Insect leaf-chewing damage tracks herbivore richness in modern and ancient forests

Phenological indicators of resources offered to leaf herbivores in restinga communities

PREMISE

Plants can limit the leaf tissue consumed by insect herbivores through chemical, structural, and nutritional leaf defenses or by escaping in space and time. Escaping is related to the phenological patterns of plants, which in turn respond to climatic factors. This study evaluated leaf production in a coastal plant community in southern Brazil to test the following hypotheses: (1) Leaves are continuously produced in this ecosystem, and (2) synchrony acts as an escape strategy from herbivory.

METHODS

We evaluated leaf production patterns of 20 herbaceous, shrub, and tree species for 2 years using the Fournier index then measured leaf consumption in the second year. The Rayleigh test was used to verify the synchrony of phenological events. Correlations between leaf production and climatic factors and between leaf production synchrony and herbivory were analyzed.

RESULTS

New leaves were continuously produced at the plant community scale, but herbaceous and shrub species showed a phenological pattern distinct from that of tree species. Trees had peaks of synchrony in leaf production that were positively correlated with amount of leaf tissue consumed, refuting the hypothesis that synchrony acts as an escape strategy.

CONCLUSIONS

The phenological and herbivory patterns in this plant community may be due to the supply of resources in the soil and the composition of the insect community.

Interactive Effects of Temperature, Aridity, and Plant Stoichiometry on Insect Herbivory: Past and Present

AbstractThe influence of climate on deep-time plant-insect interactions is becoming increasingly well known, with temperature, CO2 increases (and associated stoichiometric changes in plants), and aridity likely playing a critical role. In our modern climate, all three factors are shifting at an unprecedented rate, with uncertain consequences for biodiversity. To investigate effects of temperature, stoichiometry (specifically that of nitrogen), and aridity on insect herbivory, we explored insect herbivory in three modern floral assemblages and in 39 fossil floras, especially focusing on eight floras around a past hyperthermal event (the Paleocene-Eocene Thermal Maximum) from Bighorn Basin (BB). We find that higher temperatures were associated with increased herbivory in the past, especially among BB sites. In these BB sites, non-N2-fixing plants experienced a lower richness but higher frequency of herbivory damage than N2-fixing plants. Herbivory frequency but not richness was greater in BB sites compared with contemporaneous, nearby, but less arid sites from Hanna Basin. Compared with deep-time environments, herbivory frequency and richness are higher in modern sites, suggesting that current accelerated warming uniquely impacts plant-insect interactions. Overall, our work addresses multiple aspects of climate change using fossil data while also contextualizing the impact of modern anthropogenic change on Earth's most diverse interactions.

Tree phytochemical diversity and herbivory are higher in the tropics

A long-standing but poorly tested hypothesis in plant ecology and evolution is that biotic interactions play a more important role in producing and maintaining species diversity in the tropics than in the temperate zone. A core prediction of this hypothesis is that tropical plants deploy a higher diversity of phytochemicals within and across communities because they experience more herbivore pressure than temperate plants. However, simultaneous comparisons of phytochemical diversity and herbivore pressure in plant communities from the tropical to the temperate zone are lacking. Here we provide clear support for this prediction by examining phytochemical diversity and herbivory in 60 tree communities ranging from species-rich tropical rainforests to species-poor subalpine forests. Using a community metabolomics approach, we show that phytochemical diversity is higher within and among tropical tree communities than within and among subtropical and subalpine communities, and that herbivore pressure and specialization are highest in the tropics. Furthermore, we show that the phytochemical similarity of trees has little phylogenetic signal, indicating rapid divergence between closely related species. In sum, we provide several lines of evidence from entire tree communities showing that biotic interactions probably play an increasingly important role in generating and maintaining tree diversity in the lower latitudes.

Middle Jurassic insect mines on gymnosperms provide missing links to early mining evolution

We investigated the mining mode of insect feeding, involving larval consumption of a plant's internal tissues, from the Middle Jurassic (165 million years ago) Daohugou locality of Northeastern China. Documentation of mining from the Jurassic Period is virtually unknown, and results from this time interval would address mining evolution during the temporal gap of mine-seed plant diversifications from the previous Late Triassic to the subsequent Early Cretaceous. Plant fossils were examined with standard microscopic procedures for herbivory and used the standard functional feeding group-damage-type system of categorizing damage. All fossil mines were photographed and databased. We examined 2014 plant specimens, of which 27 occurrences on 14 specimens resulted in eight, new, mine damage types (DTs) present on six genera of bennettitalean, ginkgoalean, and pinalean gymnosperms. Three conclusions emerge from this study. First, these mid-Mesozoic mines are morphologically conservative and track plant host anatomical structure rather than plant phylogeny. Second, likely insect fabricators of these mines were three basal lineages of polyphagan beetles, four basal lineages of monotrysian moths, and a basal lineage tenthredinoid sawflies. Third, the nutrition hypothesis, indicating that miners had greater access to nutritious, inner tissues of new plant lineages, best explains mine evolution during the mid-Mesozoic.

