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First published online January 8, 2007
Journal of Experimental Biology 210, 261-268 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02631
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Growing out of a caste - reproduction and the making of the queen mole-rat

Erin C. Henry1, Christine M. Dengler-Crish2 and Kenneth C. Catania1,*

1 Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA
2 Department of Neuroscience Graduate Program, Vanderbilt University, Nashville, TN 37235, USA


Figure 1
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  		Fig. 1. Radiographs of the naked mole-rats. (A) Relative sizes of mole-rats examined in the study. All images are aligned at the base of the L8 vertebra (broken line). The solid white line is aligned to the top of the lumbar spinal column (anterior aspect of L1) in the breeding female (02-04). Only the established breeding female has a comparably long lumbar spinal column. (B) Diagram showing the width across the zygomatic arch (white line) and the labeling scheme for the lumbar vertebra, with L4 marked with an asterisk. (C) Two images of the same female mole-rat taken at the beginning and end of the study. (D) An image of a late-stage pregnant mole-rat. Scale bar for all panels=2 cm.

 

Figure 2
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  		Fig. 2. Lumbar vertebra growth over time. (A) Each dot on the graph represents the length of the L4 vertebra at the time of radiography. The three breeders (02-02, 02-04 and 02-05) show increased growth of L4 over time as compared with nonbreeders and the breeding male. Starred dots indicate the L4 measurement just prior to parturition (parturition <7 days from recorded radiograph). (B) An expanded view of pregnancy 5 for Breeder 02-04 (enlarged version of the boxed area in A). Growth occurs throughout the 10-week pregnancy, ending at parturition (starred dot).

 

Figure 3
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  		Fig. 3. Lumbar vertebra lengthening exceeds non-specific body growth. (A) The ratio of L4 length to zygomatic arch (ZA) width over time reveals that lumbar growth is occurring at a higher rate than ZA growth (a marker for general growth) in the new queens. Starred dots indicate births. (B) Bar graph plots the percentage change in L4 length and ZA width over the course of the study. The new queens (02-02, 02-04 and 02-05) all have greater increases in L4 length compared with ZA width. The other mole-rats show minimal differences in the percentage change of the two measurements.

 

Figure 4
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  		Fig. 4. Growth changes for each lumbar vertebra were normalized for general body enlargement using the ratio of L#/ZA for the eight vertebra (#=1-8) and (L1-L8)/ZA for the total lumbar spinal column, which includes intervertebral spaces. The ratios were calculated using the beginning and ending vertebrae and zygomatic arch (ZA) values to derive the percentage change over time. The results are reported for the three breeding females (02-02, 02-04 and 02-05), the nonbreeding female (02-13) and the breeding male (02-01).

 

Figure 5
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  		Fig. 5. Pregnancy periods (P) have higher growth rates compared with nonpregnancy periods (NP). (A-C) The mean growth rates for pregnancy and nonpregnancy periods, plotted on an arbitrary 10-week time scale. (A) Breeder 02-02 mean growth rates for pregnancy (N=6) and nonpregnancy (N=2) periods. (B) Breeder 02-04 mean growth rates for pregnancy (N=7) and nonpregnancy (N=2) periods. (C) Breeder 02-05 mean growth rates for pregnancy (N=5) and nonpregnancy (N=3) periods. (D) The mean L4 growth over time for the three breeders during pregnancy (black dots; N=18) and non-pregnancy (gray dots; N=7) time periods. The data from the three animals were standardized to baseline before they were averaged. The raw data used to generate the means varied in number between data points because some X-rays were excluded due to poor image quality (criteria for exclusion included images where the bones were not in focus or at an angle, which often happened if the mole-rat had moved or shifted during the X-ray exposure). Further, some of the nonpregnancy periods were less than 10 weeks in length, which also affected the number of data points. The N values for each data point used to generate this panel are listed in Table 3. Regression lines were fitted to both sets of data. Error bars in panels A-D represent ± s.e.m.

 

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© The Company of Biologists Ltd 2007