Plant biology: Insect herbivory on fossil leaves provides the oldest evidence of sleep movements in plants.

Only a few groups of plants can move their leaves at night. A new study documents sleep movements in fossil leaves that are older than the dinosaurs, suggesting that this behavior is much more ancient than previously appreciated.

Lepidoptera demonstrate the relevance of Murray's Law to circulatory systems with tidal flow.

BACKGROUND: Murray's Law, which describes the branching architecture of bifurcating tubes, predicts the morphology of vessels in many amniotes and plants. Here, we use insects to explore the universality of Murray's Law and to evaluate its predictive power for the wing venation of Lepidoptera, one of the most diverse insect orders. Lepidoptera are particularly relevant to the universality of Murray's Law because their wing veins have tidal, or oscillatory, flow of air and hemolymph. We examined over one thousand wings representing 667 species of Lepidoptera. RESULTS: We found that veins with a diameter above approximately 50 microns conform to Murray's Law, with veins below 50 microns in diameter becoming less and less likely to conform to Murray's Law as they narrow. The minute veins that are most likely to deviate from Murray's Law are also the most likely to have atrophied, which prevents efficient fluid transport regardless of branching architecture. However, the veins of many taxa continue to branch distally to the areas where they atrophied, and these too conform to Murray's Law at larger diameters (e.g., Sesiidae). CONCLUSIONS: This finding suggests that conformity to Murray's Law in larger taxa may reflect requirements for structural support as much as fluid transport, or may indicate that selective pressures for fluid transport are stronger during the pupal stage-during wing development prior to vein atrophy-than the adult stage. Our results increase the taxonomic scope of Murray's Law and provide greater clarity about the relevance of body size.

Symmetry systems on the wings of Dichromodes Guenée (Lepidoptera: Geometridae) are unconstrained by venation.

The nymphalid groundplan, an idealized schematic illustrating the essential elements of butterfly wing patterns, predicts a consistent relationship between color pattern and wing venation. Moths in the family Geometridae have wing shapes and patterns that often resemble those of butterflies, and until recently, this family was believed to be among butterflies' closest relatives. However, an examination of the geometrid genus Dichromodes Guenée, 1858 shows no consistent relationship between the central symmetry system and wing venation. Whereas the distal edge of the central symmetry system is predicted to reach the costal margin proximal to the Subcostal vein in butterflies and acronictine moths, it has no consistent relationship with the Subcostal, Radius, or Radial Sector 1 veins in Dichromodes. This finding highlights developmental diversity that was previously overlooked due to the overwhelming preference for butterflies in studies of lepidopteran wing patterns.

A Cretaceous peak in family-level insect diversity estimated with mark-recapture methodology.

The history of insects' taxonomic diversity is poorly understood. The two most common methods for estimating taxonomic diversity in deep time yield conflicting results: the 'range through' method suggests a steady, nearly monotonic increase in family-level diversity, whereas 'shareholder quorum subsampling' suggests a highly volatile taxonomic history with family-level mass extinctions occurring repeatedly, even at the midpoints of geological periods. The only feature shared by these two diversity curves is a steep increase in standing diversity during the Early Cretaceous. This apparent diversification event occurs primarily during the Aptian, the pre-Cenozoic interval with the most described insect occurrences, raising the possibility that this feature of the diversity curves reflects preservation and sampling biases rather than insect evolution and extinction. Here, the capture-mark-recapture (CMR) approach is used to estimate insects' family-level diversity. This method accounts for the incompleteness of the insect fossil record as well as uneven sampling among time intervals. The CMR diversity curve shows extinctions at the Permian/Triassic and Cretaceous/Palaeogene boundaries but does not contain any mass extinctions within geological periods. This curve also includes a steep increase in diversity during the Aptian, which appears not to be an artefact of sampling or preservation bias because this increase still appears when time bins are standardized by the number of occurrences they contain rather than by the amount of time that they span. The Early Cretaceous increase in family-level diversity predates the rise of angiosperms by many millions of years and can be better attributed to the diversification of parasitic and especially parasitoid insect lineages.

The wing pattern of Hydriomena Hübner, [1825] (Lepidoptera: Geometridae: Larentiinae) lacks a predictable relationship with venation.

