RAD-tag and mitochondrial DNA sequencing reveal the genetic structure of a widespread and regionally imperiled freshwater mussel, Obovaria olivaria (Bivalvia: Unionidae).

Obovaria olivaria is a species of freshwater mussel native to the Mississippi River and Laurentian Great Lakes-St. Lawrence River drainages of North America. This mussel has experienced population declines across large parts of its distribution and is imperiled in many jurisdictions. Obovaria olivaria uses the similarly imperiled Acipenser fulvescens (Lake Sturgeon) as a host for its glochidia. We employed mitochondrial DNA sequencing and restriction site-associated DNA sequencing (RAD-seq) to assess patterns of genetic diversity and population structure of O. olivaria from 19 collection locations including the St. Lawrence River drainage, the Great Lakes drainage, the Upper Mississippi River drainage, the Ohioan River drainage, and the Mississippi Embayment. Heterozygosity was highest in Upper Mississippi and Great Lakes populations, followed by a reduction in diversity and relative effective population size in the St. Lawrence populations. Pairwise F ST ranged from 0.00 to 0.20, and analyses of genetic structure revealed two major ancestral populations, one including all St. Lawrence River/Ottawa River sites and the other including remaining sites; however, significant admixture and isolation by river distance across the range were evident. The genetic diversity and structure of O. olivaria is consistent with the existing literature on Acipenser fulvescens and suggests that, although northern and southern O. olivaria populations are genetically distinct, genetic structure in O. olivaria is largely clinal rather than discrete across its range. Conservation and restoration efforts of O. olivaria should prioritize the maintenance and restoration of locations where O. olivaria remain, especially in northern rivers, and to ensure connectivity that will facilitate dispersal of Acipenser fulvescens and movement of encysted glochidia.

Suspended solid concentration reduces feeding in freshwater mussels.

We examined the effect of TSS concentration on the clearance rates (CR) of newly transformed juvenile and adult Lampsilis fasciola, L. siliquoidea, Ligumia nasuta, and Villosa iris, as increased total suspended solids (TSS) are thought to interfere with feeding processes. Mussel CR were measured in aerated (or swirled for juveniles) chambers at TSS concentrations up to 15mgL-1 for laboratory-transformed juveniles, and up to 100mgL-1 for adult mussels. The CR of one-week old animals increased with TSS concentration, likely due to ontological differences in feeding (pedal vs. suspension feeding) and gill development, but CR decreased monotonically with TSS concentration in older animals (two-, three- and four-week old juveniles). The CR of adult mussels were significantly lower at TSS concentrations ≥8mgL-1, which represented a threshold in CR. Although this threshold occurred at similar concentrations across the four species, the decline in CR was largest in L. fasciola (46% compared to no-TSS control), and smallest in V. iris (21%). Differences among species are likely related to differences in the TSS and substrate found in their source rivers given that greater decline occurred for species in rivers with relatively lower TSS. The decrease in CR as TSS increased is consistent across marine and freshwater bivalves, at both juvenile and adult stages. The decrease in feeding was five times greater in juvenile compared to adult bivalves, which indicates how the vulnerability to environmental stressors differ across life stages. These results demonstrate that TSS reduces suspension feeding rates in freshwater unionids, therefore TSS should be managed to ensure their survival.

Loss of reproductive output caused by an invasive species.

We investigated whether Neogobius melanostomus, an invader of biodiversity 'hot-spots' in the Laurentian Great Lakes region, facilitates or inhibits unionid mussel recruitment by serving as a host or sink for their parasitic larvae (glochidia). Infestation and metamorphosis rates of four mussel species with at-risk (conservation) status (Epioblasma torulosa rangiana, Epioblasma triquetra, Lampsilis fasciola and Villosa iris) and one common species (Actinonaias ligamentina) on N. melanostomus were compared with rates on known primary and marginal hosts in the laboratory. All species successfully infested N. melanostomus, but only E. triquetra, V. iris and A. ligamentina successfully metamorphosed into juveniles, albeit at very low rates well below those seen on even the marginal hosts. Neogobius melanostomus collected from areas of unionid occurrence in the Grand and Sydenham rivers (Ontario, Canada) exhibited glochidial infection rates of 39.4% and 5.1%, respectively, with up to 30 glochidia representing as many as six unionid species per fish. A mathematical model suggests that N. melanostomus serve more as a sink for glochidia than as a host for unionids, thereby limiting recruitment success. This represents a novel method by which an invasive species affects a native species.

Increasing rates of contralateral prophylactic mastectomy among patients with ductal carcinoma in situ.

PURPOSE: Some women with unilateral ductal carcinoma in situ (DCIS) undergo contralateral prophylactic mastectomy (CPM) to prevent cancer in the opposite breast. The use and trends of CPM for DCIS in the United States have not previously been reported. METHODS: We used the Surveillance, Epidemiology, and End Results database to analyze the initial treatment (within 6 months) of patients with unilateral DCIS diagnosed from 1998 through 2005. We determined the CPM rate as a proportion of all surgically treated patients and as a proportion of all patients who underwent mastectomy. We compared demographic and tumor variables in women with unilateral DCIS who underwent surgical treatment. RESULTS: We identified 51,030 patients with DCIS; 2,072 patients chose CPM. The CPM rate was 4.1% for all surgically treated patients and 13.5% for patients undergoing mastectomy. Among all surgically treated patients (including breast-conserving surgery), the CPM rate increased by 148% from 1998 (2.1%) to 2005 (5.2%). Among patients who underwent mastectomy to treat DCIS (excluding patients undergoing breast-conserving surgery), the CPM rate increased by 188% from 1998 (6.4%) to 2005 (18.4%). Young patient age, white race, recent year of diagnosis, and the presence of lobular carcinoma in situ were significantly associated with higher CPM rates among all surgically treated patients and all patients undergoing mastectomy. Large tumor size and higher grade were significantly associated with increased CPM rates among all surgically treated patients but lower CPM rates among patients undergoing mastectomy. CONCLUSION: The use of CPM for DCIS in the United States markedly increased from 1998 through 2005.

Increasing use of contralateral prophylactic mastectomy for breast cancer patients: a trend toward more aggressive surgical treatment.

PURPOSE: Many patients with unilateral breast cancer choose contralateral prophylactic mastectomy to prevent cancer in the opposite breast. The purpose of our study was to determine the use and trends of contralateral prophylactic mastectomy in the United States. PATIENTS AND METHODS: We used the Surveillance, Epidemiology and End Results database to review the treatment of patients with unilateral breast cancer diagnosed from 1998 through 2003. We determined the rate of contralateral prophylactic mastectomy as a proportion of all surgically treated patients and as a proportion of all mastectomies. RESULTS: We identified 152,755 patients with stage I, II, or III breast cancer; 4,969 patients chose contralateral prophylactic mastectomy. The rate was 3.3% for all surgically treated patients; 7.7%, for patients undergoing mastectomy. The overall rate significantly increased from 1.8% in 1998 to 4.5% in 2003. Likewise, the contralateral prophylactic mastectomy rate for patients undergoing mastectomy significantly increased from 4.2% in 1998 to 11.0% in 2003. These increased rates applied to all cancer stages and continued to the end of our study period. Young patient age, non-Hispanic white race, lobular histology, and previous cancer diagnosis were associated with significantly higher rates. Large tumor size was associated with a higher overall rate, but with a lower rate for patients undergoing mastectomy. CONCLUSION: The use of contralateral prophylactic mastectomy in the United States more than doubled within the recent 6-year period of our study. Prospective studies are needed to understand the decision-making processes that have led to more aggressive breast cancer surgery.