METHODS
Collection and Maintenance of Rock Shrimp
Shrimp were collected from the shallow subtidal zone of
Bahı´a La Herradura, Coquimbo, Chile (29_590S, 71_220W).
Females and typus males were collected using an airlift
sampling device while scuba diving (Correa & Thiel 2003)
or baited traps hanging from the jetty of Universidad
Cato´ lica del Norte. Male robustus were collected individually
by hand and kept in a handheld net during diving.
Shrimp were transferred to the laboratory and sexed. Sexes
were kept in separate tanks with flowing aerated water and
ad libitum food supply (dead fish, ascidian colonies and
crushed molluscs). Tanks containing females were checked
daily for shed exoskeletons revealing newly moulted
individuals. Newly moulted females were isolated and
12–36 h later were paired with a robustus male to check
for receptivity. The female was considered receptive if
she allowed the robustus male to seize her to form the
‘cage state’, in which the male confines the female
between his pereopods (Correa et al. 2000). Male subjects
were classified into the typus and robustus morphs using
criteria established by Correa et al. (2000). To use males
with the most similar mating experience, robustus males
of similar age (time in robustus moult stage) were selected
by the presence of epibionts and coloration of hair on
chelipeds. We used the fish Auchenionchus microcirrhis
(Labrisomidae) as the predator in our experiments. This
is a relatively small, benthic fish (20–25 cm) that eats
medium-sized crustaceans. Auchenionchus microcirrhis has
been observed preying on R. typus in the laboratory and
shrimp give strong escape responses when they see the
fish. The fish was kept together with some R. typus in
a tank with constant water flow and fed daily with dead
and live shrimp.