Evolutionary morphology of the Tenrecoidea (Mammalia) carpal complex

The mammalian carpus can be difficult to interpret both phylogenetically and functionally. It is evolutionarily constrained in terms of functional morphology, yet there is considerable variation among many eutherian and metatherian lower and higher level taxa. The ecologically diverse Tenrecoidea (Mammalia) is a useful model for morphological interpretation of the interplay between function and phylogenetic constraint. Elements from the wrist and hand of 13 tenrecoid species, and one species each from Macroscelididae, Solenodontidae, and Erinaceidae, were compared to test form–function hypotheses of specific carpal, metacarpal, and phalangeal characters. Qualitative comparisons illustrate that several aspects of the tenrecoid carpus can be correlated with positional behaviour. Convergences within Tenrecoidea, and between tenrecoids and nontenrecoids with similar locomotor regimes, confirm a small number of carpal characters and a larger number of distal forearm, metacarpal, and phalangeal characters that reliably correspond with functional expectations. In addition, several features of the carpus appear to be phylogenetically constrained and indicate specific affinities within Tenrecoidea. Finally, there are a significant number of carpal features that vary among the studied taxa and remain ambiguous in terms of phylogenetic and/or functional significance.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 267–288.     

Demography of Black Bears in Hunted and Unhunted Areas of the Boreal Forest of Ontario

Abstract: We estimated relative density, survival, and reproduction of American black bears (Ursus americanus) from capture-recapture and telemetry data collected from 1989 to 1999 in the unhunted Chapleau Crown Game Preserve (CCGP) and nearby hunted areas in the boreal forest of Ontario, Canada. We tested for combinations of effects of age class, sex, year, years of food shortage, encumbrance status, and residency (on or off the Game Preserve) on vital rates. Results from live captures, remote captures, and bait-station hit rates indicated that density was highest inside CCGP. Total survival of adult females, subadults, and cubs were similar among residents and nonresidents of CCGP, but yearling survival was lower among CCGP residents. Adult females were approximately twice as likely to die and nearly 10 times as likely to be cannibalized (risk ratio [RR] = 9.62, 95% CI = 2.088–44.29) while encumbered with cubs of the year. Nonresidents of CCGP had greater risk of being harvested (RR = 4.00, 95% CI = 1.19–13.46) but similar risk of being cannibalized (RR = 0.875, 95% CI = 0.300–2.55) relative to CCGP residents, suggesting that harvest mortality was additive to other forms of mortality. Residents of CCGP had older ages at primiparity and lower litter-production rates than bears resident in hunted areas. Few litters were produced in years following food shortages, but litter size was unaffected. We recommend that managers allow for additive harvest mortality and reduced survival of bears encumbered with cubs of the year, and we caution that assuming density-compensatory increases in cub production could optimistically bias estimates of population growth.     

Selection on domestication traits and quantitative trait loci in crop–wild sunflower hybrids

The strength and extent of gene flow from crops into wild populations depends, in part, on the fitness of the crop alleles, as well as that of alleles at linked loci. Interest in crop–wild gene flow has increased with the advent of transgenic plants, but nontransgenic crop–wild hybrids can provide case studies to understand the factors influencing introgression, provided that the genetic architecture and the fitness effects of loci are known. This study used recombinant inbred lines (RILs) generated from a cross between crop and wild sunflowers to assess selection on domestication traits and quantitative trait loci (QTL) in two contrasting environments, in Indiana and Nebraska, USA. Only a small fraction of plants (9%) produced seed in Nebraska, due to adverse weather conditions, while the majority of plants (79%) in Indiana reproduced. Phenotypic selection analysis found that a mixture of crop and wild traits were favoured in Indiana (i.e. had significant selection gradients), including larger leaves, increased floral longevity, larger disk diameter, reduced ray flower size and smaller achene (seed) mass. Selection favouring early flowering was detected in Nebraska. QTLs for fitness were found at the end of linkage groups six (LG6) and nine (LG9) in both field sites, each explaining 11–12% of the total variation. Crop alleles were favoured on LG9, but wild alleles were favoured on LG6. QTLs for numerous domestication traits overlapped with the fitness QTLs, including flowering date, achene mass, head number, and disk diameter. It remains to be seen if these QTL clusters are the product of multiple linked genes, or individual genes with pleiotropic effects. These results indicate that crop trait values and alleles may sometimes be favoured in a noncrop environment and across broad geographical regions.     

