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opencc-zeroApr 2021View details →

Data from: Do plant-microbe interactions support the Stress Gradient Hypothesis?

The Stress Gradient Hypothesis (SGH), which predicts increasing ratios of facilitative:competitive interactions with increasing stress, has long been a guiding framework for conceptualizing plant-plant interactions. Recently, there has been a growing recognition of the roles of microbes in mitigating or exacerbating environmental stress for their plant hosts. As such, we might predict based on the SGH that beneficial microbial effects on plant performance should be positively associated with stress. We hypothesized that support for the SGH would also vary depending on the host plant's habitat specialization such that species that specialize in high stress habitats and thus likely coevolved with the resident microbes would exhibit stronger support for the SGH than non-specialist plant species. We further hypothesized that support for the SGH would vary with germination frequency, since boosting germination of low-frequency germinators is one effective means by which microbes can benefit plant species performance. Here, we explore whether plant-microbial interactions support the SGH, using 12 plant species native to the Florida rosemary scrub. We conducted factorial experiments that manipulated the presence of microbes in nine soils collected along an elevational stress gradient, and recorded germination frequency and biomass. Microbes increased the germination frequency of four species, all of which had relatively low germination rates. Furthermore, we found support for the SGH in nearly half of the species examined, with soil microbes facilitating germination with increasing stress for five of the 12 species tested, and none of the species exhibiting the opposite trend. Support for the SGH was not predicted by either the plant hosts' habitat specialization or germination frequency. In contrast to germination, biomass results showed little support for the SGH, with four of 12 species refuting and one species supporting SGH predictions. Taken together, our study documents that interactions between the soil microbial community and plant species along a stress gradient can support the SGH, but emphasizes that these effects are life history stage-dependent. This work also identifies a common mechanism (germination facilitation) by which microbes can benefit plant species in stressful habitats.

opencc-zeroSep 2020View details →

Data from: Chloroplast population genetics reveals low levels of genetic variation and conformation to the central–marginal hypothesis in Taxus wallichiana var. mairei, an endangered conifer endemic to China

The central–marginal hypothesis predicts that geographically peripheral populations should exhibit reduced genetic diversity and increased genetic differentiation than central populations due to smaller effective population size and stronger geographical isolation. We evaluated these predictions in the endangered conifer Taxus wallichiana var. mairei. Eight plastid simple sequence repeats (cpSSRs) were used to investigate plastid genetic variation in 22 populations of Taxus wallichiana var. mairei, encompassing nearly its entire distribution range. Low levels of plastid genetic variation and differentiation were detected in the populations, and the findings were attributed to low mutation rates, small population sizes, habitat fragmentation and isolation, and effective pollen or seed dispersal. Hunan and Hubei were identified as major refugia based on the number of private haplotypes and species distribution modeling. Trends in plastid genetic diversity and genetic differentiation from central to peripheral populations supported the predictions of the central–marginal hypothesis. In scenarios wherein the future climate becomes warmer, we predict that some peripheral populations will disappear and southern and southeastern regions will become significantly less habitable. Factors that include the levels of precipitation during the driest month, annual precipitation level, and annual temperature range will be decisive in shaping the future distribution of these populations. This study provides a theoretical basis for the conservation of T. wallichiana var. mairei.

opencc-zeroOct 2020View details →

Data from: Origins of global mountain plant biodiversity: testing the "mountain-geobiodiversity hypothesis"

Aim Our objective is to analyse global-scale patterns of mountain biodiversity (vascular plants) and the driving forces leading to the observed patterns. More specifically, we test the "mountain geobiodiversity hypothesis" (MGH) which is based on the assumption that it is not mountain-uplift alone which drives the evolution of mountain biodiversity, but rather the combination of geodiversity evolution and Neogene and Pleistocene climate changes. Hence, we address the following questions: 1) Do areas of high geodiversity and high biodiversity in mountains overlap, i.e., can mountain geodiversity predict mountain biodiversity? 2) What is the role of Pleistocene climate change in shaping mountain biodiversity? 3) Did diversification rate shifts occur predominantly with the onset of more pronounced climate fluctuations in the late Neogene and Pleistocene fostering a "species pump" effect, as predicted by the MGH? Location Global. Methods We used generalized linear models to test to what extent vascular plant species diversity in mountains can be explained by net primary productivity, geodiversity and Pleistocene climate fluctuations (i.e., changes in temperature between the Last Glacial Maximum (LGM) and today). In addition, we compiled dates of diversification rate shifts from mountain systems and investigated whether these shifts occurred predominantly before or after the global major climatic fluctuations of the late Neogene and Pleistocene. Results Both net primary productivity and elevation range show a positive relationship, whereas Pleistocene climatic fluctuations show a negative impact on plant species diversity. The availability of climatic niche space during the LGM differs markedly among mountain systems. Shifts to higher diversification rates or starts of radiations showed the highest concentration from the late Miocene towards the Pleistocene, supporting the MGH. The most commonly inferred drivers of diversification were key innovations, geological processes (uplift), and climate. Main conclusions Our analyses point towards an important role of historical factors, i.e., Pleistocene climatic changes, on mountain plant species richness. Mountain systems characterised by small elevational ranges and strong modifications of temperature profiles appear to harbour fewer radiations. In contrast, mountain systems with the largest elevational ranges and stronger overlap between today´s and LGM temperature profiles are also those where most plant radiations were identified.

