Effects of age, density, and seasonality on molt pattern in the mammal genus (Peromyscus)

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1 University of New Hmpshire University of New Hmpshire Scholrs' Repository Honors Theses nd Cpstones Student Scholrship Spring 2015 Effects of ge, density, nd sesonlity on molt pttern in the mmml genus (Peromyscus) Rebecc Ctherine Grves University of New Hmpshire - Min Cmpus, rcm36@wildcts.unh.edu Follow this nd dditionl works t: Prt of the Zoology Commons Recommended Cittion Grves, Rebecc Ctherine, "Effects of ge, density, nd sesonlity on molt pttern in the mmml genus (Peromyscus)" (2015). Honors Theses nd Cpstones This Senior Honors Thesis is brought to you for free nd open ccess by the Student Scholrship t University of New Hmpshire Scholrs' Repository. It hs been ccepted for inclusion in Honors Theses nd Cpstones by n uthorized dministrtor of University of New Hmpshire Scholrs' Repository. For more informtion, plese contct nicole.hentz@unh.edu.

2 Effects of ge, density, nd sesonlity on molt pttern in the mmml genus (Peromyscus) Abstrct Molting, or replcement of pelge (hir) in mmmls, occurs during ontogeny s individuls trnsition from juveniles to dults. Environmentl fctors cn cuse vrition in molt in mny species for thermoregultory nd cmouflge purposes. Within nd mong yers molt cn vry by time nd ge or by reproductive sttus. Pst studies hve found differences in molt pttern nd timing depending upon ge, nd between cptive rered nd wild cught individuls. There hs been little investigtion into the molting chrcteristics of Peromyscus leucopus nd P. mnicultus, specificlly in comprison to dults nd juveniles. I used molt observed from museum specimens collected t Brtlett Experimentl Forest over three-yer period to determine if there re evident molt ptterns in both Peromyscus spp. Specificlly, I looked for differences in percent molt nd number of individuls molting s result of sesonlity nd ge. Molts were digitized in Photoshop nd pttern nd symmetry were nlyzed in ImgeJ. In both species, individuls show sesonl trend in molt timing nd symmetry. This my reflect differences in resource vilbility nd energy expenditure mong yers. Keywords Peromyscus leucopus, Peromyscus mnicultus, percent molt, symmerty, ontogenetic, sesonlity Subject Ctegories Zoology This senior honors thesis is vilble t University of New Hmpshire Scholrs' Repository:

3 Effects of ge, density, nd sesonlity on molt pttern in the mmml genus (Peromyscus) Rebecc Grves Deprtment of Biologicl Sciences Honors Thesis, 2015 Dr. Rebecc Rowe (Fculty Advisor) Deprtment of Nturl Resources nd the Environment

4 Abstrct Molting, or replcement of pelge (hir) in mmmls, occurs during ontogeny s individuls trnsition from juveniles to dults. Environmentl fctors cn cuse vrition in molt in mny species for thermoregultory nd cmouflge purposes. Within nd mong yers molt cn vry by time nd ge or by reproductive sttus. Pst studies hve found differences in molt pttern nd timing depending upon ge, nd between cptive rered nd wild cught individuls. There hs been little investigtion into the molting chrcteristics of Peromyscus leucopus nd P. mnicultus, specificlly in comprison to dults nd juveniles. I used molt observed from museum specimens collected t Brtlett Experimentl Forest over three- yer period to determine if there re evident molt ptterns in both Peromyscus spp. Specificlly, I looked for differences in percent molt nd number of individuls molting s result of sesonlity nd ge. Molts were digitized in Photoshop nd pttern nd symmetry were nlyzed in ImgeJ. In both species, individuls show sesonl trend in molt timing nd symmetry. This my reflect differences in resource vilbility nd energy expenditure mong yers. Introduction Mny species hve the cpcity to molt. Molting is essentilly the shedding of old or worn down exoskeleton, pelge, or skin tht will be replced by new growth. In mmmls, molting of pelge (or hir nd fur) cn occur for different resons including ontogenetic, thermoregultion, or cmouflge. Ontogenetic molt nd color chnge, s juvenile individuls trnsition to dulthood is common to mny mmmls. Mice in the genus Peromyscus undergo n ontogenetic molt chrcterized by juveniles with gry pelge tht molt to twny or cinnmon red pelge s dults (Collins 1923, Gottschng 1956, Brown 1963). Molting tht occurs for thermoregultion is centrlized round the thickness nd length of hir (Tbcru et l. 2014). During the winter months, the density nd thickness of hir is greter to retin het nd mintin functionl body temperture. In the summer seson, pelge is generlly thinner nd less dense so tht individuls do not overhet. In ddition to ontogenetic nd thermoregultory molts, predtor voidnce my trigger molting which results in cmouflge. For exmple, Ermines (Mustel ermine) nd Snowshoe hres (Lepus mericnus) will trnsition from white pelge in the winter, to brown pelge in the summer. Molting cn be ffected by both environmentl nd physiologicl fctors. Specificlly, these fctors cn ffect the occurrence nd timing of molt s well s the mount, consistency, nd sptil ptterning of molt. Age, energy expenditure, nd resource vilbility re the key fctors tht ffect molt. As previously mentioned, ontogenetic molt with ge (juvenile to dult) is common in smll mmmls. Not only does this molt often include chnge in pelge color but; pst studies hve found tht there is consistent nd relible pttern in this molt (Gottschng, 1956). Energy expenditure lso significntly ffects molt. Molting is n energeticlly expensive dpttion nd therefore it is not believed to occur t the sme time s other energeticlly expensive life processes such s reproduction (Tbcru et l. 2014). Similrly, molting will require relible nd dequte resources to sustin n individul during this process. When resources re limited, n

