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:MAMMALIANSPECIES

Sylvilagus graysoni.

No. 559, pp.1-3,3 figs.

By

FernandoA.Cervantes

Published24October1997by theAmericanSocietyofMammalogists

Sylvilagusgraysoni(J.A.Allen,1877)

TresMariasCottontail

LepusgraysoniJ. A.Allen,1877:347.Typelocality"TresMarias Islands,Nayarit,Mexico"(undoubtedlyfrom Maria Madre; Nel son,

1899).

SylvilagusgraysoniLyon,1904:336.Firstuse ofcurrentname combination.

CONTEXTANDCONTENT.OrderLagomorpha,Family

Leporidae,SubfamilyLeporinae,Genus

Sylvilagus,SubgenusSyl

vilagus (Hall,1981;Hoffmann,1993).Sylvilagusgraysonihas two subspecies(Wilson,

1991a):S.g.graysoni(J. A.Allen,1877),see above.

JuanitoIslandof the TresMariasIslands,Nayarit,Mexico." ularius skulls. ThesedifferencesfromS.jloridanuswereevidentin a dis criminant-functionanalysiswhere

S.jloridanuswasseparatedfrom

S. graysoniandS.cuniculariuson the firstdiscriminantfunction (DiersingandWilson,

1980).

markedlyshorterears,whichrangeinlength(dry) from

50.8to

60.4mm,whereaslengthsofearofS.cunicularius(samples1, 2

OncespecimenofS.cuniculariuswasresponsiblefor theoverlap.

Inaddition,

S.graysoniis morereddishon theupperparts,sides,

and legs.Cranially,

S.graysonidiffersprincipallyinhavingmuch

catedallindividualsof the twospecies(DiersingandWilson,1980;

Hall,1981).

GENERALCHARACTERS.Sylvilagusgraysoniis a me

dium-sizedtolarge arereddish-coloreddorsally,with the napeandrumpthebrightest.

Laterally,they are

palerreddish,and theventeriswhitishexcept for thebrownishthroatpatch.The skullis alsomedium-sizedto large,with a longrostrum,longdiastema,and longincisiveforam ina(Fig. 1). Themaxillarytoothrow isrelativelyshort,and the basioccipitalis narrow(Wilson,

1991a).Theposteriorextensions

of thesupraorbitalprocessesareunitedto thebraincasethroughout most of theirlengthas inS.palustris(Hall,1981).Averageexternal measurements(in mm) of19S.g.graysoniand11S.g.badistes, respectively,are as follows: totallength,466.11,436.91;lengthof tail,

50.21, 32.55;lengthofhindfoot,95.42, 90.73;lengthofear

(wet)63.75, 62.18,and (dry)56.83, 57.11(DiersingandWilson,

1980).

Meancranialmeasurements(in mm) for19S.g.graysoniand

11S.g.badistes,respectively,are:lengthof firstupperincisor,

8.93, 9.14;lengthofpalate,8.04, 7.84;

greatestlengthofskull,79.92, 78.22;basallength,64.83, 63.95;zygomaticbreadth,37.00,

37.27;

breadthofbraincase,27.33, 27.57;lengthofnasals,34.31,

34.42;

breadthofnasals,14.90, 14.97;lengthofmaxillarytoothrow (alveolar),

15.23, 16.09;breadthofmaxillarytoothrow(alveolar),

22.60, 22.49;postdentalbreadth,10.15, 10.23;lengthofincisive

foramen,

19.93, 18.57;lengthofbasioccipital,10.09, 9.99;breadth

ofbasioccipital,9.73, 10.07;lengthofdiastema,22.05, 20.19; depthofrostrum,16.47, 16.15;lengthofbulla,11.31, 11.48; breadthofbulla,27.48, 27.04;depthofshield-bullae,23.03,23.19; depthofskull,33.31, 33.20;breadthofcarotidforamina,

11.99,

11.97;breadthofinfraorbitalcanals,19.71,20.11;heightof man-dible,

38.84, 38.40;lengthofmandible,41.15, 40.64;depthof

mandibularramus,12.73, 12.66;lengthofmandibulartoothrow (alveolar),

15.71, 15.89(DiersingandWilson,1980).

