AbstractAn algivorous cichlid,
Variabilichromis moorii(
Vm), defends permanent territories in Lake Tanganyika, Africa. A zoobenthivorous cichlid,
Neolamprologus mustax(
Nm), spends 60% of daylight hours foraging in
Vmterritories, from which other zoobenthivorous fishes are chased out and consequently which are much richer in prey animals than areas outside of
Vmterritories. We conducted a field experiment to examine whether
Nmresidents and non-residents received different degrees of attacks from
Vm.
Nmfish were caught in their territories, released at a point distant from these territories, and followed to observe interactions with
Vmfish. The frequency of attacks received by the displaced
Nmfish was greater than attacks received by
Nmresidents, indicating that
Nmresidents had easier access to
Vmterritories than non-residents did. A possible mechanism for this is reduced aggression of
Vmtowards
Nmresidents, as a result of the ‘dear enemy’ effect that has been reported in territorial contests between rivals. An alternative mechanism is that tolerance towards
Nmdiffers among
Vmfish and
Nmresidents selectively visit more tolerant
Vmfish due to previous experience while non-residents randomly approach both tolerant and hostile
Vmfish. The ability of
Vmto discriminate between
Nmresidents and non-residents is essential to the former mechanism but not to the latter. To more specifically examine which mechanism works in the
Vm–
Nmcommensal system, we will need to follow individually identified
Vmfish interacting with
Nmresidents and non-residents.
Sexual dimorphism and population divergence in the Lake Tanganyika cichlid fish genus Tropheus
