67
3 Why Spawn in Aggregations?
time windows for spawning in some species this could be advantageous. To our
knowledge, the presence of mate-choice copying has never been tested in aggregation
spawning fi shes and no evidence is available to determine whether such a tactic may
be used.
The benefi t of mate choice facilitation should be greatest in species where
females are particularly choosy. Generally, females that spawn in pairs or singlemale, multiple female (i.e. harem) groups within aggregations, such as red hind
(Sadovy et al. 1994 ) and bumphead parrotfi sh, Bolbometapon muricatum (Gladstone
1986 ), are likely to be choosier than those spawning in promiscuous, multiple-male
groups, such as Nassau grouper (Colin 1992 ) , striped parrotfi sh, Scarus iserti (Colin
1978 ) , and permit (Graham and Castellanos 2005 ) . Nevertheless, an element of
mate choice may still occur in multiple-male groups. For example, females may
identify a preferred male with whom they attempt to spawn, and their spawning rush
is joined by other, ‘less attractive’ males, in a manner similar to ‘hot-shot’ lekking
(Höglund and Alatalo 1995 ) . However, in multi-male spawning groups, it seems
more likely that females gain from spawning in aggregations due to fertilisation
benefi ts.
3.3.3 Fertilisation Dynamics and Sexual Confl ict
For males, the increase in density of conspecifi cs and the choosiness of females
on spawning aggregations result in increased intraspecifi c competition. This competition could be either directly for territories and/or females, or through sperm
competition for fertilisations. The investment made by males into sperm production
refl ects directly the intensity of sperm competition (Stockley et al. 1997 ) , and there
is ample evidence that male fi sh that spawn in multi-male groups invest heavily in
sperm (e.g. several wrasses, Labridae, Robertson and Warner 1978 , Atlantic wreckfi sh, Polyprion americanus , Peres and Klippel 2003 ) . For example, in group-spawning
groupers, such as the Nassau and leopard, Mycteroperca rosacea , groupers, males
have very large testes relative to their body size (Nassau: ~10% body weight, Sadovy
and Colin 1995 ; leopard: ~2.5% body weight, Erisman et al. 2007 , Brice Semmens
personal communication) (Fig. 3.4 ) (Chap. 5 ). In comparison, pair-spawning
groupers, such as the red hind, tend to invest relatively little in sperm production
(<1% body weight, Colin et al. 1987 ; Sadovy et al. 1994 ) . Many aggregative spawners
are known to have mixed strategies where group- and pair-spawning both occur;
indeed, all group spawners studied by Colin and Clavijo ( 1988 ) also pair-spawned.
Species with such mixed strategies may provide the best tests of the effects of sperm
competition. Such comparisons between group- and pair-spawning individuals have
been made for several wrasse (Labridae) and parrotfi sh species where males exhibit
two colour patterns that are associated with these two mating tactics: initial-phase
males are small, have drab colours or appear similar to females, and usually spawn
in groups; terminal-phase males are large, brightly coloured, defend harems or
resources that attract females, and spawn in pairs. The differences in sperm alloca-
3 Why Spawn in Aggregations?
time windows for spawning in some species this could be advantageous. To our
knowledge, the presence of mate-choice copying has never been tested in aggregation
spawning fi shes and no evidence is available to determine whether such a tactic may
be used.
The benefi t of mate choice facilitation should be greatest in species where
females are particularly choosy. Generally, females that spawn in pairs or singlemale, multiple female (i.e. harem) groups within aggregations, such as red hind
(Sadovy et al. 1994 ) and bumphead parrotfi sh, Bolbometapon muricatum (Gladstone
1986 ), are likely to be choosier than those spawning in promiscuous, multiple-male
groups, such as Nassau grouper (Colin 1992 ) , striped parrotfi sh, Scarus iserti (Colin
1978 ) , and permit (Graham and Castellanos 2005 ) . Nevertheless, an element of
mate choice may still occur in multiple-male groups. For example, females may
identify a preferred male with whom they attempt to spawn, and their spawning rush
is joined by other, ‘less attractive’ males, in a manner similar to ‘hot-shot’ lekking
(Höglund and Alatalo 1995 ) . However, in multi-male spawning groups, it seems
more likely that females gain from spawning in aggregations due to fertilisation
benefi ts.
3.3.3 Fertilisation Dynamics and Sexual Confl ict
For males, the increase in density of conspecifi cs and the choosiness of females
on spawning aggregations result in increased intraspecifi c competition. This competition could be either directly for territories and/or females, or through sperm
competition for fertilisations. The investment made by males into sperm production
refl ects directly the intensity of sperm competition (Stockley et al. 1997 ) , and there
is ample evidence that male fi sh that spawn in multi-male groups invest heavily in
sperm (e.g. several wrasses, Labridae, Robertson and Warner 1978 , Atlantic wreckfi sh, Polyprion americanus , Peres and Klippel 2003 ) . For example, in group-spawning
groupers, such as the Nassau and leopard, Mycteroperca rosacea , groupers, males
have very large testes relative to their body size (Nassau: ~10% body weight, Sadovy
and Colin 1995 ; leopard: ~2.5% body weight, Erisman et al. 2007 , Brice Semmens
personal communication) (Fig. 3.4 ) (Chap. 5 ). In comparison, pair-spawning
groupers, such as the red hind, tend to invest relatively little in sperm production
(<1% body weight, Colin et al. 1987 ; Sadovy et al. 1994 ) . Many aggregative spawners
are known to have mixed strategies where group- and pair-spawning both occur;
indeed, all group spawners studied by Colin and Clavijo ( 1988 ) also pair-spawned.
Species with such mixed strategies may provide the best tests of the effects of sperm
competition. Such comparisons between group- and pair-spawning individuals have
been made for several wrasse (Labridae) and parrotfi sh species where males exhibit
two colour patterns that are associated with these two mating tactics: initial-phase
males are small, have drab colours or appear similar to females, and usually spawn
in groups; terminal-phase males are large, brightly coloured, defend harems or
resources that attract females, and spawn in pairs. The differences in sperm alloca-