Jackson Estuarine Laboratory

Geographic Variation in Western Atlantic Populations of Gammarus oceanicus Segerstråle (Amphipoda)


1. In New Hampshire populations of the circum-Atlantic species Gammarus oceanicus, 18 morphological characters were examined; ten of these characteristics were different and related to coastal or estuary habitats. 2. Comparisons of five characters in populations from Massachusetts to Hudson Bay, Canada supported this conclusion and showed that the differences were greatest between the populations of New Hampshire. 3. Six characters showed differences corresponding to the trends found in the G. locusta series from coastal to brackish and to those observed in species of the Zaddachi group in Europe, denoting a genetic basis for the variation. 4. The conjunction of characters not showing overlaps does not was not strong enough for us to recognize subspecies; the term neutral form was used. 5. Coastal forms and forms of estuaries would be inter-fertile in the laboratory but, it seems, with reduced chances of success. 6. The differentiation of the form of estuary, first in the southern part of the range of the species, is considered to be linked to the highly euryecid nature of G. oceanicus, to the absence of European species from the Zaddachi group, and at variable selection pressures from the local micro-environment

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Crustaceana © 1977