%ASmith, Chad [Department of Integrative Biology University of Texas at Austin Austin Texas]%AWeber, Jesse [Department of Integrative Biology University of Texas at Austin Austin Texas, Department of Biological Sciences University of Alaska Anchorage Alaska]%AMikheyev, Alexander [Okinawa Institute of Science &, Technology Kunigami Japan]%ARoces, Flavio [Department of Behavioral Physiology and Sociobiology, Biozentrum University of Würzburg Würzburg Germany]%ABollazzi, Martin [Section of Entomology Universidad de la República Montevideo Uruguay]%AKellner, Katrin [Department of Biology University of Texas at Tyler Tyler Texas]%ASeal, Jon [Department of Biology University of Texas at Tyler Tyler Texas]%AMueller, Ulrich [Department of Integrative Biology University of Texas at Austin Austin Texas]%BJournal Name: Molecular Ecology; Journal Volume: 28; Journal Issue: 11; Related Information: CHORUS Timestamp: 2023-09-10 12:01:35 %D2019%IWiley-Blackwell %JJournal Name: Molecular Ecology; Journal Volume: 28; Journal Issue: 11; Related Information: CHORUS Timestamp: 2023-09-10 12:01:35 %K %MOSTI ID: 10372071 %PMedium: X %TLandscape genomics of an obligate mutualism: Concordant and discordant population structures between the leafcutter ant Atta texana and its two main fungal symbiont types %XAbstract

To explore landscape genomics at the range limit of an obligate mutualism, we use genotyping‐by‐sequencing (ddRADseq) to quantify population structure and the effect of host–symbiont interactions between the northernmost fungus‐farming leafcutter antAtta texanaand its two main types of cultivated fungus. Genome‐wide differentiation between ants associated with either of the two fungal types is of the same order of magnitude as differentiation associated with temperature and precipitation across the ant's entire range, suggesting that specific ant–fungus genome–genome combinations may have been favoured by selection. For the ant hosts, we found a broad cline of genetic structure across the range, and a reduction of genetic diversity along the axis of range expansion towards the range margin. This population‐genetic structure was concordant between the ants and one cultivar type (M‐fungi, concordant clines) but discordant for the other cultivar type (T‐fungi). Discordance in population‐genetic structures between ant hosts and a fungal symbiont is surprising because the ant farmers codisperse with their vertically transmitted fungal symbionts. Discordance implies that (a) the fungi disperse also through between‐nest horizontal transfer or other unknown mechanisms, and (b) genetic drift and gene flow can differ in magnitude between each partner and between different ant–fungus combinations. Together, these findings imply that variation in the strength of drift and gene flow experienced by each mutualistic partner affects adaptation to environmental stress at the range margin, and genome–genome interactions between host and symbiont influence adaptive genetic differentiation of the host during range evolution in this obligate mutualism.

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