William B. Heed

Unique Sterol in the Ecology and Nutrition of Drosophila pachea

Drosophila pachea, which breeds only in the stems of senita cactus (Lophocereus schottii) throughout the Sonoran Desert, requires the cactus as a dietary supplement when reared on laboratory media. Δ7-Stigmasten-3β-ol, isolated from the cactus or synthesized, can replace the cactus in the diet of flies reared nonaseptically or axenically. Δ7-Cholesten-3β-ol and Δ5, 7-cholestadien-3β-ol could be substituted for the cactus sterol; Δ5, 7-stigmastadien-3β-ol produced infertile females. Cholesterol, 4α-methyl-Δ7-cholesten-3β3-ol, β-sitosterol, stigmasterol, ergosterol, and Δ7-ergosten- 3β-ol did not support larval growth.

An Analysis of the Yeast Flora Associated with Cactiphilic Drosophila and their Host Plants in the Sonoran Desert and Its Relation to Temperate and Tropical Associations

A survey was made in the Sonoran Desert of yeasts living in the decaying arms of five species of cereus cacti and the four species of Drosophila that utilize them as host plants. The most common yeasts among 132 isolates from the cacti and 187 isolates from the files, respectively, were: Pichia membranaefaciens (45% and 67%), Candida ingens (17% and 4%), Torulopsis sonorensis (12% and 11%), and Cryptococcus cereanus (8% and 7%). Eighty—eight percent of the 66 initial isolates of P. membranaefaciens from Drosophila pachea and its host, senita cactus, assimilated D—xylose while only 12% of the remaining 257 initial isolates did so. Nineteen of the 20 isolates of T. sonorensis from files were found in Drosophila mojavensis and 12 of the 14 isolates of Cryptococcus cereanus came from D. pachea. The highest mean number of yeast species per cactus was 2.77 plus or minus 0.68 in organpipe cactus and per fly was 1.63 plus or minus 0.53 in D. pachea. The flies usually carried fewer yeast species than were found in the host plant but D. pachea had almost the same mean and variance as its host, senita cactus, which had 1.64 @+ 0.40. Yeast species diversity and average niche overlap have the following rank order among habitats and localities: temperate trees > temperate flies > tropical flies > desert cacti > desert flies. Habitat diversity and average niche width show: tropical flies > temperate flies and desert cacti > desert flies and temperate trees. The physiological properties of the desert yeasts are most similar to those of the tropical yeast. However, desert yeasts have similarities with yeasts of temperate trees. Both have low fermentative ability and high assimilation ability of several alcohols and acids. The genus Pichia is by far the most common yeast genus associated with Drosophila in all habitats analyzed (36% of 1,426 isolates).

Senita cactus alkaloids: Their significance to Sonoran Desert Drosophila ecology☆

Abstract The toxicity of senita cactus (Lophocereus schotti), and the alkaloids derived from it, pilocereine (I) and lophocereine (II), have been tested against Drosophila pachea and eight other species of Drosophila of the Sonoran Desert. The cactus and pilocereine kill the adults and/or progeny of all species but D. pachea. The alkaloid is probably the main reason why no other species than D. pachea breeds in the rotting stems of senita cactus.

Sensitivity to larval density in populations of Drosophila mojavensis: Influences of host plant variation on components of fitness

SummaryChromosomally polymorphic populations of Drosophila mojavensis from Baja California feed and breed on agria cactus, Stenocereus gummosus; whereas, monomorphic Arizona populations are associated exclusively with organ pipe cactus, S. thurberi. The effects of this host plant shift in expanding the kinds of feeding and breeding sites were assessed by manipulating larval density and recording differences in egg to adult development time and viability, and adult thorax size in both populations on artificially rotted substrates of both cactus species. Older agria rots increased development time but had no effect on viability. Organ pipe rots were qualitatively poorer substrates than agria rots for both monomorphic and polymorphic populations of D. mojavensis, especially at higher larval densities causing longer egg to adult development times, lower viabilities, and smaller thorax sizes than agria.The Baja population expressed shorter development times, higher viabilities, and smaller thorax sizes than the Arizona population on both cactus substrates. No evidence for cactus host race formation was found. The Baja population was less sensitive to increasing larval densities for all fitness characters studied on both cactus substrates indicating greater developmental homeostasis than in the monomorphic Arizona population. These data support the hypothesized central-marginal population structure within this species coincident with the distribution of host plants and lend insight into the process of adaptive divergence at different life history stages caused by host plant shifts.

