Natural parasites in conjunction with behavioral and color traits explain male agonistic behaviors in a lizard

Male competition conforms to a cost-benefit model,because while aggression may increase reproductive prospects,it can also increase the risk of injury.We hypothesize that an additional cost in aggressive males would be an increase in parasite load associated with a high energy investment into sexual competition.Some of these infections,in turn,may downmodulate the level of host aggression via energetic trade-offs.We staged dyadic male contests in the lab to investigate the relationships of multiple parasites with the agonistic behavior of lizard hosts,Sceloporus occidentalis.We also included both color and behavioral traits from opponents in the analyses because(1)color patches of lizards may serve as intraspecific signals used by conspecifics to assess the quality of opponents,and(2)contests between male lizards fit classical models of escalated aggression,where lizards increase aggression displays in response to an opponent's behavior.The results conform to our hypothesis because male lizards displayed more pushups when they had more ticks.Moreover,some parasites may modulate the levels of aggression because lizards infected by hematic coccidians performed fewer pushups.Interestingly,lizards also displayed fewer pushups when both the chroma and size of the opponent's blue patch were greater.The results thus also supported the role of the blue patch of s.occidentalis as a sexual armament,because it contributed to the deterrence of aggression from opponent lizards.We revealed that natural parasitic infections in lizard hosts can contribute to their agonistic behavior.We encourage future studies to account for parasites in behavioral testswithlizards.

重新认知青藏高原围栏禁牧的作用

围栏禁牧是中国政府为恢复青藏高原等地退化草地而采取的一项重要政策.然而,关于围栏对高寒草地生态系统功能和服务及其对牧民生计的影响,人们的认识还很有限.本研究荟萃分析和基于问卷的调查显示,围栏禁牧时间长达4年和8年的时间里可以有效地促进高寒草甸以及草原的地上植被生长,更长时间的围栏并没有带来任何生态和经济效益.研究还发现,围栏限制了野生动物的活动范围,增加了非围栏地区的放牧压力,降低了牧民的满意度,且给地区和国家政府带来了巨大的财政成本.因此,建议在适当的情况下,应鼓励传统的游牧方式来利用草地,在严重退化的草地上应采用短期围栏(4~8年),在重要的野生动物栖息地应避免使用围栏,特别是受保护的大型哺乳动物分布的区域.研究结果可为青藏高原草地可持续管理提供一定的参考.

Complex relationships between physiological stress and endoparasite infections in natural populations

Short-term elevation of glucocorticoids(GCs)is one of the major physiological mechanisms by which vertebrates cope with challenging environmental or social factors(stressors).However,when exposure to stressors occurs repeatedly or over a prolonged period of time,animals may experience chronic elevation of GCs,which reduces the immune response efficiency and can lead to higher intensity of parasitic infection.Here,we used invasive gray squirrels Sciurus carolinensis in troduced in Norther n Italy and their 2 most prevale nt gastrointesti nal parasites,the n ematode Strongyloides robustus and coccidia of the genus Eimeria,as a model to investigate relati on ships among macroparasite infection and concentrations of fecal glucocorticoid metabolites(FGMs),an integrated measure of circulating GCs.Our results revealed an association of FGMs with infection by St.robustus,but not with coccidia.Individuals with higher FGMs appear to be responsible for the greatest St.robustus egg shedding within gray squirrel populations,thus possibly acting as superspreaders.However,FGMs were negatively associated with adult St.robustus,suggesting that the abundance of adults of this nematode species does not induce elevation in FGMs,but is only affected by it through immun e-mediated effects on its fecun dity.Fin ally,the relati on ship betwee n St.robustus(both eggs and adult parasites)and FGMs was not linear,suggesting that only high levels of physiological stress in fluence parasite inf ection.Our fin dings highlight that the direction and magnitude of the stress-infection relationship may depend not only on the specific hostparasite system,but also on the different life stages of the same parasite.