the crazy ants must have a strong competitive advantage.

Now, finally, we get to the meat of the post: chemical warfare. If you've been stung by a fire ant (or ants, plural, as is usually the case) then you know that they pack a wallop! They have an alkaloid venom called Solenopsin that to humans causes a painful, fiery sting, and to other ants acts as a topical insecticide. The crazy ants do not have stingers but instead possess an acidopore (a specialized exocrine gland) on the end of the abdomen that sprays their venom into a mist of formic acid. They will charge into masses of fire ants misting as they go. But the fire ants don’t just stand by idly to be sprayed with venom and die, they fight back. The fire ants “gaster flag,” extruding venom from their stingers and dabbing it onto a nearby attacking ant. Normally this would result in the death of said ant. However, LeBrun and his colleagues have observed what they are calling a “detoxifying behavior” in the attacking tawny crazy ants. In this behavior, an afflicted ant stands on its hind legs, run its front legs through its mandibles, and grooms itself vigorously, periodically reapplying its acidopore to its mandibles (check out the video!).

To test this behavior the researchers conducted a series of experiments to see if there is really a detoxifying component, to see where it is coming from, and to evaluate the species-level specificity of the behavior. For the first they staged antagonistic interactions between the two species, sealing a portion of the crazy ant acidopores, and then observing afflicted individuals for behavior and survivorship. They found that those tawny crazy ants that had had their acidopores sealed had a low survival rate (only 48 percent). However, those with working acidophores had a 98 percent survival rate, supporting the detoxifying hypothesis. The Dufour’s and venom glands (exocrine glands used for communication and defense) both duct to the acidopore in this species. To see where the detoxifying agent was coming from they applied solutions of fire ant venom and tawny crazy ant glandular products to Argentine ants (Linepithema humile), which are morphologically similar to crazy ants but do not have the detoxifying capability. These tests showed the venom gland of the crazy ant to contain the detoxifying agent. When the crazy ant’s formic acid was tested it was found to be the compound responsible for detoxifying fire ant venom.

The production and application of this antidote is a potentially costly endeavor for the crazy ants. Yes, it is the difference between life and death, but when to apply it must be considered. Why use a costly resource if you don’t have to? The authors conducted a series of ant interaction tests where they had crazy ants interact independently with eight Texas ant species including fire ants, observing when the crazy ants chose to apply their detoxifier. They found that after chemical conflict with fire ants, crazy ants detoxified themselves with almost 7 times more frequently than the average response to other ant species. This suggests that this detoxifying behavior is specifically adapted to competition with fire ants, and it is probably a key factor in the displacement of invasive fire ants now underway in the southern United States.


LeBrun, E., Jones, N., & Gilbert, L. (2014). Chemical Warfare Among Invaders: A Detoxification Interaction Facilitates an Ant Invasion Science, 343 (6174), 1014-1017 DOI: 10.1126/science.1245833


Kaspari, M., & Weiser, M. (2014). Meet the New Boss, Same as the Old Boss Science, 343 (6174), 974-975 DOI: 10.1126/science.1251272


U.S. Fish and Wildlife Service's page on Invasive Species
The University of Texas at Austin Fire Ant Project
Texas A&M AgriLife Research Extension page on Tawny Crazy Ants

Science Heroes

I recently received this video in a promotional email by Life Technologies. I haven't posted a creative, sciency ad in a while. Although, I've yet to find an ad that surpasses BioRad's The PCR Song or even Eppendorf's epMotion ad.

Science Knitting

Science Dump recently posted some creative science knitting projects. Here are a few of my favorites from their selection.

Happy Bacteria

Frog Dissection

Neurons

Heart

Chromosomes

Molecule

Skeleton

Fun with Fundulus: The Evolution of Pollution Resistance in Killifish

(credit to Evan D'Alessandro, Rosenstiel School of Marine and Atmospheric Science)

In honor of Mr. Charlie Darwin’s birthday I thought I would read an evolution paper. Put that together with the turn my career has taken into ecotoxicology (and the associated steep learning curve), I was steered towards a study about adapting to pollution.

Let me start by introducing you to today’s study organism: The mummichog (Fundulus heteroclitus) is a species of non-migratory killifish found along the Atlantic coast of North America. They can be found in the brackish waters of tidal creeks, saltwater marshes, and estuaries. These fish are remarkably hardy, adaptable, and easy to study. Throughout the decades, a great deal of knowledge has been gathered about their life history, genetics, behavior, and endocrinology. They have also been used to study embryological processes and responses to chemicals and toxins. The mummichog’s adaptability to varying temperature, salinity, and oxygen along with their ability to survive in highly polluted areas has made them a popular subject in toxicology.

