Henttonen, H. (2010). Systematic relationships of hymenolepidid cestodes of rodents and shrews inferred from sequences of 28S ribosomal RNA. -Zoologica Scripta, 39, 631-641. This study attempts to elucidate systematic relationships of hymenolepidid cestodes of rodents (18 species), shrews (13 species) and bats (one species) using sequences of partial 28S ribosomal RNA, with special reference to the genus Rodentolepis. The main finding is the presence of four multispecies clades of hymenolepidid cestodes showing pronounced morphological variation and frequent colonizations between unrelated hosts. Neither the hymenolepidid cestodes of shrews nor rodents were monophyletic. Also, the genus Rodentolepis sensu Vaucher in Czaplinski & Vaucher (1994, Keys to the Cestode Parasites of Vertebrates. Commonwealth Agricultural Bureaux International, Cambridge) is clearly nonmonophyletic. Although rostellar morphology is obviously a key feature on specific and generic levels, on higher systematic levels it seems to be a rather poor indicator of phylogenetic affinity in hymenolepidid cestodes. The presence of clades with more than one rostellar type (armed rostellum present, rudimentary unarmed rostellum present and rostellum absent) also conflicts with the proposed subfamilial and tribal classifications of hymenolepidid cestodes. The overall evidence suggests that the recent trend of splitting hymenolepidid cestodes into multiple genera will produce a more stable and practical classification than the earlier practice of favouring a few, morphologically variable genera. New classifications of hymenolepidid cestodes should, however, consider both morphological and molecular evidence.

The co-evolution between hosts and parasites has long been recognized as a fundamental driver of macro-evolutionary patterns of diversification. The effect of co-differentiation on parasite diversification is, however, often confounded by underlying geographic patterns of host distribution. In order to disentangle the confounding effects of allopatric versus host speciation, the mitochondrial cytochrome b (cyt b) gene was sequenced in seventy individuals of the parasitic nematode genus Heligmosomoides sampled in the six Apodemus mice species common in the western Palearctic region. The nuclear internal transcribed spacers (ITS) 1 and 2 were also sequenced in fifteen parasites to confirm the mitochondrial data. All lineages differentiated according to a geographic pattern and independently from the sampled host species. This suggests that host speciation did not involve concurrent parasite speciation. However, the geographic distribution range of some parasite lineages mirrors that of A. sylvaticus lineages in SW Europe, and that of A. flavicollis lineages in the Balkans and in the Middle East. Thus, regional co-differentiation likely occurred between the parasite and the two sister Apodemus hosts in different parts of their distribution range. We suggest that differences in regional abundances of A. sylvaticus and A. flavicollis are responsible for generating this pattern of regional co-differentiation. This study highlights the importance of integrating both geography and biogeographic information from potential hosts to better understand their parasite phylogeography.

Data on parasites of rodents, collected over an 18-year period on the Iberian peninsula, were used to find the determinants of parasite species richness. A total of 77 species of helminth parasites (nematodes, cestodes and digeneans) was identified among 16 species of rodents. Parasites were classified into groups according to their specificity towards their host and their life-cycle. A working phylogeny of the rodents was proposed on the basis of molecular and paleontological data and for each host the following parameters were recorded: sample size, weight, geographical range, longevity, and life-style. Two comparative methods were used, the independent comparisons method of Pagel (1992) and the distance matrix method of Legendre, Lapointe & Casgrain (1995). The second method has the advantage of measuring the relative contribution of phylogeny. Both methods gave similar results. Overall parasite species richness correlated only with host sample size. Host body size does not correlate with any subset of parasite species richness. However, host phylogeny is a good predicator of specific parasites and the species richness of digeneans correlates with host geographical range. A phylogenetic reconstruction of host relations was performed using the parasites belonging to subgroups in which richness is correlated with host phylogeny. These parasite species were treated as Dollo characters, i.e. we made the assumption that the loss of a parasite species is irreversible. The consensus tree obtained reflects the major phylogenetic divisions of the host group. Finally, this study illustrates the relative importance of processes acting at different temporal and spatial scales (evolutionary time and actual geographical range of hosts) in determining the structure of helminth parasite fauna.

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