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Because the white-eyed vireo (Vireo griseus) is a less sensitive species than the endangered black-capped vireo (V. atricapilla), it served as a proxy to quantify potentially adverse effects of sampling blood. Success of fledging was quantified using split-sampled broods with non-bled nestlings serving as a control. Sex ratio of broods was determined, and sampling and storage methods for blood were assessed. Obtaining blood from nestlings did not affect success of fledging. The male:female ratio of nestlings was 65:35.

Phylogenetic relationships within Geomys historically have been difficult to assess using morphometric and chromosomal data. DNA sequences from the nuclear-encoded interphotoreceptor retinoid-binding protein gene (Rbp3) and mitochondrial 12S ribosomal RNA (12S rRNA) gene were used to examine the relationships within Geomys. In addition, sequence data from Rbp3 and mitochondrial 12S rRNA gene regions were combined with DNA sequence data from the mitochondrial cytochrome-b gene (Cytb) reported in a previous study. Results from phylogenetic analyses support previously established relationships in the recognition of 4 species groups (breviceps, bursarius, personatus, and pinetis) and a minimum of 12 species. Additionally, results agree with previous studies in considering the elevation of G. pinetis mobilensis and G. breviceps sagittalis to species-level status and in reevaluating the taxonomic status of 2 additional subspecies (G. personatus davisi and G. p. maritimus).

Pocket gophers (Rodentia: Geomyidae) are fossorial herbivores, sister to the New World Heteromyidae, and, with one exception (Orthogeomys), are restricted in distribution to North America. Because they occur in small, isolated demes and possess an overall lack of vagility as well as conservative morphology, these rodents pose many problems with respect to their taxonomy, systematics, evolutionary history, and intrageneric affinities. Members of the genus Geomys are no exception. Species of Geomys occur in the southeastern United States and throughout much of the central and southern Great Plains westward to the eastern slope of the Rocky Mountains and south into northern Mexico (Fig. 1). Considerable uncertainty exists concerning the number of species present and the historical relationships among described taxa. Much of the confusion involves the presence of sibling species, with little or no morphological differentiation and, in some instances, high degrees of chromosomal diversification and allozymic variation. Merriam (1895), in his revision of pocket gophers of the family Geomyidae (exclusive of Thomomys), recognized 3 species groups within Geomys: the tuza (¼ pinetis) group including what is today recognized as G. pinetis; the bursarius

Nucleotide sequence analysis of the cytochrome-b gene of mtDNA and univariate and multivariate statistical analyses of cranial morphology were used to determine the evolutionary status of relictual, isolated populations of pocket gophers (genus Geomys) from the Ozark Mountains of Arkansas. Results of the mtDNA sequence analysis indicated that populations from the Ozark Mountains are most similar to G. bursarius missouriensis in Missouri and not to geographically proximate populations of G. breviceps. Morphological analyses were concordant with those results. Our findings confirm earlier work comparing similarities in allozymes and species-specific ectoparasites. Nucleotide sequence and morphological divergence between the Ozark populations and G. bursarius missouriensisare typical of differentiation between other subspecies of G. bursarius. We conclude that populations of pocket gophers isolated in the Ozark Mountains represent a discrete genetic entity and should be recognized as a new subspecies.

