(ISTORICAL "IOGEOGRAPHY OF ,ONGHORN #ACTUS "EETLES
4HE )NmUENCE OF 0LEISTOCENE #LIMATE #HANGES ON
!MERICAN $ESERT #OMMUNITIES
#HRISTOPHER )RWIN 3MITH
$EPARTMENT OF "IOLOGICAL 3CIENCES 5NIVERSITY OF )DAHO -OSCOW )$
"RIAN $ORSEY &ARRELL
-USEUM OF #OMPARATIVE :OOLOGY (ARVARD 5NIVERSITY #AMBRIDGE -!
!BSTRACTˆ-ITOCHONDRIAL SEQUENCE DATA FROM THREE SPECIES OF mIGHTLESS CACTUS BEETLES -ONEILEMA
GIGAS - ARMATUM AND - APPRESSUM WERE ANALYZED 4HE COALESCENT MODELS IMPLEMENTED IN
THE PROGRAM &,5#45!4% WERE USED TO TEST THE HYPOTHESIS THAT THESE SPECIES EXPERIENCED RANGE
CHANGES FOLLOWING THE END OF THE LAST GLACIAL PERIOD 4HE TWO DESERT SPECIES - GIGAS AND -
ARMATUM BOTH SHOWED SIGNIlCANT EVIDENCE OF POPULATION GROWTH PARTICULARLY IN NORTHERN POPULA
TIONS HOWEVER THE MONTANE SPECIES - APPRESSUM DID NOT SHOW EVIDENCE OF RANGE FRAGMENTATION
AND POPULATION DECLINE AS PREDICTED FROM PALEOCLIMATE DATA
)NTRODUCTION
4HE ARID REGIONS OF THE INTERMONTANE !MERICAN 7EST
EXPERIENCED DRAMATIC CHANGES FOLLOWING THE END OF THE MOST
RECENT GLACIAL PERIOD -ANY DESERT PLANTS AND ANIMALS EXPE
RIENCED RANGE CHANGES TO HIGHER ELEVATIONS WHERE THEY HAD
BEEN ABSENT DURING GLACIAL PERIODS AND MANY COOL CLIMATE
ORGANISMS THAT PREVIOUSLY DOMINATED THESE REGIONS RETREATED
TO ISOLATED MOUNTAINTOPS INCLUDING THE -ADREAN 3KY )SLANDS
6AN $EVENDER A B 4HE RANGE CHANGES SEEN IN THESE
CASES ARE AMONG THE BEST DOCUMENTED EXAMPLES OF PLANT RE
SPONSES TO 0LEISTOCENE CLIMATE CHANGES AND HAVE PROMPTED
A NUMBER OF PHYLOGEOGRAPHIC STUDIES THAT LOOKED FOR GE
NETIC SIGNATURES OF THESE EVENTS "ARBER -ADDISON AND
-C-AHON -ASTA 3MITH 3ULLIVAN !LTHOUGH THESE STUDIES HAVE REVEALED MUCH ABOUT POPULATION
STRUCTURE IN SPECIES WITHIN THESE REGIONS EVIDENCE FOR A DIRECT
IMPACT OF LATE 0LEISTOCENE CLIMATE CHANGES ON BIOGEOGRAPHY
OR DEMOGRAPHY IS STILL LACKING
4HE mIGHTLESS CACTUS BEETLES -ONEILEMA ARE AN APPROPRIATE
PLACE TO LOOK FOR EVIDENCE OF SUCH AN IMPACT -ONEILEMA SPP
ARE LARGE BLACK mIGHTLESS BEETLES DISTRIBUTED THROUGHOUT THE
.ORTH !MERICAN DESERTS 4HEY FEED EXCLUSIVELY ON CACTI THEIR
LARVAE BURROWING INTO THE PADS WHERE THEY COMPLETE THEIR
DEVELOPMENT ,INSLEY AND #HEMSAK 0REVIOUS RESEARCH
HAS DEMONSTRATED THAT THESE EXTREMELY SEDENTARY ANIMALS SHOW
SIGNIlCANT BIOGEOGRAPHIC STRUCTURE 3MITH AND RETAIN
GENETIC SIGNATURES OF PAST RANGE CHANGES
4HERE ARE THREE SPECIES OF -ONEILEMA THAT OCCUR IN THE
-ADREAN 3KY )SLANDS AND THE SURROUNDING DESERTS - GIGAS
,E#ONTE OCCURS IN THE 3ONORAN $ESERT BELOW CA METERS
AND IS DISTRIBUTED FROM CENTRAL !RIZONA SOUTHWARDS TO NORTHERN
3INALOA - ARMATUM ,E#ONTE OCCURS IN THE #HIHUAHUAN $ESERT
BELOW METERS FROM WESTERN .EW -EXICO EAST TO THE
USDA Forest Service Proceedings RMRS-P-36. 2005.
