WIDE-RANGING IMPLICATIONS FROM STUDIES OF FORAMINIFERAL BIOLOGY

Studies focusing on foram biology are providing solutions to long-standing mysteries. In 1997 Goldstein documented the antiquity of sexual reproduction characterized by release of free-swimming, biflagellated gametes. This informed collaboration with Alve in 2003; they found that propagule transport provides previously unrecognized potential for dispersal. Zygotes, produced by the union of two gametes, become tiny propagules that can be suspended and transported in the water column for extended periods, explaining, for example, how planktic forams can suddenly bloom in areas where they were previously not observed. When deposited in sediments, the propagules can remain inactive for months or years, explaining the abundance of “dwarf” tests in extreme habitats. When conditions temporarily improved, propagules could begin to grow, then be killed when unsuitable conditions returned. The ubiquity of propagules explains results using metabarcoding that benthic taxa are major contributors to foram diversity in open-ocean plankton samples. Recognition by Bernhard, Ross and others that post-propagule individuals can be inactive for extended periods also has provided solutions to long-standing enigmas, such as the ability of some taxa to survive intermittent hypoxia. And studies of sediment cores have recovered stained specimens from depths of tens of centimeters; were those specimens active or had they been buried, were dormant, and would eventually die unless mixed back into near-surface sediments? Other examples include the relatively common fossil assemblages with high proportions of large, microspheric shells. Recruitment of propagules of taxa hosting algal symbionts can occur in habitats where limited light penetration allows intervals of slow growth interspersed with intervals of darkness-induced dormancy. Such individuals might live for years, but seldom acquire resources required to asexually reproduce. A final example examines the question “What is the life span of a foram?” Between time spent as a cryptobiotic propagule and time spent dormant, potential “life span” could be years or decades. A more answerable question is: “What is the minimum generation time of a species?” The time required for an asexually-produced gamont to mature and produce gametes might be as little as days to weeks. These and other examples and implications will be presented.