Biology Reference
In-Depth Information
(a)
(b)
1
Tail beating
1500
Biting
1000
Mouth
Wrestling
500
Circling
0
1
0
1
Weight asymmetry
Fig. B14.1.2
Fighting in the cichlid fish,
Nannacara anomala
, is more prolonged
(a) and escalates to more dangerous stages (b) the more closely the contestants are
matched in size. Weight asymmetry is measured as the logarithm of the weight of the
heavier fish divided by the weight of the lighter fish (0 = weight ratio of 1, i.e. equal
weights). From Enquist and Leimar (1990). With permission from Elsevier.
the males orientate laterally with erect fins. (b) Then they engage in tail
beating, pushing a stream of water towards the flank of an opponent. This
involves alternating roles in which each fish takes turns between performing
a tail beat and manoeuvring into a lateral position to receive the stream from
its opponent's beat. (c) Then biting increases in frequency and the contestants
begin to orientate frontally. (d) This is followed by mouth wrestling, where
the males get a firm grip of each other's jaws and have a pushing and pulling
contest, allowing more accurate assessment of relative strength. (e) Finally,
circling occurs where both fish swim fast in a tight circle and try to bite the
back of their opponent. At the end of the contest, losing fish signal their
defeat by folding their fins, changing colour and retreating. Larger males were
more likely to win, and with very large differences in size the smaller fish gave
up more or less immediately at stage (a). As the difference in size decreased,
however, fights became longer and escalated through the sequence with
increasing risks of injury at successive stages (Fig. B14.1.2). The contests
described in the main text between red deer stags provide another example
of sequential assessment.