'ULF OF -EXICO AND SOUTHWARD TO #ENTRAL -EXICO &INALLY
- APPRESSUM ,E#ONTE IS A SKY ISLANDS ENDEMIC THAT OCCURS
ABOVE METERS ELEVATION IN SEMI DESERT GRASSLAND AND OAK
WOODLANDS THROUGHOUT !RIZONA .EW -EXICO 4EXAS 3ONORA
AND #HIHUAHUA AND EXISTS IN SYMPATRY WITH EACH OF THE TWO
DESERT SPECIES AT LOWER ELEVATIONS IN THE WESTERN AND EASTERN
EDGES OF ITS RANGE RESPECTIVELY
'IVEN THE PACKRAT MIDDEN EVIDENCE FOR CHANGES IN THE
DISTRIBUTION OF DESERT ORGANISMS FOLLOWING THE END OF THE LAST
ICE AGE 6AN $EVENDER A B WE MIGHT EXPECT THAT THESE
ORGANISMS WOULD HAVE UNDERGONE SIMILAR RANGE SHIFTS AND
THAT THAT HISTORY MIGHT BE RETAINED IN THEIR POPULATION GENETIC
STRUCTURE )NDEED PREVIOUS PHYLOGENETIC AND .ESTED #LADE
ANALYSES SUGGEST THAT THE TWO DESERT SPECIES - GIGAS AND
- ARMATUM HAVE UNDERGONE PROGRESSIVE NORTHWARD RANGE
EXPANSIONS FROM SOURCE POPULATIONS IN SOUTHERN 3ONORA AND
THE "OLSON DE -APIMI IN #OAHUILA INTO THE NORTHERN EDGE OF
THEIR CURRENT DISTRIBUTION 3MITH 3MITH AND &ARRELL IN
REVIEW ,IKEWISE .ESTED #LADE !NALYSIS SUGGESTS THAT THE 3KY
)SLAND SPECIES - APPRESSUM HAS UNDERGONE A RANGE FRAGMEN
TATION LEADING TO LOCAL DIFFERENTIATION OF ISOLATED POPULATIONS
3MITH (OWEVER COALESCENT AND MOLECULAR CLOCK BASED
ESTIMATES SUGGEST THAT IN ALL THREE SPECIES THESE DRAMATIC RANGE
CHANGES ON A CONTINENTAL SCALE OCCURRED BETWEEN AND MILLION YEARS AGO LONG BEFORE THE END OF THE LAST GLACIAL PERIOD
3MITH AND &ARRELL IN REVIEW #LEARLY THESE mIGHTLESS ANIMALS RECORD BIOGEOGRAPHIC HIS
TORY OVER VERY DEEP TIME BUT WE ALSO WANTED TO LOOK AT RANGE
CHANGES ON A SMALLER TIME SCALE )T IS POSSIBLE THAT SUPERIM
POSED ON THESE LARGE SCALE DISTRIBUTION PATTERNS THERE MAY
HAVE BEEN MORE SUBTLE LOCAL RANGE CHANGES AS CERTAIN DESERT
ORGANISMS EXPANDED FROM LOCAL REFUGIA AND MOVED INTO HIGHER
ELEVATIONS THROUGHOUT THE LAST YEARS )N ORDER TO TEST THIS
HYPOTHESIS WE EXAMINED MITOCHONDRIAL $.! SEQUENCES DRAWN
135
FROM MULTIPLE POPULATIONS IN EACH OF THESES SPECIES 7E USED
COALESCENT MODELS TO TEST THE HYPOTHESIS THAT POPULATIONS OF THE
TWO DESERT SPECIES - GIGAS AND - ARMATUM HAVE UNDERGONE
RECENT GROWTH AND THAT POPULATIONS OF THE SKY ISLAND SPECIES
- APPRESSUM HAVE UNDERGONE RECENT DECLINE
-ETHODS
3PECIMENS OF -ONEILEMA SPP WERE COLLECTED FROM ACROSS
THE RANGE OF THE 3ONORAN AND #HIHUAHUAN $ESERTS AND FROM