The relative contribution of mutation and purifying selection to transition bias has not been quantitatively assessed in mitochondrial protein genes. The observed transition/transversion (s/v) ratio is (μ s P s)/(μ v P v), where μ s and μ v denote mutation rate of transitions and transversions, respectively, andP s andP v denote fixation probabilities of transitions and transversions, respectively. Because selection against synonymous transitions can be assumed to be roughly equal to that against synonymous transversions,P s/Pv ≈ 1 at fourfold degenerate sites, so that thes/v ratio at fourfold degenerate sites is approximately μ s /μ v , which is a measure of mutational contribution to transition bias. Similarly, thes/v ratio at nondegenerate sites is also an estimate of μ s /μ v if we assume that selection against nonsynonymous transitions is roughly equal to that against nonsynonymous transversions. In two mitochondrial genes, cytochrome oxidase subunit I (COI) and cytochromeb (cyt-b) in pocket gophers, thes/v ratio is about two at nondegenerate and fourfold degenerate sites for both the COI and the cyt-b genes. This implies that mutation contribution to transition bias is relatively small. In contrast, thes/v ratio is much greater at twofold degenerate sites, being 48 for COI and 40 for cyt-b. Given that the μ s /μ v ratio is about 2, theP s/Pv ratio at twofold degenerate sites must be on the order of 20 or greater. This suggests a great effect of purifying selection on transition bias in mitochondrial protein genes because transitions are synonymous and transversions are nonsynonymous at twofold degenerate sites in mammalian mitochondrial genes. We also found that nonsynonymous mutations at twofold degenerate sites are more neutral than nonsynonymous mutations at nondegenerate sites, and that the COI gene is subject to stronger purifying selection than is the cyt-b gene. A model is presented to integrate the effect of purifying selection, codon bias, DNA repair and GC content ons/v ratio of protein-coding genes.

Analyses of protein electrophoretic and mitochondrial cytochrome b sequence data support association of Tomopeas ravus with the chiropteran family Molossidae. Although analyses of protein electrophoretic data present no clear placement of Tomopeas within the Molossidae, analyses of the sequence data support the recognition of Tomopeas as a basal and phylogenetically distant member of Molossidae. As a result of these analyses, we present a new taxonomic placement of this distinctive and taxonomically problematic bat.

Chromosomal-pairing behaviour was studied in the spermatocytes of individual goitered gazelles which were heteromorphic for a 14/15 Robertsonian translocation and which possessed an autosome-to-X translocation. Both translocations exhibited trivalent pairing configurations in pachytene and diakinesis/metaphase I nuclei. Synapsis of the sex chromosomes during pachynema was followed by end-to-end association of the X and Y during diakinesis/metaphase I. The only univalents identified were of the Y chromosome; Y univalency ranged from 15.9% at pachynema to 5.7% at diakinesis/metaphase I. Robertsonian trivalents exhibited evidence of synaptic adjustment in the paracentromeric region. Chiasmata were formed in most bivalents and trivalents; chiasmata were restricted to the autosomal portion of the autosome-to-XY trivalent. Analysis of metaphase II configurations (secondary spermatocytes) revealed no nondisjunction in individuals homozygous or heterozygous for the Robertsonian translocation. These data are consistent with the hypothesis that neither the autosomal nor the gonosomal heteromorphism reduces the meiotic fitness of male goitered gazelles.

Phylogenetic relationships among 7 of the 10 species of pocket gophers in the genera Pappogeomys and Cratogeomys were addressed using nucleotide sequence data from the entire cytochrome b gene of the mitochondrial genome (1140 base pairs). Results of parsimony analysis were concordant with the results of morphological analysis (R. J. Russell, Univ. Kans. Pub. Mus. Nat. Hist. 16: 581-776, 1968), but differed somewhat from the conclusions drawn from an allozymic study of these species (R. L. Honeycutt and S. L. Williams, J. Mammal. 63: 208-217, 1982). Phylogenetic analysis indicated that Cratogeomys is monophyletic, as are the two species groups within this genus. Estimates of levels of nucleotide sequence divergence between species of these genera indicated that the cytochrome b gene of pocket gophers may have evolved at a dramatically higher rate than in organisms examined previously (D. M. Irwin, T. D. Kocher, and A. C. Wilson, J.Mol. Evol. 32: 128-144, 1991).

