Five freshwater populations of the otherwise estuarine colonial hydrozoan Cordvlophora caspia were observed in the Connecticut River, New England. Histological comparison of the body wall of the freshwater and estuarine populations revealed no differences in cell shape or size in the epidermis and gastrodermis, either of the undifferentiated body wall or in regions of tentacles. One freshwater population examined in 2000 had polyps thatwere shorter and wider than estuarine animals and contained much fewer and smaller sporosacs. All freshwater populations examined in 200 1 had feeding polyp shape and size and sporosac size and number comparable to the estuarine population. We conclude that C. caspia has undergone physiological and ecological adjustments for existence in very soft water with low alkalinity. The species has in only a few years become abundant in certain areas of the Connecticut River and has acquired all the facies exhibited during experimentally determined optimal growth conditions. Ecologically, C. caspia is filling the niche of a benthic colonial predator; the hydroid preys on larval insects, predominately chironomids.

We discovered ferromanganese nodules that measure up to 46 cm in diameter with stromatolitic growth patterns in the western central near-shore portion of Second Connecticut Lake, Pittsburg, New Hampshire. They occur as four distinct morphotypes: irregular laminated convex plates that form concentric rings around a nucleating center (''domed-plate''), continuous pustular pavements that extend >10 m 2 (''pustular''), nonlaminated and nonnucleated masses with pebbles scattered throughout the matrix (''lattice''), and small nonnucleated laminated structures >2 cm (''cup'') in water depths between 5 and 12 m. An estimated growth rate of 26 mm/100 years was determined from oxide deposits on datable debris. X-ray fluorescence showed an elemental composition comparable with that of nodule structures in other lakes. These sedimentary structures, the first seen in any of the six New England states, are the most morphologically distinct and varied lacustrine ferromanganese nodules known so far.concretions ͉ stromatolites ͉ microbialites ͉ precipitates ͉ oncoid

The authors sampled three spatially isolated populations of a chironomid midge in the genus Axarus living in the Connecticut River both early and late in the larval life cycle of one generation. Larvae were scored for both length and inversion frequency using the polytene chromosomes from salivary gland cells. We found polymorphism for four paracentric inversions. Inversion C 1-6 exhibits a geographic cline, increasing in frequency with increasing latitude but remaining stable over time. Also stable over time were two other paracentric inversions designated A 1-5 and F 13-20 , which were present at similar frequencies in all populations. None of these inversions was associated with larval length. A complex triple inversion designated G 2-7 was significantly correlated with decreased larval length and also exhibited a significant increase in frequency (within one cohort) in the two more northerly populations. We propose that this increase is due to size-selective predation eliminating larger larvae.Résumé : Nous avons échantillonné trois populations isolées d'un chironomide du genre Axarus habitant le fleuve Connecticut, au début et à la fin de leur développement larvaire dans une même génération. Les larves ont été codées en fonction de leur longueur et de la fréquence d'inversions sur les chromosomes polytènes des cellules de leurs glandes salivaires. Il existe un polymorphisme impliquant quatre inversions paracentriques. L'inversion C 1-6 suit un gradient géographique et sa fréquence augmente avec la latitude; elle reste cependant stable dans le temps. Deux autres inversions paracentriques, A 1-5 et F 13-20 , sont aussi stables dans le temps et elles sont présentes dans toutes les populations à des fréquences semblables. Une inverse triple complexe, G 2-7 , est en corrélation négative significative avec la taille des larves; sa fréquence augmente aussi, dans une même cohorte, dans les deux populations situées plus au nord. Nous posons en hypothèse que cet accroissement est due à une prédation sélective en fonction de la taille qui élimine les plus grandes larves.[Traduit par la Rédaction] Werle et al. 129

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Connecticut River midges in the genus Axarus are constrained to semi-isolated populations associated with submerged clay exposures, and gene flow between populations is restricted. I sampled larval midges from fifteen spatially separated sites in the Connecticut River and determined karyotypes for 3111 larvae in two closely related species. In one of these species, an undescribed species referred to as Axarus species varvestris, 5 chromosomal rearrangements were present as polymorphisms. Four of these are paracentric inversions, and the fifth is a terminal insertion or deletion. I used chromosomal rearrangement frequencies to calculate Nei's genetic distance measures for all pairwise population comparisons and I constructed a neighbor-joining phenetic tree for the populations using these distances. Genetic distance between populations of A. sp. varvestris increases with geographic separation, and tree structure indicates that restricted gene flow only occurs in a downstream direction. The effect of unidirectional (downstream) gene flow on population genetic structure in riverine midges is described here for the first time. A genetic break is apparent between populations associated with 12 000-year-old sediments originating in different ancient lakes. The geological break between lakes also coincides with a break in the species composition of the Axarus populations.