DISTRIBUTION.Sylvilagusgraysoniis aninsularspecies with adistributionlimitedto the TresMariasIslands,Nayarit(Fig.

2),ca.100km off the westcoastof Mexico(21-22°N,106-107°

Magdalena

only on SanJuanito

Island(ChapmanandCeballos,1990).Ele

vationalrecordsfor thiscottontailare fromsealevelto ca.350m (Hall,

1981;Nelson,1909).No fossils are known.

cate, andit isdifficulttoskinspecimenswithouttearingthem(Nel son,

1899;Wilson,1991a).It isimpossibletocarryaspecimenby

FIG.

1.Dorsal,ventral,andlateralview ofskull,andlateral

view of tionalMuseum,

512548)from SanJuanitoIsland,Nayarit,Mexico.

Greatestlengthof

skullis75.5mm.Photosby Don E.Wilson.Downloaded from https://academic.oup.com/mspecies/article/doi/10.2307/3504378/2600164 by guest on 24 October 2023

2MAMMALIANSPECIES559

5.0 MARIA

ISLAND

km o I

MARIA MADRE

ISLAND

I

106-30'

%JSANJUANlTOISlAND

MARIA CLEOFAS<;1

ISLAND

FIG. 3.Overviewof thehabitatSylvilagusgraysonion San JuanitoIsland,Nayarit,Mexico.Photoby Don E.Wilson. FIG. 2.Geographicdistributionof the Tres Marfascottontail (Sylvilagusgraysoni;modifiedfromHall,1981).A=S.g. bad istes.

B=S.g.graysoni.

andslipwhereithadbeengraspedby thehand(Nelson,1899). The dentalformulais i2/1,·c0/0,p3/2,m3/3,total 28.There are nosignificantdifferencesincranialcharactersbetweensamples of S.graysonicollectedin1897and1960-1976(Diersingand Wilson,1980).The onlydataonreproductivebiology is from

March;11femaleswerelactating

andtwohad75-mmembryos (Wilson,

1991a).

ECOLOGY.Thehabitatof S.graysoniis morearidthanthe

mainland.Averageyearlyrainfallis

635mm, most ofwhichfalls

in the summer-ofteninviolentstormsfrom thesoutheast.Tem in extremesare 4.6° and37.5°C(Wilson,1991a).

Sylvilagusgraysoni

is atranquilrabbitand easy tocatch sinceit does not fearhumans(Acevedo,1995;Dooley,1988).The extreme tamenessoftheserabbitsmay bedueto adearthofpred ators(Wilson,1991a).Racoons(Procyon lotor),red-tailedhawks are haviorisparticularly apparentin S.graysonifrom SanJuanito Island,althoughcottontailsfrom theotherislandsshow farlessfear of man

1980).

SanJuanitois thesmallest(5 km long by 2 km wide, with a maximumelevationof ca. 50 m) andnorthwesternmostisland, sep aratedfrom MarfaMadreby ashallowchannelca. 3 km wide.The islandisrelativelyflat, butaccessto most of theinteriorismade virtuallyimpossibleby thethickcacti(Fig. 3). Theelevatedportion of the agavesca.

3-4m inheight,whereS.graysonithrives(Wilson,

1991a).

Thisislandis notinhabitedbyhumansandlacksfreshwater (Dooley,1988;Wilson,

1991a).Althoughthiscottontailwasabun

dantin someplaceson the fourislandsat thebeginningofthis century(Nelson,1899),recentlythisspecieswas found to beabun dantonly on SanJuanitoIsland(Wilson,1991a).Itstilloccurson the otherislands,but not inlargenumbers.

