. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. -1 Algal Expulsion Rate (d ) Figure 6. Correlation between mitotic index and rate of expulsion of S\inhn ijinium pulchrorum under control and elevated temperatures. 25°C control (D). °C experimental (A). )' = + : R~ = Figure 7. Mitotic indices of expelled algae (O) and algae remaining within host tissues (•) of different corals, following a incubation at 27°C. Error bars represent standard deviations of the mean. Discussion In algal-cnidarian symbioses, regulation
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. -1 Algal Expulsion Rate (d ) Figure 6. Correlation between mitotic index and rate of expulsion of S\inhn ijinium pulchrorum under control and elevated temperatures. 25°C control (D). °C experimental (A). )' = + : R~ = Figure 7. Mitotic indices of expelled algae (O) and algae remaining within host tissues (•) of different corals, following a incubation at 27°C. Error bars represent standard deviations of the mean. Discussion In algal-cnidarian symbioses, regulation of algal numbers is an essential part of the symbiotic relationship, both during "steady state" (Muscatine et id., 1975a, b; Trench, 1987) and during recovery of cnidarians from "bleaching events" (Gates, 1990; Hayes and Bush. 1990; Fitt et 1993; Jones and Yellowlees, 1997). The present study has established that pref- erential expulsion of dividing algae contributes to regulation of algal-cnidarian symbiosis. If dividing algal cells are more likely to be expelled from the host, net algal population growth (within their hosts) will be effectively regulated. Mitotic index of algae expelled naturally versus isolated mechanically Algae naturally expelled from Aiptasia pulchella and other Hawaiian marine cnidarians have a higher MI than the algae remaining in their hosts (Figs. 1,7). Suharsono and Brown (1992) and McCloskey et al. (1996) have also observed this phenomenon in other cnidarian species. Citing the most parsi- monious explanation, these studies suggested that the increase in algal division rates is perhaps due to a lack of host regulation in the released algae. The present study tests this hypothesis by addressing an alternative hypothesis—that the higher MI of the released algae could be explained by preferential expulsion of dividing algal cells. These two possibilities were tested by separating the algae from the host and observing any
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
