Killam 1BIO 192Ben KillamProfessor Timothy Sparkes1/28/2015Analysis of Biale Shell si!e an" its relation to pre"ationIntroduction:Biales are marine moll#sks $ith har" shells %onsistin& of mostly 'a'O() The *iales+ shells are often *ore" into *y their %ommon pre"ator the moon snail ,Airre et al) -.) In prior st#"ies snails/ hae "emonstrate" a preferen%e for *iales $ith thin shells rather than those $ith thi%k shells ,Airre et al) -.) 0o$eer/ it sho#l" *e note" that *iales "i" not eole thi%k shells in response to the pre"ation1 rather the thi%ker shells $ere a ran"om m#tation that $as *ene2%ial eno#&h to allo$ its+ %arrier to s#rie an" repro"#%e) The snails+ preferen%e for thin shelle" *iales is an e3ample of sele%tie press#re/ meanin& that the pop#lation is *e%omin& more heaily thi%k shelle" *e%a#se the thin shelle" *iales are *ein& preye" #pon *efore they %an repro"#%e at a &reater n#m*er than those $ith thi%ker shells ,Airre et al)1.)Therefore/ the snails+ pre"ation $as the me%hanism for nat#ral sele%tion an" the in%rease in *iale si!e oer time $as the res#lt) Killam 2In la* $e %on"#%te" an e3periment meant to test the relationship *et$een the pre"ation of *iales an" its relation to shell si!e) To "o this $e teste" o#r *iolo&i%al hypothesis 4there is an a5e%t of pre"ation preferen%e on shell si!e6) A""itionally/ $e teste" o#r n#ll hypothesis 4there is no si&ni2%ant pre"ator preferen%e on shell si!e6 an" o#r alternatie hypothesis 4the shell si!e is "etermine" *y pre"ator preferen%es6) 7#rin& the e3periment I ma"e the pre"i%tion that *iale shell si!e $o#l" in8#en%e the fre9#en%y of snail pre"ation)Methods:In or"er to "etermine the relationship *et$een pre"ation fre9#en%y an" shell len&th $e e3amine" an assortment of shells an" %lassi2e" ea%h of them as one of 2e spe%ies) To "o this $e #se" a key %ontainin& the names an" key feat#res of the 2e *iales/ s#%h as *loo" arks hain& a hain& teeth at the en" of their #m*os,Airre et al):.) The spe%ies i"enti2e" $ere yello$ %o%kles/ pon"ero#s arks/ *loo" arks/ in%on&r#o#s arks/ an" transersearks ,Airre et al) :.) On%e the *iales ha" all *een i"enti2e" the *loo" arkspe%ies $as %hosen as a fo%al spe%ies for the e3periment) In the ne3t phase of the e3periment/ 2e *loo" arks $ere meas#re" in millimeters from anterior to posterior en"s #sin& %alipers) ;e3t $e sket%he" the *iales an" looke" for the presen%e of *ore holes) After that/ the sheet %ontainin& the sket%hes an" meas#rements $as tra"e" $ith a partner so that se%on"ary o*serations an" meas#rements %o#l" *e ma"e) e%or"e" statisti%s of pre"ate" an" not pre"ate" *iales)Not predated PredatedMean (mm) (2)2? 28)95Minimum size (mm) 1?)- 19)8Maximum size (mm) 5?)(5 ?5)25Number of bivalves 11? 15Percent of total bivalves () 88)? 11)-Killam ?1 2 ( ? 5 - : 8 9 10 11 12 1(01020(0?050-0!in (upper limit" mm)#re$uenc%#i&ure 1: 0isto&ram of all shells1 2 ( ? 5 - : 8 9 10 11 12 1(012(?5-!in (upper limit" mm)#re$uenc%#i&ure ': 0isto&ram of pre"ate" shellsKillam 51 2 ( ? 5 - : 8 9 10 11 12 1( 1?0510152025(0(5?0?5!in (upper limit" mm)#re$uenc%#i&ure (: 0isto&ram of non pre"ate" shellsThe res#lts sho$ that only 11)-@ of the 129 *iales $ere pre"ate") Ofthose *iales the lar&est $as ?5)25 mm an" the smallest $as 19)8) The nonpre"ate" *iales $hi%h ma"e #p 88)?@ of the total ha" a lar&er ran&e of si!es) The lar&est non pre"ate" *iale $as 5?)(5 mm an" the smallest $as 1?)- mm) The mean al#e of the non pre"ate" *iales $as fo#n" to *e (2)2?mm $hile the mean al#e for the pre"ate" *iales $as fo#n" to *e 28)95mm) The "ata sho$s that the aera&e non pre"ate" *iale ,(2)2?mm.$as lar&er than the aera&e pre"ate" *iale ,1?)- mm.))iscussion:Base" on the res#lts an" their is#al representations in the 2res/ it issho$n that the small to me"i#m si!e" shells from ? mm to 8 mm $ere Killam -pre"ate" the most) After -mm/ the pre"ation of the *iales $ent "o$n si&ni2%antly #ntil it %ease" alto&ether at 9mm) Therefore/ the lar&er *iales from 8mm to 11mm $ere preye" #pon less than the me"i#m an" small si!e"*iales) Keepin& that I min"/ it %an *e inferre" that a &reater n#m*er of lar&er shelle" *iales are s#riin& lon& eno#&h to repro"#%e than smaller shelle" *iales) The sele%tie press#re inoke" *y the pre"ation of the snails is a me%hanism for nat#ral sele%tion that is %a#sin& the pop#lation to #n"er&o "ire%tional sele%tion p#shin& shell len&th to the lar&er en" of the spe%tr#m) The snails seem to *e preyin& on the me"i#m an" smaller si!e" *iales *e%a#se the ener&y %ost of *orin& thro#&h their shells "oes not o#t$ei&h the *ene2t of %ons#min& the *iale as it "oes in the lar&er thi%kershelle" *iales)Anfort#nately/ the "ata %olle%te" in la* %o#l" %ontain a fair amo#nt o*sere" ariation *e%a#se of the inherent "iB%#lty in hain& an entire %lass #niformly meas#re shells of aryin& morpholo&ies) A possi*le sol#tion for this $o#l" *e to "eelop a #niform metho" of meas#rin& *iale shells to limit the ariation in o*sere" si!e/ or to hae a sin&le person meas#re the entirety of the *iale spe%imens)In the se%on" nat#ral sele%tion la* the poole" "ata of all the %lasses $as "isplaye" in m#ltiple &raphs %ontainin& the pre"ation of pon"ero#s arks/*loo" arks/ an" in%on&r#o#s arks as $ell as the lo%ation they $ere &athere" from) The &raphs $ere e3amine" for the type of sele%tion o%%#rrin& in them) Bloo" arks $ere fo#n" to "emonstrate "ire%tional sele%tion *e%a#se of their lar&er shells lo$er n#m*er of pre"ation in %omparison to their small shells) Killam :The Pon"ero#s arks $ere also fo#n" to "emonstrate "ire%tional sele%tion for the same reason as the *loo" arks) The In%on&r#o#s arks "emonstrate" "isr#ptie sele%tion *e%a#se the n#m*er of pre"ate" shells on either si"e of the me"i#m si!e" shells $as ery similar) Alternatiely/ the n#m*er of pre"ate" me"i#m si!e" shells $as hi&h in %omparison) In re&ar"s to the t$o "i5erent *ea%hes an" their in8#en%e on the ark pop#lations/ ="isto arks appear to *e more often pre"ate" to$ar"s the %enter of the histo&ram ,"isr#ptie sele%tion./ $hile the