EVIDENCE OF ORIBATID MITE DETRITIVORY IN ANTARCTICA DURING THE LATE PALEOZOIC AND MESOZOIC

Journal of Paleontology, Nov 2004 by Kellogg, Derek W, Taylor, Edith L

ABSTRACT-

Despite their importance in breaking down lignified tissue today, much is still unknown about the role of mites in the fossil record, especially with reference to the Paleozoic-Mesozoic transition. This study examines permineralized peat from three localities in the central Transantarctic Mountains, ranging in age from Permian to Jurassic, for evidence of diversity and abundance of wood-boring mites. Evidence of mites, in the form of coprolites and tunnels in wood and other tissues, was found at all three localities; the Triassic site included more than 10 times as many wood borings as the Permian site. Our results supplement prior evidence of wood-boring mites during the Mesozoic and thereby fill in the known geologic range of this plant/animal interaction.

INTRODUCTION

PLANT-ARTHROPOD INTERACTIONS play a pivotal role in the major functions of today's terrestrial ecosystems, including nutrient cycling, crucial food web links, and mulualistic relationships. These interactions range from presumably positive ones, such as pollination behaviors, to negative and so-called neutral interactions, such as herbivory and detritivory. Data suggest that such interactions have been going on for nearly as long as life has been on land (e.g., Shear, 1991; Shear and Seiden, 2001). Shear (1991 ) notes that detritivory appeared first in terrestrial ecosystems and was followed later by herbivory and more complex types of interactions. Evidence for probable wounding of plants has been described from the Devonian (e.g., Kcvan et al., 1975; Banks and Colthart, 1993) and coprolites with recognizable plant contents are known from the Late Silurian on (Edwards ct al., 1995), both of which are consistent with herbivory (Labandeira, 1998). By the Mississippian, both coprolites and instances of wounding are fairly common (Scott and Taylor, 1983).

Wood boring is another type of plant-arthropod interaction that is relatively common in the fossil record. This feeding behavior involves burrowing through the xylem of woody plants and generally has a better fossil record than some other interactions because wood tends to be preserved in greater quantity and with higher quality than many other plant tissues. Wood boring pushes the limits of the definition of plant/animal interactions, due to the question of whether or not the plants were alive during the process. Since the majority of the cells in woody tissue (i.e., secondary xylem) are dead at maturity, wood-boring activity in the fossil record can rarely be conclusively designated as detritivory or herbivory. In addition to the difficulty of defining wood-boring activity is the question of determining which organisms are responsible for the borings. Most wood-boring species of arthropods today are insects, including bees, ants, moths, termites, beetles, and flies. Oribatid mites also bore through wood, but are often less well-known in the extant fauna due to their small size and the fact that they rarely bore into wood of living plants (Wallwork, 1967).

Almost all of the wood borings described prior to the Early Permian, when the first wood-boring inseets are thought to have evolved, have been attributed to oribatid mites (e.g., Cichan and Taylor, 1982; Rex and Galtier, 1986; Chaloner et al., 1991; Goth and Wilde, 1992; Labandeira et al., 1997; Tomescu et al., 2001). There are many reports of wood boring attributed to oribatid mites in lhe Mississippian and Pennsylvanian, but the record both before and after this time period is comparatively sparse (Labandeira et al., 1997). Mite body fossils have been reported from the Early Devonian Rhynie chert (Hirst, 1923; Krivolutsky and Druk, 1986; Shear and Seiden, 2001), the Middle Devonian of Gilboa, New York (Norton et al., 1988), and possibly from the Ordovician (Bagnoli et al., 2000). By the Late Triassic, insect wood borings increase in abundance and insects continue to be prevalent agents of this syndrome to the present (Jurasky, 1932; Brues, 1936; Walker, 1938; Linck, 1949; Jarzembowski, 1990). From the Early Permian to the Late Triassic, however, there are only a few reports of mite wood borers (Goth and Wilde, 1992).

We describe here evidence of wood boring, most likely produced by oribatid mites, that supplements our current knowledge of these interactions during this period of time. Late Permian, Middle Triassic, and Middle Jurassic permineralized peats from the central Transantarctic Mountains, Antarctica, have yielded anatomically preserved stems, petioles, and roots containing tunnels and coprolites within them. Using data from the Permian and Triassic, we also examine the frequency of wood borings through time.

MATERIALS AND METHODS

All fossils occur within permineralized peat deposits in the Beardmore Glacier area, Queen Alexandra Range, central Transantarctic Mountains (Taylor et al., 1989). The Late Permian peat is from Skaar Ridge (84�49'15.8''S, 163�20'18.9''E, Buckley Island Quadrangle; Barrett and Elliot, 1973). This site occurs within the upper part of the Buckley Formation of the Beacon Supergroup (Barrett et al., 1986) and has been dated Late Permian on the basis of palynomorphs within the peat (Farabee et al., 1991).