SREL Reprint #2005

 

 

 

GROWTH RATE, TIMING OF REPRODUCTION, AND SIZE DIMORPHISM IN THE SOUTHWESTERN EARLESS LIZARD (COPHOSAURUS TEXANUS SCITULUS)


DERRICK W. SUGG, LEE A. FITZGERALD, AND HOWARD L. SNELL

Savannah River Ecology Laboratory, PO Drawer E, Aiken, SC 2.9802 (DWS)
Division of Herpetology, Department of Biology,
University of New Mexico, Albuquerque, NM 8 7131 (LAF, HLS)
Charles Darwin Research Station, Puerta Ayora,
Isla Santa Cruz, Gaidpagos, Eduador (HLS)


ABSTRACT

Hypothesized explanations for sexual dimorphism in size have suggested various evolutionary forces as causal factors. The present study examines the contributions of sexual variation in energy allocation and timing of reproduction to the growth and size of southwestern Earless lizards. Growth curves were developed for snout-vent length (SVL), weight, and the ratio of these measures to examine sexual differences in size at emergence from hibernation, asymptotic size, and characteristic growth rates. The energy content of an average clutch of eggs was determined, converted to the equivalent energy content in body tissues, and used to determine the expected increase in size of females if the energy was used for growth instead of reproduction. Parameter estimates from growth curves for all measures of size differed only for asymptotic value. The patterns indicate female growth slows at an earlier age than males, probably because they must devote energy to reproduction earlier in life. The energy content in eggs can account for 63% to 90% of the difference in size depending on the hypothetical age at which females can divert stored energy to reproduction. These results suggest that hypotheses of sexual dimorphism that incorporate the cost of and timing of reproductive investments are viable alternatives to those employing sexual selection.

SREL Reprint #2005

Sugg, D.W., L.A. Fitzgerald, and H.L. Snell. 1995. Growth rate, timing of reproduction, and size dimorphism in the Southwestern earless lizard (Cophosaurus texanus scitulus). The Southwestern Naturalist 40:193-202.

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