Bioerosion of siliceous rocks driven by rock-boring freshwater insects

Macrobioerosion of mineral substrates in fresh water is a little-known geological process. Two examples of rock-boring bivalve molluscs were recently described from freshwater environments. To the best of our knowledge, rock-boring freshwater insects were previously unknown. Here, we report on the discovery of insect larvae boring into submerged siltstone (aleurolite) rocks in tropical Asia. These larvae belong to a new mayfly species and perform their borings using enlarged mandibles. Their traces represent a horizontally oriented, tunnel-like macroboring with two apertures. To date, only three rock-boring animals are known to occur in fresh water globally: a mayfly, a piddock, and a shipworm. All the three species originated within primarily wood-boring clades, indicating a simplified evolutionary shift from wood to hardground substrate based on a set of morphological and anatomical preadaptations evolved in wood borers (e.g., massive larval mandibular tusks in mayflies and specific body, shell, and muscle structure in bivalves)

Discovery of a silicate rock-boring organism and macrobioerosion in fresh water

International audienceMacrobioerosion is a common process in marine ecosystems. Many types of rock-boring organisms break down hard substrates, particularly carbonate rocks and calcareous structures such as dead corals and shells. In paleontology, the presence of rocks with boreholes and fossil macroboring assemblage members is one of the primary diagnostic features of shallow marine paleo-environments. Here we describe a silicate rock-boring organism and an associated community in submerged siltstone rock outcrops in Kaladan River, Myanmar. The rock-boring mussel Lignopholas fluminalis is a close relative of the marine piddocks, and its borings belong to the ichnospecies Gastrochaenolites anauchen. The neotectonic uplift of the area leading to gradual decrease of the sea level with subsequent shift from estuarine to freshwater environment was the most likely driver for the origin of this community. Our findings highlight that rocks with macroborings are not an exclusive indicator of marine paleo-ecosystems, but may also reflect freshwater habitats

Discovery of a silicate rock-boring organism and macrobioerosion in fresh water

Macrobioerosion is a common process in marine ecosystems. Many types of rock-boring organisms break down hard substrates, particularly carbonate rocks and calcareous structures such as dead corals and shells. In paleontology, the presence of rocks with boreholes and fossil macroboring assemblage members is one of the primary diagnostic features of shallow marine paleo-environments. Here we describe a silicate rock-boring organism and an associated community in submerged siltstone rock outcrops in Kaladan River, Myanmar. The rock-boring mussel Lignopholas fluminalis is a close relative of the marine piddocks, and its borings belong to the ichnospecies Gastrochaenolites anauchen. The neotectonic uplift of the area leading to gradual decrease of the sea level with subsequent shift from estuarine to freshwater environment was the most likely driver for the origin of this community. Our findings highlight that rocks with macroborings are not an exclusive indicator of marine paleo-ecosystems, but may also reflect freshwater habitats

Shells of <i>Margaritifera togakushiensis</i> (Kondo and Kobayashi, 2005) and <i>Margaritifera middendorffi</i> (Rosén, 1926).

<p>A—Holotype of <i>M</i>. <i>togakushiensis</i> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.ref018" target="_blank">18</a>]: 137, figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.g005" target="_blank">5</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.g008" target="_blank">8</a>. B—Lectotype of <i>M</i>. <i>middendorffi</i> (ZISP: no. 6). Photo by I. V. Vikhrev. Scale bar—2 cm.</p

Map of location of the field study areas.

<p>1—Kamchatka Peninsula (2012, I. Bolotov, Y. Bespalaya, I. Vikhrev, M. Gofarov), 2—Central Sakhalin (2012, same team), 3—southern Sakhalin (2011–2012, same team & Y. Kolosova, O. Aksenova), 4—Kunashir Island (2011, same team & Y. Kolosova, O. Aksenova), 5—Primorye (2012, same team), 6—Transbaikalia (2004–2011, O.K. Klishko). Data on the studied river sites are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s001" target="_blank">S1</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s004" target="_blank">S4</a> Tables.</p

Shells of <i>Margaritifera dahurica</i> (Middendorff, 1850).

<p>A—Lectotype (ZISP: no. 7a). B—specimen from Komarovka River, Razdolnaya River basin, Primorye. Photos by I.V. Vikhrev. Scale bar—2 cm.</p

Range map of <i>Margaritifera middendorffi</i> (Rosén, 1926) and <i>Margaritifera togakushiensis</i> (Kondo and Kobayashi, 2005).

<p>Circles—<i>M</i>. <i>middendorffi</i> locations, squares—<i>M</i>. <i>togakushiensis</i> locations. Green circles and squares are representing recent viable populations (observed since 2000), white circles—old records (until 2001), yellow squares—records without exact dates. Grey areas indicate approximate modern species ranges (showing only the large river systems). Species locality numbers on the map correspond to numbers in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s003" target="_blank">S3 Table</a>.</p

Range map of <i>Margaritifera laevis</i> (Haas, 1910).

<p>Green circles are representing recent viable populations (observed since 2000), white circles—old records (until 2001), yellow circles—records without exact dates. Grey areas indicate the approximate modern species range (showing only the large river systems). Species locality numbers on the map correspond to numbers in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s004" target="_blank">S4 Table</a>.</p