INRA, UMR, 1062, CBGP Montpellier, France.
BMC Evol Biol. 2014 Feb 5;14:15. doi: 10.1186/1471-2148-14-15.
Cannibalism is widespread in both vertebrates and invertebrates but its extent is variable between and within species. Cannibalism depends on population density and nutritional conditions, and could be beneficial during colonisation of new environments. Empirical studies are needed to determine whether this trait might facilitate invasion of a new area in natural systems. We investigated whether the propensity for cannibalism in H. axyridis differs both between native and invasive populations and between invasive populations from the core and from the front of the invasive area in Western Europe. We also compared the propensity for cannibalism of these natural populations with that of laboratory-reared biocontrol populations. We measured the cannibalism rates of eggs by first instar larvae and adult females at two different individual densities of ladybirds from three types of population (invasive, native and biocontrol), in laboratory-controlled conditions.
Cannibalism was significantly greater in larvae from invasive populations compared to native or biocontrol populations, but there was no difference in cannibalism rates between populations from the core or front of the invaded range. Cannibalism was significantly lower in larvae from biocontrol populations compared to wild (invasive and native) populations. No differences in cannibalism rates of adult females were found between any populations. While high population density significantly increased cannibalism in both larvae and adults, the norm of reaction of cannibalism to individual density did not change significantly during the invasion and/or laboratory rearing processes.
This study is the first to provide evidence for a higher propensity for cannibalism in invasive populations compared to native ones. Our experiments also shed light on the difference in cannibalism evolution with respect to life stages. However, we are still at an early stage in understanding the underlying mechanisms and several different research perspectives are needed to determine whether the higher propensity for cannibalism is a general feature of the invasion process.
在脊椎动物和无脊椎动物中，同类相食现象普遍存在，但在不同物种之间以及同一物种的不同种群之间，同类相食的程度存在差异。同类相食取决于种群密度和营养条件，在新环境的殖民过程中可能是有益的。需要进行实证研究来确定这种特性是否有助于在自然系统中入侵新的区域。我们调查了在欧洲西部，欧洲野虎甲的本地种群和入侵种群之间，以及入侵种群的核心种群和前沿种群之间，其捕食同类的倾向是否存在差异。我们还将这些自然种群的捕食同类倾向与实验室饲养的生物防治种群进行了比较。我们在实验室控制条件下，测量了来自三种种群（入侵、本地和生物防治）的初孵幼虫和成年雌性在两个不同个体密度下对卵的捕食率。
与本地种群或生物防治种群相比，入侵种群的幼虫捕食同类的比例显著更高，但核心种群和前沿种群之间的捕食同类率没有差异。与野生种群（入侵和本地种群）相比，生物防治种群的幼虫捕食同类的比例显著更低。在任何种群之间，成年雌性的捕食同类率都没有差异。虽然高种群密度显著增加了幼虫和成虫的捕食同类行为，但在入侵和/或实验室饲养过程中，捕食同类对个体密度的反应规范并没有显著变化。
本研究首次提供了证据，证明与本地种群相比，入侵种群具有更高的捕食同类倾向。我们的实验还揭示了与生活阶段有关的捕食同类进化的差异。然而，我们在理解潜在机制方面仍处于早期阶段，需要从几个不同的研究角度来确定更高的捕食同类倾向是否是入侵过程的一个普遍特征。
