AUTHOR=Martinez-Alarcón Diana , Held Christoph , Harms Lars , Auel Holger , Hagen Wilhelm , Havermans Charlotte 

TITLE=Race to the poles: the thermal response of the transcriptome of two range-expanding pelagic amphipod species

JOURNAL=Frontiers in Marine Science

VOLUME=11

YEAR=2024

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1336024

DOI=10.3389/fmars.2024.1336024

ISSN=2296-7745

ABSTRACT=<sec><title>Introduction</title><p>Hyperiid amphipods of the genus <italic>Themisto</italic> are a key polar zooplankton group in terms of biomass and play an important role as prey for higher trophic levels. They are prone to undergo changes in abundance and distribution in the course of the ongoing environmental changes. In the Southern Ocean, <italic>Themisto gaudichaudii</italic> is predicted to expand its distribution poleward. In the Arctic, the boreal-Atlantic <italic>T. abyssorum</italic> increases in abundance, resulting in an increased competition with a genuine polar congener. It is not known, however, whether <italic>T. gaudichaudii</italic> and <italic>T. abyssorum</italic> have the potential to efficiently adapt to changing water temperatures at their current distribution range or whether they will be shifting their ranges poleward.</p></sec><sec><title>Methods</title><p>We exposed the two <italic>Themisto</italic> species from different geographic populations to temperature-change experiments, a cold treatment and a heat-shock treatment. After that, we carried out transcriptome sequencing to compare gene expression patterns in the different treatments and species.</p></sec><sec><title>Results</title><p>We show that under similar heat conditions, <italic>T. gaudichaudii</italic> differentially expressed more genes (26-fold change) than <italic>T. abyssorum</italic>. Furthermore, we observed qualitative differences between genetic clusters in <italic>T. gaudichaudii</italic>.</p></sec><sec><title>Discussion</title><p>The differences observed between genetic clusters in <italic>T. gaudichaudii</italic> suggest that evolutionary divergence can be linked to changes in the regulatory pathways involved in temperature stress. These could influence the capacity of each genetic cluster to cope differently with temperature changes. In contrast to its congeneric species, <italic>T. abyssorum</italic> showed a pronounced adaptive flexibility to thermal stress; it appears to have the ability to continue its poleward expansion but may also cope with increasing temperatures in its current environments. Our findings contribute to understand the response of two range-shifting <italic>Themisto</italic> species to thermal stress in view of the environmental gradients they encounter throughout their current or future distribution ranges.</p></sec>