Intra- and interspecific diversity in a tropical plant clade alter herbivory and ecosystem resilience

Declines in biodiversity generated by anthropogenic stressors at both species and population levels can alter emergent processes instrumental to ecosystem function and resilience. As such, understanding the role of biodiversity in ecosystem function and its response to climate perturbation is increasingly important, especially in tropical systems where responses to changes in biodiversity are less predictable and more challenging to assess experimentally. Using large-scale transplant experiments conducted at five neotropical sites, we documented the impacts of changes in intraspecific and interspecific plant richness in the genus Piper on insect herbivory, insect richness, and ecosystem resilience to perturbations in water availability. We found that reductions of both intraspecific and interspecific Piper diversity had measurable and site-specific effects on herbivory, herbivorous insect richness, and plant mortality. The responses of these ecosystem-relevant processes to reduced intraspecific Piper richness were often similar in magnitude to the effects of reduced interspecific richness. Increased water availability reduced herbivory by 4.2% overall, and the response of herbivorous insect richness and herbivory to water availability were altered by both intra- and interspecific richness in a site-dependent manner. Our results underscore the role of intraspecific and interspecific richness as foundations of ecosystem function and the importance of community and location-specific contingencies in controlling function in complex tropical systems.

Leaf traits linked to structure and palatability drive plant-insect interactions within three forested ecosystems

PREMISE

Plant traits and insect herbivory have been highly studied within the modern record but only to a limited extent within the paleontological. Preservation influences what can be measured within the fossil record, but modern methods are also not compatible with paleobotanical methods. To remedy this knowledge gap, a comparable framework was created here using modern and paleobotanical methods, allowing for future comparisons within the fossil record.

METHODS

Insect feeding damage on selected tree species at Harvard Forest, the Smithsonian Environmental Research Center, and La Selva were characterized using the damage type system prevalent within paleobotanical studies and compared with leaf traits. Linear models and random forest analyses tested the influence of leaf traits on total, specialized, gall, and mine frequency and diversity.

RESULTS

Structural traits like leaf dry mass per area and palatability traits, including lignin and phosphorus concentrations, are important variables affecting gall and mine damage. The significance and strength of trait-herbivory relationships varied across forest types, which is likely driven by differences in local insect populations.

CONCLUSIONS

This work addresses the persistent gap between modern and paleoecological studies focusing on the influence of leaf traits on insect herbivory. This is important as modern climate change alters our understanding of plant-insect interactions, providing a need for contextualizing these relationships within evolutionary time. The fossil record provides information on terrestrial response to past climatic events and, thus, should be implemented when considering how to preserve biodiversity under current and future global change.

First record of insect-plant interaction in Late Cretaceous fossils from Nelson Island (South Shetland Islands Archipelago), Antarctica

Despite the enormous paleobotanical record on different islands of the Antarctic Peninsula, the evidence of insect activity associated with fossilized plants is scarce. Here we report the first evidence of insect-plant interaction from Cretaceous deposits, more precisely from a new locality at the Rip Point area, Nelson Island (Antarctic Peninsula). The macrofossil assemblage includes isolated Nothofagus sp. leaf impressions, a common component of the Antarctic paleoflora. Two hundred leaves were examined, of which 15 showed evidence of insect activity, displaying variations in size, shape, and preservation. Two types of interaction damage, galls and mines, were identified. A single specimen retained a circular scar recognized as galling scar, while meandering tracks were considered mines. These traces of herbivore insect activity, correspond to the oldest known record of this type of interaction of West Antarctica and the oldest record of insect-plant interaction in Nothofagus sp. reported so far.

Fossil leaves reveal drivers of herbivore functional diversity during the Cenozoic

Herbivorous arthropods are the most diverse group of multicellular organisms on Earth. The most discussed drivers of their inordinate taxonomic and functional diversity are high niche availability associated with the diversity of host plants and dense niche packing due to host partitioning among herbivores. However, the relative contributions of these two factors to dynamics in the diversity of herbivores throughout Earth's history remain unresolved. Using fossil data on herbivore-induced leaf damage from across the Cenozoic, we infer quantitative bipartite interaction networks between plants and functional feeding types of herbivores. We fit a general model of diversity to these interaction networks and discover that host partitioning among functional groups of herbivores contributed twice as much to herbivore functional diversity as host diversity. These findings indicate that niche packing primarily shaped the dynamics in the functional diversity of herbivores during the past 66 my. Our study highlights how the fossil record can be used to test fundamental theories of biodiversity and represents a benchmark for assessing the drivers of herbivore functional diversity in modern ecosystems.

