Using an integrative taxonomic approach to delimit a sibling species, Mycetomoellerius mikromelanos sp. nov. (Formicidae: Attini: Attina)

Cody Raul Cardenas​, Amy Rongyan Luo, Tappey H. Jones, Ted R. Schultz, Rachelle M.M. Adams​. 2021. PeerJ 9:e11622. https://doi.org/10.7717/peerj.11622

Abstract

The fungus-growing ant Mycetomoellerius (previously Trachymyrmex) zeteki (Weber 1940) has been the focus of a wide range of studies examining symbiotic partners, garden pathogens, mating frequencies, and genomics. This is in part due to the ease of collecting colonies from creek embankments and its high abundance in the Panama Canal region. The original description was based on samples collected on Barro Colorado Island (BCI), Panama. However, most subsequent studies have sampled populations on the mainland 15 km southeast of BCI. Herein we show that two sibling ant species live in sympatry on the mainland: Mycetomoellerius mikromelanos Cardenas, Schultz, & Adams and M. zeteki. This distinction was originally based on behavioral differences of workers in the field and on queen morphology (M. mikromelanos workers and queens are smaller and black while those of M. zeteki are larger and red). Authors frequently refer to either species as “M. cf. zeteki,” indicating uncertainty about identity. We used an integrative taxonomic approach to resolve this, examining worker behavior, chemical profiles of worker volatiles, molecular markers, and morphology of all castes. For the latter, we used conventional taxonomic indicators from nine measurements, six extrapolated indices, and morphological characters. We document a new observation of a Diapriinae (Hymenoptera: Diapriidae) parasitoid wasp parasitizing M. zeteki. Finally, we discuss the importance of vouchering in dependable, accessible museum collections and provide a table of previously published papers to clarify the usage of the name T. zeteki. We found that most reports of M. zeteki or M. cf. zeteki—including a genome—actually refer to the new species M. mikromelanos.

The identity crisis of ecological diversity

Miriti MN. Ecological Applications : a Publication of the Ecological Society of America, 28 Jun 2021, :e02352. DOI: 10.1002/eap.2352 PMID: 34181303 https://doi.org/10.1002/eap.2352

Abstract 

Developing the ecological scientist mindset among underrepresented students in ecology fields (Bowser and Cid, this Forum) provides timely and compelling strategies to broaden inclusion in ecology and environmental biology. Chronic underrepresentation of minorities in ecology and environmental disciplines (EE) is a crisis that is surprising to many, and even more surprising that, for African-Americans, this underrepresentation is more severe compared to other STEM disciplines. It is beyond irony that a discipline that values diversity as a cornerstone of ecological practice continues to struggle to achieve diversity in the ranks of its practitioners.

Autopolyploids of Arabidopsis thaliana are more phenotypically plastic than their diploid progenitors 

Kali Z Mattingly, Stephen M Hovick. 2021. Annals of Botany, mcab081, https://doi.org/10.1093/aob/mcab081

Abstract

Background and Aims
Polyploids are often hypothesized to have increased phenotypic plasticity compared with their diploid progenitors, but recent work suggests that the relationship between whole-genome duplication (WGD) and plasticity is not so straightforward. Impacts of WGD on plasticity are moderated by other evolutionary processes in nature, which has impeded generalizations regarding the effects of WGD alone. We assessed shifts in phenotypic plasticity and mean trait values accompanying WGD, as well as the adaptive consequences of these shifts.

Methods
To isolate WGD effects, we compared two diploid lineages of Arabidopsis thaliana wiht corresponding autotetraploids grown across different salt and nutrient conditions in a growth chamber.

Key Results
For the few cases in which diploids and polyploids differed in plasticity, polyploids were more plastic, consistent with hypotheses that WGD increases plasticity. Under stress, increased plasticity was often adaptive (associated with higher total seed mass), but in other cases plasticity was unrelated to fitness. Mean trait values and plasticity were equally likely to be affected by WGD, but the adaptive consequences of these shifts were often context dependent or lineage specific. For example, polyploids had extended life spans, a shift that was adaptive in one polyploid lineage under amenable conditions but was maladaptive in the other lineage under stress.

