Barry Chernoff

Geographic and environmental variation in Bryconops sp. cf. melanurus (Ostariophysi: Characidae) from the Brazilian Pantanal

Morphometric analyses of 220 specimens of a characid, Bryconops sp. cf. melanurus, from the Brazilian Pantanal were used to describe allometric growth in that species and determine whether specimens from highland habitats were more streamlined than those from lowland habitats. Relative warp analysis of 14 landmarks and principal component analysis of 28 interlandmark distances returned complementary results. The increased streamlining of the highland specimens is highly consistent with known inductive effects of high water velocity on fish phenotypes. Genetic differentiation and inductive effects of temperature variation are also potential explanations of the observed phenotypic differentiation.

Postglacial recolonization of eastern Blacknose Dace,Rhinichthys atratulus(Teleostei: Cyprinidae), through the gateway of New England

During the last ice age, much of North America far south as 40°N was covered by glaciers (Hewitt 2000). About 20,000 years ago, as the glaciers retreated, the hydrologic landscape changed dramatically creating waterways for fish dispersal. The number of populations responsible for recolonization and the regions from which they recolonized are unknown for many freshwater fishes living in New England and southeastern Canada. The Blacknose Dace,Rhinichthys atratulus, is one of the freshwater fish species that recolonized this region. We hypothesize that the earliest deglaciated region, modern-day Connecticut, was recolonized byR. atratulusvia a single founding event by a single population. In this paper, we test this hypothesis phylogenetically with regard to the major drainage basins within Connecticut. The mitochondrial DNA exhibits low nucleotide diversity, high haplotype diversity, and a dominant haplotype found across the state. A small percentage of individuals in the Housatonic drainage basin, however, share a haplotype with populations in New York drainage basins, a haplotype not found elsewhere in Connecticuts drainage basins. We calculated a range for the rate of divergence for NADH dehydrogenase subunit 2 (nd2) and control region (ctr) of 4.43–6.76% and 3.84–8.48% per million years (my), respectively. While this range is higher than the commonly accepted rate of 2% for mitochondrial DNA, these results join a growing list of publications finding high rates of divergence for various taxa (Peterson and Masel 2009). The data support the conclusion that Connecticut as a whole was recolonized initially by a single founding event that came from a single refugium. Subsequently, the Housatonic basin alone experienced a secondary recolonization event.

Diversity in neotropical wet forests during the Cenozoic is linked more to atmospheric CO2 than temperature

Models generally predict a response in species richness to climate, but strong climate-diversity associations are seldom observed in long-term (more than 106 years) fossil records. Moreover, fossil studies rarely distinguish between the effects of atmospheric CO2 and temperature, which limits their ability to identify the causal controls on biodiversity. Plants are excellent organisms for testing climate-diversity hypotheses owing to their strong sensitivity to CO2, temperature and moisture. We find that pollen morphospecies richness in an angiosperm-dominated record from the Palaeogene and early Neogene (65–20 Ma) of Colombia and Venezuela correlates positively to CO2 much more strongly than to temperature (both tropical sea surface temperatures and estimates of global mean surface temperature). The weaker sensitivity to temperature may be due to reduced variance in long-term climate relative to in higher latitudes, or to the occurrence of lethal or sub-lethal temperatures during the warmest times of the Eocene. Physiological models predict that productivity should be the most sensitive to CO2 within the angiosperms, a prediction supported by our analyses if productivity is linked to species richness; however, evaluations of non-angiosperm assemblages are needed to more completely test this idea.

Harttia merevari, a new species of catfish (Siluriformes: Loricariidae) from Venezuela

Harttia merevari, a new species of loricariid catfish, is described from eight specimens captured in the upper Caura River, Orinoco River basin, Venezuela. The new species is recognized by the following combination of characters: abdomen naked; two or three preanal plates; a bony plate before each branchial opening; seven lateral plates between the pectoral and pelvic fins; maxillary barbel short and attached to the oral disk by a fleshy fold; head dorsal surface and anterior portion of the body light or dark yellow with numerous, round black spots; posterior region of the body light or dark yellow with five black transverse bands, dorsal central area of the two anterior bands diffused. The discovery of this new species extends the distribution of the genus northwest to include the Orinoco River basin on the northern slope of the Guyana shield.

Molecular Phylogenetics of the Eastern and Western Blacknose Dace, Rhinichthys atratulus and R. obtusus (Teleostei: Cyprinidae)

The debate over the species status and geographic distribution of Rhinichthys atratulus and R. obtusus has persisted for decades. Morphological analyses have led to ambiguous results making field identifications possible in only some areas, further complicating the unclear and conflicting taxonomic histories of these species. In this study, we clear up some of these identification issues by analyzing two mitochondrial genes and nine microsatellite loci amplified from Blacknose Dace across the eastern half of North America. Our results show large genetic differences between R. atratulus and R. obtusus for both mitochondrial genes and microsatellites. We determine that R. atratulus inhabits streams east of the Appalachians from Nova Scotia to Virginia and the southern part of the eastern Great Lakes; R. obtusus inhabits the remaining regions west of the Appalachians to approximately Minnesota, eastern Nebraska, north into the Manitoba province and Mobile Bay drainage.

Effects of Dam Removal on Fish Community Interactions and Stability in the Eightmile River System, Connecticut, USA

New multivariate time-series methods have the potential to provide important insights into the effects of ecosystem restoration activities. To this end, we examined the temporal effects of dam removal on fish community interactions using multivariate autoregressive models to understand changes in fish community structure in the Eightmile River System, Connecticut, USA. We sampled fish for 6 years during the growing season; 1 year prior to, 2 years during, and for 3 years after a small dam removal event. The multivariate autoregressive analysis revealed that the site above the dam was the most reactive and least resilient sample site, followed in order by the below-dam and nearby reference site. Even 3 years after the dam removal event, the stream was still in a recovery stage that had failed to approximate the community structure of the reference site. This suggests that the reorganization of fish communities following dam removals, with the goal of ecological restoration, may take decades to centuries for the restored sites to approximate the community structure of nearby undisturbed sites. Results from this study also highlight the utility of multivariate autoregressive modeling for examining temporal interactions among species in response to adaptive management activities both in aquatic systems and elsewhere.

Insight into the population structure of hardhead silverside, Atherinomorus stipes (Teleostei: Atherinidae), in Belize and the Florida Keys using nd2

Abstract Little is known about the natural history, biology, and population genetic structure of the Hardhead Silverside, Atherinomorus stipes, a small schooling fish found around islands throughout the Caribbean. Our field observations of A. stipes in the cays of Belize and the Florida Keys found that populations tend to be in close association with the shoreline in mangrove habitats. Due to this potential island‐based population structuring, A. stipes represents an ideal system to examine questions about gene flow and isolation by distance at different geographic scales. For this study, the mitochondrial gene nd2 was amplified from 394 individuals collected from seven different Belizean Cays (N = 175) and eight different Floridian Keys (N = 219). Results show surprisingly high haplotype diversity both within and between island‐groups, as well as a high prevalence of unique haplotypes within each island population. The results are consistent with models that require gene flow among populations as well as in situ evolution of rare haplotypes. There was no evidence for an isolation by distance model. The nd2 gene tree consists of two well‐supported monophyletic groups: a Belizean‐type clade and a Floridian‐type clade, indicating potential species‐level differentiation.