Elucidating the dynamics of a parasitic infection requiring two hosts in a natural ecosystem can be a daunting task. Myxobolus cerebralis (Mc), the myxozoan parasite that causes whirling disease in some salmonids, was detected in the Colorado River upstream of Windy Gap Reservoir (WGR) in 1988. Subsequently, whirling disease was implicated in the decline of wild Rainbow Trout Oncorhynchus mykiss in the river when WGR was identified as a point source of Mc triactinomyxons (TAMs). Between 1997 and 2004, numerous investigations began to elucidate the etiology of Mc in WGR. During this period, Mc TAM production in WGR declined more than 90%. Explanations for the decline have included differences in stream discharge between years, changes in the thermal regime of the lake, severe drought, changes in the fish population structure in WGR, and reductions in the prevalence and severity of Mc infection in salmonids in the Colorado and Fraser rivers upstream of WGR. All of these have been discredited as explanations for the reduced TAM production. In 2005, a new study was conducted to replicate the studies completed in 1998. In this paper, the results of a new real-time polymerase chain reaction assay utilized to quantify the mitochondrial 16S rDNA specific to each of four lineages of Tubifex tubifex in pooled samples of 50 oligochaetes are presented. These results suggest that compared with 1998, the densities of aquatic oligochaetes and T. tubifex have increased, TAM production has been greatly reduced, and the decline is congruent with the dominance of lineages I, V, and VI of T. tubifex-three lineages that are refractory or highly resistant to Mc infection-in the oligochaete population. While it is possible that the resistant lineages function as biofilters that deactivate Mc myxospores, the reason for the decline in TAM production in WGR remains an enigma.

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Somatic chromosome counts were made from actively growing root tips. These were conveniently obtained by placing the plants in water which was changed daily to improve aeration. An abundant supply of relatively thick and straight roots, mostly adventitious, was produced in a week, although in winter the supply was less certain.Excellent fixation was obtained with Belling's Navashin type fixative. Owing to their small diameter, the root tips were mounted together on cards (Randolf, 1940) before embedding in,paraffin wax of m.p. about 50° C. Sections were cut transversely at 8 or io/x for the higher polyploids, with a Spencer rotary microtome. The chromosomes were stained with crystal violet by Randolf's method (quoted by Newcomer, 1938) which includes mordanting in i% chromic acid for 20 min. before staining. The best results were obtained by staining for 2| hr. in o-i% crystal violet, increasing the time in alcoholic iodine to 5 min. and shortening the differentiation to about 45 sec. in absolute alcohol and about 12 sec. in clove oil, but adding about i min. of slow differentiation in a mixture of 2 parts xylol to I part absolute alcohol, after 2 min. in xylol. The following is the complete schedule (for further details see Hancock, 1942) (La Cour, 1937)

Sea ice is believed to be a major factor shaping gene flow for polar marine organisms, but it remains unclear to what extent it represents a true barrier to dispersal for arctic cetaceans. Bowhead whales are highly adapted to polar sea ice and were targeted by commercial whalers throughout Arctic and subarctic seas for at least four centuries, resulting in severe reductions in most areas. Both changing ice conditions and reductions due to whaling may have affected geographic distribution and genetic diversity throughout their range, but little is known about range-wide genetic structure or whether it differed in the past. This study represents the first examination of genetic diversity and differentiation across all five putative stocks, including Baffin Bay-Davis Strait, Hudson Bay-Foxe Basin, Bering-Beaufort-Chukchi, Okhotsk, and Spitsbergen. We also utilized ancient specimens from Prince Regent Inlet (PRI) in the Canadian Arctic and compared them with modern stocks. Results from analysis of molecular variance and demographic simulations are consistent with recent and high gene flow between Atlantic and Pacific stocks in the recent past. Significant genetic differences between ancient and modern populations suggest PRI harbored unique maternal lineages in the past that have been recently lost, possibly due to loss of habitat during the Little Ice Age and/or whaling. Unexpectedly, samples from this location show a closer genetic relationship with modern Pacific stocks than Atlantic, supporting high gene flow between the central Canadian Arctic and Beaufort Sea over the past millennium despite extremely heavy ice cover over much of this period.