ACROSS THE -ADREAN 3KY )SLANDS !RCHIPELAGO 4HE COORDINATES
OF EACH COLLECTION LOCALITY WERE RECORDED USING A HAND HELD
'ARMIN '03 OR % MAP '03 UNIT SEE TABLES AND #OLLECTION SITES WERE CHOSEN BY CONSULTING PREVIOUS COLLEC
TIONS DATA IN PUBLISHED ACCOUNTS ,INSLEY AND #HEMSAK 2ASKE AND BY EXAMINING MUSEUM SPECIMENS AT THE
-USEUM OF #OMPARATIVE :OOLOGY AT (ARVARD THE 5NIVERSITY
OF !RIZONA INSECT COLLECTION THE %SSIG -USEUM AT 5NIVERSITY OF
#ALIFORNIA "ERKELEY THE #ALIFORNIA !CADEMY OF 3CIENCES AND
THE )NSTITUTO DE "IOLOGIA AT THE 5NIVERSIDAD .ACIONÕL !UT˜NOMA
4ABLE ˆ0OPULATIONS AND COLLECTION LOCALITIES INFORMATION FOR - GIGAS
0OPULATION
#OLLECTION
LOCALITIES
,OCATION
#OORDINATES
)NDIVIDUALS
SEQUENCED
2IO -AYO
!LAMOS -ONTE
3OUTHEAST OF !LAMOS 3ONORA ON THE ROAD TOWARDS THE
2IO #UCHIJAQUI
. 7
2IO 3ONORA
3AN #ARLOS
,AS 'UÉSIMAS
0LAYA $EL 3OL
)N THE TOWN OF 3AN #ARLOS 3ONORA
-EXICO (WY %AST OF 'UAYMAS 3ONORA -EXICO
-EXICO (WY +M %AST OF 'UAYMAS 3ONORA
-EXICO
. 7
. 7
. 7
3AN .ICOLAS
3ONORA
+M 3OUTHEAST OF (ERMOSILLO 3ONORA .EAR
)NTERSECTION WITH 2OAD TO #IUDAD /BREGON
. 7
-OCTEZUMA
3ONORA
+M .ORTHEAST OF (ERMOSILLO .EAR -OCTEZUMA
2IVER
. 7
5RES 3ON
-AZOCAHUI
3ONORA
+M .ORTHEAST OF (ERMOSILLO
KM .ORTH EAST OF (ERMOSILLO .EAR 2OAD TO
#ANANEA
. 7
. 7
+M -EXICO (WY +- NORTH OF (ERMOSILLO
3ONORA -EXICO
. 7
2IO "AVISPE
(USABAS 3ONORA
+M .ORTHEAST OF (ERMOSILLO 3ONORA NEAR
2IO "AVISPE
. 7
#HOLLA "AY
#HOLLA "AY
#HOLLA "AY WEST OF 0UERTO 0E×ASCO 3ONORA -EXICO
. 7
/FF -EXICO (WY *UST EAST OF 3ONOITA 3ONORA -EXICO
"ULLS 0ASTURE IN THE !JO -OUNTAINS /RGAN 0IPE
.ATIONAL -ONUMENT 0IMA #OUNTY !RIZONA
. 7
. 7
4ABLE -TS
3OUTH OF )NTERSTATE .EAR 4ABLE 4OP 7ILDERNESS
0INAL #OUNTY !RIZONA
. 7
"LACK -T
"ABOQUIVARI
"LACK -OUNTAIN 3OUTH OF !JO 0IMA #OUNTY !RIZONA
"ROWN #ANYON %AST OF "ABOQUIVARI -OUNTAIN
0IMA #OUNTY !:
. 7
. %
!LTAR 6ALLEY
)NTERSECTION OF !RIZONA (WY AND 0IMA
#OUNTY !:
"ETWEEN !MADO AND !RIVACA ON "ATAMOTE 2D
3ANTA #RUZ #OUNTY !RIZONA
. 7
. 7
3ANTA 2ITA -OUNTAINS !BOVE 3ANTA 2ITA
%XPERIMENTAL 2ANGE 3TATION 3ANTA #RUZ #OUNTY
!RIZONA
"OX #ANYON 2OAD BETWEEN 'REATERVILLE AND THE
3ANTA 2ITA %XPERIMENTAL 2ANGE 3TATION 3ANTA #RUZ
#OUNTY !RIZONA
. 7
. 7
. 7
. 7
. 7
. 7
. 7
!JO -OUNTAINS 3ONOITA
"ULLS 0ASTURE
!LTAR 6ALLEY
3HERIFFS -ESA
3ANTA 2ITA -TS
&LORIDA #ANYON
"OX #ANYON
