Evolution of the salmonid mitochondrial control region.

To explore the evolutionary nature of the salmonid mitochondrial DNA (mtDNA) control region (D-loop) and its utility for inferring phylogenies, the entire region was sequenced from all eight species of anadromous Pacific salmon, genus Oncorhynchus; the Atlantic salmon, Salmo salar; and the Arctic grayling, Thymallus arcticus. A comparison of aligned sequences demonstrates that the generally conserved sequence elements that have been previously reported for other vertebrates are maintained in these primitive teleost fishes. Results reveal a significantly nonrandom distribution of nucleotide substitutions, insertions, and deletions that suggests that portions of the salmonid D-loop may be under differential selective constraints and that most of the control region of these fishes may evolve at a rate similar to that of the remainder of their mtDNA genomes. Maximum likelihood and Fitch parsimony analyses of 9 kb of aligned salmonid sequence data give evolutionary trees of identical topology. These results are consistent with previous molecular studies of a limited number of salmonid taxa and with more comprehensive, classical analyses of salmonid evolution. Predictions from these data, based on a molecular clock assumption for the mtDNA control region, are also consistent with fossil evidence that suggests that species of Oncorhynchus could be as old as the Middle Pliocene and would have thus given rise to the extant Pacific salmon prior to about 5 or 6 million years ago.

High-speed cinematographic evidence for ultrafast feeding in antennariid anglerfishes.

Analyses by means of high-speed, light cinematography at 800 and 1000 frames per second have shown that members of the shallow-water anglerfish genus Antennarius are capable of producing an enormous suction pressure for prey capture by means of an extraordinarily rapid expansion of the buccal and opercular cavities. Prey is totally engulfed at speeds considerably greater than those recorded for any other fish. The structural adaptations responsible for this rapid prey engulfment provide anglerfishes with one of the fastest known vertebrate feeding mechanisms.

The compleat angler: aggressive mimicry in an antennariid anglerfish.

A case of aggressive mimicry is described in which an anglerfish of the genus Antennarius (order Lophiiformes) utilizes a lure that mimics a small fish. The lure provides not only a highly attractive visual cue but presumably also a low-frequency pressure stimulus for potential prey with a minimum of energy expenditure.