Wednesday, April 5, 2017

Cichlids and Sex

Things here at Kande Beach are as beautiful as ever. The rainy season brings lush greenery, growth and new life wherever one looks. Sex is in the air and you can feel it. The pintail whydah, a native bird here does its beautiful courtship dance for a female; singing and waving its long tail (3 times the length of its body) to show her what he can do. The flat backed toads sing every night luring the females with their chorus louder than the engine of a diesel truck. The flap-necked chameleon does an amazing colour change display for its girlfriend. These courtship rituals play an important role in what Charles Darwin called sexual selection: when the female of a species bears most of the cost of reproduction, males use extravagant displays and gifts to represent their “reproductive fitness” and females choose between them.  For many male humans, muscular displays, or shards of a crystalline form of carbon can serve to win over the female.

Sexual selection often actually works against natural selection. In situations of mainly female parental care, the reproductive success of the male is almost completely in the hands of the female. So even if a male is well camouflaged and can survive for a long time, if he doesn’t impress the female, he wont have any babies, and his genes will cease to be passed forward. In this way female choice selects for traits that sometimes actually increase the survival risks of the males. For example the agama lizard of east Africa have lost any camouflage capability when compared with their female counterparts. 

Here in Lake Malawi many cichlids have evolved a unique form of attraction. Over 200 cichlid species here build special structures to attract their females. These structures are called bowers, named after the structures built by the famous bowerbirds of Papua New Guinea. Like the bowerbirds these structures are built by male cichlids solely for the purpose of showing the girls what they can do.  In essence, the size and structure of the bower is a direct indicator of the fitness of the male. This is because, after all, if you are able to spend time digging and pushing around sand rather than finding food, you must be a strong individual with good genes to pass on.

There are two general bower types; either castles or pits and they are often built in large groups or congregations of many males called leks. Here, on Kande island there are species that build both types of bowers, but the most impressive, in my opinion, are those belonging to the species Dapidiochromis kawinge. The males of these species dig large pits often with diameters and depths greater than one meter. They do this by pushing the sand out of the way with their snouts. Every week here we do a survey of a lek near the island, and we try to track when the bowers are usually

After the bowers are constructed, the males will remain in or above the structure and display for any passing female. If the courtship is successful, the female will lay her eggs and the male will fertilize them within the bower. The female will then scoop up the eggs with her mouth and carry them away to care for them herself. 

Female cichlids do not have to build any nests or structures, as many of them have evolved an amazing ability to brood their babies in their mouths!!! This behavior allows the mother to be mobile all the while providing round the clock parental care.

Here at the island we have found a couple mouth brooding resident mothers of the species Tyrannochromis nigriventer who we love to go watch whenever we have a chance. Cichlids are some of the most caring mothers of the animal kingdom, and this puts immense evolutionary pressure on the males to be more brightly coloured, or have better mating displays, or build better bowers. Cichlids can mouth brood their offspring for upto a month! Once the babies grow up, this sexually selective cycle repeats itself. As new tastes are developed or enhanced over generations whole new species with different preferences arise, continuing the ancient process that has led to the species and behaviours that we see today.