Search

Chromosomes, allozymes, and mitochondrial DNA (mtDNA) were analyzed to examine the taxonomic and systematic relationships of coastal Peromyscus from northern Washington to southern Alaska. All three datasets indicate that Peromyscus from this region constitute two distinct groups. One group comprises P. oreas, P. sitkensis , and several currently recognized subspecies of P. maniculatus including P. m. algidus, P. m. hylaeus, P. m. keeni, P. m. macrorhinus , and P. m. prevostensis . The second group comprises only populations of P. m. austerus . The former group is differentiated from the latter by number of autosomal arms, allele-frequency differences, and mtDNA haplotypes. This dichotomy in karyotype, and the level of allozymic and mtDNA divergence between the groups suggest that the groups constitute distinct species. We recommend that P. oreas, P. sitkensis, P. maniculatus algidus, P. m. hylaeus, P. m. keeni, P. m. macrorhinus , and P. m. prevostensis be recognized under the specific epithet of Peromyscus keeni .

This paper summarizes the results of an initial effort to reconstruct the speciational history of cave spiders (Nesticus) from the southern Appalachian Mountains of eastern North America. The Appalachian Nesticus fauna includes a large series of about 30 species distributed across islandlike cave and montane habitats. Many of the species are geographically restricted; all of the species are found in allopatry. Observed patterns of morphological variation and biogeographic evidence suggest that species diversification in this lineage may have occurred recently, perhaps in response to Pleistocene climatic fluctuations. To address questions about the spatial and temporal dynamics of Nesticus speciation, while accounting for potential phylogenetic difficulties, I have gathered nuclear and mitochondrial DNA sequences for a sample of individuals from 81 populations representing 28 Nesticus species. Analyses of these data indicate that considerable genetic divergence exists within and among currently recognized morphological species. Consistent with relatively deep species divergences, most of which likely predate the Pleistocene, is a prevailing pattern of phylogenetic concordance between taxonomic species and monophyletic gene tree lineages. The few deviations from monophyly detected can be tentatively attributed to a peripatric mode of speciation. Although species limits as inferred by the molecular data are generally concordant with patterns of morphological continuity and discontinuity in genitalia, there is evidence to suggest that cryptic phylogenetic lineages exist within some morphologically continuous units. This observation, in combination with the general depth of species lineages, makes any argument about rapid evolution in Nesticus genitalic characteristics unnecessary.

Techniques for the electron microscopic visualization of synaptonemal complexes were used to investigate the XY and XXY sex chromosomal systems in Scincella lateralis. Synaptonemal complex analyses revealed differences in the pattern of synapsis between the sex chromosomal and autosomal bivalents within each cytotype, and differences in sex chromosomal pairing between the cytotypes. Sex chromosomes of the XY cytotype synapsed in homology to form a bivalent. Sex chromosomes of the X1XY cytotype synapsed in a trivalent configuration, with localized regions of nonhomologous synapsis. These data support previous hypotheses that the X1XY condition is derived from the XY system by translocation of the Y chromosome to one homolog of the smallest macrochromosomal pair, and implicate centromeric inactivation in the fusion event.