The Life History of Branchiura sowerbyi

Abstract

The life history of Branchiura sozwerbyi was studied at three locations in north-central Oklahoma. Branchiura can have a 1year or a 2-year life cycle depending upon local conditions of the habitat. Most environmental factors except temperature and oxygen apparently do not influence the life history of Branchiura. Breeding was confined to the warmer months, March through September. It appears that the organic content of the substrate has an important influence on the life cycle. In Skeleton Creek, which had the richest substrate, Branchiura had an annual life cycle. In Otter Creek and Boomer Lake, Brainchiura had a 2-year life cycle. Apparently, Branchiura is able to adapt its life cycle to local environmental conditions which would account for its wide distribution. INTRODUCTION Branchiura sowerbyi Bedd., an aquatic oligochaete, has been reported on all continents except Antarctica. It is a monospecific genus of the Tubificidae and easily recognized by dorsal and ventral gills on the posterior third of the body. Despite its widespread distribution, little is known about the biology of Branchiura. In contrast, numerous investigators have studied European tubificids extensively and assessed their value in the detection of water pollution (Aston, 1968; Brinkhurst, 1962, 1963, 1964a, b, 1965a, b; Kennedy, 1966a, b, 1969). The purpose of this study was to examine the life history of natural populations of Branchiura. COLLECTING SITES Three study sites-two streams and a reservoir-in north-central Oklahoma were selected on the basis of abundance of worms. Previous ecological and limnological studies had been done at each site (Wilhm et al., 1966; Harrel et al., 1968; Craven et al., 1969; Wade, 1968). Skeleton Creek receives large amounts of industrial and domestic effluents that originate near Enid, Okla., and much of the flow, especially in the summer, is due to these effluents. The stream bottom in Skeleton Creek is composed mainly of silt, fine sand and large amounts of decaying organic matter, especially leaves. The stream banks are fairly steep and eroded and heavily lined with trees. At the collecting site the channel width is about 6 m and the greatest depth is 2 m. Otter Creek is an unpolluted stream and the stream bed is composed mainly of fine gravel and clay. Organic materials do not accumulate in Otter Creek as much as in Skeleton Creek. The channel width at the collecting site is ca. 5 m and the depth of the water is 1 Contribution No. 481 from Zoology Department, Oklahoma State University, Stillwater 74074. 2 Present address: Department of Biology, East Texas State University, Commerce 75428.