Identifying nesting grounds for juvenile migratory birds with dual isotope: an initial test using North American raptors

Isotope geolocation and population genomics in Vanessa cardui: Short- and long-distance migrants are genetically undifferentiated

The painted lady butterfly Vanessa cardui is renowned for its virtually cosmopolitan distribution and the remarkable long-distance migrations as part of its annual, multigenerational migratory cycle. In winter, V. cardui individuals inhabit breeding grounds north and south of the Sahara, suggesting distinct migratory behaviors within the species as individuals migrate southward from Europe in the autumn. However, the evolutionary and ecological factors shaping these differences in migratory behavior remain largely unexplored. Here, we performed whole-genome resequencing and analyzed the hydrogen and strontium isotopes of 40 V. cardui individuals simultaneously collected in the autumn from regions both north and south of the Sahara. Our investigation revealed two main migratory groups: (i) short-distance migrants, journeying from temperate Europe to the circum-Mediterranean region and (ii) long-distance migrants, originating from Europe, crossing the Mediterranean Sea and Sahara, and reaching West Africa, covering up to over 4,000 km. Despite these stark differences in migration distance, a genome-wide analysis revealed that short- and long-distance migrants belong to a single intercontinental panmictic population extending from northern Europe to sub-Saharan Africa. Contrary to common biogeographic patterns, the Sahara is not a catalyst for population structuring in this species. No significant genetic differentiation or signs of adaptation and selection were observed between the two migratory phenotypes. Nonetheless, two individuals, who were early arrivals to West Africa covering longer migration distances, exhibited some genetic differentiation. The lack of genetic structure between short- and long-distance migrants suggests that migration distance in V. cardui is a plastic response to environmental conditions.

Spatial ecology of moose in Sweden: Combined Sr-O-C isotope analyses of bone and antler

The study of spatial (paleo)ecology in mammals is critical to understand how animals adapt to and exploit their environment. In this work we analysed the 87Sr/86Sr, δ18O and δ13C isotope composition of 65 moose bone and antler samples from Sweden from wild-shot individuals dated between 1800 and 1994 to study moose mobility and feeding behaviour for (paleo)ecological applications. Sr data were compared with isoscapes of the Scandinavian region, built ad-hoc during this study, to understand how moose utilise the landscape in Northern Europe. The 87Sr/86Sr isoscape was developed using a machine-learning approach with external geo-environmental predictors and literature data. Similarly, a δ18O isoscape, obtained from average annual precipitation δ18O values, was employed to highlight differences in the isotope composition of the local environment vs. bone/antler. Overall, 82% of the moose samples were compatible with the likely local isotope composition (n = 53), suggesting that they were shot not far from their year-round dwelling area. 'Local' samples were used to calibrate the two isoscapes, to improve the prediction of provenance for the presumably 'non-local' individuals. For the latter (n = 12, of which two are antlers and ten are bones), the probability of geographic origin was estimated using a Bayesian approach by combining the two isoscapes. Interestingly, two of these samples (one antler and one bone) seem to come from areas more than 250 km away from the place where the animals were hunted, indicating a possible remarkable intra-annual mobility. Finally, the δ13C data were compared with the forest cover of Sweden and ultimately used to understand the dietary preference of moose. We interpreted a difference in δ13C values of antlers (13C-enriched) and bones (13C-depleted) as a joint effect of seasonal variations in moose diet and, possibly, physiological stresses during winter-time, i.e., increased consumption of endogenous 13C-depleted lipids.

A hydrogen isoscape for tracing the migration of herbivorous lepidopterans across the Afro-Palearctic range

RATIONALE

Many insect species undertake multigenerational migrations in the Afro-tropical and Palearctic ranges, and understanding their migratory connectivity remains challenging due to their small size, short life span and large population sizes. Hydrogen isotopes (δ2 H) can be used to reconstruct the movement of dispersing or migrating insects, but applying δ2 H for provenance requires a robust isotope baseline map (i.e. isoscape) for the Afro-Palearctic.

METHODS

We analyzed the δ2 H in the wings (δ2 Hwing ) of 142 resident butterflies from 56 sites across the Afro-Palearctic. The δ2 Hwing values were compared to the predicted local growing-season precipitation δ2 H values (δ2 HGSP ) using a linear regression model to develop an insect wing δ2 H isoscape. We used multivariate linear mixed models and high-resolution and time-specific remote sensing climate and environmental data to explore the controls of the residual δ2 Hwing variability.