Landscape-level variability and insect herbivore outbreak captured within modern forests provides a framework for interpreting the fossil record

Temporal patterns of plant-insect interactions are readily observed within fossil datasets but spatial variability is harder to disentangle without comparable modern methods due to limitations in preservation. This is problematic as spatial variability influences community structure and interactions. To address this we replicated paleobotanical methods within three modern forests, creating an analogous dataset that rigorously tested inter- and intra-forest plant-insect variability. Random mixed effects models, non-metric multidimensional scaling (NMDS) ordinations, and bipartite network- and node-level metrics were used. Total damage frequency and diversity did not differ across forests but differences in functional feeding groups (FFGs) were observed across forests, correlating with plant diversity, evenness, and latitude. Overall, we found higher generalized herbivory within the temperate forests than the wet-tropical, a finding also supported by co-occurrence and network analyses at multiple spatial scales. Intra-forest analyses captured consistent damage type communities, supporting paleobotanical efforts. Bipartite networks captured the feeding outbreak of Lymantria dispar caterpillars; an exciting result as insect outbreaks have long been unidentifiable within fossil datasets. These results support paleobotanical assumptions about fossil insect herbivore communities, provide a comparative framework between paleobotanical and modern communities, and suggest a new analytical framework for targeting modern and fossil outbreaks of insect feeding.

Insect herbivore and fungal communities on Agathis (Araucariaceae) from the latest Cretaceous to Recent

Agathis (Araucariaceae) is a genus of broadleaved conifers that today inhabits lowland to upper montane rainforests of Australasia and Southeast Asia. A previous report showed that the earliest known fossils of the genus, from the early Paleogene and possibly latest Cretaceous of Patagonian Argentina, host diverse assemblages of insect and fungal associations, including distinctive leaf mines. Here, we provide complete documentation of the fossilized Agathis herbivore communities from Cretaceous to Recent, describing and comparing insect and fungal damage on Agathis across four latest Cretaceous to early Paleogene time slices in Patagonia with that on 15 extant species. Notable fossil associations include various types of external foliage feeding, leaf mines, galls, and a rust fungus. In addition, enigmatic structures, possibly armored scale insect (Diaspididae) covers or galls, occur on Agathis over a 16-million-year period in the early Paleogene. The extant Agathis species, throughout the range of the genus, are associated with a diverse array of mostly undescribed damage similar to the fossils, demonstrating the importance of Agathis as a host of diverse insect herbivores and pathogens and their little-known evolutionary history.

Sampling bias and the robustness of ecological metrics for plant-damage-type association networks

Plants and their insect herbivores have been a dominant component of the terrestrial ecological landscape for the past 410 million years and feature intricate evolutionary patterns and co-dependencies. A complex systems perspective allows for both detailed resolution of these evolutionary relationships as well as comparison and synthesis across systems. Using proxy data of insect herbivore damage (denoted by the damage type or DT) preserved on fossil leaves, functional bipartite network representations provide insights into how plant-insect associations depend on geological time, paleogeographical space, and environmental variables such as temperature and precipitation. However, the metrics measured from such networks are prone to sampling bias. Such sensitivity is of special concern for plant-DT association networks in paleontological settings where sampling effort is often severely limited. Here, we explore the sensitivity of functional bipartite network metrics to sampling intensity and identify sampling thresholds above which metrics appear robust to sampling effort. Across a broad range of sampling efforts, we find network metrics to be less affected by sampling bias and/or sample size than richness metrics, which are routinely used in studies of fossil plant-DT interactions. These results provide reassurance that cross-comparisons of plant-DT networks offer insights into network structure and function and support their widespread use in paleoecology. Moreover, these findings suggest novel opportunities for using plant-DT networks in neontological terrestrial ecology to understand functional aspects of insect herbivory across geological time, environmental perturbations, and geographic space.

Arthropod and Pathogen Damage on Fossil and Modern Plants: Exploring the Origins and Evolution of Herbivory on Land

The use of the functional feeding group-damage type system for analyzing arthropod and pathogen interactions with plants has transformed our understanding of herbivory in fossil plant assemblages by providing data, analyses, and interpretation of the local, regional, and global patterns of a 420-Myr history. The early fossil record can be used to answer major questions about the oldest evidence for herbivory, the early emergence of herbivore associations on land plants, and later expansion on seed plants. The subsequent effects of the Permian-Triassic ecological crisis on herbivore diversity, the resulting formation of biologically diverse herbivore communities on gymnosperms, and major shifts in herbivory ensuing from initial angiosperm diversification are additional issues that need to be addressed. Studies ofherbivory resulting from more recent transient spikes and longer-term climate trends provide important data that are applied to current global change and include herbivore community responses to latitude, altitude, and habitat. Ongoing paleoecological themes remaining to be addressed include the antiquity of modern interactions, differential herbivory between ferns and angiosperms, and origins of modern tropical forests. The expansion of databases that include a multitude of specimens; improvements in sampling strategies; development of new analytical methods; and, importantly, the ability to address conceptually stimulating ecological and evolutionary questions have provided new impetus in this rapidly advancing field.

