Elucidating stygofaunal trophic web interactions via isotopic ecology

Abstract

Subterranean ecosystems host highly adapted aquatic invertebrate biota which play a key role in sustaining groundwater ecological functioning and hydrological dynamics. However, functional biodiversity studies in groundwater environments, the main source of unfrozen freshwater on Earth, are scarce, probably due to the cryptic nature of the systems. To address this, we investigate groundwater trophic ecology via stable isotope analysis, employing δ 13 C and δ 15 N in bulk tissues, and amino acids. Specimens were collected from a shallow calcrete aquifer in the arid Yilgarn region of Western Australia: a well-known hotspot for stygofaunal biodiversity. Sampling campaigns were carried out during dry (low rainfall: LR) and the wet (high rainfall: HR) periods. δ 13 C values indicate that most of the stygofauna shifted towards more 13 C-depleted carbon sources under HR, suggesting a preference for fresher organic matter. Conversion of δ 15 N values in glutamic acid and phenylalanine to a trophic index showed broadly stable trophic levels with organisms clustering as low-level secondary consumers. However, mixing models indicate that HR conditions trigger changes in dietary preferences, with increasing predation of amphipods by beetle larvae. Overall, stygofauna showed a tendency towards opportunistic and omnivorous habitstypical of an ecologically tolerant community-shaped by bottom-up controls linked with changes in carbon flows. This study provides baseline biochemical and ecological data for stygofaunal trophic interactions in calcretes. Further studies on the carbon inputs and taxaspecific physiology will help refine the interpretation of the energy flows shaping biodiversity in groundwaters. This will aid understanding of groundwater ecosystem functioning and allow modelling of the impact of future climate change factors such as aridification.

Evidence for speciation underground in diving beetles (Dytiscidae) from a subterranean archipelago

“…2014; Saccò et al. 2019, 2020). However, the repeated pattern of body size differences among beetle species within more than 30 distinct calcretes (Watts and Humphreys ) offers considerable potential for future comparative population genomic analyses to investigate the genetic drivers underlying this process of ecological diversification and adaptive evolution.…”

Distribution patterns, carbon sources and niche partitioning in cave shrimps (Atyidae: Typhlatya)

“…Modern OM is a carbon source that is most available during the rainy season, when modern CO 2 and allochthonous sediment inputs increase in the cenote pools. Seasonal shifts of allochthonous inputs have been suggested to modify dietary selection in stygobiont beetles which showed a marked difference between dry and rainy seasons 40 . Considering that more than 90% of T. mitchelli diet derives from a photosynthetic origin, a reduction in allochthonous input or photosynthetic in situ production could represent a reduction of food availability, resulting in the decline of its population size or a shift in its distribution, as observed in Kankirixche and Tza Itza, where the population was smallest and mainly distributed at deeper transects during dry months (Fig.…”

Rainfall as a trigger of ecological cascade effects in an Australian groundwater ecosystem

“…1b), which are representative of the two main geological conformations of the area-calcrete (W4) and clay (D13) ( Supplementary Fig. 2)-and host stable hydrological and biotic conditions 7 . Water samples were collected using a submersible centrifugal pump (GEOSub 12 V Purging Pump) after wells were purged of three well-volumes and stabilisation of in-field parameters was observed, according to the methodology in Bryan et al 26 .…”

“…Carbon CSIA. Carbon CSIA followed the procedure described in Saccò et al 7 . Samples of roots and stygofaunal specimens were hydrolysed under vacuum with 0.5 to 1 mL of amino acid-free 6 M HCl (Sigma-Aldrich) at 110 °C for 24 h. The protein hydrolysates were dried overnight in a rotary vacuum concentrator and stored in a freezer.…”