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Sex and recombination are central processes in life generating genetic diversity. Organisms that rely on asexual propagation risk extinction due to the loss of genetic diversity and the inability to adapt to changing environmental conditions. The fungus-growing ant species Mycocepurus smithii was thought to be obligately asexual because only parthenogenetic populations have been collected from widely separated geographic localities. Nonetheless, M. smithii is ecologically successful, with the most extensive distribution and the highest population densities of any fungus-growing ant. Here we report that M. smithii actually consists of a mosaic of asexual and sexual populations that are nonrandomly distributed geographically. The sexual populations cluster along the Rio Amazonas and the Rio Negro and appear to be the source of independently evolved and widely distributed asexual lineages, or clones. Either apomixis or automixis with central fusion and low recombination rates is inferred to be the cytogenetic mechanism underlying parthenogenesis in M. smithii. Males appear to be entirely absent from asexual populations, but their existence in sexual populations is indicated by the presence of sperm in the reproductive tracts of queens. A phylogenetic analysis of the genus suggests that M. smithii is monophyletic, rendering a hybrid origin of asexuality unlikely. Instead, a mitochondrial phylogeny of sexual and asexual populations suggests multiple independent origins of asexual reproduction, and a divergence-dating analysis indicates that M. smithii evolved 0.5-1.65 million years ago. Understanding the evolutionary origin and maintenance of asexual reproduction in this species contributes to a general understanding of the adaptive significance of sex.Attini | clonality | Formicidae | thelytoky | mutualism T he vast majority of metazoans reproduces sexually, enjoying the benefits of genetic recombination (1-3) such as rapid adaptability to novel ecological conditions (4, 5) and the purging of deleterious mutations from their genomes (6, 7). However, relative to sexually reproducing organisms, an asexual female doubles its fitness by transmitting its entire genetic material to the next generation (8). Despite such obvious short-term fitness advantages, asexual organisms occur only sporadically throughout the tree of life and are predicted to be evolutionarily short-lived and doomed to early extinction (9-11). In contrast to the short-term advantages of asexuality, the adaptive value of sexuality, that is, genetic recombination, is expected to be of long-term benefit (2, 12-14). There remain in evolutionary biology significant unexplored questions about whether sexual reproduction is favored by natural selection over short evolutionary time spans and, if not, why sexual reproduction persists as the prevalent mode of reproduction, given that the selective benefits are deferred. Studying the origin and evolution of parthenogenetic lineages, and understanding how genetic diversity is generated and preserved in such linea...

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Little research has been performed on the impact of pesticides on earthworms under tropical conditions. Taking into consideration the often-limited resources in tropical countries, simple screening tests are needed. Therefore, it was investigated whether three pesticides relevant for the Brazilian Amazon (benomyl, carbendazim, lambda-cyhalothrin) affect the avoidance behavior of the earthworm Eisenia fetida. The tests were performed for two days according to ISO guideline 17512 but were adapted to tropical conditions (i.e. test substrate, test organism and temperature). The results indicate that this test gives reproducible and reliable results. Toxicity values (NOEC, EC50) are lower than those determined in 14 day-acute mortality tests and are approximately in the same range such as those found in 56 day-chronic reproduction tests with the same earthworm species, which were performed in parallel. Therefore, the use of the earthworm avoidance tests is recommended as a screening tool for the risk assessment of pesticides.

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In a recent ecological study of the ticks on animal trails within an area of Atlantic rainforest in south-eastern Brazil, Amblyomma aureolatum, A. brasiliense, A. incisum, A. ovale and Haemaphysalis juxtakochi were found questing on the vegetation. Most of the ticks recorded by a small, man-made dam on the forest border were A. dubitatum but a few A. brasiliense and A. cajennense, one A. incisum and one H. juxtakochi were also found. The seasonal activity of the ticks indicated that A. incisum and A. brasiliense had one generation/year. On the animal trails, most tick species and stages quested on the vegetation at a height of 30-40 cm above ground level. The questing larvae and adults of A. incisum tended to be found higher, however, with the greatest numbers recorded 40-50 cm (larvae) or 60-70 cm (adults) above ground level. Most of the adult ticks (81.1%-100%), nymphs (78.6%-100%) and larval clusters (100%) found on a forest trail remained questing at the same location over a 24-h period. Carbon-dioxide traps in the rainforest attracted <50% of the ticks observed questing on the nearby vegetation and, curiously, the CO2 traps set deep in the forest attracted far fewer ticks than similar traps set by the dam. The ecological relationships between the ticks, their hosts and the rainforest environment are discussed.