Body Condition of a Puerto Rican Anole

SHORTER COMMUNICATIONS 489 Journal Vol. No. 489-491,2000 of Herpetology, 34, 3, pp. study site and details of its natural are in Rea- Copyright2000 Societyfor the Study of Amphibiansand Reptiles history gan and Wade (1996). Anolis gundlachi lizards are common at the site, perching on trees and large logs within of Condition of a Puerto Rican reach human observers. Anoles were captured Body along trails within a 36 ha plot with a slip noose at- Anole, Anolis gundlachi:Effect of a tached to a pole or by hand during five periods: July Malaria Parasite and Weather Variation 1996, July 1997, January 1998, May 1998, and March 1999. Only males with an intact tail were used for this Jos. J. SCHALLAND ANJA R. PEARSON,Department of study because the mass of females would vary with Biology, University of Vermont, Burlington, Vermont reproductive condition, and animals with broken or 05405, USA. E-mail: [email protected] regenerated tails would have a body mass atypical for their SVL. Each lizard was maintained in a mesh sack until Over 70 of malaria Plasmodium species parasites, when a blood smear was made from a lizards as their vertebrate hosts evening drop spp., exploit through- of blood extracted from a SVL out the warmer of the world clipped toe, measured, regions (Schall, 1996). and mass taken with a Pesola cali- Detailed information on the of infection is body spring scale impact brated an balance. known for a few Plasmodium-lizard associations: against electronic The next morn- only all lizards were released at their of P mexicanum and Sceloporus occidentalis in California, ing, points capture. P and P in in west In the lab, the smears were fixed in absolute methanol agamae giganteum Agama agama and stained with Giemsa at 7.0 for 50 min. These Africa, and P azurophilumand Anolis gingivinus on St. pH Martin. Those data indicated that infection can reduce stained smears were scanned at 1000x for 6 min, al- success for both male and female lizards lowing examination of approximately 10,000 erythro- reproductive Both of were combined to score (Schall, 1983, 1990), the host's behavior (Schall cytes. species parasite change animals as infected or noninfected. This was and Sarni, 1987), (Schall, 1990; accept- disrupt its*physiology able because the relative lizards infect- and Schall, 1995), reduce condition prevalence (% Dunlap body of the two remained constant over the (mass vs. length) (Dunlap and Mathies, 1993), and ed) species et al., alter the competitive ability of entire popu- study period (Schall 2000a). perhaps We extracted rainfall and data from re- lations of lizards (Schall, 1992). These results are strik- temperature cords maintained the field station staff. con- ing, but should not imply that malaria parasites are by Body dition was determined from the between always important for the biology of lizard hosts. More relationship SVL and mass. A curve was fit to the data likely, additional studies will reveal variation in the body using the which uses a series pathologies induced by these parasites. JMP package (SAS Institute) of over 50 of the Plasmodium parasites commonly infect anoles third-degree polynomials segments data set. In this results in a curve that runs throughout the Caribbean islands (Staats and Schall, essence, the smoothed mean mass for each SVL. Re- 1996), but the impact of infection is poorly known (but through were see Schall, 1992). We studied malaria in a common siduals then calculated for each lizard; positive residuals indicated an animal heavier than anole, Anolis gundlachi, at the El Verde Field Station, a average, and residuals indicated an animal with re- site in the Luquillo Experimental Forest in eastern negative duce mass. animals could have a Puerto Rico (18?19'N, 65?45'W). Although five species Heavier greater mass of Anolis are abundant at El Verde, only individuals of because they contained more fat, larger muscle tissue, or more No matter P. gundlachi are frequently parasitized. Approximately perhaps were simply hydrated. 30% are infected with two species of malaria para- what the reason, we assumed heavier animals were sites, P floridense and P. azurophilum (Schall and Vogt, healthier. This method has been widely used as a mea- 1993). We examined the mass of the lizards relative to sure of lizard health (Dunlap and Mathies, 1993; Van snout-to-vent length (SVL) in order to determine the Slys, 1998; Schall et al., 2000b). effect of malaria on this indicator of overall health of Body Condition by Infection and WeatherConditions.