Alcohol Tolerance, ADH Activity, and Ecological Niche of Drosophila Species

Abstract

In vitro alcohol dehydrogenase (ADH) activity was measured in adults of species belonging to Drosophila and to the related genus Zaprionus. Data were analyzed according to the known breeding sites and the level of ethanol tolerance of these species. Alcohol dehydrogenase activity was assayed with both ethanol (E) and isopropanol (I). Our results show a very broad range of activities among the 71 species investigated, the ratio of the highest value observed (D. melanogaster) to the lowest (D. pruinosa) being 65: 1. A general positive correlation was found between the level of ADH activity and the capacity to detoxify ethanol. Nevertheless, many species show exceptions to this rule. Contrary to a logical expectation, adaptation to high alcoholic resources, which has been a recurrent evolutionary event, was not mediated by a more efficient use ofethanol, that is, an increase ofthe Ell ratio. This ratio seems to be quite variable according to the phylogeny and is especially low in the subgenus Sophophora as well as in Zaprionus. Alcohol tolerance clearly is related to the larval habitat of the species and shows that adaptation to alcoholic resources has been a major evolutionary challenge in drosophilids. This adaptation is not related to phylogeny, having occurred independently several times during the evolution of the group. Finally, it should be borne in mind that, besides metabolization and detoxification, other physiological processes such as nervous-system tolerance or ethanol excretion may be involved in ethanol tolerance, and such functions also should be investigated. Environmental ethanol, which is certainly a major ecological parameter for many drosophilids, has selected a diversity of physiological adaptations, all related to the Adh locus, but presumably much more complicated than was previously believed.

Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly

“…Given that larvae of the fruitfly Drosophila melanogaster consume yeasts growing on rotting fruit and have evolved resistance to yeast fermentation products such as ethanol [9, 10], we decided to test whether ethanol protects fruitflies from one of their most common natural parasites, endoparasitoid wasps [11-13]. Here, we show that exposure to ethanol reduces wasp oviposition into fruitfly larvae.…”

Identification of Quantitative Trait Loci and Candidate Genes Influencing Ethanol Sensitivity in Honey Bees

“…However, two homologs affecting chitin structure (dusky and miniature in Drosophila) were found in eth-1 (Table 1) and could influence ethanol absorption, although these genes have yet to be connected to ethanol sensitivity in flies. In Drosophila, the metabolism enzymes ADH and ALDH have been shown to be highly sensitive to selection (Fry et al 2004;Mercot et al 1994). Honey bees may also have at least two alleles of ADH, similar to Drosophila (Martins et al 1977).…”

Oviposition preferences for ethanol depend on spatial arrangement and differ dramatically among closely related Drosophila species

“…In split-patch assays, where the two substrates are presented without a gap between them, preferences paralleled what is known about ethanol tolerance with one major exception (detailed below). Published ethanol tolerances of adult flies, from most to least tolerant, are cosmopolitan D. melanogaster , African D. melanogaster , D. simulans , D. yakuba and finally D. mauritiana (Mercot et al, 1994). The proportion of eggs laid on ethanol here is in the same rank order as ethanol tolerance, with the cosmopolitan strain of D. melanogaster laying 72% of eggs on ethanol and D. mauritiana laying only 35% on ethanol (Fig.…”

“…Most Sub-Saharan populations have lower ethanol tolerance than cosmopolitan populations (David et al, 1986; Montooth et al, 2006), and therefore might show different preferences with respect to ethanol substrates. The sister group to D. melanogaster contains three additional species, which are still less tolerant of ethanol: the cosmopolitan D. simulans and the island endemics D. mauritiana and D. sechellia (Mercot et al, 1994; Montooth et al, 2006). This last species ( D. sechellia ) is a specialist on Morinda citrifolia (noni) fruit (R'Kha et al, 1991), and shows an extremely low tolerance for ethanol (Mercot et al, 1994).…”

“…The sister group to D. melanogaster contains three additional species, which are still less tolerant of ethanol: the cosmopolitan D. simulans and the island endemics D. mauritiana and D. sechellia (Mercot et al, 1994; Montooth et al, 2006). This last species ( D. sechellia ) is a specialist on Morinda citrifolia (noni) fruit (R'Kha et al, 1991), and shows an extremely low tolerance for ethanol (Mercot et al, 1994). An outgroup of the melanogaster-simulans clade includes another broadly distributed African species, D. yakuba , and it has a sister species ( D. santomea ) found only at high elevations on the island of São Tomé (Lachaise et al, 2000).…”