Expanding the Isotopic Toolbox to Track Monarch Butterfly (Danaus plexippus) Origins and Migration: On the Utility of Stable Oxygen Isotope (δ18O) Measurements

Abstract

The measurement of naturally occurring stable hydrogen (δ 2 H) and carbon (δ 13 C) isotopes in wings of the eastern North American monarch butterflies (Danaus plexippus) have proven useful to infer natal origins of individuals overwintering in Mexico. This approach has provided a breakthrough for monarch conservation because it is the only viable means of inferring origins at continental scales. Recently, routine simultaneous analyses of tissue δ 2 H and δ 18 O of organic materials has emerged leading to questions of whether the dual measurement of these isotopes could be used to more accurately infer spatial origins even though the two isotopes are expected to be coupled due to the meteoric relationship. Such refinement would potentially increase the accuracy of isotopic assignment of wintering monarchs to natal origin. We measured a sample of 150 known natal-origin monarchs from throughout their eastern range simultaneously for both δ 2 H and δ 18 O wing values. Wing δ 2 H and δ 18 O values were correlated (r 2 = 0.42). We found that wing δ 2 H values were more closely correlated with amount-weighted growing season average precipitation δ 2 H values predicted for natal sites (r 2 = 0.61) compared to the relationship between wing δ 18 O values and amount-weighted growing season average precipitation δ 18 O values (r 2 = 0.30). This suggests that monarch wing δ 2 H values will be generally more useful in natal assignments than δ 18 O values. Spatial information related to the use of deuterium excess in environmental waters was similarly found to be not useful when applied to monarch wings likely due to the considerable variance in wing δ 18 O values. Nonetheless, we recommend further testing of monarch wing δ 2 H and δ 18 O values from known natal sites with an emphasis on field data across a strong gradient in precipitation deuterium excess.

An insect isoscape of UK and Ireland

“…values. 12 The linear transfer function is significant, comparable in slope to, but slightly lower, than those of North American Lepidoptera 10,37 but with a lot of scatter. Whilst the δ 2 H wing isoscape follows that of δ 2 H p , one source of noise in the data revolves around Brimstone moth phenology.…”

“…Whilst many stable isotopes have been used to track long distance migration of birds, examples of insects being tracked with stable isotopes are fewer. Examples are: Monarch butterflies (Danaus plexippus 2 H,  18 O and  13 C values) [9][10][11][12] , Painted Lady butterflies (Vanessa cardui,  2 H values) 13,14 , Common Green Darner dragonflies (Anax junius,  2 H values) 15 and Globe Skimmer dragonflies (Pantala flavescens,  2 H values) 16,17 . In addition, emergent Red Admiral butterflies (Vanessa atalanta) and Silver Y moths (Autographa gamma) from several locations in western/southern Europe have been discriminated using  2 H values 18 , and six species of North American butterfly were also provenanced using  2 H values 19 .…”

Tracking cats revisited: Placing terrestrial mammalian carnivores on δ2H and δ18O isoscapes

“…This suggests that oxygen isotope ratios in keratins may be insensitive to the extent of in vivo synthesis [32] but more affected by the relative contribution of body water and the isotopic fractionation between water and carbonyl oxygen during amino acid synthesis [39]. Close isotopic coupling of oxygen isotopes between ambient water and wing material has been reported for aquatic emergent insects such as dragonflies [40], but this coupling is not as evident in birds or terrestrial insects [19, 41].…”

Origins of Six Species of Butterflies Migrating through Northeastern Mexico: New Insights from Stable Isotope (δ2H) Analyses and a Call for Documenting Butterfly Migrations

“…We depicted the origins of wild monarchs caught in Mexico using a likelihood-based assignment method [48][49][50], using the wing chitin δ 2 H isoscape (δ 2 H w ) and an amountweighted precipitation-to-wing calibration algorithm (δ 2 H w = 0.78 * δ2H p − 77.4) described by the authors of [28]. This was used to convert amount-weighted mean annual precipitation δ 2 H (δ 2 H p ) isoscapes [51,52] into δ 2 H w isoscapes.…”

“…Indeed, the most well-studied migration of any insect using stable isotope analyses of wing chitin has been that of the eastern North American population of the monarch butterfly [23]. That analytical approach has since elucidated a number of ecological components of monarch migration and conservation [24][25][26][27][28].…”