环境因子对两种海洋双壳类幼体趋性行为中的调节作用

本文研究了温度、盐度和重金属等几种因子对缢蛏和长牡蛎幼体趋地性和趋光性行为的影响。结果表明:1)降低温度能增强缢蛏幼体的正趋地性,而长牡蛎幼体却由正趋地性转变为负趋地性,同时两种幼体的正趋光性受到抑制作用;升高温度对缢蛏幼体趋光性的影响不明显,但能加强牡蛎幼体的正趋光性。2)盐度提高时缢蛏幼体的正趋光性趋于增强,正趋地性趋于减弱。3)重金属Cu和Zn在各自的亚致死浓度下具有提高缢蛏幼体正趋地性和降低正趋光性的作用,而牡蛎幼体的正趋地性却趋于减弱,正趋光性趋于增强。本文据上述幼体的行为变化,还讨论了这几种因子对幼体垂直分布的调节作用。     

Behavioural variation in natural populations. V. Morphological correlates of locomotion in the garter snake (Thamnophis radix)

A series of morphologieal and locomotor performance variables was measured in a population of newborn garter snakes to determine whether performance capacity has a significant morphological basis in these animals. Morphological traits measured were body length and mass, number of body and tail vertebrae and numbers of vertebral abnormalities. Locomotor performances included burst and mid-distance speed and distance and time crawled before anti-predator displays were assumed. All performance variables were repeatable in daily replicate trials ( P < 0.001). Individual burst speed, mid-distance speed, and distance crawled were significantly correlated pairwise ( P < 0.01). Most morphological and performance variables had a significant mass dependence (static allometry), although the effects were rather weak ( r ² < 0.1, except for body length): larger animals performed better and had fewer abnormalities. There were significant associations between some morphological traits and locomotor performance. Morphological factors accounted for 19% of the variation in mid-distance speed and 14% of the variation in antipredator behavior by multiple regression analysis. Canonical correlation of all performance and morphological variables simultaneously accounted for 24% of the observed variation in performance. Numbers of body and tail vertebrae (assayed by scale counts) had an interactive effect on speed of locomotion.     

Phylogenetic relationships of the garter snakes based on DNA sequence and allozyme variation

We estimated phylogenetic relationships among 26 species of garter snakes (genus Thamnophis ) using allozyme and mitochondrial cytochrome b gene nucleotide sequence variation. Parsimony analyses of the two data sets give substantially different estimates of phylogeny. Several lines of evidence indicate that much of this conflict is due to error associated with the restricted number of characters in each data set. Such sampling error may be reduced by combining all the characters; we therefore present an estimate of phylogeny based on parsimony analysis of all the data combined. All our analyses support several conclusions in conflict with previous views: a very distant relationship between T.errans and T. elegans , non-monophyly of the elegans group (even excluding T: errans ), and nesting of the form validus (previously considered a member of the genus Nerodia ) within Thamnophis.
The combined analysis gives an almost fully resolved tree. However, bootstrapping indicates only weak support for many clades in this tree. Furthermore, paraphyly of the assemblages of cytochrome b gene lineages within T. elegans and T. radix indicate the potential for discordance between the mitochondrial DNA (mtDNA) and species phylogenies through the sorting of ancestral mtDNA polymorphisms. These problems suggest the need for assaying additional characters, especially ones likely to be independent of those used in the present study.     

HOMOGENEITY OF THE GENETIC VARIANCE-COVARIANCE MATRIX FOR ANTIPREDATOR TRAITS IN TWO NATURAL POPULATIONS OF THE GARTER SNAKE THAMNOPHIS ORDINOIDES

Quantitative genetic models of evolution rely on the genetic variance-covariance matrix to predict the phenotypic response to selection. Both prospective and retrospective studies of phenotypic evolution across generations rely on assumptions about the constancy of patterns of genetic covariance through time. In the absence of robust theoretical predictions about the stability of genetic covariances, this assumption must be tested with empirical comparisons of genetic parameters among populations and species. Genetic variance-covariance matrices were estimated for a suite of antipredator traits in two populations of the northwestern garter snake, Thamnophis ordinoides. The characters studied include color pattern and antipredator behaviors that interact to facilitate escape from predators. Significant heritabilities for all traits were detected in both populations. Genetic correlations and covariances were found among behaviors in both populations and between color pattern and behavior in one of the populations. Phenotypic means differed among populations, but pairwise comparisons revealed no heterogeneity of genetic parameters between the populations. The structure of the genetic variance-covariance matrix has apparently not changed significantly during the divergence of these two populations.     