3ANTA
#ATALINA -TS
#ATALINA 3TATE
0ARK
"IOSPHERE ))
/RACLE !RIZONA
4IGER -INE
7ILLOW 3PRINGS
2D
136
#ATALINA 3TATE 0ARK 'ROUP 5SE !REA 0IMA #OUNTY
!RIZONA
"IOSPHERE )) #ENTER 0INAL #OUNTY !RIZONA
!RIZONA 4RAIL OFF -T ,EMON 2OAD /RACLE 0INAL
#OUNTY !RIZONA
/FF !: (79 .ORTH %AST OF /RACLE !RIZONA
0INAL #OUNTY !RIZONA
/FF !: (WY 7EST OF /RACLE !RIZONA
USDA Forest Service Proceedings RMRS-P-36. 2005.
4ABLE ˆ0OPULATIONS AND COLLECTION LOCALITIES INFORMATION FOR - ARMATUM
0OPULATION
#OLLECTION
LOCALITIES
,OCATION
#OORDINATES
)NDIVIDUALS
SEQUENCED
'ULF #OAST
#HINA
2EYNOSA
-ONTERREY
-EXICO (WY .EAR #HINA 2ESERVOIR .UEVO ,EON -EXICO
-EXICO (WY KM SOUTH OF 2EYNOSA 4AMAULIPAS
-EXICO (WY +- .ORTHWEST OF -ONTERREY .UEVO ,EON
4EXAS
. 7
. 7
. 7
%AST OF 2IO
'RANDE
#OX -TS
/FF #OUNTY (WY .ORTH OF 3IERRA "LANCA (UDSPETH
#OUNTY 4EXAS
&RANKLIN -OUNTAINS IN #OUNTY 2OAD ,OOP .ORTH OF
%L 0ASO %L 0ASO #OUNTY 4EXAS
#OUNTY 2OAD AND 53 .EAR (UECO (UDSPETH
#OUNTY 4EXAS
)NTERSTATE AT EXIT "ERNALILLO 3ANDOVAL #OUNTY
.EW -EXICO
$O×A !NA 0EAK OFF #OUNTY ROAD .ORTH OF ,AS #RUCES
$O×A !NA #OUNTY .EW -EXICO
/FF 53 .ORTHEAST OF #ARRIZOZO ,INCOLN #OUNTY
.EW -EXICO
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
&RANKLIN -TS
(UECO
"ERNALILLO
$O×A !NA -TS
6ALLEY OF &IRE
0ECOS 2IVER
6ALLEY
#ONTINENTAL
$IVIDE
#ORREO
"EAR -T
-EDLEY $RAW
/LD (ACHITA
'RANITE 'AP
!NTELOPE
4RES (ERMANAS
3IERRA ,AS 5VAS
)NTERSTATE %XIT .EAR #ORREO .EW -EXICO #IBOLA
#OUNTY .EW -EXICO
$AVIS -OUNTAINS 4EXAS *EFF $AVIS #OUNTY
4EXAS 2T NEAR WINDFARMS EAST OF &ORT $AVIS *EFF $AVIS
#OUNTY 4EXAS
/LD (ACHITA 2OAD AND .EW -EXICO (WY 7EST OF
(ACHITA 'RANT #OUNTY .EW -EXICO
!RIZONA.EW -EXICO 3TATE ,INE AT .- (WY (IDALGO #TY .EW -EXICO
.EW -EXICO (WY EAST OF !NIMAS .EW -EXICO NEAR
#ONTINENTAL $IVIDE (IDALGO #TY .EW -EXICO
.EAR 4RES (ERMANAS -OUNTAINS OFF .EW -EXICO (WY 3OUTH OF $EMING ,UNA #OUNTY .EW -EXICO
/FF .EW -EXICO (WY 3OUTH OF (ATCH $O×A !NA
#OUNTY .EW -EXICO
DE -£XICO 5.!- !DDITIONALLY BIOTIC COMMUNITIES MAPS
"ROWN AND PUBLISHED ACCOUNTS OF PALEOVEGETATION IN THE
REGION %LIAS AND 6AN$EVENDER 6AN $EVENDER A B
6AN $EVENDER AND "RADLEY WERE CONSULTED TO IDENTIFY
POTENTIAL NEW POPULATIONS AND DETERMINE WHICH WOULD BE MOST
INFORMATIVE IN RECONSTRUCTING 0LEISTOCENE CLIMATE CHANGES
!PPROXIMATELY BASE PAIRS OF MITOCHONDRIAL $.!
