Chromosome banding and phylogenetics of the golden mouse, Ochrotomys nuttalli

TOWARD A MOLECULAR PHYLOGENY FOR PEROMYSCUS: EVIDENCE FROM MITOCHONDRIAL CYTOCHROME-b SEQUENCES

One hundred DNA sequences from the mitochondrial cytochrome-b gene of 44 species of deer mice (Peromyscus (sensu stricto), 1 of Habromys, 1 of Isthmomys, 2 of Megadontomys, and the monotypic genera Neotomodon, Osgoodomys, and Podomys were used to develop a molecular phylogeny for Peromyscus. Phylogenetic analyses (maximum parsimony, maximum likelihood, and Bayesian inference) were conducted to evaluate alternative hypotheses concerning taxonomic arrangements (sensu stricto versus sensu lato) of the genus. In all analyses, monophyletic clades were obtained that corresponded to species groups proposed by previous authors; however, relationships among species groups generally were poorly resolved. The concept of the genus Peromyscus based on molecular data differed significantly from the most current taxonomic arrangement. Maximum-likelihood and Bayesian trees depicted strong support for a clade placing Habromys, Megadontomys, Neotomodon, Osgoodomys, and Podomys within Peromyscus. If Habromys, Megadontomys, Neotomodon, Osgoodomys, and Podomys are regarded as genera, then several species groups within Peromyscus (sensu stricto) should be elevated to generic rank. Isthmomys was associated with the genus Reithrodontomys; in turn this clade was sister to Baiomys, indicating a distant relationship of Isthmomys to Peromyscus. A formal taxonomic revision awaits synthesis of additional sequence data from nuclear markers together with inclusion of available allozymic and karyotypic data.

Neotomine–peromyscine rodent systematics based on combined analyses of nuclear and mitochondrial DNA sequences

Recently, sequences from two nuclear genes (exon 6 of the dentin matrix protein 1 gene and intron 7 of the beta-fibrinogen gene) and one mitochondrial gene (cytochrome b gene) were used independently in an attempt to resolve phylogenetic relationships within the neotomine-peromyscine complex. Although these studies provided testable hypotheses regarding this group of rodents, the affinities of certain tribes and genera remain uncertain. To elucidate these relationships, the three data partitions were tested for heterogeneity and then concatenated according to conditional data combination and total evidence approaches. Support was found for five clades, four of which correspond to well recognized tribes (the Neotomini, Peromyscini=Reithrodontomyini, Baiomyini, and Tylomyini). Recommendations are made regarding the recognition of Ochrotomys as a tribe of its own, the Ochrotomyini, paralleling other recent findings. The Peromyscini, Baiomyini, and Ochrotomyini are unresolved in relation to each other, but as a whole are sister to the Neotomini. The Tylomyini is basal to all clades. It appears that combined data from the nuclear and mitochondrial genes (analyzing all three partitions simultaneously) resulted in the best phylogenetic hypothesis regarding the complex.

Intragenomic movement, sequence amplification and concerted evolution in satellite DNA in harvest mice, Reithrodontomys: evidence from in situ hybridization

Three DNA probes isolated from three species of Reithrodontomys (R. montanus, R. megalotis, R. fulvescens) were used to examine within and among species variation in the chromosomal location of satellite DNA and constitutive heterochromatin. These probes hybridized to the centromeric regions on all chromosomes in six species of the subgenus Reithrodontomys. Additionally, nearly all extra-centromeric C-band positive regions (with the exception of some heterochromatic material on the X and Y) hybridized to these probes. Within the subgenus Reithrodontomys both the chromosomal distribution and organization of satellite DNA has changed throughout evolution. The evolutionary transition has been from a totally centromeric position in R. fulvescens to centromeric and non-centromeric regions in other species that have undergone extensive chromosomal rearrangements from the primitive karyotype for peromyscine rodents. In addition, the monomer repeat of the satellite sequence differs between R. fulvescens (monomer defined by PstI) and the remaining species in the subgenus Reithrodontomys (monomer defined by EcoRI). These results suggest at least two amplification events for this satellite DNA sequence. Models and mechanisms concerned with the homogenization and spread of satellite sequences in complex genomes are evaluated in light of the Reithrodontomys data. From a phylogenetic standpoint, the satellite sequences composing heterochromatic regions were restricted to the subgenus Reithrodontomys, which supports morphological differences used to recognize two subgenera, Reithrodontomys and Aporodon. Probes failed to hybridize to any part of the karyotype of R. mexicanus (subgenus Aporodon) or to seven species from other closely related genera (Baiomys, Neotoma, Nyctomys, Ochrotomys, Onychomys, Peromyscus, Xenomys), some of which are considered as potential sister taxa for Reithrodontomys.