Evidence for morph-specific substrate choice in a green-brown polymorphic grasshopper

Testing the reproducibility of ecological studies on insect behavior in a multi-laboratory setting identifies opportunities for improving experimental rigor

The reproducibility of studies involving insect species is an underexplored area in the broader discussion about poor reproducibility in science. Our study addresses this gap by conducting a systematic multi-laboratory investigation into the reproducibility of ecological studies on insect behavior. We implemented a 3 × 3 experimental design, incorporating three study sites, and three independent experiments on three insect species from different orders: the turnip sawfly (Athalia rosae, Hymenoptera), the meadow grasshopper (Pseudochorthippus parallelus, Orthoptera), and the red flour beetle (Tribolium castaneum, Coleoptera). Using random-effect meta-analysis, we compared the consistency and accuracy of treatment effects on insect behavioral traits across replicate experiments. We successfully reproduced the overall statistical treatment effect in 83% of the replicate experiments, but overall effect size replication was achieved in only 66% of the replicates. Thus, though demonstrating sufficient reproducibility in some measures, this study also provides the first experimental evidence for cases of poor reproducibility in insect experiments. Our findings further show that reasons causing poor reproducibility established in rodent research also hold for other study organisms and research questions. We believe that a rethinking of current best practices is required to face reproducibility issues in insect studies but also across disciplines. Specifically, we advocate for adopting open research practices and the implementation of methodological strategies that reduce bias and problems arising from over-standardization. With respect to the latter, the introduction of systematic variation through multi-laboratory or heterogenized designs may contribute to improved reproducibility in studies involving any living organisms.

Comments on Neoconocephalus Karny, 1907 (Orthoptera, Tettigoniidae, Conocephalinae) species described by Salvador de Toledo Piza Jr.: The first contribution to the knowledge of South American species

Neoconocephalus Karny, 1907 is the third largest genus of Tettigoniidae with 129 valid species. Distributed throughout the American continents, it has been the subject of several faunal, bioacoustic, and phylogenetic studies, but never focused on the South American fauna. Type material of 19 Neoconocephalus species described by Professor Salvador de Toledo Piza Júnior (1898-1988) deposited at the Museu de Entomologia of the Escola Superior de Agricultura "Luiz de Queiroz" (MELQ), Universidade de São Paulo, Brazil, was revised. The following nine species are considered valid (with proposed junior synonyms): Neoconocephalus boraceae Piza, 1952, N. boraceanus Piza, 1983, N. corumbaensis Piza, 1969, N. curitibensis Piza, 1952 (= N. rioclarensis Piza, 1975 syn. nov.), N. gaucho Piza, 1969 (= N. creusae Piza, 1970 syn. nov.), N. guyvalerioi Piza, 1972 (= N. precarius Piza, 1975 syn. nov., = N. matogrossensis (Piza, 1983) syn. nov.), N. incertus (Piza, 1958) (= N. ferreirai (Piza, 1971) syn. nov., = N. lavrensis Piza, 1971 syn. nov., = N. paravicinus Piza, 1973 syn. nov., = N. riparius (Piza, 1983) syn. nov., = N. xiphophorus Piza, 1975 syn. nov.), N. karollenkoi Piza, 1983, and N. vittatus (Piza, 1973) (= N. spitzi Piza, 1983 syn. nov.). Based on the study of additional specimens deposited in five other Brazilian collections, these valid species are redescribed and external morphology photographs are provided. In addition, known distribution of these species is updated, including 23 new records for the nine species for ten Brazilian states.

A macroevolutionary perspective of cryptic coloration in sexually dichromatic grasshoppers of the genus Sphenarium (Orthoptera: Pyrgomorphidae)

Background matching and disruptive coloration are defense mechanisms of animals against visual predators. Disruptive coloration tends to evolve in microhabitats that are visually heterogeneous, while background matching is favored in microhabitats that are chromatically homogeneous. Controlling for the phylogeny, we explored the evolution of the coloration and the marking patterns in the sexual dichromatic and widely distributed neotropical grasshoppers of the genus Sphenarium. These grasshoppers represent an excellent model to investigate the evolution of cryptic coloration on insects due to the heterogeneity of the environments where they have evolved. We found a correlation between the grasshoppers' coloration and disruptive markings with the chromatic properties of their environments that was inferred by the levels of precipitation during the rainy season. The results suggest that colors and marking patterns could evolve due to predation pressures. Color in both sexes could offer camouflage that is not perfectly background matched to a single habitat but instead offers a degree of resemblance to multiple backgrounds. Moreover, we found that males and females chromatic properties differ between them and precipitation levels where the species are found. This suggests that the sexes have diverged in their response to the environments, favoring the evolution of sexual dichromatism in these grasshoppers.

