World Congress of Malacology Antwerp ... - Unitas Malacologica

Interference competition in the suspension feeding Dendropoma maxima: optimal foraging or
an unresolved prisoner’s dilemma?
Gagern, Antonius; Michiels, Nico K.; Anthes, Nils
Animal Evolutionary Ecology, Zoological Institute, Eberhard Karls-Universität Tübingen, Auf der
Morgenstelle 28, 72076 Tübingen, Germany,
Email: antonius.gagern@googlemail.com, nico.michiels@uni-tuebingen.de, nils.anthes@unituebingen.de
The sessile, passive suspension feeding wormsnail Dendropoma maxima (Vermetidae) excretes a
mucous web to capture planktonic prey. In dense groups, the feeding webs of neighbouring snails
frequently overlap and stick together. This may create direct food competition between neighbours,
because the earlier retracting snail may get more than its fair share of the prey. We studied whether
web overlap triggers a phenotypic response in feeding behaviour. On day 1, focal snails were placed
in either of two treatments, solitary or with a direct neighbour. We then recorded feeding behaviour
twice, first on day 2 under the initial treatment, and second on day 4 after swapping focals to the
opposite treatment. We therefore obtained paired measurements for each focal under both treatment
conditions. We found that focals retracted their feeding web significantly earlier when close to a
neighbour than when solitary. Our experiments confirm phenotypic response through early web
retraction in D. maxima. A preliminary model shows that earlier web retraction may occur for two
rather different reasons. First, earlier web retraction in groups may represent optimal foraging if prey
accumulates more rapidly in overlapping webs. Alternatively, early web retraction may be
energetically inefficient, but result from direct interference competition between neighbours.
Predictions derived from these models will help disentangling both hypotheses in future experimental
studies.
Sexual dimorphisms in Fasciolaria tulipa (Buccinoidea, Fasciolariidae) using geometric
morphometrics
Galindo, Lee A. 1 ; López, Héctor 2
1. Dirección de Hidrografía y Navegación, Observatorio Naval Cagigal, Caracas
Venezuela or Instituto Oceanográfico de Venezuela, Universidad de Oriente,
Cumaná Venezuela, Venezuela,
Email: akamaikai@gmail.com
2. Instituto de Zoología Trópical, Universidad Central de Venezuela, Venezuela,
Email: helopez@ciens.ucve.ve
We studied sexual dimorphism evidences in adult of Fasciolaria tulipa, provided by different
morphometrics two-dimensional methods. Fifteen landmarks were analyzed employing
measurements distances arranged in a truss and TPS (relative warps and two blocks partial least
squares). The application of these methods for researching sexual dimorphism in gastropods is still
relatively new, thus, an aspect of this research is that it demonstrates potential application in this
discipline. All tools considered revealed the existence of some trades of sexual dimorphism. Size of
females is larger than males. Allometric coefficients are different between sexes. The application of
geometric morphometric offered more details in the shoulder, body whorl, shell aperture and shape.
Fasciolar and siphonal area presented more conspicuous inclination respect to spiralization axes in
males. Females are more robust, have bigger body whorl and thin and smaller anterior siphon.
According to computation, females are more similar within them than males’ configuration.
Covariance is studied among sexes. Despite differences are significant, high overlapping on
morphospace did not allow a reliable discrimination of sexes by using any variable alone.
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