The life spans of eukaryotes can be determinate or indeterminate. Examples of the latter are found from sponges to lobsters to rainbow trout that reproduce and grow until disease, predation, or environmental circumstances end their lives. Their tissues continually express the enzyme telomerase, keeping sufficient telomeres on the end of their chromosomes to avoid individual cell senescence and subsequent death. Bay scallops, on the other hand, have a well-defined life span, generally between 18–22 mo in the northeastern USA, and reproduce usually once. Argopecten irradians irradians (L.) has been found to possess fewer telomeres than a close relative, Argopecten purpuratus (L.), a cold water species found along the coasts of Peru and Chile that can live to 7 y or more. A. purpuratus contains significantly more telomeres than A. irradians in their respective tissues. It is proposed that the short lifespan of A. irradians may not be a selective advantage, but rather because of an evolutionary loss of telomeres through Robertsonian fusion and extensive chromosome arm loss. Evidence for this is seen by the bay scallop doubling its weight postspawning and storing nutrients in the form of carbohydrates, lipids, and protein for the upcoming winter and the subsequent initiation of gametogenesis in the spring. However, they rarely survive to complete a second reproductive event. This life history suggests that A. irradians is not a semelparous species (one-time reproduction) but rather an example of interrupted iteroparity (repeated reproduction) caused by losses in its genome. Adding telomeres to the ends of chromosomes of A. irradians may extend the life span of this species, possibly permitting several reproductive seasons ahead. In years when larval recruitment failure occurs without concomitant loss of adult spawners, local populations could recover in as little as a single season.
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Vol. 26 • No. 2