Responses of Clonal Reef Taxa to Environmental Change

SYNOPSIS. Many reef taxa are predominantly clonal, and theirclones can spread over tens of meters and live for hundredsof years. Colony growth, which produces large colonies, andvegetative propagation, which can generate many clonal replicatesof colonies, affect the response of clonal taxa to climate changethrough a variety of mechanisms, some of which mitigate andsome which amplify effects on individuals. The large numbersof replicate individuals generated among clonal taxa may enablesome individuals to survive catastrophic mortality events suchas storms and then expand following the perturbation. In thosecircumstances clonality buffers the effects of environmentalchange. Conversely, the genetic uniformity of populations dominatedby few genotypes may leave clonal taxa more susceptible to physiologicstress than aclonal taxa. Consequently, clonal species may bemore sensitive to climate change that has chronic and/or acuteeffects on survival. Chronic stresses that reduce recruitmentwill have less obvious effects on clonal taxa than aclonal taxa.Under conditions of reduced recruitment, clonality will allowsome species to persist as relict populations due to the longevityof genets. The presence of relict populations has the appearanceof resistance to climate change. In fact, these taxa are responding,but at a slower rate. The long generation time of genets willslow the pace of evolution among clonal species, making adaptationat projected rates of climate change unlikely. The differentialresponse of species to environmental change will lead to transitionsin community structure as climate changes.     

Expertly Validated Models and Phylogenetically-Controlled Analysis Suggests Responses to Climate Change Are Related to Species Traits in the Order Lagomorpha

Climate change during the past five decades has impacted significantly on natural ecosystems, and the rate of current climate change is of great concern among conservation biologists. Species Distribution Models (SDMs) have been used widely to project changes in species’ bioclimatic envelopes under future climate scenarios. Here, we aimed to advance this technique by assessing future changes in the bioclimatic envelopes of an entire mammalian order, the Lagomorpha, using a novel framework for model validation based jointly on subjective expert evaluation and objective model evaluation statistics. SDMs were built using climatic, topographical, and habitat variables for all 87 lagomorph species under past and current climate scenarios. Expert evaluation and Kappa values were used to validate past and current models and only those deemed ‘modellable’ within our framework were projected under future climate scenarios (58 species). Phylogenetically-controlled regressions were used to test whether species traits correlated with predicted responses to climate change. Climate change is likely to impact more than two-thirds of lagomorph species, with leporids (rabbits, hares, and jackrabbits) likely to undertake poleward shifts with little overall change in range extent, whilst pikas are likely to show extreme shifts to higher altitudes associated with marked range declines, including the likely extinction of Kozlov’s Pika (Ochotona koslowi). Smaller-bodied species were more likely to exhibit range contractions and elevational increases, but showing little poleward movement, and fecund species were more likely to shift latitudinally and elevationally. Our results suggest that species traits may be important indicators of future climate change and we believe multi-species approaches, as demonstrated here, are likely to lead to more effective mitigation measures and conservation management. We strongly advocate studies minimising data gaps in our knowledge of the Order, specifically collecting more specimens for biodiversity archives and targeting data deficient geographic regions.     

Contrasting Responses to Harvesting and Environmental Drivers of Fast and Slow Life History Species

According to their main life history traits, organisms can be arranged in a continuum from fast (species with small body size, short lifespan and high fecundity) to slow (species with opposite characteristics). Life history determines the responses of organisms to natural and anthropogenic factors, as slow species are expected to be more sensitive than fast species to perturbations. Owing to their contrasting traits, cephalopods and elasmobranchs are typical examples of fast and slow strategies, respectively. We investigated the responses of these two contrasting strategies to fishing exploitation and environmental conditions (temperature, productivity and depth) using generalized additive models. Our results confirmed the foreseen contrasting responses of cephalopods and elasmobranchs to natural (environment) and anthropogenic (harvesting) influences. Even though a priori foreseen, we did expect neither the clear-cut differential responses between groups nor the homogeneous sensitivity to the same factors within the two taxonomic groups. Apart from depth, which affected both groups equally, cephalopods and elasmobranchs were exclusively affected by environmental conditions and fishing exploitation, respectively. Owing to its short, annual cycle, cephalopods do not have overlapping generations and consequently lack the buffering effects conferred by different age classes observed in multi-aged species such as elasmobranchs. We suggest that cephalopods are sensitive to short-term perturbations, such as seasonal environmental changes, because they lack this buffering effect but they are in turn not influenced by continuous, long-term moderate disturbances such as fishing because of its high population growth and turnover. The contrary would apply to elasmobranchs, whose multi-aged population structure would buffer the seasonal environmental effects, but they would display strong responses to uninterrupted harvesting due to its low population resilience. Besides providing empirical evidence to the theoretically predicted contrasting responses of cephalopods and elasmobranchs to disturbances, our results are useful for the sustainable exploitation of these resources.     