5 individul my not molt or the molt will consist of ptchy nd inconsistent pelge regrowth (Tbcru et l nd Sre et l. 2005). In this study, the molts of both the white- footed mouse (Peromsycus leucopus) nd the deer mouse (Peromsycus mnicultus) re investigted. These species re generlists in terms of diet nd hbitt nd therefore re bundnt nd hve wide distribution. Permosyscus leucopus cn be found from Cnd to Mexico nd s fr west in the United Sttes s Arizon. Peromyscus mnicultus cn be found from Cnd to Mexico s well nd re found in every stte in the United Sttes except Florid (Hll, 1977). Pst studies on molt in Peromyscus hve focused on cptive rised individuls nd hve hd reltively smll smple sizes. These studies hve lso focused specificlly on dults or juveniles or mle individuls (e.g., Gottschng, 1956 nd Tbcru et l. 2014). Here, we use wild cught individuls nd lrge smple size encompssing mles, femles, juveniles nd dults. We focus on quntifying the sptil pttern of molting individuls. The percent molt, or the re of the individul molting, is mesured nd the symmetry of dorsl nd ventrl molts of n individul is correlted. The results from these nlyses cn be good indictor tht physiologicl nd environmentl fctors my be ffecting the molting of pelge. In ddition to using these nlyses to determine if there is evident symmetry in the molts of both Peromsycus species, we investigte if the number of individuls molting in popultion vries over the summer seson s well s if the percent of n individul molting vries over the summer seson. We test whether percent molt nd symmetry of molt re ffected by ge nd reproductive sttus. Methods The mice were collected from nine sites t the Brtlett Experimentl Forest in the White Mountins of New Hmpshire in the summers of 2012, 2013 nd Both P. leucopus (n= 240) nd P. mnicultus (n=164) hd lrge smple sizes. The individuls were given to us courtesy of long- term monitoring progrm conducted by the U.S. Forest Service. The individuls were then prepred s museum specimens. During this process, stndrd externl mesurements, weight, nd reproductive condition were noted for ech individul. The ge of ech individul ws determined by weight. For P. leucopus, lrger species, individuls tht weighed 19.0 grms or more were considered dults. For P. mnicultus, individuls tht weighed greter thn 16.0 grms were considered dults in this study. Reproductive sttus ws determined for both mles nd femles. Reproductively ctive mles were those whose testes mss ws 7.0 grms or greter. Reproductively ctive femles were those individuls tht showed evidence of lcttion, or hd embryos present during preprtion. Preprtion of study skins provides opportunity to record the pigment pooled in the hir follicle tht cn be seen from the underside of the skin. This pigment is n indictor of the molting tht is occurring in the individul. The pigment ws drwn onto molt sheets for the dorsl, ventrl nd lterl sides of ech individul. The molt sheets were then scnned nd digitized in Photoshop. ImgeJ ws then used to quntify the percent molt of the dorsl nd ventrl sides of ech individul by mesuring the pixels of the digitized molt drwings. The totl percent molt of the individul ws clculted by dding the percentges of the dorsl nd ventrl molts. ImgeJ ws lso used to quntify the symmetry of dorsl nd

