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First published online August 22, 2008
Journal of Experimental Biology 211, 2773-2778 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.019133
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Methyl farnesoate couples environmental changes to testicular development in the crab Carcinus maenas

G. P. C. Nagaraju and D. W. Borst*

Department of Biology, University of Central Florida, Orlando, FL 32816, USA


Figure 1
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  		Fig. 1. Red-phase and green-phase male Carcinus maenas differ in the occurrence of methyl farnesoate (MF) in their hemolymph and in their testicular development. (A) Red-phase males (N=37) are more likely to have detectable MF (>2 ng ml–1) in their hemolymph than green-phase animals (N=24; **P<0.01; Fisher's exact test). (B) The testicular index (TI) was 79% greater in red-phase than in green-phase crabs (values ± s.e.m.; N=12 for each group; ***P<0.001; Student's t-test).

 

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  		Fig. 2. Red-phase and green-phase male crabs respond differently to a hyposalinity challenge. Crabs were acclimated to 33 ppt seawater (SW) for one week and then transferred to 5 ppt SW for 24 h. (A) Some red-phase males (37 and 30%) had detectable MF in 33 ppt SW at 11°C and 18°C, respectively. Hyposalinity treatment increased the percentage (94 and 92%, respectively; N=12; ***P<0.001; Fisher's exact test). (B) Red-phase males with detectable MF had similar MF levels at each temperature and salinity (values ± s.e.m.; P>0.05; N=12). (C) Few green-phase crabs had detectable MF at either temperature in 33 ppt SW. Only one responded to 5 ppt SW at 11°C whereas 100% did at 18°C (N=12; ***P<0.001; Fisher's exact test).

 

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  		Fig. 3. Hemolymph levels of MF increase after eyestalk ablation (ESA). Animals without detectable methyl farnesoate (MF) were held in 33 ppt SW at 11°C until used. (A) All of the green-phase (N=6) and red-phase (N=5) males had detectable MF after ESA. On day 1, the amount of MF (values ± s.e.m.) was lower in green-phase males than in red-phase crabs (***P<0.001, t-test). By day 5 the levels were similar (P>0.05, t-test). (B) Red-phase (N=8) and (C) green-phase (N=7) males were treated with 5 or 33 ppt SW at 11 or 18°C, 5 or more days after ESA. SW at 5 ppt did not significantly increase MF levels of crabs in either color phase at either temperature. SW at 18°C increased MF levels, most notably at 5 ppt (bars with different letters = P<0.01, ns = P>0.05; ANOVA).

 

Figure 4
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  		Fig. 4. The testicular index (TI) of green-phase males increased by treatments that elevate methyl farnesoate (MF) levels. Animals were treated for 15 days and the effect on their TI was determined. (A) Green-phase males were injected on days 1, 5, and 10 with either the vehicle (N=4) or with MF (N=6). MF treatment caused a significant increase in TI (**P<0.01). (B) Green-phase males were held in 33 ppt SW at 11°C prior to the experiment. One group of animals (N=6) was analyzed on the initial day of the experiment. Animals maintained in 33 ppt SW 11°C for 15 days (Intact, N=6) had no change in their TI whereas eyestalk ablation (ESA) animals (N=5) had a significantly elevation. Transfer of animals to 33 ppt SW at 18°C (N=6) for 15 days caused a moderate increase in TI, and transfer of animals to 5 ppt SW at 18°C (N=6) caused a larger increase in TI. Bars with different letters = P<0.05; ANOVA).

 

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© The Company of Biologists Ltd 2008