MarfaMadreis thelargest

islandof thearchipelago(23 km long by

5-10km wide, with amaximumelevationof>600m).The

naturalvegetationincoastalareasistropicaldeciduousforest with acanopyheightof 4 m,althoughmost of thisforestwasremoved byhumans.TheMexicangovernmentmaintainsa penalcolony therewith apopulationof2,000-3,000,andagriculturaluse of the coastal areasiscommon.Theinteriorof theislandoriginallywas forestedwithtreesup to 30 m, but muchof theharvestabletimber

BEHAVIOR.Sylvilagusgraysoniwasabundantat theend

of thepastcentury(Nelson,1899)in old fields on anabandoned ranchat thenorthernendofMariaMadreisland.Thecottontails often sat in theirformsunderbushes,and whendrivenout into an openspacethey often satquietly.The old fields werecoveredwith a scatteredgrowth ofbushes,whichseemedmoresuitablefor the cottontails sparingly.Thecottontailsfrequentedthe roadthroughthe woods leadingfrom theshoreup over theforestedslopes,andafter1500 hcouldbe foundsittinginsmallopenplacesin theundergrowth apparentlywaitingfor sunsetbeforecomingout into theroads(Nel son,1899).S. graysonifrom MarfaMadreIslandsharesitshabitat with thenativemammalsMarmosacanescens,Oryzomysnelsoni, biaquercus,Macrotuswaterhousii, andGlossophagasoricina (Nelson,1899;Wilson,1991a).

Sylvilagusgraysoni

wasnumerousin adesertedranchon the north sideof MarfaMagdalenaIsland,but wasscarcerelsewhere onthat islandby theendof thepastcentury(Nelson,1899).This islandwasdesignatedanecologicalreserveby theMexicanGov ernment. Itis thesecondlargestisland(15 km long by 8 km wide, with amaximumelevationof ca.

500m) and isseparatedfrom

MarfaMadre

Islandby achannel8 km wide. The forest isless

disturbedthanon MarfaMadreIsland,asthereare nopermanent residents.Theislandisdenselyvegetatedin theinterior,with a relativelyflatcoastal areaalong thenorthcoast.However, the ef fects ofbrowsingbyintroduced deerand goats arenoticeable(Doo ley,1988;Wilson,

1991a).

A few S.graysonihavebeenreportedfrom MarfaCleofas

Island(Wilson,1991a).Thisis theleastdisturbedisland,where the forest appearsto be in goodcondition.Itis thesouthernmost islandand isseparatedfrom MarfaMagdalenaIslandby a 16 km. The shapeof theislandisround(5 km indiameter,with a maxi mumelevationof

400m)andthevegetationis fairlyopenwoodland

aroundthecoast,but theinterioristhick.However,portionsof the eastern sideof theislandhavebeenclearedinpreparationfor plantations.Inaddition,asmall detachmentof navypersonnelstays neartheircamponthatsideof theisland(Dooley,1988;Wilson,

1991a).

GENETICS.Thekaryotypeof S.graysoniconsistsof 2n=

42 and FN=78. Theautosomalcomplementincludes15pairsof

medium-to-smallmetacentricand submetacentricchromosomes and 5pairsofsmallacrocentricorsubtelocentricchromosomes.

Some ofthese

latterfivepairsmaybearsatelliteson theshortarms. The Xchromosomeis asmallacrocentricorsubtelocentric,where as the Y is asmallacrocentric(DiersingandWilson,1980).S. cuniculariussharesthediploidnumberwith S.graysoni,S..flori danus, and S.audubonii,whichsupportsthehypothesisofclose kinshipbetweentheformertwospecies(Lorenzo et al.,1993).

CONSERVATIONSTATUS.Populationsof S.graysoniare

declining(Dooley,1988).Anexpeditionto the Tres MarfasIslands in

1987did not find any S.g.graysoniin thethreeislandswhereDownloaded from https://academic.oup.com/mspecies/article/doi/10.2307/3504378/2600164 by guest on 24 October 2023

MAMMALIANSPECIES559

itoccurs(Dooley,1988),and nosignsof itsactivitywereseen.San

Juanito

Islandwas the only one inwhichmany wereobserved.

Sylvilagusgraysonihasbeendesignatedas anendangered species threatsto itssurvivalare huntingandextensivemodificationof its habitatbyclearanceof thevegetationandintroducedpigs andquotesdbs_dbs49.pdfusesText_49

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