opencc-zeroDec 2020View details →

Data from: The biotic interactions hypothesis partially explains bird species turnover along a lowland Neotropical precipitation gradient

Aim: We evaluated the influence of climate in determining bird communities along precipitation gradients. We argue that mechanisms responsible for community turnover along precipitation gradients are similar to mechanisms operating along temperature and latitudinal gradients. We test the hypothesis that environmental conditions affect community composition in dry forests, whereas biotic interactions affect community composition in wet forests. Location: Low-elevation forests along a precipitation gradient in Colombia where precipitation ranges from 700 – 4000 mm annually but elevation and temperature remain constant. Time period: Present day Major Taxa Studied: Tropical Forest Birds. Methods: We performed 291 bird counts in nine study areas across the ~3000 mm precipitation range. In each locality we obtained climatic characteristics, and a phylogenetic, morphological and physiological proxy data set to test predictions about the evolutionary relationships and distribution of traits. Results: Bird communities changed abruptly along the precipitation gradient and could be divided into dry and wet forest communities. Analyses of phylogenetic relationships, trait space, and observations at nests suggested that environmental filtering is more important in dry forest, especially for breeding. In contrast, we found little evidence that competition was more important in wet forest. Nest predation or competition for nest space, however, may be more critical in wetter forests. Conclusions: The two distinct bird communities we documented suggest that lowland precipitation gradients, where temperature is constant, can be as important as temperature gradients in generating high beta diversity. We conclude that the breeding process in bird communities might be crucial for determining community assembly along environmental gradients. Given that recent population declines in tropical birds have been attributed to changes in precipitation, by understanding the mechanisms underlying community assembly along precipitation gradients our study may improve our ability to understand those declines and predict the effects of climate change on neotropical avifauna.

opencc-zeroJan 2021View details →

Testing the niche differentiation hypothesis in wild capuchin monkeys with polymorphic color vision

The polymorphic color vision system of most North, Central, and South American monkeys is a textbook case of balancing selection, yet the mechanism behind it is poorly understood. Previous work has established task-specific foraging advantages to different color vision phenotypes: dichromats (red-green colorblind) are more efficient foraging for invertebrates, while trichromats (color "normal" relative to humans) are more efficient foraging for "reddish" ripe fruit, suggesting that niche differentiation may underlie the maintenance of color vision variation. We explore a prediction of the niche differentiation hypothesis by asking whether dichromatic and trichromatic capuchin monkeys (Cebus imitator) diverge in their foraging activity budget, specifically testing whether dichromats forage more frequently for invertebrates and trichromats forage more frequently for "reddish" ripe fruit. To assess this, we analyze a large dataset of behavioral scan samples (n = 21,984) from 48 wild adult female capuchins of known color vision genotype, dominance rank and reproductive status, together with models of food conspicuity. We find no significant differences between dichromats and trichromats in the frequency of scans spent foraging for different food types but do find that nursing females forage less overall than cycling females. Our results suggest that the potential for color vision-based niche differentiation in foraging time may be curtailed by the energetic requirements of reproduction, behavioral synchrony caused by group-living, and/or individual preferences. While niche differentiation in activity budgets by color vision type is not apparent, fine-scale niche differentiation may be occurring. This research enhances our understanding of the evolutionary processes maintaining sensory polymorphisms.

FIGURE 12 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 12. Illustration of Neacomys serranensis sp. nov. by wildlife artist and zoologist Velizar Simeonovski.

FIGURE 10 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 10. Comparison of the lateral profiles of the skulls of Trans-Andean species of Neacomys present in Colombia: A) Neacomys sp. nov. (UIS-MHN-M 1068, holotype). B) Neacomys tenuipes (UIS-MHN-M 1723). Note a more convex profile of the braincase, a thicker hamular process of the squamosal, a broader condylar process, a larger and laterally projected mental foramen, and the anterior margin of nasals without a hump in Neacomys sp. nov. con: condylar process; hp: hamular process of the squamosal; mf: mental foramen; nas: nasals.

