Dependence of Visual Cues on Mate Selection in Cichlids

Why the heck I chose this topic. . . Cichlids are to my dad as Black-Capped Chickadees are to Dave -I was kind of stumped on what to do for a topic, so I asked my dad – who’s major was in Biology –specifically Wildlife and Fisheries -He told me this is what he would do if he were in this class, so I took his advice, plus I knew he’d give me some helpful advice -I stole the pictures of my dad and Dave off of facebook. . . Creepy, I know. -The irony of this topic is that I'm terrified of fish. . .

So, what’s the deal? Some species of cichlids thought to be extinct in the wild Why is this happening? Nile Perch Cichlids make a tasty dinner for Nile Perch’ Pollution Loss of Visual Cues Poor mate selection Specifically in Lake Victoria (cichlids used to be found in pretty much every area of the lake)– which is becoming quite polluted In 1978 thought to be 500 cichlids species in the lake Half are now extinct Pollution – Lake Victoria is slated for ecological restoration – has been clouding up since at least the turn of the century – since forests have been cut down. Nile perch prey on algae-eating cichlids – so the lake is getting cloudy, aggravating cichlids perilous state Creating a decline in water transparency Basically, cichlids are being eaten by Nile Perch, cichlids eat algae – now there are less cichlids so there’s more algae “it’s as if they were painted into the last corner, and then that corner gets painted” –Les Kaufman of the Boston University marine Program In turbid water, cichlid females are less choosy and males are less brightly coloured Turbidity in the lake is interfering with the ability of these strongly visual fish to fine their preferred, bright mates Reuslte may be interbreeding of closesly related species and loss of the more spectacularly colored forms Research shows that even species of cichlids in areas not attacked by Nile Perch are disappearing Group of researchers from the Universtiy of Leiden in the Netherlands measured the ligh and other environmental features in these areas, along with the brightnesss of the cichlid Strongest correlation between brightly coloured cichlid and clear, well-lit water In lab experiment females chose males of their own species in strong lighting, but mated indiscriminately in limited light.

Cichlids and mate selection Sexual Selection Males Shouldn’t stick around Should have courtship displays Be bigger and brighter (than females) Females Use visual cues to pick mates Dutch researcher, Martine Maan Female fish prefer brightly coloured males Easier to see In better shape Research on two similar species Best to pick bright coloured males Fewer parasites Adaptation to infection risks Stick to your own species! --Sexual selection by females is most powerful when males play no part in parental care and can mate with lots of females in one season -this can lead to courtship displays, colours and structures -species that display these characteristics are also often larger and brighter (males) -research indicates that females could be using visual cues (of brightness of colour) to identify their mates -if this is true, sexual selection might play a key role is speciation (The evolutionary formation of new biological species, usually by the division of a single species into two or more genetically distinct ones.) -Tested in labs/aquariums, tests showed that these females actually discriminate between males during courtship by the numbre of eggspots on the anal fin -so it is, indeed visual cues Maan – studied fish speciation in the East African Lakes bright = easier to see, indicates they are in better shape -evolutionary theory predicts that species can diverge if different females choose different characteristics in males (speciation) yet they often pay attention to tratis that reveal something about the quality of a male -as a result females are likely to share the same preferences -Maan – studied fish speciation in the East African Lakes -studies 2 closely related cichlid species – one with red males, the other with blue -in both species females preferred the most brightly coloured male. -for good reason : brightly coloured males from both of those species carry fewer parasites and are in better condition -also, both these species have adapted to different infection risks -Thus it is in the females best interest to mate with males of their own species

Females actually don't need males to stick around Direct benefits of males are unlikely influence in female choice Bright colours may signal heritable quality -So, cichlids are female mouthbrooders, meaning that the males do not usually contribute to brood care -So, basically, when they are choosing a mate, they are looking for good heritable qualities, not direct benefits from the males -Bright colours may signal heritable quality

Where the problem starts. . . Females usually like to stay within species for mating Closely related species Physically look different Differ little in ecology Live nearby In murky water, hard to distinguish Female discrimination can prevent hybridisation -Because females chose which males to mate with, they play in important role in the phenotypic diversification of these species flocks -so, their preference in colour will be shown in future generations (i.e. if they decide they like red stripes they chose mates with red stripes and babies have red stripes – usually will stay within species) -There are several species which are closely related, but who differ in secondary sexual characteristics (colour or brightness) Vary little in ecology So, these species live near each other, and in clear water are easily distinguishable Put them in murky water, harder to distinguish Get crossbreeding So instead of procreating more of their own species (which is dying off) -they are creating hybrids -(possibility) eventually species will become completely extinct -Females can discriminate between males of different colours in clear water conditions, but mated at random in turbid waters with limited visibility -Female choice can prevent hybridisation between two species

More evidence that they use visual cues Staged contest Under green light Coloration masked Red males dominate in white light Competitive advantage diminished in green light Staged contest under white lights and green lights -under green light, difference between red and blue coloration was masked Red males dominated blue males under white (clear light) But competitive advantage was significantly diminished under green light *this points in direction that cichlids are, in fact using visual cues of colour to differentiate between species

Conclusions Female choice When visual cues are blocked Important factor in speciation When visual cues are blocked Murky water Wrong selection of mate Not choosing preferred males Hybridisation Resulting in possible total extinction of already dying species -Sexual selection by female choice on prominent – eye catching male colour patterns has been proposed as an important factor in the rapid speciation -the problem starts when access to visual cues is cut off -in murkiness of water (which is caused by lack of cichlids to begin with. . .) -females are making the ‘wrong’ mate selections -they are not choosing the preferred males they would chose in clear water -resulting in hybridisation instead of speciation What's wrong with hybridisation -In this case the fact that it is happening with already dying species