植物叶片形态解剖结构对环境变化的响应与适应

叶片是植物进化过程中对环境变化比较敏感且可塑性较大的器官,环境变化常导致叶的长、宽及厚度,叶表面气孔、表皮细胞及附属物,叶肉栅栏组织、海绵组织、胞间隙、厚角组织和叶脉等形态解剖结构的响应与适应。本文综述了陆生植物叶片上述形态解剖结构对水分、温度、光照、CO2浓度和UV-B辐射等环境因子变化以及多因子复合作用的响应与适应,分析了该领域的研究特点及其存在的问题,指出了未来研究的重点和方向。     

Divergent Receiver Responses to Components of Multimodal Signals in Two Foot-Flagging Frog Species

Multimodal communication of acoustic and visual signals serves a vital role in the mating system of anuran amphibians. To understand signal evolution and function in multimodal signal design it is critical to test receiver responses to unimodal signal components versus multimodal composite signals. We investigated two anuran species displaying a conspicuous foot-flagging behavior in addition to or in combination with advertisement calls while announcing their signaling sites to conspecifics. To investigate the conspicuousness of the foot-flagging signals, we measured and compared spectral reflectance of foot webbings of Micrixalus saxicola and Staurois parvus using a spectrophotometer. We performed behavioral field experiments using a model frog including an extendable leg combined with acoustic playbacks to test receiver responses to acoustic, visual and combined audio-visual stimuli. Our results indicated that the foot webbings of S. parvus achieved a 13 times higher contrast against their visual background than feet of M. saxicola. The main response to all experimental stimuli in S. parvus was foot flagging, whereas M. saxicola responded primarily with calls but never foot flagged. Together these across-species differences suggest that in S. parvus foot-flagging behavior is applied as a salient and frequently used communicative signal during agonistic behavior, whereas we propose it constitutes an evolutionary nascent state in ritualization of the current fighting behavior in M. saxicola.     

Contrasted Responses of Two Understorey Species to Direct and Indirect Effects of a Canopy Gap

Positive associations between adult trees and understorey species have been explained either by direct or indirect facilitation. We tested both models by comparing the performance of two understorey species with contrasted stress-tolerance abilities Galium odoratum and Deschampsia flexuosa. Individuals of both species were transplanted in the four combinations of two treatments (gap and removal of an herbaceous competitor, Molinia caerulea). Our experiment demonstrated that direct facilitation of adult trees may explain the restricted occurrence of the shade-demanding Galium within closed forest communities. In contrast, the shade-tolerant Deschampsia was subjected to additional competition within the forest, likely because adult trees had a higher negative effect on light availability and a similar negative effect on nitrogen availability within the forest than did Molinia in the gaps.     

Interaction of Species Traits and Environmental Disturbance Predicts Invasion Success of Aquatic Microorganisms

Factors such as increased mobility of humans, global trade and climate change are affecting the range of many species, and cause large-scale translocations of species beyond their native range. Many introduced species have a strong negative influence on the new local environment and lead to high economic costs. There is a strong interest to understand why some species are successful in invading new environments and others not. Most of our understanding and generalizations thereof, however, are based on studies of plants and animals, and little is known on invasion processes of microorganisms. We conducted a microcosm experiment to understand factors promoting the success of biological invasions of aquatic microorganisms. In a controlled lab experiment, protist and rotifer species originally isolated in North America invaded into a natural, field-collected community of microorganisms of European origin. To identify the importance of environmental disturbances on invasion success, we either repeatedly disturbed the local patches, or kept them as undisturbed controls. We measured both short-term establishment and long-term invasion success, and correlated it with species-specific life-history traits. We found that environmental disturbances significantly affected invasion success. Depending on the invading species’ identity, disturbances were either promoting or decreasing invasion success. The interaction between habitat disturbance and species identity was especially pronounced for long-term invasion success. Growth rate was the most important trait promoting invasion success, especially when the species invaded into a disturbed local community. We conclude that neither species traits nor environmental factors alone conclusively predict invasion success, but an integration of both of them is necessary.     

