Seed dispersal by ants (myrmecochory) is an asymmetric, presumably mutualistic interaction, where a few ant species benefit many plants. Myrmecochorous plants express specialized adaptations, most notably a large elaiosome, which promote interactions with efficient seed dispersers while decreasing interactions with poor dispersers, resulting in de facto partner choice. However, because variation in plants' investment in reward and ant response to them may vary spatially and temporally, it is unclear whether such specialization is consistent along geographic gradients; especially towards myrmecochory's range margin. To answer this question on context-dependent partner choice, we first estimated variation in reward investment by co-occurring myrmecochores along a steep environmental gradient in a Mediterranean region. Second, we tested whether variation in plant investment in reward was positively and consistently correlated with the quality of dispersal plant received along the same gradient. Using in situ cafeteria experiments, we simultaneously presented diaspores of locally co-occurring myrmecochorous species to ants of two guilds representing high- and low-quality dispersers. We then recorded ant-seed behaviour, seed preference and seed removal rates for each ant guild. We found both overall and within-site high variation among plant species in the total and relative investment in elaiosomes. Both ant guilds removed substantial proportion of the seeds. However, scavenging ants (high-quality dispersers) clearly preferred diaspores with larger elaiosomes, whereas granivorous ants (low-quality dispersers) exhibited no preference. Furthermore, both the variation in plant traits and the corresponding response of different ant guilds were consistent along the studied geographic gradient. This consistency holds even when granivores, which removed seeds in a non-selective fashion and provided apparently low-quality seed dispersal services, were, at least numerically, the dominant ant guild. This dominance and the consistency of the partner choice shed light on the functionality of elaiosomes at the margins of myrmecochory's distribution.

中文翻译：

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蚂蚁分散的工厂在奖励方面的投资始终沿着地理梯度选择更好的合作伙伴。

蚂蚁散播的种子（线虫）是一种不对称的相互作用，可能是相互影响的，其中一些蚂蚁物种使许多植物受益。食线虫的植物表现出特殊的适应性，最显着的是较大的弹性体，其促进与有效种子分散剂的相互作用，同时减少与不良分散剂的相互作用，导致事实上的伴侣选择。但是，由于植物在奖励和对它们的反应上的投资变化可能会在空间和时间上发生变化，因此尚不清楚这种专业化是否沿着地理梯度一致。尤其是迈步步伐的射程幅度。为了回答有关上下文依赖的伙伴选择的问题，我们首先通过在地中海地区沿陡峭的环境梯度共生变种动物来估计奖励投资的变化。第二，我们测试了奖励中植物投资的变化是否与沿相同梯度获得的分散植物的质量呈正相关一致。使用原地自助餐厅实验，我们同时向代表高品质和低品质分散剂的两个行会的蚂蚁介绍了本地同时存在的线虫物种的渗水孢子。然后，我们记录了每个蚂蚁行会的蚂蚁种子行为，种子偏好和种子去除率。我们发现，在总的和相对的投资中，植物物种之间总的和内部的高度变化在弹性体上。两个蚂蚁行会都去除了大部分种子。但是，清除剂（优质分散剂）显然更优选具有较大弹性体的水合孢子，而粒状蚂蚁（低质量分散剂）则没有表现出任何偏爱。此外，在研究的地理梯度上，植物性状的变化和不同蚂蚁行会的相应反应都一致。即使以食草动物（至少以数字方式）是主要的蚂蚁行会，即使以非选择性方式去除种子并提供明显劣质的种子传播服务的食草动物，这种一致性也保持不变。这种优势和配偶选择的一致性揭示了在寄主线分布边缘的弹性体的功能。