| Most organisms with indeterminate growth are able to repeatedly shrink and regrow under fluctuating environmental conditions. As fecundity in these organisms is generally a function of body volume, a change in size could have significant reproductive and demographic consequences. Opportunistic species may be especially susceptible to the effects of degrowth and regrowth because they generally do not possess extensive energy reserves and readily consume their own structural proteins during periods of food limitation. In this study, the individual and population level consequences of degrowth and regrowth were examined in the opportunistic polychaete Capitella sp. I. Worms repeatedly degrow and regrow along the same projected curve, although degrowth does not appear to be the physiological reverse of growth. Regrown worms attempt to compensate for time lost to reproduction by growing faster as juveniles and depositing eggs at a smaller body volume. Reproductive output is decreased in regrown worms relative to normally grown worms, possibly as a result of tissue damage incurred during starvation. Although these results suggest that regrown Capitella sp. I would be at a significant evolutionary disadvantage in a patchy environment, demographic analyses indicate that regrowth may actually represent a mechanism of long term population maintenance. Population models which incorporate degrowth and subsequent regrowth eventually stabilize at low carrying capacities; in contrast, models which incorporate only normal growth explode and go extinct within a few generations. These results provide an evolutionary explanation for the retention of the degrowth/regrowth ability in Capitella sp. I and furnish a mechanism for the nearly universal distribution of this species in nearshore marine sediments. |
