The decline of ranid frog species native to western North America is a pattern alluded to by many workers. We review the factors cited as having caused these declines, using, as primary examples, some of the ranid species native to California. We present explicit statements of four major alternative hypotheses: 1) bullfrog introduction, 2) habitat alteration, 3) predation by intro- duced fishes, and 4) commercial exploitation. Additionally, we review data relating to four other factors suggested as having caused declines: 1) toxicants, 2) pathogens and parasites, 3) acid rain, and 4) catastrophic mortality. Notably, data do not exist that suggest that the often-invoked bullfrog hypothesis is most compelling. Some factors, like commercial exploitation, are untestable because the putative causal conditions no longer exist, whereas others, like catastrophic mortality, are dif- ficult to test because of their unpredictability. Perhaps the most neglected but potentially important alternative is predation by introduced fishes. Existing data cannot distinguish adequately among three major testable alternatives: bullfrogs, habitat alteration, and introduced fish predation. In the absence of satisfactory data, the chronological priority of fish introductions over those of bullfrogs and the greater access fish may have to earlier ranid life stages make the fish predation hypothesis more compelling. Several alternative hypotheses are confounded because existing correlative data support at least two alternatives equally well. Manipulations of testable alternatives are imperative to distinguish causal factors. Over a century ago, Lockington (1879) observed that populations of Rana au- rora in the vicinity of San Francisco were diminishing. Since that time, investi- gators have repeatedly suggested that nearly every ranid frog species native to western North America has experi-

Decline of Ranid Frog Species in Western North America: Are Bullfrogs (Rana catesbeiana) Responsible?

Cercariae, like miracidia, are non-parasitic larval stages implicated in the life cycle of all trematodes for the host-to-host parasite transmission. Almost all cercariae are free-living in the external environment. With a few exceptions (cercariae of Halipegus occidualis (Halipegidae) can live several months, Shostak & Esch, 1990a), cercariae have a short active life during which they do not feed, living on accumulated reserves. Most cercariae encyst as metacercariae in second intermediate hosts which are prey of the definitive host; in certain species, the interruption of the active life is achieved by an encystment in the external environment (or a simple immobile waiting strategy in a few species). In some two-host life cycles, the cercariae develop into adults after penetration (this is the case for various species causing human schistosomiasis). Some cercariae do not leave the mollusc which must then be ingested by the definitive host.

Behaviours in trematode cercariae that enhance parasite transmission: patterns and processes.

A phylogenetic study of 8 North American and European species of frog lung flukes belonging to Haematoloechus was conducted using approximately 850 to 1,000 bases of the internal transcribed spacer region (ITS 1 + 5.8S + ITS 2) and 1,250 bases of the large subunit (LSU) of the nuclear ribosomal DNA. Adequate phylogenetic resolution could not be obtained from 5.8S or ITS 2 data. Analysis of ITS 1 data produced 2 equally parsimonious trees that differed only in the position of Haematoloechus breviplexus relative to H. medioplexus and H. varioplexus. Single, identical trees were produced by analysis of both LSU sequence data and a data set comprised of all ITS and LSU data. All trees demonstrated 3 distinct evolutionary lineages within the Holarctic Haematoloechus examined. The results confirmed the taxonomic validity of H. abbreviatus and demonstrated that the presence or absence of extracecal uterine loops is not a character meaningful to the recognition of evolutionary lineages or differentiation of gener...

Phylogenetic and biogeographical relationships among some holarctic frog lung flukes (digenea: haematoloechidae)

Physiological analyses of the behaviour of several cercarial species which actively find and invade their hosts have revealed very complex sequences of behaviour patterns and responses to very different stimuli from the environment and the host. A result of these physiological studies is that the behaviour patterns of each of the species investigated are surprisingly individual. The behavioural patterns of host-finding of those species analysed in some detail reveal profound adaptations to maximize transmission success. This can be demonstrated for movement patterns during swimming, for responses to environmental conditions such as gravity, light and temperature, for responses to stimuli emanating from the host such as shadows, water turbulence and chemical compounds and especially for the responses after contact with the host. The behaviour patterns can be interpreted as adaptations to: (1) dispersal by leaving the habitat of the snail intermediate host and distribution within the area; (2) long survival by energy saving swimming behaviour, by avoiding responses to inappropriate stimuli, by selecting favourable microhabitats and probably by avoiding predation; (3) finding and invading particular host types by selecting microhabitats frequented by the hosts and responding to sequences of specific stimuli emanating from the hosts.

