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

A Lionfish of a Problem

Lionfish are beautiful but venomous. Very recently these fish have become quite a large problem in the Caribbean, the fastest invasion documented for a marine fish. The Indo-Pacific lionfish (Pterois miles and P. volitans) are native to the reefs of the Indian and Pacific Oceans. They are also very popular aquarium fish. Whether through accidental or purposeful releases in the late 1970’s through the present, lionfish have made their way into the Caribbean. It started out as not-so-bad (as such things do) with only 5 or 6 individuals, but the problem has grown (as such things do) to a self-sustaining population that reaches over 1,000 lionfish per acre in some locations. P volitans seems to have taken up all of the reef real estate south of the Bahamas, while both species can be found north of Florida extending to Bermuda and out in the Sargasso Sea. But what makes lionfish such a problem? Well, mainly their appetite. Lionfish are generalist carnivores with voracious appetites, consuming more than 56 species of fish and many invertebrates. They have evolved to food availability in the Pacific, which may be patchy, and so they eat as much as they can whenever they can. Using this appetite, they have been known to reduce their fish prey by up to 90 percent. They are capable of permanently impacting native fish reef communities across multiple trophic levels. Another problem? They have a very high rate of reproduction. Lionfish become sexually mature at about 7 months to 1 year old and spawn in pairs. Females will release 30,000 eggs every spawning cycle, adding up to about 2 million per year in some cases. These eggs settle out as baby fish in about 30-40 days. Are you doing the math? Because that’s a lot of fish and a really big invasion problem. Today I’m going to take a look at two papers (out of an ever-growing number) that ask why lionfish are successful invaders and which habitats within their invasion zone they flourish.

The first paper looks at why lionfish are successful by comparing Kenyan and Bahamian lionfish populations. This is not an uncommon type of comparison. However, it is seldom studied in marine invaders as a whole, and since marine predatory vertebrate invaders are rare it is even less common in this realm. The idea is relatively simple: Invasive species are not a problem in their home ranges, they are kept in check by other components and members of their ecosystem. Comparing invasive species to their native counterparts can reveal shifts in ecology and behavior and can shed light on the factors contributing to a successful invasion and even some potential control methods. This study tested if lionfish on invaded Caribbean reefs have reached greater abundance than they normally reach on their native reefs, and they tested potential ecological differences by measuring lionfish body size and activity levels between the native and introduced fish. To see if lionfish are in greater abundance and/or size in introduced areas, the researchers conducted underwater visual surveys of lionfish in both their native (Kenya) and introduced (Bahamas) ranges, recording numbers of fish and total length of each fish. During these surveys, they also recorded lionfish behavior as active (i.e., either hunting, swimming, hovering in the water column or moving over the substratum) or inactive (i.e., resting motionless on the substratum).

This study found that invading Bahamian lionfish reached a higher abundance than their ecological equivalent in Kenya. However, it is important to note that when they combined the density of all five Kenyan lionfish species they were similar to Bahamian P. volitans, and that some Bahamian reefs had much greater densities than others. The Bahamian lionfish were also about 50 percent longer and had an overall biomass that was 13 times higher than Kenyan equivalents or the Kenyan lionfish species assemblage. There are several hypotheses as to why including lack of exploitation, low predation, low predator diversity and abundance, low fishing pressure, and a release from congeneric competitors. They are so numerous that they now make up a significant portion of the fish biomass on invaded reefs.

The second paper looks at the progression of lionfish into different habitats. In their native range, P. volitans and P. miles are predominately found on coral, rock, and sand substrates from <1 to 50 meters underwater. Their invasive range has been observed to be much broader, extending into habitats that include reefs, seagrass, mangroves, and in depths from 1 to >600 meters of water. Two previous studies that have looked at this habitat question have found that mangroves supported higher densities of smaller-sized individuals than nearby reefs and that lionfish in seagrass were smaller than those on reefs (both suggesting a nursery function). And while there is an international effort to document the spread of the lionfish, there has been less emphasis placed on how a new location becomes colonized. This study looks the invasion history as well as this colonization. The study area was located around South Caicos (a small island in the Turks and Caicos Islands) and Long Cay (on the eastern edge of the Caicos Bank). Five different marine habitat types were distinguished: mangrove, seagrass, sheltered shallow reef, exposed shallow reef, and deep reef. Using surveys consisting of timed swims, relative density of lionfish (number of individuals seen per observer and per unit effort) was calculated within these habitat types from 2007 to 2010. To look at size frequencies of lionfish within these habitats, individuals were caught and depth, habitat, type of shelter used, and total length were recorded. The age of individuals was estimated from total size.

