Pneumocystis organisms are airborne-transmitted fungal parasites that infect the lungs of numerous mammalian species with strong host specificity. In this study, we investigated the genetic diversity and host specificity of Pneumocystis organisms infecting Southeast Asian murid rodents through PCR amplification of two mitochondrial genes and tested the co-phylogeny hypothesis among these fungi and their rodent hosts. Pneumocystis DNA was detected in 215 of 445 wild rodents belonging to 18 Southeast Asian murid species. Three of the Pneumocystis lineages retrieved in our phylogenetic trees correspond to known Pneumocystis species, but some of the remaining lineages may correspond to new undescribed species. Most of these Pneumocystis species infect several rodent species or genera and some sequence types are shared among several host species and genera. These results indicated a weaker host specificity of Pneumocystis species infecting rodents than previously thought. Our co-phylogenetic analyses revealed a complex evolutionary history among Pneumocystis and their rodent hosts. Even if a significant global signal of co-speciation has been detected, co-speciation alone is not sufficient to explain the observed co-phylogenetic pattern and several host switches are inferred. These findings conflict with the traditional view of a prolonged process of co-evolution and co-speciation of Pneumocystis and their hosts.

In order to ascertain the extent of possible host-specialization in the Nesolechia oxyspora complex, as a pilot study ascospores from 20 collections from different parmelioid hosts representing seven genera were drawn, measured, and had length:breadth ratios calculated. The data were then subjected to multiple regression analysis using Huber-White sandwich estimators of standard errors (apparently not previously used in mycology) which take account of spores not necessarily being independent variables as they might come from the same ascus, and a statistical analysis. Significant differences between collections from seven genera were found. While the sample size was too small to reach definite conclusions, it is clear that there is a finer degree of host-relatedness than hitherto expected, which may be geno- or phenotypic. A more extensive study including species from a wider range of hosts and complemented by molecular methods will be necessary to further elucidate degrees of specificity and cryptic co-speciation in the complex. A list of the 63 reported lichen hosts is included; these are distributed though 19 genera.

The community structure of monogeneans on the gills of a catfish Pimelodus albicans, in the Río de la Plata, was studied and compared with previous findings on P. maculatus. Six Monogenea species belonging to 3 genera were found: Demidospermus majusculus Kritsky & Gutiérrez, 1998; Demidospermus armostus Kritsky & Gutiérrez, 1998; Demidospermus idolus Kritsky & Gutiérrez, 1998; Demidospermus bidiverticulatum (Suriano & Incorvaia, 1995) Kritsky & Gutiérrez, 1998; Scleroductus yuncensi Jara & Cone, 1989; and Unibarra paranoplatensis Suriano & Incorvaia, 1995. The relationships between selected host and helminth variables; the interactions between the worms and the patterns obtained from the species abundance were analysed employing appropriate statistical methodology. The results obtained revealed the following common patterns within the monogenean communities of P. maculatus and P. albicans: (a) most monogenean species belonged to the genus Demidospermus; (b) S. yuncensi was a secondary species in both communities; (c) 1 of the 3 species common to both hosts was a core species (D. bidiverticulatum); (d) the selected variables of both hosts (weight and length) were not related to the number of monogeneans or species richness; (e) the dominant species in both communities showed the highest proportion of monogeneans in more than 40 % of the infracommunities; (f ) in both communities the dominant species accounted for 40–80 % of the total number of monogeneans at component community level; (g) the number of worms correlates positively with the species richness; (h) few cases of interaction among species were found; (i) a high degree of order exists among the infracommunities compared. Finally, the proportion of common species and the phylogenetic and ecological resemblances between the hosts, P. maculatus and P. albicans support a hypothesis of co-speciation among monogeneans and pimelodids in Río de la Plata. It seems improbable that these parasite communities are recent species assemblages formed by chance. The phylogenetic resemblance of the host–monogeneans system in Río de la Plata suggests that there is a single community pattern that can be observed in congeneric and sympatric hosts.