Source–sink dynamics sustain central stonerollers (Campostoma anomalum) in a heavily urbanized catchment

1. The influence of spatial structure on population dynamics within river–stream networks is poorly understood. Utilizing spatially explicit analyses of temporal genetic variance, we tested whether persistence of central stonerollers (Campostoma anomalum) reflects differences in habitat quality and location within a highly modified urban catchment in southwestern Ohio, U.S.A. 2. Estimates of genetic diversity did not vary with habitat quality. Nevertheless, evidence of weak but temporally stable genetic structure, location‐dependent effective population sizes and rates of immigration among sites, together suggest that persistence of central stonerollers within the catchment may be attributable to source–sink dynamics driven by habitat heterogeneity. 3. Under this scenario, migrant‐pool colonization from areas of relatively high habitat quality in the upper catchment sustains the presence of central stonerollers at degraded sites in the main stem and dampens population subdivision within the catchment. However, because intact habitat is restricted to the upper portion of the catchment, it is not possible to preclude net downstream dispersal as a mechanism contributing to source–sink dynamics. The slight genetic structure that persists appears to reflect weak isolation by distance diminished by high rates of immigration. 4. This study suggests that without a systems perspective of the conditions that sustain populations in degraded waterways, environmental assessments may underestimate levels of impairment. Conservation and management of stream fishes could be improved by maintaining habitat in areas that are net exporters of migrants or by remediation of impaired habitat.     

Fish as sources and sinks of nutrients in lakes

1. The release of total phosphorus (TP) and nitrogen (N in ammonium) was measured for the five most abundant fish species (>85% of biomass) in Mouse and Ranger Lakes, two biomanipulated, oligotrophic lakes in Ontario. 2. The specific release rate of both nutrients was significantly related to fish mass; log₁₀ TP release rate (μg h^?1) = 0.793 (±0.109) [log₁₀ wet mass (g)] + 0.7817 (±0.145), and log₁₀ N release rate (μg h^?1) = 0.6946 (±0.079) [log₁₀wet mass (g)] + 1.7481 (±0.108). 3. When fish nutrient release was standardized for abundance (all populations, 1993–95) and epilimnetic volume, fish were estimated to contribute 0.083 (±0.061) μg TP L^?1 day^?1, and 0.41 (±0.17) μg N L^?1 day^?1 in Mouse L., and 0.062 (±0.020) μg TP L^?1 day^?1 and 0.31 (±0.08) μg N L^?1 day^?1 in Ranger L. 4. In comparison, concurrent rates of total planktonic P regeneration were 1.02 (±0.45) μg L^?1 day^?1 (Mouse L.) and 0.85 (±0.19) μg L^?1 day^?1 (Ranger L.). Fish represented 8% of planktonic P release in Mouse L. and 7% in Ranger L. 5. Fish dry mass had mean elemental body compositions of 39.3% carbon, 10.9% nitrogen, and 4.0% phosphorus (all fish combined), with a mean molar C : N : P ratio of 27 : 6 : 1. This comprised about 55% and 23% of the total epilimnetic particulate P and N respectively. 6. Turnover times of P and N in fish were approximately 103 and 48 days respectively. In comparison, planktonic turnover times of particulate P in Mouse and Ranger Lakes were 4.3 and 4.4 days respectively. Given their high P content and low turnover rates, fish appear to be important P sinks in lakes.     

Development in Electrofused Conjugants of Tetrahymena thermophila

Electric shock can create parabiotic fusions of living Tetrahymena cells. In this study, cells were mated and successful pairs were electrofused with either vegetatively growing cells or other mating pairs. In particular, we electrofused pairs from normal [diploid x diploid] matings with vegetatively dividing cells in G- or M-phase of the cell cycle. We also fused [diploid x diploid] conjugants with mating pairs involving an aneuploid partner [diploid x "star"], which typically undergo an abortive conjugal pathway termed genomic exclusion. Using such parabiotic fusions we identified and characterized two developmentally critical landmarks: 1) the "abort" signal, which is initiated in pairs with nuclear defects (this first becomes evident soon after the completion of Meiosis I or the beginning of Meiosis II); and 2) the "terminal commitment point", a developmental stage in normal [diploid x diploid] pairs after which conjugation no longer responds to a parabiotically transmitted abort signal (this correlates with the onset of the second postzygotic nuclear division). Finally we demonstrate that a conjugal-arrest-activity varies with the vegetative cell cycle, reaching its highest level of activity during M-phase and dropping just after cytokinesis.     

Temperature and daylength control of flower initiation in winter oilseed rape (Brassica napus L.)

The influence of low temperature and daylength on pre-floral growth and flower initiation in winter oilseed rape cv. Mikado was examined under controlled environment conditions at the University of Newcastle upon Tyne during 1985 and 1986.
The vernalisation requirement of Mikado was most effectively fulfilled by temperatures of 6 °C and 9 °C. Plants maintained at both higher and lower temperatures had an extended pre-floral growth phase. The transition from vegetative to reproductive growth in plants maintained at 12 °C was delayed by slow accumulation of the cold requirement, whereas flower initiation appeared to be delayed by limited leaf production, dry matter accumulation and/or assimilate availability in plants grown at 3 °C. The mechanism of floral induction remained unresolved but it was clear that flower initiation was not controlled by low temperature per se . Short days partially substituted for the cold requirement at 12 °C but photoperiodic induction of flower initiation was less important than the influence of low temperature.     