Relationships among members representing each of the three subgenera of the Middle American rodent genus Orthogeomys (Rodentia: Geomyidae) were studied by comparing DNA sequence data from two regions of the mitochondrial genome. Results from 527 by from the 16 S rDNA region and a 402-bp fragment of the cytochrome b gene indicate that the three subgenera are well differentiated genetically, with the subgenus Orthogeomys being distantly related to Macrogeomys and Heterogeomys , and Macrogeomys appearing as the most derived. Within the subgenus Macrogeomys , O. heterodus and O. cherriei form a distinct clade, as do O. dariensis and O. cavator . As with previous protein-electrophoretic studies, the placement of O. underwoodi could not be determined definitively within the subgenus Macrogeomys . We interpret our inability to determine phylogenetic relationships among these three clades as evidence for a rapid phyletic radiation within this subgenus. Sequence divergence estimates indicate that the Macrogeomys radiation took place following the time of completion of the Panamanian land bridge (1.9–2.9 mya). Additionally, the near identity of sequences of a newly described species, O. thaeleri , with those of O. dariensis (percentage sequence divergence = 0.3%) suggests that the two may be conspecific.

The pairing behavior of the sex chromosomes in male and female individuals representing seven species of Peromyscus was analyzed by electron microscopy of silver-stained zygotene and pachytene configurations. Six species possess submetacentric or metacentric X chromosomes with heterochromatic short arms. Sex-chromosome pairing in these species is initiated during early pachynema at an interstitial position on the X and Y axes. Homologous synapsis then progresses in a unidirectional fashion towards the telomeres of the X short arm and the corresponding arm of the heterochromatic Y chromosome. The distinctive pattern of synaptic initiation allowed a late-synapsing bivalent in fetal oocytes to be tentatively identified as that of the X chromosomes. In contrast to the other species, Peromyscus megalops possesses an acrocentric X chromosome and a very small Y chromosome. Sex-chromosome pairing in this species is initiated at the proximal telomeric region during late zygonema, and then proceeds interstitially towards the distal end of the Y chromosome. These observations suggest that the presence of X short-arm heterochromatin and corresponding Y heterochromatin interferes with late-zygotene alignment of the pairing initiation sites, thereby delaying XY synaptic initiation until early pachynema. The pairing initiation sites are conserved in the vicinity of the X and Y centromeres in Peromyscus, and consequently the addition of heterochromatin during sex-chromosome evolution essentially displaces these sites to an interstitial position.

Two unusual structural polymorphisms in the largest chromosomal pair of the Israeli mole rat, Spalax ehrenbergi, were analyzed from surface-spread and silver-stained preparations of synaptonemal complexes. A C-band negative polymorphism for the length of the 1p arm was visible as axial length differences during late zygonema and early pachynema. This region underwent synaptic adjustment resulting in a fully paired, mid-pachytene synaptonemal complex with equalized axial lengths. The somatically variable and nonargentophilic secondary constriction in the 1q arm was evident as a distinct silver-stained thickening along the synaptonemal complex. Presence of this structure on the synaptonemal complex varied both among individuals and among cells within individuals. The intraindividual variation of this region is hypothesized to represent differential biochemical activity with its cellular visualization being regulated in a manner similar to that of nucleolus organizer regions.Key words: mole rats, synaptonemal complex, chromosomal polymorphism.

Differences in length of the heterochromatic short arms of the X and Y chromosomes in individuals of Peromyscus beatae are hypothesized to result from unequal crossing over. To test this hypothesis, we examined patterns of synapsis, chiasma formation, and segregation for male P. beatae which were either heterozygous or homozygous for the amount of short-arm sex heterochromatin. Synaptonemal complex analysis demonstrated that mitotic differences in heterochromatic short-arm lengths between the X and Y chromosomes were reflected in early pachynema as corresponding differences in axial element lengths within the pairing region of the sex bivalent. These length differences were subsequently eliminated by synaptic adjustment such that by late pachynema, the synaptonemal complex configurations of the XY bivalent of heterozygotes were not differentiable from those of homozygotes. Crossing over between the heterochromatic short arms of the XY bivalent was documented by the routine appearance of a single chiasma in this region during diakinesis/metaphase I. Sex heterochromatin heterozygotes were characterized by the presence of asymmetrical chiasma between the X and Y short arms at diakinesis/metaphase I and sex chromosomes with unequal chromatid lengths at metaphase II. These data corroborate our hypothesis on the role of unequal crossing over in the production and propagation of X and Y heterochromatin variation and suggest that, in some cases, crossing over can occur during the process of synaptic adjustment.

