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Early embryonic determination of the sexual dimorphism in segment number in geophilomorph centipedes.

Brena C, Green J, Akam M - Evodevo (2013)

Bottom Line: Sexual dimorphism in segment number is not associated with terminal segment differentiation, but must instead be related to some earlier process during segment patterning.The dimorphism may be associated with a difference in the rate and/or duration of segment addition during the main phase of rapid segment addition that precedes embryonic Stage 6.This suggests that the adaptive role, if any, of the dimorphism is likely to be related to segment number per se, and not to sexual differentiation of the terminal region.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. cb508@cam.ac.uk.

ABSTRACT

Background: Most geophilomorph centipedes show intraspecific variability in the number of leg-bearing segments. This intraspecific variability generally has a component that is related to sex, with females having on average more segments than males. Neither the developmental basis nor the adaptive role of this dimorphism is known.

Results: To determine when this sexual dimorphism in segment number is established, we have followed the development of Strigamia maritima embryos from the onset of segmentation to the first post-embryonic stage where we could determine the sex morphologically. We find that males and females differ in segment number by Stage 6.1, a point during embryogenesis when segment addition pauses while the embryo undergoes large-scale movements. We have confirmed this pattern by establishing a molecular method to determine the sex of single embryos, utilising duplex PCR amplification for Y chromosomal and autosomal sequences. This confirms that male embryos have a modal number of 43 segments visible at Stage 6, while females have 45. In our Strigamia population, adult males have a modal number of 47 leg-bearing segments, and females have 49. This implies that the sexual dimorphism in segment number is determined before the addition of the last leg-bearing segments and the terminal genital segments.

Conclusions: Sexual dimorphism in segment number is not associated with terminal segment differentiation, but must instead be related to some earlier process during segment patterning. The dimorphism may be associated with a difference in the rate and/or duration of segment addition during the main phase of rapid segment addition that precedes embryonic Stage 6. This suggests that the adaptive role, if any, of the dimorphism is likely to be related to segment number per se, and not to sexual differentiation of the terminal region.

No MeSH data available.


Number of leg-bearing segments at embryonic stage 6.1, for individuals sexed after hatching. Live embryos were scored for leg-bearing segment (LBS) number at embryonic Stage 6.1, reared to the adolescens I stage, and sexed morphologically. M, males (here all with 47 LBSs at the adolescens I stage); F, females (here all with 49 LBSs).
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Figure 3: Number of leg-bearing segments at embryonic stage 6.1, for individuals sexed after hatching. Live embryos were scored for leg-bearing segment (LBS) number at embryonic Stage 6.1, reared to the adolescens I stage, and sexed morphologically. M, males (here all with 47 LBSs at the adolescens I stage); F, females (here all with 49 LBSs).

Mentions: The survival of embryos through the several post-embryonic moults that precede the adolescens I stage is greatly improved by culturing them under oil, but, even so, only 14 of the 22 individuals initially scored as embryos survived the 2 months in culture to the point at which they could be sexed. However, these surviving individuals showed a very clear relationship between the number of segments at mid-embryogenesis and the sex of the individual: all males had 42 or 43 segments visible at Stage 6.1, while all females had 44 or 45 segments (FigureĀ 3). Note that embryonic segments appear singly, at least when scored morphologically, and therefore animals are scored with both odd and even numbers of segments, in contrast to the final adult number of leg-bearing segments, which is always odd. This final number is already established in adolescens I individuals. For the animals scored here, all males showed 47 leg-bearing segments and all females show 49.


Early embryonic determination of the sexual dimorphism in segment number in geophilomorph centipedes.

Brena C, Green J, Akam M - Evodevo (2013)

Number of leg-bearing segments at embryonic stage 6.1, for individuals sexed after hatching. Live embryos were scored for leg-bearing segment (LBS) number at embryonic Stage 6.1, reared to the adolescens I stage, and sexed morphologically. M, males (here all with 47 LBSs at the adolescens I stage); F, females (here all with 49 LBSs).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750810&req=5

Figure 3: Number of leg-bearing segments at embryonic stage 6.1, for individuals sexed after hatching. Live embryos were scored for leg-bearing segment (LBS) number at embryonic Stage 6.1, reared to the adolescens I stage, and sexed morphologically. M, males (here all with 47 LBSs at the adolescens I stage); F, females (here all with 49 LBSs).
Mentions: The survival of embryos through the several post-embryonic moults that precede the adolescens I stage is greatly improved by culturing them under oil, but, even so, only 14 of the 22 individuals initially scored as embryos survived the 2 months in culture to the point at which they could be sexed. However, these surviving individuals showed a very clear relationship between the number of segments at mid-embryogenesis and the sex of the individual: all males had 42 or 43 segments visible at Stage 6.1, while all females had 44 or 45 segments (FigureĀ 3). Note that embryonic segments appear singly, at least when scored morphologically, and therefore animals are scored with both odd and even numbers of segments, in contrast to the final adult number of leg-bearing segments, which is always odd. This final number is already established in adolescens I individuals. For the animals scored here, all males showed 47 leg-bearing segments and all females show 49.

Bottom Line: Sexual dimorphism in segment number is not associated with terminal segment differentiation, but must instead be related to some earlier process during segment patterning.The dimorphism may be associated with a difference in the rate and/or duration of segment addition during the main phase of rapid segment addition that precedes embryonic Stage 6.This suggests that the adaptive role, if any, of the dimorphism is likely to be related to segment number per se, and not to sexual differentiation of the terminal region.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory for Development and Evolution, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. cb508@cam.ac.uk.

ABSTRACT

Background: Most geophilomorph centipedes show intraspecific variability in the number of leg-bearing segments. This intraspecific variability generally has a component that is related to sex, with females having on average more segments than males. Neither the developmental basis nor the adaptive role of this dimorphism is known.

Results: To determine when this sexual dimorphism in segment number is established, we have followed the development of Strigamia maritima embryos from the onset of segmentation to the first post-embryonic stage where we could determine the sex morphologically. We find that males and females differ in segment number by Stage 6.1, a point during embryogenesis when segment addition pauses while the embryo undergoes large-scale movements. We have confirmed this pattern by establishing a molecular method to determine the sex of single embryos, utilising duplex PCR amplification for Y chromosomal and autosomal sequences. This confirms that male embryos have a modal number of 43 segments visible at Stage 6, while females have 45. In our Strigamia population, adult males have a modal number of 47 leg-bearing segments, and females have 49. This implies that the sexual dimorphism in segment number is determined before the addition of the last leg-bearing segments and the terminal genital segments.

Conclusions: Sexual dimorphism in segment number is not associated with terminal segment differentiation, but must instead be related to some earlier process during segment patterning. The dimorphism may be associated with a difference in the rate and/or duration of segment addition during the main phase of rapid segment addition that precedes embryonic Stage 6. This suggests that the adaptive role, if any, of the dimorphism is likely to be related to segment number per se, and not to sexual differentiation of the terminal region.

No MeSH data available.