Methodology tune up for the assessment of desiccation resistance in natural populations of Drosophila buzzatii.

SASSI, P; HASSON, E

DROSOPHILA INFORMATION SERVICE

Oklahoma University

Lugar: Oklahoma; Año: 2008 vol. 91 p. 56 - 60

0070-7333

Arid environments impose strong selective pressures on organisms.  Particularly, insects and other terrestrial arthropods are susceptible to water  loss due to their small size, especially in desert environments (Gibbs et al., 1997).  Comparative interspecific studies have showed that in the genus Drosophila, species from arid environments exhibit physiological characteristics that allow the maintenance of water balance (Marron et al., 2003).  Intraspecific studies have focused mainly on D. melanogaster.  These studies do not agree on the mechanisms involved in the ability to cope with desiccation conditions.  In order  to investigate how hydric stress explains ecological responses and distribution patterns, it appears  appropriate to assess the adjustment to dry conditions and its intraspecific variation in desert dwelling species.  Certainly, populations can differ in a trait at a geographic scale, which could also be related to ecological diversity and/or mechanistic variations at lower organization levels.  In this sense, a comparative study must focus on the genetic basis of the genotype-environment interaction (Mackay and Anholt, 2007), and how it provides support for a species dealing with challenging and heterogeneous conditions.  Such a study requires a prior assessment of experimental conditions in pilot studies, in order to adjust the technique to the selected model species. The objective of this work was to tune up a method for measuring desiccation resistance in D. buzzatti, a cactophilic and widely distributed species in southern South America, and finally to set an experimental design that allows us to detect within and among population variation and phenotypic plasticity by means of the response of flies to different desiccation treatments.  The specific questions addressed are:  i) how intense should a desiccation treatment be to exert an effect on survival?;  ii) how subtle should desiccation be to reveal a differential effect among populations differently adjusted to dry conditions?;  iii) which is the most accurate and representative response variable to measure the effect of desiccation treatments among individuals?;  iv) does variation in the response to desiccation vary between males and females?;  v)  is there standing genetic  variation (differences among isofemale lines) in the response to desiccation?;  vi) does desiccation resistance vary among populations?