IntroductionSpeciationis the formation of distinct species within the course of evolution.
Geographicalchanges, barries (allopatric) or sexual selection (sympatric) are examples offactors which are the driving process behind speciation. Previous studiesindicate that sympatric speciation could be driven by heterogeneousenvironments when geographical obstacles are missing. An example of sympatricspeciation in a heterogeneous environment is the sensory speciation in twospecies of Chichlids in Lake Victoria. Two closely related Chichlids, Pundamilianyererei and Pundamilia pundamila live in the same lake but differ inpreference of waterdepth, and thus light intensity. Both species behave as’real’ species when they are present in their prefered habitat but hybridize inturbid habitat where. State of the artAlthough the aquatic ecosystem shows evidence invisial communication, reproductive isolation due to visual adaptation hasn’tbeen proved yet. Previous research to the effect of changing visual conditionson mate choice for killifish did not show a comprehensive result but suggesteda small effect of sensory development on color choice. This promissingsuggestion is why the link between visual system properties and visual matepreferences should be further investigated.
Another study has found that p. nyererei expresses higher long-wavelength-sensitive visualpigment and is more sensitive to red colors compared to P. pundamila. Furthermore, the characteristics of male coloration,photic environment and female preferences are correlated with the visialsystems which the Chichlids prefer.
Botch Chichlids species and theircrossbreeds are used in this experiment. The Chichlids were reared undersimulated red colored deep- (turbid) and blue colored shallow (clear) waterconditions. Afterwards the preference of females for red or blue males underdifferent light settings was tested.
Recent findingsFemale preference was significantlyaffected by the rearing light conditions. Quiver and courtship behaviour for P. pundamila and P. nyerereiwas prefered by both deep and shallow reared females however P. pundamila was more in favor byfemales which were reared in simulated shallow water habitat. The femaleChichlids which were reared in deep water habitat did not have a specificpreference for any of the male Chichlids species.
Furthermore, when female species are brood in natural habitatcircumstances there is a significant interaction between rearing light andlateral display and quiver. Female chechlids do more frequently respond to malesof the same species in reared lighting than when they are reared in artificiallighting. Whenever P. pundamilawas raised in shallow water the females preferred males of the same species butwhen P. pundamila was raised in deepwater it did not. P. nyererei did nothave any preference for either red or blue males in either shallow- or deepreared habitat.
When both P. pundamila andP. nyererei are combined in one groupand are re-organising to the natural and unnatural deep and shallow lake rearingconditions, it turned out that non random mating occurd. Sexual selection forquivering male chichlids with the same phenotype occured significantly moreoften than that females wanted to mate with a male with a different phenotype. Itturned out that females which were reared in light conditions that simulatedtheir natural habitat preferred mating with males who have a similar phenotypebut did not have a preference for any phenotype when brood under unnaturallight circumstances.
Repeatability of male preferency by hybrid and P. pundamila females was higher than whencompared to P. nyererei. Still,overall the repeatability of female preference was small. This wasn’t caused bythe different set ups nor did examinating females in two contrasting lightconditions influence the experiment. Repeatability was low in both of eachtested set up and each light condition. Although the the experimental set upsdid not influence female preference it did influence fish activity.
