Thyroid volumes and urinary iodine in Swiss school children, 17 years after improved prophylaxis of iodine deficiency

Salt iodine content in Switzerland was raised from 7.5 to 15 mg per kg in 1980, and since then dietary iodine intake has been considered to be sufficient, even though a slight decrease due to imported food has recently been reported. The aim of this study was to establish normal values for thyroid volumes of school children who can be assumed to have had a sufficient iodine intake all their lifetime. Moreover, the present investigation was undertaken to verify that iodine sufficiency had been achieved equally in two regions each served by one of the two Swiss salt producers. Mean iodine concentration in urine spot samples from school children was 16.1 μg/dl, and it was identical in both the city of Lausanne (n=215) and the city of Solothurn (n=208). Thus it can be stated that in both cities (served by two different salt producers) iodine intake is equal and sufficient. Accordingly, thyroid volumes measured by ultrasound in school children aged 6 to 16 years were the same in both Lausanne (n=202) and Solothurn (n=207). Moreover, the age-adjusted median volumes at the 97th percentiles closely agree with and validate provisional international reference values recently proposed by the World Health Organisation and by the International Council for Control of Iodine Deficiency Disease.

Partitioning of reproduction among queens in the Argentine ant, Linepithema humile

We investigated how queens share parentage (skew) in the Argentine ant, Linepithema humile, a social insect with multiple queens (polygyny). Overall, maternity of 546 male and female sexuals that mated successfully was determined with microsatellites in 26 colonies consisting of two queens and workers. The first main finding was that queens all contributed to sexual production. However, there was a significant departure from equal contribution to male and female sexual production in a notable proportion of colonies. Overall, reproductive skew for sexual (male and female) production was relatively low but higher than reproductive skew for egg production. The second interesting result was that there was a trade-off in the relative contribution of queens to male and female production. The queens contributing more to male production contributed significantly less to female sexual production. Finally, there was no significant association between colony productivity and the degree of reproductive skew. The relatively low reproductive skew is in line with predictions of the so-called concession models of reproductive skew because, in the Argentine ant, relatedness between queens is low and ecological constraints on dispersal nonexistent or weak. © 2001 The Association for the Study of Animal Behaviour.