Total iron concentrations in waters and fish tissues in the Nam Theun 2 Reservoir area (Lao PDR).

Data on total iron concentrations in waters and freshwater fish tissues in man-made reservoirs are scarce, especially in Southeast Asia. Changes in total iron concentrations in water and in fish tissues were studied after the impoundment of the Nam Theun 2 Reservoir (central Lao PDR). Water quality parameters were monitored at 11 stations (reservoir, upstream area and downstream areas) from 2008 to 2010. In 2009 and 2010, total iron concentrations were measured in three different fish tissues (viscera, gills and flesh) from 14 species belonging to the omnivorous and carnivorous feeding groups. The results indicated that iron concentrations in the water were influenced by the reservoir impoundment during the first year after the creation of the reservoir. Intra-annual variations of the total iron concentration in these waters appeared to be driven by the soil leaching processes mainly during the wet season. In fish, total iron accumulated preferentially in viscera, followed by gills and flesh. Iron concentration was highly species dependant and related to the ecology of the species whereas feeding habits (omnivorous or carnivorous) did not influence total iron concentration in fish tissues. Finally, reservoir impoundment did not affect iron concentrations in fish from the reservoir and from both downstream areas.

Reproductive system, social organization, human disturbance and ecological dominance in native populations of the little fire ant, Wasmannia auropunctata.

The invasive ant species Wasmannia auropunctata displays both ecologically dominant and non-dominant populations within its native range. Three factors could theoretically explain the ecological dominance of some native populations of W. auropunctata: (i) its clonal reproductive system, through demographic and/or adaptive advantages; (ii) its unicolonial social organization, through lower intraspecific and efficient interspecific competition; (iii) the human disturbance of its native range, through the modification of biotic and abiotic environmental conditions. We used microsatellite markers and behavioural tests to uncover the reproductive modes and social organization of dominant and non-dominant native populations in natural and human-modified habitats. Microsatellite and mtDNA data indicated that dominant and non-dominant native populations (supercolonies as determined by aggression tests) of W. auropunctata did not belong to different evolutionary units. We found that the reproductive system and the social organization are neither necessary nor sufficient to explain W. auropunctata ecological dominance. Dominance rather seems to be set off by unknown ecological factors altered by human activities, as all dominant populations were recorded in human-modified habitats. The clonal reproductive system found in some populations of W. auropunctata may however indirectly contribute to its ecological dominance by allowing the species to expand its environmental niche, through the fixation over time of specific combinations of divergent male and female genotypes. Unicoloniality may rather promote the range expansion of already dominant populations than actually trigger ecological dominance. The W. auropunctata model illustrates the strong impact of human disturbance on species' ecological features and the adaptive potential of clonal reproductive systems.

Queen movement during colony emigration in the facultatively polygynous ant Pachycondyla obscuricornis.

In ants, nest relocations are frequent but nevertheless perilous, especially for the reproductive caste. During emigrations, queens are exposed to predation and face the risk of becoming lost. Therefore the optimal strategy should be to move the queen(s) swiftly to a better location, while maintaining maximum worker protection at all times in the new and old nests. The timing of that event is a crucial strategic issue for the colony and may depend on queen number. In monogynous colonies, the queen is vital for colony survival, whereas in polygynous colonies a queen is less essential, if not dispensable. We tested the null hypothesis that queen movement occurs at random within the sequence of emigration events in both monogynous and polygynous colonies of the ponerine ant Pachycondyla obscuricornis. Our study, based on 16 monogynous and 16 polygynous colony emigrations, demonstrates for the first time that regardless of the number of queens per colony, the emigration serial number of a queen occurs in the middle of all emigration events and adult ant emigration events, but not during brood transport events. It therefore appears that the number of workers in both nests plays an essential role in the timing of queen movement. Our results correspond to a robust colony-level strategy since queen emigration is related neither to colony size nor to queen number. Such an optimal strategy is characteristic of ant societies working as highly integrated units and represents a new instance of group-level adaptive behaviors in social insect colonies.

The ladybird Thalassa saginata, an obligatory myrmecophile of Dolichoderus bidens ant colonies.

The larvae and pupae of the ladybird Thalassa saginata develop inside colonies of the dolichoderine ant Dolichoderus bidens. This association is the first specific and obligatory relationship recorded between ants and ladybirds. The ants provide shelter and protection to the larvae but the diet of the latter remains unclear. The integration of T. saginata larvae into the ant colonies is achieved by mimicking the cuticular patterns of the ants' brood. Moreover, the larvae secrete substances from their hairs and anal gland that are likely to enhance their attractiveness.