Rhode Island State Council on the Arts (1979-1992): Report 02

.csv file with the outcome data for predatory trials in the restraint experimen

Summary

Data summarizing the outcomes of trials between unrestrained trap-jaw ants (Odontomachus brunneus) and pitbuilding antlion

Mandible-Powered Escape Jumps in Trap-Jaw Ants Increase Survival Rates during Predator-Prey Encounters

<div><p>Animals use a variety of escape mechanisms to increase the probability of surviving predatory attacks. Antipredator defenses can be elaborate, making their evolutionary origin unclear. Trap-jaw ants are known for their rapid and powerful predatory mandible strikes, and some species have been observed to direct those strikes at the substrate, thereby launching themselves into the air away from a potential threat. This potential escape mechanism has never been examined in a natural context. We studied the use of mandible-powered jumping in <i>Odontomachus brunneus</i> during their interactions with a common ant predator: pit-building antlions. We observed that while trap-jaw ant workers escaped from antlion pits by running in about half of interactions, in 15% of interactions they escaped by mandible-powered jumping. To test whether escape jumps improved individual survival, we experimentally prevented workers from jumping and measured their escape rate. Workers with unrestrained mandibles escaped from antlion pits significantly more frequently than workers with restrained mandibles. Our results indicate that some trap-jaw ant species can use mandible-powered jumps to escape from common predators. These results also provide a charismatic example of evolutionary co-option, where a trait that evolved for one function (predation) has been co-opted for another (defense).</p></div

Restrained mandibles.

<p>Trap-jaw ant mandibles were glued shut to prevent ants from snapping.</p

Frequency of escape behavior by trap-jaw ants in restraint experiment.

<p>Frequency of escape by running or jumping was quantified for each interaction. Ants were unmanipulated (Control), had glue applied to the exterior edge of mandible (Mock), or had their mandibles glued shut (Restrained). Each treatment was replicated 76 times.</p

Still images from high-speed video (S2 Video) showing escape jumps of <i>Odontomachus brunneus</i> during interactions with the antlion, <i>Myrmeleon carolinus</i>.

<p>After being attacked by an antlion (location at base of pit marked by black arrows in each frame), the trap-jaw ant (white arrows in each frame) strikes the side or center of the pit with her mandibles and propels herself away from the antlion. Time stamp indicates the time elapsed since first frame (upper left). Scale bar = 1cm.</p

Distribution of first detection locations of invasive alien species in mainland China.

<p>Provincial administrative units in mainland China were separated into three groups according to their geographic position: coastal region in blue ( = provinces with sea coasts except Beijing), border region in grey ( = provinces continuous to other countries) and midland region in white ( = provinces without sea coasts or borders on other countries). Bars in red are the number of first detection locations in each province. Bars in yellow and green (for the average GDP and import value of commodities from 1986 to 2007, respectively) are standardized with same height in Guangdong province which has the highest GDP and the highest number of first detection locations. AH, BJ, CQ, FJ, GS, GD, GX, GZ, HeB, HeN, HLJ, HN, HuB, HuN, JL, JS, JX, NMG, NX, QH, SD, SaX, SaaX, SC, SH, TJ, XJ, XZ, YN and ZJ are provinces codes, standing for Anhui, Beijing, Chongqing, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hebei, Henan, Heilongjiang, Hainan, Hubei, Hunan, Jilin, Jiangsu, Jiangxi, Inner Mongolia, Ningxia, Qinghai, Shandong, Shanxi, Shaanxi, Sichuan, Shanghai, Tianjin, Xinjiang, Tibet, Yunnan and Zhejiang, respectively.</p

List of explanatory variables in China by province.

a<p>DI: Disturbance; EB: Ecological/bio-geographical variance; IP: Introduction pressure; SE: Search and recording effort; SI: Spread by unintentional introduction.</p>b<p>Data of variables except EN, AP, WP, LP, NC and NP were collected from National Bureau of Statistics of China (1986–2007) China statistical yearbook. The mean values of these variables were used for data analysis. Endemism score (EN) means the total values of endemism of species including plants, mammals and birds in each province, collected from McBeath G.A & Leng T.K. (2006) Governance of Biodiversity Conservation in China and Taiwan. Information about AP, WP, LP, NC and NP was collected from China Association of Port-of-Entry (2003) Practical Manual of Ports of Entry in China.</p>c<p>EEIQ: Entry-Exit Inspection and Quarantine.</p>d<p>Scientific research refers to state-owned research and development institutions above county level in the field of natural sciences and technology.</p

Regression tree analysis for the determinants of first detection location of invasive alien species.

<p>A: using all explanatory variables; B: using explanatory variables except those classified into “IP” category (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031734#pone-0031734-t001" target="_blank">Table 1</a>). Each node of the tree is described by the splitting variable, its splitting criteria, percentage of variance the splitter explains, mean ± standard deviation for the number of first detection locations of invasive alien species, and the number of sample (i.e. species) at that node in brackets. (<i>Inset</i>) Cross-validation processes for selection of the best regression trees. Line shows a single representative 10-fold cross-validation of the most frequent (modal) best trees with standard error (SE) estimates of each tree size. Bar charts are the numbers of the optimal trees of each size (frequency of tree) selected from a series of 50 cross-validations based on the minimum cost tree, which minimizes the cross-validated relative error (white, SE rule 0), and 50 cross-validations based on the one-SE rule (gray, SE rule 1), which minimizes the cross-validated relative error within one SE of the minimum. The most frequent trees have four terminal nodes. See the legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031734#pone-0031734-g001" target="_blank">Fig. 1</a> for province codes.</p

Descriptive statistics for each colony.

<p>Fat content is as a proportion of total dry body mass. Fat content and head width are reported as means +/- standard error with sample size in parentheses. Brood was present but not counted for colony 5. Colony 5 was collected in 2004 while the remainder in 2009.</p