Expression of maternal isotopes in offspring: implications for interpreting ontogenetic shifts in isotopic composition of consumer tissues

Abstract

When evaluating ontogenetic shifts in isotopic composition of consumer tissues within the context of a dietary analysis, the isotopic starting point of consumers in the population should not be ignored. Neonate isotopic composition may be different from that of juveniles and adults; in general, neonate tissues are built from maternal resources rather than food resources. Thus, the range of isotope values observed within a population of consumers may be significantly impacted by consumer isotope ratios at birth. Long-term goals of my research involve the use of stable isotopes to assess the role diet plays in driving population level differences in life history and demography observed among three pigmy rattlesnake (Sistrurus miliarius; family Viperidae) populations. For meaningful interpretation of field-collected data, it was important to determine starting (i.e., at birth) isotopic compositions of rattlesnakes from the study populations. We quantified isotopic composition of pregnant pigmy rattlesnake scale tissue, isotopic composition of neonate scale tissue and the degree that neonate scale tissue isotopic composition reflected the isotopic composition of maternal scale tissue. Collectively, neonate isotopic composition was highly variable among-litters; average litter δ¹³C values spanned 7 ‰ and average litter δ¹⁵N values spanned 2.8 ‰. Over 95 % of the variation in offspring isotopic composition was expressed among litters. Thus, high levels of among-litter isotopic variation were largely due to the retention of a maternal signal. Results of the enclosure study suggest that highly variable isotopic signatures in young animals within field populations could easily reflect the retention of a maternal signal rather than differences in resource utilisation among younger snakes.

Keywords:

• Animals
• Carbon-13
• Diet
• Natural isotope variations
• Neonate tissues
• Nitrogen-15
• Offspring
• Ontogenetic shifts
• Rattlesnakes

Acknowledgements

I extend many thanks to Terry Farrell, Peter May, Josh Martin, Lee Saullo, and Jason Barrow for their assistance in the field and laboratory. I am grateful to Stetson University and the University of Arkansas for providing space and equipment necessary for the completion of the enclosure study. In addition, I appreciate the cooperation and support provided by the management and staff of Lake Woodruff National Wildlife Refuge. Julie Cox and Glenn Piercey of the University of Arkansas Stable Isotope Laboratory provided invaluable assistance with isotope analyses. I would like to thank Steve Beaupre, Terry Farrell, Cindy Sagers, Kim Smith, and two anonymous reviewers for providing editorial comments on early drafts of this manuscript.

I am grateful to the funding agencies who supported portions of my dissertation research, including the enclosure study: EPA STAR Fellowship (No. U-91616001-1), AMNH Theodore Roosevelt Memorial Fund, ASIH Gaige Fund Award, Sigma-Xi GIAR, SICB GIAR, SSAR GIAR, University of Arkansas Professor Delbert Schwartz Endowed Graduate Fellowship, and University of Arkansas Causey Award. The study was approved by the University of Arkansas' Institutional Animal Care and Use Committee (Protocol No. 02015) and special use permit No. 41550-9905 from the United States Department of the Interior Fish and Wildlife Service. Manuscript preparation was supported by the United States Government, Department of Energy under Award No. DE-FC09-07SR22506 to the University of Georgia Research Foundation.

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Melissa Ann Pilgrim

Current address: Savannah River Ecology Laboratory, Drawer E, University of Georgia, Aiken, SC 29802, USA; Tel.: [phone]; Fax: [phone]; Email: [email protected]