Division time (t d ) for in situ growth measurements demonstrates thermal ecotypes of Karlodinium veneficum

• Published in: Harmful algae Vol. 131; p. 102558
• Main Authors: Broemsen, Erik L J E, Place, Allen R, Parrow, Matthew W
• Format: Journal Article
• Language: English
• Published: Netherlands 01.01.2024
• Subjects: Animals; Dinoflagellida - genetics; Ecotype; Florida; Norway; Florida; Norway; Mitotic index; In situ growth rate; Dinoflagellate; Cell cycle; Karlodinium veneficum; Harmful algal bloom; Ecotype; Cytokinesis; Duration of mitosis
• ISSN: 1568-9883; 1878-1470; 1878-1470
• DOI: 10.1016/j.hal.2023.102558

The toxic dinoflagellate Karlodinium veneficum forms fish killing blooms in temperate estuaries worldwide. These blooms have variable toxicity which may be related to bloom stage and in situ growth rates of the constituent K. veneficum cells. Measurement of in situ growth rates is challenging and methods such as the mitotic index technique require knowledge of the dynamics of cell division. In order to better understand these dynamics, we determined the duration of cell division (t ) in four geographically distinct laboratory strains of K. veneficum at three different environmentally relevant temperatures. The results demonstrated that the t value for each strain, growing at strain-specific optimal temperatures, was 1.6 ± 0.1 h. This value corresponded to a range of growth rates from 0.17 ± 0.08 d to 0.62 ± 0.07 d . Equivalent values of t spread across four geographically distinct laboratory strains and a nearly fourfold range of growth rates implies that 1.6 h represents the t value of K. veneficum. Additionally, temperature conditions yielding this value for t and the highest growth rates varied among strains, indicating cold-adapted (Norway), warm-adapted (Florida, USA), and eurythermally-adapted (Maryland, USA) strains. These differences have been apparently retained in culture over many years, indicating a conserved genetic basis that suggests distinct thermal ecotypes of the morphospecies K. veneficum. This knowledge together with the first estimate of t for K. veneficum will be useful in future field studies aimed at correlating bloom toxicity with in situ growth rate using the mitotic index technique.