An integrated leaf trait analysis of two Paleogene leaf floras

Objectives

This study presents the Integrated Leaf Trait Analysis (ILTA), a workflow for the combined application of methodologies in leaf trait and insect herbivory analyses on fossil dicot leaf assemblages. The objectives were (1) to record the leaf morphological variability, (2) to describe the herbivory pattern on fossil leaves, (3) to explore relations between leaf morphological trait combination types (TCTs), quantitative leaf traits, and other plant characteristics (e.g., phenology), and (4) to explore relations of leaf traits and insect herbivory.

Material and Methods

The leaves of the early Oligocene floras Seifhennersdorf (Saxony, Germany) and Suletice-Berand (Ústí nad Labem Region, Czech Republic) were analyzed. The TCT approach was used to record the leaf morphological patterns. Metrics based on damage types on leaves were used to describe the kind and extent of insect herbivory. The leaf assemblages were characterized quantitatively (e.g., leaf area and leaf mass per area (LM_A)) based on subsamples of 400 leaves per site. Multivariate analyses were performed to explore trait variations.

Results

In Seifhennersdorf, toothed leaves of TCT F from deciduous fossil-species are most frequent. The flora of Suletice-Berand is dominated by evergreen fossil-species, which is reflected by the occurrence of toothed and untoothed leaves with closed secondary venation types (TCTs A or E). Significant differences are observed for mean leaf area and LM_A, with larger leaves tending to lower LM_A in Seifhennersdorf and smaller leaves tending to higher LM_A in Suletice-Berand. The frequency and richness of damage types are significantly higher in Suletice-Berand than in Seifhennersdorf. In Seifhennersdorf, the evidence of damage types is highest on deciduous fossil-species, whereas it is highest on evergreen fossil-species in Suletice-Berand. Overall, insect herbivory tends to be more frequently to occur on toothed leaves (TCTs E, F, and P) that are of low LM_A. The frequency, richness, and occurrence of damage types vary among fossil-species with similar phenology and TCT. In general, they are highest on leaves of abundant fossil-species.

Discussion

TCTs reflect the diversity and abundance of leaf architectural types of fossil floras. Differences in TCT proportions and quantitative leaf traits may be consistent with local variations in the proportion of broad-leaved deciduous and evergreen elements in the ecotonal vegetation of the early Oligocene. A correlation between leaf size, LM_A, and fossil-species indicates that trait variations are partly dependent on the taxonomic composition. Leaf morphology or TCTs itself cannot explain the difference in insect herbivory on leaves. It is a more complex relationship where leaf morphology, LM_A, phenology, and taxonomic affiliation are crucial.

Insect herbivory within modern forests is greater than fossil localities

Fossilized leaves provide the longest running record of hyperdiverse plant-insect herbivore associations. Reconstructions of these relationships over deep time indicate strong links between environmental conditions, herbivore diversity, and feeding damage on leaves. However, herbivory has not been compared between the past and the modern era, which is characterized by intense anthropogenic environmental change. Here, we present estimates for damage frequencies and diversities on fossil leaves from the Late Cretaceous (66.8 Ma) through the Pleistocene (2.06 Ma) and compare these estimates with Recent (post-1955) leaves collected via paleobotanical methods from modern ecosystems: Harvard Forest, United States; the Smithsonian Environmental Research Center, United States; and La Selva, Costa Rica. Total damage frequency, measured as the percentage of leaves with any herbivore damage, within modern ecosystems is greater than any fossil locality within this record. This pattern is driven by increased frequencies across nearly all functional feeding groups within the Recent. Diversities of total, specialized, and mining damage types are elevated within the Recent compared with fossil floras. Our results demonstrate that plants in the modern era are experiencing unprecedented levels of insect damage, despite widespread insect declines. Human influence, such as the rate of global climate warming, influencing insect feeding and timing of life cycle processes along with urbanization and the introduction of invasive plant and insect species may drive elevated herbivory. This research suggests that the strength of human influence on plant-insect interactions is not controlled by climate change alone but rather, the way in which humans interact with terrestrial landscape.

