The Fascinating World of Astatotilapia: From Courtship to Evolution

Astatotilapia is a fascinating genus of fish that has captured the attention of scientists and aquarium enthusiasts alike. Astatotilapia species are found in the rivers and lakes of Africa.

One of the most interesting aspects of Astatotilapia is their courtship behavior, which involves complex rituals and displays. These displays can be triggered by the presence of a potential mate.

In the wild, Astatotilapia have been observed forming large schools, often with multiple males vying for dominance. This behavior has been observed in the genus's most well-studied species, Astatotilapia calliptera.

Sampling for the study was conducted between 2010 and 2015 in various locations around Lake Tanganyika and its inflowing rivers. Sampling was done using minnow traps or hook and line.

The researchers obtained permits from relevant authorities, including the Department of Fisheries Republic of Zambia, the Tanzanian Commission for Science and Technology, and the University of Burundi and the Ministry of Water and Environment, Republic of Burundi.

Fish handling and sampling were carried out at the University of Basel with a permit from the cantonal veterinary office, Basel.

Figure 1 is a crucial part of our study, and it's essential to understand it to grasp the methods we used.

We examined the population structure and phylogeographic history of A. burtoni throughout its entire distribution range in the Lake Tanganyika basin.

Our study extends the population sample to include specimens collected within the lake and in inflowing rivers along the entire shoreline of Lake Tanganyika.

This is a significant expansion of previous work, which only covered a small fraction of the distribution range of A. burtoni.

We reconstructed phylogenetic relationships based on sequences of the mtDNA control region (d-loop) as well as thousands of genomewide SNPs derived from RADseq.

By doing so, we aimed to provide a comprehensive understanding of the population structure and phylogeographic history of A. burtoni.

The geographic origin and genetic relationships of A. burtoni laboratory strains used in different studies are often not reported or unknown, which makes our study even more valuable.

We also included samples from different laboratory strains in phylogenetic and population genetic analyses to trace back their origins from wild populations.

Our study aimed to address the conflicting results from previous studies on population structure in A. burtoni.

By examining the population structure and phylogeographic history of A. burtoni throughout its entire distribution range, we hope to contribute to a better understanding of the biology of this species.

Sampling was carried out between February 2010 and November 2015 in the Zambian, Tanzanian, and Burundian parts of Lake Tanganyika and inflowing rivers, as well as in Lake Cohoha (Burundi) and Lake Chila (Zambia).

The researchers used a combination of minnow traps and hook and line to catch specimens, with the approval of various local authorities, including the Department of Fisheries Republic of Zambia and the Tanzanian Commission for Science and Technology.

Fish handling at the University of Basel was covered by permit no. 2317 issued by the cantonal veterinary office, Basel.

Specimens from other locations were kindly provided by researchers from Belgium, France, and Germany, including samples from the Kalambo River and the Ruzizi area in Burundi.

A total of 33 locations were sampled, including two laboratory strains of A. burtoni, which were used in research laboratories.

DNA extraction was performed using the E.Z.N.A. Tissue DNA Kit (Omega Bio-tek) according to the manufacturer's protocol.

All fish collected by the researchers were anesthetized with clove oil prior to handling, and a fin clip was taken as a DNA sample and stored in 96% ethanol.

Figure 4 illustrates the co-ancestry matrix of the RAD structure, showing the relationships between individuals from different populations. The highest levels of co-ancestry are shared among individuals from the Lufubu stream population (LF2), indicated by black and blue colors.

These colors represent the highest levels of genetic similarity, suggesting a closer relationship between individuals from this population.

The co-ancestry matrix highlights the genetic differences between populations, with the lowest levels of co-ancestry sharing given among northern and southern populations, indicated by yellow coloration. This indicates a lower level of genetic similarity between individuals from these populations.

This information is crucial for understanding the genetic diversity of the study populations and informs the analysis of genetic data.

The researchers used a technique called RADseq to derive thousands of genomewide SNPs from genomic DNA.

This data was then used to reconstruct the phylogenetic relationships of A. burtoni populations. The maximum-likelihood analyses resulted in well-resolved and congruent topologies.

The phylogenetic reconstruction of the wild specimens revealed a deep split between a northern clade and a southern clade. The northern clade includes populations from the Ruzizi River to the Igalula River and Kalemie on the western shore of Lake Tanganyika.

Within the northern clade, populations from the northern basin of Lake Tanganyika were nested within populations from the lake's central basin. The specimens from Lake Cohoha were resolved together with the Ruzizi specimens.

The phylogenetic reconstruction including laboratory strains and outgroup taxa resulted in a highly similar topology. The inclusion of outgroup taxa did not provide additional phylogenetic information.

Both laboratory strains were resolved within the northern clade. The laboratory strain from the University of Basel grouped as a sister clade to all populations from the central basin except the sample from Kalemie.

The laboratory strain from the University of Texas formed a monophyletic sister clade to the northernmost samples. The “wild” specimens from the Hofmann laboratory grouped with samples from LZL and Ka3.

Aquarium noise is a significant concern, as sound dissipates over distance and in a fish tank, sound has nowhere to go so it bounces off the glass until the signal degrades.

