You are currently browsing the monthly archive for April 2008.
WHILE MANY NICHES are ever-present in vertebrate-dominated ecosystems, sometimes we find an extinct group that was unique in some way. At various times in the past carnivores have evolved saber-teeth, but currently there are no saber-toothed predators (although the clouded leopard may be working on it). In a previous post I mentioned Simocyon, a cursorial generalized carnivore that retained arboriality in order to escape from larger predators, including the saber-toothed cats. Today I will write about Thylacoleo carnifex, the so-called marsupial lion.
I COVERED the volvocine algae recently and promised a post on some of the genes involved in the evolution of multicellularity in this group. We still know relatively little about the genomes of volvocine algae, but research has picked out three genes involved in the evolution of multicellularity. These are invA, glsA, and regA.
SCIENCE MAGAZINE has a busy day today. Appearing in the current issue are two important articles.
MOST OF OUR study of gene networks has been done by comparison of related species to reconstruct network evolution and by knocking out specific genes to determine what the effects of their absence are. In a new paper Isalan and coworkers try something new, reprogramming genetic networks in Escherichia coli and examining the mutants to detect viability and any possible benefits to genetic pathway modification.
LOTS OF GOOD stuff appearing in the blogosphere this past week. PZ Myers has a post on how chromosome counts change and can contribute to speciation. Emile writes about beetles that chemically enslave ants. On the paleontological side of things Darren Naish wraps up his series on British cat species and Brian Switek reports on a new study showing that elephants are descended from aquatic ancestors, with links to blog coverage at other sites.
I will post tomorrow about the results of an experimental addition of links to gene networks in bacteria and later this week a survey of some of the genes involved in developing multicellularity in volvocine algae.
IN MANY CASES even large phenotypic changes can occur without much genetic change. However, occasionally a species will be placed in a situation in which its ancestor’s genes are insufficient, and if the species possesses a gene that can be co-opted into a new role, selection can favor evolution of new genes and a corresponding radiation of species. The Pieridae family of butterflies lay their eggs on plants in the Brassicaceae family, which contains mustards and cabbages. These plants have evolved to produce compounds that are harmless in undamaged leaves, but when a leaf is damaged are converted to a potent insecticide. The pierids evolved a deactivating protein that diverts the chemical reaction to produce nontoxic products. This gene evolved shortly after the plants themselves, and would have allowed these butterflies’ larvae to feed upon these plants with little competition.
I PREVIOUSLY POSTED on this topic but the author of the article objected, feeling that his copyright had been violated. Unfortunately he has been unforthcoming about his specific objections and how I could correct the post, so I decided to write a second version. It is possible that my first post may have violated copyright by covering too much information. As I was writing my goal was to do the paper justice. It was the culmination of years of research, and is preceded by multiple other articles. It may be that in trying to be correct and thorough I included too much information. In this rewrite I have omitted a good deal of information and brought in a variety of other sources to cover the geography of the region.
I’ve mentioned worms and viruses here before, but this is the first time Trojans have earned a mention!
Yesterday I started seeing a weird error message on my computer saying something about kavo.exe not being able to run. This made me think, “Hmm, I’m not sure I want that to run. . .” Indeed, after searching for it I found out I did not!
VOLVOCINE ALGAE have a recent evolution of multicellularity, only 30-70 million years ago. This may produce a better record of the early history of this process than we have for other multicellular organisms. Metazoans and multicellular plants evolved over 550 million years ago (multicellular plants multiple times, and some suggest a very ancient history of multicellular algae over 800 million years ago). The fossil record for fungi is not very good, but unambiguous multicellular fungi were present by 500 million years ago. Bacteria meanwhile beat everyone out by evolving multicellularity several times perhaps 2-3 billion years ago. Since most multicellular organisms have a distant origin, extinction has eroded the base of their evolutionary trees so that the details of the transition are hard to extract. The volvocine algae have a much more recent history of multicellularity, and we have been able to determine much about their evolutionary history from phylogenetic studies of these algae and their relatives.
Earth’s first animal was the ocean-drifting comb jelly, not the simple sponge, according to a new find that has shocked scientists who didn’t imagine the earliest critter could be so complex.
What’s wrong with this? Basically, the study showed that the line leading to the ctenophores may have diverged before the other metazoan lineages. Stating comb jellies were the “first animal” is going to lead to people thinking that all animals evolved from comb jellies! Some other stories on this article do specify the ctenophore lineage diverged first, which is somewhat less misleading. However, this lineage diverging first does not mean modern ctenophores were there at the time. We might also consider that at that divergence the other lineage produced led eventually to humans, and we certainly were not swimming about in the ocean with the ctenophores waiting for land-living plants and animals to evolve so we could get out and dry off. Modern humans are much different from their early ancestors, and modern ctenophores may be as well.