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1. Tritrophic interactions reinforce a negative preference–performance relationship in the tobacco hornworm ( Manduca sexta )

   https://doi.org/10.1111/een.12852  

   Garvey, Michael A. ; Creighton, J. Curtis ; Kaplan, Ian ( February 2020 , Ecological Entomology)

   Host plants that promote development of insect herbivores are sometimes less preferred to more toxic plants, which are co‐opted for protection from natural enemies, resulting in higher fitness in communities with strong top‐down control. However, the degree to which variation in growth rate and risk of natural enemy attack drive insect plant preferences is an open question, with little field data available across diverse plant families.

   The present study investigated the preference–performance relationship and tritrophic interactions involving the hornwormManduca sexta, its natural enemies, and plants in the nightshade family (Solanaceae) using a 2‐year common garden containing 18 wild and domesticated species. The degree to which natural enemy pressure explained field patterns in the laboratory was then tested using targeted assays involving parasitism by the waspCotesia congregata.

   In the field, the most preferred plants for female oviposition tended to be inversely correlated with the species providing optimal larval growth. Hawkmoths preferred plants in the subgenusPotatoe,Nicotiana, andDaturacompared withCapsicum,Physalis, and the otherSolanumsubgenera. However, larval parasitism byC. congregatawas only significant for hornworms onPotatoe/Daturaand notNicotiana(i.e. 33% vs. 12% vs. 4% parasitism onPotatoe,Datura, andNicotiana, respectively). Experimental laboratory rearing confirmed that wasp survival is lower onNicotianasp. thanSolanum lycopersicum, which could be driven by nicotine.

   The data obtained in the present study show that the negative preference‐performance relationship in hornworms across solanaceous plants is maintained in part because by utilising noxious food plantsM. sextagains protection against parasitism.

    

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2. Differing thermal sensitivities in a host–parasitoid interaction: High, fluctuating developmental temperatures produce dead wasps and giant caterpillars

   https://doi.org/10.1111/1365-2435.13748  

   Moore, M. Elizabeth ; Hill, Christina A. ; Kingsolver, Joel G. ; Marshall, ed., Katie ( March 2021 , Functional Ecology)

   Insect parasitoids, and the arthropod hosts they consume during development, are important ecological players in almost all environments across the globe. As ectothermic organisms, both parasitoid and host are strongly impacted by environmental temperature. If thermal tolerances differ between host insect and parasitoid, then the outcome of their interaction will be determined by the ambient temperature. As mean temperatures continue to rise and extreme temperatures become more frequent, we must determine the effect of high temperature stress on host–parasitoid systems to predict how they will fare in the face of climate change.

   The majority of studies conducted on host–parasitoid systems focus on either performance under constant temperature or a fixed metric of thermal tolerance (CT_max) for individual organisms. However, performance at constant temperatures is not predictive of performance under ecologically relevant, fluctuating temperatures and measurements of thermal thresholds provide little information regarding the effects of temperature throughout development. We address this by testing the effects of increasing mean temperature in both constant and fluctuating (±10°C) environments throughout development on the performance of the parasitoid waspCotesia congregataand its lepidopteran larval host,Manduca sexta.

   The growth ofM. sextawas influenced by mean temperature, diurnal fluctuations and parasitization status. Caterpillar growth rate increased with increasing mean temperature, but decreased in response to diurnal fluctuations and parasitization byC. congregatawasps.

   Wasp survival decreased with increasing mean temperature and with diurnal fluctuations. The effect of diurnal fluctuations was stronger at higher mean temperatures. Diurnal fluctuations at our highest mean temperature treatment (30 ± 10°C) resulted in complete wasp mortality, and parasitized hosts displayed abnormal physiology, wherein they failed to exhibit wasp emergence, did not enter the prepupal stage, continued to feed and grew up to twofold larger than a normal, unparasitized caterpillar.

   Our results indicate hosts and parasitoids in this system have different thermal tolerances during development; the parasitoid wasp suffered complete mortality at a temperature regime that is mildly stressful for the unparasitized caterpillar host species. Our findings suggestC. congregatawill suffer more severely under increasing temperatures thanM. sexta, with cascading trophic and ecological effects.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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3. Evidence of fruit syndromes in the recently diverged wild tomato clade opens new possibilities for the study of fleshy fruit evolution

   https://doi.org/10.1002/ppp3.10399  

   Barnett, Jacob R. ; Sharma, Rovin ; Buonauro, Gina ; Gillis, Ian M. ; Rashidzade, Maryam ; Caicedo, Ana L. ( June 2023 , PLANTS, PEOPLE, PLANET)

   Fleshy fruits provide humans with many flavorful and nutritious crops. Understanding the diversity of these plants is fundamental to managing agriculture and food security in a changing world. This study surveyed fruit trait variation across species of tomato wild relatives and explored associations among color, size, shape, sugars, and acids. These wild tomato species native to South America can be interbred with the economically important cultivated tomato. Beyond its application to tomatoes, deepening our knowledge of how fruit traits evolve together is valuable to crop improvement efforts aimed at breeding more nutritious and appealing varieties of fruits.

