Table 5 Congeneric species showing differences in genome architecture, gene order (breakpoint distance) and gene content

From: Evolution of the mitochondrial genome of Metazoa as exemplified by comparison of congeneric species

Classification

Genus

No. of sp. (mtDNA) a

No. of AR

BDn range

Intra-genus differences in gene content

Size b

   

All

−tRNA

All

−tRNA

  

Tunicata

Ciona

3

3

2

0.08–0.41

0–0.20

None

14 706±103

 

Phallusia

2

2

2

0.71

0.80

Additional trnI, and a trnX with uncertain amino acid specificity in P. fumigata

15 057±676

Cephalochordata

Asymmetron

2 (4)c

2

2

0–0.16

0

None

15 084±24

Amphibia

Aneides

2

2

2

0.08

0.20

Additional trnE-trnP-trnF-trnL(UUR) gene cluster in A. hardii

21 191±1405

 

Batrachoseps

2

2

1

0.08

0

None

18 674±1577

 

Plethodon

3

2

1

0.08

0

Additional trnT in P. elongatus

19 334±623

Chelicerata

Leptotrombidium

3

2

2

0–0.08

0

Duplicated rrnL and a pseudogene of rrnS in L. pallidum

14 736±1769

Crustacea

Pollicipes

2

2

1

0

0

Two additional copies of trnC repeated in tandem in P. polymerus.

15 275±508

 

Tigriopus

2

2

1

0.08

0

None

14 587±58

Hexapoda

Rhagophthalmus

2

2

1

0

0

The cluster trnI-trnQ-trnM is lost in R. ohbai

15 843±197

Bivalvia

Crassostrea

2

2

2

0.32

0

Duplicated rrnS, trnK, and trnQ genes in C. gigas

17 734±694

 

Inversidens d

1 (2)

2

2

0.27

0.20

None

16 897±100

 

Mytilus d,e

3 (7)

2

1

0

0

Additional trnG, trnN, trnI, trnQ genes in the ‘recently masculinized’ type of M. trossulus.

17 561±1021

 

Venerupis d

1 (2)

2

1

0

0

Additional trnM(UAU) and duplicated trnK in the M type; duplicated trnV in the F type.

22 059±873

Enoplea

Romanomermis

3

3

3

0.47–0.78

0.50–0.79

Several gene duplications: the number of annotated genes is 48 in R. culicivorax, 40 in R. iyengari and 39 in R. nielseni

20 220±5442

 

Strelkovimermis f

1 (2)

2

2

0

0

Duplicated rrnS and rrnL in the large mtDNA haplotype

17 574±644

 

Thaumamermis f

1 (2)

2

1

0g

0

A hypervariable segment differentiates haplotypes: it contains several pseudo- and functional genes (rrnS, and tRNA genes) organized in a variable gene order

20 760±1056

Platyhelminthes

Schistosoma

5

5

2

0–0.44

0–0.36

None

14 895±1183

Porifera

Amphimedon

2

2

2

0.26

0

A. queenslandica lacks atp9 and 10 tRNA genes, whereas A. compressa lacks the elongator trnM gene

19 262±987

  1. Abbreviations: All: analysis carried out on all mt genes; −tRNA: exclusion of tRNA genes from the analysis.
  2. The normalized breakpoint distance (BDn) is the breakpoint distance (Blanchette et al., 1997) calculated on the order of the genes shared between congeneric species, and divided by the number of genes.
  3. a The number of mtDNAs is reported only when different from the number of species (indicated as sp.).
  4. b Average mtDNA length (bp)±standard deviation.
  5. c Including three representatives of the Asymmetron lucayanus species complex.
  6. d Male (M) and female (F) isoforms of the same species. The recently masculinized mtDNA isoform is available only for Mytilus trossulus.
  7. The existence of a single Mytilus edulis species complex, including M. edulis, M. galloprovincialis and M. trossulus, has also been hypothesized (Gossling, 1992).
  8. f Two haplotypes of the same species.
  9. g Gene order outside the hypervariable segment.
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