Evaluating the use of ram and suction during prey capture by cichlid fishes.
(1/403)
We characterized prey-capture strategies in seven species of cichlid fishes representing diverse trophic habits and anticipated feeding abilities. The species examined were Petenia splendida, Cichla ocellaris, Cichlasoma minckleyi, Astronotus ocellatus, Crenicichla geayi, Heros severus (formerly Cichlasoma severum) and Cyprichromis leptosoma. Three individuals per species were filmed with video at 500 Hz as they captured live adult Artemia sp. and Poecilia reticulata. For each feeding sequence, we measured the contribution of predator movement towards the prey (i.e. ram) and the movement of prey towards the predator due to suction. The use of ram differed significantly among prey types and predator species, varying as much as sixfold across predator species. High values of ram resulted in high attack velocities. Jaw protrusion contributed as much as 50% to overall ram values in some species, verifying its role in enhancing attack velocity. Suction distance did not vary significantly among species. Diversity in prey-capture behavior was therefore found to reflect differences among species in the strategy used to approach prey. Limited variation in the distance from which prey were sucked into the mouth is interpreted as the result of an expected exponential decline in water velocity with distance from the mouth of the suction-feeding predator. We propose that this relationship represents a major constraint on the distance over which suction feeding is effective for all aquatic-feeding predators. (+info)
Spironucleus vortens, a possible cause of hole-in-the-head disease in cichlids.
(2/403)
Hole-in-the-head disease is recorded in 11 discus Symphysodon discus Heckel, 1840 and 1 angelfish Pterophyllum scalare Lichtenstein, 1823 obtained from local aquarists within the Southwest of the UK. Spironucleus vortens Poynton et al. 1995, was isolated from the kidney, liver, spleen and head lesions of discus showing severe signs of the disease and from the intestines of all fish. The hexamitid was also recorded from the head lesions of the angelfish. The identity of these flagellates was confirmed as S. vortens on the basis of topographical features seen with the aid of SEM. A modified in vitro culture method was successfully developed for the detection, isolation and long-term maintenance of S. vortens. The flagellate was sub-cultured at 3 to 5 d intervals, new media being supplemented with fresh liver from Oreochromis niloticus (Linnaeus, 1757) free from infection. The results are discussed in relation to S. vortens as the causative agent for hole-in-the-head disease following systemic infection via the digestive tract. (+info)
Phylogenetic relationships and ancient incomplete lineage sorting among cichlid fishes in Lake Tanganyika as revealed by analysis of the insertion of retroposons.
(3/403)
Lake Tanganyika harbors numerous endemic species of extremely diverse cichlid fish that have been classified into 12 major taxonomic groups known as tribes. Analysis of short interspersed element (SINE) insertion data has been acknowledged to be a powerful tool for the elucidation of phylogenetic relationships, and we applied this method in an attempt to clarify such relationships among these cichlids. We studied insertion patterns of 38 SINEs in total, 24 of which supported the monophyly of three clades. The other 14 loci revealed extensive incongruence in terms of the patterns of SINE insertions. These incongruencies most likely stem from a period of adaptive radiation. One possible explanation for this phenomenon is the extensive incomplete lineage sorting of alleles for the presence or absence of a SINE during successive speciation events which took place about 5-10 MYA. The present study is the first to report the successful application of the SINE method in demonstrating the existence of such possible "ancient" incomplete lineage sorting. We discuss the possibility that it might potentially be very difficult to resolve the species phylogeny of a group that radiated explosively, even by resolving the genealogies of more than 10 nuclear loci, as a consequence of incomplete lineage sorting during speciation. (+info)
History and timing of human impact on Lake Victoria, East Africa.
