Effects of Egg Size and Temperature on Development Time on Mouthbrooding Cichlid Species.
Mouthbrooding cichlids, which hold their eggs and fry in their buccal cavity, are an interesting group in which behavior and development time have been poorly studied. Life history traits and physiology of mouthbrooding cichlids differ from substrate spawning cichlids in such a way that the effects of temperature on the relationship between egg size and development may be different between these groups. Also, mouthbrooding cichlids have egg sizes that span a much larger range than the substrate spawning cichlids, allowing one to investigate for trends over a larger range of egg sizes in cichlids. Data on development time at different temperatures provides a foundation for future investigations of costs and benefits of mouthbrooding. More specifically, experiments estimating development times over a range of temperatures and egg sizes provide a general empirical basis for estimating the parental cost of holding fry for a longer period of time.
To start to understand the effects of egg size and temperature on development time in mouthbrooder cichlid species, I looked at three things: 1) the relationship between temperature and development time for each egg size, 2) the effects of temperature on hatching rate and wriggler development to the free swimming fry stage in relation to egg size in mouthbrooding cichlids, and compared the data from mouthbrooding cichlid data to substrate-spawning cichlid data to determine if there is a significant difference in developmental time between the two groups.
South American species Geophagus steindachneri (average egg size = 2.25mm), and African species Astatotilapia calliptera (average egg size = 2.22mm), and Stomatepia pindu (average egg size = 3.52mm) were used in this experiment. Eggs were placed into five experimental tanks with target water temperatures of 20oC, 23oC, 27oC, 31oC, and 34oC. To compare development time at the different temperatures, two measurements were recorded for each set of eggs. First, I measured time of hatching, which is the time from spawning to when wrigglers became fry (defined as no egg sac present). Previously collected data from substrate spawners were then used for comparative analyses.
Regardless of egg size, temperature showed a strongly negatively, significant relationship with development time for hatching and fry stages for individual species (except S. pindu fry using the Spearman's rho test). Many analyses showed no detectable effect of egg size on development time. However, when mouthbrooder and substrate hatching data were combined, there were significant effects of egg size on development time. The same results were also seen when mouthbrooder and substrate free swimming fry data were combined. However, effects of egg size on development time could also be explained as mouthbrooder vs. substrate spawner differences.Citation
Thompson, Melissa Ellen (2004) Effects of Egg Size and Temperature on Development Time on Mouthbrooding Cichlid Species. Masters thesis, Department of Biological Sciences, California State University, Sacramento.
Lissa joined the lab in January of 2002 and finished her degree in December of 2004.