- the animals. A total of 940 male A. gundlachi anoles were sampled. Attempts to measure the virulence of a parasite are Although mean body condition seemed to follow the often confounded by the frequently cryptic nature of predicted trend, with positive residuals for noninfect- any infection-induced costs to the host. That is, such ed lizards and generally negative residuals for infect- costs may be patent only when the host is stressed, ed animals (Table 1), ANOVA revealed no effect of such as during its reproductive season or when the infection (residuals for each sample were normally environment deteriorates. Long-term studies on the distributed). There was no interaction between sample virulence of parasites may be required to reveal the and infection (F = 0.03; df = 4, 929; P = 0.998), nor often cryptic impact of parasites on host populations a significant effect of infection (F = 2.69; df = 1, 929; (Hudson et al., 1998). We therefore collected multiple P = 0.101). However, body condition differed signifi- samples of anoles at El Verde over a three-year period. cantly among samples (F = 6.36; df = 4, 929; P < During that time, the site was disturbed by hurricanes 0.0001). Because the interaction term was not signifi- and severe droughts. We sought to determine if body cant, we excluded that term from another analysis to condition was affected by weather, and if the conse- search for a possible effect of infection; again none = quences of infection were more severe after the site was detected (F = 3.24; df 1, 929; P = 0.07). A final suffered reduced rain or physical disruption by a analysis scored lizards as healthy (residual > 0) or tropical storm. Malaria may only cause harm to the unhealthy (residual < 0), and cast the data into a 2 X lizards occasionally, but still could have a substantial 2 contingency table; no effect of infection was detected influence on the population biology of A. gundlachi. (X2= 1.94;P = 0.16). Study System and Methods.-A description of the Variation in body condition could not be accounted 490 SHORTER COMMUNICATIONS TABLE 1. Mean residual from curve fitted for body mass versus SVL for infected and noninfected Anolis gundlachi collected during five sampling periods. .1- Dates of samples, standard error of mean, and sample >) 1 2261 15/98 sizes are 104 given. o.05- 96 oQ - 0 147/96 146 Sample Noninfected Infected oi - July 1996 0.042 (0.103, 63) -0.023 (0.147, 35) >-.05- July 1997 0.021 (0.050, 221) -0.045 (0.072, 152) January 1998 0.039 (0.051, 166) -0.105 (0.102, 61) co . 376 May 1998 0.045 (0.086, 79) -0.053 (0.113, 67) X--.15 - ' March 1999 0.049 (0.079, 69) 0.065 (0.119, 27) *') 7/97 Overall 0.045 -0.077 -.2 . (0.031, 598) (0.048, 342) 1000 1100 1200 1300 1400 1500 1600 1700 Rainfall(mm) in Previous 5 Months FIG. 1. Relation for by total cumulative rainfall 1-3 mo before the date between body condition (residual of mass vs. and of the sample (r = -0.256 to 0.711, P > 0.05), nor SVL) cumulative rainfall during the five mean low temperature for those periods of time (r = previous months for anoles (Anolis gundlachi) in -0.644 to -0.021; P > 0.05). However, total rainfall eastern Puerto Rico (sample sizes are given along with mean residual indicated summed over the previous 4-6 mo and mean low tem- by dots and one standard error r = perature for that period were significantly correlated by bars; 0.943). with body condition (Fig. 1, all r = 0.837-0.943 for = rainfall, and all r 0.90 for temperature, P < 0.05). Thus, body condition was highest after several months of warm, wet weather. drops. The driest period occurred during the two Discussion.-Researchers long assumed that para- months just prior to the March 1999 sample, but body sites have only a minor influence on the biology of condition was second highest among the five samples. host individuals and populations. Parasites were Hurricane Georges struck the site in December 1998, thought to be generally rather benign, with little neg- stripping most of the canopy vegetation away, but also ative impact on behavior, feeding, reproduction, depositing torrential rains that may have had a posi- growth, or other important aspects of the hosts daily tive effect on the food supply by March. This result activities. Such views have undergone substantial re- complements previous findings that availability of wa- vision in the past two decades, and parasites are now ter for drinking can increase growth rate of lizards viewed as major players in the ecology and evolution (Andrews, 1982). The correlation between rainfall and of their hosts (Dobson and Hudson, 1995; Gulland, temperature with body condition suggests that the 1995). This revised outlook has unfortunately not been mass vs. SVL measure provides a biologically mean- accompanied by a substantial increase in knowledge ingful insight into the anoles' health, at least those of the affects of parasites on their hosts under natural aspects of the lizards' activities that would increase conditions and long-term data are particularly lack- relative body mass.

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