同屬物種間的競爭抑制尼泊爾埋葬蟲的合作行為

Abstract

生態與社會因子如何影響動物合作行為的演化，一直是演化生物學家關心的核心課題。然而，多數的研究僅集中於了解親緣關係對社會生物的影響，但對於環境因子與種間競爭如何影響合作行為的演化，則著墨不多。本實驗利用擁有社會行為之物種－尼泊爾埋葬蟲（Nicrophorus nepalensis）進行研究探討，我們藉由控制不同的群體大小以及不同的環境條件，例如：溫度、海拔、種間競爭等，觀察尼泊爾埋葬蟲面臨不同壓力時的社會行為表現。由此我們提出兩種假說：非生物因子調解假說與種間競爭型式假說。前者認為種間壓力的強度受非生物因子的調控，如：溫度、雨量等；後者則認為種間競爭的型式可促使合作行為，如何在不同的競爭者間獲得資源至為關鍵。例如：速佔型競爭、競賽型競爭。結果顯示：四川夾金山山區的尼泊爾埋葬蟲族群於中低海拔段與麗蠅具有速佔型競爭，且其群體較大、於資源上的總投資時間較高；中高海拔段則與同屬埋葬蟲衿覆葬甲（N. schawalleri）進行競賽型競爭，其群體較小、於資源上的總投資時間也比較低。本研究顯示，當種間競爭壓力超出合作行為所能獲得之利益時，社會動物將選擇不合作且不同的競爭型式所導致的利益使得尼泊爾埋葬蟲選擇改變其合作行為模式，支持了種間競爭型式假說。

How ecological and social factors influence the evolution of cooperative behavior in animals has been a central concern for evolutionary biologists. However, most studies have focused on understanding the effects of kinship in social animals, but not much is known about how environmental factors and interspecific competition affect the evolution of cooperative behavior. In this experiment, we investigated the social behavior of Nicrophorus nepalensis, a burying beetle with social behavior. We controlled different group sizes and environmental conditions, such as temperature, altitude, and interspecific competition, to observe the social behavior of N. nepalensis under different stresses. Two hypotheses were proposed: the abiotic mediation hypothesis and the interspecific competition type hypothesis. The former hypothesis suggests that the intensity of interspecific pressure is regulated by abiotic factors, such as temperature and rainfall, while the latter hypothesis suggests that the type of interspecific competition can lead to cooperative behavior, and how to obtain resources among different competitors is the key, such as scramble and contest competition. The results showed that the N. nepalensis population in the Jiajin Mountains of Sichuan had a competitive pattern with the blowflies in the middle and low elevations, and its population size was larger, its total investment time spend on resources was higher, thus had cooperative behavior; while in the middle and high elevations, it competed with the another kind of burying beetles, N. schawalleri, its population size was smaller and total investment time spend on resources was lower, thus it was less cooperative. The benefits of different competition patterns are known to cause N. nepalensis to change its choice of cooperative behavior, therefor supporting the interspecific competition type hypothesis.