The emerging role of
molecular markers in
coccidian speciation:
Katarzyna B. Miska, Dagmara
Motriuk-Smith, R. Scott Seville
June 29, 2008
Why is use of molecular tools important:
Eimeria are be morphologically very similar.
-Can lead to erroneous classification
-Usually needs “an expert eye” to be carried out
correctly
Analysis of DNA sequences is fast, relatively
inexpensive, can provide information discerning
differences among closely related species or strains of
the same species.
Selecting the correct gene to answer these questions
is KEY.
Use of 18s ribosomal DNA sequences
 Historically very common
 Sequences are conserved
 Primer design and amplification is relatively easy
although complete sequence is around 1.8 kb.
 Probably represents the largest database of
available Eimerian sequences.
18s Phylogeny
Updated to include
data from other galliforme
birds: Chukars and pheasants
More questions arise:
is Eimeria of chickens and turkeys
paraphyletic
Do cecal Eimeria in galliforme
birds represent (ie E. tenella,
E. necatrix, E. adenoides)
a separate colonization of the
Gut?
Cytochrome c oxidase subunit I
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Encoded on the mitochondrial genome
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Well conserved (most highly conserved of the
mitochondrial genes
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Single copy
ITS-1 and ITS-2
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Use has been very wide especially in higher eukaryotes
Quickly evolving- very divergent even among closely
related taxa
In Apicomplexans structure and evolution or ribosomal
DNA may be VERY different
For example: Plasmodium falciparum has two
independently evolving rDNA gene, expressed
differentially among stages of the life-cycle.
Similar rDNA structures also found in Cryptosporidium,
Theileria, and possibly Eimeria maxima
This can confound phylogeny
Eimeria maxima appears
to contain at least two
highly dissimilar ITS-1
sequences (same is seen
with ITS-2)
ITS sequences are most
likely of limited use in
reconstructing species
phylogeny in Eimeria
BEWARE of ITS based
Species phylogenies
The future?
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Better sampling of species
Multi-gene phylogenies
Identify more suitable target genes to base
species phylogenies on. Such as
conserved (at least in Eimeria), single
copy, nuclear genes.