REPRODUCTIVE ISOLATION IN SONORAN DESERT DROSOPHILA

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Juvenile hormone induces ovarian development in diapausing cave-dwelling Drosophila species

Abstract Drosophila grisea and macroptera were collected in caves overwintering as adults. The females remained in a state of reproductive diapause which extended until May for macroptera and until July for grisea, whereas the males of both species had mature sperm at all times. Termination of the reproductive diapause under laboratory conditions was accomplished in grisea by exposing them to 14 hr of illumination daily and in macroptera by increasing the temperature to 20°C. Topical application of juvenile hormone (JH) on diapausing grisea caused a prompt termination of diapause and maturation of oocytes within 10 days. Yolk proteins were found in the haemolymph of diapausing flies but not in their ovaries. In the JH-treated flies, yolk proteins were found in both the haemolymph and the ovaries, suggesting that in this species JH regulates the uptake of yolk proteins.

The ecology of yeast flora associated with cactiphilic Drosophila and their host plants in the Sonoran desert

Yeasts were isolated from the rotting stems of 7 species of cereoid cacti and 4 species ofDrosophila which utilize them as host plants. The yeast most common among 132 nonidentical isolates from the cacti and 187 nonidentical isolates from the flies, respectively, were:Pichia membranaefaciens (59 and 126),Candida ingens (22 and 8),Torulopsis sonorensis (16 and 20), andCryptococcus cereanus (11 and 14). Isolates capable of utilizingd-xylose were recovered primarily fromD. pachea andL. schotti. Adult flies were present on the substrates whenP. membranaefaciens was at high concentrations. As the pH of the substrates increased, the percent ofC. ingens cells increased relative to other yeast species. Larvae were detected mainly in alkaline substrates, and since adults did not yieldC. ingens to the extent the substrates did,C. ingens may be important in larval nutrition.Torulopsis sonorensis was recovered mainly fromD. mojavensis and its host plants,M. gummosus andL. thurberi. The concentration ofT. sonorensis in the substrates was negatively correlated with the temperature of the substrate.Cryptococcus cereanus was found in high concentrations in suitable tissues for adult flies but most adults did not yield this species to any extent. The yeast habitat diversities from the substrates had the following order:L. thurberi > C. gigantea > C. gigantea soils ≫ M. gummosus > L. schotti > others. Habitat diversity is discussed in relation to the variation of the physical conditions and chemical composition of the substrates. The yeast habitat diversities from the flies had the orderD. pachea > D. mojavensis ≫ D. nigrospiracula > undescribed Species M. The degree of habitat diversity is possibly a function of the surface feeding behavior of the flies.

Niche Separation in a Pair of Homosequential Drosophila Species from the Island of Hawaii

Two exceedingly closely related species of Drosophila coexist in a sparsely vegetated xeric area on the island of Hawaii. Of the two major trees in the area, Myoporum sandwicense alone appears to support the existence of both species. Whereas both feed as adults on Myoporum flux, D. silvarentis oviposits only on fluxes which wet the trunk well above the ground surface. Drosophila heedi larvae are found exclusively in caked soil moistened by flux dripping from above. Implications of this type of niche separation for the evolution of sibling or near-sibling species are discussed.

BEHAVIORAL DIFFERENTIATION BETWEEN TWO SPECIES OF CACTOPHILIC DROSOPHILA III. OVIPOSITION SITE PREFERENCE

Oviposition site preferences of Drosophila nigrospiracula and D. mettleri were determined for cactus versus soaked-soil substrates, light versus dark areas, and upper versus lower position in an attempt to explain the behavioral basis for the separation of their larval niches. The results show that D. nigrospiracula females discriminate oviposition sites mainly on the basis of substrate type, while D. mettleri females use substrate type and position as the primary basis of their site preference. These conclusions are supported by field data. Viability studies showed that D. nigrospiracula larvae cannot survive in the soaked-soil substrate while D. mettleri larvae survive equally well in either substrate. The evolution of soil-breeding is discussed, and the distinction is made between primary and secondary preferences in the case of D. mettleri with the soaked-soil/saguaro ecosystem.

Relevance of the ecology ofCitrus yeasts to the diet ofDrosophila

A study of the yeast flora of necrotic oranges and associatedDrosophila yielded a total of 221 isolates composed ofKloeckera apiculata (75),Pichia fermentans (75),Pichia kluyveri (50),Torulopsis stellata (17),Hanseniaspora uvarum (2),P. membranaefaciens (1), andCandida vini (1). The yeast species of all samples of oranges and adultDrosophila were very similar; however, the speciesof Drosophila contained a higher proportion ofP. fermentans and a lower proportion ofK. apiculata than was found in the rotting oranges.P. fermentans was subsequently found more frequently on the surface of the necrotic tissue, where the flies feed, than was found internally. SinceP. fermentans characteristically produces a pellicle and pseudomycelium andK. apiculata does not, it is concluded that the growth characteristics of the yeasts are an important factor determining adultDrosophila diets.