Male antagonistic behaviour after spawning suggests paternal care in brown trout,Salmo trutta

Abstract – The evolution of parental care depends on the sex‐dependent resolution of a trade‐off between present and future reproduction. In salmonids, the mating systems are often characterised by fierce male–male competition, and the absence of paternal care is widely admitted in these species. However, the fact that brown trout eggs can be cannibalised by peripheral individuals just after spawning suggests that dominant males would benefit from protecting their offspring by keeping cannibals away from the nest. We used 77 field observations of brown trout spawning to document the defensive behaviour of dominant males towards peripheral individuals before and after spawning, and test whether this behaviour was related to the probability of the clutch being cannibalised. We showed that dominant males stayed on the nest and chased peripherals even after the eggs were laid and fertilised. The number of chases performed by dominant males during the 2 min following spawning was negatively correlated to the probability of egg cannibalism. This result indicates that brown trout males can provide direct benefits to females through protection against egg cannibalism by peripheral individuals.     

根瘤菌-豆科植物共生多样性与地理环境的关系

 根瘤菌与豆科植物形成的根瘤或茎瘤固氮共生体系在农、林、牧业的可持续发展中具有重要作用。 10 0多年前 ,在根瘤菌研究的起始阶段 ,人们提出的“宿主专一性”及“互接种族”2个概念一直流传至今。 2 0世纪 4 0年代 ,有学者根据实验室内豆科植物的交叉结瘤结果否定过“互接种族”的观念 ,70～ 80年代又发现某些根瘤菌在实验室条件下有广谱共生现象。但根瘤菌与豆科植物共生体与地理环境的关系却很少被涉及过。本文在对大量根瘤菌进行分类研究的基础上 ,结合宿主植物及其区域地理环境的综合分析 ,揭示出根瘤菌与豆科植物