More Like this

1. Fine‐scale genome‐wide signature of Pleistocene glaciation in Thitarodes moths (Lepidoptera: Hepialidae), host of Ophiocordyceps fungus in the Hengduan Mountains

   https://doi.org/10.1111/mec.16457  

   Wang, Zhengyang ; Pierce, Naomi E. ( April 2022 , Molecular Ecology)

   The Hengduan Mountains region is a biodiversity hotspot known for its topologically complex, deep valleys and high mountains. While landscape and glacial refugia have been evoked to explain patterns of interspecies divergence, the accumulation of intra‐species (i.e., population level) genetic divergence across the mountain‐valley landscape in this region has received less attention. We used genome‐wide restriction site‐associated DNA sequencing (RADseq) to reveal signatures of Pleistocene glaciation in populations ofThitarodes shambalaensis(Lepidoptera: Hepialidae), the host moth of parasiticOphiocordyceps sinensis(Hypocreales: Ophiocordycipitaceae) or caterpillar fungus” endemic to the glacier of eastern Mt. Gongga. We used moraine history along the glacier valleys to model the distribution and environmental barriers to gene flow across populations ofT.shambalaensis. We found that moth populations separated by less than 10 km exhibited valley‐based population genetic clustering and isolation‐by‐distance (IBD), while gene flow among populations was best explained by models using information about their distributions at the local last glacial maximum (LGM_L, 58 kya), not their contemporary distribution. Maximum likelihood lineage history among populations, and among subpopulations as little as 500 m apart, recapitulated glaciation history across the landscape. We also found signals of isolated population expansion following the retreat of LGM_Lglaciers. These results reveal the fine‐scale, long‐term historical influence of landscape and glaciation on the genetic structuring of populations of an endangered and economically important insect species. Similar mechanisms, given enough time and continued isolation, could explain the contribution of glacier refugia to the generation of species diversity among the Hengduan Mountains.

    

   more » « less
2. Phylogeny and evolution of the cryptic fungus‐farming ant genus Myrmicocrypta F. Smith (Hymenoptera: Formicidae) inferred from multilocus data

   https://doi.org/10.1111/syen.12313  

   Sosa‐Calvo, Jeffrey ; Fernández, Fernando ; Schultz, Ted R. ( July 2018 , Systematic Entomology)

   Fungus‐farming ants (Hymenoptera: Formicidae) have become model systems for exploring questions regarding the evolution of symbiosis. However, robust phylogenetic studies of both the ant agriculturalists and their fungal cultivars are necessary for addressing whether or not observed ant–fungus associations are the result of coevolution and, if so, whether that coevolution has been strict or diffuse. Here we focus on the evolutionary relationships of the species within the ant genusMyrmicocryptaand of their fungal cultivars. The fungus‐farming ant genusMyrmicocryptawas created by Fr. Smith in 1860 based on a single alate queen. Since then, 31 species and subspecies have been described. Until now, the genus has not received any taxonomic treatment and the relationships of the species within the genus have not been tested. Our molecular analyses, using ∼40 putative species and six protein‐coding (nuclear and mitochondrial) gene fragments, recoverMyrmicocryptaas monophyletic and as the sister group of the genusMycocepurusForel. The speciesM. tuberculataWeber is recovered as the sister to the rest ofMyrmicocrypta. The time‐calibrated phylogeny recovers the age of stem groupMyrmicocryptaplus its sister group as 45 Ma, whereas the inferred age for the crown groupMyrmicocryptais recovered as 27 Ma. Ancestral character‐state analyses suggest that the ancestor ofMyrmicocryptahad scale‐like or squamate hairs and that, although such hairs were once considered diagnostic for the genus, the alternative state of erect simple hairs has evolved at least seven independent times. Ancestral‐state analyses of observed fungal cultivar associations suggest that the most recent common ancestor ofMyrmicocryptacultivated clade 2 fungal species and that switches to clade 1 fungi have occurred at least five times. It is our hope that these results will encourage additional species‐level phylogenies of fungus‐farming ants and their fungal cultivars, which are necessary for understanding the evolutionary processes that gave rise to agriculture in ants and that produced the current diversity of mutualistic ant–fungus interactions.

    

   more » « less
3. 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.