SEQUENCE DATA FROM THE #YTOCHROME /XIDASE #/) GENE
WAS OBTAINED BY 0#2 AND THERMAL CYCLE SEQUENCING USING THE
METHODS DESCRIBED IN 3MITH FROM INDIVIDUALS OF -
APPRESSUM INDIVIDUALS OF - ARMATUM AND INDIVIDUALS
OF - GIGAS 3EQUENCE DATA WERE EASILY ALIGNED BY EYE USING
-AC#LADE VERSION -ADDISON AND -ADDISON #OALESCENT MODELING OF CHANGES IN POPULATION SIZE WERE
PERFORMED USING THE PROGRAM &,5#45!4% +UHNER ET AL
3AMPLES WERE GROUPED INTO POPULATIONS BASED ON PREVI
OUS ESTIMATES OF MIGRATION RATES BETWEEN COLLECTION LOCALITIES
3MITH OBTAINED FROM THE PROGRAM -$)6 .IELSEN AND
7AKELEY IF THERE WAS EVIDENCE OF SIGNIlCANT MIGRATION
BETWEEN COLLECTION LOCALITIES THESE LOCALITIES WERE COMBINED
AND ANALYZED AS A SINGLE POPULATION SEE TABLES THROUGH &,5#45!4% WAS USED TO ESTIMATE THE PARAMETERS hΘv .« AND hGv THE EXPONENTIAL RATE OF POPULATION GROWTH OR
DECLINE RELATIVE TO THE NEUTRAL MUTATION RATE FOR EACH SPECIES
7E SET THE PROGRAM TO COMPUTE THE 7ATTERSON ESTIMATE OF THETA
USDA Forest Service Proceedings RMRS-P-36. 2005.
AND ALLOWED THE POPULATION TO CHANGE IN SIZE WITH AN INITIAL
VALUE FOR hGv SET TO 7E USED SHORT -ARKOV #HAIN -ONTE
#ARLOS OF GENERATIONS EACH AND TWO LONG -ARKOV #HAIN
-ONTE #ARLOS OF GENERATIONS EACH 4HE PROBABILITY THAT
hGv IS DIFFERENT FROM ZERO WAS DETERMINED BY REFERRING TO PLOTS
OF THE LIKELIHOOD SURFACE AND THE CONlDENCE INTERVALS ABOUT G
AND THETA OUTPUT BY &,5#45!4%
2ESULTS
&,5#45!4% FOUND EVIDENCE OF POPULATION GROWTH IN ALL
THREE SPECIES IN MOST OF THE POPULATIONS TABLE %STIMATES
OF hGv WERE POSITIVE FOR ALL POPULATIONS ANALYZED BUT WERE
GENERALLY LOW WITH PER GENERATIONS GROWTH RATES BETWEEN X
AND X %STIMATES OF hGv WERE SIGNIlCANTLY GREATER
THAN ZERO P IN ALL BUT FOUR POPULATIONS
$ISCUSSION
"OTH OF THE DESERT SPECIES SHOW EVIDENCE OF POPULATION
GROWTH AS WE HAD PREDICTED !DDITIONALLY AS WE MIGHT EXPECT
THE MOST DRAMATIC RATES OF POPULATION GROWTH WERE SEEN IN
POPULATIONS ON THE NORTHERN PERIPHERY OF THE RANGE OF - GIGAS
IE THE #ATALINA -OUNTAINS !LTAR 6ALLEY AND !JO -OUNTAINS
137
4ABLE ˆ0OPULATIONS AND #OLLECTION ,OCALITIES INFORMATION FOR - APPRESSUM
0OPULATION
%AST OF 2IO
'RANDE
#ONTINENTAL
$IVIDE
3ANTA #RUZ
2IVER 6ALLEY
#OLLECTION
LOCALITIES
#OORDINATES
)NDIVIDUALS
