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First published online January 18, 2008
Journal of Experimental Biology 211, 370-376 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013458
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Swarm formation in the desert locust Schistocerca gregaria: isolation and NMR analysis of the primary maternal gregarizing agent

Gabriel A. Miller1,2, M. Saiful Islam2,3, Timothy D. W. Claridge4, Tim Dodgson1 and Stephen J. Simpson1,2,*

1 School of Biological Sciences, The University of Sydney, Heydon-Laurence Building A08, NSW 2006, Australia
2 Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
3 Department of Zoology, University of Rajshahi, Rajshahi 6205, Bangladesh
4 Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3QH, UK


Figure 1
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  		Fig. 1. Preferential solubility in polar solvents and dose-dependent behavioural effects of egg foam bioactive components. (A) Effects on hatchling phase state (represented by median Pgregarious values) when water, ethanol or hexane are applied to eggs are compared to the effects of the same solvents applied to eggs following their use for either egg-washing or extraction of egg foam compounds. Asterisks indicate significant changes relative to control (see Table 2). Solitary-reared hatchlings (egg pods in parentheses): N=50 (4). Water: control, N=14 (9); wash, N=15 (9); extract, N=15 (9). Ethanol: control, N=15 (9); wash, N=13 (9); extract, N=14 (9). Hexane: control, N=14 (9); wash, N=13 (9); extract, N=11 (9). (B) Varying doses of whole extract HPLC eluent applied to eggs reveals a significant dose-dependent effect (P=0.002, one-tailed Jonckheere–Terpstra test). The median Pgregarious value for crude (unprocessed by HPLC) foam extract at a concentration of 0.1 foam plug equivalent is shown as a broken line. Individuals per treatment are shown above bars with number of contributing egg pods in parentheses.

 

Figure 2
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  		Fig. 2. Iterative HPLC separation (A–E) and behavioural bioassay results (F–J) of egg foam compounds. Eggs treated with HPLC fractions flanked by broken red lines give rise to predominately gregariously behaving hatchlings (corresponding red histograms; median Pgregarious=0.5). In the coarsest (i.e. primary) separation, all egg foam compounds were parsed into four fractions (A; F1–F4) and tested in a logistic regression behavioural bioassay (see text) for gregarizing properties (F). In the secondary run, components of fraction 3 were collected individually (B) and tested for bioactivity (G). The tertiary (C,H) and quaternary (D,I) runs were analogous with still greater specificity. Peak labelling is hierarchical and reflects peak origin in terms of previous fractions. The top row of histograms for each trial (F–I) shows the effect of known gregarizing compounds, sometimes reiterating findings of previous runs, applied to eggs as positive controls. Histogram bin widths=0.11 Pgregarious units. Median Pgregarious values are indicated by dotted grey lines. Peak areas (in black, E), representing F3.2.1.2 (relabelled peak X for clarity) and close analogues peaks Y and Z, were recorded for later use (see Fig. 4). Control behavioural classifications of known crowd- and solitary-reared individuals are provided (J). Insects from F were randomly drawn from four egg pods, (G) from four egg pods, (H) from nine egg pods, (I) from 13 egg pods and (J) (solitary-reared) from four egg pods.

 

Figure 3
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  		Fig. 3. Structural analysis. NMR spectroscopy (A) suggests the bioactive foam agent is an alkylated L-dopa analogue with either para- or ortho-substituted hydroxyl groups (B). The alkyl side chain (R) is probably an ethyl or propyl group. NMR data are summarized in the text as well as in Table 2.

 

Figure 4
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  		Fig. 4. Relative amounts of related peaks X, Y and Z (see Fig. 2D,E) in foam from solitarious and gregarious locust egg pods. Peak Y is significantly elevated in solitarious versus gregarious foam, whereas Peak X is unchanged (Sidák-corrected Mann–Whitney, P=0.03 and P=0.22, respectively). Boxplot whiskers represent 10th and 90th percentiles.

 

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© The Company of Biologists Ltd 2008