World Congress of Malacology Antwerp ... - Unitas Malacologica

16.38±0.65) with minor reductions occuring in August and December due to recruitment peaks.
Anual production (P) was 0.32g AFDM m -2 y -1 and the mean biomass 0.99g AFDM m -2 with a P:B
relation of 0.32.
Finantial support: CAPES, CNPq, UNICAMP and USP.
Sexual selection and sex allocation in Aplysia: Hermaphrodites with nonreciprocal mating
Yusa, Yoichi
Nara Women’s University, Nara 630-8506, Japan,
Email: yusa@cc.nara-wu.ac.jp
In this presentation, I will review my own work on sex allocation and sexual selection in Aplysia spp.
(mainly A. kurodai; Gastropoda: Opisthobranchia). Most current theories predict a male-to-female
shift in sex allocation with growth and weak sexual selection on the male function in simultaneous
hermaphrodites, although empirical data for both predictions are insufficient in hermaphrodites with
nonreciprocal mating.
To address these issues, I first studied sex allocation patterns in A. kurodai. Laboratory observations
showed that both frequency and duration of egg-laying increased with body size. In a controlled
experiment, egg mass weight actually increased almost linearly with body weight. On the other hand,
both laboratory and field observations showed that frequency and duration of mating as males did not
increase with body size, suggesting that sperm usage was independent of size. Therefore, sex
allocation in A. kurodai shifted from male to female functions with growth.
Next, concerning sexual selection before and during mating, the lack of a relationship between body
size and mating activities as males suggests that there was virtually no “female” choice or inter-
“male” competition with respect to body size. However, frequency and duration of mating as females
increased with body size, suggesting a “male” choice for large, and hence more fecund, partners. This
“male” choice is further supported by the presence of size-assortative mating. In addition, the
variance in mating frequency as females was similar or larger than that as males. These results imply
that the direction of sexual selection before and during mating are weakly reversed in A. kurodai,
acting more strongly on the female than male function. However, due to multiple mating, sexual
selection after mating should act more strongly on the male function.
Population genetic structure of a sympatric squid-Vibrio mutualism in the Mediterranean Sea
Zamborsky, Daniel J.; Nishiguchi, Michele K.
Department of Biology, New Mexico State University, Box 30001, MSC 3AF
Las Cruces, NM 88003-8001, USA,
Email: nish@nmsu.edu
Squids from the genus Sepiola (Cephalopoda: Sepiolidae) living sympatrically in the Mediterranean
Sea form a mutualistic symbiosis with two species of the Vibrio genus: V. fischeri and V. logei.
Environmentally transmitted symbionts inhabit the light organs and produce ventrally-directed
luminescence used in anti-predatory behavior. The light organ expulses symbiotic bacteria daily, and
is subsequently re-colonized by the remaining Vibrio bacteria in the light organ. This diurnal event
has led to phylogeographical variation within the squid-Vibrio system in other regions of the world
(Indo-Pacific). Although the symbiosis amongst sympatric Sepiola species and both species of Vibrio
in the Mediterranean has been well documented; the genetic structure of the host squid and Vibrio
symbiont has not been described. Using nested-clade analysis we have investigated the genetic
variation within host and bacterial symbiont populations in the geographical range of the
Mediterranean. The results demonstrate a localization of haplotypes in the host squid populations
closely related to the physical range of the host. Vibrio symbionts show a broader number of
haplotypes over a wider geographic area suggesting a strong influence of migratory forces, both
biotic and abiotic. Biotic factors such as host movement within the Mediterranean as well as abiotic
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