Insect herbivory immediately before the eclipse of the gymnosperms: The Dawangzhangzi plant assemblage of Northeastern China

The Early Cretaceous terrestrial revolution involved global shifts from gymnosperm- to angiosperm-dominated floras. However, responses of insect herbivores to these changes remain unexamined. We evaluated 2 176 highly sampled plant specimens representing 62 species/morphotypes from the 126 Ma Dawangzhangzi plant assemblage of Northeastern China. Our study consisted of horsetails, ferns, ginkgoaleans, czekanowskialeans, conifers, and an angiosperm. Their herbivory was evaluated by the functional feeding groups of hole feeding, margin feeding, and surface feeding (ectophytic feeders); piercer and suckers, and ovipositing insects (ectoendophytic feeders); mining, galling, and borings (endophytic feeders); and pathogens, collectively constituting 65 damage types (DTs). The plant assemblage was assessed for herbivory richness by DT richness, component community structure, and DT specialization on plant hosts; for herbivory intensity, it was evaluated for DT frequency, herbivorized surface area, and feeding event occurrences. Using feeding event occurrences, the data supported seven species/morphotypes as most intensely herbivorized: Liaoningocladus boii (76.6%), Czekanowskia sp. 1 (8.4%), Czekanowskia rigida (4.10%), Lindleycladus lanceolatus (3.5%), Ginkgoites sp. 2 (2.0%), Podozamites sp. 1 (1.1%), and Solenites sp. 1 (0.9%). The most herbivorized taxa were pinaleans (conifers), then czekanowskialeans, and lastly ginkgoaleans; the monodominant component community was the conifer Liaoningocladus boii. DT host specialization levels were low. The plant assemblage had an overall low 0.86% of foliage removed by herbivores, explained by physical and chemical antiherbivore defenses, and parasitoid attack. Although Paleozoic, gymnosperm-dominated assemblages had greater herbivory, component community structure of the three most herbivorized taxa are more similar to modern bracken fern and willow than modern gymnosperm taxa.

Data, metrics, and methods for arthropod and fungal herbivory at the dawn of angiosperm diversification: The Rose Creek plant assemblage of Nebraska, U.S.A

The data presented in this article are related to the research article titled “Arthropod and fungal herbivory at the dawn of angiosperm diversification: The Rose Creek plant assemblage of Nebraska, U.S.A.” (Xiao et al., 2021). These data correspond to an examination of arthropod and fungal herbivory on 2084 plant specimens from the Early Cretaceous (late Albian) Rose Creek locality of southeastern Nebraska, USA. Ten datasets have been assembled to describe and contextualize the diversity and intensity of herbivory at Rose Creek, as documented in Appendices of the online supplementary material. Appendices S4 and S5 provide a list and the frequency distributions by major clade and species/morphotype of all plant taxa examined. Appendix S6 outlines general procedures for documenting herbivory on plants and how the data was acquired. Appendix S9a and S9b provide rarefaction analyses for plant taxa to demonstrate sampling sufficiency, which is paralleled by rarefaction analyses of Appendix S9c and S9d that indicate sampling of damage types are robust. The comprehensive dataset of Appendix S12 lists plant taxa horizontally by major clade/group and species/morphotype versus vertically listed feeding classes, functional feeding groups (FFGs) and damage types (DTs). The basic metrics of DTs, feeding event occurrences, DT host-plant specialization, and number of matrix cells are displayed, with data subtotals and totals. This data matrix serves as the central source of data for the study, and records the six metrics of DT richness, DT frequency, DT host-plant specialization, percent of area herbivorized, and feeding event occurrences. Three of these metrics are used for establishing component community structure of the three most herbivorized taxa (Figs 8–10), and the relationships among plant hosts and FFGs in the non-metric multidimensional scaling analysis (Fig. 11) (Xiao et al., 2021). Appendix S15 is a list DTs, with their assigned host-plant specialization of 1 for generalized, 2 for intermediate specificity, and 3 for specialized. Appendix S16 is a table that provides plant surface areas (cm²) and their percentages that have been removed due to herbivory. Appendix S18 provides descriptions and ancillary data for 14 new DTs described from Rose Creek. A listing of the herbivory index (herbivorized surface area divided by total surface area) of plant assemblages and individual plant species in Appendix S19 provides comparisons among Rose Creek, other fossil, and modern plant assemblages. Lastly, Appendix S23 lists from the literature of arthropod species forming the well-documented herbivore component communities of five modern plant species to the three most herbivorized taxa at Rose Creek shown in Fig. 12. Some of the metrics used to quantitatively measure the diversity and intensity of herbivory are recent, such as feeding event occurrences, whereas others such as herbivorized surface area and host-plant specialization values have had a longer use in plant–arthropod studies.

