Search

In 1949, Hubbs and Lagler described morphological variation among pearl dace (Margariscus margarita) of inland lakes on Isle Royale, Michigan. For Harvey Lake, Hubbs and Lagler proposed that pearl dace were sufficiently morphologically distinct to warrant subspecific status. They argued that divergence of the Harvey Lake pearl dace was due to allopatric differentiation in isolation from lower elevation lakes. Harvey Lake has been isolated by elevation from lower elevation lakes for approximately 10 to 15 thousand years. No genetic studies have been done on Isle Royale pearl dace to evaluate this hypothesis to date. Here we report the analysis of Margariscus margarita populations using a limited battery of microsatellite loci to assess the extent of and genetic divergence among the Harvey Lake and other Isle Royale lowland lake populations. Microsatellite loci were analyzed using PCR primers developed for the non-congener, longnose dace (Rhinichthys cataractae). Statistical analyses of allele frequency data indicate genetic differentiation among all Isle Royale pearl dace populations inclusive of both Harvey Lake and lowland populations concurring with Hubbs and Lagler's hypothesis that the Harvey Lake population is genetically divergent. Results also indicate that the lowland Isle Royale populations are apparently equally divergent from one another. Keywords: pearl dace, microsatellites, population divergence, Isle Royale, Margarita margariscus, INTRODUCTION In 1946, during one of the very few formal comprehensive surveys of ichthyofauna of Isle Royale, Michigan, Hubbs and Lagler (1949) identified a population of pearl dace, (Margariscus margarita) [...]

Phoxinus eos-neogaeus unisexual hybrids (Cyprinidae, Pisces) are among the few vertebrate taxa known to reproduce clonally by gynogenesis. These taxa have a broad distribution in North America, mostly located in regions previously covered by the last Pleistocene ice sheet. To assess whether asexual hybrids dispersed from glacial refuges at the end of the Pleistocene or they originated from current hybridization events, genetic diversity of mitochondrial DNA (mtDNA) sequences and microsatellite loci was determined in populations from 16 different sites in the Mississippi–Missouri River (Nebraska and Montana), Rainy River–Hudson Bay (Minnesota), and St Lawrence River (Quebec) drainages. The maternal species ( P. neogaeus) occurred in Minnesota and Nebraska but was absent from Montana sites and was restricted to only two of 11 lakes sampled in Quebec, although hybrids were present at all sites. The genetic survey revealed a total of 49 clones, originating from 14 hybridization events. Several of the lineages were characterized by mtDNA haplotypes not detected in the maternal ancestor. Lineages as well as clones frequently displayed a large geographical distribution at a regional scale. Dating of hybridization events suggested a relatively recent origin (< 50 000 years ago) from the Mississippi glacial refuge, even in regions not covered by the last Pleistocene glacier. Altogether, these results indicate P. eos-neogaeus hybrids are not the result of current hybridization events, but display a pattern predicted by postglacial dispersal. Our findings have considerable implications for the nature of selection processes affecting the diversity of these asexual taxa and their coexistence with sexual ancestors. [ABSTRACT FROM AUTHOR]

The index of biotic integrity (IBI) has been used to assess the biological quality of flowing water systems in areas throughout the United States. Yet, only rarely has biotic integrity been related to independent measures of water or habitat quality. We show that the IBI ranks sites similarly in two Illinois watersheds where conditions remained relatively stable during 3 years of sampling. Further, rankings among sites conform to prior assessments of site quality based on habitat and water quality. Neither a species diversity index (H') nor any of the individual metrics that constitute IBI performed as consistently at ranking sites as did the IBI. Sampling should be conducted during early summer to reduce variation due to seasonal fish migration and fall recruitment of young-of-the-year fish. In an Indiana watershed subject to extensive conservation planning, the IBI reflects known habitat and water quality perturbations of both natural and anthropogenic origin. Little or no improvement in biotic integrity was detected following implementation of numerous soil and water conservation practices. [ABSTRACT FROM AUTHOR]

BSTRACT: Water quality was monitored for 17 months during base flow periods in six agricultural watersheds to evaluate the impact of riparian vegetation on suspended solids and nutrient concentrations. In areas without riparian vegetation, both instream algal production and seasonal low flows appeared to be major determinants of suspended solids, turbidity, and phosphorus concentrations. Peak levels of all parameters were reached during the summer when flows were reduced and benthic algal production was high. Similar summer peaks were reached in streams receiving major point inputs but peaks occurred downstream from the input. Instream organic production was less important in regulating water quality in areas with riparian vegetation and permanent flows. Concentrations of suspended solids remained relatively constant, while phosphorus and turbidity increased in association with leaf fall in autumn. Intermittent flow conditions in summer increased the importance of instream organic production in controlling water quality, even when riparian vegetation was present. Efforts to improve water quality in agricultural watersheds during base flow should emphasize maintenance of riparian vegetation and stable flow conditions. [ABSTRACT FROM AUTHOR]