SEQUENCED
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
. 7
/RACLE !RIZONA
!RIZONA 4RAIL OFF -T ,EMON 2OAD /RACLE 0INAL #OUNTY !RIZONA . 7
'REATERVILLE
3ANTA 2ITA -TS 'REATERVILLE 2D 7EST OF !: (WY . 7
. 7
. 7
"ERNALILLO
/RGAN .-
,OCATION
)NTERSTATE AT EXIT "ERNALILLO 3ANDOVAL #OUNTY
.EW -EXICO
53 "ETWEEN ,AS #RUCES AND 7HITE 3ANDS -ISSILE 2ANGE
$O×A !NA #TY .EW -EXICO
-T 2ILEY
%AST 0ORTILLO -TS #TY 2OAD ! NORTH OF #TY 2OAD ! NEAR
53-EXICO "ORDER $O×A !NA #TY .EW -EXICO
/LD (ACHITA
/LD (ACHITA 2OAD AND .EW -EXICO (WY 7EST OF (ACHITA
'RANT #OUNTY .EW -EXICO
3ADDLEROCK
"IG "URRO -TS 3ADDLEROCK #ANYON 2D OFF 53 WEST OF
#ANYON
3ILVER #ITY 'RANT #TY .EW -EXICO
,AS 0LAYAS 6ALLEY ,AS 0LAYAS 6ALLEY 2D 3OUTH OF )NTERSECTION W .- (WY (IDALGO #TY .EW -EXICO
!NTELOPE
.EW -EXICO (WY EAST OF !NIMAS .EW -EXICO NEAR
#ONTINENTAL $IVIDE (IDALGO #TY .EW -EXICO
'RANITE 'AP
!RIZONA.EW -EXICO 3TATE ,INE AT .- (WY (IDALGO
#TY .EW -EXICO
3KELETON #ANYON 0ELONCILLO -TS 3KELETON #ANYON
4OLLHOUSE #ANYON 0ELONCILLO -TS (WY WEST OF #LIFTON 'REENLEE #TY !RIZONA
3AN 3IMON
0INALE×O -TS (WY 3OUTH OF 3AFFORD 'RAHAM #TY !RIZONA
7ILLCOX 0LAYA
2AILROAD !VENUE 3OUTHWEST OF 7ILLCOX #OCHISE #TY !RIZONA
#OCHISE
$RAGOON -TS )RONWOOD 2D %AST OF #OCHISE 2ANGER 3TATION
3TRONGHOLD
#OCHISE #TY !RIZONA
$RAGOON
$RAGOON -TS &OREST 3ERVICE 2D .ORTH OF )NTERSECTION
W )RONWOOD 2D #OCHISE #TY !RIZONA
.OGALES !RIZONA 0AJARITO -TS &OREST 3ERVICE 2D .EAR !RIZONA (WY EAST OF )NTERSTATE 3TA #RUZ #TY !RIZONA
"OX #ANYON
"OX #ANYON 2OAD BETWEEN 'REATERVILLE AND THE 3ANTA 2ITA
%XPERIMENTAL 2ANGE 3TATION 3ANTA #RUZ #OUNTY !RIZONA
WHERE POST GLACIAL RANGE CHANGES IN DESERT ORGANISMS WERE
GREATEST WHEREAS THREE POPULATIONS FROM 3ONORA INCLUDING
ONE ON THE 3EA OF #ORTEZ IE PUTATIVE DESERT REFUGIA DID NOT
SHOW RATES OF POPULATION GROWTH THAT WERE SIGNIlCANTLY DIFFER
ENT FROM ZERO !LTHOUGH THIS LATTER OBSERVATION MAY IN PART BE
AN ARTIFACT OF SMALL SAMPLE SIZE THE GEOGRAPHIC COMPONENT
AND THE FACT THAT hGv WAS OF SIMILAR SIGN AND MAGNITUDE ACROSS
ALL POPULATIONS OFFER FURTHER SUPPORT FOR A COMMON EXTRINSIC
CAUSE OF THESE DEMOGRAPHIC CHANGES
)T SHOULD BE NOTED OF COURSE THAT POPULATION GROWTH PER
SE AND RANGE EXPANSION ARE CERTAINLY DISTINCT PROCESSES BUT
