There are only two kinds of organisms on the Earth: prokaryotes and eukaryotes. Although eukaryot... more There are only two kinds of organisms on the Earth: prokaryotes and eukaryotes. Although eukaryotes are considered to have evolved from prokaryotes, there were no previously known intermediate forms between them. The differences in their cellular structures are so vast that the problem of how eukaryotes could have evolved from prokaryotes is one of the greatest enigmas in biology. Here, we report a unique organism with cellular structures appearing to have intermediate features between prokaryotes and eukaryotes, which was discovered in the deep sea off the coast of Japan using electron microscopy and structome analysis. The organism was 10 µm long and 3 µm in diameter, having >100 times the volume of Escherichia coli. It had a large 'nucleoid', consisting of naked DNA fibers, with a single nucleoid membrane and endosymbionts that resemble bacteria, but no mitochondria. Because this organism appears to be a life form distinct from both prokaryotes and eukaryotes but similar to eukaryotes, we named this unique microorganism the 'Myojin parakaryote' with the scientific name of Parakaryon myojinensis ('next to (eu)karyote from Myojin') after the discovery location and its intermediate morphology. The existence of this organism is an indication of a potential evolutionary path between prokaryotes and eukaryotes.
The extinction of the Irish elk Megaloceros giganteus has traditionally thought to have been caus... more The extinction of the Irish elk Megaloceros giganteus has traditionally thought to have been caused in one way or another by the enormous antlers of the males. Recently, a popular hypothesis for the Irish elk extinction has been their inability to cope with the nutritional demands of growing such large antlers during worsening habitat conditions. However, this hypothesis is weakened by several previously unaddressed and biologically unreasonable assumptions. We discuss these assumptions and conclude that, because antler mass is expected to have been evolutionarily labile, nutritionally sensitive, and ontogenetically variable and male mortality is expected to have had limited impact on population growth, the large antlers of Irish elk probably had little to do with the extinction. We focus on the reproductive energetics of females as a possible contributor to extinction, and model the nutritional demands of producing precocial cursorial young. Our model shows the reproductive output of females being reduced by 50% due to changes in the length of the growing season at the end of the Pleistocene when most populations of Irish elk went extinct. The model was validated with parameters from the extant wapiti, which was predicted to maintain high levels of reproduction during the Pleistocene climatic deterioration. Thus, nutritional stress on reproductive females is likely to have contributed more to the Irish elk extinction than nutritional stress on large-antlered males.
Conservation of wildlife populations requires extensive knowledge of their habitat requirements, ... more Conservation of wildlife populations requires extensive knowledge of their habitat requirements, efficient methods to evaluate habitat quality, and an understanding of the value of fragments and edges. Kibale National Park, Uganda has areas that differ in the densities of 2 species of frugivorous monkeys-Cercopithecus mitis and Lophocebus albigena-including one on an edge and forest fragments outside the park that lack both species. We compared the basal area densities of important food trees with primate densities. The density of Cercopithecus mitis correlates most strongly with the basal area density of all types of food trees combined. The density of Lophocebus albigena does not correlate with the basal area densities of any category of food trees or with fruit availability. An index of their density-number of groups seen per km walked-correlates to fruit availability but with marginal significance. Lack of a relationship between the basal area densities of food trees and density of Lophocebus albigena may be the result of a mismatch in scale between the forest area measured and their large home ranges. We compared the unused area of forest to the other areas of the forest and the fragments and found it had higher basal area densities in all food tree categories for both species than the fragments and lower basal area densities of
Seasonality in tropical forests can be more subtle than that of temperate forests but still affec... more Seasonality in tropical forests can be more subtle than that of temperate forests but still affects the resources available to wildlife. Much work has been done describing changes in fruit availability and dietary composition but the nutritional quality of any particular food item is assumed to be relatively constant. We investigated seasonal changes in the quality of the ripe fruit of Celtis durandii, a common tree that produces fruit year-round and is important in the diets of many species. The lipid content of the ripe fruit was found to be highly variable (0.3-30.8% dry matter) among months and this variation was positively correlated with the summed daily rainfalls of the previous and concurrent months. The amount of this fruit in the diets of three frugivorous primate species (Cercopithecus mitis, Cercopithecus ascanius and Lophocebus albigena) was positively related to measured or estimated lipid levels in the fruit. Such predictable changes in the quality of a constantly available fruit have not been previously reported and suggest that the resources provided by tropical forests may be more seasonal than shown by common measures of fruit availability.