(4/403)
Lake Victoria, the largest tropical lake in the world, suffers from severe eutrophication and the probable extinction of up to half of its 500+ species of endemic cichlid fishes. The continuing degradation of Lake Victoria's ecological functions has serious long-term consequences for the ecosystem services it provides, and may threaten social welfare in the countries bordering its shores. Evaluation of recent ecological changes in the context of aquatic food-web alterations, catchment disturbance and natural ecosystem variability has been hampered by the scarcity of historical monitoring data. Here, we present high-resolution palaeolimnological data, which show that increases in phytoplankton production developed from the 1930s onwards, which parallels human-population growth and agricultural activity in the Lake Victoria drainage basin. Dominance of bloom-forming cyanobacteria since the late 1980s coincided with a relative decline in diatom growth, which can be attributed to the seasonal depletion of dissolved silica resulting from 50 years of enhanced diatom growth and burial. Eutrophication-induced loss of deep-water oxygen started in the early 1960s, and may have contributed to the 1980s collapse of indigenous fish stocks by eliminating suitable habitat for certain deep-water cichlids. Conservation of Lake Victoria as a functioning ecosystem is contingent upon large-scale implementation of improved land-use practices. (+info)
Iridovirus infections in farm-reared tropical ornamental fish.
(5/403)
A systemic viral infection in both gourami Trichogaster spp. and swordtail Xiphophorus hellerii and an outbreak of lymphocystis in scalare Pterophyllum scalarae and gourami are reported to have occurred in fish reared in ornamental fish farms in Israel. The systemic infection developed in endothelial cells that became hypertrophic and their contents were modified. The presence of such cells in light-microscopically examined stained smears and sections provides an initial indication for this systemic viral infection. Infection in gourami caused hemorrhagic dropsy. Transmission electron microscopic (TEM) images of iridovirus-like particles recovered from gouramies showed them to be 138 to 201 nm from vertex to vertex (v-v); those from swordtails were 170 to 188 nm v-v. TEM images of lymphocystis virions from scalare were 312 to 342 nm v-v and from gourami 292 to 341 nm v-v. Lymphocystis cells from the gourami were joined by a solid hyaline plate, which was lacking in the infection in scalare where the intercellular spaces between the lymphocystis cells consisted of loose connective tissue. (+info)
Patterns in fish radiation are compatible with Pleistocene desiccation of Lake Victoria and 14,600 year history for its cichlid species flock.
(6/403)
Geophysical data are currently being interpreted as evidence for a late Pleistocene desiccation of Lake Victoria and its refilling 14,600 years ago. This implies that between 500 and 1000 endemic cichlid fish species must have evolved in 14,600 years, the fastest large-scale species radiation known. A recent review concludes that biological evidence clearly rejects the postulated Pleistocene desiccation of the lake: a 14,600 year history would imply exceptionally high speciation rates across a range of unrelated fish taxa. To test this suggestion, I calculated speciation rates for all 41 phylogenetic lineages of fish in the lake. Except for one cichlid lineage, accepting a 14 600 year history does not require any speciation rates that fall outside the range observed in fishes in other young lakes around the world. The exceptional taxon is a lineage of haplochromine cichlids that is also known for its rapid speciation elsewhere. Moreover, since it is unknown how many founding species it has, it is not certain that its speciation rates are really outside the range observed in fishes in other young lakes. Fish speciation rates are generally faster in younger than in older lakes, and those in Lake Victoria, by far the largest of the young lakes of the world, are no exception. From the speciation rates and from biogeographical observations that Lake Victoria endemics, which lack close relatives within the lake basin, have such relatives in adjacent drainage systems that may have had Holocene connections to Lake Victoria, I conclude that the composition of the fish assemblage does not provide biological evidence against Pleistocene desiccation. It supports a hypothesis of recent colonization from outside the lake basin rather than survival of a diverse assemblage within the basin. (+info)
What, if anything, is a Tilapia?-mitochondrial ND2 phylogeny of tilapiines and the evolution of parental care systems in the African cichlid fishes.
