Wallace D. Dawson

Inheritance of burrow building in Peromyscus.

Burrow construction abilities of laboratory-reared oldfield mice (Peromyscus polionotus), deermice (P. maniculatus), and their F1 hybrids were compared using a spacious earth-filled test chamber. Mated paris with nursing litters were individually introduced into the chamber for 4 days in each test. Oldfield mice bred in metal or plastic cages for 20 or more generations constructed elaborate burrows, with entrance and escape tunnels, tunnel plugs, next chambers, and nests, essentially like those of wild mice of this species. Prairie deermice maintained for 25 or more generations in captivity constructed shallow or superficial burrows characteristic of deermice in nature. F1 hybrids made burrows like those of oldfield mice, complete in all particulars. First-generation backcross animals tested for burrow building exhibited a spectrum of performances. Species difference in burrow construction is principally genetic in origin, and during 20–25 generations in captivity no substantial loss of this ability occurred. F1 hybrid data indicate that the more complex burrow building exhibits genetic dominance, and backcross results show that at least two and probably more gene loci strongly influence the trait.

Evolution of Monogamy, Paternal Investment, and Female Life History in Peromyscus

The timing of reproductive development and associated trade-offs in quantity versus quality of offspring produced across the life span are well documented in a wide range of species. The relation of these aspects of maternal life history to monogamy and paternal investment in offspring is not well studied in mammals, due in part to the rarity of the latter. By using five large, captive-bred populations of Peromyscus species that range from promiscuous mating with little paternal investment (P. maniculatus bairdii) to social and genetic monogamy with substantial paternal investment (P. californicus insignis), we modeled the interaction between monogamy and female life history. Monogamy and high paternal investment were associated with smaller litter size, delayed maternal reproduction that extended over a longer reproductive life span, and larger, higher quality offspring. The results suggest monogamy and paternal investment can alter the evolution of female life-history trajectories in mammals.

Peromyscus (deer mice) as developmental models

Deer mice (Peromyscus) are the most common native North American mammals, and exhibit great natural genetic variation. Wild‐derived stocks from a number of populations are available from the Peromyscus Genetic Stock Center (PGSC). The PGSC also houses a number of natural variants and mutants (many of which appear to differ from Mus). These include metabolic, coat‐color/pattern, neurological, and other morphological variants/mutants. Nearly all these mutants are on a common genetic background, the Peromyscus maniculatus BW stock. Peromyscus are also superior behavior models in areas such as repetitive behavior and pair‐bonding effects, as multiple species are monogamous. While Peromyscus development generally resembles that of Mus and Rattus, prenatal stages have not been as thoroughly studied, and there appear to be intriguing differences (e.g., longer time spent at the two‐cell stage). Development is greatly perturbed in crosses between P. maniculatus (BW) and Peromyscus polionotus (PO). BW females crossed to PO males produce growth‐restricted, but otherwise healthy, fertile offspring which allows for genetic analyses of the many traits that differ between these two species. PO females crossed to BW males produce overgrown but severely dysmorphic conceptuses that rarely survive to late gestation. There are likely many more uses for these animals as developmental models than we have described here. Peromyscus models can now be more fully exploited due to the emerging genetic (full linkage map), genomic (genomes of four stocks have been sequenced) and reproductive resources.

Mus and Peromyscus chromosome homology established by FISH with three mouse paint probes

Abstract. Fluorescence-labeled DNA probes constructed from three whole house mouse (Mus domesticus) chromosomes were hybridized to metaphase spreads from deer mouse (Peromyscus maniculatus) to identify homologies between the species. Mus Chr 7 probe hybridized strongly to the ad-centromeric two-thirds of Peromyscus Chr 1q. Most of Mus 3 probe hybridized principally to two disjunct segments of Peromyscus Chr 3. Mus Chr 9 probe hybridized entirely to the whole Peromyscus Chr 7. Three Peromyscus linkage groups were assigned to chromosomes, based on linkage homology with Mus. The data also are useful in interpretation of chromosomal evolutionary history in myomorphic rodents.

Linkage relationships among eleven biochemical loci in Peromyscus

Interspecific F1 hybrids of Peromyscus maniculatus (deermice) and P. polionotus (oldfield mice) were backcrossed to P. maniculatus. Backcross progeny were electrophoretically typed for 11 variant protein markers: albumin, transferrin, leucine aminopeptidase, amylase, 6-phosphogluconate dehydrogenase, nucleoside phosphorylase, dipeptidase, tripeptidase, glutamate oxaloacetate transaminase, alcohol dehydrogenase, and sorbitol dehydrogenase. Genetic variation for each protein was attributed to a single autosomal locus. The alcohol dehydrogenase (Adh), salivary amylase (Amy), and albumin (Alb) loci appeared to be linked in the sequence of Adh—11.5 cM—Amy—33.3 cM—Alb. The tripeptidase locus, Pep-2, also may be loosely linked to Alb in this group. Variants at all other loci assorted independently. These and other known linkage relationships in Peromyscus correspond closely to those of the house mouse, Mus musculus. The available evidence in Peromyscus further supports the concept of linkage conservation by natural selection.

