Astatotilapia burtoni
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''Astatotilapia burtoni'' is a species of
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
in the family
Cichlidae Cichlids are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, the Labroidei, along with the wrasses ( Labridae), in the order Perciformes, but molecular studies have contradicted thi ...
. It is found in
Lake Tanganyika Lake Tanganyika () is an African Great Lake. It is the second-oldest freshwater lake in the world, the second-largest by volume, and the second-deepest, in all cases after Lake Baikal in Siberia. It is the world's longest freshwater lake. ...
and its surrounding waterways, including parts of
Burundi Burundi (, ), officially the Republic of Burundi ( rn, Repuburika y’Uburundi ; Swahili language, Swahili: ''Jamuhuri ya Burundi''; French language, French: ''République du Burundi'' ), is a landlocked country in the Great Rift Valley at the ...
,
Rwanda Rwanda (; rw, u Rwanda ), officially the Republic of Rwanda, is a landlocked country in the Great Rift Valley of Central Africa, where the African Great Lakes region and Southeast Africa converge. Located a few degrees south of the Equator ...
,
Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
, and
Zambia Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most cent ...
. Its natural
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s are
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
s, intermittent rivers,
swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
s, freshwater
lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s, freshwater
marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
es, intermittent freshwater marshes, and inland deltas. ''Astatotilapia burtoni'' has been used as a
model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...
to study the behaviors and physical systems of cichlids, including their development and
embryogenesis An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
. Moreover, the
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
position of this particular species makes it an ideal model system for comparative genomic research. ''A. burtoni'' belongs under the
haplochromine __NOTOC__ The haplochromine cichlids are a tribe of cichlids in subfamily Pseudocrenilabrinae called Haplochromini. This group includes the type genus (''Haplochromis'') plus a number of closely related genera such as '' Aulonocara'', '' Astat ...
s, which is the
lineage Lineage may refer to: Science * Lineage (anthropology), a group that can demonstrate its common descent from an apical ancestor or a direct line of descent from an ancestor * Lineage (evolution), a temporal sequence of individuals, populati ...
of cichlids with the most species, and has been discovered to be a
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
to both the
Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after ...
region superflock (which has about 600 species) and the species flock of
Lake Malawi Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania. It is the fifth largest fre ...
(which has about 1,000 species).


Social behavior


Reversible male social roles

The males of the ''Astatotilapia burtoni'' come in two
phenotypes In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
that are reversible. The males can readily switch between being territorial and non-territorial based on the social environment they are in: dominant,
territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
males possess bright coloration, aggressive behavior while defending territory, and an active role in sexually reproducing with the females; subordinate and non-territorial males possess coloration similar that of the females, lack initiative to pursue female counterparts, and are reproductively suppressed due to regressed
gonads A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sperm ...
. The transitions between different social roles cause several changes in the brain and reproductive system, such that the social transformation affects them both behaviorally and physically. To expand on reversibility, if a territorial male is placed with an individual that is significantly larger in size, it will then rapidly socially transform into the non-territorial type. This change can be detected by the behavior and alternate coloration that follows. The change in reproductive competence, however, occurs about three weeks after the formerly territorial male loses its territory to the larger fish. In regards to the other social transition, when a non-territorial male becomes the territorial type, it will almost immediately exhibit aggressive behavior and an
eyebar In structural engineering and construction, an eyebar is a straight bar, usually of metal, with a hole ("eye") at each end for fixing to other components. Eyebars are used in structures such as bridges, in settings in which only tension, and ne ...
, while the physiological changes will follow in about one week.


A result of hormones

Several studies have been done in order to pinpoint the biological basis on which this reversal occurs, and they suggest that the stress
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...
may have a direct role in social status, because cortisol may change the biological priorities of the cichlid's system. Under chronic stress, the animal may experience reproductive regression (as shown in the territorial's male shift to the non-territorial type) as a result of the body's efforts to combat the stressor, as opposed to using the metabolic energy for long-term goals like reproduction. Moreover, studies have also shown that the male cichlid's social phenotype directly influences the
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
levels of
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
and 11-ketotestosterone.
Plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
concentrations of these
androgens An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...
in both the territorial males and non-territorial males were measured and assessed, and it was found that the territorial males have drastically higher plasma concentrations of both
hormones A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...
.


A result of nearby females

The cichlid males' behavior of shifting between dominant and subordinate states as a result of the social environment can also be related to females in their vicinity, for females may alternate between reproductive states as well, but independently of social conditions. Females use a complex integration of cues in order to make their mate preferences, which may be from genetic factors, learned behaviors, or
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
levels. They can socially transform between a
gravid In biology and human medicine, gravidity and parity are the number of times a woman is or has been pregnant (gravidity) and carried the pregnancies to a viable gestational age (parity). These terms are usually coupled, sometimes with additional te ...
reproductive state, which is egg-bearing, and a non-gravid reproductive state, and it was shown in a study that the mating preferences of the female highly depended on the reproductive state in which the female was in. Gravid female cichlids will prefer to spend time with the dominant male type instead of the subordinate male type, whereas the non-gravid females do not have a preference for either one. This may be explained by the fact that because for spawning to occur, the gravid females must be courted by the dominant males, suggesting that gravid females' preference for dominant males is a behavioral
priming Priming may refer to: * Priming (agriculture), a form of seed planting preparation, in which seeds are soaked before planting * Priming (immunology), a process occurring when a specific antigen is presented to naive lymphocytes causing them to di ...
mechanism.