Insect herbivory on Catula gettyi gen. et sp. nov. (Lauraceae) from the Kaiparowits Formation (Late Cretaceous, Utah, USA)

The Upper Cretaceous (Campanian Stage) Kaiparowits Formation of southern Utah, USA, preserves abundant plant, invertebrate, and vertebrate fossil taxa. Taken together, these fossils indicate that the ecosystems preserved in the Kaiparowits Formation were characterized by high biodiversity. Hundreds of vertebrate and invertebrate species and over 80 plant morphotypes are recognized from the formation, but insects and their associations with plants are largely undocumented. Here, we describe a new fossil leaf taxon, Catula gettyi gen et. sp. nov. in the family Lauraceae from the Kaiparowits Formation. Catula gettyi occurs at numerous localities in this deposit that represent ponded and distal floodplain environments. The type locality for C. gettyi has yielded 1,564 fossil leaf specimens of this species, which provides the opportunity to circumscribe this new plant species. By erecting this new genus and species, we are able to describe ecological associations on C. gettyi and place these interactions within a taxonomic context. We describe an extensive archive of feeding damage on C. gettyi caused by herbivorous insects, including more than 800 occurrences of insect damage belonging to five functional feeding groups indicating that insect-mediated damage on this taxon is both rich and abundant. Catula gettyi is one of the best-sampled host plant taxa from the Mesozoic Era, a poorly sampled time interval, and its insect damage is comparable to other Lauraceae taxa from the younger Late Cretaceous Hell Creek Flora of North Dakota, USA.

Ecology and Evolution of Gall-Inducing Arthropods: The Pattern From the Terrestrial Fossil Record

Insect and mite galls on land plants have a spotty but periodically rich and abundant fossil record of damage types (DTs), ichnotaxa, and informally described gall morphotypes. The earliest gall is on a liverwort of the Middle Devonian Period at 385 million years ago (Ma). A 70-million-year-long absence of documented gall activity ensues. Gall activity resumes during the Pennsylvanian Period (315 Ma) on vegetative and reproductive axial organs of horsetails, ferns, and probably conifers, followed by extensive diversification of small, early hemipteroid galler lineages on seed-plant foliage during the Permian Period. The end-Permian (P-Tr) evolutionary and ecological crisis extinguished most gall lineages; survivors diversified whose herbivore component communities surpassed pre-P-Tr levels within 10 million years in the mid-to late Triassic (242 Ma). During the late Triassic and Jurassic Period, new groups of galling insects colonized Ginkgoales, Bennettitales, Pinales, Gnetales, and other gymnosperms, but data are sparse. Diversifying mid-Cretaceous (125–90 Ma) angiosperms hosted a major expansion of 24 gall DTs organized as herbivore component communities, each in overlapping Venn-diagram fashion on early lineages of Austrobaileyales, Laurales, Chloranthales, and Eurosidae for the Dakota Fm (103 Ma). Gall diversification continued into the Ora Fm (92 Ma) of Israel with another 25 gall morphotypes, but as ichnospecies on a different spectrum of plant hosts alongside the earliest occurrence of parasitoid attack. The End-Cretaceous (K-Pg) extinction event (66 Ma) almost extinguished host–specialist DTs; surviving gall lineages expanded to a pre-K-Pg level 10 million years later at the Paleocene-Eocene Thermal Maximum (PETM) (56 Ma), at which time a dramatic increase of land surface temperatures and multiplying of atmospheric pCO2 levels induced a significant level of increased herbivory, although gall diversity increased only after the PETM excursion and during the Early Eocene Climatic Optimum (EECO). After the EECO, modern (or structurally convergent) gall morphotypes originate in the mid-Paleogene (49–40 Ma), evidenced by the Republic, Messel, and Eckfeld floras on hosts different from their modern analogs. During subsequent global aridification, the early Neogene (20 Ma) Most flora of the Czech Republic records several modern associations with gallers and plant hosts congeneric with their modern analogs. Except for 21 gall DTs in New Zealand flora, the gall record decreases in richness, although an early Pleistocene (3 Ma) study in France documents the same plant surviving as an endemic northern Iran but with decreasing associational, including gall, host specificity.

Extinction at the end-Cretaceous and the origin of modern Neotropical rainforests

The end-Cretaceous event was catastrophic for terrestrial communities worldwide, yet its long-lasting effect on tropical forests remains largely unknown. We quantified plant extinction and ecological change in tropical forests resulting from the end-Cretaceous event using fossil pollen (>50,000 occurrences) and leaves (>6000 specimens) from localities in Colombia. Late Cretaceous (Maastrichtian) rainforests were characterized by an open canopy and diverse plant-insect interactions. Plant diversity declined by 45% at the Cretaceous-Paleogene boundary and did not recover for ~6 million years. Paleocene forests resembled modern Neotropical rainforests, with a closed canopy and multistratal structure dominated by angiosperms. The end-Cretaceous event triggered a long interval of low plant diversity in the Neotropics and the evolutionary assembly of today's most diverse terrestrial ecosystem.