Conclusions
Our work shows that increased phenotypic plasticity can result from WGD alone, independent of other evolutionary processes. We find that the effects of WGD can differ depending on the genotype of the progenitor and the environmental context. Though our experiment was limited to two genotypes of a single species, these findings support the idea that WGD can indeed increase plasticity.

Microbial colonization promotes model cockroach gut tissue growth and development

Benjamin C.Jahnes, Keyshap Poudel, Amelia M.Staats, Zakee L.Sabree. Journal of Insect Physiology Volume 133, August–September 2021, 104274. https://doi.org/10.1016/j.jinsphys.2021.104274

Abstract

Background
Digestive tissues are essential for diet processing and nutrient accessibility, especially in omnivores, and these functions occur despite and in collaboration with dynamic microbial communities that reside within and upon these tissues. Prolonged host development and reduced digestive tissue sizes have been observed in germ-free animals, and normal host phenotypes were recovered following the re-introduction of typical gut microbiomes via coprophagy.

Results
High-resolution histological analyses of Periplaneta americana cockroach digestive tissues revealed that total prevention of microbial colonization of the gut had severe impacts on the growth and development of gut tissues, especially the posterior midgut and anterior hindgut subcompartments that are expected to be colonized and inhabited by the greatest number of bacteria. Juveniles that were briefly exposed to normal gut microbiota exhibited a partial gut morphological recovery, suggesting that a single inoculation was insufficient. These data highlight gut microbiota as integral to normal growth and development of tissues they are in direct contact with and, more broadly, the organism in which they reside.

Conclusions
We draw on these data, host life history traits (i.e. multigenerational cohousing, molting, and filial coprophagy and exuvia feeding), and previous studies to suggest a host developmental model in which gut tissues reflect a conflict-collaboration dynamic where 1) nutrient-absorptive anterior midgut tissues are in competition with transient and resident bacteria for easily assimilable dietary nutrients and whose growth is least-affected by the presence of gut bacteria and 2) posterior midgut, anterior hindgut, and to a lesser degree, posterior hindgut tissues are significantly impacted by gut bacterial presence because they are occupied by the greatest number of bacteria and the host is relying upon, and thus collaborating with, them to assist with complex polysaccharide catabolism processing and nutrient provisioning (i.e. short-chain fatty acids).

Plant herbivore protection by arbuscular mycorrhizas: A role for fungal diversity?

Adam Frew, Pedro M. Antunes, Duncan D. Cameron, Sue E. Hartley, Scott N. Johnson, Matthias C. Rillig, Alison E. Bennett. EcoEvoRxiv. July, 2021. FEMS Microbiology Ecology 88: 333–344

Our purpose here is to (i) briefly outline key mechanisms by which the AM symbiosis enhances plant defences to insect herbivores, (ii) summarise where research has made progress in understanding the role of fungal diversity in plant defences against insect herbivory, (iii) emphasise why it is important to focus efforts on understanding how AM fungal diversity determines plant defence outcomes while highlighting the key knowledge gaps to be addressed.

Integrative taxonomy and phylogeography of Telenomus remus (Scelionidae), with the first record of natural parasitism of Spodoptera spp. in Brazil.

Wengrat, A.P.G.S., Coelho Junior, A., Parra, J.R.P. et al. Sci Rep 11, 14110 (2021). https://doi.org/10.1038/s41598-021-93510-3

Abstract

The egg parasitoid Telenomus remus (Hymenoptera: Scelionidae) has been investigated for classical and applied biological control of noctuid pests, especially Spodoptera (Lepidoptera: Noctuidae) species. Although T. remus was introduced into Brazil over three decades ago for classical biological control of S. frugiperda, this wasp has not been recorded as established in corn or soybean crops. We used an integrative approach to identify T. remus, combining a taxonomic key based on the male genitalia with DNA barcoding, using a cytochrome c oxidase subunit I mitochondrial gene fragment. This is the first report of natural parasitism of T. remus on S. frugiperda and S. cosmioides eggs at two locations in Brazil. We also confirmed that the T. remus lineage in Brazil derives from a strain in Venezuela (originally from Papua New Guinea and introduced into the Americas, Africa, and Asia). The occurrence of T. remus parasitizing S. frugiperda and S. cosmioides eggs in field conditions, not associated with inundative releases, suggests that the species has managed to establish itself in the field in Brazil. This opens possibilities for future biological control programs, since T. remus shows good potential for mass rearing and egg parasitism of important agricultural pests such as Spodoptera species.

