Thermal autecology describes the occurrence patterns of four benthic diatoms in McMurdo Dry Valley streams.

Benthic microbial mats in the glacial-fed meltwater streams are hotspots of productivity in the McMurdo Dry Valleys (MDV), Antarctica. Benthic diatoms are common in these mats and the >45 primarily endemic taxa represent the most diverse group of eukaryotes in the MDV. In this harsh polar desert, streams are thermally dynamic with daily water temperatures varying 6-9 °C and daily maximum temperatures as high as 15 °C. Stream temperature may play a role in determining growth rates and survival strategies. To understand taxon-specific adaptations to their environment, we measured the growth rates of unialgal cultures of four diatom taxa ( Psammothidium papilio, Hantzschia abundans, Hantzschia amphioxys, and Hantzschia amphioxys f . muelleri) under three temperature conditions (7.6, 10, and 15 °C) that were representative of maximum daily stream temperatures. We found that P. papilio exhibited a constant growth rate across the full temperature range; this species is most common in streams that begin to flow early in the summer and with less variable thermal regimes. Growth rates for H. abundans were greatest at 15 °C, but showed a non-linear relationship with temperature. H. amphioxys f . muelleri grew faster than the other taxa studied and thrived at 10 °C. Hantzschia amphioxys grew only at the two lower temperatures. These results aligned with the observed relationships between each taxon's relative abundance and stream temperatures in the long-term record maintained by the MDV Long-Term Ecological Research program. Overall, our observations suggest that differences in thermal optima may be one factor contributing to and maintaining the diversity of benthic diatom flora in the MDV. [ABSTRACT FROM AUTHOR]