For all audiences: Incorporating immature stages into standardised spider inventories has a major impact on the assessment of biodiversity patterns

Abstract

Although arthropods are the largest component of animal diversity, they are traditionally underrepresented in biological inventories and monitoring programmes. However, no biodiversity assessment can be considered informative without including them.Arthropod immature stages are often discarded during sorting, despite frequently representing more than half of the collected individuals. To date, little effort has been devoted to characterising the impact of discarding nonadult specimens on our diversity estimates. Here, we used a metabarcoding approach to analyse spiders from oak forests in the Iberian Peninsula, to assess (1) the contribution of juvenile stages to local diversity estimates, and (2) their effect on the diversity patterns (compositional differences) across assemblages. We further investigated the ability of metabarcoding to inform on abundance. We obtained 363 and 331 species as adults and juveniles, respectively. Including the species represented only by juveniles increased the species richness of the whole sampling in 35% with respect to those identified from adults.Differences in composition between assemblages were greatly reduced when immature stages were considered, especially across latitudes, possibly due to phenological differences. Moreover, our results revealed that metabarcoding data are to a certain extent quantitative, but some sort of taxonomic conversion factor may be necessary to provide accurate informative estimates. Although our findings do not question the relevance of the information provided by adult-based inventories, they also reveal that juveniles provide a novel and relevant layer of knowledge that, especially in areas with marked seasonality, may influence our interpretations, providing more accurate information from standardised biological inventories.

Overcoming life stage‐centric biases illuminates arthropod diversity, systematics and biology

“…Such potential seems to have been appreciated most acutely by arachnologists. When explicitly incorporating immatures, Domènech et al (2022) found that not only were juvenile spiders the most abundant individuals across several sampling techniques and areas, they contributed nearly 30% to the final species total. Similar results were found in spider surveys by Ding et al (2023) and Blagoev et al (2013).…”

“…The emphasis in systematics on one semaphoront has limited, whether by design or by necessity, biodiversity inventory efforts to focusing preferentially on the most identifiable specimens, ignoring or regarding others as uninformative, or as an unavoidable nuisance (Domènech et al, 2022). For instance, in insects, the most widely publicized data associated with reports of overall declines have been entirely based on flying (therefore adult) insects collected by light and Malaise traps (Hallmann et al, 2017;Lister & Garcia, 2018;Mata et al, 2021), and many more general inventory attempts focus mainly on flight-trapped insects, mostly excluding other semaphoronts (Chimeno et al, 2023;Kaczmarek et al, 2022;Li et al, 2023;Montgomery et al, 2021;Srivathsan et al, 2023;Steinke et al, 2021).…”

“…A number of authors have also demonstrated successful associations of sexes in dimorphic species (Corley & Ferreira, 2017; Ekrem et al, 2010; Ferreira & Ivie, 2022; Gariepy et al, 2022). In addition, biodiversity inventories that have explicitly included immature stages in molecular assessments report significantly greater results (Blagoev et al, 2013; Ding et al, 2023; Domènech et al, 2022; Köhler et al, 2022), outside of entomology as well as within (Garcia‐Vazquez et al, 2021; Kimmerling et al, 2017; Lira et al, 2022). Nonetheless, it seems to us that the broad‐scale integration of all semaphoronts into biodiversity surveys and systematic studies remains to be openly and widely embraced.…”

SLAM Project - Long Term Ecological Study of the Impacts of Climate Change in the natural forest of Azores: IV - The spiders of Terceira and Pico Islands (2019-2021) and general diversity patterns after ten years of sampling

“…Spider juvenile identification is very important in spider studies ( Domènech et al 2022 ). Most juveniles, with the exception of some exotic Erigoninae , were also included in the data presented in this paper, since the low diversity of spiders in the Azores allows a relatively precise species-level identification of this life-stage.…”

A new trans-Ionian spider species for the Italian fauna: Habrocestum graecum Dalmas, 1920 (Araneae, Salticidae)

“…DNA barcoding relies on the analysis of a specific small genomic region (for metazoans usually a fragment of the mitochondrial cytochrome c oxidase subunit 1) for molecular species identification. This is particularly useful in spiders for identifying juvenile specimens, in which diagnostic morphological characters are still not visible, for matching males and females of the same species and as an aid to traditional 2 taxonomy when dealing with cryptic or problematic taxa (Hebert et al 2003, Domènech et al 2022b. In contrast to other European countries (see, e.g., Astrin et al 2016, Domenec et al 2022a, in Italy no projects are currently focusing on creating a DNA barcode library of Italian spider species.…”