Decomposing decomposition: isolating direct effects of temperature from other drivers of detrital processing.

Wilmot OJ, Hood JM, Huryn AD, Benstead JP. Ecology. 2021 Jul:e03467. DOI: 10.1002/ecy.3467. PMID: 34236706.

Abstract 

Understanding the observed temperature dependence of decomposition (i.e., its "apparent" activation energy) requires separation of direct effects of temperature on consumer metabolism (i.e., the "inherent" activation energy) from those driven by indirect seasonal patterns in phenology and biomass, and by longer-term, climate-driven shifts in acclimation, adaptation, and community assembly. Such parsing is important because studies that relate temperature to decomposition usually involve multi-season data and/or spatial proxies for long-term shifts, and so incorporate these indirect factors. The various effects of such factors can obscure the inherent temperature dependence of detrital processing. Separating the inherent temperature dependence of decomposition from other drivers is important for accurate prediction of the contribution of detritus-sourced greenhouse gases to climate warming and requires novel approaches to data collection and analysis. Here, we present breakdown rates of red maple litter incubated in coarse- and fine-mesh litterbags (the latter excluding macroinvertebrates) for serial approximately one-month increments over one year in nine streams along a natural temperature gradient (mean annual: 12.8°-16.4°C)from north Georgia to central Alabama, USA. We analyzed these data using distance-based redundancy analysis and generalized additive mixed models to parse the dependence of decomposition rates on temperature, seasonality, and shredding macroinvertebrate biomass. Microbial decomposition in fine-mesh bags was significantly influenced by both temperature and seasonality. Accounting for seasonality corrected the temperature dependence of decomposition rate from 0.25 to 0.08 eV. Shredder assemblage structure in coarse-mesh bags was related to temperature across both sites and seasons, shifting from "cold" stonefly-dominated communities to "warm" communities dominated by snails or crayfish. Shredder biomass was not a significant predictor of either coarse-mesh or macroinvertebrate-mediated (i.e., coarse- minus fine-mesh) breakdown rates, which were also jointly influenced by temperature and seasonality. Unlike fine-mesh bags, however, temperature dependence of litter breakdown did not differ between models with and without seasonality for either coarse-mesh (0.36 eV) or macroinvertebrate-mediated (0.13 eV) rates. We conclude that indirect (non-thermal) seasonal and site-level effects play a variable and potentially strong role in shaping the apparent temperature dependence of detrital breakdown. Such effects should be incorporated into studies designed to estimate inherent temperature dependence of slow ecological processes.

Spatial and Temporal Changes in Testis Morphology and Sperm Ultrastructure of the Sportfish Sauger (Sander canadensis)

Bryan Blawut, Barbara Wolfe, Christoper Premanandan, Gustavo Schuenemann, Stuart A. Ludsin, D. N. Rao Veeramachaneni, Marco A. Coutinho da Silva. 2021. https://doi.org/10.1111/azo.12399