Differential Survival and Background Selection in Cryptic Trunk-Dwelling Arthropods in Fire-Prone Environments

AbstractFire events change background color, impairing camouflage strategies. However, selection for polymorphic populations may increase camouflage and survival by reducing predation risks. We conducted experiments addressing background selection and predation pressures on the effectiveness of arthropod camouflage against predation in burned and unburned trunks. We tested color and luminance contrasts, as well as trunk preferences, in a color polymorphic grasshopper and praying mantis species with melanic and brown morphs, and a spider species with a single dark color. To expand the scope of our study, we used two distinct visual models of avian predators: ultraviolet sensitive and violet sensitive. We also performed predation experiments using theoretical prey exhibiting black and brown color and human "predators" to understand the effectiveness of color polymorphism against different trunk conditions. Melanic morphs had lower achromatic contrast in burned backgrounds for both visual systems, suggesting that melanism promotes advantages against predation over long distances. However, only spiders actively selected the low-contrasting burned trunks, indicating habitat specialization. The predation experiments showed that black models benefited from camouflage on burned trunks. Conversely, brown models elicited more time and reduced distance in predator searching compared with the black targets on unburned trunks. We suggest that postfire effects can enhance color contrasts and increase predation over color-mismatching individuals, which translates into selection pressures for color polymorphism and matching background choices.

Niche construction and the environmental term of the price equation: How natural selection changes when organisms alter their environments

Organisms construct their own environments and phenotypes through the adaptive processes of habitat choice, habitat construction, and phenotypic plasticity. We examine how these processes affect the dynamics of mean fitness change through the environmental change term of the Price Equation. This tends to be ignored in evolutionary theory, owing to the emphasis on the first term describing the effect of natural selection on mean fitness (the additive genetic variance for fitness of Fisher's Fundamental Theorem). Using population genetic models and the Price Equation, we show how adaptive niche constructing traits favorably alter the distribution of environments that organisms encounter and thereby increase population mean fitness. Because niche-constructing traits increase the frequency of higher-fitness environments, selection favors their evolution. Furthermore, their alteration of the actual or experienced environmental distribution creates selective feedback between niche constructing traits and other traits, especially those with genotype-by-environment interaction for fitness. By altering the distribution of experienced environments, niche constructing traits can increase the additive genetic variance for such traits. This effect accelerates the process of overall adaption to the niche-constructed environmental distribution and can contribute to the rapid refinement of alternative phenotypic adaptations to different environments. Our findings suggest that evolutionary biologists revisit and reevaluate the environmental term of the Price Equation: owing to adaptive niche construction, it contributes directly to positive change in mean fitness; its magnitude can be comparable to that of natural selection; and, when there is fitness G × E, it increases the additive genetic variance for fitness, the much-celebrated first term.

Ontogeny of color development in two green-brown polymorphic grasshopper species

Many insects, including several orthopterans, undergo dramatic changes in body coloration during ontogeny. This variation is particularly intriguing in gomphocerine grasshoppers, where the green and brown morphs appear to be genetically determined (Schielzeth & Dieker, 2020, BMC Evolutionary Biology, 20, 63; Winter et al., 2021, Heredity, 127, 66). A better understanding of how these color morphs develop during ontogeny can provide valuable insights into the evolution and ecology of such a widespread color polymorphism. Here, we focus on the color development of two green-brown polymorphic species, the club-legged grasshopper Gomphocerus sibiricus and the steppe grasshopper Chorthippus dorsatus. By following the color development of individuals from hatching to adulthood, we found that color morph differences begin to develop during the second nymphal stage, are clearly defined by the third nymphal stage, and remain stable throughout the life of an individual. Interestingly, we also observed that shed skins of late nymphal stages are identifiable by color morphs based on their yellowish coloration, rather than the green that marks green body parts. Furthermore, by assessing how these colors are perceived by different visual systems, we found that certain potential predators can chromatically discriminate between morphs, while others may not. These results suggest that the putative genes controlling color morph are active during the early stages of ontogeny, and that green color is likely composed of two components, one present in the cuticle and one not. In addition, the effectiveness of camouflage appears to vary depending on the specific predator involved.

Evidence for morph-specific substrate choice in a green-brown polymorphic grasshopper

Orthopteran insects are characterized by high variability in body coloration, in particular featuring a widespread green-brown color polymorphism. The mechanisms that contribute to the maintenance of this apparently balanced polymorphism are not yet understood. To investigate whether morph-dependent microhabitat choice might contribute to the continued coexistence of multiple morphs, we studied substrate choice in the meadow grasshopper Pseudochorthippus parallelus. The meadow grasshopper occurs in multiple discrete, genetically determined color morphs that range from uniform brown to uniform green. We tested whether three common morphs preferentially choose differently colored backgrounds in an experimental arena. We found that a preference for green backgrounds was most pronounced in uniform green morphs. If differential choices improve morph-specific performance in natural habitats via crypsis and/or thermoregulatory benefits, they could help to equalize fitness differences among color morphs and potentially produce frequency-dependent microhabitat competition, though difference appear too small to serve as the only explanation. We also measured the reflectance of the grasshoppers and backgrounds and used visual modeling to quantify the detectability of the different morphs to a range of potential predators. Multiple potential predators, including birds and spiders, are predicted to distinguish between morphs chromatically, while other species, possibly including grasshoppers themselves, will perceive only differences in brightness. Our study provides the first evidence that morph-specific microhabitat choice might be relevant to the maintenance of the green-brown polymorphisms in grasshoppers and shows that visual distinctness of color morphs varies between perceivers.