We know that animal populations adapt to environmental stressors through genetic and epigenetic (heritable changes in gene activity that are not caused by changes in the DNA sequence) changes. Changes that, in turn, affect gene expression and/or protein function. In this way, toxic chemicals can drive selection. A big part of the field of toxicology is understanding the molecular basis of these changes as natural populations adapt to altered environments. The mummichog’s ability to live in grossly contaminated waters has been used to better test and understand the molecular mechanisms by which natural populations adapt to long-term, multi-generational exposure to pollution.

Toxicologists, like geneticists, seem to love acronyms. And once you start reading chemical names, you know why. So let’s get some chemical terminology out of the way first. There are several chemicals that are under the umbrella of “dioxin-like compounds” (DLCs) which are by-products of various industrial processes and are all highly toxic. Aromatic hydrocarbons such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polycyclic aromatic hydrocarbons (PAHs) all cause toxicity similar to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and DLCs. This toxicity manifests as interference in embryonic development, reproductive problems, immune impairment, and other not-so-pretty consequences.

A new study in BMC Evolutionary Biology takes a look at the Fundulus of New Bedford Harbor, Massachusetts. This 18,000 acre estuary and seaport is one of the EPA’s Superfund sites. It is highly contaminated with PCBs and heavy metals. Through their various stages of development and into adulthood, the killifish of these waters are less sensitive and/or resistant to the effects of the toxins. The researchers took a candidate gene approach to investigate the molecular basis of this adaptation to DLCs. To do this, they went to New Bedford Harbor and other polluted sites to collect fish. They also collected from reference sites where the PCB sensitivities of the killifish have been characterized and measured. Their methods included a lot of genetic work that, for the sake of space and sanity, I’m not going to detail. Let’s just skip along to the results shall we?

The researchers found a repeated evolution of resistance to DLCs in widely separated populations of Fundulus along the east coast of the U.S. There is strong evidence that this adaptation involves altered sensitivity of the aryl hydrocarbon receptor (AHR). Genes encoding proteins in the (AHR)-dependent signaling pathway are a master regulator of responses to many of the most toxic DLCs. The AHR is a ligand-activated transcription factor that exhibits high affinity for DLCs, regulates the expression of a large set of genes in response to DLC exposure, and is required for TCDD or PCB toxicity in fish (and mammals too). Two paralogs (or clades) of the AHR pathway have been identified in mummichog, AHR1 and AHR2, as well as an AHR repressor (AHRR). The loci (gene locations) for these three genes were found to contain a large number of polymorphisms, many of which encoded changes in amino acids. Perhaps most interesting was AHR2, the predominant form expressed in many fishes which has 951 amino acids whose variants lead to 26 different forms of the protein. The genetic diversity at these the three loci was not significantly different between contaminated and reference sites except in the case of AHR2. This paralog had significant FST values (the fixation index that measures population differentiation due to genetic structure) and showed very low nucleotide variability (0.1%).

So what's happening here? When polluted sites are compared to reference sites there is similar genetic diversity. However, when you look at specific nucleotides you see a story start to emerge. AHR1, AHR2, and AHRR are resistance genes that mediate toxic effects, and populations of killifish exhibit strong genetic structure at all three of these loci. The selection observed at AHR1 and AHR2, specifically the latter, at the highly polluted New Bedford Harbor site suggests an adaptation to the PCBs present there. AHR2 seems to be one of the genes, possibly the major one, involved in this resistance and may be one of the recurring targets for selection during local adaptation to DLCs. This adaptation allows the mummichog to survive in a really polluted environment. These results are consistent with several lines of evidence from similar studies both in the field and the lab.

Witnessing, quantifying, and mapping these mechanisms greatly advances our understanding of the consequences of environmental toxins. Overall, this is a very interesting example of adaptation in an ever changing environment.


Adam M. Reitzel, Sibel I. Karchner, Diana G. Franks, Brad R. Evans, Diane Nacci, Denise Champlin, Verónica M. Vieira, & Mark E. Hahn (2014). Genetic variation at aryl hydrocarbon receptor (AHR) loci in populations of Atlantic killifish (Fundulus heteroclitus) inhabiting polluted and reference habitats BMC Evolutionary Biology, 14 (1) DOI: 10.1186/1471-2148-14-6


Read more about this study in the Woods Hole Oceanographic Institute's New Release "Solving An Evolutionary Puzzle New Bedford Harbor Pollution Prompts PCB-Resistance in Atlantic Killifish"
(also the source of the above image)

EPA's New Bedford Harbor Superfund Site page

And you can learn more about how the mummichog became a model organism here:
Atz, J. W. 1986. Fundulus heteroclitus in the Laboratory: A History. Amer. Zool. 26(1): 111-120. DOI: 10.1093/icb/26.1.111 (LINK)