Comparisons of Secondary Production, Life History, and Mouthpart Functional Morphology Between Two Populations of the Amphipod Gammarus minus

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Date
1997-01-21Author
Haley, Carol J.
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In this study, features of ecology, behavior, and
functional morphology related to feeding activity of
two populations of the amphipod Gammarus minus
were compared. The two populations occupied
different habitats, and I attempted to determine
whether differences observed between the two
populations were related to habitat. Annual
production and life history of the populations were
compared and their relationship to factors such as
temperature, water-chemistry, and quantity of
available organic matter were examined. Mouthpart
and foregut morphology were compared between the
two populations and between immature and mature
amphipods with light and scanning electron
microscopy. Measurements of structure were
analyzed by linear regression. A behavioral study,
comparing feeding of immature and mature G. minus,
was conducted in the laboratory. Annual production
of G. minus occupying a habitat characterized by the
presence of watercress, gravel substrate, and constant
temperature (Site 1) was 3.9 g/sq.m (95% C.I.: 3.2-
4.5), while that in the habitat characterized by leaf
detritus and fluctuating temperatures (Site 2) was 1.8
g/sq.m (95% C.I.: 1.6-2.1). Breeding occurred
throughout the year at Site 1, but there was a yearly
cycle at Site 2. The greatest numbers of the smallest
size classes of amphipod were present at Site 2 when
the quantity of ash-free dry mass (AFDM) of wood
and bark was greater than AFDM of leaf detritus. Of
nine mouthpart and foregut structures studied, three,
the number of cuspidate setae on outer plates of
maxillipeds, the length of the dactyl on maxilliped
palps, and the number of hook setae on the foregut
ampullae, were found to be correlated with body
length. Of these, rates of increase in maxilliped setae
numbers and hook setae numbers were greater for
immature than mature animals, and the number of
hook setae for a given sized animal was generally
greater for animals at Site 1 than Site 2. Animals
presented with ground-up leaf material in the
laboratory exhibited twenty-one recognizable
behaviors. The frequencies of six behaviors were
found to be statistically different between immature
and mature animals. The differences suggest that
immatures may prefer a food type or size other than
that provided in the experiment.
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- Doctoral Dissertations [14977]