BARRING DRAMATIC CHANGES IN POPULATION DENSITY THE ONE WOULD
SEEM TO REQUIRE THE OTHER !DDITIONALLY WHILE IT IS NOT POSSIBLE
TO ACCURATELY INFER WHEN THESE DEMOGRAPHIC CHANGES OCCURRED
THEY MUST HAVE BEEN RECENT ENOUGH THAT THE GENETIC SIGNATURES
OF THESE EVENTS HAVE NOT BEEN LOST THROUGH GENETIC DRIFT 7E
THEREFORE VIEW THESE RESULTS AS COMPELLING EVIDENCE THAT THE
TWO DESERT INSECTS HAVE UNDERGONE RECENT RANGE EXPANSIONS
WHICH MAY HAVE BEEN A RESPONSE TO CLIMATE CHANGES SINCE THE
END OF THE LAST GLACIAL PERIOD
(OWEVER 4HE MONTANE SPECIES - APPRESSUM NOT ONLY DOES
NOT SHOW EVIDENCE OF POPULATION DECLINE AS WE HAD PREDICTED
BUT IN FACT INDICATES STRONG EVIDENCE OF POPULATION EXPANSION
IN TWO OF THE THREE POPULATIONS ANALYZED )T IS POSSIBLE THAT
138
GROUPING SEQUENCES FROM DIFFERENT LOCALITIES COULD PRODUCE
ERRONEOUS ESTIMATES OF COALESCENT PARAMETERS PARTICULARLY IF
DEMOGRAPHIC HISTORIES DIFFERED BETWEEN LOCALITIES OR IF GEO
GRAPHIC SAMPLING WERE UNEVEN (OWEVER IN THIS CASE THERE
WAS STILL SIGNIlCANT EVIDENCE OF POPULATION EXPANSION WHEN
THE DATA FROM PARTICULAR COLLECTION LOCALITIES WERE ANALYZED
SEPARATELY # 3MITH UNPUBLISHED !DDITIONALLY WE SUSPECT
THAT IF GROUPING POPULATIONS WERE TO HAVE BIASED OUR RESULTS AT
ALL IT WOULD HAVE PRODUCED LOWER ESTIMATES OF hGv ON AVERAGE
BECAUSE SAMPLING MULTIPLE POPULATIONS SHOULD INCREASE THE
MEAN TIME TO COALESCENCE IN OUR SAMPLE
3O IT APPEARS THAT THE EVIDENCE OF POPULATION EXPANSION
IN - APPRESSUM IS NOT AN ARTIFACT OF THE ANALYSIS 4HIS RESULT
IS SOMEWHAT CONFUSING HOWEVER AS BOTH PHYLOGENETIC AND
.ESTED #LADE ANALYSES INDICATE THAT THIS SPECIES HAS UNDERGONE
RANGE FRAGMENTATION ALBEIT MUCH LONGER AGO THAN THE END OF
THE LAST GLACIAL PERIOD 3MITH /NE POSSIBLE EXPLANATION
MIGHT BE THAT MORE RECENT DEMOGRAPHIC CHANGES HAVE ERASED
ANY EVIDENCE OF PRIOR POPULATION DECLINE !LTERNATIVELY IT MAY
BE THAT THIS SPECIES SIMPLY DID NOT RESPOND TO POST 0LEISTOCENE
CLIMATE CHANGES BY UNDERGOING SIGNIlCANT RANGE FRAGMENTA
TION )T HAS LONG BEEN KNOWN THAT PARTICULAR PLANTS AND ANIMALS
RESPONDED IDIOSYNCRATICALLY TO CLIMATE CHANGE FOLLOWING THE
END OF THE LAST ICE AGE RATHER THAN RESPONDING EN MASSE AS AN
USDA Forest Service Proceedings RMRS-P-36. 2005.
