Data from: Time-limited environments affect the evolution of egg - body size allometry

Initial offspring size is a fundamental component of absolute growth rate, where large offspring will reach a given adult body size faster than smaller offspring. Yet, our knowledge regarding the co-evolution between offspring and adult size is limited. In time-constrained environments, organisms need to reproduce at a high rate and reach a reproductive size quickly. In order to rapidly attain a large adult body size, we hypothesize that, in seasonal habitats, large species are bound to having a large initial size, and consequently, the evolution of egg size will be tightly matched to that of body size, compared to less time-limited systems. We tested this hypothesis in killifishes, and found a significantly steeper allometric relationship between egg size and body size in annual, compared to non-annual species. We also found higher rates of evolution of egg and body size in annual compared to non-annual species. Our results suggest that time-constrained environments impose strong selection on rapidly reaching a species-specific body size, and reproduce at a high rate, which in turn imposes constraints on the evolution of egg sizes. In combination, these distinct selection pressures result in different relationships between egg and body size among species in time-constrained versus permanent habitats.

子代初始体型是绝对生长速率的核心构成要素，体型较大的子代相较于体型较小的个体，能够更快达到既定的成体体型。然而，目前学界对于子代体型与成体体型之间的协同演化机制仍知之甚少。在时间受限的生境中，生物需要以较高的速率进行繁殖，并快速达到繁殖所需的体型。为了快速获得较大的成体体型，我们提出假说：在季节性生境中，大型物种必然拥有较大的初始体型；因此，相较于时间限制较弱的系统，卵型的演化将与体型演化紧密耦合。我们以鳉鱼（killifishes）为研究对象验证了该假说，结果发现：相较于非一年生物种，一年生鳉鱼的卵型与体型间的异速生长关系显著更陡。同时我们还发现，相较于非一年生物种，一年生鳉鱼的卵型与体型的演化速率更高。研究结果表明，时间受限的生境会对物种快速达到物种特异性体型以及高效繁殖施加强烈的选择压力，进而对卵型的演化形成约束。综上，这些差异化的选择压力使得时间受限生境与永久生境中的物种，呈现出不同的卵型与体型间的关联模式。