''Tropheus moorii'' (blunthead cichlid) is a species of
cichlid endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
to
Lake Tanganyika in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. Over 40 different
color morphs of this species are dispersed throughout the lake, ranging from dark green to flame red and yellow. They mostly feed on
filamentous algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
on the rocky shallows they inhabit.
''T. moorii'' is a maternal
mouthbrooder
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 ...
, so eggs are fertilized and young are carried in the mouth of the female while they hatch and develop.
Territorialism
Both male and female adults occupy individual feeding
territories
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 ...
.
Blunthead cichlids inhabiting territories at greater depth tend to have smaller adult body sizes and larger territories compared to those in shallows.
Males have larger territories than females. A female leaves her territory to pair with a male and usually visits several territories multiple times before choosing a male. After the male and female form a pair bond, the female forages in his territory up to three weeks under his protection before
spawning
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...
. A female's
ovaries
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
do not fully mature until she pairs with a male and feeds from his territory. After spawning, the female leaves the male's territory to occupy a small unclaimed area for the mouthbrooding period. In contrast to the frequent movement of females, a male usually remains in his territory for months even if he is never visited by females.
Interspecies interactions
Often, blunthead cichlid feeding territories are adjacent to territories of
conspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
and
heterospecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
neighbors. A male ''T. moorii'' usually courts a female conspecific, which visits his feeding territory.
In Lake Tanganyika, blunthead cichlids coexist with other
herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
cichlids ''
P. trewavasae'', ''
P. orthognathus'', ''
P. polyodon'', and ''
T. temporalis''.
''T. moorii'', ''P. polyodon'', and ''T. temporalis'' individuals are not aggressive towards one another, but are aggressive towards individuals of other species and conspecifics. Although their territories often overlap, individuals of the three species do not usually interact due to the dietary differences that exist. For example, ''P. polyodon'' and ''P. trewavasae'' mostly feed on
unicellular algae rather than filamentous algae.
Having overlapping territories with'' P. polyodon'' may benefit ''T. moorii'' individuals since ''P. polyodon'' removes silt from the rock surface as they feed. This allows ''T. moorii'' to easily scrape filamentous algae from the rocks.
Having overlapping territories with ''P. trewavasae'' may benefit ''T. moorii'' individuals because both defend their territory from much larger ''P. orthognathus'' individuals. They also are able to drive them away, whereas an individual blunthead cichlid may not be able to defend territory successfully. This is an example of
commensalism
Commensalism is a long-term biological interaction ( symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fr ...
rather than
mutualism because individuals would defend their territories regardless.
Size-dependent dominance hierarchies
''T. moorii'' participates in size-dependent
dominance hierarchies when defending territory from intruders. If an individual intrudes on a ''T. moorii'' territory, the interaction may be a one-sided (territory owner towards the intruder) attack, one-sided display (spread and quiver fins/tail to intimidate), mutual attack, or mutual displays. These usually occur at or near the borders of the territories. In a one-sided attack, the territory owner chases the intruder until it leaves the territory.
Interactions vary depending on the relative size of the territory owner and intruder. Individuals tend to perform one-sided attacks on neighbors smaller than them and perform one-sided displays towards those larger than them. Attacks may occur inside or outside the feeding territory of the territory owner, while displays usually take place within the territory. Displays are very rare when a large difference in body size (more than 2.5 cm)exists, and more common when the difference is smaller (less than 2 cm). Mutual attacks are very likely to occur when the individuals are of similar size. Neighbors (having an adjacent territory) are more likely to respond to an attack with a display compared to a non-neighbor. In observed interactions between specifically ''P. orthognathus'' and'' T. moorii'' individuals with adjacent territories, the larger fish attacked the smaller one regardless of species, and no displays occurred.
Mating and reproduction
The mating system of ''T. moorii'' is
serial monogamy
Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time ( serial monogamy) — as compared to the various forms of non-monogamy (e.g., pol ...
. A male and female establish a temporary monogamous pair bond and spawn. The female mouthbroods the eggs and
young
Young may refer to:
* Offspring, the product of reproduction of a new organism produced by one or more parents
* Youth, the time of life when one is young, often meaning the time between childhood and adulthood
Music
* The Young, an American roc ...
with no direct assistance from the male, so after spawning, the male is free to
pair bond
In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of offspring and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is freque ...
with other females.