Responses of Two CAM Species to Different Irradiances during Growth and Susceptibility to Photoinhibition by High Light

Two CAM species, Kalanchoë daigremontiana Hamet et Perrier and Hoya carnosa (L.) R. Br., were grown under a range of five photon flux area densitites (PFD) and then characterized. Significant acclimation to shade was indicated by progressive decreases in leaf thickness, rates of respiratory O₂ uptake, light compensation point, maximum rates of photosynthetic O₂ evolution, nocturnal acid accumulation, and δ¹³C values, and increases in chlorophyll concentration and absolute levels of room temperature (25°C) and 77K fluorescence. Quantum yields (as measured by O₂ exchange) and the ratio of variable 77K fluorescence over the maximum yield (F_v/F_m) were relatively constant across the treatments. The only significant deviation from the above characteristics was in H. carnosa grown under full glasshouse PFD, where it apparently experienced photoinhibition. Following a photoinhibitory treatment, K. daigremontiana exhibited increases in the light compensation point and progressively greater reductions in the quantum yield, maximum photosynthetic rate, F_v/F_m, and the variable component of room temperature fluorescence with increasing shade during growth. Thus although Crassulacean acid metabolism plants can adjust to shaded conditions, they are susceptible to photoinhibition when exposed to higher PFD than that experienced during growth.     

Parental Responses to Changes in Costs and Benefits Along an Environmental Gradient

We evaluated the effects of dissolved oxygen on offspring survival, parental costs, and the pattern of parental care in Florida flagfish, Jordanella floridae (Cyprinodontidae). Specifically, we quantified (1) embryonic development and survival in the absence of parental care, (2) behavior of non-reproductive adults, and (3) behavior of parental males across a gradient in dissolved oxygen. Embryo developmental rates and survivorship increased with dissolved oxygen, with a relatively sharp increase in survival between medium and high oxygen treatments. Non-reproductive adults increased their frequency of aquatic surface respiration, reduced overall activity, and increased opercular beat rate as oxygen declined, suggesting increased costs of activity with reduced oxygen. Taking these cost measures together, costs appear to increase slowly as oxygen starts to decline and then increase sharply as conditions approach hypoxia. In contrast, parental effort increased gradually with dissolved oxygen. We conclude that the increase in care from low to medium oxygen primarily results from a sharp decline in physiological costs, whereas the continued increase in care from medium to high oxygen primarily results from an increase in offspring value. In addition, our results highlight that the benefits of fanning for offspring are not well understood and that they may increase with oxygen, contrary to what has been previously assumed.     

两种热带木质藤本幼苗形态、生长和光合能力对光强和养分的响应

比较了两种不同攀援习性,卷须缠绕种薄叶羊蹄甲（Bauhinia tenuiflora）和茎缠绕种刺果藤（Byttneria aspera）,木质藤本植物的形态、生长及光合特性对不同光强（4％、35％和全光照）和土壤养分（高和低）的响应。两种藤本植物大部分表型特征主要受光照的影响,而受土壤养分的影响较小。弱光促进地上部分生长,弱光下两种植物均具有较大的比叶面积（specific leaf area,SLA）、茎生物量比（stem mass ratio,SMR）和平均叶面积比（mean leaf area ratio,LARm）。高光强下,两种植物的总生物量和投入到地下部分的比重增加,具有更大的根生物量比（root mass ratio,RMR）、更多的分枝数、更高的光合能力（maximum photosynthetic rate,Pmax）和净同化速率（net assimilation rate,NAR）,综合表现为相对生长速率（relative growth rate,RGR）增加。两种藤本植物的Pmax与叶片含氮量的相关性均未达显著水平,但刺果藤的Pmax与SU志间呈显著的正相关,而薄叶羊蹄甲的Pmax与SLA之间相关性不显著。在相同光照强度和土壤养分条件下,卷须缠绕种薄叶羊蹄甲的RGR显著高于茎缠绕种刺果藤。薄叶羊蹄甲的RGR与NAR呈显著正相关,其RGR与SLA、平均叶面积比（EARm）及Pmax之间相关性不显著。刺果藤的RGR与NAR呈显著的正相关,而与SLA存在显著的负相关。上述结果表明,与土壤养分相比,光照强度可能是决定木质藤本分布更为重要的生态因子。卷须缠绕种薄叶羊蹄甲由于具有特化的攀援器官,在形态上和生理上具有更大的可塑性,这使得卷须缠绕种木质藤本在与其它植物的竞争中更具优势。     

