World Congress of Malacology Antwerp ... - Unitas Malacologica

Threshold dimorphism in ejaculate characteristics associated with alternative reproductive
behaviours in the squid Loligo bleekeri
Yoko, Iwata; Yasunori, Sakurai
Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido
041-8611, Japan,
Email: iwayou@fish.hokudai.ac.jp; sakurai@fish.hokudai.ac.jp
Male dimorphism has been thought to correlate with alternative reproductive behaviours. Alternative
reproductive behaviours promote asymmetry in sperm competition, and sperm competition theory in
a "fair raffle" process (the more sperm put in, the higher the chances of success) predicts that males
invest more energy on sperm production and ejaculate more when they have disadvantages in
behavioural competition. Coastal squid Loligo bleekeri has body-size related alternative mating
behaviours and characteristic sperm competition situation. Females have two sperm storage sites in
their body, and males have two mating behaviours (mate-guarding and sneaking) associated with
each sperm storage site. We show that there is clear dimorphism in internal character (spermatophore
length) in males using allometric analysis. Larger individuals made discontinuously longer
spermatophores than smaller individuals, although no such discontinuity was observed for external
characters. Sperm mass ejaculated from long-type spermatophores had a rope-like shape, and those
ejaculated from short-type spermatophores had a drop-like shape. Observations on each sperm mass
attached on the different body parts of females showed that the rope-like sperm mass were attached in
the sperm storage site of females, where paired males pass spermatophores during mate-guarding
copulations. In contrast, the drop-like sperm mass were attached on the sperm storage site of females,
where small males pass spermatophores during sneaking copulations. The clear internalmorphological
switch could be an adaptation to the characteristic alternative mating behaviours of
loliginid squid, in which males employing each mating tactics pass spermatophores on different
sperm storage sites of females. The result that small males make relatively shorter spermatophore
suggests that male squid may allocate sperm resources dependent on rules other than a standard "fair
raffle" principle. Our results indicated that alternative reproductive behaviours promote
morphological adjustment in internal character, under different roles of sperm competition game.
Population dynamics, growth and secondary production of Nassarius vibex (Say, 1825)
Yokoyama, Leonardo Q. 1,2 ; Amaral, A. Cecília Z. 2
1. Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo,
SP, Brasil,
Email: lqyokoyama@gmail.com
2. Departamento de Zoologia, Instituto de Biologia, Universidade Estadual de Campinas,
Campinas, SP, Brasil, CEP: 13083-970, CP: 6109,
Email: ceamaral@unicamp.br
The growth, production and population dynamics of Nassarius vibex (Gastropoda, Nassaridae) were
analysed in a population at Camaroeiro sandy beach (23º37’62’’S, 45º23’86’’W), north coast of São
Paulo state, Brazil. The species ocurred in a soft bottom bed of Mytella charruana (Bivalvia,
Mytilidae) (Area A) and in its superior adjacent region (Area B). Four replicates were obtained in
each area, using a quadrat with 1m² of area. The shell length of 1465 gastropods was measured with a
digital caliper. Significative diference (T=-7.57, p