''T. moorii'' broods show
genetic monogamy, with all eggs having been fertilized by a single male. Other cichlid species that exhibit similar social monogamy in mating, such as ''
V. moorii,'' do not always show genetic monogamy due to
parasitic spawning (males fertilizing eggs of a female paired to another male). Spawning occurs on a rock surface, with the female laying up to 20 eggs which are bright orange in color. Eggs are incubated for 30 to 35 days, and when the young emerge from their mother's mouth, they are advanced enough in their physical development to live like adults.
Buccal feeding
Buccal feeding refers to the feeding a mouthbrooding mother does to feed her young located in her
buccal cavity
The buccal space (also termed the buccinator space) is a fascial space of the head and neck (sometimes also termed fascial tissue spaces or tissue spaces). It is a potential space in the cheek, and is paired on each side. The buccal space is super ...
. ''T. moorii'' females have unusually high
parental investment in their offspring since they produce large eggs and buccally feed their young. Among cichlids, ''T. moorii'' has a very high egg to adult body size ratio.
In the early stages of mouthbrooding, a female rarely feeds, but after the eggs hatch, she begins feeding to nourish them. The mother effectively starves herself during the mouthbrooding period, since all nourishment she takes in goes to feed the young.
The yolk sacs of the eggs are depleted around the 25th day of mouthbrooding, but the offspring are not released for several more days, so in that time, all of their nourishment must come from buccal feeding.
Buccal feeding is costly in terms of energy for the female since it requires more swimming. Buccal feeding does not shorten the mouthbrooding period; instead, young that are fed buccally are larger, heavier, and faster than unfed young. These benefits are very advantageous to the young since they lower their
predation risk and size is usually the determining factor in conflicts over resources.
Sexual selection and color morphs
Since male blunthead cichlids provide no brood care or other parental investment after spawning, the
operational sex ratio In the evolutionary biology of sexual reproduction, operational sex ratio (OSR) is the ratio of sexually competing males that are ready to mate to sexually competing females that are ready to mate, or alternatively the local ratio of fertilizable fe ...
in a
population
Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
is strongly biased towards males. A male's reproductive success varies based on how many times he can mate during his life. Females, by discriminating between males to decide a mate, strongly influence male reproductive success. Experimentally, females have been shown to share preferences for the same males when given two to choose from, meaning some males get to reproduce more often than others.
''T. moorii'' shows very great diversity in
color morphs, and color morph is a typical target for
mate choice sexual selection.
A female is more likely to choose a mate that has the same morph she does and this is probably what drove the proliferation and maintenance of the many color morphs.
''T. moorii'' individuals of a particular color morph are usually found in the same geographic area, so color morphs are also maintained by the relative isolation of ''T. moorii ''populations.
There is a level of
genetic differences between some populations, and it is possible that these (notably the so-called ''Tropheus'' sp. "Black" and ''Tropheus'' sp. "Mpimbwe") represent separate species.
Sexual differences
As a
sexually monomorphic species, ''T. moorii'' can be quite challenging to sex. The upper lip of males is more prominent (i.e., larger) than that of females. Males' lips on average tend to be more off-white, as well, due to their constant lip-locking aggression. Furthermore, males tend to have a turned-up nose, while females tend to have a greater slope and rounded nose, making the shape of their heads ellipsoid. Males generally grow at a faster rate and display their adult colors sooner. Males' coloration is also often more bold than females' because they display when courting females. Adult males also tend to have a deeper body, whereas females appear more slim and streamlined.
Feeding and habitat
''T. moorii'' is strictly herbivorous like all ''Tropheus'' species. They spend the majority of their time scraping algae from the rocks. In the wild, blunthead cichlids are found in shallow bays and in the upper reaches of the lake over rocky reefs where the water is quite illuminated, because this is where the algae and other vegetable matter grow most thickly. Consequently, they are adapted to bright light.
Etymology
The
specific name honours the discoverer of this species,
John Edmund Sharrock Moore (1870-1947).
References
{{Taxonbar, from=Q135331
moorii
Taxa named by George Albert Boulenger
Fish described in 1898