Allozyme Variation in Mojave Populations of the Desert Tortoise, Gopherus agassizi

Rainboth, Walter J.; Buth, Donald G.; Turner, Frederick

doi:10.2307/1445612

Cited by 20 publications

(16 citation statements)

References 18 publications

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“…I homogenized six eggs (32.9 ± 5.1 g) from five desert tortoises (Rainboth et al 1989, Meienberger et al 1993) in order to measure their lipid content (2.04 ± 0.52 g or 6.13% of fresh mass; see Henen 1991) and energy content (egg E tot : 142.4 ± 41.2 kJ/g, N = 6) by bomb calorimetry. Most of the lipids that I saw during carcass analyses appeared to be in the follicles, so the egg lipids and body lipids should have similar energy densities.…”

Section: Methodsmentioning

confidence: 99%

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SEASONAL AND ANNUAL ENERGY BUDGETS OF FEMALE DESERT TORTOISES (GOPHERUS AGASSIZII)

Henen

1997

Ecology

143

130

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How do female desert tortoises (Gopherus agassizii) reproduce every year despite variability in winter rainfall and food availability? To answer this question, I measured energy budgets of individual female desert tortoises from July 1987 to July 1989. Females produced eggs in years with low levels of winter annual plants by relaxing their control of energy and water homeostasis. They tolerated large deficits and surpluses in their body dry‐matter composition (both nonlipid and lipid) on a seasonal, annual, and longer time scale. They could increase body energy content (lipid and nonlipid energy) before winter and use this reserve (especially nonlipid energy) the following spring to produce eggs. Females used high‐protein foods and rainwater, when available, to achieve energy surpluses that helped them survive periods of low resource availability (e.g., during hibernation and droughts). Adjusting seasonal and annual field metabolic rates (FMR) and food requirements to levels of food availability, they still managed to produce eggs, even in a drought year. Egg production in 1988 (mean ± 1 sd: 3.56 ± 1.94 eggs, N = 9) did not differ from that in 1989 (3.00 ± 2.69 eggs, N = 9); both were lower than during 1983–1987 (6.75 ± 3.05 eggs, N = 100). Energy per se did not limit egg production in 1988 and 1989, but the availability of nonlipid energy (probably protein) limited egg production in 1988 and was limiting in spring 1989. Yet, water was the primary resource limiting egg production in 1989. Females forgoing egg production in 1989 accumulated body nonlipid energy and lost less total body water than did females producing eggs. Females that produced eggs in 1989 forfeited body nonlipid energy. In 1988 and 1989, the paucity of new annual plants in spring contributed to a lower egg production. The amount of annuals that germinate in summer can affect egg production, because females stored nonlipid energy during summer 1988 when eating these annuals, and allocated this energy to eggs in the following spring (1989). Tortoises stored lipids during summer when consuming dry annuals. These lipids are critical for surviving the winter, but females forfeited body water and nonlipid dry matter to digest the dry annuals. Reproductive effort (RE) was higher during the drought year (July 1988–July 1989: RE = 26.1%) than during the wetter year (July 1987–July 1988: RE = 13.0%) because tortoises reduced FMR by 70–90% in 1989. Compared to two other chelonians, RE of desert tortoises was consistent with the K‐selected trend of lower RE for larger, long‐lived, and late‐maturing species. Forfeiting body condition to produce only a few eggs, even under a great environmental stress, was consistent with a life history strategy called bet hedging.

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Section: Methodsmentioning

confidence: 99%

“…I homogenized six eggs (32.9 Ϯ 5.1 g) from five desert tortoises (Rainboth et al 1989, Meienberger et al 1993 in order to measure their lipid content (2.04 Ϯ 0.52 g or 6.13% of fresh mass; see Henen 1991) and FEMALE TORTOISE ENERGETICS FIG. 1.…”

Section: Egg Investmentsmentioning

confidence: 99%

SEASONAL AND ANNUAL ENERGY BUDGETS OF FEMALE DESERT TORTOISES (GOPHERUS AGASSIZII)

Henen

1997

Ecology

143

130

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“…The original recovery units reflected the best available scientific evidence at the time of its listing as a threatened species (USFWS 1994). The units were delineated to capture and preserve the considerable diversity in morphology (Weinstein and Berry 1987), ecology (Germano et al 1994), and genetics (Lamb et al 1989;Rainboth et al 1989).…”

Section: Introductionmentioning

confidence: 99%

Defining population structure for the Mojave desert tortoise

Hagerty

Tracy

2010

Conserv Genet

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We used highly variable microsatellite markers to identify population structure, movement, and biological boundaries for populations of the desert tortoise, Gopherus agassizii, in the Mojave and Colorado Deserts of the southwestern United States. The Mojave desert tortoise (listed as ''threatened'' by the U.S. Fish and Wildlife Service) has a large geographic range, long generation time, low population densities, and little above-ground activity. Additionally, the dispersal patterns of individual tortoises are virtually unknown, making indirect methods to assess movement among populations valuable. Using Bayesian assignment tests, we detected hierarchical structuring within the Mojave desert tortoise. Three basal groups were identified, and these corresponded to the mitochondrial DNA haplotypes reported in 1989. Additional population structure was evident within each basal unit, and this structure corresponds with major geographic barriers. Our analyses suggest that gene flow among populations was historically high because levels of population differentiation were low across the range. Geographic distance explained a large proportion of variation in genetic distance (68%), which pinpoints that dispersal is limited only on a regional scale. In light of these new analyses of the genetic population structure of the Mojave desert tortoise, we make new recommendations for the number and locations of recovery units for conservation of this species.

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“…Many population genetics and phylogeographic studies of chelonians have documented geographic structure in genetic diversity and assessed implications for conservation (e.g., Walker and Avise 1998;Fritz et al 2005). Studies of G. agassizii in the Mojave Desert revealed a fine-scale geographic population structure that was shaped by the Colorado River and the basin and range (Lamb et al 1989;Rainboth et al 1989;Britten et al 1997). Gopherus polyphemus also displays genetic assemblages that were historically isolated by the Apalachicola River basin (Osentoski and Lamb 1995).…”

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confidence: 99%

Genetic Variation and Population Structure of the Texas Tortoise, Gopherus berlandieri (Testudinidae), with Implications for Conservation

Fujii

Forstner

2010

Chelonian Conservation and Biology

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Allozyme Variation in Mojave Populations of the Desert Tortoise, Gopherus agassizi

Cited by 20 publications

References 18 publications

SEASONAL AND ANNUAL ENERGY BUDGETS OF FEMALE DESERT TORTOISES (GOPHERUS AGASSIZII)

SEASONAL AND ANNUAL ENERGY BUDGETS OF FEMALE DESERT TORTOISES (GOPHERUS AGASSIZII)

Defining population structure for the Mojave desert tortoise

Genetic Variation and Population Structure of the Texas Tortoise, Gopherus berlandieri (Testudinidae), with Implications for Conservation

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