Data from: Gape-limited predators as agents of selection on the defensive morphology of an invasive invertebrate

Invasive species have widespread and pronounced effects on ecosystems and
adaptive evolution of invaders is often considered responsible for their
success. Despite the potential importance of adaptation to invasion, we
still have limited knowledge of the agents of natural selection on
invasive species. Bythotrephes longimanus, a cladoceran zooplankton,
invaded multiple Canadian Shield lakes over the past several decades.
Bythotrephes have a conspicuous caudal process (tail spine) that provides
a morphological defense against fish predation. We measured viability
selection on the longest component of the Bythotrephes spine, the distal
spine segment, through a comparison of the lengths of first and second
instar Bythotrephes collected from lakes differing in the dominance of
gape-limited predation (GLP) and non-gape-limited predation (NGLP) by
fish. We found that natural selection varied by predator gape-limitation,
with strong selection (selection intensity: 0.20-0.79) for increased
distal spine length in lakes dominated by GLP, and no significant
selection in lakes dominated by NGLP. Further, distal spine length was 17%
longer in lakes dominated by GLP, suggesting the possibility of local
adaptation. As all study lakes were invaded less than twenty years prior
to our collections, our results suggest rapid divergence in defensive
morphology in response to selection from fish predators.

入侵物种对生态系统具有广泛且显著的影响，入侵种的适应性进化常被认为是其成功的关键因素。尽管适应对入侵的潜在重要性不容忽视，但我们对入侵物种自然选择的驱动因子仍知之甚少。Bythotrephes longimanus（一种枝角类浮游动物）在过去几十年中入侵了加拿大盾地区的多个湖泊。该物种具有显著的尾突（尾刺），可作为抵御鱼类捕食的形态学防御机制。我们通过比较来自不同鱼类捕食主导类型（口裂限制捕食（GLP）与非口裂限制捕食（NGLP））湖泊中采集的Bythotrephes第一龄和第二龄个体的尾刺最长部分——远端刺段的长度，测量了该段的生存选择强度。研究发现，自然选择强度因捕食者的口裂限制特性而异：在GLP主导的湖泊中，远端刺段长度存在强烈的选择压力（选择强度：0.20-0.79）；而在NGLP主导的湖泊中，未检测到显著的选择效应。此外，GLP主导湖泊中的Bythotrephes远端刺段长度比其他湖泊长17%，这表明存在局部适应的可能性。由于所有研究湖泊在样本采集前被入侵的时间均不足二十年，我们的结果表明，入侵种的防御形态可针对鱼类捕食压力快速发生分化。