   Fleshy fruits display a striking diversity of traits, many of which are important for agriculture. The evolutionary drivers of this variation are not well understood, and most studies have relied on variation found in the wild. Few studies have explored this question on a fine‐grained scale with a group of recently diverged species while controlling for environmental effects.

   We developed the tomato clade as a novel system for fruit trait evolution research by presenting the first common garden‐based systematic survey of variation and phylogenetic signal in color, nutrition, and morphology traits across all 13 species of tomato wild relatives (Solanum sect.Lycopersicon). We laid the groundwork for further testing of potential evolutionary drivers by assessing patterns of clustering and correlation among disperser‐relevant fruit traits as well as historical climate variables.

   We found evidence of two distinct clusters of associated fruit traits defined by color, sugar type, and malic acid concentration. We also observed correlations between a fruit's external appearance and internal nutrient content that could function as honest signals to dispersers. Analyses of historical climate and soil variables revealed an association between red/orange/yellow fruits and high annual average temperature.

   Our results establish the tomato clade as a promising system for testing hypotheses on the drivers of divergence behind early‐stage fleshy fruit evolution, particularly selective pressure from frugivores.

    

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4. The interactive effects of heat stress, parasitism and host plant quality in a host–parasitoid system

   https://doi.org/10.1111/1365-2435.14498  

   Parker, Anna L. ; Kingsolver, Joel G. ( January 2024 , Functional Ecology)

   Species interactions are expected to change in myriad ways as the frequency and magnitude of extreme temperature events increase with anthropogenic climate change.

   The relationships between endosymbionts, parasites and their hosts are particularly sensitive to thermal stress, which can have cascading effects on other trophic levels.

   We investigate the interactive effects of heat stress and parasitism on a terrestrial tritrophic system consisting of two host plants (one common, high‐quality plant and one novel, low‐quality plant), a caterpillar herbivore and a specialist parasitoid wasp.

   We used a fully factorial experiment to determine the bottom‐up effects of the novel host plant on both the caterpillars' life history traits and the wasps' survival, and the top‐down effects of parasitism and heat shock on caterpillar developmental outcomes and herbivory levels.

   Host plant identity interacted with thermal stress to affect wasp success, with wasps performing better on the low‐quality host plant under constant temperatures but worse under heat‐shock conditions.

   Surprisingly, caterpillars consumed less leaf material from the low‐quality host plant to reach the same final mass across developmental outcomes.

   In parasitized caterpillars, heat shock reduced parasitoid survival and increased both caterpillar final mass and development time on both host plants.

   These findings highlight the importance of studying community‐level responses to climate change from a holistic and integrative perspective and provide insight into potential substantial interactions between thermal stress and diet quality in plant–insect systems.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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5. Root herbivory controls the effects of water availability on the partitioning between above‐ and below‐ground grass biomass

   https://doi.org/10.1111/1365-2435.13661  

   Franco, André L. C. ; Gherardi, Laureano A. ; de Tomasel, Cecilia M. ; Andriuzzi, Walter S. ; Ankrom, Katharine E. ; Bach, Elizabeth M. ; Guan, Pingting ; Sala, Osvaldo E. ; Wall, Diana H. ; Holeski, ed., Liza ( August 2020 , Functional Ecology)

   The fraction of primary productivity allocated below‐ground accounts for a larger flow of carbon than above‐ground productivity in most grassland ecosystems. Here, we addressed the question of how root herbivory affects below‐ground allocation of a dominant shortgrass prairie grass in response to water availability. We predicted that high levels of root herbivory by nematodes, as seen under extreme drought in sub‐humid grasslands, would prevent the high allocation to root biomass normally expected in response to low water availability.

   We exposed blue gramaBouteloua gracilis, which accounts for most of the net primary productivity in the shortgrass steppe of the central and southern Great Plains, to three levels of water availability from extreme low to intermediate and extreme high crossed with a gradient of root­herbivore per cent abundance relative to the total nematode community in soil microcosms.

   As hypothesized, the effect of water availability on below‐ground biomass allocation was contingent on the proportion of root herbivores in the nematode community. The relationship between below‐ground biomass allocation and water availability was negative in the absence of root herbivory, but tended to reverse with increasing abundance of root feeders. Increasing abundance of root‐feeding nematodes prevented grasses from adjusting their allocation patterns towards root mass that would, in turn, increase water uptake under dry conditions. Therefore, below‐ground trophic interactions weakened plant responses and increased the negative effects of drought on plants.

   Our work suggests that plant responses to changes in precipitation result from complex interactions between the direct effect of precipitation and indirect effects through changes in the below‐ground trophic web. Such complex responses challenge current predictions of increasing plant biomass allocation below‐ground in water‐stressed grasslands, and deserve further investigation across ecosystems and in field conditions.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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