Environmental conditions modulate hermaphroditic pathways in Salpa thompsoni near the Western Antarctic Peninsula

Field observations during summer-fall of 2018 in the Antarctic Peninsula region provided the first morphological evidence that under certain environmental conditions, Salpa thompsoni blastozooid development can deviate from its traditional sequential protogynous hermaphroditism (SPH). Early male testis development at female blastozooid stages points to a wide-spread overlapping protogynous hermaphroditism (OPH) in regions where warm Antarctic Circumpolar Current waters mix with colder Antarctic Coastal waters. Our findings highlight the importance of the environmental setting in determining the reproductive pathway in S. thompsoni. OPH was observed in cooler and less productive waters, while SPH occured in both warmer and cooler productive waters. It appears that food availability may offset the effect of decreasing water temperatures for warm-water S. thompsoni reproductive development. It is plausible that OPH may permit the establishment of the S. thompsoni populations in the high Antarctic under the warming trend in the Southern Ocean by allowing for more efficient reproduction.