6 ventrl molt drwings by overlying the left nd right sides of designted molt nd clculting the correltion between the imges. For ech yer (2012, 2013, nd 2014) the number of molting dults nd juveniles in popultion were nlyzed over the summer months of July, August, nd September. T- tests were used to test for significnce between juveniles nd dults in the designted summer months for verge dorsl symmetry, percent molt, nd reproductive sttus with p- vlue of 0.05 being the indictor of significnt difference or not. Smple numbers of individuls from both Peromyscus species were combined during ssessment of percent of individuls molting, verge dorsl symmetry, verge percent molt, nd reproductive sttus. Dt from 2012, 2013, nd 2014 ws combined to ssess verge dorsl symmetry, verge percent molt, nd reproductive sttus, but not percent of individuls molting. Results Timing of molt vried mong juveniles nd dults. For 2014, juveniles hve higher number of molting individuls in the erly summer months (July nd erly August) while in lte August nd September the number of molting individuls decreses (Figure 1). There is n opposite trend in the dults s the number of molting individuls is low in erly in the seson nd increses in lte August nd September (Figure 1). The verge dorsl symmetry of the molts of juveniles nd dults ws ssessed over July, August, nd September. There is significnt difference between the dorsl symmetry of juveniles nd dults in July (p= ) but not in August (p= 0.439) nd September (p=0.687) (Figure 2). There is grdul decrese in dorsl symmetry over the three months for juveniles but grdul increse in dorsl symmetry for dults. The verge percent molt, or re of n individul molting over July, August, nd September is shown in Figure 3. In July, there is significnt difference between re of juveniles molting nd re of dults molting (p= ). In both August (p= 0.584) nd September (p=0.871) there is not significnt difference between re of molt in juveniles nd dults. Effect of reproductive sttus on molt ws tested for both mles nd femles. Averge percent molt of n individul versus reproductive sttus (non- breeding nd breeding femles nd mles) did not differ between non- breeding individuls nd breeding individuls for mles (p= 0.463) or femles (p= 0.825). It is worth noting tht there is smll smple size (n=7) of breeding femles; however, mles hve lrge smple size for both breeding nd non- breeding individuls nd demonstrte similr results.

7 Figure 1 Grph of percent of individuls molting in popultion over July, August, nd September in the yer Number of juveniles molting decreses over the summer. Number of dults molting increses over the summer.

8 Averge Dorsl Symmetry b July August September Time Juvenile Adult Figure 2 This grph shows the verge dorsl symmetry (correltion coefficient) of the molts of juveniles nd dults over three- month period for yers combined. Trends in dorsl symmetry cn be seen in both dults nd juveniles. The dt from 2012, 2013 nd 2014 ws combined to ssess verge dorsl symmetry. Different letters bove the brs indicte significnt difference (p < 0.05) between the juvenile nd the dult vlues per month. The smple size of ech group is lso given in the bottom of ech br.

9 Averge Percent Molt b July August September Time Juvenile Adult Figure 3 Grph of the verge percent molt of both juvenile nd dult Peromyscus over three- month period cross smpling yers. Molting trends cn be seen in both juveniles nd dults. The dt from 2012, 2013 nd 2014 ws combined to ssess verge percent molt. Different letters bove the brs indicte significnt difference (p < 0.05) between the juvenile nd the dult vlues within month. Smple sizes re given in the bottom of ech br.

10 Averge Percent Molt Non- breeding Femle Breeding Femle Non- breeding Mle Breeding Mle Reproductive Sttus Figure 4 The verge percent molt of n individul in regrds to sex nd reproductive sttus. No significnt differences were detected between sex nd reproductive sttus in terms of percent molt. The dt from 2012, 2013 nd 2014 ws combined to ssess reproductive sttus. Discussion The process of molting is ffected by mny fctors, both environmentl nd physiologicl. This study focused on reproductive sttus, ge, nd sesonlity. In the erly seson of July, the increse in juvenile percent molt nd verge dorsl symmetry re most likely function of ontogenetic development. The pek- breeding seson for Peromyscus is in lte My nd erly June. Juveniles tend to retin their gry pelge for bout 40 dys before they strt their trnsitionl dulthood molt (Gottschng, 1956). July would correspond with the timing of this trnsition nd could explin why there is greter percent of individuls molting, greter verge percent of the re of n individul molting, nd greter verge dorsl symmetry in juveniles. Averge dult percent molt nd verge dorsl symmetry re lower in the month of July compred to juveniles. This could be becuse of two resons tht re distinguishble between mles nd femles. These dults will hve just ended their pek- breeding seson. For mles, the physiologicl stress of trying to cquire mtes nd breed cn often vry the time these individuls spend forging nd cn limit their resource intke, which cn led to less, more inconsistent molt (Tbcru et l nd Sre et l. 2005). On the other hnd, reproduction is very

