Evolution of egg deposition strategies, exaptations of exuvia, and thanatochresis in tardigrades

IF 16.4 1区 化学 Q1 CHEMISTRY, MULTIDISCIPLINARY
Roberto Guidetti
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Abstract

The cuticle is the tardigrade exoskeleton that, limiting animal growth, needs to be periodically shed. New cuticles must be formed (within the old ones) before getting rid of the obsolete exoskeletons at the end of moulting process. After ecdysis (the release of the old cuticle), the exuvia has different destinies according to tardigrade evolutionary lines. In the marine tardigrades (Heterotardigrada), the exuvia is lost and useless, while in the other taxa, it acquires interesting uses to be considered exaptations, since the cuticle previously shaped by natural selection for a function (i.e. as exoskeleton) is coopted for new adaptive scopes. These are related to egg deposition, parental care, mating, and diapause. Egg deposition within the exuvia is one of the three different egg deposition strategies developed by tardigrades: smooth eggs can be laid freely or within the exuvia, while ornamented eggs are laid freely. A new scenario for the evolution of such egg deposition strategies is characterised by five schematic steps: smooth eggs laid freely (ancestral state), synchronization of egg maturation with moulting (developed in tardigrade ancestor in sea), use of the exuvia for oviposition (for enhanced mechanical and physiological egg protection), acquisition of egg ornamentation, and ornamented eggs laid freely (related to a risk-spreading strategy). An interesting thanatochresis case related to the release of free eggs in crustaceans exuviae, convergently developed in two distant taxa of eu- and heterotardigrades, is presented and discussed.

Abstract Image

沙蜥的产卵策略、外泌液和比泌尿系统的进化
角质层是沙蜥的外骨骼,它限制了动物的生长,需要定期脱落。在蜕皮过程结束时,新的角质层(在旧的角质层内)必须形成,然后才能摆脱过时的外骨骼。蜕皮(释放旧的角质层)后,外骨骼会根据不同的沙蜥进化路线有不同的命运。在海洋沙蜥(Heterotardigrada)中,蜕膜失去了作用,而在其他类群中,蜕膜获得了有趣的用途,可被视为外适应,因为之前通过自然选择形成的角质层功能(即作为外骨骼)被用于新的适应范围。这与卵的沉积、父母照顾、交配和休眠有关。在外骨骼内产卵是沙蜥三种不同的产卵策略之一:光滑的卵可以自由产在外骨骼内,也可以产在外骨骼内,而带装饰的卵则可以自由产在外骨骼内。这种产卵策略进化的新方案有五个步骤:自由产光滑卵(祖先状态)、卵的成熟与蜕皮同步(在海洋中的沙蜥祖先中形成)、利用外膜产卵(加强对卵的机械和生理保护)、获得卵的装饰和自由产装饰卵(与风险分散策略有关)。本文介绍并讨论了一个有趣的与甲壳动物卵室中自由产卵有关的 "比孵化 "案例。
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来源期刊
Accounts of Chemical Research
Accounts of Chemical Research 化学-化学综合
CiteScore
31.40
自引率
1.10%
发文量
312
审稿时长
2 months
期刊介绍: Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance. Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.
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