Ant-Mimicking Spider Relies on a “Double-Deception” Strategy to Fool Different Audiences

From snakes that look like they have two heads to color-shifting chameleons, deception is at the heart of many animals’ survival strategies.  Both visual and chemical predator deterrence are well-documented phenomena in the animal world, but new research on ant-mimicking spiders, published in PLOS ONE, may be the first documented case of a species that uses visual deception to elude one group of predators, and chemical deception to escape another.

Ant mimicry, or myrmecomorphy, is a tactic used by numerous spider species, and with good reason, since many predators steer clear of preying on ants due to their aggressive tendencies and often unpleasant taste. Ant-mimicking spiders can have body shapes that closely resemble those of ants, as well as colored patches that look like ant eyes.  Combine these characteristics with behaviors such as waving their front legs in the air to resemble probing ant antennae, and these spiders can successfully convince predators to look elsewhere for their next meal.  The jumping spider Peckhamia picata is one such ant mimic whose visual signals are an effective deterrent for visually focused predators, such as other species of jumping spiders.  The picture below shows a jumping spider on the left and the ant it imitates on the right.

1 Ant mimic and predators

The PLOS ONE study shows that the ant-mimicking spider can also elude predators that rely heavily on chemical signals to identify their prey.  In the current study, the spiders successfully eluded spider-hunting mud-dauber wasps (pictured below), and received significantly less aggression from the ants they mimic than other non-mimicking jumping spiders. The researchers presented wasps with a choice between freshly killed ant-mimicking and non-mimicking spiders. In all of the trials conducted, the wasp probed both types of spiders with their antennae, but every time the wasps chose to sting and capture a spider (seven out of eight times), it chose the non-mimicking spider.The researchers also staged encounters between Camponotus ants and live ant-mimicking and non-mimicking spiders.  After probing them with their antennae, the ants were significantly less likely to bite the ant-mimicking spiders than non-mimicking ones.  These results demonstrate that the jumping spider has a remarkably effective ability to deceive potential predators who focus on chemical cues when selecting prey.

2 wasp

The researchers point out that the spider is not a chemical mimic of the ant species it emulates. Insects rely heavily on hydrocarbons secreted from their cuticles (the hard outer covering of invertebrates) to identify and signal one another. It turns out that ant-mimicking spiders have very low levels of these molecules, only a small fraction of the amount found in non-mimicking spiders and the ants themselves. While further research is required to fully explain the jumping spider’s chemical mechanism for predator evasion, a likely explanation is that the low level of these chemicals does not register as significant to a probing ant or wasp, and the chemical evasion is accomplished in this way.

This study may be the first to describe an animal using a “double-deception” strategy:  visual tricks and a deceptive chemical signature, both intended for different audiences.  The authors hypothesize that this kind of chemical deception is likely widespread among other visual mimics in the animal kingdom.

Related links:

Video of a ramblin’ ant-mimicking jumping spider (great music)

Spiders gather in groups to impersonate ants

Citation: Uma D, Durkee C, Herzner G, Weiss M (2013) Double Deception: Ant-Mimicking Spiders Elude Both Visually- and Chemically-Oriented Predators. PLoS ONE 8(11): e79660. doi:10.1371/journal.pone.0079660

Images:  Images come from Figure 1 of the manuscript

Bird Enthusiasts & Coffee Aficionados, Unite!

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Do you like fancy coffee? Birds do too, but not for the morning pick-me-up that millions of people rely on every day.

Agroforestry, the practice of growing crops alongside larger native trees and shrubs in a heterogeneous landscape, can provide a host of benefits to farmers and the environment, from increased crop productivity and soil fertility to protection against erosion, winds, and flooding. In Costa Rica, where coffee is often grown in agroforests, there may be yet another advantage to this kind of land use: birds have taken a liking to these shade-grown coffee plantations.

In the past, global conservation efforts were largely focused on setting aside as much pristine land as possible, but increasingly, the effort to protect the environment includes recommending steps we can take to use land in a more eco-friendly way. Given the habitat loss from shrinking forests in Costa Rica, researchers from the University of Georgia asked how well shade-grown coffee plantations could function as a “surrogate habitat” for birds. Past research has found a high degree of biodiversity in Costa Rica’s coffee agroforests, but much of it was limited in scope or focused on individual species. This latest research, published in PLOS ONE, provides a detailed analysis of avian populations in these coffee agroforests.

