Interpopulation Differences In Tolerance To Creosote Bush Resin In Desert Woodrats - Neotoma Lepida - Statistical Data Included

ANTONIO M MANGIONE [1]

M DENISE DEARING [2]

Abstract. Plant secondary metabolites (PSMs) can affect survival, reproduction, and distribution of herbivores. Individuals with a high capacity to tolerate PSM will experience fewer and smaller adverse results than less tolerant individuals. Theoretically, the capacity to tolerate PSM can be acquired during disclosure modulated during adulthood, or genetically fixed. We studied tolerance to phenolic resin from creosote bush (Larrea tridentata) in sum of two units populations of desert woodrats as a first pace in understanding phenotypic habituation and genetic adaptation of this species to creosote resin. single population was from Mojave desolate habitat where woodrats eat creosote bush, and the other from the Great Basin waste where creosote bush is not not away and woodrats consume mainly juniper (Juniperus osteosperma). For [greater than] 1 mo in the laboratory, woodrats from the two populations were fed rabbit chow with increasing amounts of phenolic resin extracted from creosote bush until they missing body mass or show ed any sign of sickness. Woodrats from the Mojave population maintained material substance mass at higher concentrations of resin and remained in the experiment longer There were no differences between populations in nutrition intake across all resin levels; however, maximum resin intake was 25% higher for the Mojave population. diet intake decreased with increasing resin intake. Glucuronic acid excretion in urine, individual indicator of detoxification capacity, did not differ between populations. Water consumption increased with increased horizontals of creosote resin in the diet in woodrats from the pair populations. The results are consistent with the idea of differential tolerance to creosote bush phenolic resin in wild woodrat populations. Woodrats appear to be a promising natural a whole to study the developmental or genetic factors underlying vertebrate adaptation to plant secondary metabolites.

lock opener words: creosote bush; desert woodrats; detoxification; glucuronic acid; Great Basin; Mojave Desert; Larrea tridentata; Neotoma lepida; phenolic resin; plant secondary metabolites; tolerance.

INTRODUCTION

The ability to cope with or tolerate PSM (plant secondary metabolites) has abysmal implications for animal population ecology by the agency of influencing diet selection (Freeland and Janzen 1974 Belovsky and Schmitz 1991) mortality, and hence population dynamics (Haukioja 1980 Bryant et al. 1991) Tolerance to a PSM can be measured as the highest intake of the mingle (as mass per unit time or as percentage of diet) that permits survival, ability to maintain material substance mass, or normal growth. In insects tolerance to PSM differs between populations within species (Fox and Morrow 1981 Futuyma and Peterson 1985 Ayres and Scriber 1994) Intraspecific tolerance to secondary mingles has not been investigated in mammals, and the forsaken woodrat (Neotoma lepida) is a advantageous species to study potential intraspecific differences in tolerance to PSM Woodrats of this species are widely distributed, in all North American wastes except the Chihuahuan. Neotoma lepida be met withs in many habitat types, i.e., creosote bush, pinyon-juniper woodland, chaparral, oak woodland, and coastal clean (Cameron and Rainey 1972). Populations in these habitats have diets dominated by the agency of different plant species with different secondary metabolite composition. Opuntia spp are rich in oxalates (Shirley and Schmidt-Nielsen 1967 Justice 1985) Juniper spp are rich in terpene (Schwartz et al. 1980 Adams et al. 1981) and Larrea tridentata (creosote bush) is rich in phenolics. Leaves of creosote bush contain 10-25% free from moisture mass of a phenolic resin. The resin is compos of 40% dried mass of NDGA (nordihydroguaiaretic acid) and the remainder of the resin is a mixed mixture of partially o-methylated flavones and flavonols (Mabry et al. 1977 Rhoades and Cates 1976)

There are hardly any species of animals that fe upon creosote bush (Meyer and Karasov 1991) Creosote bush phenolic resin is known to prevent feeding by arthropods and to compound with protein in vitro (Rhoades and Cates 1976) Laboratory rats f NDGA at 05 1 or 3% of aliment dry mass, produced cysts in the kidney and vacuolation of kidney tubular epithelium (Grice et at. 1968 Goodman et al. 1970) Animals that naturally fe upon creosote bush are very selective regarding the age and part of the plant on which they feed. For example, jackrabbits (Lepus californicus) and N lepida bring forward the mature over the young leaves presumably because phenolic resin horizontals are lower in the mature individuals (Hayden 1966, Meyer and Karasov 1989 Ernest 1994)

We focused our investigation of differential tolerance to PSM upon two particular populations of waste woodrats: (1) individuals from three sites in the Mojave desolate (hereafter called Mojave woodrats) and (2) individuals from sum of two units sites in the Great Basin untilled (hereafter called Great Basin woodrats). The composition of plant species in the couple habitats and consequently the diets of these sum of two units populations of desert woodrats differed greatly between the sum of two units habitats. Mojave woodrats eat creosote bush, whereas Great Basin woodrats rely for the greatest part on juniper (Juniperus osteosperma) (A. M Mangione, personal observation). We measured tolerance of woodrats as defined through maintenance of mass balance when ingesting creosote bush resin and/or the lack of any signs of adverse effects