Leenders, Twan A. A. M.

Watkins-Colwell, Gregory J.

Phyllomedusa Journal of Herpetology

English

Cadernos Espinosanos (E-Journal)

		Morphological and behavioral adaptations inBolitoglossa colonnea (Caudata, Plethodontidae) inrelation to habitat use and daily activity cycleTwan A. A. M. Leenders1 and Gregory J. Watkins-Colwell2Division of Vertebrate Zoology, Yale Peabody Museum of Natural History, 170 Whitney Avenue, P. O. Box 208118,New Haven Connecticut 06520-8118, USA. E-mails: twanleenders@scinax.com, gregory.watkins-colwell@yale.edu.		 !!"#$$%	Bolitoglossa colonnea is a member of theBolitoglossa striatula group (sensu Wake andLynch 1976) that inhabits low to intermediateelevations on the Caribbean slope of Costa Ricaand Panama, and the Golfo Dulce area insouthwestern Costa Rica and extreme westernPanama. Due to their secretive habits and thelow density in which these tropical salamandersgenerally occur, observations are rare and theirnatural history remains poorly known. Here wepresent data from field observations and abehavioral experiment that extend ourunderstanding of the biology of this tropicalsalamander.Both Dunn (1926) and Taylor (1952)reported observing specimens of B. colonnea atnight crawling on fallen logs and on lowvegetation near a small fast-flowing stream.Bruce (1997) invariably found thesesalamanders close to the forest floor, either onthe upper surfaces of broad-leaved herbaceousplants, on a pinnatifid fern, or on the verticalstem of a small plant. A single individual wasobserved crawling on leaf litter on the forestfloor. The latter author remarked upon not beingable to locate any salamanders during theKeywords: Caudata, Plethodontidae, Bolitoglossa colonnea, daily activity cycle, anti-predator behavior, color change, skin texture change.daytime, in spite of extensively raking leaf litter,and inspecting logs and arboreal bromeliads.Long-term field studies by one of us (TL)on the herpetofauna of Rara Avis RainforestReserve, Heredia Province, Costa Rica(84°02’50"W, 10°17’00" N, 550-700 melevation) led to the occasional discovery ofadult B. colonnea in the leaf litter of premontanerainforest habitat during the daytime, or perchedon top of the foliage of understory vegetationat night. The salamanders uncovered during theday were invariably curled up inside a dead leaf,often hanging upside-down. In order toinvestigate the daytime retreat preference ofthese salamanders a brief experiment wasdesigned.On the nights of March 7 and 8, 2002, twoadult individuals of B. colonnea wereencountered along a road cut through a sectionof secondary vegetation in Rara Avis, on theupper surfaces of broad-leaved plants(Melastomataceae), approximately 50 cm abovethe forest floor. Both salamanders were capturedand subsequently released into an experimentalarena during multiple observation periods whiletheir behavior was being noted.The experimental setup consisted of a100x100-cm patch of secondary forest,representative of the original habitat ofBolitoglossa colonnea, surrounded by an arearoughly 50 cm wide cleared of vegetation to		Leenders and Watkins-Colwellprevent escape. Within this study plot, thesalamanders had access to similar retreats andvegetation as in their natural habitat. Duringdaylight hours, six separate 20-minuteobservation periods were carried out in whicheach salamander was placed on a broad leaf ata height of approximately 50 cm above theforest floor and its subsequent behaviorrecorded. Observations were repeated at nightduring two 3-hour periods between 20:00 and23:00 h (Central Standard Time), after which thesalamanders were released on the site of captu-re again. Total time in captivity for each indivi-dual salamander did not exceed 24 hours.Observations on Bolitoglossa colonnea duringthe behavioral experiments confirmed previousanecdotal field observations and revealedsurprising additional natural history traits.At night, individual B. colonnea had asalmon to tan dorsal coloration with very slight,dark mottling. Coloration of the ventral and la-teral surfaces was of a lighter, cream hue (Fi-gure 1A). By daytime, this color pattern hadchanged to a mottled ruddy to dark brown withscattered, irregularly shaped dark blotches. Inaddition to this conspicuous color change, thesurface structure of the skin changed as well.The salamander’s perfectly smooth integumentat night, was roughened and marked withstriking skin folds during the day. Apart from thecharacteristic transverse occipital ridge, the skinof B. colonnea displayed a series of short, raisedlongitudinal dermal folds during daylight hours(Figure 1B).Throughout all observation periods, indivi-dual B. colonnea moved with very slow,deliberate movements in a stop-and-go fashion,often superimposing a rocking motion of thebody on their forward movement. Locomotionoccurred in the manner typical for bolitoglossinesalamanders with only one foot off the substrateat any given time (Savage 2002). Movement bythe observers triggered an immediatetermination of any forward motion in thesalamander. During times that wind moved thevegetation within the experimental setup, thesalamander would immediately increase itswalking speed to a continuous gait, resuming itsstop-and-go tempo again as soon as the windsubsided.Individual salamanders placed on anexposed section of vegetation during thedaytime occasionally reacted with an explosivetail flip that propelled the entire animal off thevegetation. The salamander would scurry intothe leaf litter and curl up inside a dead leaf.Information in literature on B. colonneamostly concerns morphological descriptions andbrief notes on microhabitat or activity at