Coggins B L, Pearson A C, Yampolsky L Y
Department of Biological Sciences, East Tennessee State University, Johnson City TN, 37601, USA; Department of Biological Sciences, University of Notre Dame, IN, 46556, USA.
Department of Biological Sciences, East Tennessee State University, Johnson City TN, 37601, USA.
J Therm Biol. 2021 May;98:102934. doi: 10.1016/j.jtherbio.2021.102934. Epub 2021 Apr 5.
Geographic variation in thermal tolerance in Daphnia seems to represent genetic load at the loci specifically responsible for heat tolerance resulting from conditional neutrality. We see no evidence of trade-offs between fitness-related traits at 25 °C vs. 10 °C or between two algal diets across Daphnia magna clones from a variety of locations representing the opposite ends of the distribution of long-term heat tolerance. Likewise, we found no evidence of within-environment trade-offs between heat tolerance and fitness-related traits in any of the environments. Neither short-term and long-term heat tolerance shows any consistent relationship with lipid fluorescence polarization and lipid peroxidation across clones or environments. Pervasive positive correlations between fitness-related traits indicate differences in genetic load rather than trade-off based local adaptation or thermal specialization. For heat tolerance such differences may be caused by either relaxation of stabilizing selection due to lower exposure to high temperature extremes, i.e., conditional neutrality, or by small effective population size followed by the recent range expansion.
水蚤耐热性的地理差异似乎代表了在特定基因座上的遗传负荷，这些基因座专门负责由条件中性导致的耐热性。我们没有发现来自代表长期耐热性分布两端的不同地点的大型溞克隆在25°C与10°C下与适应度相关性状之间存在权衡的证据，也没有发现两种藻类食物之间存在权衡的证据。同样，我们在任何环境中都没有发现耐热性与适应度相关性状在环境内部存在权衡的证据。无论是短期还是长期耐热性，在不同克隆或环境中与脂质荧光偏振和脂质过氧化均未表现出任何一致的关系。适应度相关性状之间普遍存在正相关，这表明是遗传负荷的差异，而不是基于权衡的局部适应或热特化。对于耐热性而言，这种差异可能是由于高温极端情况暴露较少导致稳定选择放松，即条件中性，或者是由于有效种群规模较小以及近期的范围扩张所致。
