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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.


Duplex PCR assay for sex determination in Strigamia maritima. (A) Positive control. Sex-determination assay on adults of known sex. Two males, M1 and M2 generate PCR bands at 398 bp and 288 bp corresponding to the autosomal band and Y chromosome band, respectively. Two females, F1 and F2 generate a single band at 398 bp corresponding to the autosomal band. (B) Experimental assay. Sex determination of single embryos of unknown sex. Lanes 1, 2, 3, 6 and 7 generate single PCR bands (398 bp) and so are inferred to contain DNA derived from female embryos. Lanes 4 and 5 generate two PCR bands (398 bp, 288 bp) and so are inferred to be from males. NTC, no template control (generates no bands). The sizes of a 1 kb (L1) and 100 bp (L2) DNA ladder are shown.
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Figure 2: Duplex PCR assay for sex determination in Strigamia maritima. (A) Positive control. Sex-determination assay on adults of known sex. Two males, M1 and M2 generate PCR bands at 398 bp and 288 bp corresponding to the autosomal band and Y chromosome band, respectively. Two females, F1 and F2 generate a single band at 398 bp corresponding to the autosomal band. (B) Experimental assay. Sex determination of single embryos of unknown sex. Lanes 1, 2, 3, 6 and 7 generate single PCR bands (398 bp) and so are inferred to contain DNA derived from female embryos. Lanes 4 and 5 generate two PCR bands (398 bp, 288 bp) and so are inferred to be from males. NTC, no template control (generates no bands). The sizes of a 1 kb (L1) and 100 bp (L2) DNA ladder are shown.

Mentions: For the sex-determination PCR, two sets of primers were used in each reaction. The first primer set amplifies a 398 bp region of genomic scaffold 7180001247533 (Smar genome assembly 1.0 [17]), which from its representation in the genomic sequence reads is inferred to be autosomal, and which amplifies in both male and female adults (Figure 2A). The second primer set amplifies a 288 bp region of genomic DNA from scaffold 7180001247258, which is underrepresented in the genomic sequence reads, and which is inferred to be Y chromosomal (J Green and colleagues, in preparation). This set amplifies only in adult males (Figure 2A). Male samples thus generate two PCR bands of distinct sizes, whereas female samples generate only a single PCR band (Figure 2).


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

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

Duplex PCR assay for sex determination in Strigamia maritima. (A) Positive control. Sex-determination assay on adults of known sex. Two males, M1 and M2 generate PCR bands at 398 bp and 288 bp corresponding to the autosomal band and Y chromosome band, respectively. Two females, F1 and F2 generate a single band at 398 bp corresponding to the autosomal band. (B) Experimental assay. Sex determination of single embryos of unknown sex. Lanes 1, 2, 3, 6 and 7 generate single PCR bands (398 bp) and so are inferred to contain DNA derived from female embryos. Lanes 4 and 5 generate two PCR bands (398 bp, 288 bp) and so are inferred to be from males. NTC, no template control (generates no bands). The sizes of a 1 kb (L1) and 100 bp (L2) DNA ladder are shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Duplex PCR assay for sex determination in Strigamia maritima. (A) Positive control. Sex-determination assay on adults of known sex. Two males, M1 and M2 generate PCR bands at 398 bp and 288 bp corresponding to the autosomal band and Y chromosome band, respectively. Two females, F1 and F2 generate a single band at 398 bp corresponding to the autosomal band. (B) Experimental assay. Sex determination of single embryos of unknown sex. Lanes 1, 2, 3, 6 and 7 generate single PCR bands (398 bp) and so are inferred to contain DNA derived from female embryos. Lanes 4 and 5 generate two PCR bands (398 bp, 288 bp) and so are inferred to be from males. NTC, no template control (generates no bands). The sizes of a 1 kb (L1) and 100 bp (L2) DNA ladder are shown.
Mentions: For the sex-determination PCR, two sets of primers were used in each reaction. The first primer set amplifies a 398 bp region of genomic scaffold 7180001247533 (Smar genome assembly 1.0 [17]), which from its representation in the genomic sequence reads is inferred to be autosomal, and which amplifies in both male and female adults (Figure 2A). The second primer set amplifies a 288 bp region of genomic DNA from scaffold 7180001247258, which is underrepresented in the genomic sequence reads, and which is inferred to be Y chromosomal (J Green and colleagues, in preparation). This set amplifies only in adult males (Figure 2A). Male samples thus generate two PCR bands of distinct sizes, whereas female samples generate only a single PCR band (Figure 2).

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.