RESULTS

A strong linear relationship was found between δ2 Hwing and δ2 HGSP values (r2  = 0.53). The resulting isoscape showed strong patterns across the Palearctic but limited variation and high uncertainty for the Afro-tropics. Positive residuals of this relationship were correlated with dry conditions for the month preceding sampling whereas negative residuals were correlated with more wet days for the month preceding sampling. High intra-site δ2 Hwing variance was associated with lower relative humidity for the month preceding sampling and higher elevation.

CONCLUSION

The δ2 Hwing isoscape is applicable for tracing herbivorous lepidopteran insects that migrate across the Afro-Palearctic range but has limited geolocation potential in the Afro-tropics. The spatial analysis of uncertainty using high-resolution climatic data demonstrated that many African regions with highly variable evaporation rates and relative humidity have δ2 Hwing values that are less related to δ2 HGSP values. Increasing geolocation precision will require new modeling approaches using more time-specific environmental data and/or independent geolocation tools.

Assigning harvested waterfowl to geographic origin using feather δ2H isoscapes: What is the best analytical approach?

Establishing links between breeding, stopover, and wintering sites for migratory species is important for their effective conservation and management. Isotopic assignment methods used to create these connections rely on the use of predictable, established relationships between the isotopic composition of environmental hydrogen and that of the non-exchangeable hydrogen in animal tissues, often in the form of a calibration equation relating feather (δ2Hf) values derived from known-origin individuals and amount-weighted long-term precipitation (δ2Hp) data. The efficacy of assigning waterfowl to moult origin using stable isotopes depends on the accuracy of these relationships and their statistical uncertainty. Most current calibrations for terrestrial species in North America are done using amount-weighted mean growing-season δ2Hp values, but the calibration relationship is less clear for aquatic and semi-aquatic species. Our objective was to critically evaluate current methods used to calibrate δ2Hp isoscapes to predicted δ2Hf values for waterfowl. Specifically, we evaluated the strength of the relationships between δ2Hp values from three commonly used isoscapes and known-origin δ2Hf values three published datasets and one collected as part of this study, also grouping these data into foraging guilds (dabbling vs diving ducks). We then evaluated the performance of assignments using these calibrations by applying a cross-validation procedure. It remains unclear if any of the tested δ2Hp isoscapes better predict surface water inputs into food webs for foraging waterfowl. We found only marginal differences in the performance of the tested known-origin datasets, where the combined foraging-guild-specific datasets showed lower assignment precision and model fit compared to data for individual species. We recommend the use of the more conservative combined foraging-guild-specific datasets to assign geographic origin for all dabbling duck species. Refining these relationships is important for improved waterfowl management and contributes to a better understanding of the limitations of assignment methods when using the isotope approach.

Metals and metal isotopes incorporation in insect wings: Implications for geolocation and pollution exposure

Anthropogenic activities are exposing insects to elevated levels of toxic metals and are altering the bioavailability of essential metals. Metals and metal isotopes have also become promising tools for the geolocation of migratory insects. Understanding the pathways of metal incorporation in insect tissues is thus important for assessing the role of metals in insect physiology and ecology and for the development of metals and metal isotopes as geolocation tools. We conducted a diet-switching experiment on monarch butterflies [Danaus plexippus (L.)] with controlled larval and adult diets to evaluate the sources of 23 metals and metalloids, strontium isotopes, and lead isotopes to insect wing tissues over a period of 8 weeks. Concentrations of Ca, Co, Mo, and Sb differed between the sexes or with body mass. Ni and Zn bioaccumulated in the insect wing tissues over time, likely from the adult diet, while increases in Al, Cr, Cd, Cu, Fe, and Pb were, at least partially, from external sources (i.e., dust aerosols). Bioaccumulation of Pb in the monarch wings was confirmed by Pb isotopes to mainly be sourced from external anthropogenic sources, revealing the potential of Pb isotopes to become an indicator and tracer of metal pollution exposure along migratory paths. Concentrations of Ba, Cs, Mg, Na, Rb, Sr, Ti, Tl, and U appeared to be unaffected by intrinsic factors or additions of metals from adult dietary or external sources, and their potential for geolocation should be further explored. Strontium isotope ratios remained indicative of the larval diet, at least in males, supporting its potential as a geolocation tool. However, the difference in strontium isotope ratios between sexes, as well as the possibility of external contamination by wetting, requires further investigation. Our results demonstrate the complexity of metal incorporation processes in insects and the value of studying metals to develop new tools to quantify pollution exposure, metal toxicity, micronutrient uptake, and insect mobility.