Two simple models have been successfully applied to predict the relationship between wing pattern and venation in various lineages of Lepidoptera. However, neither of these models holds for the geometrid genus Hydriomena Hübner, 1825. Wing patterns in Hydriomena were studied intensively during the 1920s after the description of the nymphalid groundplan, an idealized schematic that outlines the primary elements of butterfly wing patterns; geometrids strongly resemble butterflies and, until recently, were considered to be among their closest relatives. The evolution of wing pattern in Geometridae has been neglected since the 1930s. Here, the relationship between wing pattern and venation is examined for Hydriomena costipunctata Barnes and McDunnough, 1912 and the Hydriomena speciosata (Packard, 1873) group. These two lineages have some of the simplest wing patterns in Hydriomena, consisting of large, well-defined dark and light pattern elements. The relationship between wing pattern and venation varies considerably within and between these lineages and can even vary between the right and left wings on the same individual. Although many different wing patterns were observed among the individuals examined for this study, not one can be reconciled with either of the models that successfully predict the relationship between wing pattern and venation in many other groups of Lepidoptera. This suggests that bands occurring on the wings of Hydriomena are not homologous with those on the wings of butterflies or of Acronictinae (Macroheterocera: Noctuidae), the only other two obtectomeran lineages for which the relationship between wing pattern and venation has been examined in recent years.

The importance of sampling standardization for comparisons of insect herbivory in deep time: a case study from the late Palaeozoic.

Sampling standardization has not been fully addressed for the study of insect herbivory in the fossil record. The effects of sampling within a single locality were explored almost a decade ago, but the importance of sampling standardization for comparisons of herbivory across space and time has not yet been evaluated. Here, we present a case study from the Permian in which we evaluate the impact of sampling standardization on comparisons of insect herbivory from two localities that are similar in age and floral composition. Comparisons of insect damage type (DT) diversity change dramatically when the number of leaves examined is standardized by surface area. This finding suggests that surface area should always be taken into account for comparisons of DT diversity. In addition, the three most common metrics of herbivory-DT diversity, proportion of leaves herbivorized and proportion of leaf surface area herbivorized-are inherently decoupled from each other. The decoupling of the diversity and intensity of insect herbivory necessitates a reinterpretation of published data because they had been conflated in previous studies. Future studies should examine the divergent ecological factors that underlie these metrics. We conclude with suggestions to guide the sampling and analysis of herbivorized leaves in the fossil record.

Phanerozoic pO2 and the early evolution of terrestrial animals.

Concurrent gaps in the Late Devonian/Mississippian fossil records of insects and tetrapods (i.e. Romer's Gap) have been attributed to physiological suppression by low atmospheric pO2 Here, updated stable isotope inputs inform a reconstruction of Phanerozoic oxygen levels that contradicts the low oxygen hypothesis (and contradicts the purported role of oxygen in the evolution of gigantic insects during the late Palaeozoic), but reconciles isotope-based calculations with other proxies, like charcoal. Furthermore, statistical analysis demonstrates that the gap between the first Devonian insect and earliest diverse insect assemblages of the Pennsylvanian (Bashkirian Stage) requires no special explanation if insects were neither diverse nor abundant prior to the evolution of wings. Rather than tracking physiological constraint, the fossil record may accurately record the transformative evolutionary impact of insect flight.

Color Patterning in Hard Ticks (Acari: Ixodidae).

Among the hard ticks (Acari: Ixodidae), many species in the section Metastriata have intricate ornamentation on the scutum that is often used as a taxonomic character. However, the biological function(s) of this ornamentation remains unknown. Here, we summarize the main functions of color patterns recognized in the animal kingdom-thermoregulation, aposematism, camouflage, aggregation, mate recognition, and sexual signaling-and evaluate the potential of each of these to explain ornamentation in hard ticks. We also note the challenges and uncertainties involved in interpreting ornamentation in ticks as well as potential approaches for future research.

The wing pattern of Moerarchis Durrant, 1914 (Lepidoptera: Tineidae) clarifies transitions between predictive models.

The evolution of wing pattern in Lepidoptera is a popular area of inquiry but few studies have examined microlepidoptera, with fewer still focusing on intraspecific variation. The tineid genus Moerarchis Durrant, 1914 includes two species with high intraspecific variation of wing pattern. A subset of the specimens examined here provide, to my knowledge, the first examples of wing patterns that follow both the 'alternating wing-margin' and 'uniform wing-margin' models in different regions along the costa. These models can also be evaluated along the dorsum of Moerarchis, where a similar transition between the two models can be seen. Fusion of veins is shown not to effect wing pattern, in agreement with previous inferences that the plesiomorphic location of wing veins constrains the development of colour pattern. The significant correlation between wing length and number of wing pattern elements in Moerarchis australasiella shows that wing size can act as a major determinant of wing pattern complexity. Lastly, some M. australasiella specimens have wing patterns that conform entirely to the 'uniform wing-margin' model and contain more than six bands, providing new empirical insight into the century-old question of how wing venation constrains wing patterns with seven or more bands.