Consistent community genetic effects in the context of strong environmental and temporal variation in Eucalyptus

Provenance translocations of tree species are promoted in forestry, conservation, and restoration in response to global climate change. While this option is driven by adaptive considerations, less is known of the effects translocations can have on dependent communities. We investigated the relative importance and consistency of extended genetic effects in Eucalyptus using two species-E. globulus and E. pauciflora. In E. globulus, the dependent arthropod and pathogen canopy communities were quantified based on the abundance of 49 symptoms from 722 progeny from 13 geographic sub-races across 2 common gardens. For E. pauciflora, 6 symptoms were quantified over 2 years from 238 progeny from 16 provenances across 2 common gardens. Genetic effects significantly influenced communities in both species. However, site and year effects outweighed genetic effects with site explaining approximately 3 times the variation in community traits in E. globulus and site and year explaining approximately 6 times the variation in E. pauciflora. While the genetic effect interaction terms were significant in some community traits, broad trends in community traits associated with variation in home-site latitude for E. globulus and home-site altitude for E. pauciflora were evident. These broad-scale trends were consistent with patterns of adaptive differentiation within each species, suggesting there may be extended consequences of local adaptation. While small in comparison to site and year, the consistency of genetic effects highlights the importance of provenance choice in tree species, such as Eucalyptus, as adaptive divergence among provenances may have significant long-term effects on biotic communities.

Persistent biotic interactions of a Gondwanan conifer from Cretaceous Patagonia to modern Malesia

Many plant genera in the tropical West Pacific are survivors from the paleo-rainforests of Gondwana. For example, the oldest fossils of the Malesian and Australasian conifer Agathis (Araucariaceae) come from the early Paleocene and possibly latest Cretaceous of Patagonia, Argentina (West Gondwana). However, it is unknown whether dependent ecological guilds or lineages of associated insects and fungi persisted on Gondwanan host plants like Agathis through time and space. We report insect-feeding and fungal damage on Patagonian Agathis fossils from four latest Cretaceous to middle Eocene floras spanning ca. 18 Myr and compare it with damage on extant Agathis. Very similar damage was found on fossil and modern Agathis, including blotch mines representing the first known Cretaceous-Paleogene boundary crossing leaf-mine association, external foliage feeding, galls, possible armored scale insect (Diaspididae) covers, and a rust fungus (Pucciniales). The similar suite of damage, unique to fossil and extant Agathis, suggests persistence of ecological guilds and possibly the component communities associated with Agathis since the late Mesozoic, implying host tracking of the genus across major plate movements that led to survival at great distances. The living associations, mostly made by still-unknown culprits, point to previously unrecognized biodiversity and evolutionary history in threatened rainforest ecosystems.

The fossil flip-leaves (Retrophyllum, Podocarpaceae) of southern South America

PREMISE OF THE STUDY

The flip-leaved podocarp Retrophyllum has a disjunct extant distribution in South American and Australasian tropical rainforests and a Gondwanic fossil record since the Eocene. Evolutionary, biogeographic, and paleoecological insights from previously described fossils are limited because they preserve little foliar variation and no reproductive structures.

METHODS

We investigated new Retrophyllum material from the terminal Cretaceous Lefipán, the early Eocene Laguna del Hunco, and the early/middle Eocene Río Pichileufú floras of Patagonian Argentina. We also reviewed type material of historical Eocene fossils from southern Chile.

KEY RESULTS

Cretaceous Retrophyllum superstes sp. nov. is described from a leafy twig, while Eocene R. spiralifolium sp. nov. includes several foliage forms and a peduncle with 13 pollen cones. Both species preserve extensive damage from sap-feeding insects associated with foliar transfusion tissue. The Eocene species exhibits a suite of characters linking it to both Neotropical and West Pacific Retrophyllum, along with several novel features. Retrophyllum araucoensis (Berry) comb. nov. stabilizes the nomenclature for the Chilean fossils.

CONCLUSIONS

Retrophyllum is considerably older than previously thought and is a survivor of the end-Cretaceous extinction. Much of the characteristic foliar variation and pollen-cone morphology of the genus evolved by the early Eocene. The mixed biogeographic signal of R. spiralifolium supports vicariance and represents a rare Neotropical connection for terminal-Gondwanan Patagonia, which is predominantly linked to extant Australasian floras due to South American extinctions. The leaf morphology of the fossils suggests significant drought vulnerability as in living Retrophyllum, indicating humid paleoenvironments.

