McIntyre, T. | bioRxiv Science

bioRxiv2025

Shedding dynamics of the Ross seal (Ommatophoca rossii) whiskers investigated through carbon and nitrogen bulk stable isotope composition

Understanding the trophic ecology of pinnipeds is essential to define their role in ecosystems and anticipate their responses as top predators to environmental changes. Incremental analyses of carbon ({delta}13C) and nitrogen ({delta}15N) stable isotopes along their whiskers provide valuable records of their foraging habitat and trophic level over time. The effectiveness of this approach relies on knowledge of species-specific whisker shedding dynamics and growth rates. We investigated the shedding dynamics of Ross seal (Ommatophoca rossii) whiskers and attempted to evaluate the time captured in these tissues by combining whiskers bulk{delta} 13C and{delta} 15N incremental measurements with satellite tracking data, collected after whisker growth. Our tracking data are consistent with previous studies, in that Ross seals migrate post-moult between the marginal ice zone and the Antarctic Polar Front. Stable isotope profiles of whiskers did not show the typical decrease in{delta} {superscript 1}3C and increase in{delta} {superscript 1}N values at the whiskers tip that would be expected if shedding coincided with the annual fur moult, when fasting typically occurs. The occurrence of similar isotope variations, which were offset between the left and right whiskers of the same individual in relation to distance from the muzzle, further suggest asynchronous, non-seasonal whisker shedding. Our inability to identify known cyclic phenological events (i.e., fasting periods or seasonal migrations) prevented the determination of the average growth rate of whiskers. The additional data on whisker shedding dynamics of Ross seals is a valuable first step in support of future ecological studies based on the whiskers of this species.

ecology↗

bioRxiv2023

Cold tolerance and diapause within across trophic levels: endoparasitic wasps and their fly host have similar phenotypes

Low temperatures associated with winter can limit the survival of organisms, especially ectotherms whose body temperature is similar to their environment. Important adaptations for overwintering such as cold hardiness and diapause have been well-explored in many insect taxa. However, there is a gap in understanding how overwintering may vary among groups of species that interact closely, such as multiple parasitoid species that attack the same host insect. Our study investigated cold tolerance and diapause phenotypes in three endoparasitoid wasps of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae): Utetes canaliculatus, Diachasma alloeum, and Diachasmimorpha mellea (Hymenoptera: Braconidae). Using a combination of respirometry and eclosion tracking, we detected diapause phenotypes in all three wasp species, remarkably similar to the fly host. Weak diapause was rare (< 5%) in all three wasp species, and while most D. mellea (93%) entered prolonged diapause under warm conditions, the majority of U. canaliculatus (92%) and D. alloeum (72%) averted diapause (non-diapause). There was limited interspecific variation in acute cold tolerance among the three wasp species: wasps and flies had similarly high survival (>87%) following exposure to extreme low temperatures (- 20{degrees}C) as long as their body fluids did not freeze. The wasp species showed little interspecific variation in survival following prolonged exposure to mild chilling of 8 or more weeks at 4{degrees}C. This study shows remarkable conservation of cold tolerance and diapause phenotypes within and across trophic levels. The interaction between diapause phenotype and cold hardiness in these parasitoids is an interesting direction for future research. Graphical Abstract and Highlights O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/522725v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@826a3aorg.highwire.dtl.DTLVardef@c3963org.highwire.dtl.DTLVardef@8baa33org.highwire.dtl.DTLVardef@1530d03_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIThe apple maggot fly and its parasitoids exhibit the same three diapause phenotypes C_LIO_LIEach parasitoid wasp species exhibits different proportions of these phenotypes C_LIO_LIUtetes canaliculatus and Diachasma alloeum are freeze-avoidant, like their host fly C_LIO_LIThese wasps and flies survive to similarly extreme low temperatures (c. -20{degrees}C) C_LIO_LIEach wasp species survives prolonged exposure to mild chilling (4{degrees}C) similarly well C_LI

physiology↗