The signal crayfish is not a single species: cryptic diversity and invasions in the Pacific Northwest range of Pacifastacus leniusculus

1. We used historical sources, morphology‐based taxonomy and mtDNA sequence data to address questions about the signal crayfish Pacifastacus leniusculus. These included evaluating unrecognised cryptic diversity and investigating the extent to which P. leniusculus may have been introduced within its presumed native range in the Pacific Northwest region of North America. Our study builds and expands on Pacific Northwest phylogeographic knowledge, particularly related to patterns of glacial refugia for freshwater species. 2. Extensive collections (824 specimens) from British Columbia (Canada), Idaho, Nevada, Oregon and Washington (United States) were used to characterise P. leniusculus at the mitochondrial 16S rRNA gene. Genetic groups within the species were elucidated by phylogenetics and amova ; evolutionary relationships within the most common and diverse group were investigated using a statistical parsimony haplotype network, a nested amova , and tests of isolation by distance. Morphological measurements were used to relate findings of molecular analyses to three historically recognised P. leniusculus subspecies and characterise cryptic diversity by morphology. 3. We found substantial cryptic diversity, with three groups highly distinct from P. leniusculus in discrete geographic regions: the Chehalis River glacial refugium, Central Oregon and the Okanagan Plateau. Disjunct distributions of P. leniusculus relative to these cryptic groups and known patterns of Pleistocene glaciation and landscape evolution cast doubt on whether P. leniusculus is native to some areas such as coastal drainages of northern Washington and southern British Columbia. Morphological traits previously used to characterise P. leniusculus subspecies still persist but may be incapable of distinguishing P. leniusculus from newly discovered cryptic groups. 4. Cryptic diversity found within P. leniusculus highlights the pressing need for a thorough investigation of the genus Pacifastacus using data based on more extensive gene and taxon sampling. It also warrants conservation attention, as introductions of P. leniusculus within the Pacific Northwest may carry risks of hybridisation and introgression for cryptic groups. Owing to high genetic diversity and limited dispersal capacity relative to more vagile organisms like freshwater fish, crayfish of the genus Pacifastacus offer powerful potential insights into the geological history and phylogeography of the Pacific Northwest region. Finally, by shedding light on the long‐neglected native range of P. leniusculus, our results should also better inform our understanding of potential source populations for, and the ecology of, this important invasive species in regions including Europe, Japan and elsewhere in North America.     

Vertical partitioning of CO2 production within a temperate forest soil

The major driving factors of soil CO₂ production – substrate supply, temperature, and water content – vary vertically within the soil profile, with the greatest temporal variations of these factors usually near the soil surface. Several studies have demonstrated that wetting and drying of the organic horizon contributes to temporal variation in summertime soil CO₂ efflux in forests, but this contribution is difficult to quantify. The objectives of this study were to partition CO₂ production vertically in a mixed hardwood stand of the Harvard Forest, Massachusetts, USA, and then to use that partitioning to evaluate how the relative contributions of CO₂ production by genetic soil horizon vary seasonally and interannually. We measured surface CO₂ efflux and vertical soil profiles of CO₂ concentration, temperature, water content, and soil physical characteristics. These data were applied to a model of effective diffusivity to estimate CO₂ flux at the top of each genetic soil horizon and the production within each horizon. A sensitivity analysis revealed sources of uncertainty when applying a diffusivity model to a rocky soil with large spatial heterogeneity, especially estimates of bulk density and volumetric water content and matching measurements of profiles and surface fluxes. We conservatively estimate that the O horizon contributed 40–48% of the total annual soil CO₂ efflux. Although the temperature sensitivity of CO₂ production varied across soil horizons, the partitioning of CO₂ production by horizon did not improve the overall prediction of surface CO₂ effluxes based on temperature functions. However, vertical partitioning revealed that water content covaried with CO₂ production only in the O horizon. Large interannual variations in estimates of O horizon CO₂ production indicate that this layer could be an important transient interannual source or sink of ecosystem C.     

Sixteen microsatellite loci for the Bufo boreas group

The four species that comprise the Bufo boreas group of toads are critically imperiled in all or portions of their geographical ranges. We present data from 16 microsatellite loci isolated from B. boreas that cross‐amplify in these four species. These markers have proven useful in the analyses of population structure and conservation genetics, and provide a powerful tool for future researchers who seek to understand the conservation genetics of these rare toad species. Polymorphism was assessed for 339 individuals from seven populations representing the four species. All loci were polymorphic (X? = 8, range of four to 19 alleles). Three loci were not in Hardy–Weinberg equilibrium (HWE) in one population, and one of these loci was out of HWE in a second population (P < 0.003 after Bonferroni correction for multiple tests). However, there were no systematic deviations from HWE across all study populations. Small populations in fragmented habitat appear to explain the existing HWE deviations.