Biological Sciences
LSU Biologist Identifies Twist in African Cichlids’ Courtship Ritual LSU Assistant Professor of Biological Sciences Karen Maruska is making new gains with her research on African cichlids and their use of acoustics and chemoreception for courtship. The African cichlid fish species peaked Maruska’s interest because of their social behaviors and ease of manipulation. This species, Astatotilapia burtoni, which can be found in Lake Tanganyika in East Africa, houses two types of males: subordinate and dominant. Within a population, dominants make up 10 to 30 percent of males. The environmental composition dictates who has subordinate or dominant status at any given time. Much like other dominant organisms, the dominant males protect their respective territories and attract mates while the subordinate fish associate frequently with the females. The subordinate males' lack of territory ownership and absence of dominance behaviors greatly lessens his chances for breeding. Fortunately for the subordinate males, small windows of opportunity arise for them to supersede their status and become dominant. This phenomenon can occur when a dominant male is removed from the territory or is successfully challenged by a subordinate. Within a short period of time (minutes), the newly promoted male transforms his physiology, behavior, and reproductive system to model the dominant male. Future research in the Maruska lab is aimed at identifying the mechanisms that might initiate and control this sudden transformation. “It makes sense that these animals would want to transition really quickly because the sooner they get into the territory, the sooner they can advertise to everyone around them that this is their new territory and then they can focus on attracting females to mate with,” said Maruska. Maruska and colleagues from Stanford University conducted a series of studies in which they manipulated males by transforming a subordinate male to a dominant status and vice versa. These manipulations provided ample opportunities to examine how the brain and reproductive system changes as these males transition between high-ranking and low-ranking status, a phenomenon that occurs in most animals living in social groups.
Top left: the African cichlid fish Astatotilapia burtoni; bottom left: Maruska's lab with tanks of the African Cichlids
Dominant males initiate their courtship ritual with visual body quivers and simultaneously produce a distinct sound. Females that are sexually receptive hear this sound better than females that have already spawned, and females prefer males that are making sounds over ones that are not. Males and females also signal to each other by releasing pulses of urine,
The
Courtship By Otisha Paige
Karen Maruska feeds the African Cichlids in her lab.
presumably carrying pheromone compounds. These recent discoveries of the courtship ritual open the door to future work aimed at discovering where these different senses are processed in the fish brain, how they interact, and how they can influence behavior. Special spots on the male’s fin called egg spots trick the female into thinking she left some eggs behind, so her initial response is to pick those eggs up. This stimulates the male to release sperm and fertilize the eggs inside her mouth. The female holds the developing eggs in her mouth for two weeks as they grow and the mother risks emaciation due to lack of eating. The females’ mouthbrooding behavior allows the researchers to shed light on how the brain controls feeding and reproduction at the appropriate times. This work may also provide insights relevant to weightrelated human health issues. There are a few thousand species of cichlids in existence. These various groups provide researchers like Maruska with excellent models for studying the neural, molecular, and evolutionary bases of social behaviors. “I have a great group of students here at LSU and some great collaborators at other institutions that help out with these projects, and there is always something new to discover.” said Maruska. Maruska received a bachelor’s degree from University of New Hampshire, a master’s degree from Florida Tech, a Ph.D. from University of Hawaii, and was a postdoctoral scholar at Stanford University. She is a 2013 recipient of the Ralph E. Powe Junior Faculty Enhancement Award, an award given to junior faculty by Oak Ridge Associated Universities.