Variable wing venation in Agathiphaga (Lepidoptera: Agathiphagidae) is key to understanding the evolution of basal moths.

Details of the ancestral groundplan of wing venation in moths remain uncertain, despite approximately a century of study. Here, we describe a 3-branched subcostal vein, a 5-branched medial vein and a 2-branched cubitus posterior vein on the forewing of Agathiphaga vitiensis Dumbleton 1952 from Vanuatu. Such veins had not previously been described in any Lepidoptera. Because wing veins are typically lost during lepidopteran evolutionary history, rarely-if ever-to be regained, the venation of A. vitiensis probably represents the ancestral character state for moths. Wing venation is often used to identify fossil insects as moths, because wing scales are not always preserved; the presence of a supposedly trichopteran 3-branched subcostal vein in crown Lepidoptera may decrease the certainty with which certain amphiesmenopteran fossils from the Mesozoic can be classified. And because plesiomorphic veins can influence the development of lepidopteran wing patterns even if not expressed in the adult wing, the veins described here may determine the location of wing pattern elements in many lepidopteran taxa.

Forewing color pattern in Micropterigidae (Insecta: Lepidoptera): homologies between contrast boundaries, and a revised hypothesis for the origin of symmetry systems.

BACKGROUND: Despite the great importance of lepidopteran wing patterns in various biological disciplines, homologies between wing pattern elements in different moth and butterfly lineages are still not understood. Among other reasons, this may be due to an incomplete understanding of the relationship between color pattern and wing venation; many individual wing pattern elements have a known relationship with venation, but a framework to unite all wing pattern elements with venation is lacking. Though plesiomorphic wing veins are known to influence color patterning even when not expressed in the adult wing, most studies of wing pattern evolution have focused on derived taxa with a reduced suite of wing veins. RESULTS: The present study aims to address this gap through an examination of Micropterigidae, a very early-diverged moth family in which all known plesiomorphic lepidopteran veins are expressed in the adult wing. The relationship between wing pattern and venation was examined in 66 species belonging to 9 genera. The relationship between venation and pattern element location, predicted based on moths in the family Tortricidae, holds for Sabatinca just as it does for Micropterix. However, the pattern elements that are lightly colored in Micropterix are dark in Sabatinca, and vice-versa. When plotted onto a hypothetical nymphalid wing in accordance with the relationship between pattern and venation discussed here, the wing pattern of Sabatinca doroxena very closely resembles the nymphalid groundplan. CONCLUSIONS: The color difference in pattern elements between Micropterix and Sabatinca indicates that homologies exist among the contrast boundaries that divide wing pattern elements, and that color itself is not a reliable indicator of homology. The similarity between the wing pattern of Sabatinca doroxena and the nymphalid groundplan suggests that the nymphalid groundplan may have originated from a Sabatinca-like wing pattern subjected to changes in wing shape and reduced expression of venation.

Attack risk for butterflies changes with eyespot number and size.

Butterfly eyespots are known to function in predator deflection and predator intimidation, but it is still unclear what factors cause eyespots to serve one function over the other. Both functions have been demonstrated in different species that varied in eyespot size, eyespot number and wing size, leaving the contribution of each of these factors to butterfly survival unclear. Here, we study how each of these factors contributes to eyespot function by using paper butterfly models, where each factor is varied in turn, and exposing these models to predation in the field. We find that the presence of multiple, small eyespots results in high predation, whereas single large eyespots (larger than 6 mm in diameter) results in low predation. These data indicate that single large eyespots intimidate predators, whereas multiple small eyespots produce a conspicuous, but non-intimidating signal to predators. We propose that eyespots may gain an intimidation function by increasing in size. Our measurements of eyespot size in 255 nymphalid butterfly species show that large eyespots are relatively rare and occur predominantly on ventral wing surfaces. By mapping eyespot size on the phylogeny of the family Nymphalidae, we show that these large eyespots, with a potential intimidation function, are dispersed throughout multiple nymphalid lineages, indicating that phylogeny is not a strong predictor of eyespot size.

Conservation threats and the phylogenetic utility of IUCN Red List rankings in Incilius toads.