(7/403)
We estimated a novel phylogeny of tilapiine cichlid fish (an assemblage endemic to Africa and the Near East) within the African cichlid fishes on the basis of complete mitochondrial NADH dehydrogenase subunit 2 (ND2) gene sequences. The ND2 (1,047 bp) gene was sequenced in 39 tilapiine cichlids (38 species and 1 subspecies) and in an additional 14 nontilapiine cichlid species in order to evaluate the traditional morphologically based hypothesis of the respective monophyly of the tilapiine and haplochromine cichlid fish assemblages. The analyses included many additional cichlid lineages, not only the so-called tilapiines, but also lineages from Lake Tanganyika, east Africa, the Neotropics and an out-group from Madagascar with a wide range of parental care and mating systems. Our results suggest, in contrast to the historical morphology-based hypotheses from Regan (1920, 1922 ), Trewavas (1983), and Stiassny (1991), that the tilapiines do not form a monophyletic group because there is strong evidence that the genus Tilapia is not monophyletic but divided into at least five distinct groups. In contrast to this finding, an allozyme analysis of Pouyaud and Agnese (1995), largely based on the same samples as used here, found a clustering of the Tilapia species into only two groups. This discrepancy is likely caused by the difference in resolution power of the two marker systems used. Our data suggest that only type species Tilapia sparrmanii Smith (1840) should retain the genus name TILAPIA: One particular group of tilapiines (composed of genera Sarotherodon, Oreochromis, Iranocichla, and Tristramella) is more closely related to an evolutionarily highly successful lineage, the haplochromine cichlids that compose the adaptive radiations of cichlid species flocks of east Africa. It appears that the highly adaptable biology of tilapiines is the ancestral state for all African cichlids and that the more stenotypic lifestyle of the haplochromine cichlids is derived from this condition. We reconstructed the evolution of the highly variable parental care systems on the basis of the most inclusive composite phylogeny to date of the African, Neotropical, and Madagascan cichlids with special emphasis on a group of tilapiines comprising the substrate-spawning genus Tilapia, and the mouthbrooding genera Sarotherodon and OREOCHROMIS: We demonstrate several independent origins of derived mouthbrooding behaviors in the family Cichlidae. (+info)
Mosaic structure and retropositional dynamics during evolution of subfamilies of short interspersed elements in African cichlids.
(8/403)
The African cichlid (AFC) family of short interspersed elements (SINEs) is found in the genomes of cichlid fish. The alignment of the sequences of 70 members of this family, isolated from such fish in Africa, revealed the presence of correlated changes in specific nucleotides (diagnostic nucleotides) that allowed us to categorize the various members into six subfamilies, which were designated Af1 through Af6. Dividing the SINE consensus sequence into a 5'-head and 3'-tail region, these subfamilies were defined by various combinations of four types of head region (A-D) and three types of tail region [X, Y, and (YX)], with each region of each type including unique diagnostic nucleotides. The observed structures of the subfamilies Af1 through Af6 were AX, AY, CY, A(YX), BY, and DX, respectively. The formation of such structures might have involved the shuffling of head or tail regions among preexisting and existing (or both) subfamilies of the AFC family (and, probably, even another SINE family or a pseudogene for a tRNA in the case of the Af6 subfamily) by recombination at the so-called core region during the course of evolution. By plotting the timing of the retroposition of individual members of each subfamily on a phylogenetic tree of AFCs, we found that the Af3 and Af6 subfamilies became active only recently in the evolutionary history of these fish. The integrity of the 3'-tails of SINEs, which are, apparently, recognized by reverse transcriptase, has been reported to be indispensable for retention of retropositional activity. Therefore, we postulate that recombination might have been involved in the apparent recent activation of the retroposition of the Af3 and Af6 subfamilies via introduction of active tails (types Y and X, respectively) into potential ancestral sequences that might have had inactive tails. If this hypothesis is correct, shuffling of tail regions among subfamilies by recombination at the core region might have played a role in the recycling of dead copies of AFC SINEs. (+info)