Mitochondrial DNA differentiation during the speciation process in Peromyscus

We address the problem of the possible significance of biologicalspeciation to the magnitude and pattern of divergence of asexuallytransmitted characters in bisexual species. The empirical data for thisreport consist of restriction endonuclease site variability in maternallytransmitted mitochondrial DNA (mtDNA) isolated from 82 samples ofPeromyscus polionotus and P. leucopus collected from major portions of therespective species' ranges. Data are analyzed together with previouslypublished information on P. maniculatus, a sibling species to polionotus.Maps of restriction sites indicate that all of the variation observed canbe reasonably attributed to base substitutions leading to loss or gain ofparticular recognition sites. Magnitude of mtDNA sequence divergence withinpolionotus (maximum approximately equal to 2%) is roughly comparable tothat observed within any of five previously identified mtDNA assemblages inmaniculatus. Sequence divergence within leucopus (maximum approximatelyequal to 4%) is somewhat greater than that within polionotus. Considerationof probable evolutionary links among mtDNA restriction site maps allowedestimation of matriarchal phylogenies within polionotus and leucopus.Clustering algorithms and qualitative Wagner procedures were used togenerate phenograms and parsimony networks, respectively, for thebetween-species comparisons. Three simple graphical models are presented toillustrate some conceivable relationships of mtDNA differentiation tospeciation. In theoretical case I, each of two reproductively definedspecies (A and B) is monophyletic in matriarchal genealogy; the commonfemale ancestor of either species can either predate or postdate thespeciation. In case II, neither species is monophyletic in matriarchalgenotype. In case III, species B is monophyletic but forms a subcladewithin A which is thus paraphyletic with respect to B. The empiricalresults for mtDNA in maniculatus and polionotus appear to conform closelyto case III. These theoretical and empirical considerations raise a numberof questions about the general relationship of the speciation process tothe evolution of uniparentally transmitted traits. Some of theseconsiderations are presented, and it is suggested that the distributionpatterns of mtDNA sequence variation within and among extant species shouldbe of considerable relevance to the particular demographies of speciation.