DNA sequences for the gene encoding mitochondrial cytochrome oxidase I in a group of rodents (pocket gophers) and their ectoparasites (chewing lice) provide evidence for cospeciation and reveal different rates of molecular evolution in the hosts and their parasites. The overall rate of nucleotide substitution (both silent and replacement changes) is approximately three times higher in lice, and the rate of synonymous substitution (based on analysis of fourfold degenerate sites) is approximately an order of magnitude greater in lice. The difference in synonymous substitution rate between lice and gophers correlates with a difference of similar magnitude in generation times.

The pairing behavior of the sex chromosomes in male and female individuals representing seven species of Peromyscus was analyzed by electron microscopy of silver-stained zygotene and pachytene configurations. Six species possess submetacentric or metacentric X chromosomes with heterochromatic short arms. Sex-chromosome pairing in these species is initiated during early pachynema at an interstitial position on the X and Y axes. Homologous synapsis then progresses in a unidirectional fashion towards the telomeres of the X short arm and the corresponding arm of the heterochromatic Y chromosome. The distinctive pattern of synaptic initiation allowed a late-synapsing bivalent in fetal oocytes to be tentatively identified as that of the X chromosomes. In contrast to the other species, Peromyscus megalops possesses an acrocentric X chromosome and a very small Y chromosome. Sex-chromosome pairing in this species is initiated at the proximal telomeric region during late zygonema, and then proceeds interstitially towards the distal end of the Y chromosome. These observations suggest that the presence of X short-arm heterochromatin and corresponding Y heterochromatin interferes with late-zygotene alignment of the pairing initiation sites, thereby delaying XY synaptic initiation until early pachynema. The pairing initiation sites are conserved in the vicinity of the X and Y centromeres in Peromyscus, and consequently the addition of heterochromatin during sex-chromosome evolution essentially displaces these sites to an interstitial position.

Two unusual structural polymorphisms in the largest chromosomal pair of the Israeli mole rat, Spalax ehrenbergi, were analyzed from surface-spread and silver-stained preparations of synaptonemal complexes. A C-band negative polymorphism for the length of the 1p arm was visible as axial length differences during late zygonema and early pachynema. This region underwent synaptic adjustment resulting in a fully paired, mid-pachytene synaptonemal complex with equalized axial lengths. The somatically variable and nonargentophilic secondary constriction in the 1q arm was evident as a distinct silver-stained thickening along the synaptonemal complex. Presence of this structure on the synaptonemal complex varied both among individuals and among cells within individuals. The intraindividual variation of this region is hypothesized to represent differential biochemical activity with its cellular visualization being regulated in a manner similar to that of nucleolus organizer regions.

Historical flood records for the Rio Grande Valley of New Mexico suggest that a pocket gopher (Thomomys bottae) hybrid zone previously thought to be 10,000 years old may actually be closer to 50 years old. Measured zone width (defined genetically) is consistent with the hypothesis of recent contact, if we assume a reasonable dispersal distance of approximately 400 m/year for pocket gophers. A five-year study of movement of the contact zone between the two species of chewing lice that parasitize these pocket gophers also is consistent with the hypothesis of recent origin of the zone.

Silver-stained synaptonemal complexes were analyzed to examine chromosomal pairing in two species of Sceloporus (S. graciosus and S. undulatus) that have indistinct sex chromosomes. Electron microscopic analyses revealed distinct length heteromorphism between the lateral elements of one of the largest microchromosomal synaptonemal complexes in each species. The morphology and behavior of the heteromorphic synaptonemal complex in S. graciosus and S. undulatus were congruous with those described for heteromorphic sex bivalents in other vertebrates and are hypothesized to represent synapsis of the sex chromosomes. Synaptic behavior of the heteromorphic bivalents was similar between species and differed from that of the homomorphic (autosomal) bivalents within each species. In both species, synapsis of the heteromorphic bivalent was characterized by the formation of a buckle in the synaptonemal complex at early to mid-pachynema. Synaptic adjustment was observed to result in equalization in length of the lateral elements.