thetime of collecting, the main exception being thedescription of this species’ reproductive cycleby Bruce (1997). In this publication, Brucestates that even his limited data illustrates howlife history trends in neotropical plethodontidsdiffer from those of North American species.Sudden flipping motions of the body and/or tailthrough rapid contraction of the trunk or tailmusculature as a means of predator escape isknown from other terrestrial salamanders buthas not been reported yet for members of thegenus Bolitoglossa. Savage (2002) mentions thatbody flipping is used by some bolitoglossinesalamanders of the closely-related genusOedipina as a means of defense againstpredators, especially if the disturbance is violentor if the salamander is touched. Individual B.colonnea observed during the current study didnot display body or tail flip behavior whentouched or picked up while on the ground. Si-milar observations were made by Taylor (1952)who noted the mild disposition of thesesalamanders and their lack of response uponcapture. A more general anti-predator defensein Bolitoglossa appears to be to raise the tail,which is easily lost, and present it to a potentialpredator (e.g. Lee 2000, who reports thisbehavior for Bolitoglossa rufescens). Apart fromthe advantage of rapidly escaping a potentiallyhazardous situation, B. colonnea may use thebody flip behavior when positioned onvegetation to return quickly to its daytime retreatin the leaf litter. If surface activity in B.~~		Morphological and behavioral adaptations in the plethodontid salamander Bolitoglossa colonneaFigure 1 - The plethodontid salamander Bolitoglossa colonnea. (A) Night-time coloration (note the smooth skin); (B)B. colonnea during the day, showing the dark, mottled brown coloration and strongly ridged skin. Photographs© Twan Leenders.AB~~		Leenders and Watkins-ColwellReferencesBruce, R. C. 1997. Life history attributes of the salamanderBolitoglossa colonnea. Journal of Herpetology 31:592-594.Dunn, E. R. 1926. The Salamanders of the FamilyPlethodontidae. Northampton, Massachusetts. SmithCollege Fiftieth Anniversary Publications. 441 pp.Lee, J. C. 2000. A Field Guide to the Amphibians andReptiles of the Maya World; the lowlands of Mexico,northern Guatemala, and Belize. Ithaca. CornellUniversity Press. 402 pp.Nickerson, M. A., R. A. Sajdak and R. W. Henderson.1978. Notes on the movements of some Neotropicalsnakes (Reptilia, Serpentes). Journal of Herpetology12: 419-422.Savage, J. M. 2002. The Amphibians and Reptiles of CostaRica - a herpetofauna between two continents,between two seas. Chicago. University of ChicagoPress. 934 pp.Taylor, E. H. 1952. The salamanders and caecilians ofCosta Rica. University of Kansas Science Bulletin 34:695-791.Wake, D. B. and J. F. Lynch. 1976. The distribution,ecology, and evolutionary history of plethodontidsalamanders in tropical America. Natural HistoryMuseum of Los Angeles County, Science Bulletin 25:1-65.colonnea continues until daybreak, utilizing thistechnique in order to avoid prolonged exposureto daylight when climbing slowly down thevegetation, will effectively extend thesalamander’s surface activity period. Personalobservations (by TL) indicate that thesesalamanders are actively moving around on thevegetation as late as 1:00 h (Central StandardTime), but information on the duration ofnocturnal activity patterns in tropicalbolitoglossines is lacking.Previous field observations on Bolitoglossacolonnea and observations during this studyseem to indicate that individuals of this speciesuse curled, dead leaves for a daytime retreat.The salamander will tightly curl the tail aroundits body and adhere to the surface of the leaf,often in an upside-down position. B. colonneaappears to occur primarily in middle elevationrainforest habitat with a high annualprecipitation and no pronounced dry season.Individual curled leaves frequently fill withwater during downpours and may retain waterfor several days in closed-canopy rainforesthabitat. The upside-down position that thesesalamanders assume inside the curled leafpossibly is a strategy to avoid exposure to rainwater. The fact that these animals are hiddeninside individual leaves may explain why Bruce(1997) was unable to uncover B. colonnea byraking the leaf litter in suitable habitat.The combination of a mottled browncoloration and strongly ridged skin makesmotionless B. colonnea look strikingly similarto a dead twig. Their slow, deliberatemovements and the fact that individual B.colonnea remain motionless when potentialthreats are perceived all aid in resembling aninanimate object. The wind-induced change inlocomotion pattern of these salamanders isanother characteristic that adds to thecamouflage of this salamander. Similar behaviorhas been noted for an assembly of neotropicalvine snakes, which display a rocking motionsuperimposed on their forward movement,supposedly this oscillating motion serves tomimic a wind-blown twig (Nickerson et al.1978). Similar movement patterns are seen inmantids and Old World chameleons. Thedaytime skin texture and coloration of B.colonnea appear to complement this behavior,improving its resemblance to a small branch.AcknowledgementsWe would like to thank Chris Freimuth andSara Mooser and the Forman School RainforestProject for their help with the observations. Thisstudy was carried out under permit numbers027-ACCVC and resolution 190-96-OFAUissued by the Ministerio de Ambiente y Energía,Costa Rica.

Morphological and behavioral adaptations in Bolitoglossa colonnea (Caudata, Plethodontidae) in relation to habitat use and daily activity cycle

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