Evolutionary Relationships of the Hawaiian and North American Telmatogeton (Insecta; Diptera: Chironomidae)

Species of Telmatogeton and the closely related genus Paraclunio generally live on the rocky shores of the intertidal zone. Species of Telmatogeton have evolved from the marine environment into torrential freshwater streams of the Hawaiian Islands . An analysis of the banding sequences of the polytene chromosomes of species of Telmatogeton and Paraclunio from the Hawaiian Islands and North America suggests that there were at least two separate invasions from the marine to freshwater environments. One is through the marine species T. japonicus to an undescribed freshwater species found on east Maui . The other invasion requires a marine hypothetical species that gave rise to the Hawaiian freshwater species T. abnormis and T. torrenticola. SPECIES OF THE FAMILY Chironomidae are generally found in aquatic or semiaquatic environments. Species in only 13 genera of chironomids, including the Telmatogeton and Paraclunio, occupy the marine environment (Hashimoto 1976, Sublette and Wirth 1980). The life cycle of most species of Telmatogeton and Paraclunio is spent on the rocky shores of the intertidal zone. In the Hawaiian Islands , species of Telmatogeton have evolved from the marine environment into torrential freshwater streams (Wirth 1947). Wirth (1947, 1959) describes the discovery and naming of species of the Telmatogeton and Paraclunio . The genus Telmatogeton was established by J. R. Schiner in 1866, and the first species, T. sancti-pauli, was described by him in 1868 from specimens collected on St. Paul Island in the Indian Ocean . D. W. Coquillett described the second species, T. alaskensis, from specimens collected from Yakutat, Alaska, during the Harriman Expedition of 1899. The first Hawaiian freshwater species was described by F. W. Terry in 1913. J. J. Kieffer established the marine genus Paraclunio in 1911 for P. trilobatus, collected on the coast of California, and in 1915, J. R. Malloch moved T. alaskensis to the genus Paraclunio. The major morpholog1 Portland State University, Department of Biology, P.O. Box 751, Portland, Oregon 97207. 56 ical feature distinguishing the genera is a sexual dimorphism of the front femur and tibia . These structures are narrow and undifferentiated in males and females of Telmatogeton and in females of Paraclunio. The front femur of Paraclunio males is broad, and an angular projection of the distal portion of the femur fits into a corresponding notch in the base of the tibia. Because of the morphological similarity of the two genera, the genus Paraclunio should be synonymized with the Telmatogeton (Peter Cranston, personal communication). The Telmatogeton and Paraclunio are thus essentially treated together in this discussion. The natural history and ecology of the Telmatogeton and Paraclunio are described by Kronberg (1986), Morley and Ring (1972), and Robles (1982). Two important points relative to the current discussion are features that lead to the isolation of populations and the adaptation of species to a severe environment. Adults of both marine and freshwater species exhibit a peculiar swarming behavior; they are generally seen running about on intertidal rocks and on stream banks seeking mates. Adults are not strong fliers and thus may have limited vagility. Adults of the marine species are believed to be short-lived ; they emerge on an outgoing tide, mate and lay eggs, and are washed out to sea on the incoming tide. Eggs of the marine species are laid singly in rock Evolutionary Relationships of Telmat ogeton-rt-aswws i« 57 crevices, and larvae feed by grazing on the , thin film of algae growing on the rock surfaces and on macroscopic green and red algae. Larvae build silky tubes from their salivary gland secretion; pupation occurs in reinforced tubes . The tubes protect larvae and pupae of the marine species from wave action at high tide and predation and desiccation at low tide, and thus allow larvae and pupae of the freshwater species to live in torrential streams and waterfalls in the Hawaiian Islands . In 1971, Hampton Carson discovered the Hawaiian Telmatogeton as a material suitable for chromosome analysis (personal communication). He found the giant polytene chromosomes of the larval salivary glands to be well banded and likely to give information relative to the evolution of the freshwater species. This proved to be true , for Newman (1977) established a standard band map and proposed a pro visional set of evolutionary relationships for the Hawaiian freshwater Telmatogeton. All the species examined to date have polytene chromosomes suitable for detailed band ana lysis. Each species has six long chromosome ' arms with well-developed bands and a single unbanded short arm . The six long arms were designated by the letters A-F and the short arm by the letter G. A sequence of bands within arms A-F common to most of the Hawaiian freshwater species was chosen as the Telmatogeton standard (Newman 1977). The chromosome arms of most of the species examined have the standard sequence or differ from it by paracentric inversions . A paracentric inversion is a chromosomal mutation in which a series of bands that does not contain the centromere is rotated 180 • The specific break points of the inversion may be determined by comparing the inverted and standard band sequences. Inversions are designated by giving the arm letter of the inversion with a subscript arabic number. An inversion may be homozygous in all animals of a population or species; that is, it is fixed or it may exist along with the standard as a polymorphism. In some cases, the rearrangement of bands in a portion or even an entire arm may be so complicated by multiple inversions that it cannot be described in terms of simple inversions. These are referred to as complex portions of an arm or complex arms . Chromosome numbers in the Telmatogeton and Paraclunio range from n = 7 to n = 3/4 (Newman 1977). It has been proposed that the primitive number is n = 7 and that the other numbers are derived by centric fusions. Each centric fusion reduces the chromosome number by 1. Telmatogeton hirtus (n = 3/4) has an XY1Y z sex chromosome system that may be seen in both polytene and nonpolytene chromosomes . Telmatogeton abnormis (n = 4) has an XY chromosome system that may be seen only in the polytene chromosomes. Other species do not have differentiated sex chromosomes. Inversion sequences have been used to gain insight into possible evolutionary relationships among species. Species that share inversions are more closely related than species that do not share inversions . Carson (reviewed in Carson and Yoon 1982) used this type of analysis to determine the evolutionary relationships of over 100 species of Hawaiian Drosophila . Similar techniques are used here to propose a set of relationships in which there were at least two separate invasions of marine Telmatogeton into fresh water in the Hawaiian Islands . MATERIALS AND METHODS The giant banded polytene chromosomes were examined from cells of the salivary gland of fourth instar larvae fixed in acetic alcohol and stained in lactoacetic orcein. Nonpolytene chromosomes for the determination of chromosome numbers were derived from lactoacetic orcein squashes of testes and other developing larval tissues (details in Newman 1977).