4ABLE ˆ%XPONENTIAL GROWTH RATES ESTIMATED BY &,5#45!4%
3PECIES
0OPULATION
4HETA
G T«
R T .E
R T GENERATION
P
'IGAS
!LAMOS
2IO 3ONORA
2IO "AVISPE
#HOLLA "AY
!JO -TS
!LTAR 6ALLEY
3ANTA 2ITAS
#ATALINAS
X X X X X X X X !RMATUM
#ONTINENTAL $IVIDE
'ULF #OAST
0ECOS 2IVER
2IO 'RANDE
X X X X !PPRESSUM
%AST OF 2IO 'RANDE
#ONTINENTAL $IVIDE
3ANTA #RUZ 2IVER
X X X ENTIRE COMMUNITY 6AN$EVENDER A !LTHOUGH MANY PINE
AND OAK WOODLAND SPECIES DID RETREAT TO HIGHER ELEVATIONS IT
MAY BE THAT - APPRESSUM AND THEIR HOSTS REMAINED IN PLACE
AS THE ENVIRONMENT CHANGED AROUND THEM
#ONCLUSIONS
4HE RESULTS FOR ALL THREE OF THESE SPECIES SUGGEST A COMPLEX
BIOGEOGRAPHIC HISTORY IN WHICH RECENT RANGE CHANGES HAVE BEEN
OVERLAID ON AN OLDER BIOGEOGRAPHIC HISTORY 0REVIOUS STUDIES
SUGGEST THAT THE DESERT SPECIES - GIGAS AND - ARMATUM HAVE
BEEN UNDERGOING PROGRESSIVE NORTHWARD EXPANSION THROUGHOUT
THE 0LEISTOCENE BUT THE EVIDENCE PRESENTED HERE SUGGESTS THAT
POPULATIONS FROM ACROSS THE RANGE OF BOTH OF THESE SPECIES
HAVE ALSO EXPERIENCED LOCAL DEMOGRAPHIC CHANGES AND POPULA
TION GROWTH FOLLOWING THE END OF THE LAST ICE AGE #ONVERSELY
WHEREAS PREVIOUS STUDIES SUGGEST THAT THE MONTANE SPECIES -
APPRESSUM UNDERWENT SIGNIlCANT RANGE FRAGMENTATION IN THE
PAST THE EVIDENCE PRESENTED HERE SUGGESTS RECENT EXPANSION
IN SOME POPULATIONS
2EFERENCES
"ARBER 0 ( 0HYLOGEOGRAPHY OF THE CANYON TREEFROG (YLA
ARENICOLOR #OPE BASED ON MITOCHONDRIAL $.! SEQUENCE DATA
-OLECULAR %COLOGY "ROWN $ "IOTIC #OMMUNITIES 3OUTHWESTERN 5NITED 3TATES
AND .ORTHWESTERN -EXICO 5NIVERISTY OF 5TAH 0RESS
%LIAS 3 ! 4 2 6AN$EVENDER )NSECT FOSSIL EVIDENCE OF LATE
1UATERNARY ENVIRONMENTS IN THE NORTHERN #HIHUAHUAN DESERT OF
4EXAS AND .EW -EXICO COMPARISONS WITH THE PALEOBOTANICAL
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USDA Forest Service Proceedings RMRS-P-36. 2005.
-ADDISON 7 0 $ -ADDISON -AC#LADE VERSION 3INAUER
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OF THE -EXICAN WOODRAT .EOTOMA MEXICANA IN THE !MERICAN
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"IOGEOGRAPHY 6AN $EVENDER 4 2 A ,ATE QUATERNARY VEGETATION AND CLIMATE
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4UCSON 6AN $EVENDER 4 2 %NVIRONMENTAL HISTORY OF THE 3ONORAN
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HERPETOFAUNA )N (ERPETOLOGY OF THE .ORTH !MERICAN $ESERTS
3OUTHWESTERN (ERPETOLOGISTS 3OCIETY 139