Responses of Wetland Tree Species to Hydrology and Soils

We conducted a study of the flood tolerance of nine wetland tree species on seven soil types. Seedlings were subjected to 11 months of continuous shallow inundation or moist soil conditions on three mineral soils, two organic soils, a manufactured soil designed to mimic the practice of layering muck over mineral soil, and a stockpiled topsoil. Taxodium ascendens, T. distichum, Acer rubrum, and Pinus serotina suffered no mortality; Fraxinus carolininna (1%), Liquidambar styraciflua (8%), P. elliottii (8%), and Gordonia lasianthus (24%) suffered low to moderate mortality; and Persea palustris (46%) suffered significant mortality. In general, greatest net height and total biomass were achieved on moist organic soils, and least net height and total biomass were achieved on stockpiled topsoil and inundated soils. Responses to hydrological conditions were less pronounced for Taxodium spp. If the results of this experiment are transferable to the field, then Acer rubrum, Fraxinus caroliniana, Pinus serotina, Taxodium ascendens, and Taxodium distichum seedlings can reasonably be expected to survive at least one year under a broad range of hydrological and edaphic conditions. With the exception of Taxodium spp., first-year growth for the species of this study can be facilitated by maintaining moist but not inundated conditions. These findings suggest that transfer of organic soils will benefit restoration and creation efforts, and that layering organic soil over mineral soil is more effective than using mineral soils or stockpiled topsoil.     

Population Responses to Environmental Change in a Tropical Ant: The Interaction of Spatial and Temporal Dynamics

Spatial structure can have a profound, but often underappreciated, effect on the temporal dynamics of ecosystems. Here we report on a counterintuitive increase in the population of a tree-nesting ant, Azteca sericeasur, in response to a drastic reduction in the number of potential nesting sites. This surprising result is comprehensible when viewed in the context of the self-organized spatial dynamics of the ants and their effect on the ants’ dispersal-limited natural enemies. Approximately 30% of the trees in the study site, a coffee agroecosystem in southern Mexico, were pruned or felled over a two-year period, and yet the abundance of the ant nests more than doubled over the seven-year study. Throughout the transition, the spatial distribution of the ants maintained a power-law distribution – a signal of spatial self organization – but the local clustering of the nests was reduced post-pruning. A cellular automata model incorporating the changed spatial structure of the ants and the resulting partial escape from antagonists reproduced the observed increase in abundance, highlighting how self-organized spatial dynamics can profoundly influence the responses of ecosystems to perturbations.     

Responses of Ecosystem Carbon Cycling to Climate Change Treatments Along an Elevation Gradient

Global temperature increases and precipitation changes are both expected to alter ecosystem carbon (C) cycling. We tested responses of ecosystem C cycling to simulated climate change using field manipulations of temperature and precipitation across a range of grass-dominated ecosystems along an elevation gradient in northern Arizona. In 2002, we transplanted intact plant?Csoil mesocosms to simulate warming and used passive interceptors and collectors to manipulate precipitation. We measured daytime ecosystem respiration (ER) and net ecosystem C exchange throughout the growing season in 2008 and 2009. Warming generally stimulated ER and photosynthesis, but had variable effects on daytime net C exchange. Increased precipitation stimulated ecosystem C cycling only in the driest ecosystem at the lowest elevation, whereas decreased precipitation showed no effects on ecosystem C cycling across all ecosystems. No significant interaction between temperature and precipitation treatments was observed. Structural equation modeling revealed that in the wetter-than-average year of 2008, changes in ecosystem C cycling were more strongly affected by warming-induced reduction in soil moisture than by altered precipitation. In contrast, during the drier year of 2009, warming induced increase in soil temperature rather than changes in soil moisture determined ecosystem C cycling. Our findings suggest that warming exerted the strongest influence on ecosystem C cycling in both years, by modulating soil moisture in the wet year and soil temperature in the dry year.     