    

   more » « less
4. Simulated folivory increases vertical transmission of fungal endophytes that deter herbivores and alter tolerance to herbivory in Poa autumnalis

   https://doi.org/10.1093/aob/mcaa021  

   Gundel, Pedro E ; Sun, Prudence ; Charlton, Nikki D ; Young, Carolyn A ; Miller, Tom E ; Rudgers, Jennifer A ( February 2020 , Annals of Botany)

   Abstract Background and Aims The processes that maintain variation in the prevalence of symbioses within host populations are not well understood. While the fitness benefits of symbiosis have clearly been shown to drive changes in symbiont prevalence, the rate of transmission has been less well studied. Many grasses host symbiotic fungi (Epichloë spp.), which can be transmitted vertically to seeds or horizontally via spores. These symbionts may protect plants against herbivores by producing alkaloids or by increasing tolerance to damage. Therefore, herbivory may be a key ecological factor that alters symbiont prevalence within host populations by affecting either symbiont benefits to host fitness or the symbiont transmission rate. Here, we addressed the following questions: Does symbiont presence modulate plant tolerance to herbivory? Does folivory increase symbiont vertical transmission to seeds or hyphal density in seedlings? Do plants with symbiont horizontal transmission have lower rates of vertical transmission than plants lacking horizontal transmission? Methods We studied the grass Poa autumnalis and its symbiotic fungi in the genus Epichloë. We measured plant fitness (survival, growth, reproduction) and symbiont transmission to seeds following simulated folivory in a 3-year common garden experiment and surveyed natural populations that varied in mode of symbiont transmission. Key Results Poa autumnalis hosted two Epichloë taxa, an undescribed vertically transmitted Epichloë sp. PauTG-1 and E. typhina subsp. poae with both vertical and horizontal transmission. Simulated folivory reduced plant survival, but endophyte presence increased tolerance to damage and boosted fitness. Folivory increased vertical transmission and hyphal density within seedlings, suggesting induced protection for progeny of damaged plants. Across natural populations, the prevalence of vertical transmission did not correlate with symbiont prevalence or differ with mode of transmission. Conclusions Herbivory not only mediated the reproductive fitness benefits of symbiosis, but also promoted symbiosis prevalence by increasing vertical transmission of the fungus to the next generation. Our results reveal a new mechanism by which herbivores could influence the prevalence of microbial symbionts in host populations. 

   more » « less
5. Cold adaptations along a range limit in an obligate symbiosis

   https://doi.org/10.1111/1365-2435.14120  

   Senula, Sarah F. ; Scavetta, Joseph T. ; Mueller, Ulrich G. ; Seal, Jon Nicholas ; Kellner, Katrin ( July 2022 , Functional Ecology)

   Symbionts can have profound effects on host fitness, adaptations and range distributions. Stress‐induced evolution is difficult to show in obligate symbioses; however, adaptive evolution within an obligate symbiosis can be investigated experimentally or by correlating trait variation with stress along an ecological cline (i.e. temperature‐stress gradient).

   We investigated the cold tolerance of the fungus‐growing antTrachymyrmex septentrionalisby performing cold tolerance assays comparing two populations collected from either the southernmost range of their distribution (Bastrop, Texas) or from a site that is approximately 600 km further north (Norman, Oklahoma). We first compared isolated fungal symbionts grown on artificial media to determine cold tolerance of fungus alone. Subsequently, we conducted cross‐fostering experiments between northern and southern host and symbionts to test for synergisms between the partners in generating adaptations of cold tolerance.

   Ants of the northern fungal populations were more cold adapted than southern fungal populations. Northern nests were deeper and northern colonies initially rejected fungi from the southern population. The cross‐fostering experiments demonstrated that only one partner must be cold tolerant to confer maximum cold tolerance to the ant–fungus symbiosis, because northern ants growing southern fungus under cold stress performed just as well as northern ants growing northern fungi.

   Our results suggest that cold stress has been an important selective factor during the migration of this ant–fungus symbiosis into northern latitudes during the last 10,000 years, and that cold tolerance likely is an energetically demanding trait that may be traded off with other aspects of the symbiosis' life history. The symbiosis also appears to have evolved several additional adaptations that increase survival in cold environments, such as building deeper nests that insulate the fungi from cold surface.

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

    

   more » « less