|Evolution and Systematics of Lampreys
At this website we hope that you can benefit from the knowledge gained through our NSF funded study entitled Systematics and Biogeography of Lampreys ("Agnatha": Petromyzontiformes) and the Evolution of Parasitic and Non-Parasitic Life Cycles Based Upon Morphological and DNA Sequence Character Variation to Richard L. Mayden and Kevin J. Roe. This has been an extremely ambitious large-scale study with multiple collaborators deeply interested in the biology and evolution of these fishes.
|This study involves the generation of a molecular data set using the complete sequences ofthe two mitochondrial gene Cytochrome b. While other genes are viewed as useful in accomplishing the objectives of this study, the generation of homologous data across these vastly diverse lineages has demonstrated to be highly problematic. The morphological and molecular data sets are analyzed separately and using a total evidence approach. Specific objectives of the study are to examine the alternative hypotheses of relationships between hagfishes, lampreys, and gnathostomes, test the monophyly of Petromyzontiformes and constituent families, and determine species relationships and generic boundaries within the order. Hypotheses of phylogenetic relationships will provide an historical framework to provide the first test of the "satellite species" hypothesis and examine the (1) evolutionary origins of parasitic and non-parasitic life histories, (2) evolutionary transitions between anadromous and freshwater life cycles, (3) patterns of speciation and associated molecular and morphological divergences, (4) the evolutionary transitions of the ancestral vertebrate eye morphology, and (5) biogeographic history of Petromyzontiformes.
This research uses existing museum collections and new field samples as sources for specimens. Most specimens required for morphological data are in existence, however many of the specimens for the molecular portion of the study must be collected live from extant populations. This study builds on the accumulated expertise of Ian Potter, Howard Gill, and Claude Renaud (morphology) and Richard Mayden, Nick Lang, and Kevin Roe (DNA sequencing, phylogenetic analysis) and many other collaborators around the World. Training includes multiple postdoctoral researchers, undergraduate and graduate students in diverse character evaluation, morphological and molecular techniques, and phylogenetic analysis.
This research has been gracioiusly supported through competitive proposal review by the National Science Foundation (DEB-0296162) and Saint Louis University.
Lampreys represent one of the two surviving groups of jawless vertebrates; the other group includes the hagfishes (Myxini). Both of these groups have traditionally been placed in a group referred to "Agnatha" (without jaws) and include elongate or eel-like, slimy, and morphologically "simple" fishes. The evolutionary relationships of these jawless vertebrates to themselves and gnathostomes remains an area of continued controversy. Some researchers have arged that Agnatha is a monophyletic group (they shared a common ancestor) and others have argued that lampreys, or Petromyzontiformes, are more closely related to the Gnathostomata then they are to the hagfishes.
Lampreys, as a group, include 38 species displaying an anti-tropical distribution consistent with vicariant events indicative of the break up of Pangea and post-Pangean histories of Laurasia and Gondwana. The species are freshwater or are anadromous. The Northern Hemisphere freshwaters are occupied only by species of the family Petromyzontidae. The families Mordaciidae and Geotriadae are endemic to the Southern Hemisphere and may not be closest relatives. Recent genetic analyses by our laboratory and that of Silver et al (2004) strongly indicate that Geotria australis, the only currently recognized species in the Geotridae may be the closest relative to the Petromyzontidae, and that the three species of Mordacia in Mordaciidae may be the basal sister group in the order. Should these relationships prove to withstand further testing with additional data, these relationships would clearly indicate that the divergence between the monophyletic Mordaciidae and the common ancestor shared between Geotriidae and Petromyzontidae would have diverged prior to the breakup of Pangea.
First unambiguous fossil lampreys date to 300-280 MYA. These include Mayomyzon pieckoensis and Pipiscius zangerli from central Illinois and Hardistiella montanensis from Montana, in North America. All of the fossil materials are from shallow marine areas, indicating that at least during this time these taxa were either marine or anadromous in their habits. The well-preserved specimens of M. pieckoensis show prominent eyes and the diagnostic tongue-like piston and annular cartilage.
Lampreys are a very interesting group in many ways and for many reasons. Where investigated, the different lamprey species possess lamprey-specific substances. These include Lamphedrin, an anticoagulant that is secreted through their oral glands. This is particularly well developed in the parasitic species wherein they feed on blood and body fluids. Personal observations by our research team indicate that when a parasitic species is displaced from its host, there is conspicuous bleeding and fluids flowing from the wound area. However, shortly after a host fish is placed in freshwater within minutes after the lamprey oral disk is removed the bleeding ends. Lampreys also have a substance referred to as Petromyzonol, a bile acid pheromone used to attract migratory adults to breeding grounds. During spawning in high-gradient streams the breeding adults apparently release this compound and others migrating up the river or moving within lake systems looking for breeding grounds detect this substance that will lead them to appropriate habtiats for spawning. The other compound possessed by lampreys is Lampricide chemical poison that lampreys,
While an incredibly interesting group of Crainiates, the group has had limited attention as to their phylogenetic relationships and evolution. Historically, morphological similarities between parasitic and non-parasitic species have been interpreted as evidence that different extant non-parasitic species evolved multiple times from parasitic species. These ancestor-descendant pairs have been termed "paired species" or "satellite species." Current hypotheses suggest that the evolution of non-parasitism may be due to a protracted larval stage. Despite agreement among lamprey researchers as to the validity of the satellite species hypothesis, no phylogenetic analysis has been conducted to support such relationships or hypotheses. If corroborated via phylogenetic analyses, the satellite species hypothesis would represent one of the most remarkable cases of multiple convergences ever documented in vertebrates.
Lampreys also display complex life history patterns as both parasitic and nonparasitic species, as well has an interesting pattern of evolution of adaptations for either a freshwater or anadromous existence. Their diets, spawning habits, and general adaptations to their environments differ tremendously across species and clades. Some species are parasitic and use other fishes as their primary hosts wherein they attach themselves with an oral disk with varied, large teeth. Parasistic species generally use host species that are large, scaleless or weak-scaled fishes (catfish, suckers, pike, clupeiform taxa, etc.). With a piston-like tongue they feed on blood, body fluids, and/or flesh. Some species are non-parasitic and following their transformation they mature, spawn, and die. Some populations of species very interestinlgy produce both parasitic and nonparasitic forms.
Parasitism of some species can have a major impact of host species. The Sea Lamprey, Petromyzon marinus, was introduced into the Great Lakes system, after which populations of the lake trout and other species experienced a dramatic decline in numbers. This had a major impact on the fisheries industry of non-lamprey species with the fall of the harvest. To the control the Sea Lamprey populations over time they have made use of the pheromones given off by ammocetes in streams that are appropriate for spawning and released these to attract spawning adults to streams. Once they enter the streams they use lampricides to kill the migratory and mature adults.
Unfortunately, several species of lampreys are faced with concervation concerns and are either likely extinct (Tetrapleurodon spacicea of Mexico) or are on a trajectory of extinction if something is not done to protect the species.
Fish illustrations copyrighted
by Joseph R. Tomelleri and
used with permission.