Physiological analyses of host-finding behaviour in trematode cercariae : adaptations for transmission success

Parasites play an important role in the structure and function of arctic ecosystems, systems that are currently experiencing an unprecedented rate of change due to various anthropogenic perturbations, including climate change. Ungulates such as muskoxen, caribou, moose and Dall's sheep are also important components of northern ecosystems and are a source of food and income, as well as a focus for maintenance of cultural traditions, for northerners. Parasites of ungulates can influence host health, population dynamics and the quality, quantity and safety of meat and other products of animal origin consumed by people. In this article, we provide a contemporary view of the diversity of nematode, cestode, trematode, protozoan and arthropod parasites of ungulates in arctic and subarctic North America and Greenland. We explore the intricate associations among host and parasite assemblages and identify key issues and gaps in knowledge that emerge in a regime of accelerating environmental transition.

http://phthiraptera.info/sites/phthiraptera.info/files/94945.pdf

Parasites in ungulates of Arctic North America and Greenland: a view of contemporary diversity, ecology, and impact in a world under change.

Previous experimental and field studies have shown that variations within the genus Haematoloechus may result from differences in age and degree of maturity, extent of crowding, species of host, and other factors.Based on these observations, only 6 of the 15 previously known species from Canada and the United States are considered valid. The valid species and their synonyms are as follows: Haematoloechus longiplexus Stafford, 1902; H. breviplexus Stafford, 1902; H. varioplexus Stafford, 1902 (= H. parviplexus, = H. buttensis, = H. similiplexus, = H. floedae, and H. uniplexus); H. kernensis Ingles, 1932 (= H. tumidus); H. medioplexus Stafford, 1902; and H. complexus (Seely, 1906) (= H. coloradensis, = H. confusus, = H. oxyorchis).The existence of three species groups is hypothesized. Haematoloechus longiplexus and H. breviplexus constitute one group, characterized by little geographical variation and a narrow host range. They are typically parasites of Rana catesbeiana and R. clamitans. Haematoloechus vari...

A revision of species of the genus Haematoloechus Looss, 1899 (Trematoda: Haematoloechidae) from Canada and the United States

Oochoristica javaensis n. sp. is described from the intestines of geckoes, Gehyra mutilata (type host), Cosymbotus platyurus, and Hemidactylus frenatus from Bogor, Java, Indonesia. The seven specie...

Oochoristica javaensis n. sp. (Eucestoda: Linstowiidae) from Gehyra mutilata and other gekkonid lizards (Lacertilia: Gekkonidae) from Java, Indonesia

Acanthocephalus bufonis (Shipley, 1903) Southwell and Macfie, 1925 is redescribed on the basis of specimens collected from the black-spotted toad, Bufo melanostictus Schneider, 1799, from Indonesia...

A redescription of Acanthocephalus bufonis (Shipley, 1903) Southwell and Macfie, 1925 (Acanthocephala: Echinorhynchidae) from the black-spotted toad, Bufo melanostictus, from Bogor, Indonesia

The life cycle of Haematoloechus buttensis was maintained in the laboratory by using the usual natural hosts: Rana pretiosa, Physa nuttalli, and Ischnura perparva. Morphological variations in important taxonomic characters were studied and compared with those found when one of the usual hosts was replaced by a sympatric, but usually uninfected, host. In all, six species of Amphibia, three of Insecta, and three Mollusca were used.The effect of host size, sex, and ambient temperature was also studied using R. pretiosa as definitive host.The most reliable taxonomic characters were determined to be the sucker ratio, egg size of 21-day-old and older worms, position of the testes, and the anterior extent of the extracaecal uterine loops.The unreliability of other characters and their prior use as species-specific features suggests that many of the currently recognized species of Haematoloechus are not valid.

Host-induced variations in Haematoloechus buttensis (Trematoda: Haematoloechidae).

A total of 2162 lung flukes constituting eight species of Haematoloechus from freshly killed frogs in addition to 422 preserved specimens borrowed from private and institutional collections were ex...

Murray J. Kennedy

Papers

A revision of species of the genus Haematoloechus Looss, 1899 (Trematoda: Haematoloechidae) from Canada and the United States

Oochoristica javaensis n. sp. (Eucestoda: Linstowiidae) from Gehyra mutilata and other gekkonid lizards (Lacertilia: Gekkonidae) from Java, Indonesia

A redescription of Acanthocephalus bufonis (Shipley, 1903) Southwell and Macfie, 1925 (Acanthocephala: Echinorhynchidae) from the black-spotted toad, Bufo melanostictus, from Bogor, Indonesia

Host-induced variations in Haematoloechus buttensis (Trematoda: Haematoloechidae).

Geographical variation in some representatives of Haematoloechus Looss, 1899 (Trematoda:Haematoloechidae) from Canada and the United States