Nunney Leonard
Department of Biology, University of California, 92521, Riverside, CA, USA.
Oecologia. 1996 Nov;108(3):552-561. doi: 10.1007/BF00333733.
The guild of "cosmopolitan" Drosophila coexist almost worldwide and yet the mechanisms that underlie this coexistence are unknown. The larval resource of the guild is decaying fruit and vegetables, but the species show little specialization and can coexist on a single resource, such as oranges. In southern California the guild includes D. simulans (SIM), D. melanogaster (MEL), D. pseudoobscura (OBS), D. immigrans (IMM), D. hydei (HYD) and D. busckii (BUS). These species show consistent differences in their colonization of decaying organges, differences that may promote their coexistence. This study tested whether the colonization pattern of a species is determined primarily by attraction to specific resource types (decayed or fresh organges), by ability to colonize new resource patches, or by dependence on a successional sequence of Drosophila species. The experiments compared oranges that were pre-aged prior to a colonization period and showed that the colonization pattern of each species (except OBS) was driven primarily by its decay-dependent attraction to oranges. While OBS exhibited a pattern of colonization independent of pre-aging, the remaining species all showed some preference for older (7-day pre-aged) over fresh oranges. Their overall pattern of attraction, ordered by high relative abundance on fresher organges, was SIM>MEL=IMM>HYD=BUS. BUS, a specialist on decaying plant material, was the only species that showed a preference for 11-day over 7-day oranges. Pre-aging the oranges under covers, to prevent prior colonization by Drosophila, did not change the interspecific pattern of colonization, indicating that microbial decay was driving the changes in attraction. The patterns of attraction separated two ecologically similar pairs (SIM from MEL; IMM from HYD) and published data on ethanol tolerance show that, in each pair, the earliest colonizer has the lower tolerance. This suggests an important interplay between colonization patterns and physiological optima.
“世界性”果蝇群体几乎在全球范围内共存，但其共存背后的机制尚不清楚。该群体的幼虫资源是腐烂的水果和蔬菜，但这些物种几乎没有表现出专业化，并且可以在单一资源（如橙子）上共存。在南加州，该群体包括拟暗果蝇（SIM）、黑腹果蝇（MEL）、伪暗果蝇（OBS）、移民果蝇（IMM）、海德氏果蝇（HYD）和布氏果蝇（BUS）。这些物种在腐烂橙子的定殖方面表现出一致的差异，这些差异可能促进了它们的共存。本研究测试了一个物种的定殖模式是主要由对特定资源类型（腐烂或新鲜橙子）的吸引力、定殖新资源斑块的能力，还是对果蝇物种演替序列的依赖性决定的。实验比较了在定殖期之前预先老化的橙子，结果表明每个物种（除了OBS）的定殖模式主要是由其对橙子的腐烂依赖性吸引力驱动的。虽然OBS表现出与预先老化无关的定殖模式，但其余物种都表现出对较老（预先老化7天）橙子而非新鲜橙子的某种偏好。它们的总体吸引力模式，按在更新鲜橙子上的相对丰度从高到低排序为：SIM>MEL=IMM>HYD=BUS。BUS是腐烂植物材料的专家，是唯一表现出对11天橙子而非7天橙子有偏好的物种。将橙子放在盖子下预先老化，以防止果蝇先前定殖，并没有改变种间定殖模式，这表明微生物腐烂驱动了吸引力的变化。吸引力模式区分了两对生态相似的物种（SIM与MEL；IMM与HYD），并且已发表的关于乙醇耐受性的数据表明，在每一对中，最早定殖的物种耐受性较低。这表明定殖模式与生理最适值之间存在重要的相互作用。
