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Telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase complex that regulates telomerase activity to maintain telomere length for all animals with linear chromosomes. As the Mus musculus (MM) laboratory mouse has very long telomeres compared to humans, a potential alternative animal model for telomere research is the Peromyscus leucopus (PL) mouse that has telomere lengths close to the human range and has the wild counterparts for comparison. We report the full TERT coding sequence (pTERT) from PL mice to use in the telomere research. Comparative analysis with eight other mammalian TERTs revealed a pTERT protein considerably homologous to other TERTs and preserved all TERT specific-sequence signatures, yet with some distinctive features. pTERT displayed the highest nucleotide and amino acid sequence homology with hamster TERT. Unlike human but similar to MM mice, pTERT expression was detected in various adult somatic tissues of PL mice, with the highest expression in testes. Four different captive stocks of PL mice and wild-captured PL mice each displayed group-specific average telomere lengths, with the longest and shortest telomeres in inbred and outbred stock mice, respectively. pTERT showed considerable numbers of synonymous and nonsynonymous mutations. A pTERT proximal promoter region cloned was homologous among PL and MM mice and rat, but with species-specific features. From PL mice, we further cloned and characterized ribosomal protein, large, P0 (pRPLP0) to use as an internal control for various assays. Peromyscus mice have been extensively used for various studies, including human diseases, for which pTERT and pRPLP0 would be useful tools., (Published by Elsevier B.V.)

Many wildlife species are propagated in captivity as models for behavioral, physiological, and genetic research or to provide assurance populations to protect threatened species. However, very little is known about how animals evolve in the novel environment of captivity. The histories of most laboratory strains are poorly documented, and protected populations of wildlife species are usually too small and too short-term to allow robust statistical analysis. To document the evolutionary change in captive breeding programs, we monitored reproduction and behavior across 18 generations in six experimental populations of Peromyscusleucopus mice started from a common set of 20 wild-caught founders. The mice were propagated under three breeding protocols: a strategy to retain maximal genetic diversity, artificial selection against stereotypic behaviors that were hypothesized to reflect poor adaptation to captivity, and random bred controls. Two replicates were maintained with each protocol, and inter-replicate crosses at generations 19 and 20 were used to reverse accumulated inbreeding. We found that one of the stereotypic behaviors (repetitive flipping) was positively associated with reproductive fitness, while the other (gnawing) was relatively invariant. Selection to reduce these stereotypic behaviors caused marked reduction in reproduction, and populations not under artificial selection to reduce these behaviors responded with large increases in flipping. In non-selected populations, there was rapid evolution toward much higher proportion of pairs breeding and more rapid conception. Litter size, pup survival, and weaning mass all declined slowly, to the extent that would be predicted based on inbreeding depression. Inter-crossing between replicate populations reversed these declines in fitness components but did not reverse the changes in behavior or the accelerated breeding. These findings indicate that adaptation to captivity can be rapid, affecting reproductive patterns and behaviors, even under breeding protocols designed to minimize the rate of genetic change due to random drift and inadvertent selection.

Measurements of size and asymmetry in morphology might provide early indications of damaging effects of inbreeding or other genetic changes in conservation breeding programs. We examined the effects of inbreeding on size and fluctuating asymmetry (FA) in skull and limb bone measurements in experimental populations of three subspecies of Peromyscus polionotus mice that had previously been shown to suffer significant reductions in reproductive success when inbred. Inbreeding caused significant depression in mean size in two of the subspecies (P. p. rhoadsi and P. p. subgriseus), but the effects were smaller in the third (P. p. leucocephalus). Inbreeding caused an increase in FA of just one of eight bilateral traits in one subspecies (P. p. rhoadsi). Inbreeding depression in size was more easily detected than the effects of inbreeding on FA. FA may be much less sensitive to inbreeding and other stresses than are more direct measures of fitness such as reproductive output and body mass growth rate. Given the large sample sizes and statistical complexity required to assess changes to typically very small levels of FA in captive populations, FA will not likely provide a useful measure of inbreeding depression in captive populations., (© 2012 Wiley Periodicals, Inc.)

