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, HbI ^f, HbI^r, and HbI ^o, at a duplicated site controlling the six adult phenotypes. The HbI ^fallele 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.     

A possible role for the thyroid in reproductive inhibition in laboratory populations of the prairie deermouse (Peromyscus maniculatus)

Serum thyroxine concentrations were determined and found to be reduced in reproductively inhibited deermice selected from controlled growth laboratory populations. Daily injections of 1 microgram thyroxine in reproductively inhibited male deermice were shown to significantly increase testis weight and the number of spermatids with acrosome formation. Daily feeding of thyroxine to a controlled growth population promoted an increase in the mean weights of the reproductive organs of both sexes that was intermediate between reproductively inhibited and capable deermice. Also, two females in the population produced the first surviving young after 250 days of inhibition.     

Reproductive performance of a laboratory colony of the deermouse, Peromyscus maniculatus gambelii.

During a 23-mo period approximately 600 litters and 2,500 offspring were produced in a laboratory colony established with wild-trapped deermice (Peromyscus maniculatus gambelii). The incidence of pregnancy and size of litters increased with domestication. Average litter size was 4.3 for all litters and 4.1 and 4.7 for litters born to wild-trapped and first generation females, respectively. Litter size increased up to the seventh sequential pregnancy for both wild-caught and first-generation females and then tapered off. In all litters more males were born than females. The departure from a 1:1 ratio was significant for the combined data and for litters of first-generation females, but not for litters of wild-caught females.     

Nest-dismantling behavior of yellow-bellied prinia in mainland and island populations

Nest-dismantling behavior in birds is considered a fitness-maximizing adaptive behavior. Here, we compared nest-dismantling behavior and associated predation rates and nest characteristics in yellow-bellied prinia (Prinia flaviventris) on mainland China and the island of Taiwan during the breeding season from 2010 to 2014. Our results indicated that the proportion of individuals showing nest-dismantling behavior was higher on the island than on the mainland (29.3 vs. 0.8%). Nest-dismantling behavior was most frequent at the peak of the breeding season and mainly involved removing the upper halves of the nests and reusing the materials to construct new nests. The time taken to dismantle old nests and use the materials to build new ones was shorter than the time needed to build completely new nests. Nest predation, fidelity to the nest site, distance between old and new nests, and the costs of searching for nest materials could influence nest-dismantling behavior. Our results suggested that saving time and energy searching for new nest materials was the primary motivation behind nest-dismantling behavior in yellow-bellied prinia.     

Hypothyroidism in reproductively inhibited prairie deer mice (Peromyscus maniculatus bairdi) from laboratory populations

Several thyroid function parameters were compared between reproductively inhibited prairie deer mice of both sexes taken from laboratory populations and corresponding reproductively capable controls. The results of these experiments indicated the following: 1) prairie deer mice females had a statistically significant daily variation in mean serum thyroxine concentration and males displayed a similar trend; 2) total serum thyroxine and triiodothyronine were significantly lower in both male and female reproductively inhibited population animals compared with reproductively capable controls; 3) several morphometric characteristics of the thyroid of male and female population prairie deer mice were significantly different from that of control males and females, suggesting functional hypothyroidism in both sexes; 4) thyroid histology of male population deer mice was different from that of female population animals. In males, the data suggested that thyroid-stimulating hormone (TSH) stimulation was deficient due to some undetermined secondary hypothyroidism. In females, reduced serum thyroxine and triiodothyronine concentrations were observed due to primary hypothyroidism of unknown origin. The interrelationship between thyroid and adrenal function is discussed here and it is concluded that each of the systems may contribute to the observed reproductive inhibition. In particular, it was noted that the mechanism of response between population males and females may be quite different. No conclusive data are available to suggest whether one or the other system is the primary controller of the reproductive inhibition.     

Microsatellite variation and evolution in the Peromyscus maniculatus species group

Variation at 12 pure-repeat dinucleotide microsatellites from Peromyscus maniculatus was analyzed for samples of all species in the P. maniculatus species group and P. leucopus. Except for one locus (Pml08) that amplified a product only for P. maniculatus, these microsatellites yielded reliable estimates of variation across these species; per-locus polymorphism and allele-size distribution were not significantly different among or between any of the species sampled from mainland populations. Significantly lower levels of variation and the distribution of alleles in the two populations of the insular-endemic P. sejugis were consistent with the expectation of substantial founder effect and suggest a lack of recent gene flow between these populations. Phenetic analyses of genetic distances based on shared allele frequencies uniformly produced well-supported trees that were entirely concordant with the a priori corroborated relationships within the P. maniculatus species group; this result was not obtained with analyses of a genetic distance computed from differences in allele sizes. The microsatellite data do not support the hypothesis that P. sejugis should be considered conspecific with P. maniculatus but yield a strongly supported sister-group association between P. sejugis and P. keeni.     

