Over the last weeks, the O. nasuta fish have been reproducing several times. After egg laying, the females pick up the eggs in their mouth until the juvenile fish are big enough to survive. The left picture shows the open mouth of a female with three yellow eggs visible, the right picture shows very young juveniles still feeding on the yolk of the egg.
One of the major aims of the GENBAS project is to investigate which genes are triggered in the female brain during the mating process and when she is confronted with a male from the same species or with a male from a different species. Genes that are differentially expressed may have been an important trigger for the speciation process.
We have tested the applicability of the Quantseq 3′ kit, a relatively new RNAseq approach that allows quantification of gene expression in 96 samples at once. We analysed gene expression in six brainparts (CE: cerebellum, OB: olfactory bulbs, OT: optic tectum, TE: telencephalon, DI: diencephalon, BS: brain stem) of five O. nasuta and O. ventralis females that have never been exposed to males. The (dis)similarities in gene expression between samples can be visualised through a PCA plot. As shown in the figure below, samples from the two species clustered according to brain part. This suggests that under the control conditions, both species are experiencing their environment in a very similar way.
Fifteen weeks after their arrival in Liège, one female has fallen for the charmes of the dominant male in her tank. Male Ophthalmotilapia create a bower in the sandy bottom and start a display to attract the attention of the female. When the female decides to enter the bower, she deposits eggs, one by one, and takes them up in her buccal cavity. The male defends the bower during the whole process. The male releases sperm in the water, which is then taken up by the female. Fertilisation presumably occurs in the mouth of the female. The female in the movie ended up with 16 eggs in her mouth.
Movie: deposition and uptake of five eggs by a female O. ventralis. The male guards the bower.
Beginning of Octobre 2014, we recieved young tilapia’s from the aquaculture facility in Tihange to practice dissection of the brain and to optimise the RNA extraction procedures in the molecular lab. Tilapia’s are cichlids that are cultured in large quantities for human consumption. Their brain size and form are very similar to that of Ophthalmotilapia.
Ever wondered how the brain of a cichlid fish looks like? It consists of six parts that can be easily distinguished from each other: the brain stem, cerebellum, optic tectum, telencephalon, diencephalon and olfactory bulbs. In the GENBAS project, we will investigate gene expression patterns in those regions of the brain that are involved in mate pairing.