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First published online January 31, 2008
Journal of Experimental Biology 210, 4390-4398 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.010876

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Regulation of polyphenic caste differentiation in the termite Reticulitermes flavipes by interaction of intrinsic and extrinsic factors

Michael E. Scharf^*, Caitlin E. Buckspan, Traci L. Grzymala and Xuguo Zhou

Entomology and Nematology Department, University of Florida, Gainesville, FL 32611-0620, USA

View larger version (11K): [in this window] [in a new window]   Fig. 1. Impacts of temperature and juvenile hormone (JH) on soldier caste differentiation. Results shown represent cumulative presoldier formation on day 15 of assays that were conducted under four different conditions of 22° and 27°C, with and without ectopic JH. Two colonies were tested at three different times over a 1-year period. Bars with the same letter within the colony are not significantly different by non-parametric Kruskal–Wallis tests (P<0.05, N=3).

View larger version (23K): [in this window] [in a new window]   Fig. 2. Feeding over time as related to different combinations of juvenile hormone (JH) and temperature. (A) Mean (± s.d.) feeding for four treatments over time. Groups of bars within days are not significantly different (NS), as determined by non-parametric Kruskal–Wallis tests (P>0.05, N=3). (B) Linear regression results (mean ± s.d.) for feeding over time among different treatments. All regressions were significant (P<0.05, N=3). Slope values shown at the right with the same letter are not significantly different by linear regression analysis (GLM; P>0.05). Note that feeding rates were highest for the 27°C untreated controls, which have exposure to only endogenous JH.

View larger version (33K): [in this window] [in a new window]   Fig. 3. Impacts of temperature and juvenile hormone (JH) on protein abundance. Blue and red boxes indicate 22° and 27°C treatments, respectively, across assay days (d) 5, 10 and 15. Colony workers (CW) were sampled directly from colonies and used to start assays on day 0. (A) Single replicate SDS-PAGE gel after Coomassie staining (10 µg protein per lane). Noteworthy proteins are indicated, which include unknown 100 and 50 kDa proteins as well as the caste regulatory Hex-1 and Hex-2 proteins that occur in the 80–85 kDa range. The lane labeled as Mr indicates molecular mass standards in kilodaltons (kDa). (B) Mean results for densitometric scans of three SDS-PAGE gels from three independent experimental replicates. Error bars represent s.e.m.

View larger version (19K): [in this window] [in a new window]   Fig. 4. Western blot showing impacts of temperature and juvenile hormone (JH) on JH-binding by various proteins. All colors and labeling correspond identically to that described for Fig. 3. Blots were probed with anti-JH antiserum, which directly enables identification of JH covalently bound to denatured proteins. Three key proteins were identified by the anti-JH, including the Hexamerin-1 (Hex-1) protein, an unknown 100 kDa protein and another unknown group of proteins in the 50 kDa range. Molecular mass markers were pre-stained and visible before immunodetection.

View larger version (14K): [in this window] [in a new window]   Fig. 5. Linear regression analysis of (A) body mass and (B) feeding vs combined hexamerin-1 and -2 protein abundance. The regression shown in A, which is not significant, indicates no relationship between body mass and hexamerin abundance. Alternatively, the regression shown in B of feeding vs hexamerin abundance is significant (P<0.05). Note also that the two highest feeding amounts recorded were in each of the untreated controls at assay day 15; these treatments had high hexamerin levels and no presoldier differentiation.

View larger version (11K): [in this window] [in a new window]   Fig. 6. Diagram integrating conclusions of previous studies on R. flavipes caste regulation with those of the present study. Solid arrows indicate known/observed relationships, and broken arrows represent putative or proposed relationships. (A) Relationship between juvenile hormone (JH), hexamerin and JH-responsive developmental gene networks [taken from Zhou et al. (Zhou et al., 2007)]. The two principal effects observed in the present study were those of temperature (B) and feeding/nutritional status (C). Significant temporal developmental effects were also observed; however, the potential influences of this remain unclear, as well as their effects on downstream factors such as feeding and nutritional status.