Microsatellite genetic structure and cytonuclear discordance in naturally fragmented populations of deer mice (Peromyscus maniculatus)

The Great Lakes impose high levels of natural fragmentation on local populations of terrestrial animals in a way rarely found within continental ecosystems. Although separated by major water barriers, woodland deer mouse (Peromyscus maniculatus gracilis) populations on the islands and on the Upper Peninsula (UP) and Lower Peninsula (LP) of Michigan have previously been shown to have a mitochondrial DNA contact zone that is incongruent with the regional landscape. We analyzed 11 microsatellite loci for 16 populations of P. m. gracilis distributed across 2 peninsulas and 6 islands in northern Michigan to address the relative importance of geographical structure and inferred postglacial colonization patterns in determining the nuclear genetic structure of this species. Results showed relatively high levels of genetic structure for this species and a significant correlation between interpopulation differentiation and separation by water but little genetic structure and no isolation-by-distance within each of the 2 peninsulas. Genetic diversity was generally high on both peninsulas but lower and correlated to island size in the Beaver Island Archipelago. These results are consistent with the genetic and demographic isolation of Lower Peninsula populations, which is a matter of concern given the dramatic decline in P. m. gracilis abundance on the Lower Peninsula in recent years.     

Nuclear and mitochondrial DNA reveal contrasting evolutionary processes in populations of deer mice (Peromyscus maniculatus)

We investigated a major geographic break in mitochondrial DNA (mtDNA) haplotypes in deer mice, Peromyscus maniculatus, by analysing spatial variation in a 491‐bp fragment of the mtDNA control region from 455 samples distributed across a north–south transect of 2000 km in Western North America. To determine whether the mtDNA break was reflected in the nuclear genome, we then compared spatial variation in 13 nuclear microsatellites of 95 individuals surrounding the mtDNA break. Using a canonical correlation analysis we found that nuclear genomic variation was not correlated with mtDNA differentiation. The contrasting patterns of variation in mtDNA and nuclear DNA are consistent with a hypothesis of historic genetic drift that occurred in isolated refugia combined with recent gene flow between the formerly isolated refugial populations. A Mantel test of genetic vs. geographic distance revealed that recent gene flow between deer mouse populations has been high. We conclude that past vicariant events associated with Pleistocene climate changes together with recent gene flow have created the observed intra‐specific cytonuclear discordance in Western North America.     

Recovery of reproductive function by prairie deermice (Peromyscus maniculatus bairdii) from asymptotic populations

Prairie deermice greater than 100 days of age and non-reproductive in laboratory populations provided with surplus food and water were paired either with fertile mates or with other inhibited population animals. Following pairing, more than 75 per cent of all animals reproduced. The rates of reproductive recovery did not differ significantly between males and females. The average time required for reproduction by population animals paired with proven mates was less than that for pairs composed of population animals. The significantly slower rate of reproductive recovery for population pairs suggests that mutual stimulation is involved in recovery and is initially lacking or minimal in these pairs. A period of physiological and behavioural adjustment following removal from the populations appears necessary before reproduction. Mechanisms preventing reproduction within the populations are unknown.     

Genetic and morphometric differentiation between island and mainland southern elephant seal populations

We compare genetic (both nuclear and mitochondrial) and morphometric measures between two putative populations of southern elephant seal (Mirounga leonina), and interpret the results in the context of data from mark-recapture and satellite-telemetric studies. One population is on the Argentine mainland, while the other is 2,400 km away on South Georgia island. We found pronounced differentiation at the mitochondrial DNA (mtDNA) control region that was distinct from the pattern of variation seen among island rookeries. Some morphometric characters and seven out of ten nuclear-DNA markers also showed differentiation between the island and mainland sites. Diversity at nuclear markers was high in both populations but mtDNA diversity was low in the mainland population, suggesting a founder event and little subsequent immigration of females. Morphological differences may suggest different selective environments at the two sites.     