There are only two kinds of organisms on the Earth: prokaryotes and eukaryotes. Although eukaryot... more There are only two kinds of organisms on the Earth: prokaryotes and eukaryotes. Although eukaryotes are considered to have evolved from prokaryotes, there were no previously known intermediate forms between them. The differences in their cellular structures are so vast that the problem of how eukaryotes could have evolved from prokaryotes is one of the greatest enigmas in biology. Here, we report a unique organism with cellular structures appearing to have intermediate features between prokaryotes and eukaryotes, which was discovered in the deep sea off the coast of Japan using electron microscopy and structome analysis. The organism was 10 µm long and 3 µm in diameter, having >100 times the volume of Escherichia coli. It had a large 'nucleoid', consisting of naked DNA fibers, with a single nucleoid membrane and endosymbionts that resemble bacteria, but no mitochondria. Because this organism appears to be a life form distinct from both prokaryotes and eukaryotes but similar to eukaryotes, we named this unique microorganism the 'Myojin parakaryote' with the scientific name of Parakaryon myojinensis ('next to (eu)karyote from Myojin') after the discovery location and its intermediate morphology. The existence of this organism is an indication of a potential evolutionary path between prokaryotes and eukaryotes.
The extinction of the Irish elk Megaloceros giganteus has traditionally thought to have been caus... more The extinction of the Irish elk Megaloceros giganteus has traditionally thought to have been caused in one way or another by the enormous antlers of the males. Recently, a popular hypothesis for the Irish elk extinction has been their inability to cope with the nutritional demands of growing such large antlers during worsening habitat conditions. However, this hypothesis is weakened by several previously unaddressed and biologically unreasonable assumptions. We discuss these assumptions and conclude that, because antler mass is expected to have been evolutionarily labile, nutritionally sensitive, and ontogenetically variable and male mortality is expected to have had limited impact on population growth, the large antlers of Irish elk probably had little to do with the extinction. We focus on the reproductive energetics of females as a possible contributor to extinction, and model the nutritional demands of producing precocial cursorial young. Our model shows the reproductive output of females being reduced by 50% due to changes in the length of the growing season at the end of the Pleistocene when most populations of Irish elk went extinct. The model was validated with parameters from the extant wapiti, which was predicted to maintain high levels of reproduction during the Pleistocene climatic deterioration. Thus, nutritional stress on reproductive females is likely to have contributed more to the Irish elk extinction than nutritional stress on large-antlered males.
Conservation of wildlife populations requires extensive knowledge of their habitat requirements, ... more Conservation of wildlife populations requires extensive knowledge of their habitat requirements, efficient methods to evaluate habitat quality, and an understanding of the value of fragments and edges. Kibale National Park, Uganda has areas that differ in the densities of 2 species of frugivorous monkeys-Cercopithecus mitis and Lophocebus albigena-including one on an edge and forest fragments outside the park that lack both species. We compared the basal area densities of important food trees with primate densities. The density of Cercopithecus mitis correlates most strongly with the basal area density of all types of food trees combined. The density of Lophocebus albigena does not correlate with the basal area densities of any category of food trees or with fruit availability. An index of their density-number of groups seen per km walked-correlates to fruit availability but with marginal significance. Lack of a relationship between the basal area densities of food trees and density of Lophocebus albigena may be the result of a mismatch in scale between the forest area measured and their large home ranges. We compared the unused area of forest to the other areas of the forest and the fragments and found it had higher basal area densities in all food tree categories for both species than the fragments and lower basal area densities of
Seasonality in tropical forests can be more subtle than that of temperate forests but still affec... more Seasonality in tropical forests can be more subtle than that of temperate forests but still affects the resources available to wildlife. Much work has been done describing changes in fruit availability and dietary composition but the nutritional quality of any particular food item is assumed to be relatively constant. We investigated seasonal changes in the quality of the ripe fruit of Celtis durandii, a common tree that produces fruit year-round and is important in the diets of many species. The lipid content of the ripe fruit was found to be highly variable (0.3-30.8% dry matter) among months and this variation was positively correlated with the summed daily rainfalls of the previous and concurrent months. The amount of this fruit in the diets of three frugivorous primate species (Cercopithecus mitis, Cercopithecus ascanius and Lophocebus albigena) was positively related to measured or estimated lipid levels in the fruit. Such predictable changes in the quality of a constantly available fruit have not been previously reported and suggest that the resources provided by tropical forests may be more seasonal than shown by common measures of fruit availability.
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Papers by Cedric Worman