Figure 1.
Individuals of a) Pseudotropheus fainzilberi and b) P. emmiltos were collected at Mpanga Rocks, Luwino Reef, and Chirwa Island off the North Western shore of Lake Malawi. The two species are sympatric at Mpanga Rocks and Luwino Reef. Photograhs show males in full nuptial dress and are courtesy of Ad Konings.
Figure 2.
Three-Dimensional Model of the β1 Domain of Cichlid MHC Class II.
The tertiary structure prediction was based on Psemmil_m58_c exon 2 sequence (Accession number: EF540049) of 41% homology with mouse MHC sequence gi|13399459 in the Protein Data Bank (http://www.pdb.org/pdb/home/home.do) using the 3D-jigsaw server v.2.0 (http://www.bmm.icnet.uk/~3djigsaw/). The graphical representation was created using the program Pymol v.0.99. Amino acid residues under significant positive selection in Pseudotropheus fainzilberi and P. emmiltos and corresponding to peptide binding sites in humans are highlighted in orange. Residues shown in red were under significant positive selection in P. fainzilberi and P. emmiltos but do not correspond with peptide binding sites in humans. Residues in yellow are human peptide binding sites that were not found to evolve under positive selection in cichlids. The 84 amplified exon 2 codons are numbered 1-84 on the graph. Those correspond to codons 6-89 of the mature protein.
Figure 3.
Comparison of Secondary Structure of Mouse and Cichlid MHC Class II Exon 2.
Structure predictions were obtained from the PSIPRED server (http://bioinf.cs.ucl.ac.uk/psipred/psiform.html) for a) mouse sequence gi:13399459 and b) cichlid sequence Psemmil_m58_c (Accession number: EF540049). Mammalian and fish secondary structures are similar except for an additional short alpha-helix at position 46–49 predicted for the mouse sequence, and an additional short strand at position 74 predicted for the cichlid sequence.
Figure 4.
Comparison of Genetic Divergence Between Heterospecific Sympatric Populations and Conspecific Allopatric Populations.
Fst values (HudSon et al. 1992) from pairwise comparisons of conspecific allopatric populations (Mpanga Rocks (Mpg), Luwino Reef (Lwo), and Chirwa Island (Chw)) and between heterospecific sympatric populations of P. fainzilberi (fainz.), and P. emmiltos (emm.). Neutral Fst estimates were obtained from intron 1 p-distances, modified Nei and Gojobori synonymous distances at exon 2, and from amino acid EX distance at exon 2 sites outside the putative ABS region (dN/dS≤1) and functional Fst were obtained from EX distance at putative exon 2 ABS (dN/dS>1). Negative Fst estimates were forced to zero. Evidence of significant genetic divergence between pairs of allopatric populations was found only for neutral Fst estimates between P. emmiltos populations from Luwino Reef and Mpanga Rocks. Evidence of significant genetic divergence between pairs of P. fainzilberi and P. emmiltos sympatric populations was found only at putative ABS at Mpanga Rocks. *Significantly different from zero (p<0.05; 200 permutations)
Table 1.
Neutral and functional genetic differentiation estimates between Pseudotropheus fainzilberi and P. emmiltos samples.
Table 2.
Proportions of private and shared alleles between Pseudotropheus fainzilberi and P. emmiltos at MHC class II B intron 1 alleles and exon 2 amino acid alleles.
Table 3.
Parasite infections of Pseudotropheus emmiltos and P. fainzilberi: eigenvectors of the first four factors explaining 84% of the original variance returned from a principal component analysis on incidence and abundance of 16 types of parasites transformed according to equation 12 in Legendre and Gallagher [38].
Table 4.
Sum of squares (SS) and degrees of freedom (df) of a multivariate general linear model testing the effect of host species, collection site, host sex, and host standard length on four principal component analysis factors (PC1-PC4) representing 84% of the original variance of the incidence and prevalence of 16 different types of parasites.