Insect herbivory fluctuations through geological time

Arthropods and land plants are the major macroscopic sources of biodiversity on the planet. Knowledge of the organization and specialization of plant-herbivore interactions, such as their roles in food webs is important for understanding the processes for maintaining biodiversity. A limited number of studies have examined herbivory through geological time. The most have analyzed localities from one restricted interval within a geological period, or a time transition such as the Paleocene-Eocene boundary interval. In the present study, we analyzed the frequency of herbivory and density of damage type (DT) from the Middle Devonian to the early Miocene. The data were compiled from literature sources and focused on studies that describe occurrences of leaves with DTs indicating herbivore consumption as a proportion of the total number of leaves analyzed. The data were standardized based on the DT categories in the Damage Type Guide, and the age of each locality was updated based on the most recent geochronological standard and expressed in millions of years. Temperature and geological age were the best descriptors of the variation in herbivory frequency, which tended to increase at higher temperatures. Two models were equivalent to explain DT density: the interaction between CO₂ levels and geological age, and O₂ levels and geological age had the same predictive power. The density of DT tended to increase with higher content of atmospheric CO₂ and O₂ compared to modern values. The frequency of herbivory and the density of DTs appear to be influenced by long-term atmospheric variables.

From Fossil Parasitoids to Vectors: Insects as Parasites and Hosts

Within Metazoa, it has been proposed that as many as two-thirds of all species are parasitic. This propensity towards parasitism is also reflected within insects, where several lineages independently evolved a parasitic lifestyle. Parasitic behaviour ranges from parasitic habits in the strict sense, but also includes parasitoid, phoretic or kleptoparasitic behaviour. Numerous insects are also the host for other parasitic insects or metazoans. Insects can also serve as vectors for numerous metazoan, protistan, bacterial and viral diseases. The fossil record can report this behaviour with direct (parasite associated with its host) or indirect evidence (insect with parasitic larva, isolated parasitic insect, pathological changes of host). The high abundance of parasitism in the fossil record of insects can reveal important aspects of parasitic lifestyles in various evolutionary lineages. For a comprehensive view on fossil parasitic insects, we discuss here different aspects, including phylogenetic systematics, functional morphology and a direct comparison of fossil and extant species.

Genetic and ontogenetic variation in an endangered tree structures dependent arthropod and fungal communities

Plant genetic and ontogenetic variation can significantly impact dependent fungal and arthropod communities. However, little is known of the relative importance of these extended genetic and ontogenetic effects within a species. Using a common garden trial, we compared the dependent arthropod and fungal community on 222 progeny from two highly differentiated populations of the endangered heteroblastic tree species, Eucalyptus morrisbyi. We assessed arthropod and fungal communities on both juvenile and adult foliage. The community variation was related to previous levels of marsupial browsing, as well as the variation in the physicochemical properties of leaves using near-infrared spectroscopy. We found highly significant differences in community composition, abundance and diversity parameters between eucalypt source populations in the common garden, and these were comparable to differences between the distinctive juvenile and adult foliage. The physicochemical properties assessed accounted for a significant percentage of the community variation but did not explain fully the community differences between populations and foliage types. Similarly, while differences in population susceptibility to a major marsupial herbivore may result in diffuse genetic effects on the dependent community, this still did not account for the large genetic-based differences in dependent communities between populations. Our results emphasize the importance of maintaining the populations of this rare species as separate management units, as not only are the populations highly genetically structured, this variation may alter the trajectory of biotic colonization of conservation plantings.

Novel insect leaf-mining after the end-Cretaceous extinction and the demise of cretaceous leaf miners, Great Plains, USA

Plant and associated insect-damage diversity in the western U.S.A. decreased significantly at the Cretaceous-Paleogene (K-Pg) boundary and remained low until the late Paleocene. However, the Mexican Hat locality (ca. 65 Ma) in southeastern Montana, with a typical, low-diversity flora, uniquely exhibits high damage diversity on nearly all its host plants, when compared to all known local and regional early Paleocene sites. The same plant species show minimal damage elsewhere during the early Paleocene. We asked whether the high insect damage diversity at Mexican Hat was more likely related to the survival of Cretaceous insects from refugia or to an influx of novel Paleocene taxa. We compared damage on 1073 leaf fossils from Mexican Hat to over 9000 terminal Cretaceous leaf fossils from the Hell Creek Formation of nearby southwestern North Dakota and to over 9000 Paleocene leaf fossils from the Fort Union Formation in North Dakota, Montana, and Wyoming. We described the entire insect-feeding ichnofauna at Mexican Hat and focused our analysis on leaf mines because they are typically host-specialized and preserve a number of diagnostic morphological characters. Nine mine damage types attributable to three of the four orders of leaf-mining insects are found at Mexican Hat, six of them so far unique to the site. We found no evidence linking any of the diverse Hell Creek mines with those found at Mexican Hat, nor for the survival of any Cretaceous leaf miners over the K-Pg boundary regionally, even on well-sampled, surviving plant families. Overall, our results strongly relate the high damage diversity on the depauperate Mexican Hat flora to an influx of novel insect herbivores during the early Paleocene, possibly caused by a transient warming event and range expansion, and indicate drastic extinction rather than survivorship of Cretaceous insect taxa from refugia.