Mice (Peromyscus leucopus noveboracensis) from a captive-breeding program were used to test the effects of three genetic breeding protocols (minimizing mean kinship [MK], random breeding, and selection for docility [DOC]) and inbreeding levels on sperm traits and fertility. Earlier, in generation 8, one DOC replicate went extinct because of poor reproductive success. By generation 10, spermatozoa from DOC mice had more acrosome and midpiece abnormalities, which were shown to be strong determinants of fertility, as well as lower sperm production and resistance to osmotic stress. In addition, determinants of fertility, including male and female components, were assessed in a comprehensive manner. Results showed that the probability (P) of siring litters is determined by sperm number, sperm viability, and midpiece and acrosome abnormalities; that the P of siring one versus two litters is determined by tail abnormalities; and that the total number of offspring is influenced by female size and proportion of normal sperm, showing the relative importance of different sperm traits on fertility. On average, males with 20% normal sperm sired one pup per litter, and males with 70% normal sperm sired eight pups per litter. Interestingly, the proportion of normal sperm was affected by docility but not by relatively low inbreeding. However, inbreeding depression in sperm motility was detected. In the MK group, inbreeding depression not only affected sperm motility but also fertility: An increase in the coefficient of inbreeding (f) of 0.03 reduced sperm motility by 30% and translated into an offspring reduction of three pups in second litters. A genetic load of 48 fecundity equivalents was calculated.

The severity of inbreeding depression appears to vary among taxa, but few ecological or other patterns have been identified that predict accurately which taxa are most sensitive to inbreeding. To examine the causes of heterogeneity in inbreeding depression, the effects of inbreeding on reproduction, survival, and growth were measured in three replicate experimental stocks for each of three subspecies of Peromyscus polionotus mice. Inbreeding of the dam reduced the probability of breeding, the probability of producing a second litter, and litter size. Inbreeding of the litter caused depression of litter size, juvenile viability, and mass at weaning, and caused an increase in the within-litter variance in mass. In spite of differences between the subspecies in natural population sizes, genetic variation, and mean rates of reproduction and survival, all variation observed between experimental populations in their responses to inbreeding could be attributed to random founder effects. The genetic load of deleterious alleles in each replicate was unequally partitioned among its founder pairs, and different founders contributed to the load affecting different fitness components. Thus, inbreeding depression for any one fitness component, in our experimental environment, must be due to relatively few deleterious alleles with major effects. Genetic loads so comprised would be expected to diverge among natural populations due to both random drift and selective removal of recessive deleterious alleles during population bottlenecks. The near universality of inbreeding depression would be maintained, however, if different alleles contribute to inbreeding depression of different fitness components and in different environments., (© 1996 The Society for the Study of Evolution.)

Inbreeding is known to lead to decreased survival and reproduction in captive populations of animals. It is also important to know whether inbreeding has deleterious effects in natural habitats. An estimate was made of the effects of inbreeding in white-footed mice, Peromyscus leucopus noveboracensis, derived from a wild population. This study demonstrates that inbreeding had a significant detrimental effect on the survivorship of mice reintroduced into a natural habitat. This effect was more severe than the effect observed in laboratory studies of the population.

We tested the hypothesis that small, isolated populations would show less depression in fitness when inbred than would large, central populations. Laboratory stocks of Peromyscus leucopus and P. polionotus were established from insular, peninsular, and central populations. The isolated populations had one-third to one-half the genic diversity of central populations. Responses to inbreeding were highly varied: some populations had smaller litters, others experienced higher mortality, some showed slower growth rates, and one displayed no measurable effects when inbred. These results suggest that inbreeding depression is controlled by a small number of genes and that the size of the genetic load depends on which alleles are present in the founders of a population. The severity of fitness depression in inbred litters did not correlate with initial genic diversity of the stocks nor, therefore, with the size of the wild populations. Fitness measures appeared linearly related to the inbreeding coefficient of the liters, with no diminution of deleterious effects through subsequent generations of inbreeding. Thus overdominance of fitness traits probably contributed as much to the genetic load as did deleterious recessive alleles. The inbreeding level of the dam negatively affected the size, growth, and survival of litters only in genetically diverse populations, indicating that the load of recessive alleles negatively impacting maternal care may have been reduced by selection in the more peripheral populations during past bottlenecks.