Genetic structure of island and mainland populations of a Neotropical bumble bee species

As a consequence of founder effects, small population size and demographic constraints, island populations are often characterized by low genetic diversity and high inbreeding. The effects of inbreeding are more pronounced in haplo-diploid insects like bees than in similar diploid species, because their method of sex determination requires heterozygosity at a sex locus. Inbreeding leads to homozygosity at the sex locus and the production of non-viable diploid males. This means that island populations of bees are particularly prone to extinction. Here we determine the levels of diversity and isolation between islands and mainland populations of the bumble bee Bombus morio in southeast Brazil. We analyzed 659 individuals from 24 populations, sequencing two mitochondrial genes (COI and Cytb) and genotyping all individuals at 14 microsatellite loci. Surprisingly, genetic diversity was high and genetic isolation was low in all populations except Teodoro Sampaio (mainland) and Ilha da Vitória (island). Genetic diversity is not significantly correlated with island area, but is lower in populations that are more distant from the mainland. Except perhaps for Ilha da Vitória, we suggest that the island populations are unlikely to go extinct due to genetic factors. Finally, based on its genetic distance from all other populations, we identify a putative new subspecies in the Teodoro Sampaio region.     

Within-population craniometric variability of insular populations of deer mice, Peromyscus maniculatus, elucidated by landscape configuration

Within-population genetic variability of twelve insular and four mainland populations of deer mice ( Peromyscus maniculatus ) was assessed using craniometric characters, and compared to results previously obtained from RAPD data. An index of Craniometric Variance ( CVar ) was computed from pairwise distances among all specimens. Variations in CVar measures were then compared to landscape variables using a linear regression approach. Our results suggest that CVar decreases in presence of large number of a competitive species (the boreal redback vole, Clethrionomys gapperi ; r =−0.527, p <0.037) in deer mouse populations. Island remoteness ( r =−0.251, p <0.220) and the geometry of the bank opposite to each island ( r =−0.459, p <0.067) were marginally correlated with CVar , but the linear combination of these two variables, forming a composite isolation index, represented the major factor explaining the observed CVar ( r =−0.648, p <0.011). Using a multiple regression model, 76.3% of the CVar was explained by a combination of this isolation index and the competitors' abundance. These results suggest that taking into account landscape barriers as well as the dispersal behavior of small mammals might provide sounder ecological variables than geographical distances alone for predicting within-population genetic variability in a network of habitat patches.     

Variation in dispersability among mainland and island populations of three wind dispersed plant species

Reduced dispersability of species living on islands relative to mainland has been documented in both plants and animals. One evolutionary scenario explains this trend by strong selection against dispersal, once the species has reached the island, to reduce dispersal out to sea. In this study, we compare the dispersal ability of three wind dispersed plant species (Cirsium arvense, Epilobium angustifolium, and E. hirsutum) from populations on mainland and three islands. Dispersal ability was estimated directly as drop time of diaspores, and indirectly using a morphological measure relating the weight of the diaspore to the size of the pappus (Cirsium) or seed hairs (Epilobium). Positive correlation between the morphological measure of dispersal ability and drop time of diaspores were found for all study species. Dispersal ability varied significantly among mainland and islands, and among species. C. arvense showed a significant reduction in dispersal ability on islands compared to mainland, whereas the reverse was found for the two Epilobium species. Overall Epilobium diaspores had a 2–4 times higher dispersability than C. arvense, indicating that degree of isolation of islands vary among study species. Significant differences in dispersability among plants within populations were detected in all species suggesting that this trait may have a genetic component.     

Photoperiodic time measurement in the male deer mouse, Peromyscus maniculatus

Weanling male deer mice, Peromyscus maniculatus, were exposed for three weeks either to light-dark (LD) cycles with periods (T=L+D) ranging from T=23 (1L:22D) to T=25.16 (1L:24.16D) or to 24-h LD cycles with photoperiods ranging from 1 (1L:23D) to 19 (19L:5D) h. Both the circadian locomotor activity rhythms and the response of the reproductive system to these LD cycles were assessed. The results demonstrate that the photoperiodic effectiveness of light depends on the phase of the light relative to the animal's circadian system, as marked by the circadian activity rhythm. Light falling during the animal's subjective night, from activity onset to at least 11.8 h after activity onset, stimulates growth and maturation of the reproductive system, whereas light falling during the rest of the circadian cycle is nonstimulatory.