FIGURE 8 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 8. Ventral perspectives of adult specimens illustrating the striking difference in ventral fur of the two Trans-Andean species of Neacomys present in Colombia: A) Holotype of Neacomys sp. nov (UIS-MHN-M 1068). B) Section of the holotype of Neacomys sp. nov. showing its characteristic gray-based ochraceous-buff ventral fur. C) Neacomys tenuipes (UIS-MHN-M 1723); note the contrasting entirely white ventral fur of this species.

FIGURE 7 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 7. Frontal perspectives of adult specimens belonging to the two Trans-Andean species of Neacomys present in Colombia: A) Holotype of Neacomys sp. nov (UIS-MHN-M 1068); note the distinctive broad ochraceous-orange patches in the sides of the muzzle of this species. B) Neacomys tenuipes (UIS-MHN-M 1723).

FIGURE 6 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 6. Dorsal perspectives of adult specimens belonging to the two Trans-Andean species of Neacomys present in Colombia: A) Holotype of Neacomys sp. nov (UIS-MHN-M 1068). B) Neacomys tenuipes (UIS-MHN-M 1723); note that a portion of the tail is missing in this specimen.

FIGURE 5. A in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 5. A) Montane forest habitat along the left Bank of the La San Guillerma stream, adjacent to the type locality of Neacomys sp. nov. (municipality of El Carmen de Chucurí) (Photograph by Juliette Gualdrón) B) View of the forest remnant where the second specimen of Neacomys sp nov. was collected (municipality of Hato) (Photograph by Juliette Gualdrón). C) Topography of the western slope of the Serranía de los Yariguíes from the campsite "Finca Buenos Aires"; near the type locality of Neacomys sp. nov. D) Educational activity with members of the community in the municipality of El Carmen del Chucurí, Vereda la Bodega, Sector Manchurrias, illustrating the importance of government funded projects (like Santander BIO expeditions), not only to inventory the biodiversity of remote areas, but also to teach local people to preserve it.

FIGURE 4 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 4. Scatterplots of the Principal Components Analyses: PC1 and PC2 are represented in the graphics. A. PCA of the external and craniodental variables of all the small-bodied species of Neacomys; B. PCA of the craniodental variables of N. tenuipes and Neacomys sp. nov. Miniatures in the right side correspond to the Bayesian Cytb phylogeny recovered here (FIGURE 3): species in the scatterplots and the phylogenies are same colored.

FIGURE 3 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 3. Bayesian Inference topology based on Cytb sequence data used to assess the position of Neacomys sp. nov. in relation to other species in the genus (BI and ML analyses resulted in congruent topologies). Support values are indicated for each node (Bayesian posterior probabilities to the left, and percentages of 1,000 bootstrap replicates to the right). Each terminal is identified by country of origin, the next largest political unit, and GenBank accession number (in red). For specimens of N. tenuipes and Neacomys sp. nov. sequenced here, collection numbers are provided, as well as a number referring to localities mapped in FIGURE 2 and listed in Appendix I. Shaded colored boxes enclose the species groups proposed by Hurtado & Pacheco (2017) and Semedo et al. (2020). Abbreviations: BO (Bolivia), BR (Brazil), CO (Colombia), EC (Ecuador), FG (French Guyana), GU (Guyana), PE (Peru), and SU (Suriname).

FIGURE 11 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 11. Selected qualitative morphological traits differentiating Trans-Andean species of Neacomys present in Colombia: A), C), E) Neacomys sp. nov. B), D), F) N. tenuipes. Note the tegmen tympani exposed above the dorsal surface of the ectotympanic, the opened ectotympanic ring, the larger orbicular apophysis of the malleus, the bifurcated paraoccipital process, the deeper folds of the upper molars, and the divided mesoflexus of M1 in the new species. ab: auditory bullae; adeect: anterodorsal edge of the ectotympanic; hyp: hypoflexus; hp: hamular process of the squamosal; M1 prc: procingulum of first upper molar; mes: mesoflexus; met: metaflexus; mt: mastoid tubercle; oa: orbicular apophysis; par: paraflexus; pgf: postglenoid foramen; pp: paraoccipital process; pro: protoflexus; ssf: subsquamosal fenestra; tt: tegmen tympani.

FIGURE 2 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 2. Map showing collection localities of the named and unamed small-bodied species of Neacomys (except N. pictus) along with salient topographic features of northern South America. Localities of N. tenuipes and Neacomys sp. nov are numbered according to Appendix I. Localities of the remaining species are detailed in Voss et al. (2001), Sánchez-Vendizú et al. (2018), and Semedo et al. (2020). Miniature in the right side of the map corresponds to the Bayesian Cytb phylogeny recovered here (FIGURE 3): species in the map and phylogeny are same colored; the numbers in some nodes correspond to the median divergence times estimated by Upham et al. (2019) within Neacomys.