Abstract

The objective of this study was to assess testicular morphology and spermatozoal structure spatially within the reproductive tract and temporally among seasons in the sauger (Sander canadensis). The testis exists as two separate lobes joined at the urogenital pore and were characterised as unrestricted lobular with seminiferous tubules terminating at the ventral periphery and coalescing dorsally on the main sperm duct. Differences were observed between the pre-breeding season (November) and breeding season (March), with every stage of spermatogenesis occurring in spermatocysts in pre-breeding season in contrast to only spermatozoa being present in the tubules and main duct during the breeding season. Longitudinal folds in the main duct epithelium increased in number with increasing proximity to the urogenital pore, greatly increasing epithelial height regardless of season. Sauger spermatozoa consisted of an ovoid head, a midpiece containing 2 – 4 mitochondria incorporated into the head and a single flagellum containing an asymmetrical lateral ribbon. Motile spermatozoa were found throughout the testis during the breeding season. A decrease in sperm concentration was quantified moving proximally, suggesting a hydration effect by the main duct epithelium during the breeding season. These observations fill an important knowledge gap regarding reproductive biology of this impactful recreational fish species.

Disturbance-accelerated succession increases the production of a temperate forest

Christopher M. Gough, Gil Bohrer, Brady S. Hardiman, Lucas E. Nave, Christoph S. Vogel, Jeff W. Atkins, Ben Bond-Lamberty, Robert T. Fahey, Alexander T. Fotis. 2021. https://doi.org/10.1002/eap.2417

Abstract

Many secondary deciduous forests of eastern North America are approaching a transition in which mature early-successional trees are declining, resulting in an uncertain future for this century-long carbon (C) sink. We initiated the Forest Accelerated Succession Experiment (FASET) at the University of Michigan Biological Station to examine the patterns and mechanisms underlying forest C cycling following the stem girdling-induced mortality of >6,700 early-successional Populus spp. (aspen) and Betula papyrifera (paper birch). Meteorological flux tower-based C cycling observations from the 33-ha treatment forest have been paired with those from a nearby unmanipulated forest since 2008. Following over a decade of observations, we revisit our core hypothesis: that net ecosystem production (NEP) would increase following the transition to mid-late-successional species dominance due to increased canopy structural complexity. Supporting our hypothesis, NEP was stable, briefly declined, and then increased relative to the control in the decade following disturbance; however, increasing NEP was not associated with rising structural complexity but rather with a rapid 1-yr recovery of total leaf area index as mid-late-successional Acer, Quercus, and Pinus assumed canopy dominance. The transition to mid-late-successional species dominance improved carbon-use efficiency (CUE = NEP/gross primary production) as ecosystem respiration declined. Similar soil respiration rates in control and treatment forests, along with species differences in leaf physiology and the rising relative growth rates of mid-late-successional species in the treatment forest, suggest changes in aboveground plant respiration and growth were primarily responsible for increases in NEP. We conclude that deciduous forests transitioning from early to middle succession are capable of sustained or increased NEP, even when experiencing extensive tree mortality. This adds to mounting evidence that aging deciduous forests in the region will function as C sinks for decades to come.

Environmental gradients drive physiological variation in Hawaiian corals. Coral Reefs

McLachlan, R.H., Price, J.T., Muñoz-Garcia, A. et al. 2021. https://doi.org/10.1007/s00338-021-02140-8

Abstract

To evaluate potential coral adaptive mechanisms, we investigated physiological traits (biomass, lipid, protein, chlorophyll, and isotopic proxies for trophic strategy) in eight Hawaiian corals species along an environmental gradient of significant wave height, sea surface temperature, and seawater chlorophyll a concentration around the island of O‘ahu, Hawai‘i. We used the amount of physiological variation expressed in corals, and the proportion of this variation that could be explained by environmental variables, to construct hypotheses about the relative capacity for each species to adapt or acclimatize to differing conditions. Genus-level analyses indicated that Montipora and Pocillopora phenotypes are influenced more strongly by the environment than Porites corals. Species-level analyses revealed that Montipora capitata and Pocillopora acuta have the widest physiological niche boundaries, whereas Porites evermanni and Pocillopora meandrina are more physiologically restricted. Correlations between individual traits and the environmental gradient provided insight into potential adaptive mechanisms employed by each species that allow them to persist in reefs such as those within Kāne’ohe Bay, where water flow is lowest, and temperature, acidity, and nutrient concentrations are highest relative to other reefs around O‘ahu. Potential adaptive mechanisms included (a) increased surface-area-to-volume ratios to facilitate higher material flux across the diffusive boundary layer and/or to maximize light harvesting (M. capitata and P. acuta), (b) strategic investment of metabolic energy toward energy reserves (Montipora and Pocillopora), (c) changes in protein management likely via differential expression and function (Porites), and d) increased chlorophyll concentration per Symbiodiniaceae cell to maximize photosynthesis (Porites compressa). Comparison of our results with established patterns in the relative abundance of these species around O‘ahu suggests that species with wide physiological niche boundaries like M. capitata and M. flabellata might be expected to do better under predicted future ocean conditions and outcompete species such as P. evermanni and P. meandrina, making them potential candidates for coral conservation efforts.

