C re a ting m a na g e m e nt g uide line s fo r hyb rid pla nts. The c a se o f Narc issus x pe re zlarae Fo nt Q ue r. I. MARQ UES & D. DRAPER Unive rsid a d e d e Lisb o a , Muse u Na c io na l d e Histó ria Na tura l, Ja rd im Bo tâ nic o , Rua d a Esc o la Po lité c nic a 58, 1250-110 Lisb o a , Po rtug a l. e -m a il: im a rq ue s@ fc .ul.p t Sum m a ry Pla nt hyb rid iza tio n is o ne o f the m o st c o ntro ve rsia l a sp e c ts in p la nt c o nse rva tio n. Se ve ra l kind s o f ha b ita t c ha ng e a nd a lie n sp e c ie s c a n inc re a se the p ro b a b ility a nd ra te o f hyb rid iza tio n a nd the re fo re it ha s b e c o m e a sub je c t o f re c e nt a tte ntio n. Ad d itio na lly, the re c o g nitio n o f the histo ric a l ro le o f hyb rid iza tio n a s a n e vo lutio na ry p ro c e ss ha s c a use a re -e va lua tio n o f c o nse rva tio n p o lic ie s. Ho w e ve r, hyb rid iza tio n c a n a lso b e a thre a t to the lo ng -te rm p e rsiste nc e o f sc a rc e o r p ro te c te d sp e c ie s, thro ug h a ssim ila tio n o r o utb re e d ing d e p re ssio n a nd thus, the p re d o mina nt vie w is the ne g a tive sc e na rio in whic h it ha s c o ntrib ute d to the e xtinc tio n o f ma ny sp e c ie s thro ug h d ire c t a nd ind ire c t m e a ns. Altho ug h the se sc e na rio s a re c o ntra d ic to ry it se e m s c le a r tha t m a na g e m e nt g uid e line s a re ne c e ssa ry to d e a l with the se situa tio ns. In this w o rk, w e p re se nt so m e p ro c e d ure s fo r the na tura l hyb rid , N. x p e re zla ra e , a s w e ll a s so m e g uid e line s to he lp in m a na g e m e nt d e c isio ns. Intro duc tio n The im p o rta nc e o f na tura l hyb rid iza tio n in the e vo lutio na ry p ro c e ss ha s b e e n ne g le c te d thro ug h m a ny c e nturie s. Da rwin re c o g nize d its e xiste nc e , b ut ha s d e nie d it a n e vo lutio na ry p a rtic ip a tio n sta ting tha t inte rc ro sse d sp e c ie s ra re ly p ro d uc e o ffsp ring a nd w he n it ha p p e ns, the fe w ind ivid ua ls fo rm e d a re func tio na lly im p o te nt (DARWIN, 1859). Ea rlie r in this c e ntury, e xte nd ing thro ug h the m o d e rn synthe sis, so m e a utho rs a rg ue d this p re d o m ina nt c o nc e p t p ro m o ting a n im p o rta nt ro le fo r na tura l hyb rid iza tio n in the e vo lutio n (ANDERSO N, 1949; STEBBINS, 1959). Ho w e ve r, with the e m p ha sis o n sp e c ie s inte g rity this q ue stio n w a s re je c te d a nd hyb rid iza tio n vie we d a s a vio la tio n o f sp e c ie s b o und a rie s, thus d e ta ining the d ive rg e nc e p ro c e ss (MAYR, 1963). No ne the le ss, re p o rts o f p la nt hyb rid s c o ntinue d to a rise d e fe nd ing its c re a tive im p o rta nc e to the fo rma tio n o f ne w sp e c ie s (se e ARNO LD, 1997). C o nse q ue nc e s o f hyb rid iza tio n p ro c e sse s Se ve ra l o utc o m e s m a y re sult fro m hyb rid iza tio n: intro g re ssio n, e xtinc tio n o f sp e c ie s, a nd sta b iliza tio n o f the hyb rid zo ne o r hyb rid sp e c ia tio n. So m e e ffe c ts a re ne g a tive in te rm s o f d ive rsity, na me ly, the me rg ing o f the hyb rid izing fo rms a nd the g e ne tic a ssimila tio n o f g e o g ra p hic a lly re stric te d sp e c ie s (LEVIN e t a l., 1996), thre a te n the ir surviva l (RHYMER & SIMBERLO FF, 1996). O the r o utc o m e s m a y inc lud e the re info rc ing o f re p ro d uc tive b a rrie rs thro ug h se le c tio n fo r a sso rte d m a ting (DO BZHANSKY, 1970) o r the p ro d uc tio n o f a d a p tive c ha ra c te rs tha t a llo w the m to c o lo nize ne w ha b ita ts o r inc re a se the ir fitne ss, in the ir e xiste nc e nic he , m o re ra p id ly tha n thro ug h m uta tio n (STEBBINS, 1959; LEWO NTIN a nd BIRC H, 1966). The m a jo r p o ssib le e vo lutio na ry c o ntrib utio n o f hyb rid iza tio n is the fo rm a tio n o f ne w hyb rid sp e c ie s (G RANT, 1981; ARNOLD, 1997). Why c o nse rve p la nt hyb rid s? The no tio n tha t inte rsp e c ific hyb rid s a re ra re is ina d e q ua te . A re c e nt re vie w sug g e sts the e xiste nc e o f 27.500 na tura l hyb rid s wo rld wid e , a m o ng the 250.000 d e sc rib e d a ng io sp e rm sp e c ie s d e sc rib e d (RIESEBERG , 1997). Na tura l hyb rid s a re a lso une ve nly d istrib ute d ta xo no m ic a lly. O nly 16%-34% o f p la nt fa m ilie s a nd 6%-16% o f g e ne ra ha ve o ne o r m o re re p o rte d hyb rid s (ELLSTRAND e t a l., 1996). Thus, sp o nta ne o us hyb rid iza tio n is no t a s unive rsa l a s b e lie ve d b ut a p p e a rs to b e c o nc e ntra te d in a sm a ll fra c tio n o f p la nts. Mo re o ve r, hyb rid zo ne s a p p e a r to a c t a s im p o rta nt p o ints o f b io d ive rsity a nd p ro vid e ha b ita t fo r o the r sp e c ie s (ARNO LD, 1997). The e xc lusio n o f hyb rid s fro m p ro te c tio n a nd the ir e ra d ic a tio n thre a te ns the o rig in o f ne w sp e c ie s tha t m a y b e a b le to survive in a c ha ng ing wo rld . It is a lso im p o rta nt to c o nsid e r tha t na tura l