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In this study, scientists hung mist nets in both undeveloped forest patches and in coffee agroforests, to capture and count nearly one hundred different bird species in the Monteverde region of Costa Rica, a major ecotourism hotspot (arial photo of collection site below). Using models that accounted for seasonal differences in the two habitats, capture rates for different bird species, and bird community behaviors, the researchers described three different bird communities–insectivores, omnivores, and frugivores (fruit eaters)–in secondary forest habitats and in shade-grown coffee agroforests.  In particular, the analysis showed that the bird community composition and dynamics in shade-grown coffee plantations embedded in the tropical landscape are very similar (although not identical) to those found in secondary forests, a finding which supports the hypothesis that coffee agroforests can be a suitable surrogate habitat for birds.

Figure 1

The authors also suggest that the coffee agroforests may serve as wildlife corridors for birds, allowing them to move freely between larger patches of forest within a fragmented landscape. This kind of habitat linkage is critical, as connecting wild spaces via such corridors maximizes the ecological benefits they provide. The authors do caution that providing managed habitat for birds in the form of shade-grown coffee should be viewed as a complementary rather than a contradictory strategy for protecting bird habitat, as nothing can substitute for the preservation of forest habitat. But in a region where ecotourism and birdwatchers are primary economic drivers (the Three-wattled Bellbird and Resplendent Quetzal are two prominent locals), this knowledge could help inform the land management decisions that are so crucial to birds and humans alike.

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Read more about conservation efforts in the forests of Borneo

What animals might you find in southern California avocado orchards?

Citation: Hernandez SM, Mattsson BJ, Peters VE, Cooper RJ, Carroll CR (2013) Coffee Agroforests Remain Beneficial for Neotropical Bird Community Conservation across Seasons. PLoS ONE 8(9): e65101. doi:10.1371/journal.pone.0065101

Image 1: Coffee agroforest in Costa Rica from Wikipedia

Image 2: Image of a Resplendent Quetzal on Flickr by Frank Vassen

Image 3: Figure 1 of the manuscript

Whisker Shape and Orientation Help Seals and Sea Lions Minimize Self-Noise

While it doesn’t always pay to take the path of least resistance, sometimes it’s best to just go with the flow. New research on seal and sea lion whiskers help explain how they are adapted to do just that.

Whiskers, more technically known as vibrissae, provide their owners with important sensory information about the world around them. The follicle of each whisker is connected to many nerves, allowing an animal to “feel” its surroundings by picking up tiny vibrations in air or water. Sea lions (pictured left) and seals (right), like land mammals, are equipped with a highly sensitive array of whiskers that allows them to detect disturbances from afar or zero in on the wake of their next meal. A new study published in PLOS ONE explores the characteristics of seal and sea lion whiskers that make them particularly well-suited to underwater signal detection.

Researchers at the University of Florida investigated the hydrodynamic properties — the natural properties of liquids in motion — of whiskers from three different pinniped species: harbor seals, northern elephant seals, and California sea lions. Using CT scanning, researchers precisely measured the shape of each species’ whiskers.  While the cross sections of whiskers in land mammals are almost perfectly circular, seal and sea lion whiskers are somewhat flattened, in the shape of an oval. In this study, the researchers ran water currents over the pinniped whiskers at different angles, watched how the whiskers responded, and, measured the amount of whisker vibration at different orientations relative to the current.

The orientation of the whiskers, it turns out, affects how much they vibrate. The authors found that when the skinny edge of the whisker angled into the flow of water, the whisker vibrated far less than when the flat side faced the current.

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The authors suggest that the flat shape of each whisker and its resting orientation — specifically, skinny side angled into the flow of water — may minimize the amount of self-induced whisker vibration generated by normal, forward swimming (video). The reduced base-level “whisker noise” may help whiskered marine mammals better detect important vibrations in the water, caused by the environment and nearby animals. And that, really, is what the whiskers are there for in the first place.

Citation: Murphy CT, Eberhardt WC, Calhoun BH, Mann KA, et al. (2013) Effect of Angle on Flow-Induced Vibrations of Pinniped Vibrissae. PLoS ONE 8(7): e69872. doi:10.1371/journal.pone.0069872

Image: Image comes from Figure 5 of the manuscript