Responses of Calcicole and Calcifuge Poaceae Species to Iron-Limiting Conditions

Six differently distributed Poaceae species were compared in order to identify morphological and/or physiological properties that ensure calcicole species but not calcifuge species a sufficient Fe supply on CaCO₃ rich soils. When grown at a range of FeEDTA supply from deficient to adequate, the calcicole species had higher Fe productivities and relative yields at low Fe supply than the calcifuges. Specific root surface and Fe uptake requirements were lower in calcicoles than in calcifuges. Root exudation of Fe-mobilizing compounds was monitored in plants grown either with or without added FeEDTA in hydroponic culture. Under Fe deficiency, typically more than 80% of soluble root exudates of Poaceae are phytosiderophores (Marschner et al., 1989; Römheld, 1987). Maximum exudation rates of Fe mobilizing compounds were 6.6 to 11.5 μmol g^?1 root dry wt 2 hr^?1 in calcicoles and 0.48 to 1.64 in calcifuges. If Fe requirement is defined as mean Fe uptake rate required for 90 % of the maximal relative growth rate, the exudation rates of Fe mobilizing compounds were at least 11.7 to 31.9 times higher than Fe requirements in calcicoles and 0.38 to 5.36 times higher in calcifuges. Growth response to a precipitated versus a chelated Fe source was determined. The relative ability to grow with Fe(OH)₃ precipitate was correlated with the Fe mobilization rate of the species. The present results give evidence for the importance of Fe efficiency in wild plants. Calcicoles are able to live on calcareous soils partly because they produce larger amounts of Fe mobilizing compounds and have lower tissue Fe requirements than calcifuges.     

Short- and Long-day Responses in the Pre-adult Developmental Duration of Two Species of Camponotus Ants

We assessed the effect of different day/night lengths on the pre-adult developmental time of two species of Camponotus ants that normally develop in dark underground nests. We assayed larval (egg-to-pupal formation), pupal (pupal formation-to-adult emergence), and pre-adult (egg-to-adult emergence) durations in these ants under three different light/dark (LD) cycles of 12:12?h, 10:14?h, and 14:10?h. We observed that the pre-adult development time of ants under these day lengths was significantly different. Although both species developed fastest under 12:12?h LD, when asymmetric LD cycles were compared, night-active species (Camponotus compressus) developed faster under short days (10:14?h) and day-active species (C. paria) developed faster under long days (14:10?h). This day/night-length-mediated difference in pre-adult developmental duration was mostly due to modulation of larval duration; however, in day-active species it was also via altered pupal duration. These results thus indicate that the two species of Camponotus ants respond differently to short and long days, suggesting that seasonal timers regulate pre-adult development time in tropical ant species living in dark underground nests. (Author correspondence: vsharma@jncasr.ac.in/vksharmas/gmail.com)     

Immunodominant HIV-Specific CD8+ T-Cell Responses Are Common to Blood and Gastrointestinal Mucosa,and Gag-Specific Responses Dominate in Rectal Mucosa of HIV Controllers

