Phylogeny, taxonomy and grouping of Trypanosoma rangeli isolates from man, triatomines and sylvatic mammals from widespread geographical origin based on SSU and ITS ribosomal sequences

Phylogenetic relationships among Trypanosoma rangeli isolates from man, wild mammals and triatomine bugs from widespread geographical origin were inferred by comparison of the small subunit of ribosomal gene sequences. The phylogenetic trees indicated that the subgenus Herpetosoma is polyphyletic and strongly supported division of this group into two monophyletic lineages, one made up of T. rangeli, T. rangeli-like and allied species and other consisting of T. lewisi and related taxa. Based on phylogenetic analysis, morphology, behaviour in vertebrate and invertebrate hosts and epidemiology we propose: a) the validation of Herpetosoma as a taxon comprised only for species of group lewisi and the maintenance of T. lewisi as the type-species of this subgenus; b) the classification of T. rangeli, T. rangeli-like and allied species into a ‘T. rangeli-clade’ more closely related to Schizotrypanum than to T. lewisi or T. brucei. The phylogenetic tree disclosed at least 4 groups within the clade T. rangeli, all confirmed by polymorphism of the internal transcribed spacer, thus conferring for the first time phylogenetic support to groups of T. rangeli and corroborating the high complexity of this taxon. Grouping was independent of their mammalian host-species and geographical origin, indicating that other factors are determining this segregation.

Species identification of Hypoderma affecting domestic and wild ruminants by morphological and molecular characterization

Cuticular structures and the sequence of the cytochrome oxidase I gene were compared for Hypoderma bovis (Linnaeus), Hypoderma lineatum (De Villers), Hypoderma actaeon Brauer, Hypoderma diana Brauer and Hypoderma tarandi (Linnaeus) (Diptera, Oestridae). Third-stage larvae of each species were examined by scanning electron microscopy revealing differences among species in the pattern and morphology of spines on the cephalic and thoracic segments, by spine patterns on the tenth abdominal segment, and by morphology of the spiracular plates. The morphological approach was supported by the molecular characterization of the most variable region of the cytochrome oxidase I (COI) gene of these species, which was amplified by polymerase chain reaction and analysed. Amplicons were digested with the unique restriction enzyme, BfaI, providing diagnostic profiles able to simultaneously differentiate all Hypoderma species examined. These findings confirm the utility of morphological characters for differentiating the most common Hypoderma larvae and reconfirm the power of the COI gene for studying insect identification and systematics.

Molecular characterization of the mitochondrial cytochrome oxidase I gene of Oestridae species causing obligate myiasis

A 688-bp region of the mitochondrial cytochrome oxidase I gene was sequenced from larvae of 18 species of Oestridae causing obligate myiasis. Larvae belonged to the four Oestridae subfamilies (Cuterebrinae, Gasterophilinae, Hypodermatinae and Oestrinae), which are commonly found throughout the world. Analysis of both nucleotide and amino acid data was performed. Nucleotide sequences included 385 conserved sites and 303 variable sites; mean nucleotide variation between all species was 18.1% and variation within each subfamily ranged from 5.3% to 13.34%. Intraspecific pairwise divergences ranged from 0.14% to 1.59%, and interspecific variation ranged from 0.7% to 27%. Of the 229 amino acids, 76 were variable (60 of which were phylogenetically informative), with some highly conserved residues identified within each subfamily. Phylogenetic analysis showed a strong divergence among the four subfamilies, concordant with classical taxonomy based on morphological and biological features. This study provides the first molecular data set for myiasis-causing Oestridae species, providing an essential database for the molecular identification of these parasites and the assessment of phylogenetic relationships within family Oestridae.

Discounting and reciprocity in an Iterated Prisoner's Dilemma

The Iterated Prisoner's Dilemma (IPD) is a central paradigm in the study of animal cooperation. According to the IPD framework, repeated play (repetition) and reciprocity combine to maintain a cooperative equilibrium. However, experimental studies with animals suggest that cooperative behavior in IPDs is unstable, and some have suggested that strong preferences for immediate benefits (that is, temporal discounting) might explain the fragility of cooperative equilibria. We studied the effects of discounting and strategic reciprocity on cooperation in captive blue jays. Our results demonstrate an interaction between discounting and reciprocity. Blue jays show high stable levels of cooperation in treatments with reduced discounting when their opponent reciprocates, but their levels of cooperation decline in all other treatment combinations. This suggests that stable cooperation requires both reduced discounting and reciprocity, and it offers an explanation of earlier failures to find cooperation in controlled payoff games.

Paraphyly in Hawaiian hybrid blowfly populations and the evolutionary history of anthropophilic species

Complementary nuclear (28S rRNA) and mitochondrial (COI + II) gene markers were sequenced from the blowflies, Lucilia cuprina and Lucilia sericata, from Europe, Africa, North America, Australasia and Hawaii. Populations of the two species were phylogenetically distinct at both genes, with one exception. Hawaiian L. cuprina possessed typical L. cuprina-type rRNA, but had L. sericata-type mitochondrial (COI + II) sequences. An explanation for this pattern is that Hawaiian flies are hybrids and comparison of observed levels of sequence divergence to possible introduction events, e.g. Polynesian colonization, suggests that Hawaiian L. cuprina may be evolving rapidly. Moreover, the monophyly of these flies also suggests that the L. sericata mtDNA haplotype was apparently fixed in Hawaiian L. cuprina by lineage sorting, indicating a population bottleneck in the evolutionary history of these island flies.