青藏高原东缘中生代若尔盖古高原的发现及其地质意义

40 Ma B.P."原青藏高原"的提出使得青藏高原的早期隆升历史受到越来越多的关注,但其向东的延伸情况不明。青藏高原东缘若尔盖高原、龙门山冲断带和四川盆地有机地构建了一个完整的原-山-盆体系,成为揭示青藏高原隆升和生长的理想场所,而位于高原内部若尔盖地块的红参1井更为此提供了宝贵素材。基于红参1井的构造恢复和低温热年代学研究结果,结合区域上已有的低温热年代学和古高程数据,提出青藏高原东缘在早新生代印-亚大陆碰撞之前就已形成了高原,称之为若尔盖古高原,并从基底构造属性、构造变形、地壳缩短与增厚、沉积记录等方面对其进行了论证。红参1井钻井剖面构造恢复结果揭示所钻遇7 000余米的三叠系复理石层系实际上有46%的厚度是由构造重复所致,连同广泛发育的晚三叠世埃达克质花岗岩以及利用中性岩浆岩Sr/Y比值估算的地壳厚度,共同表明青藏高原东部松潘-甘孜地区在晚三叠世就已发生了实质性的地壳加厚。红参1井多重低温热年代学[锆石(U-Th)/He,磷灰石裂变径迹和(U-Th)/He]测试结果揭示若尔盖地块分别在白垩纪中期(约120 Ma B.P.和约80 Ma B.P.)经历了2次快速的冷却事件,累计剥蚀厚度达5 km,之后转入极其缓慢的冷却过程,暗示其已进入高原化阶段;而在整个新生代期间处于近乎"零"剥蚀的状态而被动地抬升到现今高度(不同于常见的山脉隆升,地块隆升代表了一定范围的区域整体抬升)。因此,青藏高原东部若尔盖地块最晚在白垩纪末期就已形成高原,即若尔盖古高原,其范围可能包括三叠系复理石层系覆盖的大部分松潘-甘孜地区,并可能向西与羌塘古高原相连,构成羌塘-若尔盖古高原。若尔盖古高原的形成不仅造成四川盆地西缘在白垩纪中期出现了重要的物源转变,更重要的是加剧了青藏高原东缘白垩纪气候干旱化,出现了大量沙漠沉积和膏盐沉积。若尔盖古高原的发现不仅有助于深化对青藏高原隆升和生长过程的理解,也将引发对青藏高原形成机制的重新思考以及对其气候-环境-资源效应的关注。

Comparative water relations of co-occurring trees in a mixed podocarp-broadleaf forest

Aims As extreme climatic events including droughts and heat waves become more common in a changing climate,tree mortality has increased across the globe.In order to determine whether certain species have a competitive advantage over others,we explored the water-relations and leaf-gas exchange of four co-occurring spe-cies in a forest in northern Aotearoa-New Zealand.We studied the ecologically and culturally significant foundation species,Agathis australis(a conifer),two additional conifers,Phyllocladus tricho-manoides and Podocarpus totara and the angiosperm Knightia excelsa.Methods We measured sap flow,leaf-gas exchange and xylem water poten-tials of leaves and terminal branches with concurrent measures of micrometeorological data on days with very few clouds.We derived whole tree hydraulic conductance and instantaneous water-use efficiency(WUEi)at our remnant forest in west Auckland during February 2015(southern hemisphere summer).Important Findings The four species behaved similarly in their diurnal curves of gas exchange and water potential.Rates of assimilation,stomatal con-ductance and WUEi were similar among trees of different species.Whole tree hydraulic conductance was also similar among species.These results indicate functional convergence in water relations,possibly driven by low nutrient soils at the site.Our results suggest that there is no species with a clear adaptive advantage over the others in the context of climate change.

Reply to comment by Durkin et al.on “Using a modern analogue to interpret depositional position in ancient fluvial-tidal channels:Example from the McMurray Formation,Canada” by A.D.La Croix,S.E.Dashtgard,and J.A.MacEachern

1.Introduction We are pleased to have the opportunity to discuss our paper (La Croix et al.,2019) with Durkin et al.(2020).Their critique demonstrates the wide interest in the McMurray Formation held by both academic and industry geoscientists,especially given the economic importance of the stratigraphic interval.Furthermore,it highlights the various working interpretations for the unit’s paleoenvironmental setting and stratigraphic architecture;two highly contested scientific questions.Durkin et al.

Males armed with big weapons win fights at limited cost in ant-mimickingjumping spiders

A core assumption of sexual selection theory is that sexually selected weapons,specialized morphological structures used directly in male con-tests,can improve an individual's reproductive success but only if the bearer can overcome associated costs,the negative effects on the bear-er's fitness components.However,recent studies have shown that producing and wielding exaggerated weapons may not necessarily be costly.Rather,some traits can be selected for supporting,or compensating for,the expense of producing and wielding such exaggerated weapons.n the ant-mimicking jumping spider Myrmarachne gisti,exaggerated chelicerae are borne only by adult males and not females,showing sexual dimorphism and steep positive allometry with body size.Here,we determine the potential benefits of bearing exaggerated chelicerae during male contests and explore the potential for costs in terms of prey-capture efficiency and compensation between chelicera size and neighboring trait size.While males with longer chelicerae won most of their male-male contests,we found no significant differences in prey-capture effi-ciency between males and females regardless of whether prey was winged or flightless.Males'elongated chelicerae thus do not impede their efficiency at capturing prey.Furthermore,we found that the sizes of all neighboring traits are positively correlated with chelicera size,suggesting that these traits may be under correlational selection.Taken together,our findings suggest that M.gisti males armed with the exaggerated chelicerae that function as weapons win more fights at limited cost for performance in prey capture and compensate for neighboring structures.

Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider

In aggressive mimicry,a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey.The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings(BDs)in order to avoid predation.However,Phrynarachne spiders may also aggressively mimic BDs in order to deceive potential prey.To date,there is no experimental evidence to support aggressive mimicry in masquerading crab spiders;therefore,we performed a field survey,a manipulative field experiment,and visual modeling to test this hypothesis using Phrynarachne ceylonica.We compared prey-attraction rates among BDs,spiders,and control empty leaves in the field.We found that although all prey combined and agromyzid dipterans,in particular,were attracted to BDs at a higher rate than to spiders,other dipterans and hymenopterans were attracted to BDs at a similar rate as to spiders.Both spiders and BDs attracted insects at a significantly higher rate than did control leaves.As predicted,prey was attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders.Finally,visual modeling suggested that spiders and BDs can be detected by dipterans and hymenopterans against background leaves,but they are indistinguishable from each other.Taken together,our results suggest that insects lured by spiders may misidentify them as BDs,and bird-dropping masquerading may serve as aggressive mimicry in addition to predator avoidance in P.ceylonica.