A role of asynchrony of seasons in explaining genetic differentiation in a Neotropical toad. 

Thomé, M.T.C., Carstens, B.C., Rodrigues, M.T. et al. Heredity (2021). https://doi.org/10.1038/s41437-021-00460-7

Abstract

The process of diversification can be studied at the phylogeographic level by attempting to identify the environmental features that promote and maintain population divergence. Here we investigate diversification in Rhinella granulosa, a Neotropical toad from northeastern Brazil, by testing a range of hypotheses that encompass different putative mechanisms reducing gene flow among populations. We sequenced single nucleotide polymorphisms and examined individual predictions related to the role of geographic barriers (rivers), ecological gradients, historical habitat stability, and spatial variation in climate seasonality, also known as the asynchrony of seasons hypothesis. This hypothesis postulates that temporal asynchrony of wet and dry seasons over short distances causes parapatric populations to become isolated by time. After determining genetic structure, inferring past distributions, ranking demographic models, and estimating the power of monthly climatic variables, our results identified two populations that are not associated with geographic barriers, biome gradients, or historical refugia. Instead, they are predicted by spatial variation in monthly rainfall and minimum temperature, consistent with the asynchrony of seasons hypothesis, supported also by our comparative framework using multiple matrix regression and linear mixed effects modeling. Due to the toad’s life history, climate likely mediates gene flow directly, with genetic differentiation being provoked by neutral mechanisms related to climate driven population isolation, and/or by natural selection against migrants from populations with different breeding times. The asynchrony of seasons hypothesis is seldom considered in phylogeographic studies, but our results indicate that it should be tested in systems where breeding is tightly coupled with climate.

Potential local adaptation in populations of invasive reed canary grass (Phalaris arundinacea) across an urbanization gradient

Leah M. Weston, Kali Z. Mattingly, Charles T. C. Day, Stephen M. Hovick. 2021. https://doi.org/10.1002/ece3.7938

Abstract

Urban stressors represent strong selective gradients that can elicit evolutionary change, especially in non-native species that may harbor substantial within-population variability. To test whether urban stressors drive phenotypic differentiation and influence local adaptation, we compared stress responses of populations of a ubiquitous invader, reed canary grass (Phalaris arundinacea). Specifically, we quantified responses to salt, copper, and zinc additions by reed canary grass collected from four populations spanning an urbanization gradient (natural, rural, moderate urban, and intense urban). We measured ten phenotypic traits and trait plasticities, because reed canary grass is known to be highly plastic and because plasticity may enhance invasion success. We tested the following hypotheses: (a) Source populations vary systematically in their stress response, with the intense urban population least sensitive and the natural population most sensitive, and (b) plastic responses are adaptive under stressful conditions. We found clear trait variation among populations, with the greatest divergence in traits and trait plasticities between the natural and intense urban populations. The intense urban population showed stress tolerator characteristics for resource acquisition traits including leaf dry matter content and specific root length. Trait plasticity varied among populations for over half the traits measured, highlighting that plasticity differences were as common as trait differences. Plasticity in root mass ratio and specific root length were adaptive in some contexts, suggesting that natural selection by anthropogenic stressors may have contributed to root trait differences. Reed canary grass populations in highly urbanized wetlands may therefore be evolving enhanced tolerance to urban stressors, suggesting a mechanism by which invasive species may proliferate across urban wetland systems generally.