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Comparative feeding behaviour and morphology of mysids (Crustacea: Mysidacea)

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Metillo, EB (1994) Comparative feeding behaviour and morphology of mysids (Crustacea: Mysidacea). PhD thesis, University of Tasmania.

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Abstract

Behavioural and morphological studies were made to determine whether
feeding niche partitioning occurs in three sympatric coastal mysids, Anisomysis mixta
australis, Paramesopodopsis rufa, and Tenagomysis tasmaniae.
All three species showed optimal chemoreception as judged from stereotyped
food capturing response to mixtures of feeding stimulant (either betaine-HCl or
glycine) and suppressant (ammonia). The strongest responses were to 50:50 mixtures
of both betaine-ammonia and glycine-ammonia solutions. In general, the response
curve to the different mixtures tested was bell-shaped. A. mixta australis only showed
the normal curve in response to the glycine-ammonia mixture. The platykurtic curve
in T. tasmaniae suggests less optimal response to the betaine-HCl-ammonia solution.
P. rufa reacted more strongly to the betaine-ammonia than to the glycine-ammonia
solutions, and more of its individuals responded to both solutions than the other two
species. These results suggest that sensitivity to betaine-HCl- and glycine-rich fresh
and decomposing animal tissue is most sharp in P. rufa. Acuteness, however, may be
diminished with duration of decomposition as indicated by reduced responses to
mixtures with >50% ammonia. High concentrations of either stimulant also had a
suppression effect.
Similar mechanisms are used by all three to capture fine particles. Particle size
selection overlapped in the two larger species, P. rufa and T. tasmaniae, which
ingested a full range of sizes of inert beads from 10 to 90 μm. The smallest species,
A. mixta australis, differed from the other two by mainly ingesting the smallest beads.
P. rufa and A. mixta australis both form their feeding appendages into 'cages'
(primary composed of mouthparts and the secondary of thoracic endopods) to grasp
live prey. T. tasmaniae uses mainly the primary cage because its thoracic endopods
remained spread, a feature associated with its behaviour of resting on the substrate. P.
rufa was the most efficient predator of the euryhaline daphniid prey, Daphniopsis
australis. It showed a steeper linear functional response curve for this prey than the
two other species which showed similar flat linear curves. All three species showed similar predation success on Artemia sp. nauplii, and similar predation failure for the
calanoid copepod Gladioferens pectinatus.
In situ feeding selectivity experiments using 14C-labelled Artemia sp. nauplii
and phytoplankton, and 3H thymidine-labelled macroalgal detritus showed that all
three species preferentially ingested the animal food, i.e. Artemia sp. nauplii.
The activity of the digestive enzyme laminarinase was analyzed over one year
to assess herbivorousness in the three mysid species. High levels of activity in T.
tasmaniae were sustained throughout the entire year and peaked in August. P. rufa
showed levels 2.5 to 4 times lower than those in T. tasmaniae, and remained constant
through the year. A. mixta australis showed a bimodal pattern with peaks in February
and August comparable to those in T. tasmaniae. The minimum levels were similar to
those in P. rufa. Significant interaction between species and sampling date suggests
that the peak of activity in August (late winter) may be associated with all three species
ingesting relatively high levels of macroalgal detritus. The peak in February (late
summer) shown by A. mixta australis reflects similar high levels of consumption of
both macroalgal and laminarin producing phytoplanktonic particles. Short term (24 h)
starvation reduced activity in P. rufa, but not in the other two species. Medium term
(9 d) feeding on the non-laminarin producing dinoflagellate, Scrippsiella trochoidea,
reduced activity in T. tasmaniae on day 9, and on day 5 in A. mixta australis.
However, the latter species returned to the initial levels on day 7. No definite
conclusion can be drawn from the P. rufa results, because all animals died after 3 d.
Marked reduction in activity was also observed when juveniles of T. tasmaniae and A.
mixta australis had grown to maturity using Artemia sp. nauplii as food. Therefore,
laminarinase is likely to be substrate specific in T. tasmaniae, but not in A. mixta
australis.
Growth rates of the juvenile stages of the three species held separately in the
laboratory were similar when fed with excess amounts of Artemia sp. nauplii. When
all three species were held together and fed with reduced amounts of nauplii, P. rufa
grew faster than the other two species which showed similar rates. Of the three
species, only a few T. tasmaniae individuals showed slight growth when fed aged algal detritus and the diatom Phaeodactylum sp. Although P. rufa grew best on animal
food the other two species are equally dependent on the same type of food.
Foregut and mouthparts morphological data indicate three major feeding
adaptations: predominantly macrophagous feeding on tough macrophyte particles (type
Ia) for T. tasmaniae, predominantly macrophagous feeding on large animal
prey/detritus (type lb) for P. rufa, and mainly microphagous and/or suction feeding on
smaller animal prey and fine particulate matter (type le) for A. mixta australis.
These studies suggest that probable strong competition associated with
overlapping feeding habits in the three species is reduced by differences in size and
feeding structure, and by microhabitat partitioning (shown by other authors) with P.
rufa and A. mixta australis spending more time aggregated in the water column while
T. tasmaniae is found on, or a few centimetres above, the sandy substrate.
The foreguts of 45 more species, three from Tasmania and 42 from different
biogeographical zones of the globe, were surveyed to test the hypothesis that feeding
adaptation is more important than phylogeny in shaping foregut structure. The
spheroidal shape shown in the initial three Tasmanian species, and the tubular form
were the two main foregut types observed. From evidence on diet and feeding
behaviour, a series of four basic feeding adaptations were recognized: the three types
(Ia, lb, le) found in the initial three Tasmanian species, and the mainly suction feeding
exemplified by the tubular foregut type (type II). Cladistic analysis suggests that the
type I adaptations appear to have evolved several times within clade. The specialized
suction feeding seems to have been derived from type Ia. These data suggest that the
need to collect food seems to have been such a strong selective force that adaptations
of the feeding apparatus have masked phylogenetic relationships within these
structures in mysids.

Item Type: Thesis (PhD)
Keywords: Mysidacea
Copyright Holders: The Author
Copyright Information:

Copyright 1995 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Includes bibliographical references (leaves 278-302). Thesis (Ph.D.)--University of Tasmania, 1995

Date Deposited: 03 Feb 2015 03:03
Last Modified: 11 Apr 2016 22:50
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