Experimental data on photophysiology and growth rates of the invasive foraminifera Amphistegina lobifera showing high thermal tolerance from the Eastern Mediterranean and the Gulf of Aqaba

Invasive species allow an investigation of trait retention and adaptations after exposure to new habitats. Recent work on corals from the Gulf of Aqaba (GoA) shows that tolerance to high temperature persists thousands of years after invasion, without any apparent adaptive advantage. Here we test whether thermal tolerance retention also occurs in another symbiont-bearing calcifying organism. To this end, we investigate the thermal tolerance of the benthic foraminifera Amphistegina lobifera from the GoA (29° 30.14167 N 34° 55.085 E) and compare it to a recent "Lessepsian invader population" from the Eastern Mediterranean (EaM) (32° 37.386 N, 34°55.169 E). We first established that the studied populations are genetically homogenous but distinct from a population in Australia, and that they contain a similar consortium of diatom symbionts, confirming their recent common descent. Thereafter, we exposed specimens from GoA and EaM to elevated temperatures for three weeks and monitored survivorship, growth rates and photophysiology. Both populations exhibited a similar pattern of temperature tolerance. A consistent reduction of photosynthetic dark yields was observed at 34°C and reduced growth was observed at 32°C. The apparent tolerance to sustained exposure to high temperature cannot have a direct adaptive importance, as peak summer temperatures in both locations remain <32°C. Instead, it seems that in the studied foraminifera tolerance to high temperature is a conservative trait and the EaM population retained this trait since its recent invasion. Such pre-adaptation to higher temperatures confers A. lobifera a clear adaptive advantage in shallow and episodically high temperature environments in the Mediterranean under further warming.

入侵物种为探究物种进驻新栖息地后的性状保留与适应性演化提供了理想研究模型。此前针对亚喀巴湾（Gulf of Aqaba, GoA）珊瑚的研究显示，物种在入侵后数千年仍可保留高温耐受性，且未显现出任何明显的适应性优势。
本研究旨在验证另一类携带共生体的钙化生物中是否同样存在高温耐受性保留现象。为此，我们检测了采自亚喀巴湾（29° 30.14167°N，34° 55.085°E）的底栖有孔虫（benthic foraminifera）双盖虫（Amphistegina lobifera）的高温耐受性，并将其与采自东地中海（Eastern Mediterranean, EaM）的新近莱塞普斯入侵种群（32° 37.386°N，34° 55.169°E）进行对比。
本研究首先确认，本次研究的两个种群在遗传上均一，但与澳大利亚种群存在显著差异；二者携带的硅藻共生体群落组成相似，证实它们拥有新近的共同祖先。
随后，我们将采自亚喀巴湾与东地中海的样本置于高温环境中培养三周，并监测其存活率、生长速率与光生理特性（photophysiology）。
两个种群均表现出相似的高温耐受性模式：在34℃条件下，光合暗产率（photosynthetic dark yields）持续下降；在32℃条件下，生长速率出现显著降低。
由于两地夏季最高气温均低于32℃，这种对持续高温暴露的表观耐受性并不具备直接的适应性意义。
由此可见，在所研究的有孔虫中，高温耐受性属于保守性状，东地中海入侵种群自近期入侵以来便保留了这一性状。
在未来气候持续变暖的背景下，这种对高温的预适应性将为双盖虫（Amphistegina lobifera）在东地中海浅海及间歇性高温环境中带来显著的适应性优势。