In vitro oxidative inactivation of glutathione S-transferase from a freeze tolerant reptile

We have previously reported that when garter snakesThamnophis sirtalis parietalis, a freeze tolerant species, were exposed to 5 h freezing at –2.5° C organs showed increases in the activities of anti-oxidant enzymes, especially catalase in skeletal muscle. This was interpreted to be an adaptation to deal with the potentially injurious postischemic situation of thawing. The present work analyzesin vitro oxidative inactivation of a possible target of postischemic-induced free radical damage, the secondary anti-oxidant defense glutathione-S transferase, and the protective role of endogenous catalase. Approximately 50% of GST activity from snake muscle homogenates was lost within 2 min after addition of H₂O₂ plus Fe(II) (0.4–2 mM) in media containing azide whereas addition of iron alone resulted in no damaging effects. The opposing effects of dimethyl sulfoxide and EDTA in modifying this process strongly suggested the involvement of ·OH radicals in the GST inactivation. A partial recovery of the activity was promoted by mercaptoethanol, indicating that sulphydryl groups oxidation participate in the mechanism of GST inactivation. Pre-incubation of the reaction media containing H₂O₂ caused protection of the GST activity only in the absence of azide, indicating that endogenous catalase modulates the extent of oxyradical damage. The protective pre-incubation effect was more efficacious when employing homogenates from lung and liver, organs that have higher catalase activities, as well as homogenates from freezing-exposed muscle (that show an 80% increase in catalase activity, compared with control). The protection against GST inactivation observed in muscle from frozen snakes demonstrates that increased anti-oxidant defenses during freezing exposure can be a key factor in controllingin vitro oxyradical damage. The implications for natural freeze tolerance are discussed.     

Do positive interactions between marine invaders increase likelihood of invasion into natural and artificial habitats?

Positive species interactions such as facilitation are important for enabling species to persist, especially in stressful conditions, and the nature and strength of facilitation varies along physical and biological gradients. Expansion of coastal infrastructure is creating hotspots of invasive species which can spillover into natural habitats, but the role of positive species interactions associated with biological invasions remains understudied. Theory suggests that stronger biotic pressure in natural habitats inhibits invasion success. In space-limited marine systems, sessile organisms can overcome this limiting resource by settling as an epibiont on a substrate organism – basibiont. Using a series of spatially extensive surveys, we explored the role of invasive and native basibionts in providing habitat for other invasive and native epibionts, and tested whether environmental context (i.e. if the receiving habitat was natural or artificial), altered ecological outcomes. Overall, provision of space by basibionts was more important for invasive epibionts than for native epibionts but was dependent on the environmental context. Invasive basibionts facilitated invasive epibionts in natural habitats, and appeared to be more important for native epibionts in artificial habitats respectively. Native basibionts facilitated invasive, but not native epibionts in both natural and artificial habitats. These results advance our understanding of facilitation and highlight the idiosyncratic nature of biofouling and epibiosis, and the potentially important influence of environmental context. The degree to which native habitat-forming species versus invasive habitat-forming species either do or do not facilitate other native or non-native species is a rich area for investigation. Experimental work is required to disentangle the processes underpinning these patterns.     

