Supporting Information Table S7 Major gene ontology (GO) terms with significant enrichment among genes with evidence of positive selection compared to all genes covered in this whole-genome resequencing effort.						
		Significantly enriched GO term in genes with signal of positive selection  	P. alba		P. tremula	
	GO ID		# genes 	#  Pos. sel. genes 	# genes 	#  Pos. sel. genes 
(a)	Molecular function					
	GO:0000155	phosphorelay sensor kinase activity	17	9*	16	7
	GO:0000166	nucleotide binding	2515	955***	2375	961*
	GO:0004097	catechol oxidase activity	5	4*	5	1
	GO:0004435	phosphatidylinositol phospholipase C activity	6	2	5	4*
	GO:0004672	protein kinase activity	1131	475***	1091	486***
	GO:0004674	protein serine/threonine kinase activity	58	32***	56	32***
	GO:0004842	ubiquitin-protein transferase activity	77	30	78	36**
	GO:0004888	transmembrane signaling receptor activity	77	42***	76	40**
	GO:0005216	ion channel activity	54	18	48	25**
	GO:0005515	protein binding	2598	919***	2431	943***
	GO:0005516	calmodulin binding	20	12**	19	10
	GO:0005524	ATP binding	2067	827***	1970	836***
	GO:0008026	ATP-dependent helicase activity	114	37	103	45*
	GO:0008762	UDP-N-acetylmuramate dehydrogenase activity	51	20	50	28***
	GO:0010333	terpene synthase activity	16	11**	17	9
	GO:0015662	"ATPase activity, coupled to transmembrane movement of ions, phosphorylative mechanism"	26	14*	24	10
	GO:0016758	"transferase activity, transferring hexosyl groups"	361	118*	352	128**
	GO:0016887	ATPase activity	336	118*	313	121*
	GO:0031625	ubiquitin protein ligase binding	9	4	6	5*
	GO:0035091	phosphatidylinositol binding	10	7*	9	5
	GO:0042802	identical protein binding	54	24*	55	19
	GO:0043531	ADP binding	192	98***	187	96***
	GO:0046872	metal ion binding	1243	393*	1170	375
	GO:0050660	flavin adenine dinucleotide binding	139	46	135	56*
	GO:0050664	"oxidoreductase activity, acting on NAD(P)H, oxygen as acceptor"	10	4	9	6*
	GO:2001070	starch binding	8	5	9	6*
(b)	Cellular component					
	GO:0000145	exocyst	29	13*	31	14*
	GO:0000151	ubiquitin ligase complex	85	34*	83	40**
	GO:0016020	membrane	1865	538*	1735	539**
	GO:0016459	myosin complex	15	8*	13	7
	GO:0030288	outer membrane-bounded periplasmic space	20	10*	18	8
	GO:0031224	intrinsic component of membrane	763	229***	729	232***
	GO:0031461	cullin-RING ubiquitin ligase complex	9	4	6	5**
"#genes, tolt number of annotated genes; # Pos. Sel. Genes, number of genes with evidence of outlier status for positive selection as identified by alpha tests. Molecular function (a) and Cellular component (b) of genes with significantly enriched GO terms. Significance levels for Fisher’s exact test are abbreviated ***P<0.001; **P <0.01; * P<0.05."