Previous studies have suggested that polyfunctional mucosal CD8⁺ T-cell responses may be a correlate of protection in HIV controllers. Mucosal T-cell breadth and/or specificity may also contribute to defining protective responses. In this study, rectal CD8⁺ T-cell responses to HIV Gag, Env, and Nef were mapped at the peptide level in four subject groups: elite controllers (n = 16; viral load [VL], <75 copies/ml), viremic controllers (n = 14; VL, 75 to 2,000 copies/ml), noncontrollers (n = 14; VL, >10,000 copies/ml), and antiretroviral-drug-treated subjects (n = 8; VL, <75 copies/ml). In all subject groups, immunodominant CD8⁺ T-cell responses were generally shared by blood and mucosa, although there were exceptions. In HIV controllers, responses to HLA-B27- and HLA-B57-restricted epitopes were common to both tissues, and their magnitude (in spot-forming cells [SFC] per million) was significantly greater than those of responses restricted by other alleles. Furthermore, peptides recognized by T cells in both blood and rectal mucosa, termed “concordant,” elicited higher median numbers of SFC than discordant responses. In magnitude as well as breadth, HIV Gag-specific responses, particularly those targeting p24 and p7, dominated in controllers. Responses in noncontrollers were more evenly distributed among epitopes in Gag, Env, and Nef. Viremic controllers showed significantly broader mucosal Gag-specific responses than other groups. Taken together, these findings demonstrate that (i) Gag-specific responses dominate in mucosal tissues of HIV controllers; (ii) there is extensive overlap between CD8⁺ T cells in blood and mucosal tissues, with responses to immunodominant epitopes generally shared by both sites; and (iii) mucosal T-cell response breadth alone cannot account for immune control.Despite more than two decades of intensive research, the immunologic correlates of protection from human immunodeficiency virus (HIV) infection and disease progression remain incompletely understood. To date, the majority of studies of HIV-specific T-cell responses have focused on the measurement of such responses in peripheral blood lymphocytes. Nevertheless, the majority of the body''s lymphocytes are housed in mucosal tissues, notably the gastrointestinal (GI) tract (18, 33, 40). The gastrointestinal mucosa also serves as a major target of HIV infection and CD4⁺ T-cell depletion (7, 25, 36), as well as an important site of transmission (18, 33, 40). Antigen-experienced T cells may preferentially traffic to tissue sites of infection (50), where they may also expand in an antigen-driven manner. Because of the unique role of the gastrointestinal mucosa in HIV pathogenesis, detailed studies of HIV-specific immune responses in this compartment may contribute important insights to our understanding of the disease process.An important question is the degree to which T-cell responses in mucosal tissues are “compartmentalized” and distinct in specificity and/or clonality from those found elsewhere in the body, including in peripheral blood. Because of the technical challenges associated with obtaining large numbers of viable lymphocytes from mucosal biopsy specimen tissue, comprehensive mapping of the fine specificity of mucosal HIV-specific T-cell responses has been difficult. Relying on a polyclonal expansion approach, Ibarrondo and colleagues successfully mapped HIV-specific CD8⁺ T-cell responses in blood and rectal mucosa of chronically infected persons to the level of peptide pools but not to individual epitopes (29). Their studies revealed a similar pattern of responses, and nearly identical immunodominance hierarchies, in the two tissue sites.We have focused our recent studies of mucosal immunity on a group of individuals who control HIV infection in the absence of antiretroviral therapy. These are often called “long-term nonprogressors” (LTNP) (14), referring to their ability to maintain normal CD4⁺ T-cell counts for more than 10 years without medication. LTNP are believed to account for 5 to 15% of the HIV-infected population. Several recent studies have used the term “HIV controllers,” defined as those who maintain undetectable plasma HIV RNA levels (“elite controllers”) and those who have persistently detectable but low plasma HIV RNA levels (“viremic controllers”). Elite controllers represent less than 1% of the HIV-infected population (14). In contrast, individuals with viral loads of >10,000 copies/ml in the absence of therapy are termed “noncontrollers.” Recently, we found that “polyfunctional” HIV-specific T cells, producing multiple antiviral factors, were significantly more abundant in gastrointestinal mucosa of HIV controllers than in those of noncontrollers or subjects on highly active antiretroviral therapy (HAART) (20). Furthermore, in many cases these strong, polyfunctional mucosal T-cell responses were not mirrored in peripheral blood, suggesting that HIV-specific T cells either preferentially traffic to or undergo expansion within mucosal tissues.Because of these findings, we undertook a follow-up study to determine the breadth and fine specificity, to the peptide level, of mucosal CD8⁺ T-cell responses to HIV Gag, Env, and Nef among HIV controllers, noncontrollers, and individuals on HAART. We hypothesized that controllers might harbor an unusually broad repertoire of HIV-specific CD8⁺ T cells in mucosal tissues. We found a similar response breadth in mucosal tissues of all three subject groups, arguing against a critical role for mucosal T-cell response breadth in determining the extent of HIV control. In contrast, we found that high-magnitude mucosal responses directed at well-conserved regions in Gag were a strong and consistent correlate of control. Finally, concordant responses, defined as those common to blood and mucosa, were generally stronger than discordant responses, underscoring the observation that T cells responding to immunodominant epitopes are broadly distributed throughout the body in both controllers and noncontrollers.