The Genetic Structure and Evolutionary Fate of Parthenogenetic Amphibian Populations as Determined by Markovian Analysis

SYNOPSIS. One-locus, two-allele models are presented which describethe genetic consequences of naturally occurring andexperimentallyinduced parthenogesis in triploid and diploid amphibians. Themodels may in general be used to investigate genetic changeresulting from apomictic (ameiotic) and automictic (meiotic)parthenogenetic reproduction. These models quantify the influence of mutation, segregation,and selection upon genetic variability in parthenogeneticpopulations.They also allow an estimate of the relative importance of stochasticforces in altering this variability. They thus provide a basisfor understanding evolution in these populations. Some of the conclusions derived from this study contradict previouspredictions regarding genetic variability in parthenogeneticpopulations. First, if mutation is the sole source of geneticchange (i.e., strict apomixis), parthenogenetic populationsshould not become completely heterozygous. Second, small amountsof segregation occurring in apomictic populations have enormouseffects upon the genetic variability of these populations, i.e.,they should lose much of their heterozygosity. In addition to these conclusions, the results of this studysuggest that studies of protein variability in parthenogeneticspecies should contribute toward answering the question: Howmuch of the genetic variability observed in nature is evolutionarilyrelevant?     

Dating of graptolite zones by sedimentation rates: implications for rates of evolution

Preliminary determinations of ancient pelagic sedimentation rates agree with modern rates at about 4 meters per million years. By combining data on the thickness of graptolite zones from the North American Cordillera with data from other parts of the world, we have refined the Early Silurian time scale and obtained much better resolution than is possible for radiometric dates. The new Early Silurian time scale allows estimation of true rates of change in graptolite diversity. The Llandoverian diversity explosion is twice as rapid as was previously thought. The brevity of diversity lows and rapidity of speciation support modern theories of quantum evolution.     

Indirect Effects of Impoundment on Migrating Fish: Temperature Gradients in Fish Ladders Slow Dam Passage by Adult Chinook Salmon and Steelhead

Thermal layering in reservoirs upstream from hydroelectric dams can create temperature gradients in fishways used by upstream migrating adults. In the Snake River, Washington, federally-protected adult salmonids (Oncorhynchus spp.) often encounter relatively cool water in dam tailraces and lower ladder sections and warmer water in the upstream portions of ladders. Using radiotelemetry, we examined relationships between fish passage behavior and the temperature difference between the top and bottom of ladders (∆T) at four dams over four years. Some spring Chinook salmon (O. tshawytscha) experienced ∆T ≥ 0.5 °C. Many summer and fall Chinook salmon and summer steelhead (O. mykiss) experienced ∆T ≥ 1.0 °C, and some individuals encountered ΔT > 4.0°C. As ΔT increased, migrants were consistently more likely to move down fish ladders and exit into dam tailraces, resulting in upstream passage delays that ranged from hours to days. Fish body temperatures equilibrated to ladder temperatures and often exceeded 20°C, indicating potential negative physiological and fitness effects. Collectively, the results suggest that gradients in fishway water temperatures present a migration obstacle to many anadromous migrants. Unfavorable temperature gradients may be common at reservoir-fed fish passage facilities, especially those with seasonal thermal layering or stratification. Understanding and managing thermal heterogeneity at such sites may be important for ensuring efficient upstream passage and minimizing stress for migratory, temperature-sensitive species.     

In-depth qualitative and quantitative analysis of composite glycosylation profiles and other micro-heterogeneity on intact monoclonal antibodies by high-resolution native mass spectrometry using a modified Orbitrap

Here, we describe a fast, easy-to-use, and sensitive method to profile in-depth structural micro-heterogeneity, including intricate N-glycosylation profiles, of monoclonal antibodies at the native intact protein level by means of mass spectrometry using a recently introduced modified Orbitrap Exactive Plus mass spectrometer. We demonstrate the versatility of our method to probe structural micro-heterogeneity by describing the analysis of three types of molecules: (1) a non-covalently bound IgG4 hinge deleted full-antibody in equilibrium with its half-antibody, (2) IgG4 mutants exhibiting highly complex glycosylation profiles, and (3) antibody-drug conjugates. Using the modified instrument, we obtain baseline separation and accurate mass determination of all different proteoforms that may be induced, for example, by glycosylation, drug loading and partial peptide backbone-truncation. We show that our method can handle highly complex glycosylation profiles, identifying more than 20 different glycoforms per monoclonal antibody preparation and more than 30 proteoforms on a single highly purified antibody. In analyzing antibody-drug conjugates, our method also easily identifies and quantifies more than 15 structurally different proteoforms that may result from the collective differences in drug loading and glycosylation. The method presented here will aid in the comprehensive analytical and functional characterization of protein micro-heterogeneity, which is crucial for successful development and manufacturing of therapeutic antibodies     

