Invertebrates evolution

The cause of nucleotide bias is unknown. DeSalle et al. (1987) suggested that for some unknown reason the Drosophila mitochondrial genome is functionally constrained to remain high in A s and T s such that, "at any given time the ntunber of silent sites able to fix a base substitution.. . is small because most substitutions (which would be transitions) would lower the content of adenine and thymine." Perhaps the random acquisition of a high A+T genome in invertebrate evolution resulted in the fixation of... 

Kelly, D.W., Macisaac, H.J., and Heath, D.D. (2006) Vicariance and dispersal effects on phy-logeographic structure and speciation in a widespread estuarine invertebrate. Evolution, 60 257-267. 

Aquatic organisms, such as fish and invertebrates, can excrete compounds via passive diffusion across membranes into the surrounding medium and so have a much reduced need for specialised pathways for steroid excretion. It may be that this lack of selective pressure, together with prey-predator co-evolution, has resulted in restricted biotransformation ability within these animals and their associated predators. The resultant limitations in metabolic and excretory competence makes it more likely that they will bioacciimiilate EDs, and hence they may be at greater risk of adverse effects following exposure to such chemicals. 

Stecca, B., Southwood, C. M., Gragerov, A. et al. The evolution of lipophilin genes from invertebrates to tetrapods DM-20 cannot replace proteolipid protein in CNS myelin. /. Neurosci. 20,4002-4010, 2000. 

Alkaloids take part in the life processes of some invertebrates as pheromones, inducers of sexual behaviour, and in reproduction. A case study of quinolizidine alkaloids and population changes proved that these alkaloids occur in all legume species studied but not, however, in all individuals. The distribution and frequency changes of alkaloidal and non-alkaloidal plants in populations is a direct expression of natural selection natural hybridization and micro-evolution can be considered as an evidence of current evolutionary responses by ecological and genetic systems. 

Regev, A., Lamb, M.J. and Jablonka, E. (1998) The role of DNA methylation in invertebrates developmental regulation or genome defense Molecular Biology and Evolution 1 5, 880-891. 

Now that tunicates as well have a bridgehead on land, it still would not seem reasonable to draw the intermediates between a tunicate and a pig and then revert from a pig to a whale or to construct any common ancestry via this route. Nor is it plausible to say that relaxin in the pig evolved to its present state via evolutionary pressure in the pig when the gene had already been present at the tunicate stage. This was troublesome for the traditionalist. One scientific foray into the world of marine invertebrates provided a fascinating result what would a systematic survey bring out It would, I am sure, make an even more persuasive case against evolution via descent with variation. Species and proteins do not support that scheme, and therefore our funding institutions do not support that research. 

Grosberg, R.K., The evolution of allorecognition specificity in marine invertebrates, Quart. Rev. Biol., 63, 377, 1988. 

Strathmann, R.R., Feeding and nonfeeding larval development and life-history evolution in marine invertebrates, Ann. Rev. Ecol. Syst., 16, 339, 1985. 

Lenhoff, H. M. and Heagy, W., Aquatic invertebrates model systems for the study of receptor activation and evolution of receptor proteins, Am. Rev. Pharmacol. Toxicol., 17, 243, 1977. 

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