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El Cichlid Room Companion

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Something Old Doing Something New

Por , 1999. print format
Publicado
Ron Coleman, 2000

Traductor Manuel Zapater Galve (10-dic-1999)
Versiones English
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Especies tratadas en este documento: Julidochromis marlieri Pelvicachromis pulcher

(This article was originally published in Cichlid News Magazine, Apr-98 pp. 30-31, It is reproduced here with the permission of author Ronald Coleman).
Pelvicachromis pulcher

Pelvicachromis pulcher male in the aquarium. Photo by Roger Häggström.

The number of known species of cichlids continues to increase almost daily, and it is hardly surprising that some of these are strange in interesting ways. But what about the old-timers - the fish that have been in the hobby for years? Do they hold any surprises?

Cichlids exhibit some of the greatest diversity in reproductive styles of any vertebrate

A trio of recent papers illustrate that even fish which many of us have kept for a long time may be hiding a thing or two, particularly in terms of their reproductive behavior. Cichlids exhibit some of the greatest diversity in reproductive styles of any vertebrate, from guarding to mouth-brooding; male care, female care, and biparental care; monogamy to harems. And yet, these three papers show that there are still things going on that we never imagined.

Julidochromis marlieri has been in the hobby for a number of years. From Lake Tanganyika, it is a substrate-spawner of the tribe Lamprologini. As with most cichlids, lamprologine males are generally larger than their females. But in the genus Julidochromis, the reverse is true: the females are usually larger than the males. What is going on?

Satoshi Yamagashi and Masanori Kohda (Osaka City University) investigated a group of 28 J. marlieri at Bemba,Congo. In most cases they found the situation typically seen in an aquarium - a male and female together raising a brood. They were surprised however by the largest female they studied. Over a period of two months all the fish observed had stable territories and yet the largest female had something extra. She had two territories, each complete with a resident male. One of these males was raising a group of fry. Every day, 2-4 times per hour, the female would visit each of her males even though they were separated by several meters.

This observation suggests that under the right circumstances J. marlieri may be polyandrous. Polyandry is a rare arrangement among animals in which a female has more than one mate, and the male provides parental care predominantly. Further work is needed to discover if polyandry is really occurring, and if so, why, and under what circumstances.

Metriaclima zebra is a mainstay of cichlid aquarists. The intense coloration of the various color morphs continues to attract people to the hobby. Metriaclima are relatively easy fish to breed and they can be kept at high densities, which mirrors their distribution in the wild. Females choose a mate from amongst the numerous males ready and willing to serve as "sire." Typically the female follows a male to a secluded spot, and they mate. The female then orally incubates the eggs and embryos, and parental care ends when the fry are released. But is it that simple?

Alex Parker and Irv Kornfield (University of Maine) thought that the high density of males from which a female can choose, and the fact that she seems to respond to the courtship of more than just one, might leave open another possibility: perhaps she mates with more than one male.

Direct observation of spawning events by mouthbrooders can be tricky. Indeed people may keep mbuna for years and never actually see them spawn. In the wild it is even harder. To test the idea that a single female carries eggs fertilized by more than one male, Parker and Kornfield resorted to the tools of molecular biology. They collected females holding eggs at Thumbi Island West (Malawi), and then analyzed the microsatellites (part of the genetic material) of the parents and embryos. Of the seven broods examined, averaging 14 offspring per brood, six had more than one father. Only the smallest brood, one of four eggs, had a single father. The others had as many as six fathers!

Pelvicachromis pulcher, the common krib, is a beautiful West African dwarf cichlid that breeds readily and consistently in artificial caves such as flowerpots. The females are as colorful as the males, and both sexes actively court the opposite sex. The curving courtship display of a female krib is one of the most beautiful displays in the realm of animal behavior. A pair of kribs with offspring is a formidable defensive team, often vanquishing much larger cichlids to the far end of the tank.

If that isn't enough to make this fish noteworthy, in a just-published paper, Elisabeth Martin and Michael Taborsky (Konrad Lorenz Institute, Vienna, Austria) reveal that kribs do a whole lot more.

Since the mid-60s people have recognized that not all kribs are the same. There are several related species, e.g., P. taeniatus and P. subocellatus, but even among those fish identified as P. pulcher there are two distinct forms of the males: red morphs and yellow morphs. Red morphs have dark red opercula and a band of red from the edge of the mouth to the belly region. Yellow morphs have yellow opercula and yellow lips. Male morphology is inherited, i.e., red morphs come from red morph parents.

Martin and Taborsky studied kribs in very large aquaria (3.60 m x 2.20 m x 0.6 m / 12' x 7.5' x 2' deep) which resembled their natural habitat, including roots, rocks, shallow areas, and deeper, fastwater zones. In this large aquarium setup, some of the males and females paired up as aquarists are used to seeing: one male with one female. But many did not. Some males became harem owners, courting and spawning with two or more females at a time. Others became "satellite" males. Satellite males lived in the territories of harem males, where they were tolerated, and helped defend the territory and the offspring in it. When there was more than one satellite in a harem, these would form a sort of "pecking order" with a most dominant satellite male, the next most dominant satellite male, and so on. Sometimes these satellites mated with the females in the harem.

Which behavior a male exhibited depended on two factors, his morph and his size. Red morph males became either harem masters or monogamous pair spawners (but never satellites). Some red males switched between these two options during the experiment. Of the 100 red morph males, roughly 50 were harem masters and 50 were pair spawners.

Yellow morph males became either pair spawners or satellites, depending on their size. Larger ones became pair spawners, while smaller ones became satellites. Martin and Taborsky had 78 satellite males. Satellite males never took over a harem, even if the harem master died. They did at times, however, become pair spawners (5 cases). Why are there different kinds of males? This is where things get really interesting.

By carefully observing, recording, and analyzing the behavior of each of the male types over many breeding attempts and by using genetic tools, Martin and Taborsky revealed a complex and fascinating picture. Monogamous pair males father lots of offspring, but they invest heavily in protecting the offspring from predators and in protecting the nest-site from competitors. Harem males, with their multiple female partners, father more offspring, in fact three times as many offspring as a typical monogamous pair male. In general, satellite males do much more poorly than harem males, but the dominant satellite male often fathers almost as many offspring as a typical monogamous pair male. Subdominant satellites may fertilize few eggs, if any.

So why do satellite males exist? It appears that satellite males might be biding their time. They father some offspring, but are waiting for a chance to pair up with a female to become a pair spawner. Harem owners tolerate the satellites because the satellites actively defend the offspring of the harem. On the other hand, while harem owners produce many offspring, harem owners appear to die much sooner than pair males (3 years versus 5.5 years) while satellite males live the longest (7.5 years).

There are still unanswered questions about each of these fishes, but if nothing else it shows that even cichlids which we think we know well have secrets to discover. Watch closely, your cichlids may be doing things you never suspected!

References Cited

Cita:

Coleman, Ron. (junio 26, 1999). "Something Old Doing Something New". El Cichlid Room Companion. Consultado en abril 18, 2014, desde: http://www.cichlidae.com/article.php?id=116&lang=es.