Unravelling the secrets of satyrisation

US researchers have added another piece to the puzzle that is satyrisation, one of the most complex aspects of the mosquito world.

It only occurs in mosquitoes, in fact, but is of increasing interest as mosquito-borne diseases emerge as problems worldwide.

In Greek mythology a satyr is a lusty fertile woodland deity, but satyrisation is the opposite. It occurs when the male of one species mates with the female of another, but instead of producing a hybrid, the result is no offspring at all. In fact, the unfortunate female is rendered sterile. 

Satyrisation is also the mechanism by which introduced mosquito species displace native mosquito species, particularly island endemics. 

Mosquito borne diseases such as dengue, zika, chikungunya and yellow fever are transmitted by two highly invasive mosquito species, the yellow fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus). 

The ecology, life history and interactions between the two species have been subject to intense study since the 1980s as researchers seek to control present populations, and map future outbreaks.

Satyrisation occurs where the ranges of these species overlap; for example, in Florida in the US, Ae aegypti populations have been rapidly displaced by Ae albopictus.{%recommended 7772%} 

Now new research published in the Journal of Medical Entomology shows that resistance to satyrisation also only occurs when the two species overlap, and that this resistance trait disappears rapidly if Ae albopictus mosquitoes are removed. 

The findings also reveal that in these two species mosquito age significantly affects interspecific mating rates – with older mossies far less choosy in their mate choice.

To carry out the study, researchers from the University of Florida, US, led by Irka Bargielowski, raised multiple populations of the two species in the laboratory.

In the first series of experiments, it only took eight generations for Ae aegypti to lose satyrisation resistance. The authors suggest that “the preservation of this trait is costly and can only be maintained in the presence of satyrisation pressure from Ae albopictus”; but the reasons for this cost are still unclear. 

The next series of experiments assessed the importance of age in mate choice between the species. 

The team found that mosquito age significantly affects interspecific mating rates, with older mosquitoes (male and female) engaging in interspecific mating more frequently than younger ones. 

This pattern may be related to reduced fitness as the mosquitoes age, creating less mate choosiness, or a possibly a breakdown in some unknown “age-related signal variation causing breakdown of mating barriers as they age”, the study suggests.

This finding is important as transmission dynamics of these viruses are affected by the longevity of the adult female mosquito.