 They found that by the end of 2010, lionfish had been observed in all five habitats with relative densities consistently rising throughout the course of the study period. Back-calculation of settlement dates indicated that lionfish may have started settling there as early as 2004. Sightings during their surveys initially showed that the density of lionfish in seagrass was 20 times higher than on deep reefs, but as the study went on the relative densities became similar across the habitat types with the concluding year showing the deep reefs to have over an order of magnitude higher lionfish density than any other habitat. There was also a significant difference in the sizes of lionfish caught in different habitats. Lionfish in deep reef habitats were significantly larger than those in seagrass and sheltered reefs, but they found no size differences in individuals from shallow habitats. Individuals found in these shallow habitats were younger than those found on deep reefs. Most of the lionfish were found to shelter on, in, under, or around other structures (corals, rocks, seawalls, trash, etc.). Observations of exposed reef habitats found lionfish to be conspicuously absent until 2010. They were found preferentially (but not exclusively) to settle in shallow habitats (seagrass, sheltered reefs, mangroves) before moving to deeper water once they had grown larger. However, they would have had to pass through these exposed reefs on their way to the deep reefs. The few individuals found on exposed reefs may be a result of this movement combined with the turbulent conditions associated with this habitat type. This evidence supports the idea that seagrass, mangroves, and sheltered shallow reef areas may serve as nursery habitats and adult fish move to deeper reef habitats later.

From all I’ve gone through today, the story looks pretty bleak. And I’ll be the first to admit that it doesn’t look optimistic. But there is good news. There are several lionfish research programs and international efforts to control or even eradicate these fish from the Caribbean (see some links below). And another bonus? Apparently they taste great!

Emily S. Darling, Stephanie J. Green, Jennifer K. O’Leary, & Isabelle M. Coˆte (2011). Indo-Pacific lionfish are larger and more abundant on invaded reefs: a comparison of Kenyan and Bahamian lionfish populations Biological Invasions, 13 (9), 2045-2051.: 10.1007/s10530-011-0020-0
 
John Alexander Brightman Claydon, Marta Caterina Calosso, & Sarah Beth Traiger (2012). Progression of invasive lionfish in seagrass,mangrove and reef habitats Marine Ecology Progress Series, 448, 119-129.: 10.3354/meps09534


Here are a couple of  websites to get you started looking in to this problem:
CCFHR: Invasive Lionfish
REEF Lionfish Program
Interview with Chris Flock from Ocean Support Foundation

Something's Fishy

Humans have introduced non-native animal and plant species into aquatic and terrestrial habitats around the world at an unprecedented rate. Fish have been accidentally or intentionally introduced into river systems for over 150 years. Introduced fish are known to modify average body sizes in habitats around the world. A new study in the journal Ecology Letters reports that non-native fish are, on average, 12 cm larger than native species. This change in body size can, in many situations, greatly modify aquatic ecosystems.

After cross-referencing freshwater fish data from 1,058 river basins worldwide, the authors found that introduced fish are, on average 12 cm larger than native species. Overall, this increases the average body size of fish in a given assemblage by 2 cm. Remember back in the story about shrinking songbirds when I defined Bergmann's Rule? Its the warmer climates have larger critters rule. The authors here are suggesting that the change in fish body size affects Bergmann's Rule. Additionally, the non-natives alter the functioning of the ecosystem, whether they be predators, herbivores, or detritovores. This alteration of the food chain affects other species within the change as well as the cycling of organic matter within the system. The changes in body size worldwide are likely part of this change.

As you can probably tell there is more to the story. You can find more details in the article itself here: http://www3.interscience.wiley.com/journal/123248911/abstract (DOI: 10.1111/j.1461-0248.2009.01432.x)

(image from animals.nationalgeographic.com)