Comparative genetics of hamster amylases

Syrian (Mesocricetus auratus) and Chinese (Cricetulus griseus) hamsters were phenotyped by electrophoresis for salivary and pancreatic amylases. Syrian hamsters possess two salivary amylase electromorphs, the more anodal (fast) being invariant in 250 outbred and 17 representatives of 5 highly inbred lines. The slow electromorph had activity equal to that of the fast amylase (heavy), or had distinctly less activity (light), or was absent (null). The slow electromorph is inherited as an autosomal semidominant trait with two alleles, Amys and Amyo. Amys homozygotes produce heavy, Amyo homozygotes null, and heterozygotes light phenotypes, respectively. Five inbred strains of hamsters were homozygous Amyo. Pancreatic amylase was monomorphic. Eight outbred Chinese hamsters showed no salivary amylase activity with electrophoresis, but slight activity with long incubation on starch-agar plates. However, pancreatic amylase activity in the Chinese hamster exceeded that in Syrian hamsters. Site duplication and apparent “null” alleles for amylase genes occur in muroid rodents. The evolutionary implications are discussed.

Genetic and Developmental Variation of Hemoglobin in the Deermouse, Peromyscus maniculatus

A genetic investigation of electrophoretic hemoglobin variants of the deermouse, Peromyscus maniculatus, shows three alleles, HbIf, HbIr, and HbIo, at a duplicated site controlling the six adult phenotypes. The HbIfallele has not been described previously. The hemoglobin locus is not closely linked to the albino locus. Fetal hemoglobin is distinct from any of the adult components and has a slower electrophoretic mobility. The fetal phenotype changes to the adult type between the days 15 and 18 of prenatal life.

Serum Protein Polymorphisms in Peromyscus polionotus of South Carolina

Serum proteins were sampled from 318 old field mice, Peromyscus polionotus , collected from 21 sites along a 90-mile transect through central South Carolina. Polymorphisms of transferrin, albumin, prealbumin, postalbumin, and other proteins were demonstrated by electrophoresis. The inheritance of two transferrins C and E was controlled by co-dominant alleles, Trf c , and Trf e . Abnormal segregation ratios involving a third transferrin, D , were observed. Significant differences in the frequency of one allele, Trf e , were observed among the three major areas of the transect, which were separated by river-swamp systems, with the allele apparently being absent at the northeast extreme. Marked variation in frequency of the Trf e allele between neighboring, but semi-isolated, collection sites was interpreted as evidence of founder effect.

Comparative progesterone concentrations in two Peromyscus species

1. Plasma progesterone concentrations were measured by radioimmunoassay in the oldfield mouse (Peromyscus polionotus) and the deermouse (P. maniculatus) at estrus and at 5-day intervals during pregnancy. 2. P. polionotus had significantly higher progesterone levels, both at estrus and during gestation. 3. The level was markedly less in female P. polionotus bearing interspecific (P. polionotus x P. maniculatus) hybrid conceptuses than in those with conspecific conceptuses. 4. It is postulated that the reduced progesterone level in females bearing hybrid fetuses may be responsible for reproductive failure which regularly occurs when this cross is attempted. 5. An endocrine difference of this magnitude could represent an incipient reproductive isolating mechanism.

Comparative thyroid activity in two species of Peromyscus

Abstract Thyroid activity in two species of deermice, Peromyscus maniculatus and P. polionotus , was compared by using protein bound iodine (PBI), thyroid secretion rate (TSR), and gland histology as criteria. Peromyscus polionotus showed a significantly higher mean PBI than P. maniculatus bairdii , 2.75 versus 2.22 μg%. In terms of proportion of epithelium and colloid, P. polionotus also averaged approximately 9% more gland epithelium than P. maniculatus bairdii . While significant differences in TSR between the species were not detected, P. polionotus did show a higher mean rate, 1.96 compared with 1.61 μg thyroxine per 100 gm body weight. Thyroid histological structure of these two species was compared. Adult mice were used in all studies. The differences in thyroid activity in the two species are probably insufficient to induce the physiological and developmental disruptions which occur when they are hybridized.