TEMPERATURE RESPONSES OF DISJUNCT TEMPERATE BROWN-ALGAE INDICATE LONG-DISTANCE DISPERSAL OF MICROTHALLI ACROSS THE TROPICS

• Main Authors: PETERS, AF, BREEMAN, AM
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1992
• Subjects: BIOGEOGRAPHY; PALEOCLIMATE; PHAEOPHYCEAE; TEMPERATURE TOLERANCE; NORTH-ATLANTIC OCEAN; LIFE-HISTORY; MARINE-ALGAE; NEW-ZEALAND; DESMARESTIA PHAEOPHYCEAE; UNDARIA-PINNATIFIDA; GROWTH; TOLERANCE; SCYTOTHAMNUS; REQUIREMENTS; New Zealand; Pacific; North Atlantic
• Online Access: http://hdl.handle.net/11370/7e93469e-99f5-447a-bc3c-721dec173996; https://research.rug.nl/en/publications/temperature-responses-of-disjunct-temperate-brownalgae-indicate-longdistance-dispersal-of-microthalli-across-the-tropics(7e93469e-99f5-447a-bc3c-721dec173996).html

We examined the temperature tolerance of microscopic phases from geographically disjunct isolates of eight species or closely related, putatively conspecific taxa of temperate brown algae with disjunct distributions. Maximum within-taxon differences were small and ranged from 1.6-degrees to 4.3-degrees-C. Desmarestia aculeata and Sphaerotrichia divaricata, both with northern hemisphere amphioceanic distributions, showed little or no significant intraspecific variation between the mean upper survival limits (USL) of Atlantic and Pacific strains (delta-USL less-than-or-equal-to 1.4-degrees-C), which would agree with a relatively recent separation of the respective populations. Among the plants with bipolar distributions, there was likewise very little difference (delta-USL 0-1.1-degrees-C) between northern and southern hemisphere strains in Striaria attenuata and in the species pair Desmarestia viridis/D. willii. In Desmarestia ligulata, and in the species pairs Desmarestia firma/D. munda, Dictyosiphon foeniculaceus/D. hirsutus, and Scytothamnus australis/Scytothamnus sp., significant differences occurred, which indicate longer divergence times. Delta-USL in these cases ranged from 1.7-degrees to 2.7-degrees-C, without overlap between strains from the northern and southern hemispheres. All species that passed the equator during cooler epochs had a USL of 26-27-degrees-C, at least in some geographical isolates. The NE Asian kelp Undaria pinnatifida, which passed the equator in recent times, had a USL of 29.6-degrees-C. We hypothesize that the mechanism of spreading in the amphipolar species studied was migration of vegetative microthalli. The more unlikely alternative hypothesis of continuous populations through the tropics during a cooler epoch would imply a drop in seawater temperatures to approximately 20-degrees-C in summer and 15-degrees-C in winter, which is not supported by paleoclimatic evidence.