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.

The taxonomic significance of two chromosomal races of Geomys bursarius lutescens Merriam was analyzed using morphometric, karyotypic, and electrophoretic methods. The two races, one northern and the other southern, were well differentiated both genically and morphometrically. Neither hybridization nor introgression was observed, and the two chromosomal races appear, therefore, to be acting as separate species. However, each of the chromosomal races has genetic affinities with a more eastern nominal taxon, and previous investigators have regarded the eastern taxa as conspecific or even consubspecific. Moreover, morphometric similarities between the chromosomal races are equivalent to those found between one of the races and another chromosomal race that is regarded as a separate subspecies. The two chromosomal races of G. b. lutescens may be at an intermediate stage of speciation and reasonably could be treated as semispecies. However, for now they warrant recognition only as subspecies, one of which is described and named as new.

We measured hematocrit and serum albumin concentration at birth and red blood cell and plasma volume soon after birth in prematurely born infants with erythroblastosis fetalis of varying severity and examined the realtionships between these variables and the presence and severity of hydrops fetalis. Blood volumes in most of these infants were similar to the established normals for newborn infants without erythroblastosis. There was no simple association between blood volume and the presence of hydrops. Nonhydropic and severely hydropic infants had, on the average, similar and normal blood volumes, while mildly hydropic infants had low blood volumes. Anemia correlated fairly well with severity of hydrops but almost a quarter of the infants with severe hydrops were only mildly anemic. Red blood cell volume decreased and plasma volume increased proportionally with the degree of anemia at birth. Thus, hydropic infants with severe anemia had large plasma volumes while those with milder anemia did not. On the other hand, hypoalbuminemia was common and correlated closely with severity of hydrops. We suggest that hydrops results at least in part from low plasma colloid osmotic pressure due to hypoalbuminemia.

Chromosomal pairing and chiasma formation were studied two individuals of Peromyscus beatae heterozygous for the presence of a large block of interstitial heterochromatin. Although the modified chromosome was of medium size, analysis of C-banded diakinetic configurations revealed that it was the homolog of one of the smallest autosomes. Analysis of silver stained synaptonemal complexes indicated that synapsis was either unidirectional from initiation at one set of telomeres or was bidirectional from initiation at both sets of telomeres. Each pattern resulted in characteristic heteromorphic pairing configurations (interstitial asynapsis or terminally positioned unpaired segments) in early pachynema. These configurations underwent synaptic adjustment and, by mid-pachynema, the lateral elements of the polymorphic bivalent either appeared typical of homomorphic bivalents or exhibited regional heteropycnosis in one or both axes. Synaptonemal complex data for Peromyscus and many other mammalian species reflect an apparent need for fully paired, linear bivalents prior to the end of pachynema.

Chromosomal pairing and chiasma formation were studied two individuals of Peromyscus beatae heterozygous for the presence of a large block of interstitial heterochromatin. Although the modified chromosome was of medium size, analysis of C-banded diakinetic configurations revealed that it was the homolog of one of the smallest autosomes. Analysis of silver stained synaptonemal complexes indicated that synapsis was either unidirectional from initiation at one set of telomeres or was bidirectional from initiation at both sets of telomeres. Each pattern resulted in characteristic heteromorphic pairing configurations (interstitial asynapsis or terminally positioned unpaired segments) in early pachynema. These configurations underwent synaptic adjustment and, by mid-pachynema, the lateral elements of the polymorphic bivalent either appeared typical of homomorphic bivalents or exhibited regional heteropycnosis in one or both axes. Synaptonemal complex data for Peromyscus and many other mammalian species reflect an apparent need for fully paired, linear bivalents prior to the end of pachynema.