Ontogenetic changes in stable isotope composition (δ¹³C, δ¹⁵N) of two synanthropic woodlice species

Abstract

Woodlice, as one of the key groups, contribute to the decomposition of litter in ecosystems. However, the resource use by woodlice, which likely depends on the body size and developmental stage, remains poorly understood. Understanding ontogenetic shifts in the composition of stable isotopes δ¹³C and δ¹⁵N is essential for assessing the position of woodlice in soil food webs. We applied the stable isotope analysis of carbon and nitrogen to four ontogenetic stages of two synanthropic cosmopolitan woodlice species, Cylisticus convexus and Oniscus asellus, along with their potential food resources in a city park in Moscow, Russia. We compared mancas, juveniles, young adults, and adults. In C. convexus, the δ¹³C values remained constant, while juveniles, young adults and adults were enriched in ¹⁵N compared to mancas. In O. asellus, δ¹³C values remained constant except for the last age (adults), when they were enriched in ¹³C by about 1.5‰, compared to other ages. Young adults of O. asellus were depleted in ¹⁵N compared to other ages. Bayesian mixing models (MixSIAR) indicated leaf litter as the primary dietary resource for both species, with species-specific differences in the contribution of fungi and moss. These results suggest ontogenetic shifts in resource use within woodlice populations. We demonstrate the need to consider the age of woodlice when interpreting isotopic data and assessing their trophic roles in soil ecosystems.

Graphical abstract

Keywords

terrestrial isopods / ontogenesis / trophic ecology / city / isotope analysis / SIA

Highlight

	● δ13C and δ15N values were assessed for isopods across ontogenetic stages.
	● Woodlice of two species were collected in an urban park in Moscow.
	● Our data indicate ontogenetic shifts in resource use within woodlice populations.
	● Age of woodlice should be considered when interpreting stable isotope data.

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