FIGURE 1 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 1. Map of collecting localities of the specimens of Neacomys sp. nov. (stars) 1. Colombia, Department of Santander, Municipality of El Carmen de Chucurí, vereda La Bodega, sector Manchurrias, western slope of the Serranía de los Yariguíes, Finca Buenos Aires, in the basin of the La San Guillerma stream (Type locality); 2. Colombia, Department of Santander, Municipality of Hato, vereda Hoya Negra. Numbers also correspond to the localities listed in Appendix I. Dashed lines represent boundaries of the municipalities encompassing the two localities. Green polygon represents the area comprised by the Serranía de los Yariguíes National Natural Park.

FIGURE 9 in Calling for a reassessment of rodent diversity in Colombia: description of a new species of Neacomys (Cricetidae: Oryzomyini) from the Magdalena Valley, with a new phylogenetic hypothesis for the genus and comments on its diversification

FIGURE 9. Comparison of the dorsal and ventral views of the skulls of Trans-Andean species of Neacomys present in Colombia: A), C) Neacomys sp. nov. (UIS-MHN-M 1068, holotype). B), D) Neacomys tenuipes (UIS-MHN-M 1723). Note the nasals more expanded anteriorly, the shallower zygomatic notches, the less developed supraorbital ridges, the procingulum of M1 flattened laterally, and the incisive foramina extending almost to anterior alveolus of M1 in Neacomys sp. nov. if: incisive foramen; M1 prc: procingulum of first upper molar; nas: nasal bone; sob: supraorbital beads; zn: zygomatic notch.

opencc-zeroDec 2017View details →

Data from: The theory of island biogeography, the sample-area effect, and the habitat diversity hypothesis: complementarity in a naturally fragmented landscape of lake islands

Aim: Investigate relationships between fragmentation and species diversity in the context of the theory of island biogeography, sample-area effect, and habitat diversity hypothesis. Location: Lake of the Woods, Canada. Taxon: Vascular plants Methods: Vascular plant species diversity was inventoried on 30 islands, organized into two island sets. Each island set contained four size classes that varied in degree of fragmentation while controlling for the sample-area effect (small island set: 8×0.1-ha, 4×0.2-ha, 2×0.4-ha, and 1×0.8-ha islands; large island set: identical pattern utilizing 1.0-ha to 8.0-ha islands). Fragmentation effects were then examined using SLOSS-based analyses, addressing whether single large or several small islands contained more species: (1) direct comparisons of species and habitat richness across size classes; (2) extrapolations of species-area relationships; and (3) analyses of species and habitat accumulation curves. Multigroup path analysis was next used to quantify effects of habitat diversity, island area, and isolation on species richness for both island sets. Finally, pairwise and multiple-site dissimilarity was estimated for both species and habitats across 0.1-ha and 1.0-ha islands to investigate whether: (1) variation in species composition was related to habitat composition; and (2) species dissimilarity increased with inter-island distance. Results: SLOSS-based analyses indicated that several small islands contained more species than single large islands in both island sets. This pattern was also observed for habitats, but only in the small islands set. Path analysis suggested that island area had significant direct and indirect effects (mediated by habitat diversity) on species richness. Habitat diversity and island isolation had significant positive and negative effects on species richness, respectively, independent of island area. Species and habitat dissimilarities were significantly related across 0.1-ha but not 1.0-ha islands, and showed no relationship to inter-island distance. Main Conclusions: The overall positive relationship between fragmentation and species richness may be attributed to greater habitat diversity and increased species dissimilarity across smaller islands relative to larger islands. However, negative isolation effects indicate that landscape configuration is still an important conservation consideration. These results each align with different predictions of the theory of island biogeography, sample-area effect, and habitat diversity hypothesis, questioning the exclusivity of these theoretical frameworks.

opencc-zeroDec 2011View details →

Data from: Support for the immunocompetence handicap hypothesis in the wild: hormonal manipulation decreases survival in sick damselflies

The immunocompetence handicap hypothesis (ICHH) states that hormones enhance sexual trait expression but impair immunity. Previous tests of the ICHH have been hampered by experimental design problems. Here we report on an experimental test of the ICHH that includes manipulations of both hormones and infections in males of the territorial damselfly, Hetaerina americana, with accurate survival measurements. We conducted a fully factorial experiment subjecting each individual to one of three topical treatments: methoprene (a juvenile hormone analog), acetone, or control, and one of three injection treatments: bacteria, PBS, or control. We measured survival of manipulated males in both the wild and in captivity. As predicted, survival was most heavily impaired in methoprene-bacteria males than in the other groups in the wild, and no survival differences emerged in captive animals. This result confirms that survival is one cost an animal pays for increased hormonal levels. This corroborates theoretical predictions of the ICHH.