11 energeticlly expensive for femles tht must not only crry their young prior to birth, but must provide for them fter birth in the form of lcttion, nother physiologiclly expensive process (Tbcru et l. 2014). Without proper energy expenditure dedicted to molt these individuls would most likely hve inconsistent nd limited molt s well. During August nd September, the increse in number of individuls molting nd the similrity between juvenile nd dult molt could be explined by sesonlity nd for juveniles, timing of birth. At this point, the summer seson is ending nd the colder winter seson is pproching. Adults re now strting to molt nd trnsition into their winter pelge tht is thicker for thermoregultion purposes (Tbcru et l nd Sre et l. 2005). This sesonl trnsition molt would cuse the mount of dults tht re molting to increse nd would lso increse the verge percent or re of the individul molting nd the verge dorsl symmetry of the molt. While lte My through erly June is known to be the pek- breeding seson for Peromsycus, lter breeding period cn occur mid- summer. These lter born individuls re just now undergoing their ontogenetic molt; which could explin the similrity in symmetry nd percent molt of juveniles to dults.. Pst studies hve stted tht molt will not occur during times of other energeticlly expensive life processes such s reproduction (Tbcru et l nd Sre et l. 2005). However, my results suggest breeding does not influence molt in both femle nd mle individuls of P. leucopus nd P. mnicultus. For femles, smll smple size my hve contributed to the non- significnt difference in re of percent molt between breeding nd non- breeding individuls. Although we did hve lrger smple size of breeding mles, we lso detected no significnt difference between the percent molt of breeding nd non- breeding mles. In ddition, these individuls were collected during the lter/summer breeding period (July nd erly August) nd not the pek- breeding seson (lte My- erly June), which could hve skewed the results in terms of percent molt in breeding individuls. Our results cn lso be explined by requisite winter molt. Whether the individuls we collected were breeding in the lter seson or not, they must begin their sesonl trnsition to winter pelge in order to survive the winter months. This would lso explin the similrity in percent molt of breeding nd non- breeding individuls. Molting of pelge is n extremely vrible process. As previously mentioned, there re mny fctors tht cn ffect molt. The verge dorsl symmetry nd percent molt of the studied individuls indicte tht both environmentl nd physiologicl fctors do hve implictions on molt in terms of sesonl trnsition nd ontogenetic development. In the future it would be interesting to ttin individuls from the pek- breeding seson nd determine if in fct individuls truly restrict their molt during such n energeticlly expensive time. In order to get more ccurte timing of vrition in molt between juveniles nd dults, ging individuls by tooth wre cn give more precise understnding of trends in molt over time. In ddition there is potentil for molt to be used to better understnd diet. Stble isotope nlysis on hir provides n integrted signl of n individul s diet spnning from few weeks to yer. Smpling hir following known molting episodes my help isolte the contribution of food items to diet during discrete time periods. Compring molt to isotopic nlysis of hir cn crete ides bout trophic reltionships.

12 Acknowledgements A very big thnks is owed to PhD student Ryn Stephens. Thnks to the U.S Forest Service monitoring progrm nd to Mriko Ymski nd Chris Costello for providing us with the cptured individuls nd ssocited dt. Also thnks to Krrh Kwsnik for technicl ssistnce nd lb technicins: Andrew Uccello, Tyler Remick, Chris Burke, nd Mriss Cyr. Literture Cited Brown, L. N Mturtionl molts nd sesonl molts in Peromyscus boylii. Americn Midlnd Nturlist 70: Collins, H.H Studies of the pelge phses nd of the nture of colour vrition in mice of the genus Peromyscus. Journl of Experimentl Zoology 38: Gottschng, J "Juvenile Molt in Peromyscus Leucopus Noveborcensis." Journl of Mmmlogy 37.4: Hll, R. The Mmmls of North Americ, Volume 1. Ann- Arbor: Wiley- Interscience, Sre, D., J. Millr, nd F. Longstffe Moulting ptterns in Clethrionomys gpperi. Act Theriologic 50.4: Tbcru, C., J. Millr, nd F. Longstffe "Sesonl Moulting in Deer Mice (Peromyscus Mnicultus) in the Rocky Mountins, Albert." The Cndin Field- Nturlist 125.2: