Gradients in density variations of small rodents: the importance of latitude and snow cover

Summary Microtine rodents are known to show extreme population variations (cycles) but non-cyclic populations have also been recognized during recent years. The cyclic populations have been widely thought to be regulated by intrinsic mechanisms. However, such predictions for cyclic populations are usually not applicable to non-cyclic ones and extrinsic factors may have to be included in any explanation.A hypothesis that the degree of fluctuations in small rodent numbers is related to the sustainable number of generalist predators was tested on mainly literature data by computing indices of cyclicity for local populations. These indices were related to latitude and snow cover (two measures) as these variables will affect the amount of alternative prey available for these generalists. Within Fennoscandia such indices for Clethrionomys glareolus and Microtus agrestis were clearly positively related to latitude and snow cover. The fraction of populations with summer declines in numbers, characterizing highly cyclic populations, increased in the same way. Cyclicity indices in Great Britain were similar to those in southern Fennoscandia, both areas being poor in snow, but were higher at the same latitudes in eastern Europe with more snow. Indices of density variations were generally low in North American Clethrionomys species and very variable in Microtus species.The gradients observed and differences between continents are interpreted as due to microtine-vegetation interactions in northern European areas poor in generalist predators but with important small mustelid predation, and to similar snowshoe hare-vegetation interactions in mainly Canada-Alaska, where small rodents may serve as alternative prey for numerically fluctuating hare predators, at least in the forests. Western European microtine populations, and probably many others, seem to be regulated by generalist predators.     

Molecular systematics and evolutionary history of catenotaeniid cestodes (Cyclophyllidea)

Phylogenetic relationships, evolutionary history and systematics of tapeworms of the family Catenotaeniidae were studied using nucleotide sequences of the partial 28S nuclear rDNA (ca. 1,500 bp) and mitochondrial 12S–16S DNA (ca. 820 bp) genes. The tapeworm material consists of 29 species, including type species of the genera Catenotaenia Janicki, 1904, Catenotaenioides Haukisalmi, Hardman and Henttonen, 2010, Pseudocatenotaenia Tenora, Mas‐Coma, Murai and Feliu, 1980, Skrjabinotaenia Akhumyan, 1946, Meggittina Lynsdale, 1953, and Hemicatenotaenia Tenora, 1977. The basal phylogenetic structure of the Catenotaeniidae remains unresolved, but it is shown that most of the catenotaeniids in Eurasia and Africa comprise a large clade represented by species of Catenotaenia, Catenotaenioides, Skrjabinotaenia and Meggittina, parasitizing murid, cricetid, nesomyid and sciurid rodents. The results suggest that the divergence and early radiation of this clade have occurred in murid rodents (represented by Apodemus spp. and Mus musculus in the present material) in western Eurasia, followed by colonization of Africa, most likely independently of the colonization of their murid hosts between these continents. There is very little evidence of cophylogeny between hosts and parasites, suggesting that host transfers have played a major role in the divergence of catenotaeniids. In Africa, catenotaeniids have radiated in other murid and nesomyid rodents, and later colonized Madagascar and recolonized Eurasia. The results also show that the subfamily Skrjabinotaeniinae (including Skrjabinotaenia and Meggittina) is monophyletic, but the Catenotaeniinae (including Catenotaenia, Catenotaenioides, Pseudocatenotaenia and Hemicatenotaenia) is clearly non‐monophyletic. In addition, the genera Catenotaenia and Skrjabinotaenia were both found to be non‐monophyletic. Based on the phylogenetic and morphological evidence, several taxonomical changes, mainly new combinations, are proposed. Overall, the present results suggest that the family Catenotaeniidae is in need of major systematic revision.     

Molecular systematics and Holarctic phylogeography of cestodes of the genus Anoplocephaloides Baer, 1923 s. s. (Cyclophyllidea,Anoplocephalidae) in lemmings (Lemmus,Synaptomys)

The present molecular systematic and phylogeographic analysis is based on sequences of cytochrome c oxidase subunit 1 (cox1) (mtDNA) and 28S ribosomal DNA and includes 59 isolates of cestodes of the genus Anoplocephaloides Baer, 1923 s. s. (Cyclophyllidea, Anoplocephalidae) from arvicoline rodents (lemmings and voles) in the Holarctic region. The emphasis is on Anoplocephaloides lemmi (Rausch 1952) parasitizing Lemmus trimucronatus and Lemmus sibiricus in the northern parts of North America and Arctic coast of Siberia, and Anoplocephaloides kontrimavichusi (Rausch 1976) parasitizing Synaptomys borealis in Alaska and British Columbia. The cox1 data, 28S data and their concatenated data all suggest that A. lemmi and A. kontrimavichusi are both non‐monophyletic, each consisting of two separate, well‐defined clades, that is independent species. As an example, the sister group of the clade 1 of A. lemmi, evidently representing the ‘type clade’ of this species, is the clade 1 of A. kontrimavichusi. For A. kontrimavichusi, it is not known which one is the type clade. There is also fairly strong evidence for the non‐monophyly of Anoplocephaloides dentata (Galli‐Valerio, 1905)‐like species, although an earlier phylogeny suggested that this multispecies assemblage may be monophyletic. The results suggest a deep phylogenetic codivergence of Lemmus spp. and A. lemmi, primarily separating the two largely allopatric host and parasite species at the Kolyma River in east Siberia. There are also two allopatric sublineages within each main clade/species of A. lemmi and Lemmus, but the present distributions of the sublineages within the eastern L. trimucronatus and clade 1 of A. lemmi are not concordant. This discrepancy may be most parsimoniously explained by an extensive westward distributional shift of the easternmost parasite subclade. The results further suggest that the clade 1 of A. kontrimavichusi has diverged through a host shift from the precursor of L. trimucronatus to S. borealis.     

The impact of climatic factors and host density on the long-term population dynamics of vole helminths

Summary The seasonal and long-term population dynamics of helminths parasitizing voles suggested that density-dependent factors might be important in the population dynamics of common species, whereas density-independent factors predominate in the regulation of the rare species. To test this, we used single and multiple regression to analyse the effects of climatic factors and host density on populations of six species of vole helminths over 12 years. The data do support the idea of a difference between common and rare species of helminths, but they clearly do not support the above hypothesis. The common helminths Heligmosomum mixtum (Nematoda) and Catenotaenia sp. (Cestoda) responded to changes in temperature sum (>5° C days) and precipitation during summer. The combined effect of climatic factors and host density explained most of the variation in the long-term dynamics of these common species. By contrast, the long-term dynamics of the rare helminths Paranoplocephala kalelai (Cestoda), Mastophorus muris, Capillaria sp. and Syphacia petrusewiczi (Nematoda) were explained less well by weather and host density than those of the common ones. Furthermore, the common and rare helminths differed in some ways in their responses to climatic factors.