东太平洋赤道海域茎柔鱼的营养生态位和肠道微生物组成

掌握海洋生物的营养生态位特征及其应对环境变化的响应机制,对于评估渔业和气候变化对海洋生态系统功能的影响至关重要。茎柔鱼(Dosidicus gigas)是东太平洋重要的渔业经济物种,在生态系统中具有承上启下的重要生态作用。在气候变化的大背景下,掌握茎柔鱼应对气候变化的响应过程将有利于合理把控其资源状况。本研究采用稳定同位素和高通量技术手段,分别从宏观和微观角度量化比较分析了正常时期和厄尔尼诺时期赤道海域的茎柔鱼营养生态位、肠道长度及肠道微生物组成。结果表明: 不同气候时期茎柔鱼的δ¹³C值存在显著差异,说明食物来源具有差异性;其肠道微生物主要由放线菌门、拟杆菌门、蓝细菌门、厚壁菌门、变形菌门和软壁菌门组成,不同时期微生物群落组成无显著差异,但多样性和相对丰度差异显著。在厄尔尼诺时期,茎柔鱼个体具有较小的营养生态位、较长的肠道、更高的肠道微生物群落多样性及丰富度;肠道微生物的差异主要体现在厚壁菌门、拟杆菌门、螺旋体门、WPS-2和Kiritimatiellaeota,样本距离更为集中。这表明由厄尔尼诺事件导致的栖息地环境及食物变化可能限制茎柔鱼的活动,改变其肠道微生物的结构和功能,有利于其适应环境及食性的变化。     

Field Chronobiology of a Molluscan Bivalve: How the Moon and Sun Cycles Interact to Drive Oyster Activity Rhythms

The present study reports new insights into the complexity of environmental drivers in aquatic animals. The focus of this study was to determine the main forces that drive mollusc bivalve behavior in situ. To answer this question, the authors continuously studied the valve movements of permanently immersed oysters, Crassostrea gigas, during a 1-year-long in situ study. Valve behavior was monitored with a specially build valvometer, which allows continuously recording of up to 16 bivalves at high frequency (10?Hz). The results highlight a strong relationship between the rhythms of valve behavior and the complex association of the sun-earth-moon orbital positions. Permanently immersed C. gigas follows a robust and strong behavior primarily driven by the tidal cycle. The intensity of this tidal driving force is modulated by the neap-spring tides (i.e., synodic moon cycle), which themselves depend of the earth–moon distance (i.e., anomalistic moon cycle). Light is a significant driver of the oysters' biological rhythm, although its power is limited by the tides, which remain the predominant driver. More globally, depending where in the world the bivalves reside, the results suggest their biological rhythms should vary according to the relative importance of the solar cycle and different lunar cycles associated with tide generation. These results highlight the high plasticity of these oysters to adapt to their changing environment. (Author correspondence: d.tran@epoc.u-bordeaux1.fr)     

TLR4-dependent effects of ISAg treatment on conventional T cell polarization in vivo

We recently demonstrated that the polysaccharide component of the Korean medicinal herb Angelica gigas (immuno-stimulatory fraction of A. gigas; ISAg) induces anticancer effects in mice by activating natural killer (NK) and natural killer T (NKT) cells. However, it is unclear whether the use of ISAg in vivo can affect the differentiation of conventional T cells. Here, we investigated the effects of ISAg on the activation of conventional CD4⁺ and CD8⁺ T cells. We found that the administration of ISAg induced the polarization of CD4⁺ T cells toward the acquisition of the Th1 phenotype in vivo. Additionally, in mice treated with ISAg, CD8⁺ T cells produced more IFNγ than in control mice treated with PBS. Moreover, treatment with ISAg activated CD4⁺ and CD8⁺ T cells as well as NK and NKT cells, resulting in the secretion of Th1-type cytokines in a toll-like receptor 4 (TLR4)-dependent manner, implying that TLR4 is critical for an optimal Th1 response. Interestingly, ISAg treatment increased the number of Foxp3⁺ Treg cells, but not of Th2 cells, compared to control mice treated with PBS, indicating that ISAg possesses an immunomodulatory capacity that can control adaptive immune responses. Taken together, our results indicate that ISAg possesses a Th1-enhancing activity that could be used to treat Th2-mediated allergic immune diseases such as atopic dermatitis.     

Microsatellite markers and multiple paternity in the garter snake thamnophis sirtalis

Data from four microsatellite loci developed for the common garter snake, Thamnophis sirtalis, show that multiple paternity is common in a natural population on Beaver Island, Michigan. Six of eight litters tested, and all litters with five or more neonates, were multiply sired. At least triple paternity was documented in the largest litter examined (n = 13 neonates). Inheritance patterns and genotype frequencies in the wild population indicate the presence of null allele(s) at one of the microsatellite loci. Garter snakes are widely used in quantitative genetics research, and paternity testing is essential in studies that rely on sibling analysis.