Reproductive behavior


Male courtship and maternal mouthbrooding

''Astatotilapia burtoni'', like ''
Oreochromis mossambicus ''Oreochromis'' is a large genus of oreochromine cichlids, fishes endemic to Africa and the Middle East. A few species from this genus have been introduced far outside their native range and are important in aquaculture. Many others have ver ...
'', is a lekking species, so the dominant males will have male displays of
courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
in order to attract and lure females that are passing by. The behavior starts with the male attempting to catch the female's attention by displaying his side to the female while quivering his body. The male will then try to lead the female back to a spawning site, and if she follows and thus is ready to
spawn Spawn or spawning may refer to: * Spawn (biology), the eggs and sperm of aquatic animals Arts, entertainment, and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** '' Spawn: ...
she will peck at egg-shaped spots on the male's anal fin as he quivers again. The female will then lay her eggs, collect them in her mouth, then peck at the egg spots on the male. The male releases sperm and fertilizes the eggs in the female's mouth. This pecking and fertilizing behavior repeats until the female is done laying eggs. Once the females are enticed and enter the male's territory to
spawn Spawn or spawning may refer to: * Spawn (biology), the eggs and sperm of aquatic animals Arts, entertainment, and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** '' Spawn: ...
, after spawning, the females will rear the young in their mouths, a behavior called
mouthbrooding Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a va ...
. After about two weeks of incubation have passed, the females will release their young. However, exposure to excess noise during maternal mouthbrooding can cause cannibalization or premature release of the brood. Following brood release, after several more weeks have passed, the female cichlids will have recovered physiologically enough to be able to spawn again. Maternal mouthbrooding is recognized to affect
hormones A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...
and reproductive cycles for the female cichlids, but the effects as a result of neural processing and food deprivation are not known. A study particularly focused on this subject matter examined the effects that maternal mouthbrooding may have on a wide variety of physiological practices, in order to see if they are consequences of food deprivation, and indeed it was found that many of the changes (not all) are explained by food deprivation.


Communication


Acoustic signals

Many animals use multimodal communication, having multiple
sensory modalities Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, ...
at their disposal for reproductive interactions, and the ''Astatotilapia burtoni'' has been used as a model to study the production of the wide variety sexual signal types. ''A. burtoni'' incorporate multiple sensory systems, including
chemosensory A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance ( endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecep ...
, visual, acoustic, to be able to socially interact in their complex manner. East African cichlids, in general, are especially known for their vibrantly colored bodies and the role that coloration plays in courting and mating, but the ''A. burtoni'' is known to be phenotypically distinct in its use of a completely different form of sensory communication: acoustic communication. Sounds and the corresponding behaviors of the male sex of these particular African cichlids have been studied while observing the female mate preference, and behavioral experiments demonstrated that acoustic information does indeed play a significant role in sexual reproduction. This reliance on non-visual sensory information in order to coordinate complex social behaviors indicates that acoustic signaling is important for the ''A. burtoni''. This suggests that there are internal cues in these cichlid fish that can significantly change the way in which the fish respond to auditory signals because the physiological state of the fish can directly affect the perception of the auditory signals. Thus, more efforts have been made to understand how the females perform sexual selection by closely examining the signaling systems and how they relate to the neural processing in the fish to result in such behaviors.


Reproductive purpose

A particular study showed that dominant males will issue auditory signals in order to court females, and that these courtship sounds are similar to those that they themselves could perceive. The study found that the
broadband In telecommunications, broadband is wide bandwidth data transmission which transports multiple signals at a wide range of frequencies and Internet traffic types, that enables messages to be sent simultaneously, used in fast internet connections. ...
sounds that the dominant males produced were associated with body quivers, suggesting that the sounds were produced intentionally for courting and not a by-product of the quivers, as not all the quivers were accompanied by sounds. The data also suggested that auditory perception of ''A. burtoni'' changes in accordance with the reproductive cycle of the fish. This may be potentially due to levels of circulating
hormones A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...
. Intra- and inter-sexual social communications in males can also be affected by underwater noise exposure. Noise exposure was even found to change when and how males produced courtship behaviors, such as producing mating calls by quivering inside their spawning shelters instead of near a female. This behavioral change likely decreases the chance of females hearing male mating calls.


References

* {{Taxonbar, from=Q1017137 burtoni Fish described in 1894 Taxa named by Albert Günther Cichlid fish of Africa Fish of Burundi Fish of Rwanda Fish of Tanzania Fish of Zambia Taxonomy articles created by Polbot