Filters, air pumps, and other equipment can create numerous noises that are exacerbated in small, enclosed spaces like aquariums.

Reducing aquarium noise is not unrealistic, and it's possible to make some adjustments to minimize the impact.

Karen Maruska's research on noise effects on cichlid social behavior is particularly relevant to aquarium owners.

Maruska and her co-author Julie Butler introduced tonal noises of specific frequency ranges in aquaria to observe effects on social behaviors.

Higher frequencies negatively affect both stress and reproductive behavior in Astatotilapia burtoni, a beautiful little haplochromine cichlid.

This research highlights the importance of considering aquarium noise when designing and maintaining aquariums.

Astatotilapia are a type of fish that are native to the rivers and lakes of Africa.

They are a relatively small species, typically growing up to 20 centimeters in length.

Astatotilapia are known to be quite social creatures and are often found in large schools.

In the wild, they feed on a variety of food sources including algae, insects, and small crustaceans.

Despite their small size, Astatotilapia are capable of producing a loud, high-pitched sound to communicate with other members of their species.

Astatotilapia courtship is a complex and fascinating display of behavior. Dominant male A. burtoni produce pulsed broadband sounds during body quivers associated with courtship behaviors.

These sounds are not a by-product of body movements, but rather a deliberate action by the male to communicate with females. The sounds are produced intentionally because not all quiver behaviors are associated with sound production.

The sounds are made primarily in close proximity to females and are of relatively low intensity, indicating that they're intended for close-range communication. Larger males are more likely to produce a sound along with their quivers, suggesting that male experience or age may play a role in acoustic communication.

The quiver body movements also produce strong hydrodynamic components that can be detected by the female's lateral line system. This multimodal communication is essential to understanding the driving forces and mechanisms of diversification in cichlids.

Figure 3 is a map showing the sampling locations of LT, which includes Lake Tanganyika, Lake Cohoha, and Lake Chila.

These locations were chosen for their unique characteristics, with Lake Tanganyika having 31 sampled populations.

A total of 117 individuals were used to create the unrooted maximum-likelihood tree based on 19,037 SNPs.

The tree shows a deep split between northern and southern lineages, indicating a significant genetic difference between these two groups.

The colors in the phylogeny correspond to the colors on the map, making it easy to visualize the relationships between the different populations.

Samples from locations 17, 20, 21, and 29 were included for mtDNA analysis only, suggesting that these individuals were studied in more detail.

The animals used in this study were adult laboratory-bred cichlid fish A. burtoni, which were derived from wild-caught stock in Lake Tanganyika, Africa.

These fish were maintained in aquaria under environmental conditions that mimic their natural habitat, including a temperature of 28°C and a pH of 8.0.

The aquaria contained gravel-covered bottoms with half terra cotta pots that served as shelters and spawning territories for the fish.

Fish were fed cichlid flakes and pellets each morning to ensure they received a balanced diet.

The experimental procedures were approved by the Stanford Administrative Panel for Laboratory Animal Care, ensuring that the animals were treated with care and respect.

Cichlids use a unique form of communication called multimodal courtship, which involves a combination of visual and auditory signals.

Dominant male A. burtoni produce pulsed broadband sounds during body quivers associated with courtship behaviors, which are intentionally produced and not just a by-product of body movements.

These sounds are primarily made in close proximity to females and are of relatively low intensity, indicating that they are intended for close-range communication.

In fact, the proximity to other individuals and the rapid attenuation of the sounds produced by signaling males suggest that sound production in A. burtoni is intended for close-range communication.

The sounds themselves are a stimulus that can be detected by both the inner ear and mechanosensory lateral line system, but how this information might be differentially used by the female remains unknown.

Gravid females in our experiment heard the courtship sounds before they could see the males, suggesting that overhearing the sound production itself provides the female with valuable information.

The inclusion of control noise playbacks in our study also demonstrates that female preference in A. burtoni is not simply a response to any sound, but is specific to the natural courtship sounds produced by males.

This eavesdropping function is further supported by the improved hearing ability in females that are gravid and ready to spawn, which would allow them to detect courting males at greater distances.

The temporal and spectral characteristics of A. burtoni courtship sounds were also similar to those previously described in other cichlid species, suggesting a shared mechanism of sound production.

The mechanism of sound production in A. burtoni is not known, but it may involve the pharyngeal jaws and swimbladder as proposed for other cichlids, or be similar to that described for the related cichlid O. niloticus.

Astatotilapia males produce courtship sounds during body quivering displays, which are intended for close-range communication to advertise their presence, reproductive readiness, and quality.

These sounds are likely energetically expensive, making them honest signals used during mate choice.

Gravid females can detect these sounds at greater distances due to their improved hearing ability, which would allow them to detect courting males and potentially increase their reproductive fitness.

The proximity of other individuals to the signaling male and the rapid attenuation of the sounds suggest that sound production in A. burtoni is intended for close-range communication.

The sounds alone influenced the female's preference before she acquired any visual cues from the male, suggesting that overhearing the sound production provides valuable information about a reproductively motivated male.

Female preference in A. burtoni is not simply a response to any sound, but is specific to the natural courtship sounds produced by males.