Research ArticleEVOLUTIONARY BIOLOGY

Evolutionary trade-off in reproduction of Cambrian arthropods

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Science Advances  29 Apr 2020:
Vol. 6, no. 18, eaaz3376
DOI: 10.1126/sciadv.aaz3376
  • Fig. 1 Comparative morphology of †C. ovata (early Cambrian, Chengjiang) and †W. fieldensis (middle Cambrian, Burgess Shale).

    (A and B) Complete specimen of †C. ovata (YKLP14400) and †W. fieldensis (USNM 114259) showing general morphology in lateral view. (C and D) Anterior part of †C. ovata (YKLP14401) and †W. fieldensis (USNM 138231) in dorsal view. (E and F) Posterior part of †C. ovata (YKLP14402) and †W. fieldensis (USNM 138231) with a tripartite tail fan (segments numbered). (G) Oblique ventral view of †C. ovata (YKLP14403) showing a dislocated carapace, anterior uniramous appendages [small box, see (H)], and posterior lamellate appendages [large box, see (J)]. (H and I) Details of uniramous appendages in †C. ovata and †W. fieldensis (ROMIP 64281). (J and K) Details of lamellate appendages in †C. ovata (six on the right-hand side labeled) and †W. fieldensis (USNM 275504), each composed of an annulated shaft fringed with lamellae. Aa, anterior (uniramous) appendage; An, anus; As, abdominal segment; At, antennule; Ca, carapace; Cl, claws; Ey, eye; La, (posterior) lamellate appendage; Lm, lamellae; Gu, gut; Sf, shaft of lamellate appendage; Tf, tail fan. Scale bars, 2 mm (A, G, and K), 5 mm (B to F), and 1 mm (H to J). Photo credit: Jean Vannier, Université Lyon 1 (A to K).

  • Fig. 2 Egg clusters in †C. ovata.

    (A) Laterally compressed specimen (ELEL-SJ081254A) showing a cluster of eggs under its left carapace valve. (B) Interpretative drawing of (A) illustrating largely hexagonal packing of eggs; poorly preserved eggs represented by dashed circles. (C) Detail of egg cluster. (D) Close-up of focus area in (C); arrows indicate possible remains of embryonic tissues. (E to L) Images of left three eggs in (D) obtained by fluorescence (FL) microscopy, backscattered electron (BSE) microscopy, and energy-dispersive x-ray spectroscopy (EDX; Fe, P, S, C, Pt, and Co), respectively. Ab, abdomen; At, antennule; Cal, left valve of carapace; Car, right valve of carapace; Ey, eye; Os, organic stains. Scale bars, 2 mm (A and B), 1 mm (C), and 200 μm (D to L). Photo credit: Qiang Ou, China University of Geosciences, Beijing (A, C, and D).

  • Fig. 3 Egg clusters in †C. ovata.

    (A) Oblique-laterally compressed specimen (ELEL-MF140101A) with eggs under its right carapace valve. (B) Interpretative drawing of (A); poorly preserved eggs represented by dashed circles. (C) Volume rendering from micro–computed tomography (micro-CT) data of (A); eggs highlighted in red. (D) Laterally compacted specimen (YRCP 0010) with eggs. (E) Detail of egg cluster in (D). (F) Volume rendering from micro-CT data of (D); arrowheads indicate eggs. (G to L) Images of hexagonally arranged eggs [focus area in (E)] obtained by BSE microscopy and EDX (Fe, P, S, Cu, and Co), respectively. Aa, anterior (uniramous) appendage; Ab, abdomen; At, antennule; Cal, left valve of carapace; Car, right valve of carapace; La, lamellate appendage. Scale bars, 2 mm (A to D and F) and 500 μm (E and G to L). Photo credit: Qiang Ou, China University of Geosciences, Beijing (A); Ailin Chen, Yuxi Normal University (D and E).

  • Fig. 4 Artistic reconstruction of the waptiids †C. ovata and †W. fieldensis with brooded eggs.

    Scale bar, 5 mm (for both species). Artwork credit: X. D. Wang.

  • Table 1 Measurements of ovigerous specimens of †C. ovata and †W. fieldensis.

    Abbreviations: Ave D, average diameter of eggs; Bl, body length (measured from the anterior end of carapace to the posterior end of tail fan); Ch, carapace height; Cl, carapace length; Cs, carapace surface area (one valve); Es, carapace surface area covered by preserved eggs; Es/Cs, ratio of Es to Cs; Max D, maximum diameter of eggs; Min D, minimal diameter of eggs; N, number of eggs preserved; *, extrapolated measurement.

    SpecimenSectionNMin D
    (mm)
    Max D
    (mm)
    Ave D
    (mm)
    Bl (mm)Cl (mm)Ch (mm)Es (mm2)Cs (mm2)Es/Cs (%)
    C. ovata
    ELEL-
    SJ081254
    Sanjiezi500.4050.5880.52022.509.886.5610.6250.9520.84
    ELEL-
    MF140101
    Mafang380.4350.6170.55422.859.806.407.5146.2616.23
    YRCP 0010Ercaicun360.4000.5500.48923.009.606.666.7650.6713.34
    ELEL-
    EJ081702
    Erjie>180.4430.6060.53027*12*7.85>4.069*>5.7
    W. fieldensis (11)
    ROMIP
    63357
    Walcott
    Quarry
    132.252.622.463.720.7?58.8288*20.4
    ROMIP
    63354
    Walcott
    Quarry
    122.062.362.1860*19.617.044.828016.0

Supplementary Materials

  • Supplementary Materials

    Evolutionary trade-off in reproduction of Cambrian arthropods

    Qiang Ou, Jean Vannier, Xianfeng Yang, Ailin Chen, Huijuan Mai, Degan Shu, Jian Han, Dongjing Fu, Rong Wang, Georg Mayer

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    This PDF file includes:

    • Systematic Paleontology
    • Taphonomy and Preservation
    • Figs. S1 to S11
    • Table S1
    • References

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