Drosophila sechellia is a dietary specialist fruit fly that evolved from a generalist ancestor to specialize on the toxic fruit of Morinda citrifolia. This species pair has been the subject of numerous studies where the goal has largely been to determine the genetic basis of adaptations associated with host specialization. Because one of the most striking features of M. citrifolia fruit is the production of toxic volatile compounds that kill insects, most genomic studies in D. sechellia to date have focused on gene expression responses to the toxic compounds in its food. In this study, we aim to identify new genes important for host specialization by profiling gene expression response to 3,4-dihydroxyphenylalanine (L-DOPA). Recent work found it to be highly abundant in M. citrifolia, critical for reproductive success of D. sechellia, and supplementation of diet with the downstream pathway product dopamine can influence toxin resistance phenotypes in related species. Here we used a combination of functional genetics and genomics techniques to identify new genes that are important for D. sechellia ecological adaptation to this new niche. We show that L-DOPA exposure can affect toxin resistance phenotypes, identify genes with plastic responses to L-DOPA exposure, and functionally test an identified candidate gene. We found that knock-down of Esterase 6 (Est6) in a heterologous species alters toxin resistance suggesting Est6 may play an important role in D. sechellia host specialization.

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SummaryThe evolution of annual or perennial strategies in flowering plants may depend on a broad array of temperature and precipitation variables. Previously documented correlations between life history strategy and climate appear to be clade-specific and fail to consider the coevolution of climatic niches and life history strategies.Here we combine annual and perennial life history data with geographic distribution for 9,939 flowering plant species and utilize a recently developed method that accounts for the joint evolution of continuous and discrete traits to evaluate two hypotheses: (1) annuals tend to evolve in highly seasonal regions prone to extreme heat and drought, and (2) annuals tend to have faster rates of climatic niche evolution than perennials.We find temperature, particularly the maximum temperature of the warmest month, is the most consistent climatic factor influencing life history evolution in flowering plants. Unexpectedly, we find that the rates of climatic niche evolution are faster in perennials than in annual lineages.We propose that annuals are consistently favored in areas prone to extreme heat due to their ability to escape heat stress as seeds, but they tend to be outcompeted by perennials in regions where extreme heat is uncommon or nonexistent.

Summary The evolution of annual or perennial strategies in flowering plants likely depends on a broad array of temperature and precipitation variables. Previous documented climate life‐history correlations in explicit phylogenetic frameworks have been limited to certain clades and geographic regions. To gain insights which generalize to multiple lineages we employ a multi‐clade approach analyzing 32 groups of angiosperms across eight climatic variables. We utilize a recently developed method that accounts for the joint evolution of continuous and discrete traits to evaluate two hypotheses: annuals tend to evolve in highly seasonal regions prone to extreme heat and drought; and annuals tend to have faster rates of climatic niche evolution than perennials. We find that temperature, particularly highest temperature of the warmest month, is the most consistent climatic factor influencing the evolution of annual strategy in flowering plants. Unexpectedly, we do not find significant differences in rates of climatic niche evolution between perennial and annual lineages. We propose that annuals are consistently favored in areas prone to extreme heat due to their ability to escape heat stress as seeds, but they tend to be outcompeted by perennials in regions where extreme heat is uncommon or nonexistent.

Paleobotanists have debated whether the fossil leaf record is biased towards an overrepresentation of small leaves. Previous studies have found a "small leaf bias" in both present-day leaf assemblages and fossil floras. However, few of these studies exist, especially in fossil floras, due to a lack of reliable methods for reconstructing full leaf area from fragments. Here, using a methodology for inferring leaf area from vein density scaling in fragments, I examine whether a small leaf bias exists in paleofloras from the Fort Union and Hell Creek Formations in the Williston Basin of southwestern North Dakota and northwestern South Dakota. Since paleobotanists use leaf area of complete leaves to estimate mean annual precipitation (MAP), I also tested whether including reconstructed areas from fragments can skew MAP measurements. I found no meaningful difference between the average reconstructed areas of complete and fragmented fossils in 42 morphotype-site pairs, suggesting that these floras are not considerably biased against large leaves. Differences between MAP estimates made using complete leaf areas and those made using reconstructed areas of both completes and fragments did not seem particularly meaningful, though other paleobotanists may disagree. My results indicate that paleobotanists working on floras from these locations can be confident that complete leaf fossils represent average leaf size with reasonable accuracy. Additionally, small leaf bias will probably not skew paleoclimate estimates made using leaves from these floras.