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.     

The N-terminal region of wheat streak mosaic virus coat protein is a host- and strain-specific long-distance transport factor

Understanding the genetics underlying host range differences among plant virus strains can provide valuable insights into viral gene functions and virus-host interactions. In this study, we examined viral determinants and mechanisms of differential infection of Zea mays inbred line SDp2 by Wheat streak mosaic virus (WSMV) isolates. WSMV isolates Sidney 81 (WSMV-S81) and Type (WSMV-T) share 98.7% polyprotein sequence identity but differentially infect SDp2: WSMV-S81 induces a systemic infection, but WSMV-T does not. Coinoculation and sequential inoculation of SDp2 with WSMV-T and/or WSMV-S81 did not affect systemic infection by WSMV-S81, suggesting that WSMV-T does not induce a restrictive defense response but that virus-encoded proteins may be involved in differential infection of SDp2. The viral determinant responsible for strain-specific host range was mapped to the N terminus of coat protein (CP) by systematic exchanges of WSMV-S81 sequences with those of WSMV-T and by reciprocal exchanges of CP or CP codons 1 to 74. Green fluorescent protein (GFP)-tagged WSMV-S81 with CP or CP residues 1 to 74 from WSMV-T produced similar numbers of infection foci and genomic RNAs and formed virions in inoculated leaves as those produced with WSMV-S81, indicating that failure to infect SDp2 systemically is not due to defects in replication, cell-to-cell movement, or virion assembly. However, these GFP-tagged hybrids showed profound defects in long-distance transport of virus through the phloem. Furthermore, we found that four of the five differing amino acids in the N terminus of CP between the WSMV-S81 and WSMV-T isolates were collectively involved in systemic infection of SDp2. Taken together, these results demonstrate that the N-terminal region of tritimoviral CP functions in host- and strain-specific long-distance movement.     

Winter Distribution,Movements, and Annual Survival of Radiomarked Vancouver Canada Geese in Southeast Alaska

ABSTRACT Management of Pacific Flyway Canada geese (Branta canadensis) requires information on winter distribution of different populations. Recoveries of tarsus bands from Vancouver Canada geese (B. canadensis fulva) marked in southeast Alaska, USA, ≥4 decades ago suggested that ≥83% of the population was non-migratory and that annual adult survival was high (Ŝ = 0.836). However, recovery distribution of tarsus bands was potentially biased due to geographic differences in harvest intensity in the Pacific Flyway. Also, winter distribution of Vancouver Canada geese could have shifted since the 1960s, as has occurred for some other populations of Canada geese. Because winter distribution and annual survival of this population had not recently been evaluated, we surgically implanted very high frequency radiotransmitters in 166 adult female Canada geese in southeast Alaska. We captured Vancouver Canada geese during molt at 2 sites where adults with goslings were present (breeding areas) and 2 sites where we observed nonbreeding birds only. During winter radiotracking flights in southeast Alaska, we detected 98% of 85 females marked at breeding areas and 83% of 70 females marked at nonbreeding sites, excluding 11 females that died prior to the onset of winter radiotracking. We detected no radiomarked females in coastal British Columbia, or western Washington and Oregon, USA. Most (70%) females moved ≤30 km between November and March. Our model-averaged estimate of annual survival (Ŝ = 0.844, SE = 0.050) was similar to the estimate of annual survival of geese marked from 1956 to 1960. Likely <2% of Vancouver Canada geese that nest in southeast Alaska migrate to winter areas in Oregon or Washington where they could intermix with Canada geese from other populations in the Pacific Flyway. Because annual survival of adult Vancouver Canada geese was high and showed evidence of long-term consistency, managers should examine how reproductive success and recruitment may affect the population.