Parthenogenetic development of dwarf surf dam,Mulinia lateralis,oocytes treated with polar body suppressing agents

Summary

Parthenogenesis following oocyte activation has been observed in a number of marine invertebrates, but the fate of parthenogenesis in bivalve mollusc embryos is unclear. We used the dwarf surf clam, Mulinia lateralis, to examine parthenogenetic development of KC1-activated oocytes using the polar body suppressing agents caffeine and heat or cytochalasin B. Development was followed by epifluorescence microscopy and flow-cytometric analysis using the DNA-specific fluorochrome DAPI. All agents suppressed polar body formation to some degree, putatively increasing the ploidy level and retaining a meiotic centrosome in the zygote; but the zygotes failed to develop normally. Failure of the zygotes to develop suggests that the meiotic centrosome is incapable of participating in mitosis in bivalves.     

Gravel dredging alters diversity and structure of riverine fish assemblages

1. Human activities affect fish assemblages in a variety of ways. Large‐scale and long‐term disturbances such as in‐stream dredging and mining alter habitat and hydrodynamic characteristics within rivers which can, in turn, alter fish distribution. Habitat heterogeneity is decreased as the natural riffle–pool–run sequences are lost to continuous pools and, as a consequence, lotic species are displaced by lentic species, while generalist and invasive species displace native habitat specialists. Sediment and organic detritus accumulate in deep, dredged reaches and behind dams, disrupting nutrient flow and destroying critical habitat for habitat specialist species. 2. We used standard ecological metrics such as species richness and diversity, as well as stable isotope analysis of δ¹³C and δ¹⁵N, to quantify the differences in fish assemblages sampled by benthic trawls among dredged and undredged sites in the Allegheny River, Pennsylvania, U.S.A. 3. Using mixed‐effects models, we found that total catch, species richness and diversity were negatively correlated with depth (P < 0.05), while species richness, diversity and proportion of species in lithophilic (‘rock‐loving’) reproductive guilds were lower at dredged than at undredged sites (P < 0.05). 4. Principal components analysis and manova revealed that taxa such as darters in brood hider and substratum chooser reproductive guilds were predominantly associated with undredged sites along principal component axis 1 (PC1 and manova P < 0.05), while nest spawners such as catfish and open substratum spawners including suckers were more associated with dredged sites along PC2 (P < 0.05). 5. Stable isotope analysis of δ¹³C and δ¹⁵N revealed shifts from reliance on shallow water and benthic‐derived nutrients at undredged sites to reliance on phytoplankton and terrestrial detritus at deep‐water dredged sites. Relative trophic positions were also lower at dredged sites for many species; loss of benthic nutrient pathways associated with depth and dredging history is hypothesised. 6. The combination of ecological metrics and stable isotope analysis thus shows how anthropogenic habitat loss caused by gravel dredging can decrease benthic fish abundance and diversity, and that species in substratum‐specific reproductive guilds are at particular risk. The effects of dredging also manifest by altering resource use and nutrient pathways within food webs. Management and conservation decisions should therefore consider the protection of relatively shallow areas with suitable substratum for spawning for the protection of native fishes.     

Twelve polymorphic microsatellite loci from the Asian citrus psyllid,Diaphorina citri Kuwayama,the vector for citrus greening disease,huanglongbing

Twelve polymorphic microsatellite markers were developed from microsatellite‐enriched DNA libraries and mined from an expressed sequence tags library of Diaphorina citri, the vector of the citrus greening disease (huanglongbing). Analysis of 288 individuals from Florida, Texas, and Brazil showed that allelic diversity ranged from three to eight alleles per locus and observed and expected heterozygosities ranged from 0.014 to 0.569 and from 0.052 to 0.653, respectively. These variable microsatellite loci can provide means for assessing overall genetic variation and migration patterns for this agriculturally important pest species. This information can be used to aid in developing successful management strategies.