Impact of body melanisation on contrasting levels of desiccation resistance in a circumtropical and a generalist Drosophila species

Abstract

We investigated the role of cuticular lipids, body melanisation and body size in conferring contrasting levels of desiccation resistance in latitudinal populations of Drosophila melanogaster and Drosophila ananassae on the Indian subcontinent. Contrary to the well known role of cuticular lipids in water proofing in diverse insect taxa, there is lack of geographical variations in the amount of cuticular lipids per fly in both the species. In D. ananassae, quite low levels of body melanisation are correlated with lower desiccation resistance. By contrast, increased levels of desiccation resistance are correlated with quite high melanisation in D. melanogaster. Thus, species specific cuticular melanisation patterns are significantly correlated with varying levels of desiccation resistance within as well as between populations and across species. Role of body melanisation in desiccation resistance is further supported by the fact that assorted dark and light flies differ significantly in cuticular water loss, hemolymph and dehydration tolerance. However, similar patterns of body size variation do not account for contrasting levels of desiccation resistance in these two Drosophila species. Climatic selection is evidenced by multiple regression analysis with seasonal amplitude of thermal and humidity changes (Tcv and RHcv) along latitude on the Indian subcontinent. Finally, the contrasting levels of species specific distribution patterns are negatively correlated with RHcv of sites of origin of populations i.e. a steeper negative slope for D. ananassae corresponds with its desiccation sensitivity as compared with D. melanogaster. Thus, evolutionary changes in body melanisation impact desiccation resistance potential as well as distribution patterns of these two Drosophila species on the Indian subcontinent.

Divergent strategies for adaptations to stress resistance in two tropical Drosophila species: effects of developmental acclimation for D. bipectinata and the invasive species - D. malerkotliana

“…Similar relationships are evident between laboratory-selected desiccation resistant and control strains of D. melanogaster (Gibbs et al, 1997). However, it is not clear whether tropical Drosophila species of the subgenus Sophophora have evolved changes in the amount of cuticular lipids to confer greater desiccation resistance in the subtropics, even though no such changes in the cuticular lipids were found in the related species, Drosophila ananassae (Parkash et al, 2010). Furthermore, association between cuticular permeability and quantity of cuticular lipids can be demonstrated through treatment of cuticular surfaces with organic solvents such as hexane or chloroform:methanol (Hadley, 1989;Hadley, 1994;Hadley and Quinlan, 1989).…”

“…We assessed changes in the amount of cuticular lipids in D. malerkotliana and D. bipectinata resulting from developmental acclimation despite lack of such evidence in D. melanogaster or D. ananassae (Gibbs et al, 1997;Parkash et al, 2010). Interestingly, there was a threefold increase in the amount of cuticular lipid of D. malerkotliana reared at 17°C compared with 25°C, whereas there was a modest increase of 50% in D. bipectinata.…”

Direct and correlated responses to laboratory selection for body melanisation inD. melanogaster: support for melanism- desiccation resistance hypothesis.

“…behavioural thermoregulation and body colouration are co-adapted traits in the pygmy grasshopper (Tetrix subulata) (Forsman, 2000). Co-adapted traits are also represented by associations between body melanisation-and desiccation-related traits (Parkash et al, 2008a;Parkash et al, 2010a) and thermoresistance traits in D. melanogaster (Parkash et al, 2010b). Cuticular hydrocarbons are also subject to natural selection, being important in providing desiccation resistance for many insect species (Gibbs and Rajpurohit, 2010).…”

Local adaptation for body color in Drosophila americana: commentary on Wittkopp et al.

“…For example, the occurrence of dark-pigmented populations of several Drosophila spp. has been associated with dry environments (for example, Parkash et al, 2010). This relationship represents the main hypothesis tested by Wittkopp et al (2011), and the authors conclude that pigmentation and desiccation resistance are not unequivocally linked among the populations investigated.…”