American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Ecological transitions in grouping benefits explain the paradox of environmental quality and sociality”

Posted on

Mark Liu (劉彥廷), Shih-Fan Chan (詹仕凡), Dustin R. Rubenstein, Syuan-Jyun Sun (孫烜駿), Bo-Fei Chen (陳伯飛), and Sheng-Feng Shen (沈聖峰) (May 2020)

Sociality is favored under a wide range of environmental conditions

Read the Article (Just Accepted)

Group size manipulation experiment at the field site. To create pair and group treatments, a locally trapped beetles was releasing in a breeding chamber.<br />(Credit: Mark Liu)
Group size manipulation experiment at the field site. To create pair and group treatments, a locally trapped beetles was releasing in a breeding chamber.
(Credit: Mark Liu)

Abstract

Both benign and harsh environments promote the evolution of sociality. This paradox—societies occur in environments of such contrasting quality—may be explained by the different types of benefits that individuals receive from grouping: resource defense benefits that derive from group-defended critical resources versus collective action benefits that result from social cooperation among group member. Here, we investigate cooperative behavior in the burying beetle Nicrophorus nepalensis along an elevational gradient where environmental quality (climate and competiton) varies with altitude. We show that climate (temperature) and competition (both intra- and interspecific) independently and synergistically influence sociality via different grouping benefits that vary along the gradient. At low elevations where interspecific competition for resources is intense, groups gain from the collective action benefit of increased interspecific competitive ability. In contrast, pairs have higher fitness at intermediate elevations where intraspecific competition for resources is greatest because resource defense is the key grouping benefit. However, groups and pairs have similar fitness at high elevations, suggesting that there is no grouping benefit in such physiologically challenging environments. Our results demonstrate that sociality is favored for different reasons under a range of environmental conditions, perhaps explaining why animal societies occur in environments of such contrasting quality.

合作利益隨著生境的轉換解釋在不同環境下社會行為演化的悖論

良性和惡劣環境都可能促進社會行為的演化,此一悖論或可透過個體從群體合作中獲得不同類型的合作利益來解釋。在良性環境中,高族群密度導致相對激烈的種內競爭,增加了排除種內競爭的成本。透過共享並共同防禦資源,可提高種內競爭的能力(資源防禦利益),故促進合作群體的形成。反之,在惡劣環境中,動物可以透過合作來克服環境挑戰或種間競爭,以獲得各種生存及繁殖上的利益(集體加成利益)。為了確定不同的合作利益能否解釋社會行為為何能在不同的環境條件下出現,我們研究了尼泊爾埋葬蟲(Nicrophorus nepalensis)的合作行為在台灣沿著海拔梯度的改變。我們的研究顯示,埋葬蟲群體在不同海拔受氣候(氣溫)和資源競爭(種內與種間)的單獨及協同影響,因而獲得不同類型的合作利益。在種間資源競爭強烈的低海拔地區,形成合作群體可獲得較高的集體加成利益,群體的人均生產率要高於單對個體。反之,在中海拔地區,由於有較強烈的種內資源競爭,形成群體可獲得較高的資源防禦利益,但單對個體的人均生產力卻高於群體。在高海拔地區,群體和單對個體人均生產率則相似,顯示埋葬蟲在這種生理狀況受到嚴峻挑戰的高海拔環境中並沒有群體優勢。我們的結果說明,在不同的環境條件下,生物的合作行為皆可能為其帶來優勢,這也許可以解釋為何動物社會可以在不同環境條件下形成的悖論。