Not putting all their eggs in one basket: bet-hedging despite extraordinary annual reproductive output of desert tortoises JEFFREY E. LOVICH 1 *, JOSHUA R. ENNEN 1,2 , CHARLES B. YACKULIC 1 , KATHIE MEYER-WILKINS 3 , MICKEY AGHA 1,4 , CALEB LOUGHRAN 1,5 , CURTIS BJURLIN 6 , MEAGHAN AUSTIN 7 and SHEILA MADRAK 8 1 U.S. Geological Survey, Southwest Biological Science Center, 2255 N. Gemini Dr. Flagstaff, AZ 86001, USA 2 Tennessee Aquarium Conservation Institute, 201 Chestnut St., Chattanooga, TN 37402, USA 3 19233 Stratford Way, Apple Valley, CA 92308, USA 4 Department of Forestry, University of Kentucky, Lexington, KY 40546, USA 5 University of New Mexico, Department of Biology, 167 Castetter Hall,, Albuquerque, NM 87131, USA 6 Stantec Consulting, 209 Commerce Parkway,, Cottage Grove, WI 53527, USA 7 Trileaf Environmental Corporation, 19442 East Warner Road, Suite 220, Mesa, AZ 85212, USA 8 Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA Received 21 November 2014; revised 2 January 2015; accepted for publication 2 January 2015 Bet-hedging theory makes the counter-intuitive prediction that, if juvenile survival is low and unpredictable, organisms should consistently reduce short-term reproductive output to minimize the risk of reproductive failure in the long-term. We investigated the long-term reproductive output of an Agassiz’s desert tortoise (Gopherus agassizii) population and conformance to a bet-hedging strategy of reproduction in an unpredictable but compara- tively productive environment. Most females reproduced every year, even during periods of low precipitation and poor germination of food plants, and the mean percentage of reproducing females did not differ significantly on an annual basis. Although mean annual egg production (clutch size × clutch frequency) differed significantly among years, mean clutch size and mean clutch frequency remained relatively constant. During an El Niño year, mean annual egg production and mean annual clutch frequency were the highest ever reported for this species. Annual egg production was positively influenced by maternal body size but clutch size and clutch frequency were not. Our long-term results confirm earlier conclusions based on short-term research that desert tortoises have a bet-hedging strategy of producing small clutches almost every year. The risk of long-term reproductive failure is minimized in unpredictable environments, both through time by annually producing multiple small clutches over a long reproductive lifespan, even in years of low resource availability, and through space by depositing multiple annual clutches in different locations. The extraordinary annual reproductive output of this population appears to be the result of a typically high but unpredictable biomass of annual food plants at the site relative to tortoise habitat in dryer regions. Under the comparatively productive but unpredictable conditions, tortoises conform to predictions of a bet-hedging strategy of reproduction with relatively small but consistent clutch sizes. Published 2015. This article is a U.S. Government work and is in the public domain in the USA, Biological Journal of the Linnean Society, 2015, 115, 399–410. ADDITIONAL KEYWORDS: annual plant biomass – clutch size – clutch frequency – Gopherus agassizii – productivity – renewable energy – Sonoran Desert – turtle – wind energy – winter rainfall. *Corresponding author. E-mail: jeffrey_lovich@usgs.gov Biological Journal of the Linnean Society, 2015, 115, 399–410. With 4 figures Published 2015. This article is a U.S. Government work and is in the public domain in the USA, Biological Journal of the Linnean Society, 2015, 115, 399–410 399 Downloaded from https://academic.oup.com/biolinnean/article-abstract/115/2/399/2236002 by guest on 12 June 2020