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First published online June 27, 2008
Journal of Experimental Biology 211, 2358-2368 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.015263
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Phylogeny, scaling, and the generation of extreme forces in trap-jaw ants

Joseph C. Spagna1,2,*, Antonis I. Vakis1,3, Chris A. Schmidt4, Sheila N. Patek5, Xudong Zhang1,3, Neil D. Tsutsui6 and Andrew V. Suarez1,2

1 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
2 Department of Entomology and Department of Animal Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
3 Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
4 Graduate Interdisciplinary Program in Insect Science, University of Arizona, Tucson, AZ 85721, USA
5 Department of Integrative Biology, University of California, Berkeley, CA 94720, USA
6 Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA


Figure 1
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  		Fig. 1. Majority-rule combined-data Bayesian tree for taxa of interest and outgroups, with branch lengths proportional to genetic change. Names of species providing jaw-strike data are in bold.

 

Figure 2
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  		Fig. 2. Histogram of lag time between jaw firing in two-jaw strikes from all species (N=79 strikes), mode=30–40 µs, mean=54 µs. First bin represents simultaneous closure.

 

Figure 3
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  		Fig. 3. Isometric scaling of independent contrast values for Odontomachus species. OLS regressions of normalized independent contrast values (IC) for body mass, jaw length and jaw mass against head width, with intercept set to the origin. All have slopes that do not depart significantly from null hypothesis of isometry for linear scaling (slope=1) or for mass scaling (slope=3), as follows: jaw length: P=0.0053, slope=1.12, 95% confidence interval for slope=0.61–1.63, r2=0.75; jaw mass: P=0.0018 slope=3.26, 95% CI=2.07–4.45, r2=0.82; body mass: P<0.001, slope=2.94, 95% CI=2.03–3.85, r2=0.87.

 

Figure 4
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  		Fig. 4. Mean maximum radial speeds for all jaws of eight species of Odontomachus. One-way ANOVA significant (P<0.001). Species arranged from left to right by mean mass (lowest to highest). Species with the same letters (A–E) are statistically indistinguishable from each other at the P<0.05 level in post-hoc pairwise tests. Maximum jaw speeds of O. clarus desertorum and O. erythrocephalus (group A) are significantly higher than previous highest reported value for self-propelled prey strike in animals [O. bauri (Patek et al., 2006Go)].

 

Figure 5
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  		Fig. 5. (A) Mean (± s.d.) maximum angular acceleration ({alpha}) by species, in radians s–2. Species arranged from lowest mean mass to largest, left to right. Secondary error bars (dotted lines) represent digitization error for groups in which this was estimated. (B) Scatterplot and regression of independent contrast (IC) values for log10-transformed jaw accelerations vs log10 head width (P=0.04, slope=–1.54, 95% CI=–2.72 to –0.354, r2=0.52).

 

Figure 6
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  		Fig. 6. (A) Mean maximum single-jaw forces (± s.d.), by species. Species arranged from lowest mean mass to largest, left to right Modeling force as a product of jaw length, jaw mass and maximum acceleration (see Eqn. 2) reveals significant differences in force production (one-way ANOVA, P<0.001). (B) Comparison of species means (squares) to model predictions from phylogenetic comparative model (line), with quantitative x-axis.

 

Figure 7
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  		Fig. 7. Phylogeny, head size and force production in Odontomachus. Head sizes are species means, scaled to 2 mm bar. Bar graph shows force production predicted by independent-contrast model (blue bars), species mean data (maroon bars), and star-phylogeny model (beige bars) for each species studied. Forces calculated from actual species means differed from head width-based predictions from phylogenetically corrected models by an absolute mean value of 12%, and from the uncorrected models by 11%. Predictions derived from uncorrected (star-phylogeny) and phylogeny-corrected models differed by an average of 3%.

 

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© The Company of Biologists Ltd 2008