Phylogenetic analysis of extinction threat is an emerging tool in the field of conservation. However, there are problems with the methods and data as commonly used. Phylogenetic sampling usually extends to the level of family or genus, but International Union for Conservation of Nature (IUCN) rankings are available only for individual species, and, although different species within a taxonomic group may have the same IUCN rank, the species may have been ranked as such for different reasons. Therefore, IUCN rank may not reflect evolutionary history and thus may not be appropriate for use in a phylogenetic context. To be used appropriately, threat-risk data should reflect the cause of extinction threat rather than the IUCN threat ranking. In a case study of the toad genus Incilius, with phylogenetic sampling at the species level (so that the resolution of the phylogeny matches character data from the IUCN Red List), we analyzed causes of decline and IUCN threat rankings by calculating metrics of phylogenetic signal (such as Fritz and Purvis' D). We also analyzed the extent to which cause of decline and threat ranking overlap by calculating phylogenetic correlation between these 2 types of character data. Incilius species varied greatly in both threat ranking and cause of decline; this variability would be lost at a coarser taxonomic resolution. We found far more phylogenetic signal, likely correlated with evolutionary history, for causes of decline than for IUCN threat ranking. Individual causes of decline and IUCN threat rankings were largely uncorrelated on the phylogeny. Our results demonstrate the importance of character selection and taxonomic resolution when extinction threat is analyzed in a phylogenetic context.

Color Pattern on the Forewing of Micropterix (Lepidoptera: Micropterigidae): Insights into the Evolution of Wing Pattern and Wing Venation in Moths.

Wing patterns are key taxonomic characters that have long been used in descriptions of Lepidoptera; however, wing pattern homologies are not understood among different moth lineages. Here, we examine the relationship between wing venation and wing pattern in the genus Micropterix, among the most basal extant Lepidoptera, in order to evaluate the two existing predictive models that have the potential to establish wing pattern element homologies for the order. The location of wing pattern elements along the costal margin of the wing in Micropterix is consistent with the predictions of the model proposed for Tortricidae by Brown and Powell in 1991, later modified by Baixeras in 2002. The predictive power of this model for such distantly related taxa suggests that the model may hold across various superfamilies within Lepidoptera, and supports the long-held notion that fasciae, not spots, are the most likely primitive wing pattern elements for the order. In addition, the location of wing pattern elements suggests that the wing vein commonly termed Sc1 may in fact be a different vein, which Comstock identified in Trichoptera and referred to as "a."

Nymphalid eyespots are co-opted to novel wing locations following a similar pattern in independent lineages.

BACKGROUND: Variation in the number of repeated traits, or serial homologs, has contributed greatly to animal body plan diversity. Eyespot color patterns of nymphalid butterflies, like arthropod and vertebrate limbs, are an example of serial homologs. These eyespot color patterns originated in a small number of wing sectors on the ventral hindwing surface and later appeared in novel wing sectors, novel wings, and novel wing surfaces. However, the details of how eyespots were co-opted to these novel wing locations are currently unknown. RESULTS: We used a large data matrix of eyespot/presence absence data, previously assembled from photographs of contemporary species, to perform a phylogenetic investigation of eyespot origins in nine independent nymphalid lineages. To determine how the eyespot gene regulatory network acquired novel positional information, we used phylogenetic correlation analyses to test for non-independence in the origination of eyespots. We found consistent patterns of eyespot gene network redeployment in the nine lineages, where eyespots first redeployed from the ventral hindwing to the ventral forewing, then to new sectors within the ventral wing surface, and finally to the dorsal wing surface. Eyespots that appeared in novel wing sectors modified the positional information of their serial homolog ancestors in one of two ways: by changing the wing or surface identity while retaining sector identity, or by changing the sector identity while retaining wing and surface identity. CONCLUSIONS: Eyespot redeployment to novel sectors, wings, and surfaces happened multiple times in different nymphalid subfamilies following a similar pattern. This indicates that parallel mutations altering expression of the eyespot gene regulatory network led to its co-option to novel wing locations over time.

Evolution of a complex behavior: the origin and initial diversification of foliar galling by Permian insects.

A central notion of the early evolution of insect galling is that this unique behavior was uncommon to rare before the diversification of angiosperms 135 to 125 m.yr. ago. However, evidence accumulated during recent years shows that foliar galls were diverse and locally abundant as early as the Permian Period, 299 to 252 m.yr. ago. In particular, a diversity of leaf galling during the Early Permian has recently been documented by the plant-damage record of foliar galls and, now, our interpretation of the body-fossil record of culprit insect gallers. Small size is a prerequisite for gallers. Wing-length measurements of Permian insects indicate that several small-bodied hemipteroid lineages originated early during the Permian, some descendant lineages of which gall the leaves of seed plants to the present day. The earliest foliar gallers likely were Protopsyllidiidae (Hemiptera) and Lophioneuridae (Thripida). Much of the Early Permian was a xeric interval, and modern galls are most common in dry, extra-tropical habitats such as scrubland and deserts. Plant-damage, insect body fossils, and the paleoclimate record collectively support the ecological expansion of foliar galling during the Early Permian and its continued expansion through the Late Permian.